ML20141C934
| ML20141C934 | |
| Person / Time | |
|---|---|
| Site: | 05200003 |
| Issue date: | 06/19/1997 |
| From: | Kemper R, Ohkawa D, Sloane B WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP. |
| To: | |
| Shared Package | |
| ML20141C931 | List: |
| References | |
| WCAP-14800, NUDOCS 9706260098 | |
| Download: ML20141C934 (569) | |
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Westinghouse Non-Proprietary Class 3
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AP600 PRA Thermall Hydraulic Uncertainty Evaluation for Passive System Reliability Westinghouse Energy Systems 2 6 f[f# 883 553IS"co nw
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ATTACHMENTS: DCP #/REV. INCORPORATED IN THIS DOCUMENT REVISION:
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EPRI CONFIDENTIALITY / OBLIGATION CATEGORIES CATEGORY "A"- (See Delivered Data) Consists of CONTRACTOR Foreground Data that is contained in an issued reported.
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WESTINGHOUSE NON-PROPRIETARY CLASS 3 i
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AP600 PRA Thermal / Hydraulic l Uncertainty Evaluation for Passive System Reliability l
l D. K. Ohkawa B. D. Sloane !
R. Kemper C. M. Thompson D. W. Golden !
t N. Petkov l S. Sancaktar l J. M. Freeland June 1997
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l Westinghouse Electric Corporation Energy System Business Unit l P.O. Box 355 Pittsburgh, PA 15230-0355
'p C 1997 Westinghouse Electric Corporation
<g All Rights Reserved i
l o:\3661w.wpf;1t>451997 l
iii ACKNOWLEDGEMENTS O The authors would like to acknowledge the efforts of many individuals in the review and production of this report. The authors would foremost like to thank the technical advisors and reviewers who have provided invaluable direction during various phases of the TIH uncertainty evaluation process: J. H. Scobel, L. E. Hochreiter, T. L. Schulz, J. A. Gresham, and M. E. Nissley. The authors would also like to recognize and thank C. L. Haag for her project management of the program, and persistent review of the integrated report. There are also numerous people who have prepared the figures and tne report text; we gratefully acknowledge the exceptional efforts of P. Kennevan, A. Forgie, D. Morgan, and all the individuals in word processing for their efforts on the report. And finally, our appreciation is extended to N. Gibbs for the editing and coordination that brought the elements of the report together.
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V
- TABLE OF CONTENTS Section Title Page LIST OF TAB LES . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viii LIST OF FIGURES . . . . . . . . . . . . . . ......................................xii LIST OF ACRONYMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xxix EXECUTIVE
SUMMARY
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .....................1 1
1 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1 2 . DEFINITION OF THERMAL-HYDRAULIC UNCERTAINTY . . . . . . . . . . . . . . . 2-1 3 EVALUATION PROCESS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1 l
l 4 EXPANDED EVENT TREES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1 4.1 Expanded PRA Event Tree Methodology . . . . . . . . . . .. . . . . . . . . . . . . . 4-1 f
4.2 Scope of Expanded Event Trees . . . . . . . . . . . . ................... 4-6 i 4.3 Impact of Focused PRA versus Be&c PRA ...................... 4-9 4.4 Results of Expanded Event Trees and Frequency Quantification . . . . . . . 4-10 q
l Cl 5 CATEGORIZATION METHOD OF SUCCESS SCENARIOS . . . . . . . . . . . . . . . . 5-1 5.1 CMT and Accumulator Injection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1
- 5.2 IRWST Gravity Injection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-2 l 5.3 Long-Term Recirculation Cooling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-3 6 CATEGORIZATION OF SUCCESS PATHS FOR SHORT-TERM COOLING . . . . 6-1 6.1 OK Categories Similar to Design Basis . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-2 l
6.1.1 Category OK1 ....................................... 6-5 6.1.2 Category OK2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-33 6.1.3 Category OK3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-37 6.1.4 Category OK4 .......................................6-41 6.1.5 Categories OK5A, OK5B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-57 L 6.1.6 Category OK6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-61 1
6.1.7 Category OK7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-63 6.1.8 Category OK8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..... 6-65 6.1.9 Category OK9 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-67 f
o:\3661w.wpf:1b.061997 June 1997
vi TABLE OF CONTENTS (cont.)
Section Title Page O
6.2 UC Categories of Low-Margin Accident Scenarios . . . . . . . . . . . . . . . . . . 6-85 6.2.1 Category UC1 ........... ...................... .... 6-87 6.2.2 Category UC2A and UC2B . . . . . ........................ 6-91 6.2.3 Category UC3 . . . . . . . ............... ............... 6-95 6.2.4 Category UC4 . . . . . . . . . . . . . . . ..... ........... . . . . . 6-97 6.2.5 Ca tegory UC5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-99 6.2.6 Category UC6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-103 6.2.7 Category UC7 . . . . ....... . . . . . . . . . . . . . . . . . . . . . . . . 6-107 6.2.8 Category UC8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-109 6.2.9 Category UC9 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-111 6.3 Potentially Risk-Significant Scenarios for Short-Term Cooling . . . . . . . . 6-113 6.3.1 Definition of Potentially Risk-Significant Categories . . . . . . . . . . 6-113 6.3.2 Definition of Low-Margin, Potentially Risk Significant Cases . . . 6-117 7 CATEGORIZATION OF SUCCESS PATHS FOR LONG-TERM RECIRCULATION COOLING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1 7.1 Grouping of Success Scenarios for Long-Term Recirculation Cooling . . . . 7-1 7.2 PRA-Important Success Sequence Groups for Long-Term Recirculation Cooling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-5 7.2.1 Sequences Already Covered by Design Basis Analyses . . . . . . . . . . 7-5 7.2.2 Containment Isolation Status . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-11 7.2.3 DVI Break versus Non-DVI Break . . . . . . . . . . . . . . . . . . . . . . . . 7-11 7.2.4 Fourth Grouping: ADS Capacity . . . . . . . . . . . . . . . . . . . . . . . . 7-29 7.2.S Additional Long-Term Recirculation Cooling-Specific Expanded Event Tree Sequence Consideratic.ns . . . . . . . 7-29 7.3 Summary of LTC Risk Importance Groupings and Selection of Cases for TlH Analysis .... ......................... ....... 7-39 8 COMPARISON OF SHORT-TERM COOLING AND LONG-TERM 1 COOLING CASE DEFINITIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1 8.1 Short-Term and Long-Term Cooling Cases for Non-DVI Line Breaks with Containment Isolation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-2 8.2 Short-Term and Long-Term Cooling Cases for DVI Line Breaks with l Containment Isolation . . . . . . . . . . . . . . . . ....................... 8-5 I 8.3 Short-Term and Long-Term Cooling Cases for Non-DVI Line Breaks without Containment Isolation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ........ 8-7 8.4 Short-Term and Long-Term Cooling Cases for DVI Line Breaks without Containment Isolation . . . . . . . . . ..... .. .... . ............. 8 o:\3661w.wpf:1b-061997 June 1997
l vii
(~) TABLE OF CONTEN*IS (cont.)
V Section Title Page i
9 T/H UNCERTAINTY ANALYSES FOR SHORT-TERM COOLING . . . . . . . . . . 9-1 9.1 NOTRUMPILOCTA Analyses of Small LOCAs .... . . . . . . . . . . . . . 9-1 9.1.1 NOTRUMP/LOCTA Analysis Methodology . . . . . . . . . . . . . . . . 9-2 9.1.2 NOTRUMP/LOCTA Results . . . . . . . . . . . . . . . . . . . . ...... .. 9-4 l 9.2 LVCOBRAfrRAC Analysis of Large-Break LOCA . . . . ...... . . . . . . 9-107 l
9.2.1 WCOBRA/ TRAC Analysis Methodology ... . . . . . . . . . . . . . 9-108 9.2.2 WCOBRA/ TRAC Results for Large-Break LOCA . . . . . . . . . . . . 9-110 9.2.3 Uncertainty Evaluation . ............. . . . . . . . . . . . . . . . . 9-171 i 10 T/H UNCERTAINTY ANALYSIS FOR LONG-TERM COOLING . . . . . . . . . .. . 10-1 10.1 Long-Term Cooling Analysis Modeling and Assumptions . . . . . . . . . . . 10-1 10.1.1 WCOBRA/ TRAC Modeling Methodology . . ................ 10-1 10.1.2 Modeling and Boundary Conditions for Cases with ;
Containment Isolated . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-4 l 10.1.3 Modeling and Boundary Conditions for Cases with i Failure to Isolate Containment . . . . . . . . . . . . . . . . . . . . . . . . . 10-12 es 10.2- Long-Term Cooling Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 18 h 10.2.1 LTC Results with Containment Isolated . . . . . . . . . . . . . . . . . . . 10-18 i 10.2.2 Results with Failure to Isolate Containment . . . . . . . . . . . . . . . . 10-99 11
SUMMARY
OF RESULTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-1 11.1 Focused PRA Assessment . . . ......... .... . . . . . . . . . . . . . . . 11 -1 11.2 Baseline PRA Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-3 12 CONCLUSION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. ........ 12-1 13 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-1 i
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viu LIST OF TABLES Table No. Title Page O
4-1 Comparison of Equipment on Event Tree Success Path to Equipment Assurnptions in Supporting Analysis . . . ....................... 4-3 4-2 Options for Expanding Event Tree Success Paths . . . . . . ..... ... . 4-4 4-3 Correlation of Expanded Event Trees to Focused PRA Event Trees . . . . . 4-7 5-1 Summary of Potential PRA Impacts on Long-Term Recirculation . . ... 5-5 6.1.1 Summary of OK Categories ... . ............... ........... 6-3 6.1.1-1 Success Category OK1 . . . . . . . . . . . . . . . . . . . . . . . . ............. 6-6 6.1.1-2 Sequence of Events for High-Pres.sure Scenarios in Category OK1 ... 6-7 6.1.2-1 Success Category OK2 . . . . . . . . . .... ..... .... . .. .... 6-34 6.1.3-1 Success Category OK3 . . . . . . . . . ........................... 6-38 6.1.4-1 Success Category OK4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-43 6.1.5-1 Success Category OK5A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-58 6.1.5-2 Success Category OK5B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-59 6.1.6 1 Success Category OK6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-62 6.1.7-1 Success Category OK7 ................... ................ 6-64 6.1.8-1 Success Category OK8 . . . . . . . . . . . . . . ............... ...... 6-66 6.1.9-1 Success Category OK9 . . . . . ...............................6-68 6.2-1 Summary of UC Categories ................................. 6-86 6.2.1 -1 Success Category UC1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-88 6.2.2-1 Success Category UC2A . . . . . . . . . . . . .............. ........ 6-92 l
l l 6.2.2-2 Success Category UC2B . . . . . . . . . . ......................... 6-93 6.2.3-1 Success Category UC3 . . . . . . ...... . . . . . . . . . . . . . . . . . . . . . 6-9 6 6.2.4-1 Success Category UC4 . . . . . . . . ...................... . . . . . 6-98 1
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ix LIST OF TABLES (cont.)
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V Table No. Title Page 62.5-1 Success Category UC5 . . . ............. ....... .......... 6-100 6.2.6-1 Success Category UC6 . . . . . . . . . . . . . . . ... ................ 6-104 6.2.7-1 Success Category UC7 . . . . . . . ........................... 6-107 6.2.8-1 Success Category UC8 . .......................... . . . . . . . 6-109 6.2.9-1 Success Ca tegory UC9 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-112 6.3.1-1 Potential Risk-Significance of UC Categories . . . . . . . . . . . . . . . . . . . 6-115 6.3.2-1 Dominant Accident Sequences for Low-Margin, Potentially Risk-Significant Categories ........................ 6-118 6.3.2-2 Cases for Analysis with Detailed T/H Codes . . . . . . . . . . . . . . . . . . . 6-120 7.1-1 Summary of Manner in Which Parameters Important to Long-Term Cooling are Addressed in Grouping of Sequences . . . . . . . . ......... 7-3 p 7.2.1-1 Summary of Sequences with DBA /or Better than DBA) Conditions . . . . 7-7
%) 7.2.3-1 DVI Line Break Success Paths with Successful Containment Isolation . . 7-12 7.2.3-2 DVI Line Break Success Paths with Failed Containment Isolation . . . . . 7-13 7.2.3-3 Success Paths for Events Other Than DVI Line Breaks, with Successful Containment Isolation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-14 7.2.3-4 Success Paths for Events Other Than DVI Line Breaks, with Failed Contairunent Isolation . . . . . . . . . . . . . . . . . . ................... 7-23 7.3-1 Success Frequencies for Sequence Groups, Sorted by Containment Isolation Status and ADS Stage 4 Valve Availability for DVI Line Break and Non-DVI Line Break Events . . . . . . . . . . . . . . . . ........ 7-40 7.3-2 Summary of Cases Representing Potentially Risk-Important Conditions .............................. .............. 7-45 8-1 Potentially Risk-Significant Short-Term Cooling Categories for Loss of CMTs/ Accumulators with Successful Containment isolation ... ... 8-3 8-2 Comparison of STC and LTC Specification of DVI Line Break with Containment Isolation . . . . . ... ............. ........ . 8-6 i
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LIST OF TABLES (cont.)
Table No. Title Page 9.1.2-1 UCI Sequence of Events . . . . . . . . . . . . . . . . . . . . . . . . . . . ... .... 9-6 9.1.2-2 UC2B Sequence of Events . . . . . . . . . . . . . . . .......... ........ 9-24 9.1.2-3 UC5 Sequence of Events . . . . . . . . . . . . . ............ . . . . . . . . . 9-40 9.1.2-4 UC61 Sequence of Events . . . . . . . ................. .... . . . . 9-S8 9.1.2-S UC62 Sequence of Events .................................. 9-76 9.1.2-6 UC7 Sequence of Events . . . . . . . . ........................... 9-92 10.1-1 Common Assumptions Bounding TlH Uncertainties . . . . . . . . . . . . . . 10-3 10.1.2-1 Summary of Isolated-Containment Cases . . . .. ............. . 10-9 10.1.2-2 Boundary Conditions for 2-Inch Cold-Leg Break during IRWST Injection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-9 10.1.2-3 Summary of 2-Inch Cold-Leg Break Calculations during IRWST Injection . . . . .................................. . . 10-9 10.1.2-4 Boundary Conditions for 2-Inch Cold-lag Break with Isolated Containment during Sump Injection (Recirculation) . . ............ 10-9 10.1.2-S Summary of 2-Inch Cold-Leg Break Calculations during Sump Injection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-10 10.1.2-6 Equipment Available for Double-Ended DVI Line Break during IRWST Injection . . . . . . . . . . . . . . . . . .... . . . . . . . . . . . . . . . . . . 10-10 10.1.2-7 Boundary Conditions for Double-Ended DVI Line Break with Isolated Containment during IRWST Injection . . . . . . . . . . . . . . . . . . 10-10 10.1.2-8 Equipment Available for Single-Ended DVI Line Break with Isolated Containment during Sump Injection . . . . . . . . . . . . . . . . . . . 10-11 10.1.2-9 Boundary Conditions for Single-Ended DVI Line Break with Isolated Containment during Sump Injection . . . . . . . . . . . . . . . . . . 10-11 10.1.3-1 Boundary Conditions for Double-Ended DVI Line Break with Failure to Isolate Containment during IRWST Injection Time Wind ow . . . . . . . . . . . . . . . . . . . . . . . . . . . .... .............. 10-1S O
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xi LIST OF TABLES (cont.)
' Title Page Table No.
10.1.3-2 Equipment Conditions for Double-Ended DVI Line Break with Failure to Isolate Containment during IRWST Injection Time Wind ow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-15 10.1.3-3 Equipment Conditions for Double-Ended DVI Line Break with
' Failure to' Isolate Containment during Sump Injection Time Wind ow . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . 10-17 10.1.3-4 Boundary Conditions for Double-Ended DVI Line Break with Failure to Isolate Containment during Sump Injection Time Wmd ow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-17 i
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xii l
LIST OF FIGURES Figure No. Title Page O
3-1 AP600 PRA T/H Uncertainty Evaluation Process
.................3-3 4-1 MLOCA Event Tree in Focused PRA . . . . . . . . . . . . . . . . . . . . . . .4-5 ...
4-2 Expanded LLOCA Event Tree
...............................4-11 4-3 Expanded MLOCA Event Tree . . . . . . . . . . . . .
............. . . . 4-13 4-4 Expanded CMTLB Event Tree . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-15 4-5 Expanded SILB Event Tree . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . 4-17 4-6 Expanded NLOCA Event Tree . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-19 4-7 Expanded SLOCAW Event Tree with Success of PRHR . . . . . . . . . . . . 4-21 4-8 Expanded SLOCWO Event Tree with Failure of PRHR . . . . . . . . . . . . . 4-23 4-9 Expanded SGTRW Event Tree with Success of PRHR . . . . . . . . . . . . . . 4-25 4-10 Expanded SGTRWO Event Tree with Failure of PRHR . . . . . . . . . . . . . 4-27 4-11 Expanded TRAN Event Tree . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-29 6.1.1-1 RCS Pressure for 1.0-Inch Break in Category OK1. . . . . . . . . . . . . . . . . . 6-8 6.1.1-2 CMT and Accurnulator Water for 1.0-Inch Break in Category OK1. . . . . . . . ...... ........
.................. 6-9 6.1.1-3 IRWST Injection for 1.0-Inch Break in Category OK1 . . . . . . . . . . . . . . 6-10 6.1.1-4 Pressurizer Water Inventory for 1.0-Inch Break in Category OK1 . . . . . 6-11 6.1.1-5 RCS Coolant Inventory for 1.0-Inch Break in Category OK1 . . . . . . . . . 6-12 6.1.1-6 Vessel Mixture Level for 1.0-Inch Break in Category OK1. . . . . . . . . . . 6-13 6.1.1-7 RCS Pressure for 0.5-Inch Break in Category OK1. . . . . . . . . . . . . . . . . 6-14 6.1.1-8 CMT and Accumulator Water for 0.5-Inch Break in Category OK1. . . . 6-15 6.1.19 IRWST Injection for 0.5-Inch Break in Category OK1 ............. . 6-16 6.1.1-10 Pressurizer Water Inventory for 0.5-Inch Break in Category OK1 . . . . . 6-17 6.1.1-11 RCS Coolant Inventory for 0.5-Inch Break in Category OKI . . . .... .6-18 O o:\3661w.wpf:1M61997 June 1997
Xiii LIST OF FIGURES (cont.)
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'u Figure No. Title Page 6.1.1-12 Vessel Mixture Level for 0.5-Inch Break in Category OK1. . . . ..... . 6-19 6.1.1-13 RCS Pressure for SGTR in Category OK1. . ......... . . . . . . . . 6-20 6.1.1-14 CMT and Accumulator Water for SGTR in Category OK1 ....... . 6-21 6.1.1-15 IRWST Injection for SGTR in Category OK1. . . . . . . . . . . . . . . ..... 6-22 6.1.1-16 Pressurizer Water Inventory for SGTR in Category OK1. . . . . . . . . . . . 6-23 6.1.1-17 RCS Coolant Inventory for SGTR in Category OK1. . . . . .......... 6-24 6.1.1-18 Vessel Mixture Level for SGTR in Category OK1 . . . . . . . . . . . . . . . . . 6-25 6.1.1-19 RCS Pressure for Transient (Loss of FW) in Category OK1. . . . . . 6-26 l 6.1.1-20 CMT and Accumulator Water for Transient (Loss of FW)
I in Category OK1. . . . . . . . . . . . . . . . . . . . ................... 6-27 6.1.1-21 IR'WST Injection for Transient (Loss of FW) in Category OK1. ... . . 6-28
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A 6.1.1-22 Pressurizer Water Inventory for Transient (Loss of FW) in Category OK1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-29 6.1.1-23 RCS Coolant Inventory for Transient (Loss of FW) in Category OK1 . . . . . . . . . . . . . . . . . . . . ....................... 6-30 6.1.1-24 Vessel Mixture Level for Transient (Loss of FW) in Category OK1 . . . . 6-31 6.1.4-1 Minimum Vessel Mixture Level for Category OK4 . . . . . . . . . . . . . . . 6-45 6.1.4-2 Time of Minimum Vessel Mixture I.evel for Category OK4 . . . . . . . . . 6-46 6.1.4-3 RCS Pressure for 0.5-Inch Break in Category OK4 . . . . . . . . . . . . . . . . 6-47 6.1.4-4 CMT and Accumulator Water for 0.5-Inch Break in Category OK4 . . . . 6-48 i
6.1.4-5 IRWST Injection for 0.5-Inch Break in Category OK4 . . . . . . . . . . . . . . 6-49 6.1.4-6 RCS Coolant Inventory for 0.5-Inch Break in Category OK4 . . . . . . .. 6-50 6.1.4-7 Vessel Mixture Level for 0.5-Inch Break in Category OK4 .. .. 6-51 6.1.4-8 RCS Pressure for 1.0-Inch Break in Category OK4 . . . . . . .......... 6-52
/_i 6.1.4-9 CMT and Accumulator Water for 1.0-Inch Break in Category OK4 . . . . 6-53 on3661w.wpf:1b.061997 June 1997
XIV LIST OF FIGURES (cont.)
Figure No.
6.1.4-10 Title Page Oll IRWST Injection for 1.0-Inch Break in Category OK4 .... ..... . . . 6-54 l 6.1.4-11 RCS Coolant Inventory for 1.0-Inch Break in Category OK4 . . . . . . . . 6-55 l 6.1.4-12 Vessel Mixture Level for 1.0-Inch Break in Category OK4 . . . . . . . . . . 6-56 I 6.1.9-1 RCS Pressure for 1.0-Inch Break in Category OK9 . . . . ............ 6-69 i
6.1.9-2 Accumulator Water for 1.0-Inch Break in Category OK9 . . . . . . . . . . . . 6-70 6.1.9-3 IRWST Injection for 1.0-Inch Break in Category OK9 . . . . . . . . . . . . . . 6-71 6.1.9-4 RCS Coolant Inventory for 1.0-Inch Break in Category OK9 . . . . . . . . . 6-72 6.1.9-5 Vessel Mixture Level for 1.0-Inch Break in Category OK9 . . . . . . . . . . . 6-73 6.1.9-6 RCS Pressure for SGTR in Category OK9 . . . . . . . . . . ............ 6-74 6.1.9-7 Accumulator Water for SGTR in Category OK9 . . . . . . . . . . . . . . . . . . 6-75 6.1.9-8 IRWST Injection for SGTR in Category OK9 . . . . . . . . . . . . . . . . . . . . . 6-76 6.1.9-9 RCS Coolant Inventory for SGTR in Category OK9 . . . . . . . . . . . . . . . . 6-77 6.1.9-10 Vessel Mixture Level for SGTR in Category OK9 . . . . . . . . . . . . . . . . . 6-78 6.1.9-11 RCS Pressure for Transients (Loss of FW) in Category OK9 . . . . . . . . . 6-79 6.1.9-12 Accumulator Water for Transients (Loss of FW) in Category OK9 .... 6-80 6.1.9-13 IRWST Injection for Transients (Loss of FW) in Category OK9 . . . . . . . 6-81 6.1.9-14 RCS Coolant Inventory for Transients (Loss of FW) in Category OK9 . . 6-82 6.1.9-15 Vessel Mixture Level for Transients (Loss of FW) in Category OK9 . . .6-83 6.2.1-1 Effect of Break Size and Accumulator Injection on Time of Core Uncovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-89 6.3.2.1-1 Minimum Vessel Mixture Level for Category UC1 . . . . . . . . . . . . . . . 6-122 6.3.2.4-1 Minimum Vessel Mixture Level for Non-DVI Line Breaks in
, Category UC5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-127 6.3.2.S-1 Minimum Vessel Mixture Level for Category UC6 with 2 Stage 4 ADS . . . . . . . . . . . . . . . . . . ...... . . . . . . . . . . . . . . . . 6-131 0:\3661w.wpf:1b-061997 June 1997
xv 3 LIST OF FIGURES (cont.)
V) Figure No. Title Page 6.3.2.5-2 Duration of Core Uncovery for Cate 2 Stage 4 ADS . . . . . . . . . . . . . .... gory UC6 with
... .... . . . . . . . . . . . . . . 6-132 6.3.2.S-3 Minimum Vessel Mixture Level for Category UC6 with 1 Stage 3 and 2 Stage 4 ADS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-133 6.3.2.5-4 Duration of Core Uncovery for Category UC6 with 1 Stage 3 and 2 Stage 4 ADS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-134 7.2.5-1 Expansion of Recirculation Branch Showing Probabilities of Success for Each Possible Number of Open Paths . . . . . . . . . . . . . . . 7-32 9.1.2.1-1 Case UC1 Break Liquid Flow . . . . . . . . . . . . . . .................. 9-7 9.1.2.1-2 Case UC1 Break Vapor Flow ................................. 9-8 9.1.2.1-3 Case UCI Pressurizer Pressure . . . . . . . . . . . . . . . ............... 9-9 9.1.2.1-4 Case UCI Pressurizer Level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-10 9.1.2.1-5 Case UC1 Core Makeup Tank Injection Flow . . . . . . . . . . . . . . . . . . . . 9-11 (o') 9.1.2.1-6 Case UC1 Downcomer Mixture Level . . . . . . . . . . . . . . . . . . . . . . . . . . 9-12 9.1.2.1-7 Case UCI Hot Leg to Pressurizer Mass Flow . . . . . . . . . . . . . . . . . . . . 9-13 9.1.2.18 Case UCI Accumulator Injection Flow . . . . . . . . . . . . . . . . . . . . . . . . . 9-14 9.1.2.1-9 Case UC1 First through Third Stage ADS Vapo: Flow . . . . . . . . . . . . 9-15 9.1.2.1-10 Case UCI 4th Stage ADS Liquid Flow through All Open Paths . . . . . . 9-16 l 9.1.2.1-11 Case UC1 Reactor System Coolant Inventory . . . . . . . . . . . . . . . . . . . . . 9-17 l 9.1.2.1-12 Case UCI Upper Plenum and Core Mixture Level . . . . . . . . . . . . . . . . 9-18 9.1.2.1-13 Case UC14th Stage ADS Vapor Flow . . . . . . . . . . . . . . . . . . . . . . . . . . 9-19
, 9.1.2.1-14 Case UC1 IRWST Injection Flow . . . ...... ........... . . . . . . . 9-20 1 l l 9.1.2.1-15 Case UCI Peak Cladding Temperature ................ ... ... 9-21 i
9.1.2.2-1 Case UC2B Break Liquid Flow . . . . . . . ............. ....... . 9-25 l
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Figure No. Title Page O
l 9.1.2.2-3 Case UC2B Pressurizer Pressure .............................9-27 l 1
9.1.2.2-4 Case UC2B Pressurizer Level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-28 9.1.2.2-5 Case UC2B Core Makeup Tank Injection Flow . . . . ..... . . . . . . . . 9-29 l
l 9.1.2.2-6 Case UC2B Downcomer Mixture Level . . . . . . . . . . . . . . . . . . . . . . . . . 9-30 l 1
9.1.2.2-7 Case UC2B Hot Leg to Pressurizer Mass Flow . . . . . . . . . . . . . . . . . . . 9-31 9.1.2.2-8 Case UC2B Accumulator Injection Flow . . . . . . . . . . . . . . . . . . . . . . . 9-3 2 9.1.2.2-9 Case UC2B First through Third Stage ADS Vapor Flow . . . . . . . . . . . . 9-33 9.1.2.2-10 Case UC2B 4th Stage ADS Liquid Flow through All Open Paths ..... 9-34 1
9.1.2.2-11 Case UC2B Reactor System Coolant Inventory . . . . . . . . . . . . . . . . 9-35 9.1.2.2-12 Case UC2B Upper Plenum and Core Mixture Level . .... . . . . . . . . 9-36 9.1.2.2-13 Case UC2B 4th Stage ADS Vapor Flow . . . . . . . . . . . . . . . . . . . . . . . . . 9-37 9.1.2.2-14 Case UC2B IRWST Injection Flow . . . . . . ..... . . . . . . . . . . . . . . . . 9-38 9.1.2.3-1 Case UC5 Break Liquid Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-41 9.1.2.3-2 Case UC5 Break Vapor Flow ................ ... ........... 9-42 9.1.2.3-3 Case UC5 Pressurizer Pressure . . ............................9-43 9.1.2.3-4 Case UC5 Pressurizer Level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-44 9.1.2.3-5 Case UC5 Core Makeup Tank Injection Flow . . . . . . . . . . . . . . . . . . . . 9-45 9.1.2.3-6 Case UC5 Downcomer Mixture Level . . . . . . . . . . . . . . . . . . . . . . . . . 9-46 9.1.2.3-7 Case UC5 Hot Leg to Pressurizer Mass Flow . . . . . . . . . . . . . . . . . . . 9-47 9.1.2.3-8 Case UC5 Accumulator Injection Flow . . . . . . . . . . . ...... .... . 9-48 9.1.2.3-9 Case UC5 First through Third Stage ADS Vapor Flow . . . . . . . . . . . . 9-49 9.1.2.3-10 Case UC5 4th Stage ADS Liquid Flow through All Open Paths ..... 9-50 9.1.2.3-11 Case UC5 Reactor System Coolant Inventory . . ....... . . . . . 9-51 o:\3661w.wpf:1b-061997 June 1997
l xvii LIST OF FIGURES (cont.)
Figure No. 'Iltle Page 9.1.2.3-12 Case UC5 Upper Plenurn and Core Mixture Level . . . . . . . . . . . . . . . . 9-52 9.1.2.3-13 Case UC5 4th Stage ADS Vapor Flow . . .................. . . . . 9 53 9.1.2.3-14 Case UC5 IRWST Injection Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-54 l
9.1.2.3-15 Case UC5 Peak Cladding Temperature . . . . . . . . . . . . . . . . . . . . . . . . . 9-55 9.12A-1 Case UC61 Break Liquid Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-59 i' 9.1.2.4-2 Case UC61 Break Vapor Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-60 9.1.2.4-3 i
Case UC61 Pressurizer Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-61 9.1.2.4-4 Case UC61 Pressurizer Level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-62 9.1.2.4-5 Case UC61 Core Makeup Tank Injection Flow . . . . . . . . . . . . . . . . . . . 9-63 l
9.1.2.4-6 Case UC61 Downcomer Mixture Level . . . . . . . . . . . . . . . . . . . . . . . . . 9-64 l
9.1.2.4-7 Case UC61 Hot Leg to Pressurizer Mass Flow ................... 9-65 9.1.2.4-8 Case UC61 Accumulator Injection Flow . . . . . . . . . . . . . . . . . . . . . . . . 9-66 9.1.2.4-9 Case UC61 First through Third Stage ADS Vapor Flow . . . . . . . . . . . . 9-67 9.1.2.4-10 Case UC614th Stage ADS Liquid Flow through All Open Paths . . . . . . 9-68 l 9.1.2.4-11 Case UC61 Reactor Systern Coolant Inventory . . . . . . . . . . . . . . . . . . . 9-69 i
9.1.2.4-12 Case UC61 Upper Plenum and Core Mixture Level . . . . . . . . . . . . . . . 9-70 9.1.2.4-13 Case UC614th Stage ADS Vapor Flow . . . . . . . . . . . . . . . . . ....... 9-71 9.1.2.4-14 Case UC61 IRWST Injection Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-72 9.1.2.4-15 Case UC61 Peak Cladding Temperature . . . . . . . . . . . . . . . . . ...... 9-73 9.1.2.5-1 Case UC62 Break Liquid Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-77 9.1.2.5-2 Case UC62 Break Vapor Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-78
, 9.1.2.!c3 Case UC62 Pressurizer Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-79
- 9.1.2.5-4 Case UC62 Pressurizer Level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-80 o:\3661w.wpf;1b-061997 I""'1997
xvui LIST OF FIGURES (cont.)
Figure No. T1tle Page G
9.1.2.5-5 Case UC62 Core Makeup Tank Injection Flow . . . . . . . . . . . . . . .... 9-81 9.1.2.54 Case UC62 Downcomer Mixture Level . . . ... ................ 9-82 9.1.2.5-7 Case UC62 Hot Leg to Pressurizer Mass Flow ............... ... 9-83 9.1.2.5-8 Case UC62 Accumulator Injection Flow . ................. .... 9-84 9.1.2.5-9 Case UC62 First through Third Stage ADS Vapor Flow ........... .9-85 9.1.2.5-10 Case UC62 4th Stage ADS Liquid Flow through All Open Paths . . . . . . 9-86 9.1.2.5-11 Case UC62 Reactor System Coolant Inventory . . . . ............. 9-87 9.1.2.5-12 Case UC62 Upper Plenum and Core Mixture Level . . . . . . . . . . . . . . . 9-88 9.1.2.5-13 Case UC62 4th Stage ADS Vapor Flow . . . . . . . . . . . . . . . . . . . . . . . . . 9-89 9.1.2.5-14 Case UC62 IRWST Injection Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-90 9.1.2.6-1 Case UC7 Break Liquid Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-93 9.1.2.6-2 Case UC7 Break Vapor Flow ... ........... . . . . . . . . . . . . . . . . 9-9 4 9.1.2.6-3 Case UC7 Pressurizer Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-95 9.1.2.6-4 Case UC7 Pressurizer Level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-96 9.1.2.6-5 Case UC7 Core Makeup Tank Injection Flow . . . . . . . . . . . . . . .. . . 9-97 9.1.2.6-6 Case UC7 Downcomer Mixture Level . . . . . . . . . . . . . . . . . . . . . . . . . . 9-98 i 9.1.2.6-7 Case UC7 Hot Leg to Pressurizer Mass Flow . . . . . . . . . . . . . . . . . . . . 9-99 9.1.2.6-8 Case UC7 Accumulator Injection Flow . . . . ............ . . . . . 9-100 l
9.1.2.6-9 Case UC7 First through Third Stage ADS Vapor Flow . . . . . . . . . . . . 9-101 9.1.2.6-10 Case UC7 4th Stage ADS Liquid Flow through All Open Paths . . . . . 9-102 9.1.2.6-11 Case UC7 Reactor System Coolant Inventory . . . . . . . . . . . . . . . . . . 9-103 9.1.2.6-12 Case UC7 Upper Plenum and Core Mixture Level . .. ... .. . 9-104 9.1.2.6-13 Case UC7 4th Stage ADS Vapor Flow . . . ........... . . . . . . . . 9-105 oA3661w.wpf:1b-061997 June 1997 l
l
LIST OF FIGURES (cont.)
- Figure No. Title Page
! 9.1.2.6-14 Case UC7 IRWST Injection Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-1%
J 9.2.2.1-1 Peak Cladding Temperatures for Case UC41 . . . . . . . . . . . . . . . . . . . , 9-114 9.2.2.1-2 .
Case UC41 Hot Rod Tclad at Elevation 9.11 Feet . . . . . . . . . . . . . . . . . 9-115 '
i l 9.2.2.1-3 Case UC41 Hot Assembly Top Flows . . . . . . . . . . . . . . . . . . . . . . . . . 9-116 '
1
- 9.2.2.1-4a Case UC41 Upper Head Vessel Pressure . . . . . . . . . . . . . . . . . . . . . . . . 9-117 '
1 l 9.2.2.1-4b Case UC41 Upper Head Vessel Pressure . . . . . . . . . . . . . . . . . . . . . . . 9-118 '
9.2.2.1-5 . Case UC41 Accumulator /CMT Injection Flows . . . . . . . . . . . . . . . . . . 9-119 l 9.2.2.1-6 Case UC41 Peripheral Channel Top Flows . . . . . . . . . . . . . . . . . . . . . . 9-120 9.2.2.1-7 Case UC41 Open Hole / Support Col. Channel Top Flows . . . . . . . . . . 9-121 l
o 9.2.2.1-8 Case UC41 Guide Tube Channel Top Flows . . . . . . . . . . . . . . . . . . . . 9-122 9.2.2.1-9 Case UC41 Peripheral Channel Rod 5 Tclad . . . . . . . . . . . . . . . . . . . . . 9-123 9.2.2.1-10 Case UC41 Open Hole / Support Col. Rod 3 Tclad ................ 9-124 9.2.2.1-11 Case UC41 Guide Tube Rod 4 Tclad . . . . . . . . . . . . . . . . . . . . . . . . . . 9-125 9.2.2.1-12 Case UC41 Core Hot Assembly Void Fraction . . . . . . . . . . . . . . . . . , . 9-126 i 9.2.2.1-13 Case UC41 Lower Plenum Collapsed Liquid Level . . . . . . . . . . . . . . . 9-127 l 9.2.2.1-14 Case UC41 Downcomer Collapsed Liquid Level . . . . . . . . . . . . . . . . . 9-128 i
9.2.2.1-15 Case UC41 Hot Assembly Collapsed Liquid Level . . . . . . . . . . . . . . 9-129 l
9.2.2.1-16 Case UC41 Loop Side Break Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-130 9.2.2.1-17 Case UC41 Vessel Side Break Flow . . . . . . . . . . . . . . . . . . . . . . . . . . 9-131 9.2.22-1 Peak Cladding Temperatures for Case UC41 . . . . . . . . . . . . . . . . . . . 9-134 9.2.2.2-2 Case UC41 Hot Rod Tclad at Elevation 9.11 Feet . . . . . . . . . . . . . . . . . 9-135 3
9.2.22-3 Case UC41 Hot Assembly Top Flows . . . . . . . . . . . . . . . . . . . . . . . . . 9-136 ]
9.222-4a Case UC41 Upper Head Vessel Pressure . . . . . . . . . . . . . . . . . . . . . . . 9-137 i
l o:\3661w.wpf:1b-061997 ,
June 1997 I
l l l
xx LIST OF FIGURES (cont.)
Figure No. Title Page O
9.2.2.2-4b Case UC41 Upper Head Vessel Pressure . . . . . . . . . . . . . . .... . . . 9-138 9.2.2.2-5 Case UC41 Accumulator /CMT Injection Flows ....... ....... 9-139 9.22.2-6 Case UC41 Peripheral Channel Top Flows . . . . . . . . . . . . . . . . . . . . . 9-140 9.2.2.2-7 Case UC41 Open Hole / Support Col. Channel Top Flows . . . . . . . . . . 9-141 9.2.2.2-8 Case UC41 Guide Tube Channel Top Flows . . . . . . . . . . . . . . . . . . . . 9-142 9.2.2.2-9 Case UC41 Peripheral Channel Rod S Tclad ........... . . . . . . . 9-143 9.2.2.2-10 Open Hole / Support Col. Rod 3 Tclad - 9-144 9.2.2.2-11 Case UC41 Guide Tube Rod 4 Tclad . . . . . . . . . . . . . . . . . . . . . . . . . . 9-145 9.2.2.2-12 Case UC41 Core Hot Assembly Void Fraction . . . . . . . . . . . . . . . . . 9-146 9.2.2.2-13 Case UC41 Lower Plenum Collapsed Liquid Level . . . . . . . . . . . . . . . 9-147 9.2.2.2-14 Case UC41 Downcomer Collapsed Liquid Level . . . . . . . . . . . . . . . . . 9-148 9.2.2.2-15 Case UC41 Hot Assembly Collapsed Liquid Level . . . . . . . . . . . . . . . 9-149 9.2.2.2-16 Case UC41 Split Break Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-150 9.2.2.3-1 Case UC42 Peak Cladding Temperatures for Case UC42 . . . . . . . . . . . 9-152 9.2.2.3-2 Case UC42 Hot Rod Tclad at Elevation 9.11 Feet . . . . . . . . . . . . . . . . . 9-153 9.2.2.3-3 Case UC42 Hot Assembly Top Flows . . . . . . . . . . . . . . . . . . . . . . . . 9-154 9.2.2.3-4a Case UC42 Upper Head Vessel Pressure . . . . . . . . . . . . . . . . . . . . . . 9-155 9.2.2.3-4b Case UC42 Upper Head Vessel Pressure . . . . . . . . . . . . . . . . . . . . . . . 9-156 9.2.2.3-5 Case UC42 Accumulator /CMT Injection Flows . . . . . . . . . . . . . . . . . . 9-157 9.2.2.3-6 Case UC42 Peripheral Channel Top Flows . . . . . . . . . . . . . . . . . . . . . 9-158 9.2.2.3-7 Case UC42 Open Hole / Support Col. Channel Top Flows . . . . . . . . . . 9-159 9.2.2.3-8 Case UC42 Guide Tube Channel Top Flows . . . . . . . . . . . . . . . . . . 9-160 9.2.2.3-9 Case UC42 Peripheral Channel Rod 5 Tclad ................... . 9-161 o:\3661w.wpf;1b-061997 June 1997
. \
xxx i
LIST OF FIGURES (cont.) l l
l Figure No. Title Page l 9.2.2.3-10 Case UC42 Open Hole / Support Col. Rod 3 Tclad . . . . . . . . . . . . . . . . 9-162 l 9.2.2.3-11 Case UC42 Guide Tube Rod 4 Tclad . . . . . . . . . . . . . . . . . . . . . . . . . . 9-163 9.2.2.3-12 Case UC42 Core Hot Assembly Void Fraction . . . . . . . . . . . . . . . . . . 9-164 9.2.2.3-13 Case UC42 Lower Plenum Collapsed Liquid Level . . . . . . . . . . . . . . . 9-165 I 9.2.2.3-14 Case UC42 Downcomer Collapsed Liquid Level . . . . . . . . . . . . . . . . . 9-166 9.2.2.3-15 Case UC42 Hot Assembly Collapsed Liquid Level . . . . . . . . . . . . . . . 9-167 1
1 9.2.2.3-16 Case UC42 Loop Side Break Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-168 l
9.2.2.3-17 Case UC42 Vessel Side Break Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-169 1
10.2.1.1-1 Downcomer Collapsed Liquid Level-2 in CLB with 3 ADS l Stage 4 Paths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-22 10.2.1.1-2 Liquid Mass Flow Rate into Core-2 in CLB with 3 ADS Stage 4 Paths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-23 s
10.2.1.1-3 Core Collapsed Liquid Level-2 in CLB with 3 ADS Stage 4 Paths . . . 10-24 10.2.1.1-4 Void Fraction Lower Half of Core-2 in CLB with 3 ADS S ta ge 4 Pa ths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-25 10.2.1.1-5 Void Fraction Upper Half of Core-2 1 CLB with 3 ADS Stage 4 Paths ............................ . . . . . . . . . . . . . . . 10-26 10.2.1.1-6 Peak Cladding Temperature-2 in CLB with 3 ADS Stage 4 Paths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-27 10.2.1.1-7 Core E)it Vapor Mass Flow Rate-2 in CLB with 3 ADS Stage 4 Paths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-28 10.2.1.1-8 Core Exit Liquid Mass Flow Rate-2 in CLB with 3 ADS Stage 4 Paths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 0-2 9 10.2.1.1-9 Core Exit Droplet Mass Flow Rate-2 in CLB with 3 ADS Stage 4 Paths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-30 2
10.2.1.1-10 Upper Plenum Collapsed Liquid Level-2 in CLB with 3 ADS Stage 4 Paths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-31 o:\3661w.wpf:1b-061997 June 1997
xxii l
LIST OF FIGURES (cont.)
l Figure No. 'Iitle Page O
1 l 10.2.1.1-11 PRHR Loop ADS Stage 4 Mass Flow Rate-2 in CLB with 3 ADS Stage 4 Paths ............ .. .................... 10-32 10.2.1.1-12 Non-PRHR Loop ADS Stage 4 Mass Flow Rate-2 in CLB with 3 ADS Stage 4 Pa ths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-33 10.2.1.1-13 PRHR Loop Hot Leg Collapsed Liquid Level-2 in CLB with 3 ADS Stage 4 Paths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-34 10.2.1.1-14 Non-PRHR Loop Hot Leg Collapsed Liquid Level-2 in CLB with 3 ADS Stage 4 Paths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-35 10.2.1.1-15 Upper Plenum Pressure-2 in CLB with 3 ADS Stage 4 Paths . . . . . . . 10-36 1
10.2.1.1-16 Pressure Difference across Vessel-2 in CLB with 3 ADS Stage 4 Paths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-37 l 10.2.1.1-17 DVI Injection Mass Flow Rate-2 in CLB with 3 ADS Stage 4 Paths . . . . . . . . . . . . ............... . . . . . . . . . . . . . . 10-38 10.2.1.2-1 Downcomer Collapsed Liquid Level-2 in CLB with 3 ADS Stage 4 Paths . .............. ............ ... . . . . . . . . . 10-4 '
10.2.1.2-2 Liquid Mass Flow Rate into Core-2 in CLB with 3 ADS Stage 4 Paths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-43 10.2.1.2-3 Core Collapsed Liquid Level-2 in CLB with 3 ADS Stage 4 Paths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-44 10.2.1.2-4 Void Fraction Lower Half of Core-2 in CLB with 3 ADS Stage 4 Paths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-45 10.2.1.2-5 Void Fraction Upper Half of Core-2 in CLB with 3 ADS Stage 4 Paths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-4 6 10.2.1.2-6 Peak Cladding Temperature-2 in CLB with 3 ADS i
Stage 4 Pa ths . . . . . . . . . . . . . . . . . . . . . . . . . . . ....... . . . . . . . 10-47 10.2.1.2-7 Core Exit Vapor Mass Flow Rate-2 in CLB with 3 ADS l Stage 4 Paths . ......................................... 10-48 l 10.2.1.2-8 Core Exit Liquid Mass Flow Rate-2 in CLB with 3 ADS Stage 4 Paths . . . . . . . . . . . . . . . . . . . . .... . . . . . . . . . . . 10-49 10.2.1.2-9 Core Exit Droplet Mass Flow Rate-2 in CLB with 3 ADS Stage 4 Paths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-5 0 l
l o:\3661w.wpf:lb.061997 June 1997
i xxiii 1
LIST OF FIGURES (cont.)
!(' I Figure No. Title Page 10.2.1.2-10 Upper Plenum Collapsed Liquid Level-2 in CLB with 1
3 ADS Stage 4 Pa ths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-51 i
1 I
i 10.2.1.2-11 PRHR Loop ADS Stage 4 Mass Flow Rate-2 in CLB with l 3 ADS Stage 4 Paths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-52 l
l 10.2.1.2-12 Non-PRHR Loop ADS Stage 4 Mass Flow Rate--2 in CLB
. with 3 ADS Stage 4 Paths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . 10-53 10.2.1.2-13 PRHR LOOP Hot Leg Collapsed Liquid Level-2 in CLB with 3 ADS Stage 4 Paths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-54 10.2.1.2-14 Non-PRHR Loop Hot Leg Collapsed Liquid Level-2 in l CLB with 3 ADS Stage 4 Paths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-55 10.2.1.2-1S Upper Plenum Pressure-2 in CLB with 3 ADS Sta Pa ths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .................
. . . ge 4 10-56 l
10.2.1.2-16 Pressure Difference Across Vessel-2 in CLB with 3 ADS Stage 4 Pa ths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-57
( 10.2.1.2-17 DVIInjection Mass Flow Rate--2 in CLB with 3 ADS l Sta ge 4 Paths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-58 10.2.1.3-1 Downcomer Collapsed Liquid Level-Double Ended DVI ;
Break with Isolated Containment . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-62 l 10.2.1.3-2 Liquid Mass Flow Rate Into Core-Double Ended DVI l l Break with Isolated Containment . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-63 10.2.1.3-3 Core Collapsed Liquid Level-Double Ended DVI Break with Isolated Containment . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-64 l 10.2.1.3-4 Void Fraction Lower Half of Core-Double Ended DVI Break with Isolated Containment . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-65 10.2.1.3-5 Void Fraction Upper Half of Core-Double Ended DVI
- j. Break with Isolated Containment . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-66 l
10.2.1.3-6 Peak Cladding Ternperature-Double Ended DVI Break with Isolated Containment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-67 10.2.1.3-7 Core Exit Vapor Mass Flow Rate-Double Ended DVI Break with Isolated Containment . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-68 o:\3661w.wpf:1t>061997 June 1997 l
_l XXIV l
LIST OF FIGURES (cont.)
O l
Figure No. 'iitle Page 10.2.1.3-8 Core Exit Liquid Mass Flow Rate-Double Ended DVI Break with Isolated Containment . . . . . . . . . . . .... ....... .. . 10-69 10.2.1.3-9 Core Exit Droplet Mass Flow Rate-Double Ended DVI Break with Isolated Containment . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-70 1
10.2.1.3-10 Upper Plenum Collapsed Liquid Level-Double Ended DVI Break with Isolated Containment . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-71 10.2.1.3-11 PP.HR Loop ADS Stage 4 Mass Flow Rate-Double Ended DVI Break with Isolated Containment . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-72 10.2.1.3-12 Non-PRHR Loop ADS Stage 4 Mass Flow Rate-Double Ended DVI Break with Isolated Containment . . . . . . . . . . . . . . . . . . 10-73 10.2.1.3-13 PRHR Loop Hot Leg Collapsed Liquid Level-Double Ended DVI Break with Isolated Containment . . . . . . . . . . . . . . . . . . . . . . . . . 10-74 10.2.1.3-14 Non-PRHR Loop Hot Leg Collapsed Liquid Level-Double Ended DVI Break with Isolated Containment . . . . . . . . . . . . . . . . . . . 10-75 10.2.1.3-15 Upper Plenum Pressure-Double Ended DVI Break with Isolated Containment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-76 10.2.1.3-16 Pressure Difference across Vessel-Double Ended DVI Break with Isolated Containment . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-77 10.2.1.3-17 DVI Injection Mass Flow Rate-Double Ended Break with Isolated Containment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-78 10.2.1.4-1 Downcomer Collapsed Liquid Level-Single Ended DVI Break with Isolated Containment . . . . . . . . . . . . . . . . . . . . . . ... . 10-82 10.2.1.4-2 Liquid Mass Flow Rate Into Core-Single Ended DVI Break with Isolated Containment . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-83 10.2.1.4-3 Core Collapsed Liquid Level-Single Ended DVI Break with Isolated Containment . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-84 10.2.1.4-4 Void Fraction Lower Ha!( of Core-Single Ended DVI Break with Isolated Containment . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-85 10.2.1.4-5 Void Fraction Upper Half of Core-Single Ended DVI
. 10-86 Break with Isolated Containment . . . . . . . . . . . . . . . ..........
e o:\3661w.wpf:lt>&l997 June 1997
XXV LIST OF FIGURES (cont.)
Figure No. 'Iltle Page 10.2.1.4-6 Peak Cladding Temperature-Single Ended DVI Break with Isolated Containment . . . . . . . . . . . . . . . . . . . ............. 10-27 10.2.1.4-7 Core Exit Vapor Mass Flow Rate-Single Ended DVI .
Break with Isolated Containment . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-86 l I
10.2.1.4-8 Core Exit Liquid Mass Eow Rate-Single Ended DVI -
Break with Isolated Containment . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-89 102.1.4-9 Core Exit Droplet Mass Flow Rate-Single Ended DVI Break with Isolated Containment . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-90 10.2.1.4-10 Upper Plenum Collapsed Liquid Level-Single Ended DVI Break with Isolated Containment . . . . . . . . . . . . . . . . . . . . . . . . . 10-91 10.2.1.4-11 PRHR Loop /.DS Stage 4 Mass Flow Rate-Single Ended DVI Break with Isolated Containment . . . . . . . . . . . . . . . . . . . . . . . . . 10-92 10.2.1.4-12 Non-PRHR Loop ADS Stage 4 Mass Flow Rate-Single Ended DVI Break with Isolated Containment . . . . . . . . . . . . . . . . . . . 10-93 10.2.1.4-13 PRHR Loop Hot Leg Collapsed Liquid Level-Single l Ended DVI Break with Isolated Containment . . . . . . . . . . . . . . . . . . . 10-94 10.2.L4-14 Non-PRHR Loop Hot Leg Collapsed Liquid Le,rel-Single Ended DVI Break with Isolated Containment . . . . . . . . . . . . . . 10-95 l 10.2.1.4-15 Upper Plenum Pressure-Single Ended DVI Break with Isolated Containment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-96 10.2.1.4-16 Pressure Difference across Vessel-Single Ended DVI Break with Isolated Containment . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-97 10.2.1.4-17 DVI Injection Mass Flow Rate-Single Ended DVI Break with Isolated Containment . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-98 10.2.2.1-1 Downcomer Collapsed Liquid Level-Double Ended DVI Break with Unisolated Containment . . . . . . . .. . . . . . . . . . . . . . . . . .10-102 10.2.2.1-2 , Liquid Mass Flow Rate into Core-Double Ended DVI Break with Unisolated Containment . . . . . . . . . . . . . . . . . . . . . . . . .10-103 10.2.2.1-3 Core Collapsed Liquid Level-Double Ended DVI Break with Unisolated Containment . . . . . . . . . . . . . . . . . . . . . . . . .10-104 O
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I xxvi i
L!5I' OF FIGURES (cont.)
Figure No. Title Page 911 10.2.2.1-4 Void Fraction Lower Half of Core-Double Ended DVI Break with Unisolated Containment . . . . . ... . . . . . . . . . . . . . . .10-105 10.2.2.1-5 Void Fraction Upper Half of Core-Double Ended DVI Break with Unisolated Containment . . . . . . . . . . . . . . . . . . . . . . . . .10-106 10.2.2.1-6 Peak Cladding Temperature-Double Ended DVI Break with Unisolated Containment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19137 10.2.2.1-7 Core Exit Vapor Mass Flow Rate-Double Ended DVI Break with Unisolated Containment . ..... ..... . . . . . . . . . . .10-108 ;
1 10.2.2.1-8 Core Exit Liquid Mass Flow Rate-Double Ended DVI Break with Unisolated Containment . ... ....... . . . . . . . . . . .10-109 l 10.2.2.1-9 Core Exit Droplet Mass Flow Rate-Double Ended DVI i Break with Unisolated Containment . . . . . . . . . . . . . . . . . . . . . . . .10-110 1 10.2.2.1-10 Upper Plenum Collapsed Liquid Level-Double Ended DVI Break with Unisolated Containment . . . . . . . . . . . . . . . . . . . . .10-111 1 10.2.2.1-11 PRHR Loop ADS Stage 4 Mass Flow Rate-Double Ended DVI Break with Unisolated Containment .... . . . . . . . . . . . . . . . .10-112 10.2.2.1-12 Non-PRHR Loop ADS Stage 4 Mass Flow Rate-Double Ended DVI Break with Unisolated Containment . . . . . . . . . . . . . . . .10-113 10.2.2.1-13 PRHR Loop Hot Leg Collapsed Liquid Level-Double Ended DVI Break with Unisolated Containment . . . . . . . . . . . . . ..10-114 10.2.2.1-14 Non-PRHR Loop Hot Leg Collapsed Liquid Level-Double Ended DVI Break with Unisolated Containment . . . . . . . . . . . . . . . .10-115 10.2.2.1-15 Upper Plenum Pressure-Double Ended DVI Break with Unisolated Containment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-116 10.2.2.1-16 Pressure Difference across Vessel-Double Ended DVI Break with Unisolated Containment ....... . . . . . . . . . . . . . . . .10-117 10.2.2.1-17 DVI Injection Mass Flow Rate-Double Ended DVI Break with Unisolated Containment . . . . . . . . . . . . . . . . . . . . . . . . .10-118 10.2.2.2-1 Downcomer Collapsed Liquid Level-Single Ended DVI l
Break with Unisolated Containment . . . . . . . . . . . . . . . . . . . . . . . .10-122 I
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xxvii
- LIST OF FIGURES (cont.)
Title Page Figure No.
10.2.2.2-2 Liquid Mass Flow Rate into Core-Single Ended DVI Break with Unisolated Containment . . . . . . . . . . . . . . . . . . . . . . . . .10-123 10.2.2.2-3 Core Collapsed Liquid Level-Single Ended DVI Break with Unisolated Containment . . . . . . . . . . . . . . . . . . . . . . . . .10-124 102.2.2-4 Void Fraction Lower Half of Core-Single Ended DVI l Break with Unisolated Containment . . . . . . . . . . . . . . . . . . . . . . . . .10-125 10.2.2.2-5 Void Fraction Upper Half of Core-Single Ended DVI Break with Unisolated Containment . . . . . . . . . . . . . . . . . . . . . . . . .10-126 10.2.2.2-6 Peak Cladding Temperature-Single Ended DVI Break with Unisolated Containment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-127 10.2.2.2-7 Core Exit Vapor Mass Flow Rate-Single Ended DVI Break with Unisolated Containment . . . . . . . . . . . . . . . . . . . . . . . . .10-128 10.2.2.2-8 Core Exit Liquid Mass Flow Rate-Single Ended DVI Break with Unisolated Containment . . . . . . . . . . . . . . . . . . . . . . . . .10-129
/G V 10.2.2.2-9 Core Exit Droplet Mass Flow Rate-Single Ended DVI Break with Unisolated Containment . . . . . . . . . . . . . . . . . . . . . . . . .10-130 10.2.22-10 Upper Plenum Collapsed Liquid Level-Single Ended DVI Break with Unisolated Containment . . . . . . . . . . . . . . . . . . . . .10-131 10.2.2.2-11 PRHR Loop ADS Stage 4 Mass Ilow Rate-Single Ended DVI Break with Unisolated Containment . . . . . . . . . . . . . . . . . . . . .10-132 10.2.22-12 Non-PRHR Loop ADS Stage 4 Mass Flow Rate-Single Ended DVI Break with Unisolated Contamment . . . . . . . . . . . . . . . .10-133 10.2.2.2-13 PRHR Loop Hot Leg Collapsed Liquid I.evel-Single Ended DVI Break with Unisolated Contamment . . . . . . . . . . . . . . . .10-134 10.2.22-14 Non-PRHR Loop Hot Leg Collapsed Liquid Level-Single Ended DVI Break with Unisolated Containment . . . . . . . . . . . . . . . .10-135 t
10.2.2.2-15 Upper Plenum Pressure-Single Ended DVI Break with Unisolated Containment . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . .10-136 10.2.2.2-16 Pressure Difference across Vessel-Single Ended DVI Braak with Unisolated Containment . . . . . . . . . . . . . . . . . . . . .10-137
{
t l
I o:\3661w.wpt:1b-061997 June 1997 l
I I
xxviii LIST OF FIGURES (cont.)
Figure No.
Title Page 10.2.2.2-17 DVIInjection Mass Flow Rate-Single Ended DVI Break with Unisolated Containment . ....... ........... .10-138 10.2.2.3-1 Downcomer Collapsed Liquid Level, Sump Window-Single Ended DVI Break with Unisolated Containment . . . . . . . . . . .10-140 10.2.2.3-2 Core Collapsed Liquid Level, Sump Window-Single Ended DVI Break with Unisolated Containment . . . . . . . . . . . . . . . .10-141 10.2.2.3-3 Peak Cladding Temperature, Sump Window-Single Ended DVI Break with Unisolated Containment . . . . . . . . . . . . . . .10-142 10.2.2.3-4 Core Exit Vapor Flow, Sump Window-Single Ended DVI Break with Unisolated Containment . . ............... . . . . . .10-143 10.2.2.3-5 DVI Injection, Sump Window-Single Ended DVI Break with Unisolated Containment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-144 10.2.2.3-6 Core Exit Vapor Flow-Single Ended DVI Break with Unisolated Containment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10-145 10.2.2.3-7 DVI Injection-Single Ended DVI Break with i
Unisolated Containment . . . . . . . . . . . . . . ...
. . . . . . . . . . . . . . .10-146 l
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. _ _ _ _ . . _ _ _ _ _ _ . _ _ _ _ . _ . . _ . _ . _ . _ _ . - _ _ _. .. _ _ m _ . _ . _ -
xxix LIsr OF ACRONYMS O ADS Automatic depressurization system ATWS Anticipated transient without scram CCS Component cooling water system CD - Discharge coefficient CDF Core damage frequency
' CI Containment isolation CMT Core makeup tank DAS _ Diverse actuation system DBA Design basis accident DECLG Double-ended cold-leg guillotine (break)
DECLS Double-ended cold-leg split (break)
.DNB Departure from nudeate boiling DVI Direct vessel injection HL Hot leg IRWST In-containment refueling water storage tank ITAAC Inspection, tests, analysis, and acceptance criteria j LB Line break LLOCA Large loss-of-coolant accident LRF Large release frequency LTC Long-term recirculation cooling MFW Main feedwater MLOCA Medium loss-of-coolant accident MSIV Main steam isolation valve i NLOCA Intermediate loss-of-coolant accident l NRC Nuclear Regulatory Commission l OSU Oregon State University l PCS Passive containment cooling system l PCT Peak cladding temperature l PIRT Phenomena identification and ranking table l PMS Protection and safety monitoring system l PRA Probabilistic risk assessment l PRHR Passive residual heat removal system
! PXS Passive core cooling system l RCS Reactor coolant system RNS Normal residual heat remov'al system SFW Startup feedwater SGTR Steam generator tube rupture SI Safety injection l SLB Steam line break j -SLOCA Small loss-of-coolant accident SSAR Standard Safety Analysis Report STC Short-term cooling SV Safety valve SWS Service water system i TlH Thermallhydraulic LO
+
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1 l
EXECUTIVE
SUMMARY
l This report documents an evaluation that was performed to support the passive system reliability assessment of the AP600 plant. The thermallhydraulic (TE) uncertainty i evaluation process was developed to address concems that uncertainties in predicting small changes in the AP600 plant conditions could lead to different conclusions on the success of I core cooling in the AP600 Probabilistic Risk Assessment (PRA). This concern is due to the passive nature of the safety-related systems in AP600. The goal of the TE uncertainty evaluation process is to demonstrate that the sets of equipment that have been credited as providing successful core cooling in the PRA (i.e., success criteria) are indeed successful, even with the consideration of TE uncertainty. ,
The TE uncertainty evaluation process focuses on the accident progressions that occur when there are multiple equipment failures, and evaluates the plant response to specific equipment failures and successes. The accident progression is divided into short-term cooling and long-term cooling concerns. The short-term phase of the accident starts with the accident initiation, proceeds through core makeup tank (CMT) and accumulator injection, and concludes with the establishment of gravity injection from the in-containment refueling water storage tank (IRWST). The long-term phase of the accident starts with the final period of IRWST gravity injection, and continues with the long-term steady-state sump recirculation.
O The TE uncertainty evaluation process integrates information from the PRA with TM analyses. Rather than performing TH analyses on the most limiting combinations of equipment failures, cases for TH analyses are defined based on their relative potential risk importance as determined in the PRA. The success paths on the PRA event trees are
, . dissected, and then categorized based on the plant response. The categorization is performed l primarily based upon existing analyses and an understanding of how equipment failures could impact the important elements in the accident progression. The categorization process is fully documented in Sections 6 and 7 of the report.
The categorization of the success paths leads to a list of potentially risk-significant accident l scenarios for short-term cooling and long-term cooling should the paths not be success. TH l' analyses are performed on these PRA-important accident scenarios, using computer codes l
and methods that are consistent with design basis accidents (DBAs). The difference between the TH uncertainty analyses and the DBA analyses is the additional equipment failures that are most important to the PRA results. This process bounds the TH uncertainty rather than quantifying it. The results of the TE analyses are documented in Sections 9 and 10 of the
- report.
}
- j. The comprehensive process undertaken to address the potential impact of TH uncertainty J
on the AP600 PRA proWdes a considerable basis for the claims of successful core coolhg for r.
l o:\3661w.wpf:1b-061797 June 1997
2 multiple-failure accidents. The result of the process is confirmation that the majority of the success criteria specified in the AP600 PRA for passive-only accident sequences lead to successful core cooling, even when conservatisms consistent with design basis methodology are applied. For multiple-failure accident sequences that exceed the 2200 F PCT core cooling criterion using conservative assumptions, the effect on both the Focused PRA and the Baseline PRA was determmed. The effect on the PRA is small, and the Focused PRA total core damage frequency and large release frequency remain within the goals established in SECY-94-84. More importantly, the conclusions and insights drawn from the PRA results are not affected.
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1-1 1 INTRODUCTION
'd The AP600 design incorporates passive engineered safety features that perform safety-related functions to mitigate accidents and to establish safe shutdown conditions following an event in which active nonsafety-related systems are unable to do so. An extensive range of activities have been completed as part of the AP600 design certification process to provide confidence in the design capabilities and reliability of the safety-related, passive systems and components.- An overview of these activities, and references to the appropriate documentation, are provided in Ref.1. One of the remaining efforts to resolve passive system reliability issues, as' identified in Ref.1, is to evaluate the potential impact of j thermalhydraulic uncertainties on the PRA.
The purpose of a PRA is to provide insights into any risk-significant vulnerabilities of the plant. This is done by modeling plant response to potential core damage initiating events, and quantifying core damage frequency (CDF) and large-release frequency (LRF), and the
- important contributors to these measures. One of the elements in performing a PRA is to l define success criteria, which specify the minimum sets of equipment needed to prevent core l
damage under various conditions. The PRA generally defines success criteria based on the -
nominal performance of the plant. The purpose of nominal assumptions is to maintain the
! PRA plant model as close to reality as possible, allowing one to obtain the most accurate insights on any risk vulnerabilities of the plant. However, the TM uncertainty issue is based
! on a concern that the use of nominal conditions ignores the potential impact of uncertainties in predicting the effects of small changes in system conditions on system performance. The goal of the TIH uncertainty evaluation process is to show that the consideration of TM -
uncertainty does not significantly affect the PRA results.
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Introduction . June 1997 o:\3661w.wpf:lt>061697 i
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2-1 l
2 DEFINITION OF THERMAL-HYDRAULIC UNCERTAINTY l The term "TM uncertainty" is used in relationship to predicting the behavior of passive systems in AP600. Because of the passive nature of the safety-related systems in AP600 and l the reliance on small changes in pressure for driving fluid circulation, a concern has been expressed that uncertainties in predicting the system conditions could lead to different conclusions on the success of core cooling. The small changes in system conditions could be due to different accident conditions than modeled, or uncertainty in analytical models.
Specific sources of TE uncertainty that have been identified as potential concerns are:
l .
Initial and boundary conditions, l .
Code uncertainty (based on testing and scaling uncertainties),
l .
User-selected inputs and modeling methods.
To achieve the goal of this program, it must be shown that the consideration of TIH uncertairities does not significantly inryact the PRA results. Furthermore, because the concem is passive system reliability, the Focused PRA is the primary basis for comparison and determination of impact. The Focused PRA is a sensitivity study to the AP600 PRA.
The sensitivity study does not include active systems for accident mitigation purposes. Use of the Focused PRA ensures that active systems will not camouflage the importance of passive systems, or the uncertainty in predicting their performance. The impact on the g Baseline PRA is also addressed, but is of secondary importance, as discussed in Section 43.
As described in the following sections, the TH uncertainty evaluation process does not quantify the sources of uncertainty, nor is it solely a TE analysis exercise. Rather, the TE vncertainty evaluation process identifies a set of low T/H margin, FRA-important accident scenarios, and shows acceptable TE performance when the uncertainties are bounded.
l
- p LU Definition of Thermal-Hydraulic Uncertainty Jui*1997 o
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- . . - -- - ~_- - - _-_ - - - ~ . _ .. - _ - .. - . - . - . - - ..
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3-1 i
- .3 EVALUATION PROCESS l
-t The PRA TH uncertainty evaluation process integrates PRA information with results from l TM analyses. The overall goal is to show that the successful core cooling paths in the l
l AP600 PRA have been defined so that the results and conclusions of the PRA are not affected by the consideration of TE uncertainty. In other words,- the success criteria are defined l broadly to encompass a range of accident conditions, typically with substantial margin to l core damage. The emphasis of the TM uncertainty evaluation process is on the success paths in the PRA, while the PRA usually focuses on the definition and assessment of core damage paths. This section provides an overview of the entire process, and serves as a
. roadmap to the rest of the report.
The overall process begins and ends with the AP600 PRA. Both the Baseline and Focused PRA are considered, as explained in Section 43. The success paths on the AP600 PRA event p trees are " expanded," which means that more questions are asked than in the PRA event trees, to differentiate the failed equipment from the functioning equipment. The method and l_ scope of the event tree expansion are discussed in Sections 4.1 and 4.2. The results of the l event tree expansions, along with the frequency quantification of each success path, are documented in Section 4.4. The ev.nt tree expansion and success path quantification provide j useful information that is used to better understand which accident scenarios (i.e., equipment failures) are most significant to the PRA.
L The information from the expanded event trees is used to address both the short-term cooling (STC) accident progression through IRWST injection and the long-term cooling (LTC) accident progression through sump recirculation. Two parallel efforts are undertaken to categorize different types of accidents, define limiting PRA-important cases for further TH analyses, and to perform TM analyses with detailed codes and conservative methods.
The short-term accident progression work scope considers an accident from initiation, through the injection of the CMTs and accumulators, and concludes when IRWST injection is
- established. The success paths on the expanded event trees are grouped into two types of categories based on the plant response through IRWST injection. Sections 5.1 and 5.2 provide information on how the categorization is performed. The first type of category, discussed in Section 6.1, is designated as "OK." OK categories generally contain success paths in which the core remains covered. Many of the OK categories are supported by DBA analyses, including large-break loss-of-coolant accident (LOCA) with up to one single failure in which the core does not remain covered. Additional support of OK categories is provided by !
MAAP4 analyses to show that the core remains covered, and therefore TE uncertainty is j not likely to impact the conclusion of successful core cooling. The MAAP4 code is used in a l l manner consistent with the MAAP4NOTRUMP benchmarking documented in Ref. 2. I l l Resolution Process June 1997 i o:\3661w.wpf:1b-061697 !
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The second short-term category type is designated as "UC." UC categories contain success !
paths in which some core uncovery is anticipated. Section 6.2 discusses the definition of each of the UC categories. Supporting analyses are not provided unless the category is i determined to be PRA-important. In Section 6.3.1, the category is designated as PRA- I important if the total frequencies of the success paths in the category exceed 1 percent of the I Focused PRA CDF or LRF. An assessment is also made to determine if any of the success paths would impact the Baseline PRA CDF or LRF by at least 1 percent. In Section 6.3.2, MAAP4 analyses for the low-margin, PRA-important scenarios are used to define lirniting l cases for further TlH analyses. Once again, the MAAP4 code is used in a manner consistent l with the MAAP4/NOTRUMP benchmarking documented in Ref. 2.
A separate categorization process is performed, using the same set of PRA success sequences, I for long-term cooling in which the core is cooled by passive sump recirculation. However, as discussed in Section 5.3, there are different factors that may affect long-term cooling. In addition, there is no existing analysis basis to refine categories based on whether core uncovery is anticipated. Therefore, the long-term cooling categorization that is documented in Section 7 defines several groups of sequences, of varying potential PRA importance, based on equipment availability effects on recirculation cooling rather than on the basis of " low margin."
Section 8 compares the results of the short-term categorization to the long-term categorization and explains the similarities and differences in the PRA-important cases that are defined for further TM analyses.
For both short-term and long-term cooling, TH analyses are performed using detailed DBA codes. Equipment successifailure is defined by scenarios that are PRA-important. The TM analysis assumptions and inputs are as consistent as possible with those used for design basis accidents. Success is based on maintaining adequate core cooling, generally consistent with DBA decay heat requirements per 10CFR50.46, Appendix K. Significant sources of uncertainty are bounded in the TM analyses by using conservative assumptions and inputs.
For short-term cooling analyses of large-break LOCAs, however, methods consistent with best-estimate LOCA are employed. The short-term analyses are documented in Section 9, and the long-term analyses are documented in Section 10.
The final step in the PRA TM uncertainty evaluation process is to assess the impact of the TH analysis results on the AP600 PRA. For most of the cases, successful core cooling is demonstrated with conservative analysis assumptions, confirming the validity of the success criteria definitions in the AP600 PRA. For a limited set of accident conditions, the j conservative analyses do not show successful core cooling, and Section 11 provides a i discussion of the significance of these conditions to the results and conclusions of the AP600 PRA. The overall process is summarized in a schematic in Figure 3-1.
(
Resolution Process June 1997 o:\3661w.wpf:1M61897
_ . ._. . . - . . _ _ .-_._-_.m , _ _._ - .~ - - . _ _ _ _ _ . . .._--m_ _mm I
4 3-3 l 1
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1 Expand and Quantify Paths
- I on PRA Event Trees
'Short-Term Long Term "Ihrough IRWSTInjection Sump Recirculation Categorize 5.1.516 53.7.1.7.2 Success Paths Based on Group Success l
Similarities Paths Based on Similar ptnent
" 6.1 ' 6.2 Failures )
OK Categories UC Categories
! ir ir 3r 7.2.1 63.1 73 Determine Low- Determine y Margin PRA-Important by DBA important Scenarios Scenarios 73
( if 63.2 e ir 3*I# **8 Select Limiting Compare Cases Cases for T/H
- for Short-Term & 6 Multiple-Failcre s
Analyses Long-Term Cooling , }or _TM I
' 'f to 9 l j I' 0""
Perform !
Conservative 8 Cmative TM An yses T/H Analyses e 11 Determine the Significanceof the
- TM Analyses Results on the Results and Conclusions of the AP600 PRA
- The numbers outside each box indicate the corresponding report sections.
l' I
, Figure 3-1. AP600 PRA TlH Uncertainty Evaluation Process 4
Resolution Process June 1997 o:\3661w.wpf:1b-061897 l
l _ _
- .- - - . ~ _ - - . - - .- - ----.-._- - - -
4-1
! 4 EXPANDED EVENT TREES lO V
4.1 EXPANDED PRA EVENT TREE METHODOLOGY p The first step of the TlH uncertainty evaluation process is to expand the Focused PRA event l trees and to quantify the frequency of the success paths. Success paths are not normally l quantified in a PRA, since core damage is the focus. The purpose of quantifying the frequency r,f success paths for the T/H uncertainty evaluation is to gain perspective on the relative 4equency of specific success scenarios. This information will ultimately be used to define PRA-important scenarios that could be impacted by TlH uncertainty.
l l " Expanding" the event trees is necessary to differentiate between scenarios that are grouped together in the PRA. A single success path in the AP600 PRA represents many combinations of equipment failures and successes. As an example, Figure 4-1 shows the medium loss-of-l coolant accident (MLOCA) event tree as it appears in the Focused PRA. Table 4-1 lists the
- functioning equipment that is included within the top success path on the MLOCA event tree. Table 4-1 also identifies the equipment assumptions that are made in the corresponding accident analysis that supports the success path.
As shown in Table 4-1, the equipment configuration that has previously been used in the success analysis (Appendix A of Ref. 3) to justify a specific success path is the most
'O* pessimistic set of functioning equipment for that path. An assumption of minimum functioning equipment leads to the most limiting thermallhydraulic prediction of the accident progression. Even if the bounding scenario analysis shows core uncovery, there are many other accident scenarios (or sets of functioning equipment) represented by the same success path that may not result in core uncovery. Therefore, for this evaluation of TlH uncertainty, the success paths on the event trees need to be refined or expanded to show the various equipment success combinations so that differences in accident progressions can be assessed.
There are options for how to expand the success paths on an event tree. There are four key elements to the method that was developed to perform the expansion.
- 1. There are many top-level events that could be used to ask questions and further refine the success paths. Table 4-2 summarizes the options that were considered, and why they were or were not selected.
- 2. The expansion of the event tree does not change the definition of success. All success l paths on the expanded event tree are represented within an existing success path in the Focused PRA. All core damage paths on the expanded event tree are core damage paths in the Focused PRA.
1 Expanded Event Trees June 1997 o:\3661w.wpf:1b-061697
4-2 Fundamental to the expansion is the necessity to ask additional equipment questions l that are not explicitly modeled in the PRA. However, each question only differentiates between distinct successful accident progressions that are grouped within a success path -
in the PRA. The additional questions can better represent reality, but tney cannot cause success definitions to become either eore or less conservative.
- 3. Success paths containing more than three system failures are not further expanded.
Occurrence of three failures is deemed to sufficiently decrease the frequency of a path.
Imposing the three-failure limit also helps to restrict the event tree expansion to a manageable size. The net effect of this restriction is that paths toward the top of the expanded tree are broken into more detail than those toward the bottom.
An alternative approach is to expand an event tree until the success paths reach a cut-off frequency. However, this would require quantification results to be integrated with the construction of the event tree. The three-system-failure expansion method was chosen because it is a systematic, understandable method that allows event tree development independent of the quantification results.
- 4. Top events are arranged in an order to nurunuze the number of paths. This changes the location of the injection and recirculation line question from the last top event in the Baseline and Focused PRA event trees to the first top event in the expanded event trees.
9 9
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4-3 Table 4-1 Comparison of Equipment on Event Tree Success Path to Equipment Assumptions in O Supporting Analysis Equipment That May Function for Success Path 1 on Bounding Scenario Typically Used for MLOCA Event Tree in Focused PRA PRA Accident Analysis 1 or 2 CMTs 1CMT 0,1, or 2 stage 1 ADS
- 0 stage 3 ADS 2,3, or 4 stage 4 ADS 2 stage 4 ADS 1 0,1, or 2 accumulators
- 0 accumulators 1 or 2 IRWST injection lines 1 IRWST line 21 recirculation line 21 recirculation line Success or failure of containment isolation
- Failure of complete containment isolation Note:
- Not broken out by a top-event question, but implicit within scenario possibilities.
1 O
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4-4 Table 4-2 Options for Expanding Event Tree Success Paths Option Used? Reason Break Size No Break size and location are already used to define different initiating events. Although within an initiating event there remains some variability in plant response Break Location depending on the size and location of the break, there ;
was no added benefit to further refinement on the event trees.
Number of CMTs Yes Whether there is 1 or 2 CMTs does not make a significant difference in the course of the accident progression. )
However, the CMTs are highly reliable, and make an ;
important contribution to refinement of the frequency of a 4 given accident scenario. That is, for a given scenario, the most likely condition is both CMTs available.
Number of Stage 1 ADS No Stage 1 ADS li , ., are small, and do not significantly Lines impact the course of the accident progression.
Number of Stage 2G ADS Yes Stage 2 and 3 ADS lines can impact the ability to achieve Lines IRWST gravity injection.
Number of Stage 4 ADS Yes Stage 4 ADS lines can impact the ability to achieve IRWST Lines gravity injection and long-term recirculation cooling.
)
Number of Accumulators Yes The number of accumulators is important to the core uncovery issues discussed in Section 6.3.
Number of IRWST Lines Nom The ability to achieve IRWST gravity injection and long-term recirculation is most dependent on the number of open ADS lines and whether the containment is isolated.
Number of Recirculation The number of lines open, as long as there is a pathway Lines f r injection, is not as crucial an element to successful core cooling.
Whether Containment is Yes The containment backpressure that occurs when the Fully Isolated contamment is isolated can impact the ability to achieve IRWST gravity injection. Containment isolation also affects the amount of water available in the sump for recirculation. Also, containment isolation impacts the large release frequency calculation if the accident scenario is counted as core damage.
Notes:
(1) A iutther breakdown of the number of successful recirculation paths is performed for long-term cooling, and is documented in Section 7.2.
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. . . . , _ . . _ _ . . _ - . ~ . . . _ . _ _ . _ _ . . _ _ . _ _ _ _ _ _ _ _ . . _ . .
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l l
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- 2,3 or 4 Acc 0 l
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~
OK = Successful Core Cooling l
i CD = Core Damage 1
l l
Figure 41 MLOCA Event Tree in Focused PRA o
Expanded Event Trees June 1997 o:\3661w.wpf 1t>461697 l
l l
, 4-6 l
4.2 SCOPE OF EXPANDED EVENT TREES There are ten expanded event trees developed for the T/H uncertainty evaluation. They further define the equipment available for the majority of the success paths modeled in the Focused PRA. The relationship between the expanded event trees and the Focused PRA event trees is shown in Table 4-3.
The success paths that are not included on the expanded event trees are ones in which successful core cooling can be achieved without ADS actuation. An example of this is a loss of main feedwater event, which is successful without ADS if the passive residual heat removal system (PRHR) functions. The PRHR is the safety-related method of removing decay heat, and leads to successful core cooling as demonstrated in Chapter 15 of the AP600 Standard Safety Analysis Report (SSAR) (Ref. 4). Primary coolant is not lost, and there is no need for inventory makeup from the CMTs, accumulators, IRWST gravity injection, or long-l term recirculation. In addition to the PRHR, decay heat removal can occur from other active,
, nonsafety-related systems. These options are modeled in the Baseline PRA, but are conservatively not modeled in the Focused PRA.
Therefore, the success paths that are expanded for the T/H uncertainty evaluation are loss-of-coolant accidents (LOCAs). The loss of coolant can either be the initiating event, or can be the result of a loss-of-heat-sink accident. The loss of coolant is severe enough to require l
inventory makeup, first from the CMTs and accumulators, then from IRWST gravity injection, and finally from long-term recirculation.
h The quantification of the success path frequency on an event tree includes the consideration of any events that transition to that event tree. For example,if a pressurizer safety valve sticks open in a transient event (e.g., loss of feedwater), the accident progression transitions to the intermediate loss-of-coolant accident (NLOCA) event tree (Figure 4-6). The NLOCA l success path quantification accounts for the transient events with loss of PRHR and a stuck-open pressurizer safety valve. This is just an example of the consequential effects that have been included in the expanded event tree quantification.
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l Expanded Event Trees June 1997
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4-7 i p Table 4-3 Correlation of Expanded Event Trees to Focused PRA Event Trees Break Size Expanded Event Initiating Event Diameter Tree Designator Event Trees from Focused PRA Large LOCA 29.0" lloca LLOCA i
Medium LOCA 6.0" - 9.0" mloca MLOCA CMT Line Break s 8.0" cmtib CMTLB DVI Line Break $ 4.0" silb SI-LB Intermediate 2.0" - 6.0" nloca NLOCA LOCA Small LOCA < 2.0" slocaw SLOCA (1) with PRHR RCS Leak (1)
Small LOCA < 2.0" slocwo SLOCA (2) without PRHR Inventory loss RCS Leak (2) can also occur PRHR Tube Rupture through pressurizer safety valve SGTRs with 1 tube sgtrw SGTR(1)
PRHR that
! Require ADS SGTRs without 1 tube sgtrwo SGTR (2)
PRHR that Require ADS Transients that Inventory loss tran Loss of MFW to both SGs (4)
Require ADS through Loss of Offsite Power (4) pressurizer Loss of Compressed Air (4) safety valves Loss of CCSSWS (4)
Loss of Condenser (4)
Ioss of Reactor Coolant Flow (4)
Power Excursion Event Tree (4)
SLB Downstream of MSIVs (4)
SLB Upstream of MSIVs (4)
Stuck-Open Secondary-Side SV (4)
Transients with MFW (4)
ATWS (3)
Notes:
(1) Portion of tree with PRHR (2) Portion of tree without PRHR i (3) Includes success of PRHR and success of pressurizer safety valves I
(4) Includes failure of PRHR
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4-9 l
l 4.3 IMPACT OF FOCUSED PRA VERSUS BASELINE PRA The Focused PRA results are the point of comparison for the TlH uncertamty evaluation l process. The Focused PRA models only the passive, safety-related systems in the AP600 l plant. Active, nonsafety-related systems are not credited in the mitigation of the accident.
For this reason, the Focused PRA most clearly demonstrates the importance of passive systems, and is the appropriate point of comparison for the T/H uncertainty issue related to passive system reliability.
l'
- The choice of the Focused PRA versus the Baseline PRA affects the frequency values that are quantified for the success paths. Because active systems are ignored in the Focused PRA, the passive-only accident progressions are often quantified with higher-than-realistic frequencies of occurrence. For example, most LOCA events lead to reactor coolant system (RCS) l >
inventory makeup from the IRWST. The IRWST water can be supplied from either a pumped system, i.e., the normal residual heat removal system (RNS), or gravity draining of l
the IRWST. The reliability of the RNS is such that it operates approximately 9 out of 10 times needed. Therefore, for a given success scenario with a frequency of IE-7/ year, the passive-only accident progression with IRWST gravity injection would occur with a frequency of less than IE-8/ year. However, in the Focused PRA, the IRWST gravity injection success path is the only option considered, and the frequency of this passive-only accident progression is overestimated at 1E-7/ year.
The above example illustrates the impact of crediting or not crediting the RNS, assuming that the scenario is one where the RCS pressure is low enough for either RNS injection or IRWST -
gravity injection to work. However, if the RNS were credited, there are additional possible l success paths with fewer ADS lines open than required for IRWST gravity injection.
Therefore, even more of the postulated accident progressions would end with the utilization L of active systems; passive-only scenarios are much less frequent.
!- So that the importance and uncertainties of the passive systems can be studied without being skewed by the contributions of the nonsafety-related active systems, the Focused PRA is chosen for the expanded event tree development and quantification. The frequency of a success path that is calculated based on the Focused PRA assumptions cannot be compared to frequencies calculated based on the Baseline PRA conditions. As illustrated above, the l frequency can be more than an order of magnitude different. This becomes very important l
when the frequencies are compared to the core damage frequency and large release frequency to determine PRA importance.
The above discussion has been based on the majority of the LOCA accident progressions and
! event tree structures. However, when considering the impact of using the Focused PRA
- . U Expanded Event Trees June 1997 o:\3661w.wpf:1b-061997
l 4-10 versus the Baseline PRA, there are some additional effects on some of the initiating events. If the Baseline PRA were used instead of the Focused PRA, the following effects would be seen.
- 1. Transients and steam generator tube ruptures (SGTRs) would decrease in relative importance to other events because there are multiple operator actions and nonsafety-related systems that can prevent core damage, and are credited in the Baseline PRA. It is the failure of these other systems that leads to the LOCA-like accident progression that requires ADS for successful mitigation.
- 2. Large loss-of-coolant accidents (LOCAs) and direct vessel injection (DVI) line breaks would increase in relative importance to other events. This is because all equipment credited in the Baseline PRA LLOCA and safety injection line break (SILB) event trees is in safety-related systems, and provides the same options considered in the Focused PRA. The LLOCA and SILB quantification does not change, while the frequency of the passive-only success paths for other initiating events decreases in the Baseline PRA.
Therefore, the LLOCA and DVI line break relative importance is larger in the Baseline PRA than in the Focused PRA. This aspect will be considered when the LLOCA and SILB success paths are examined for PRA importance, and when the assessment of TE I uncertainty results on the PRA is made.
4.4 RESULTS OF EXPANDED EVENT TREES AND FREQUENCY QUANTIFICATION The expanded event trees are contained in Figures 4-2 through 4-11. The figures include not only the event tree structure, but quantification results and success path categories defined for short-term cooling. The success path categories are discussed in Sections 6.
The quantification method used to calculate the success path frequencies is the same method used to quantify the core damage paths in the PRA. ADS cases are modeled in more detail and SLOCA, SGTR, and similar events are modeled with and without PRHR to capture the effects of this system.
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4 Expanded Event Trees June 1997 c:\3661w.wpf-1b-061997
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L'As 8 UC6 2.0E46 owi- e CORE DAht40E 4 to OK2 2.1E46 twa 13 ,4 j las 11 OK3 5.3E47 4
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~ -1.ws 22 OK3 .
1 23 OK3 4.2E-10 4 24 OK2 8.eE-10 ts w a s I lis.s 25 OK4 2.1E-10 t
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&s w a vas aas 30 OK2 5.9E-12 e s eut" 31 CORE DAt44GE
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Figure 4-9 Expanded SGTRW Event Tree with Success of PRHR b
T10lo%o0%D%
3
- .i t
IRWST &
RECMC IEV-SGTRWO LMES !CI CUT ACCUM ADS 4 ADS 2,3
. i OK1 tswa l
- 'Ihe fault tree for the failure of 3 or 4 stage 4 4
' * * '~
ADS also considers the failure of all stage 2 ,,,4 and 3 ADS. ,. , w e (
Ia = s 5 OK4 3.4E-10 18
- f_ 8 1 6 OK4 1.4E 12 s 7 UC6 3.5E-11 2 2 I l1.2,3 8 UC6 4.0E-11 owe- 0 CORE DAMAGE 4 10 OK2 4.9E49 twa 1. s e d j las 11 OK3 1.2E 00 4
e 12 OK3 5.0E 12 swa 4 13 OK2 1.0E-11 tswa s l 112.3 14 OK4 2.4E-12 e
t a 15 UC6 2.7E-13 owI- 16 CORE DAMAGE 4 17 UC5 3.DE 11
[
4 1
! I t.a.s 18 UC* 7.sE-12 ts w a o ses te UC5 6.1E-14 ome- 20 CONE DAMALE 4 21 OK2 8.7E-10
- 2. s 4 I e=2 12 e s 22 OK3 2.2E 10 4
1 23 OK3 8.5E-13 swa 4 24 OK2 1.eE 12 tswa s I ha,s 25 OK4 4.1E-13 a
e 26 UC6 4.6E 84 ow1 " . 27 CORE DAMAGE
- 2 4 28 OK2 6.5E-12 4 I It2.s 29 OK3 1.5E-12 2.s e 4 ws aws 30 OK2 1.5E-14 1 1 owI~ 31 CORE DAMAGE __
t ,.
1 i _
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1 1
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E 6
E 6E 8 E
2 E E G E0 E E G E7 G A E E E o E
E E
G E
- E E E
= 8 1 2 1 1 A 6 0 A 5 3 4 4 9 G o o m6 1 6 M MM 1 5 2 3 A A A M mM 1 5 6 0 A M M 2 M 7 1 1 5 A A A A A M D D D D A A A A A A D D D o D E E E E A 8 8 C o o R 9 D 6 R 9 R R 5 5 5 8 e G E
R A5 R C E
R E A 8 R
E E E E e O K N 6 5 5 R R R R R C O O C" C. OOKCO CO C K KO OK KO CU C UO CK O K K O C O K O O C U KC O O Ok CO 5 t 5 L*,
9 O K O O O C O C C C
- 3 4 5 6 7 0 0 0 2 3 4
- 3 3 3 3 3 3 3 4 41 4 4 4 5 6 7 e 6 0 1 2 3 4 5 e 7 8 0 o 2 3 4 4 4 d 4 5 5 5 5 5 5 S 1
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- The fault tree foi the failure of 3 or 4 stage 4 in n s 2 M 6.6E45 ADS also considers the failum of all stage 2 1 3 OK3 3.iE47 and 3 ADS. 4 4 OK, 6.iE4, tswa l laws 5 OK4 1.5E47 a.s w 4 s I 6 OK4 6.5E-10 4 7 UC6 1.6E4e t I lt 2 3 8 UC6 1.9E48 ont" 9 CORE DAMAGE 4 10 OK2 2.2E46 twa tswa I its 11 OK3 5.5E47 4
e 12 OK3 2.4E 49 sor e 4 13 OK2 4.8E4s 13 , 4 s !
It2.s 14 OK4 1.1E40 t
t a 15 UC6 1.2E-10 owt- to CORE DAMAGE 4 17 UC5 1.8E48 4 l I t.a.s is UC5 3.6E 40 2.s = 4 e 2ws 10 UC5 2.GE-11 ew8" 20 CORE DAMAGE 4 21 CK2 3.9E47 t s ar d l 1wa It= s 22 OK3 0.8E48 4
1 23 OK3 4.1E-10 swa 4 24 OK2 8.2E-10 to w e s !
I t2.s 25 OK4 1.8E-10 2
2 26 UC8 2.tE-11 0=t- 27 CORE DAMAGE 1=t 4 OK2 S.CE49 4 l 112.2 29 OK3 6.8E-10 t.s w 4 vus sas 30 OK2 6.0E.12 e t ent" 31 COAE DAMAGE
Il!I i 1lIliiI ijill1jilll1lI Ii) te _
4 9 1 1 7 s 0 0 4 4 1 1 4 4 1 1 1 1 9 0 2 1 0 1 '3 2 1 E E E E E E E E E E 1 1 E 4 1 1
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K K 5 6 5 9 R n R K
C O C O C O C C O O O O U U C O O O C U C O O O C UO CC O O C K C OCo O 3 4 5 6 7 0 9 0 1 2 3 4 5 4 7 9 9 3 3 3 3 3 3 3 4 4 4 4 0 1 2 3 4 5 8 7 0 9 0 2 4 4 4 4 4 4 5 $ 5 5 5 t 3 5 5 $ 5 $ 6 e e 6
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5-1 1
5 CATEGORIZATION METHOD OF SUCCESS SCENARIOS
] Success paths on event trees represent many accident scenarios with different combinations of equipment success and failure. In the expanded event trees, the success paths on the AP600 PRA event trees are further refined to differentiate the functioning equipment in each scenario. The expanded success paths are then binned into categories that distinguish the i
accident progression. This process of "binning" the end-states is the same concept used for l core damage sequences in the Level 1/ Level 2 PRA interface. Core damage paths from Level 1 are identified as different accident classes for further study in Level 2. In the l expanded event trees for the TlH unce-tainty evaluation, this same concept is applied, but the categorization is made of success paths rather than core damage paths. The categorization of the success paths is a systematic method of defining different types of possible accident progressions that lead to successful core cooling. The categorization enables a thorough assessment and greater understanding of the different successful equipment ,
combinations.
The purpose of this section is to provide high-level information on factors considered in the categorization of the success paths. Separate categorization efforts are performed for short-term cooling and long-term cooling. The factors influencing short-term cooling are discussed in Sections 5.1 and 5.2, while long-term considerations are summarized in Section 5.3. The
,^ results of the categorization efforts are do umented in Sections 6 and 7 for short-term cooling
\ and long-term cooling, respectively.
5.1 CMT AND ACCUMULATOR INJECTION The first part if the accident, when the accumulators and CMTs provide makeup inventory, is similar to design basis accident conditions as long as there is at least 1 CMT and 1 accumulator. CMTs and accumulators are tanks, each containing close to 2000 ft$ or approximately 100,000 lbm of water. Accumulators are designed for rapid inventory makeup when the RCS pressure falls below 700 psig. CMTs also play a role in early inventory makeup, starting at higher pressures, but injection rates are not as rapid as accumulators.
Furthermore, CMTs are important because low CMT levels provide the actuation signal for ADS. There are 2 CMTs and 2 accumulators, and the loss of one CMT and/or accumulator leaves the remaining tanks to fulfill the plant functions described. Therefore, a scenario with at least 1 CMT and at least 1 accumulator contains a similar accident progression to a scenario with all CMTs and accumulators functioning. This observation is supported by the l MAAP4/NOTRUMP benchmarking effort (Ref. 2).
l The ability to lose up to 1 CMT and 1 accumulator without significantly impacting the I
accident progression is one of the fundamental elements in the categorization of the success paths. The categorization requires that judgements be made on which equipment losses have Categorization of Success Scenarios June 1997 o:\3661w.wpf:1b-061697
l 5-2 the largest impact on the accident progression. Although the loss of a CMT and/or accumulator may impact the event and its timing slightly, this impact is less significant than other equipment losses. The loss of I CMT and/or 1 accumulator does not jeopardize the ability to successfully cool the core. Therefore, categories are defined based on other distinctions, and the following CMUaccumulator possibilities can be grouped into the same category.
. 2 CMTs and 2 accumulators
= 2 CMTs and 1 accumulator
. 1 CMT and 2 accumulators
. 1 CMT and 1 accumulator The exception to this method of grouping is for large LOCAs. For a LLOCA, the operation of 1 accumulator versus 2 accumulators can have an impact on the accident progression, and these possibilities are considered separately. Also note that the DBA analysis of the double-ended guillotine DVI line break only includes 1 CMT and 1 accumulator; the other CMT and accumulator spill out the break.
The loss of both CMTs or both accumulators becomes a basis for defining a short-term cooling success category. This is because the loss of both CMTs or the loss of both accumulators removes a specific function from the plant response. Furthermore, the accident progression may be different depending on whether the initiating event is an SLOCA, NLOCA, MLOCA, LLOCA, or other event. These issues are discussed further in Sections 6.1 and 6.2, where the categories are defined.
5.2 IRWST GRAVITY INJECTION The second injection part of the accident progression, IRWST gravity injection, is generally dominated by the number of ADS lines open and whether containment is isolated. ADS stages 1,2, and 3 vent from the pressurizer to the IRWST, while ADS stage 4 vents from the hot leg directly to containment. Therefore, the plant response to ADS stages 1 through 3 is different from the plant response to ADS-4, and this is considered within the categorization.
The plant's response to ADS actuation can also depend on whether there is an accumulator available in a high-pressure (> 700 psig) scenario. Without either accumulator, analyses have shown that core uncovery can occur when a large depressurization is needed, ADS is actuated, and there is no makeup inventory to offset the inventory loss through the ADS lines.
- One of the items that is not differentiated on the expanded event trees is the number of DVI lines that are available for IRWST gravity injection. The PRA success criterion is that 1 out of 1
l Categorization of Success Scenarios June 1997 o:\3661w.wpf:1b-061697 1
j l
5-3 l l
2 lines is sufficient. All short-term analyses related to supporting the PRA have been done I
,j with 1 line, and have shown this to be a successful option for IRWST gravity injection. !
5.3 LONG-TERM RECIRCULATION COOLING Long-term cooling (LTC) refers to core cooling that is required following the initial phases of the plant response to a transient or accident. For AP600, depending on the initiating event and event progression, long-term cooling may be provided by operation of the startup feedwater system (SFW), PRHR, RNS, or gravity recirculation.
)
i For events in which stage 4 of the ADS is actuated but RNS is unavailable, the PRA models l operation of IRWST gravity injection (for short-term cooling) and natural recirculation of l water from the containment sump (for long-term cooling) as leading to a successful outcome. I This safety-related, passive mode of natural recirculation is referred to as long-term recirculation cooling, and is the subject of the long-term cooling TIH uncertainty evaluation.
This rnode of cooling occurs in events in which sufficient inventory is lost to fill the reactor cavity with water. These events may be the result of LOCA initiators or of other events in which ADS actuation and IRWST injection have occurred following loss of normal decay heat removal capability via main feedwater, startup feedwater, and passive RHR. ]
Factors that may affect long-term cooling by natural recirculation are the height of the water (q/
l pool in the containment sump, the steam venting capability from the RCS, the flow resistance l in the injection lines, the containment pressure, and the amount of decay heat to be removed.
These factors, and their potential effect on long-term recirculation cooling success, are examined in this TlH uncertainty evaluation process.
Within the process defined for the T/H uncertainty evaluation as applied to short-term cooling, scenarios that are not supported by existing analyses have generally been included in the UC categories. The potentially PRA-important UC scenarios are analyzed, including consideration of TlH uncertainties, to verify claims of successful core cooling. For the long-term recirculation cooling thermallhydraulic uncertainty analysis, there are two main objectives:
1 Provide an analytical basis for the PRA success criteria for long-term recirculation following beyond-design-basis events; and Demonstrate that consideration of long-term recirculation thermallhydraulic uncertainty in the PRA success criteria analyses does not significantly affect the conclusions of the PRA.
3 O
Categorization of Success Scenarios June 1997 o \3(61w.wpf:1b-061797 I
S-4 To meet these objectives, the potentially PRA-important cases for long-term recirculation are l
defined from all success paths of the expanded focused PRA event trees (i.e., both UC and OK categories), since only limited analytical bases (i.e., from the design basis analyses) exist.
That is, multiple TIH analyses (e.g., various break sizes and locations, equipment failures, operator actions) without uncertainties have not been made for each LTC PRA success sequence and, consequently, " low-margin" sequences have not been predefined relative to long-term cooling.
The set of these success paths is organized (in Section 7), based on equipment failures and T/H conditions resulting from the initiating event, into groups with similar characteristics.
Table 5-1 summarizes the potential differences between the PRA scenarios and the design basis accident scenarios, and identifies how the important factors may affect the recirculation cooling capability.
The potentially PRA-important long-term recirculation scenarios are defined as those involving only passive systems and that would have a significant impact on core damage frequency or large release frequency, based on the Focused PRA results,if they were considered failures instead of successes. These can be identified from the sequence groupings. The most risk-important scenarios are expected to be similar to DBA scenarios, i.e., involving single failures rather than multiple failures. The success criteria bases for these are the DBA analyses. The other scenarios are used to define a set of analytical cases to support long-term recirculation modeling in the PRA.
I 1
91 Categorization of Success Scenarios June 1997 o:\3661w.wpf:1b-061697
5-5
(~T Table 5-1 Summary of Potential PRA Impacts on Long-Term Recirculation
()
Element Equipment Loss in PRA Height of the Water Pool The failure of one or more CMTs and/or accumulators to drain Affects the Driving Head for may result in a lower water level in containment.
Natural Circulation The type of break (i.e., DVI line break) may allow water to be diverted to normally dry compartments and result in a lower sump water level.
The failure of a containment isolation line may allow water inventory to be lost.
RCS Steam Venting The failure of lines of ADS to open results in less venting capability, Capability which may impact the ability to maintain the RCS pressure low enough for recirculation.
Resistance u! DMtioni The failure of valves to open in injection! recirculation lines may Recirculation Liries impact the system flow resistance and influence the recirculation flow rate.
Containment Pressure The failure of a containment isolation line may lower the containment backpressure, and result in loss of containment inventory.
Decay Heat The failure of one or more CMTs and/or accumulators can impact ;
the timing of the accident progression, and cause an earlier
( ) transition into long-term recirculation, thereby requiring
() recirculation cooling at a higher decay heat.
Break size or type can affect the timing of the start of recirculation, and therefore decay heat level at the start of recirculation.
1979 ANS best-estimate decay heat is typically used for analyses that support the PRA. Uncertainties on the decay heat need to be considered for TlH uncertainty evaluation.
l 1
1 l
i l
l l
l 4
]
v I
l Categorization of Success Scenarios June 1997 o:\3661w.wpf:1b-061697
I 6 CATEGORIZATION OF SUCCESS PATHS FOR SHORT-TERM
,O i COouso l
Section 6 documents the categorization of the expanded event tree success paths to address l
, the short-term accident progression. The short-term accident progression considers an ;
accident from initiation, through the injection of the CMTs and accumulators, and concludes 1 when IRWST injection is established. General elements considered in the categorization i process were discussed in Sections 5.1 and 5.2.
! l 4
L The nomenclature of the categories defines two main groups of success paths: OK categories 1 l and UC categories. OK categories are accident progressions that are similar to design basis accidents. Although most OK categories are not identical to design basis, the differences can - l be defined and the similarities explained. - Accident scenarios that are defined within an 1 OK category are noj " low margin" and are not further considered within the TH uncertainty evaluation process. Success scenarios that do not fit within OK categories are grouped into UC categories. The categorization as a UC category occurs for two reasons: 1) analyses of 1 l the accident progression predict core uncovery, or 2) analyses have not been done to support the accident scenario. The UC categories are accident scenarios that are considered " low margin" and will be further considered in the TM uncertainty evaluation process.
1 There are 10 OK categories and the same number of UC categories. The number of categories was not predefined; rather, categories were created based on the need to group similar accident progressions together. The following items are noteworthy about the categorization performed for short-term cooling, and will clarify the discussion of the individual categories.
l l 1. Each success path is classified in only one category, although there are some success paths that fit the definition of multiple categories. A choice was made to generally include these success paths in a category based on the loss of CMTs or accumulators. I However, success paths with enough failures to fit multiple category definitions are I low-frequency scenarios, and choice of where to include them does not impact the l results of the process.
l 2. Expanded event trees do not always separate the success path to differentiate the exact j equipment defined by the category. Once again, this only occurs in success paths of low frequency. The choice of where to categorize this type of success path does not impact the results of the TH uncertainty evaluation process. However, the success 3 path is generally categorized with the equipment successifailure that is known to be rnost probable. For example, a success path that does not distinguish between 2 and
- 3 stage 4 ADS valves may be included within a category that is defined as having at
!J Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:1b-061997
6-2 least 3 stage 4 ADS valves. In all such cases, the frequency of the success path is low, and the fraction that is 2 stage 4 ADS is negligible.
The grouping of sequences into OK categories is discussed in Section 6.1; the grouping of sequences into UC categories is discussed in Section 6.2. The UC categories are further assessed in Section 6.3, where PRA importance of the category is deternuned. For the low-margin, PRA-important categories, cases are defined for further, conservative TE analyses.
6.1 OK CATEGORIES SIMILAR TO DESIGN BASIS The first part of the categorization for short-term cooling is to identify the success paths that do not need to be further addressed within the TM uncertainty evaluation process. A success path can meet this criterion because it is already addressed by DBA analyses, is similar enough to DBA analyses that there is no additional challenge to core cooling, or is a multiple-failure accident in which there is ample margin to core uncovery. Ten categories designated with the alpha OK are defined for these success paths that are not considered further within the TH uncertainty evaluation process.
Table 6.1-1 provides an overview of the ten OK categories, and the frequencies that have been quantified for each category. Sections 6.1.1 to 6.1.9 contain more information about each of the OK categories. For each OK category, there is also a table that lists all the applicable success paths from the expanded event trees and the calculated frequency of each path. 'Ihe OK categories are generally ordered so that the greatest similarities to DBA exist in the first OK categories, and the greatest differences from the DBA exist in the latter OK categories.
O Categorization of Success Paths for Short-Term Cooling June 1997 o;\3661w.wpf:1t>461997
6-3 I I
,' Table 6.1-1 Summary of OK Categories
( l Description, Relative Total Frequency Number to Design Basis Detailed Description (per year)
OK1 More ADS 4 No failures beyond 6.9E-3 initiating event 1
OK2 Design Basis 2 DBA ADS (1) 2.6E-5 l 21 CMT, l acc.
Containment isolated OK3 More ADS 4 > DBA ADS-4 5.8E-4 Less ADS 1,2,3 < DBA ADS 1, 2, 3 21 C? iT,1 acc. j Containment isolated OK4 Less ADS 1,2,3 DBA ADS 4 1.4E-6
< DBA ADS 1,2, 3 21 CMT,1 acc.
Containment isolated OKSA More ADS-4 > DBA ADSil) 2.6E-6 Containment Isolation Fails > 1 CMT, I acc. I Containment isolation failure i
,q OK5B More ADS-4 > DBA ADS 4 6.7E-7
(') Less ADS 1,2,3 Containment Isolation Fails
Containment isolation failure OK6 Containment Isolation Fails DBA ADS (l) 5.9E-9 21 CMT, I acc.
Containment isolation i failure l OK7 2 Accumulators - Design Basis 2 accumulators 2.7E-S I for LLOCA 2 DBA ADS 4 j s DBA ADS 1,2,3 21CMT OK8 DVI Line Break with 0 CMTs 9.6E-8 l Automatic ADS Actuation 1 injecting accumulator l
from Faulted CMT 2 DBA ADS 4 s DBA ADS 1,2,3 OK9 Loss of CMTs for Smaller 0 CMTs 8.8E-7 ,
Breaks 1 Note:
(1) "DBA ADS" is all stage 1,2, and 3 ADS and 3 out of 4 stage 4 ADS.
.t O i
, U/
l Categorization of Sur. cess Paths for Short-Term Cooiing June 1997 o:\3661w.wpf;1141997 l
l l
t
- 6-5 6.1.1 Category OK1 The success paths designated as category OK1 are listed in Table 6.1.1-1. The definition for
this category is that all equipment functions, except equipment disabled as part of the initiating event. These are the top paths on the expanded event trees in Section 4. The OK1 paths are bounded by the LOCA design basis accident analyses because the OK1 paths include the actuation of more ADS-4 lines than considered in the DBA analyses. This basis is straightforward for the top success path on most of the expanded event trees.
l l- For some of the expanded event trees, such as the transient initiating events in Figure 4-11, the top success path is also bounded by the DBA analyses, although the connection is not as
without the loss of pnmary coolant and without the actuation of ADS. This success path is
- modeled in the Baseline and Focused PRA event trees, but is outside the scope of the
! - expanded event trees. The expanded event tree defines the " initiating event" as the transient initiator plus the loss of PRHR. Therefore, the top path of the expanded transient event tree represents a loss of all heat removal,in which primary coolant is lost when the pressurizer safety valves open. The loss of coolant through the pressurizer safety valves leads to an accident progression similar to LOCA initiating events, but with lower decay heat, which is a benefit to achieving successful core cooling.
! . The loss of PRHR is also included as part of the " initiating event" for two expanded event .
trees that address SLOCA without PRHR and SGTR without PRHR. The loss of PRHR keeps the RCS pressure higher than occurs in the DBA analyses. But with the successful operation of all other equipment, including more ADS valves than credited for DBA, the accident . ,
progression does not challenge core cooling.
Analyses to demonstrate the plant response to a high-pressure accident for the OK1 category are provided in Figures 6.1.1-1 to 6.1.1-24. The analyses are performed with the MAAP4 code, which has been benchmarked against the NOTRUMP code (Ref. 2). Results are presented for four cases of the high-pressure scenarios without PRHR: SLOCA (1 inch and 0.S inch), SGTR, and a loss-of-feedwater transient. For each case, the following output parameters are provided as a function of time: RCS pressure, CMT and accumulator inventory, IRWST injection, the pressurizer water inventory, the RCS water inventory, and the vessel mixture level. The mixture level remains well above the top of the core in all the OK1 cases. The sequence of events for each case is provided in Table 6.1.1-2.
l l.
iO l
i Categorization of Success Paths for Short-Term Cooling June 1997 c:\3661w.wpf:1b-061997
, - ~ _ - , __
6-6 Table 6.1.1-1 Success Category OK1 (Sorted by Descending Frequency)
Equipment Assumptions Success Frequency Path CI CMT Acc ADS 4 ADS 2,3 (per year) sgtrw01 Yes 2 2 4 4 5.5E-3 nloca01 Yes 2 2 4 4 5.9E-4 tran01 Yes 2 2 4 4 1.9E-4 slocwo01 Yes 2 2 4 4 1.8E-4 mioca01 Yes 2 2 4 4 1.2E-4 slocaw01 Yes 2 2 4 4 1.1E-4 lloca01 Yes 2 2 4 4 7.6E-5 silbO1 Yes 1 1 4 4 7.6E-5 cmtibO1 Yes 1 2 4 4 6.5E-5 sgtrwo01 Yes 2 2 4 4 4.2E-7 TOTAL 6.9E-3 9
1 1
9!
Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:lt461997 t
6-7 l
^\ Table 6.1.1-2 Sequence of Events for High-Pressure Scenarios in Category OKI l
(V (Tune in Seconds) l Item 1.0 Inch 0.5 Inch SGTR Transient Event Initiator 0 0 0 0 Reactor Trips 460 m 1981 m 504 m 20 m CMT Actuation 539
- 2118 m 612 m 4085
- SGs Empty not applicable 13,430 19250
- 2489 CMT Draining Begins 8200 16,800 18,500 11,400 ADS-1 Opens 10,062 17,418 21,382 12,645 ADS-2 Opens 10,182 17,538 21,502 12,765 l
Accumulators Start 10,210 17,630 21,560 12,860 ADS-3 Opens 10,302 17,658 21,622 12,385 ADS-4 Opens 10,718 17,826 21,977 13,061 Accumulators Empty 10,725 17,942 22.031 13,178 IRWST Injection Starts 10,827 17,904 22,122 13,139 CMTs Empty 11,040 18,110 22,260 13,350
() Notes:
(1) Reactor trip on low pressurizer pressure (2) CMT actuation on low pressurizer pressure (3) Reactor trip on low SG level (4) CMT actuation on either high containment pressure or high hot-leg temperature coincident with low SG level (5) Time intact SG empties l
l l
l l
'O Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf 1b-061997 i
6-8 O
Figure 6.1.1-1 RCS Pressure For 1.0 Inch Break in Category OK1 3000 2500 -
~
n .-
2000 -
a ~
v g 1500 -
u m,J
[ 1000 -- -
t
~
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1 500 --
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l
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0 l l l ;
O 3000 6000 9000 12000 1500 0 Time (s)
O Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf 1b-061997
j 6-9 t
l Figure 6.1.1 -2 l CMT and Accumulator Water For 1.0 Inch' Break in Category OK1 CMT
-f- - - - A c c u m u l a t o r 250000
~
q 200000 --- + + : +: -+ : ;+: : + + -h i
o i
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l
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!O Categorization of Success Paths for Short-Term Cooling June 1997 l o:\3661w.wpf:1t>.061997 I
6-10 l
1 O
l l Figure 6.1.1-3 IRWST injection For 1.0 Inch Break in Category OK1 120 m
m 100 --
N E _
_a v 80 --
~
as a 60 --
oc
~
3::
O 40 --
L I l
m I w l c 20 --
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l l
0 0 30'00 6000 90'00 12dO0 1500 0 l Iime (s) l 9
Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:1W1997
i 6-11 0
Figure. 6.1.1 -4 Pressurizer Water Inventory For 1.0 Inch Break in Category OK1 80000 _
70000 - }-
60000 - }-
, i n
E 50000 -
. _a -
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m :
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O Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:ll>W>1997 t
6-12 O I Figure 6.1.1-5 RCS Coolant Inventory i For 1.0 Inch Break in Category OK1 350000 !
^
- I i
300000 --
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0 l l l l 0 3000 6000 9000 12000 1500 0 Time (S)
O Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:1b-061997
6-13 O
1 Figure 6.1.1-6 Vessel Mixture Leve1 For 1.0 Inch Break in Category OK1
-t- - - - T o p of Core 30 26 --
m
- 22 --
=+l +-l + l + l ++l +l ++;++;+l +l +-
r 18 --
CD -
C .
- 14 --
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10 --
-6. l l ! 'l '
0 3000 6000 9000 12000 1500 0-Time (S) i e
O Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:Ib-061997
6-14 l
O1 1
Figure 6.1.1-7 l l
RCS Pressure I For 0.5 Inch Break in Category OK1 !
I 3000
$ I l
2500 -- b
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C
] 2000 -
- c. -
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0 5000 10000 15000 20000 2500 0 1 Time (s)
O l Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:1bE1997
6-15 i
i O
i Figure 6.1.1-8 i
CMT and Accumulator Water
! For 0.5- 'I n c h Break i n Category OK1 CMT
-t- ,--AccumuIotor 250000
^ l i I I i ii I I I I I I I I l I il i 1 1 iiiiiii1I i i 1 I I I I i i i i I I I I I I I I I Il o 200000 -- i v -
i en -
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_ l H I 0 l l l "'l 0 5000 10000 15000 20000 2500 0 Iime (S) l lO Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:1b41997
6-16 9
Figure 6.1.1 -9 IRWST Injection For 0.5 Inch Break in Category OK1 120 m
m 100 --
N E _
_o v 80 --
o 60 --
O e
~
O 40 --
LL m
M o 20 --
E 0 l l l l O 5000 10000 15000 20000 2500 0 Iime (s)
O Catego, tzation of Success Paths for Short-Term Cooling June 1997 o:\3661w.w,-':1b-061997
6-17 O ,
Figure 6.1.1-10 Pressurizer Water. Inventory. i
'For. 0.5 Inch Break in. Category OK1 i 80000 _
_ 1
~
70000 -- -
l
_ \
60000 --
l : I
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- D l~d l
t j Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:1b-061997 l
i 6-18 l
O Figure 6.1.1-11 RCS Coolant Inventory For 0.5 Inch Break in Category OK1 350000 300000--
250000-f
^ _
E -
_a -
200000--
v
~
~
m 150000 -- i w _
\
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f 0 l l l l 0 5000 10000 15000 20000 2500 0 Time (s) 9 Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:1t>M1997
6-19 l
i n l V l
! Figure 6.1.1-12.
VesseI Mixture Level L For 0.5 i nch Break i n Category OK1
-f- - - - T o p of Core 30 m'u>
I 26 --
A
- 2 2.--
l U _
,-N -I lI iI rI 4 1 1^I i i i 1 i 1 il 1 I ii t I it ie 1 i l i l 1 i i i l iiliiiiI I i I I I I I I I I I I i 1 I I I I I I I I I I I I I I i i I ( I I I II II y 18 ---
~
en -
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t 6
0 50'00 10dO0 15000 20000 2500 0 i Time (s) i i
Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:1M)61997
6-20 Figure 6.1.1-13 RCS Pressure For SGTR in Category OK1 3000 -
2500 --
~
m --
2000 -
1 ._
v g 1500 -
u g 1000 -
u 1
500 --
0 l l l l 0 5000 10000 15000 20000 2500 0 Time (s)
O Categorization of Success Paths for Short-Term Cooling Jtme 1997 o:\3661w.wpf:ll>461997
6-21 I O
Figure 6.1.1-14 CMT and Accumulator Water For SGTR in . Category OK1 l
CMT j + - - - A c c um u l a t o r -
250000
^ iiii i i>iiiiiiiiiiiiiiiiiiiiiiiiiii, l oE -200000 -- -
i
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- i. . . ., ,i.l ,i,,,ii 0 50'00 10b00 15b00 20000 2500 0 Time (s) i l Categorization of Success Paths for Short-Term Cooling June 1997 j o:\3661w.wpf:1b-061997
1 6-22 Oi i
l Figure 6.1.1-15 !
IRWST Injection For SGTR in Category OK1 120 n
m 100 --
N E _
_a v 80 --
o 60 --
9 cc
~
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1 40 -- l k l 1
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O Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf;1b-061997
1 s-n
,h 1
1 Figure 6.1.1-16 Pressurizer Water I n v e n-t o r y F-o r- SGTR in Category OK1 l
80000 _
70000 - _-
~
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n ~
E 50000 --
l .c
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~
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l 10000 -- _
~
' ' ' ' ' ' ' \'
0- l l l l 0 5000 10000 15000 20000 2500 0
'Iime (S) l O-Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:1b-061997 l
l
6-24 l
i l
O Figure 6.1.1-17 RCS Coolant Inventory l For SGTR in Category OK1 I l
350000 1
N 300000 -- _
250000 - f E -
_a
- 200000 --
g m 150000 --
w .
o -
P
- E 100000 -- "
50000 --
o l l l l 1 0 5000 10000 15000 20000 2500 0 '
Iime (s)
O Categorization of Success Paths for Short-Term Cooling June 1997 l o:\3661w.wpf:1b441997 i 1
- 52s i
O l
- Figure 6.1.1-18 l l
VesseI Mixture Level
- For SGTR i n -Category OK1
-t- - - - T o p of Core l
30 l
~
26 --
l
- i m
- 22 --
! v _
l- - 1 i i glil i I i t i 1 ii1 i111 I t ii1 1 i 1 l l 1 iiiiii1 i i i i i I l.I I I I I I i i I I I I I I l l T I I i i I iI I I l 1 I l l I I I II i I i 1 I
_c 18 -~
l I
l l
[ c _
O 14 __
- -J _
10 --
19
~
l i . i , , , . , , ,
i , , ,
6 I i . ,
0 5000 10000 15000 20000 2500 0-Time (s) 1
!O Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf Ib-061997
6-26 l
91 l
Figure 6.1.1-19 RCS Pressure For Transient (Loss of FW) in Category OK1 3000 2500 - - -
.Q n L O
2000 --
ct -
v g 1500 --
- 9 u
m -
en en e 1000 --
u c_ _
500 --
h 0 ' ' ' ' ' ' '
''l
l ' '
l 0 3000 6000 9000 12000 1500 0 Time (s) 9\
Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:1W1997 I
. ~ _ _ _ . . _ _ . . _. _ . _ _ _ . _ . . .____ ._ . _
6-27 i
l O
Figure 6.1.1-20 :
CMT and Accumulator Water For Transient (Loss of FW) in Category OK1 i CMT
+ --- Ac c umu l a t o r 250000
^
j f 200000 --
-+++++++!l+ l l l++l + + l l l li i
l -
i m -
i- s I
cn -
l C
s/
m 150000 --
o _
I l
1 - i l-
-' i
! u l
! cu i
i - 100000 - -
i o -
t 3i!: -
1 1
x -
i i
5 50000 -- -
I 1
l -
O l l' 'l !~;'"
0 3000 6000 9000 12000 1500 0'
- Time (s)
!O J
Categorization of Success Paths for Short-Term Cooling June 1997 c:\3661w.wphlb41997 I
I
6-28 O
Figure 6.1.1-21 IRWST Injection For Transient (Loss of FW) in Category OK1 120
~
m cn 100 --
N E _
_a v 80 --
co A
- W o 60 --
cr 3e O
40 --
u_
~
cn cn a 20 --
s 0 l l
l 0 3000 6000 90'00 12b00 1500 0 Iime (S)
O Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:1b-061997
6-29
,7 U
Figure 6.1.1-22 Pressurizer Water Inventory For Transient (Loss of FW) in Category OK1 80000 _
70000 --
~
60000 -
n E 50000 -:
_a 7 _
.,Y W ~
40000- t m :
m _
a 30000 -- -
- E - -
\
20000 - }-
\
10000 -- _
~
0 l l l ' '
l ' ' ' '
0 3000 6000 9000 12000 1500 0 Iime (s)
' em (s._f)
Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:1141997 I
l
6-30 l
O Figure 6.1.1-23 I RCS Coolant Inventory For Transient (Loss of FW) in Category OK1 350000 300000 --
250000 --
E -
_a -
- 200000 --
g I
g m 150000 --
m _
o j
s :
100000 -- t --
50000 --
~
0 il' 3010
'l ''!
0 6000 9000 12000 1500 0 Ilme (s)
O j Categorization of Success Paths for Short-Term Cooling June 1997
! o:\3661w.wpf:16461997 i
6-31 1
lO 1 ,
i l
! l
! l l Figure 6.1.1-24 l l
Vessel Mixture Level For Transient (Loss of FW) in Category OK1
-t- - - - T o p o f Core 30 i
26 --
n
_,_, 22 --
p v _
v =+l +l +-+-+ l ++l+ l !+l++ l + l +l !-
g 18 --
w -
c _
_a
- 14 --
4 10 --
6 ' ' ' ' ''''''''''''''''''''
0 30'00 60'00 90'00 12b00 1500 0 Time (S)
- O Categorization of Success Paths for Short-Term Cooling June 1997 o
- \3661w.wpf;1b41997
. _. _ _ _ . - . __. _ . _ _ . _ . . _ ~ _ _ _ ___
6-33 6.1.2 Category OK2
- The success paths designated as category OK2 are listed in Table 6.1.2-1. The definition for this category is based on the DBA analyses
- all stage 1,2, and 3 ADS and at least 3 stage 4 ADS, with successful containment isolation. Therefore, the DBA analyses have already -
demonstrated that these success paths have adequate venting capability to achieve successful core cooling via IRWST gravity injection without core uncovery. The applicability of DBA i
analyses to bound the high-pressure events without PRHR is the same as discussed for category OK1 in Section 6.1.1. No MAAP4 analyses are performed for category OK2.
't
, Prior to IRWST gravity injection, makeup coolant inventory is provided by the CMTs and accumulators. As discussed in Section 5.1, the presence of at least 1 CMT and at least 1 accumulator provides a similar plant response as 2 CMTs and 2 accumulators. Therefore, success paths with the loss of 1 CMT and/or the loss of I accumulator are grouped within
- category OK2, if the ADS and containment isolation criteria are met. This category applies to.
all the initiating events except for large LOCA. LLOCA is excluded because its results are i dependent on the number of accumulators, and thus it is considered in separate categories.
4 i
l i
V
.i .
O V
Categorization of Success Paths for Short-Term Cooling June 1997 oA3661w.wpf:lt41997
l l
6-34 l
Table 6.1.21 Success Category OK2 (Sorted by Descending Frequency)
Equipment Assumptions Success Frequency Path CI CMT Acc ADS-4 ADS 2,3 (per year) nloca10 Yes 2 1 4 4 6.9E-6 sgtrwl0 Yes 2 1 4 4 3.4E-6 tran10 Yes 2 1 4 4 2.2E-6 slocwo10 Yes 2 1 4 4 2.1E-6 nloca04 Yes 2 2 3 4 1.9E-6 I mloca10 Yes 2 1 4 4 1.4E-6 slocawl0 Yes 2 1 4 4 1.3E-6 nloca21 Yes 1 2 4 4 12E-6 sgtrw04 Yes 2 2 3 4 9.3E-7 cmtlb10 Yes 1 1 4 4 7.6E-7 tran04 Yes 2 2 3 4 6.1E-7 sgtrw21 Yes 1 2 4 4 6.1E-7 slocwo04 Yes 2 2 3 4 5.8E-7 tran21 Yes 1 2 4 4 3.9E-7 I slocwo21 Yes 1 2 4 4 3.8E-7 mloca(M Yes 2 2 3 4 3.8E-7 slocaw04 Yes 2 2 3 4 3.5E-7 mloca21 Yes 1 2 4 4 2.5E-7 silb04 Yes 1 1 3 4 2.4E-7 slocaw21 Yes 1 2 4 4 2.3E-7 ,
1 cmtib04 Yes 1 2 3 4 2.1E-7 nlxa13 Yes 2 1 3 4 1.6E-8 l
nloca28 Yes 1 1 4 4 1.0E-8 l
sgtrw13 Yes 2 1 3 4 7.9E-9 sgtrw28 Yes 1 1 4 4 5.1E-9 l
slocwo13 Yes 2 1 3 4 4.9E-9 9
Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:1b-06199/
6-35 f)
V Table 6.1.21 (cont.)
Success Category OK2 (Sorted by Descending Frequency)
Equipment Assumptions Success Frequency Path CI CMT Ace ADS-4 ADS 2,3 (per year) sgtrwo10 Yes 2 1 4 4 4.9E-9 tran13 Yes 2 1 3 4 4.8E-9 slocwo28 Yes 1 1 4 4 3.2E-9 mioca13 Yes 2 1 3 4 3.2E-9 tran28 Yes 1 1 4 4 3.0E-9 slocaw13 Yes 2 1 3 4 3.0E-9 nloca24 Yes 1 2 3 4 2.9E-9 mioca28 Yes 1 1 4 4 2.1E-9 slocaw28 Yes 1 1 4 4 1.9E-9 cmtib13 Yes 1 1 3 4 1.8E-9 sgtrw24 Yes 1 2 3 4 1.4E-9
(% sgtrwo04 Yes 2 2 3 4 1.3E-9 slocwo24 Yes 1 2 3 4 8.8E-10 sgtrwo21 Yes 1 2 4 4 8.7E-10 tran24 Yes 1 2 3 4 8.2E-10 mloca24 Yes 1 2 3 4 5.7E-10 slocaw24 Yes 1 2 3 4 5.3E-10 nloca30 Yes 1 1 2,3* 0-4
- 2.5E-11 sgtrw30 Yes 1 1 2,3* 0-4
- 1.2E-11 sgtrwo13 Yes 2 1 3 4 1.1E-11 tran30 Yes 1 1 2,3* 0-4
- 7.0E-12 sgtrwo28 Yes 1 1 4 4 6.6E-12 slocwo30 Yes 1 1 2,3* 0-4* 5.9E-12 mloca30 Yes 1 1 2,3* 0-4* 4.9E-12 slocaw30 Yes 1 1 2,3* 0-4
- 4.5E-12 O
Categorization of Success Paths for Short-Term Cooling June 1997 )
o:\3661w.wpf lb-061997 1 l
6-36 Table 6.1.2-1 Success Category OK2 (Sorted by Descending Frequency)
(cont.)
Equipment Assumptions Success Frequency Path CI CMT Acc ADS 4 ADS 2,3 (per year) sgtrwo24 Yes 1 2 3 4 1.8E-12 sgtrwo30 Yes 1 : 2,3* 04* 1.SE-14 TOTAL 2.6E-5 Note:
These success paths include accident scenarios with more failures than defined by category OK2. The inclusion of additional equipment failures in these paths is of negligible importance because of the low frequency of the paths.
9 O
Categorization of Success Paths for Short-Terrn Cooling June 1997 o:\3661w.wpf:1b-061997
6-37 6.1.3 Category OK3 C
d The success paths designated as category OK3 are listed in Table 6.1.3-1. The success paths within this category have more ADS stage 4 lines open (4 rather than 3) but fewer ADS 1,2, and 3 lines when compared to DBA. Containment isolation is successful, and there is at least 1 functioning CMT and 1 functioning accumulator. This category applies to all the initiating events except for large LOCA. LLOCA is excluded because its results are dependent on the number of accumulators, and thus it is considered in separate categories.
L Stage 4 ADS is a more effective vent path than the other stages of ADS. The stage 4 lines are t
attached to the hot legs, and the venting outlet is directly to the containment. The stage 1,2, and 3 ADS valves are much smaller than stage 4 ADS valves, and their location may be less
, effective for some accident sequences. Stage 1,2, and 3 ADS lines are located at the top of l the pressurizer, and the venting path is to the IRWST water. The MAAP4NOTRUMP benchmarking report, Ref 2, includes cases that vary the number of ADS valves credited.
l The results of the benchmarking cases demonstrate that an additional stage 4 ADS valve can offset the loss of stage 1,2, and 3 ADS lines. No additional MAAP4 analyses are performed for category OK3.
l l
r sq b
l l
l l
l b
. G 1
Categorization of Success Paths for Short-Term Cooling June 1997 c:\3661w.wpf:1b-061997
. . . - . _ - . . - _ ~ - . _. . . .-- .
6-38 Table 6.1.31 Success Category OK3 (Sorted by Descending Frequency)
Equipment Assumptions Success Frequency Path CI CMT Acc ADS-4 ADS 2,3 (per year) nloca02 Yes 2 2 4 2,3 2.1E-4 sgtrw02 Yes 2 2 4 2,3 1.0E4 tran02 Yes 2 2 4 2,3 6.6E-5 slocwo02 Yes 2 2 4 2,3 6.3E-5 mioca02 Yes 2 2 4 2,3 4.1E-5 slocaw02 Yes 2 2 4 2,3 3.8E-5 silbO2 Yes 1 1 4 2,3 2.6E-5 cmtlbO2 Yes 1 2 4 2,3 2.3E-5 nloca03 Yes 2 2 4 0,1 1.9E-6 nlocall Yes 2 1 4 2,3 1.7E-6 sgtrw03 Yes 2 2 4 0,1 9.5E-7 sgtrwil Yes 2 1 4 2,3 8.6E-7 tran11 Yes 2 1 4 2,3 5.5E-7 slocwo11 Yes 2 1 4 2,3 5.3E-7 rnloca03 Yes 2 2 4 0,1 3.9E-7 slocaw03 Yes 2 2 4 0,1 3.6E-7 mlocall Yes 2 1 4 2,3 3.5E-7 slocaw11 Yes 2 1 4 2,3 3.2E-7 nloca22 Yes 1 2 4 2,3 3.1E-7 tran03 Yes 2 2 4 0,1 3.1E-7 slocwo03 Yes 2 2 4 0,1 2.8E-7 silbO3 Yes 1 1 4 0,1 2.5E-7 cmtibO3 Yes 1 2 4 0,1 2.1E 7 cmtib11 Yes 1 1 4 2,3 1.9E-7 sgtrw22 Yes 1 2 4 2,3 1.5E-7 O
Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:1b-061997
6-39 Q
l \. ,j s
Table 6.1.3-1 (cont.)
Success Category OK3 (Sorted by Descending Frequency) l Equipment Assumptions Success Frequency
, Path CI CMT Acc ADS-4 ADS 2,3 (per year) l l sgtrwo02 Yes 2 2 4 2,3 1.5E-7 l l tran22 Yes 1 2 4 2,3 9.8E-8 slocwo22 Yes 1 2 4 2,3 9.5E-8 mloca22 Yes 1 2 4 2,3 6.2E-8 slocaw22 Yes 1 2 4 2,3 5.8E-8 nloca12 Yes 2 1 4 0,1 1.6E-8 l sgtrw12 Yes 2 1 4 0,1 7.9E-9 mioca12 Yes 2 1 4 0,1 3.2E-9 slocaw12 Yes 2 1 4 0,1 3.0E-9 nloca23 Yes 1 2 4 0,1 2.9E-9 l nloca29 Yes 1 1 4 0-3 2.6E-9 tran12 Yes 2 4 0,1 2.4E-9 l( 1
\ sloewo12 Yes 2 1 4 0,1 2.4E-9 cmtib12 Yes 1 1 4 0,1 1.8E-9 sgtrw23 Yes 1 2 4 0,1 1.4E-9 sgtrwo11 Yes 2 1 4 2,3 1.2E-9 sgtrw29 Yes 1 1 4 0-3 1.2E-9 slocwo29 Yes 1 1 4 0-3 7.8E-10 tran29 Yes 1 1 4 0-3 6.8E-10 sgtrwo03 Yes 2 2 4 0,1 6.4E-10 mioca23 Yes 1 2 4 0,1 5.7E-10 slocaw23 Yes 1 2 4 0,1 5.2E-10 mioca29 Yes 1 1 4 0-3 5.0E-10 slocaw29 Yes 1 1 4 0-3 4.6E-10 slocwo23 Yes 1 2 4 0,1 4.2E-10 r%
Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:16-061997 1
6-40 Table 6.1.3-1 Success Category OK3 (Sorted by Descending Frequency)
(cont.) I Equipment Assumptions ;
Success Frequency Path CI CMT Acc ADS 4 ADS 2,3 (per year) tran23 Yes 1 2 4 0,1 4.1E-10 sgtrwo22 Yes 1 2 4 2,3 2.2E-10 sgtrwo12 Yes 2 1 4 0,1 5.0E-12 sgtrwo29 Yes 1 1 4 0-3 1.5E-12 I sgtrwo23 Yes 1 2 4 0,1 8.5E-13 TOTAL 5.8E-4 I
O O
Categorization of Success Paths for Short-Terrn Cooling June 1997 o:\3661w.wpf:1b41997 i
_ __-_______________ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ _ _ _ _ _ _ _ _ _ _ ___-_____a
6-41 6.1.4 Category OK4 O The success paths designated as category OK4 are listed in Table 6.1.4-1. Category OK4 is similar to category OK3, except stage 4 ADS is the same as design basis. The only ~ difference in category OK4 when compared to design basis is the loss of some ADS stage 2 and 3 lines.
This category definition extends to the loss of all ADS stage 2 and 3 lines, although the frequency is less than 5E-9/ year for this possibility; the highest-frequency success paths in '
category OK4 have the loss of no more than half of the stage 2 and 3 ADS lines. The frequency for the total category is 1.4E-6/ year.
The number of stage'2 and 3 ADS lines that actuate has a relatively minor impact on the ability to achieve IRWST gravity injection. The number of stage 4 ADS lines that actuate ,
determines whether the RCS is depressurized fast enough to achieve IRWST injection prior to core uncovery. Stage 4 lines are on the hot legs'and vent directly to containment, providing a more effective depressurization than the stage 2 and 3 lines, which vent from the top of the pressunzer to the IRWST water. The highest-frequency success paths in category OK4 also have both accumulators and both CMTs, providing ample short-term water supply until IRWST gravity injection is established.
?
This category applies to all the initiating events except for large LOCA. LLOCA is excluded t i because its results are dependent on the number of accumulators, and thus it is considered in ;
separate categories. ;
Although the grouping of the success paths into category OK4 is based on the rationale provided above, a set of MAAP4 analyses was performed to confirm the categorization basis.
This category includes success paths that may have the following failures: 1 stage 4 ADS, all stage 2 and 3 ADS,1 CMT,1 accumulator, and PRHR. A spectrum of break sizes was analyzed with the failure of stage 1 ADS and the success of only 1 path in 1 line for IRWST injection, in addition to the above failures. An exception to the general equipment assumptions is for transients and SLOCAs, in which 1 stage 2 or 3 ADS valve is credited because this is part of the success criterion requirement to avoid core damage.
, The minimum vessel mixture level versus break size is shown in Figure 6.1.4-1. The core
- j. remains covered in all cases, and is most limiting for the transients and small breaks, which !
are discussed below. For all break sizes, the time of the minimum vessel mixture level l- (Figure 6.1.4-2) is determmed by the start of accumulator injection. Therefore,3 stage 4 ADS is adequate venting capacity to allow IRWST gravity injection to be established, without challenging core cooling.
1 l Details of the plant response versus time can be seen in the MAAP4NOTRUMP benchmarking report (Ref. 2) for a 5-inch break with 1 CMT and 1 accumulator (case 10)
! '. or 2 CMTs and 2 accumulators (case 11). Results from both MAAP4 and NOTRUMP show 1
- Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:1b-061997 l
6-42 that the minimum mixture level remains well above the top of the core. The benchmarking cases contain the same assumptions as identified above, except no containment backpressure is modeled, and the IRWST line resistances correspond to 2 paths rather than 1 path.
The most limiting sets of conditions for category OK4 are high-pressure scenarios. If the break size is very small, or if the event is a transient with the loss of heat removal, the RCS pressure will inc ease to the pressurizer safety valve setpoint prior to ADS actuation. When ADS valves open, there is a loss of coolant through the ADS lines. CMT water helps make up the inventory loss, but no rapid injection source of water is available until the RCS pressure falls below 715 psia and the accumulator (s) begin to inject. When the RCS pressure is approximately 2500 psia at the time of ADS actuation, there is a several-hundred-second delay until the RCS can depressurize enough so that accumulators can inject. 'Ihis delay corresponds to the tunmg of the muumum vessel mixture level in the high-pressure scenarios.
The plant response for a 0.5-inch break is shown in Figures 6.1.4-3 to 6.1.4-7 to illustrate a high-pressure accident scenario. The RCS pressure, CMT and accumulator water inventory, IRWST injection flow rate, RCS coolant inventory, and vessel mixture level are used to provide a summary of the plant response. Figures 6.1.4-3 to 6.1.4-5 show the response to the 0.5-inch break described above, with only 1 CMT credited. Figures 6.1.4-6 and 6.1.4-7, which show the RCS coolant inventory and the vessel mixture level trends, also include the results of a case with both CMTs credited. The purpose of the 2-CMT case is to show that the minimum mixture level of the more probable high-pressure accident scenario is more similar h
to the larger breaks. A second CMT provides additional makeup inventory, and also prolongs the event, which causes the decay heat to be lower when ADS actuates.
Finally, the plant response for a 1-inch break is shown in Figures 6.1.4-8 to 6.1.4-12 to illustrate the less limiting response when the break is a little larger. The most limiting equipment failures identified above, with only 1 CMT, were modeled. Although also defined as a high-pressure scenano, the 1-inch break is at a pressure between 1600 and 1700 psia when ADS is actuated. The pressurizer safety valves are never actuated, and less coolant inventory is held up in the pressurizer than when the pressurizer safety valves are opened.
There is substantial margin to core uncovery for the 1-inch break. l l
l 9
Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:1b-061997
1 a .
6-43 1
l lg^g Table 6.1.41 Success Category OK4 (Sorted by Descending Frequency) l Equipment Assumptions l Success Frequency l
l Path CI CMT Acc ADM ADS 2,3 (per year) l nloca05 Yes 2 2 3 2,3 5.0E-7 sgtrw05 Yes 2 2 3 2,3 2.4E-7 tran05 Yes 2 2 3 2,3 1.5E-7 slocwo05 Yes 2 2 3 2,3 1.5E-7 mloca05 Yes 2 2 3 2,3 9.8E-8 slocaw05 Yes 2 2 3 2,3 9.2E-8 silb05 Yes 1 1 3 2,3 6.3E-8 cmtib05 Yes 1 2 3 2,3 5.4E-8 nloca% Yes 2 2 3 0,1 4.4E-9 l nloca14 Yes 2 1 3 0-3 4.0E-9
- sgtrw06 Yes 2 2 3 0,1 2.1E-9 l
sgtrw14 Yes 2 1 3 0-3 1.9E-9 slocwo14 Yes 2 1 3 1-3 1.2E-9 tran14 Yes 2 1 3 1-3 1.1E-9 mioca06 Yes 2 2 3 0,1 8.8E-10 slocaw06 Yes 2 2 3 0,1 8.1E-10 mloca14 Yes 2 1 3 0-3 7.9E-10 i nloca25 Yes 1 2 3 0-3 7.4E-10 l slocaw14 Yes 2 1 3 0-3 7.2E-10 tran06 Yes 2 2 3 1 6.5E-10 slocwo06 Yes 2 2 3 1 6.5E-10 silb06 Yes 1 1 3 0,1 5.5E-10 cmtib06 Yes 1 2 3 0,1 4.8E-10 cmtibl4 Yes 1 1 3 0-3 4.2E-10 sgtrwo05 Yes 2 2 3 2,3 3.4E-10 l 1 l !
A
\
Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wph1W197 I
l
6-44 Table 6.1.4-1 Success Category OK4 (Sorted by Descending Frequency)
(cont.)
Equipment Assumptions Success Frequency Path CI CMT Acc ADS-4 ADS 2,3 (per year) tran25 Yes 1 2 3 1-3 1.8E-10 mioca25 Yes 1 2 3 0-3 1.5E-10 slocaw25 Yes 1 2 3 0-3 1.2E-10 sgtrwo14 Yes 2 1 3 1-3 2.4E-12 sgtrwo06 Yes 2 2 3 1 1.4E-12 sgtrwo25 Yes 1 2 3 1-3 4.1E-13 TOTAL 1AE-6 O
O Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:1t>461997
6-45 k
, 'w/
I Figure 6.1.4-1 Minimum Vessel Mixture LeveI for Category OK4 m 0 I
v _
3--
e e
-.a e
0-- - - - - - - - - - - - - - - - _ _ _T_o .g _ o_ f _ c o_ r_e _ _ _ _ _ _ _ _
' _ l
, =
l _
( x
_3 __
s _
e -
[ -
e _
E a _g__
E -
C 2 ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' '
-12 i i i i i i
, i 0 1 2 3 4 5 6 7 8 9 Break ID (inch) r~,
( )
LJ Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wphlb-061997
6-46 1
l l
'e Figure 6.1.4-2 Time of Minimum Vessel Mixture Level for Category OK4 14000 12000 - -
10000 -
n _
o
- 8000 --
en h 6000- -
w -
4000 --
2000 --
0 l l l l l ;
O 1 2 3 4 5 6 7 8 9 l Break ID (inch)
O Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:1W1997
i 6-47 1
LO l Figure 6.1.4-3 RCS Pressure F o r. 0.5 inch Break in Cotegory OK4 3000 2500 -- t m 1 l -
)
l; 2 0 0 0 --
a _
v' _ ,
, 1500 - _
l- u
! 2 M --
l 1000 --
- u
- j. 500 --
( ' ' ' '
0 0 40'00 80'00 12800 160'00 2000 0 Time (S)
Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:1b-061997
G48 m
Figure 6.1.4-4 !
CMT and Accumulator Water For 0.5 inch Break in Category OK4 CMT
Accumulator 160000 m
E -
_a 120000 --
v cn m
I g
a _
I W
s I 80000 -- I I
u e -
I
-._, I a l l
3: _
I x 40000 -- I c I o -
I w -
I I
_ l
' ' ' ' ' ' ' ' ' ' 'I ' ' ' ' '
0 l l l 0 4000 8000 12000 16000 2000 0 Time (s) l 9
Categonzanon of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf-1b-061997 1
6-49
,n.
t ,'
yg:
Figure 6.1.4-5 IRWST Injeetion For 0.5 Inch Break in Category OK4 -
120 m
ca 100 --
I N
E _
_a 1 I
v 80 --
, 8, e
\_J o 60 --
oc 2::
o 40 --
u_
to en o 20 --
CEE l
~
l 1
' ' ' ' i i i i , , , , , , ,
0 l ; , ,
0 4000 8000 12000 16000 2000 0l '
I,lme (S)
- s, i x__,
Categor'ization of Success Paths for Short-Term Cooling jun,1997 o:\3661w.wpf:1b-061997
6-50 O
Figure 6.1.4-6 RCS Coolant Inventory For 0.5 inch Break in Category OK4 1 CMT
2 CMTs 350000 _
~ ~ --
300000 -- ~ ~ ,
_ s s
_ s s
s s
250000 -- s s
-s s E : 's
_a
- 200000 --
's '
's, g
- I 1
I m 150000 -2 '
w -
\
g k i
~
15 _
{
100000 -- t i- ~it.. ....
\l 50000 --
~
0 l l 0 4000 8000 12000 16000 2000 0 Time (s)
O Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:1b-061997
6-51 l
V)
Figure 6.1.4-7 Vessel Mixture Level For 0.5 Inch Break in Category OK4 1 CMT 2 CMTs
+ - - - Top of Core 30 ---
l
_ l L 26-- ;
m - ~~T~~~y
~ 22 - -
t % _
, s v _
=++++++l ll l l+++++l l+lll lllll g 18--
~
~
Cn C -
CD 14--
l _; _
10--
~
l 6 l l l l 0 4000 8000 12000 16000 2000 0 Time (s) i Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:1b 061997
6-52 O
Figure 6.1.4-8 RCS Pressure For 1.0 Inch Break in Category OK4 1 CMT 3000 2500 --
n o
3 2000 -- _
o.
- e g 1500 - 5 u
a m I o 1000 -- _
ct -
500 --
- 1 0 - '
0 30'00 60'00 90'00 1200 0 Time (s)
O Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf;1M61997
1 1
6-53 l i
l
,D l l U !
l l Figure 6.1.4-9 1 ;
CMT and Accumulator Water l For 1.0 Inch Break in Category OK4 ,
j CMT I Accumulator l
I 160000 E -
_a
- 120000 --
v m ----------
O
~
Cn \
i \ o _. t E t 80000 -- t u i
, co i I ~ 1 l
l c i 3 _ l ;
I x 40000 -- i C I o -
i H _ l I
l 0 i i i
0 3000 6000 90'00 1200 0 Iime (S) i Categorization of Success Paths for Short-Term Cooling June 1997 l o:\3661w.wpf 1t>461997 1
s.s4 O
Figure 6.1.4-10 IRWST Injection For 1.0 Inch Break in Category OK4 i 120 i
m cn 100 --
N E _
/
_a v 80 --
eu o 60 --
9 m
3::
o 40 --
u_
cn en o 20 --
IEE
' ' i i i , , , , ,
0 ;
0 3000 60'00 90'00 1200 0 I,Ime (s) l 9
Categorization of Success Paths for Short-Term Cooling 3# I"7 o:\Elw.wpf:1b41997
- 6-55 O
Figure 6.1.4-11 RCS Coolant Inventory
- For 1.0 Inch Break in Category OK4 l
l 350000 300000 --
l -
250000 -- _
i
- ^ _ !
E -
_a _
L- - -200000 -- l l t w -
m 150000 -2 m _
- o -
. :liE p
100000 --
A 50000 --
0 i i
! 0 3000 6000 90'00 1200 01 Time (s)
<O r
Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:1b-061997
5 56 O
Figure 6.1.4-12 Vessei Mixture LeveI For 1.0 Inch Break in Category OK4
+--- Top of Core 30 26 --
~
n
~ 22 --
( l
=
l l + l l l l +-+-+ l l l +-+-+-+-+--
, 18 --
~
cn -
c _
- 14 --
_J 10 --
' ' ' ' ' ' ' i 6 l l l 0 3000 6000 9000 12000 l I iin e (S) l l
l l
9 Categorization of StE:ess Paths for Short-Term Cooling June 1997 l o:\3661w.wpf:lt461997 l l
l 6-57 l
6.1.5 Categories OK5A, OK5B p
O Categories OK5A and OK5B consider the failure of complete containment isolation without any failures in the stage 4 ADS actuation. The failure of containment isolation lowers the containment backpressure, which can have an impact on the accident progression. The distinction between categories OK5A and OK5B is the number of stage 2 and 3 ADS lines that are assumed. The separation of the categories is done to illustrate that the highest-frequency success paths have more successful ADS lines:
Catecory Frequency OK5A No ADS failure 2.6E-6/ year OK5B Some ADS stage 2 and 3 failure 6.7E-7/ year l'
The success paths corresponding to these categories are listed in Tables 6.1.5-1 and 6.1.5-2.
Compared to design basis accidents, these success paths have an extra stage 4 ADS valve open, but do not have the containment fully isolated. The containment backpressure is lower l when the containment is not isolated, which can make IRWST gravity injection more difficult I to achieve. However, the extra venting from the stage 4 ADS line offsets the negative impact from the lack of containment isolation. Nevertheless, there is no need to demonstrate this with new analyses, because DBA analyses have already demonstrated successful core cooling with an atmospheric containment backpressure, and fewer stage 4 ADS valves. The SSAR (Ref. 4) Chapter 15 small-break LOCA analyses show successful core cooling, without core uncovery, with no elevated containment backpressure.
l l Categories OK5A and OK5B apply to all initiating events except large LOCA. Large LOCA l is not incluoed because the DBA large-break LOCA analyses take credit for a containment backpressure. In addition, LLOCA is excluded bccause of its dependency on the number of j
accumulators. As with other OK categories, a requirement for categories OK5A and OK5B is that there must be at least 1 functioning CMT and 1 functioning accumulator.
l l
l l
t V
Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:1b41997
i l
l 6-58 i
)
1 Table 6.1.5-1 Success Category OK5A (Sorted by Descending Frequency)
Equipment Assumptions Success Frequency !
Path CI CMT Ace ADS 4 ADS 2,3 (per year) nloca41 No 2 2 4 4 9.5E-7 sgtrw41 No 2 2 4 4 4.6E-7 I tran41 No 2 2 4 4 3.0E-7 slocwo41 No 2 2 4 4 2.9E-7 mioca41 No 2 2 4 4 1.9E-7 l slocaw41 No 2 2 4 4 1.8E-7 Iloca31 No 2 2 4 4 1.3E-7 silb33 No 1 1 4 4 1.2E-7 l l
cmtib33 No 1 2 4 4 1.0E-7 j nloca48 No 2 1 4 4 8.0E-9 j sgtrw48 No 2 1 4 4 3.9E-9 slocwo48 No 2 1 4 4 2.5E-9 tran48 No 2 1 4 4 2.3E-9 l mloca48 No 2 1 4 4 1.6E-9 slocaw48 No 2 1 4 4 1.5E-9 nloca54 No 1 2 4 4 1.4E-9 cmtib40 No 1 1 4 4 8.7E-10 sgtrwS4 No 1 2 4 4 7.0E-10 sgtrwo41 No 2 .2 4 4 6.6E-10 slocwoS4 No 1 2 4 4 4.4E-10 tran54 No 1 2 4 4 3.5E-10 mioca54 No 1 2 4 4 2.8E-10 slocawS4 No 1 2 '
4 2.6E-10 sgtrwo48 No 2 1 4 4 5.0E-12 sgtrwoS4 No 1 2 4 4 7.6E-13 TOTAL 2.6E-6 O
Categorizati.en of Success Paths for Short-Term Cooling June 1997 o:\3661w.wn:.1':41997
6-59 i
,Og Table 6.1.5-2 Success Category OK5B (Sorted by Descending Frequency)
V Equipment Assumptions Success Frequency Path CI CMT Acc ADS 4 ADS 2,3 (per year) nloca42 No 2 2 4 2,3 2.4E-7 sgtrw42 No 2 2 4 2,3 1.2E-7 tran42 No 2 2 4 2,3 7.4E-8 slocwM2 No 2 2 4 2,3 7.3E-8 mloca42 No 2 2 4 2,3 4.7E-8 slocaw42 No 2 2 4 2,3 4.4E-8 silb34 No 1 1 4 2,3 3.0E-8 cmtlbM No 1 2 4 2,3 2.6E-8 nloca43 No 2 2 4 0,1 2.2E-9 nloca49 No 2 1 4 0-3 2.0E-9 l sgtrw43 No 2 2 4 0,1 1.1E-9 sgtrw49 No 2 1 4 0-3 9.2E-10
'I slocwo49 No 2 1 4 0-3 6.0E-10
- %)
tran49 No 2 1 4 0-3 4.4E-10 mioca43 No 2 2 4 0,1 4.3E-10 slocaw43 No 2 2 4 0,1 3.9E-10 mioca49 No 2 1 4 0-3 3.8E-10 nloca55 No 1 2 4 0-4 3.6E-10 slocaw49 No 2 1 4 0-3 3.5E-10 slocwM3 No 2 2 4 0,1 3.2E-10 tran43 No 2 2 4 0,1 2.8E-10 l silb35 No 1 1 4 0,1 2.7E-10 l cmtib35 No 1 2 4 0,1 23E-10 cmtlb41 No 1 1 4 0-3 2.0E-10 sgtrwo42 No 2 2 4 2,3 1.6E-10 l
Categorization of Success Paths for Short-Terrn Cooling June 1997 o:\3661w.wpf:1M61997 l
l
l I
"O l l
l Table 6.1.5-2 Success Category OK5B (Sorted by Descending Frequency)
(cont.)
Equipment Assumptions Success Frequency Path CI CMT Acc ADS-4 ADS 2,3 (per year) sgtrwSS No 1 2 4 0-4 1.6E-10 slocwoS5 No 1 2 4 0-4 1.0E-10 mioca55 No 1 2 4 0-4 7.2E-11 tran55 No 1 2 4 0-4 6.2E-11 slocawSS No 1 2 4 0-4 5.8E-11 sgtrwo49 No 2 1 4 0-3 9.6E-13 sgtrwo43 No 2 2 4 0,1 5.8E-13 sgtrwo55 No 1 2 4 0-4 1.3E-13 TOTAL 6.7E-7 9
l l
9 1 Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:ll>.061997
L 6-61 i
6.1.6 Category OK6 s A i V Category OK6 also assumes the failure of containment isolation. While categories OK5A 1
l and OK5'B had a compensating effect of more stage 4 ADS lines open than design basis, category OK6 does not. Category OK6 is the LOCA design basis scenario with the L additional failure of containment isolation. The requirement for this category is intended to ;
! be all stage 1,2,3 ADS and 3 stage 4 ADS. However, with the failure of contamment I isolation and 1 stage 4 ADS, the expanded event trees only differentiate one more failure.
Therefore, some of the success paths listed in Table 6.1.6-1 include the possibility of more ADS failures. The frequencies of these paths are small, and the effect of including them l within this category is negligible and does not impact the definition of this category.
l Although the design basis scenario includes containment isolation, no credit is taken in most of the DBA analyses for a contairunent backpressure. The AP600 SSAR Chapter 15 small-break LOCA analyses show successful core cooling through the IRWST gravity injection phase with no elevated containment backpressure. The Chapter 15 small-break LOCA break sizes correspond to the PRA LOCA initiating events smaller than LLOCA. Thus, the SSAR analyses directly apply to this category, and no MAAP4 analyses are performed. LLOCA is not included in category OK6 because of its dependency on the number of accumulators.
The success paths corresponding to this category are listed in Table 6.1.6-1.
l lO l
! l i
l l
l l
l l
Categorization of Success Paths for Short Term Cooling June 1997 o:\3661w.wpf Ib-061997
6-62 I
Table 6.1.6-1 Success Category OK6 (Sorted by Descending Frequency)
Equipment Assumptions Success Frequency Path CI CMT Ace ADS-4 ADS 2,3 (per year) l l
nloca44 No 2 2 3 4 2.2E-9 sgtrw44 No 2 2 3 4 1.1E-9 slocwc44 No 2 2 3 4 6.7E-10 tran44 No 2 2 3 4 5.6E-10 mioca44 No 2 2 3 4 4.4E-10 slocaw44 No 2 2 3 4 4.1E-10 silb36 No 1 1 3 4 2.8E-10 cmtib36 No 1 2 3 4 2.4E-10 nloca50 No 2 1 2,3' 0-1 1.9E-11 sgtrw50 No 2 1 2,3* 0-4 9.2E-12 tran50 No 2 1 2,3' 0-4 4.5E-12 mioca50 No 2 1 2,3' 0-4 3.8E-12 slocaw50 No 2 1 2,3* 0-4 3.4E-12 nloca56 No 1 2 2,3* 0-4 3.4E-12 slocwoSO No 2 1 2,3' 0-4 3.1E-12 cmtib42 No 1 1 2,3' 0-4 2.0E-12 sgtrw56 No 1 2 2,3' 0-4 1.6E-12 sgtrwo44 No 2 2 3 4 1.2E-12 slocwo56 No 1 2 2,3' 0-4 8.3E-13 mloca56 No 1 2 2,3* 0-4 6.5E-13 tran56 No 1 2 2,3' 0-4 6.3E-13 slocaw56 No 1 2 2,3* 0-4 5.9E-13 sgtrwo50 No 2 1 2,3' 0-4 9.9E-15 sgtrwoS6 No 1 2 2,3' 0-4 1.4E-15 TOTAL 5.9E-9 Note:
These success paths include accident scenarios with more failures than defined by category OK2. The inclusion of additional equipment failures in these paths is of negligible importance because of the low frequency of the paths.
Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:1W)61997
-.- - - -- -.- ..~ . _ - .~ - .-.. . . .. -. . .. - - -.- .
[
6-63 6.1.7 Category OK7
' O- The success paths designated as category OK7 are listed in Table 6.1.7-1. Category OK7 is >
devoted exclusively to the large LOCA initiating event, and includes most of the LLOCA success paths with 2 accumulators.
l L This category is considered to be design basis for LLOCA. The plant response in the first hundreds of seconds is dictated by the plant and fuel design, and the number of accumulators. CMT performance does not impact the limiting portion of the accident progression. : However, at least 1 CMT is needed so that a low-low CMT level actuation signal will open the squib valves to the IRWST. Failure of both CMTs is assumed to lead to l core damage for this initiating event, since it is assumed that the operator would not have enough time to mac 1 ally actuate the IRWST squib valves.
- The success paths designated as category OK7 are addressed by DBA analyses documented in Chapter 15 of the AP600 SSAR. The OK7 success paths with successful containment y isolation must have at least 3 lines of stage 4 ADS. Loss of stage 2 or 3 is allowed within this category, since the impact of the ADS lines on the pressurizer has a negligible effect on the ability to achieve IRWST gravity injection, especially for a LLOCA that provides additional L venting capability through the break.' No MAAP4 analyses are performed for this category, l because large-break LOCAs are outside the applicability of the MAAP4 code.
- .O
- Success paths with the failure of containment isolation are also included within this category.
L Although a containment backpressure is credited within the DBA analyses, the limiting PCT occurs within tens of seconds of the break initiation. The status of the containment isolation system does not impact the plant response this quickly. However, for the small end of the i LLOCA break spectrum, the containment isolation status could impact the results. Therefore, l an additional stage 4 ADS line is required for this category if there is a containment isolation failure. (It is also noteworthy that a LLOCA case with the failure of containment isolation is defined in Section 6.3 as PRA-important. Results of the analysis are presented in Section 9.2, with more limiting equipment than defined by the success paths in category OK7.)
l i
i d
I O
Categorization of Success Paths for Short-Tenn Cooling June 1997 o:\3661w.wpf:1b-061997
6-61 Table 6.1.7-1 Success Category OK7 (Sorted by Descending Freq: .> 'cy)
Equipment Assumptions Success Frequency Path CI CMT Ace ADS-4 ADS 2,3 (per year) lloca02 Yes 2 2 4 2,3 2.7E-5 lloca03 Yes 2 2 4 0,1 2.5E-7 Iloca04 Yes 2 2 3 4 2.5E-7 lloca18 Yes 1 2 4 4 1.6E-7 lloca31 No 2 2 4 4 1.3E-7 lloca05 Yes 2 2 3 2,3 6.4E-8 lloca19 Yes 1 2 4 2,3 4.0E-8 Iloca32 No 2 2 4 2,3 3.4E-8 Iloca06 Yes 2 2 3 0,1 5.6E-10 lloca21 Yes 1 2 3 4 3.7E-10 lloca20 Yes 1 2 4 0,1 3.6E-10 lloca33 No 2 2 4 0,1 3.0E-10 lloca45 No 1 2 4 4 2.0E-10 lloca22 Yes 1 2 3 0-3 8.0E-11 lloca46 No 1 2 4 0-3 4.4E-11 TOTAL 2.7E-5 9
~
Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:1b-061997
_ . . . . . _ _ . . . . _ . ~ _ _ . . _ . _ . _ . . _ _ . _ _ _ _ . _ . _ _ . _ .
l 6-65 i
6.1.8 Category OK8 O The success paths designated as category OK8 are listed in Table 6.1.8-1. Category OK8 addresses an accident scenario that is unique to a break in the DVI line. If the CMT isolation valve on the ! alted loop opens, the water inventory from that CMT will be lost through the l break. If the intact CMT fails, there are no CMTs to provide makeup inventory to the RCS.
j However, the CMT spilling out the break will drain and provide the low-level signals for l ADS actuation. This is the only initiating event that can have "no CMTs," and yet automatic j ADS actuation occurs without operator intervention. This possibility is considered in the SFa expanded event trees with the top event "CMTSP." This event is used to differentiate whc aer the isolation valve on the faulted CMT opens. The success paths listed in Table 6.1.8-1 for category OK8 include success of the CMTSP top event. ,
l
- The success paths in this category have 1 accumulator injecting into the RCS and at least 3 stage 4 ADS. Other than the possible loss of some stage 2 and 3 ADS lines, the only other distinction from the design basis DVI line break scenario is the failure of the CMT on the intact loop. As can be seen in Chapter 15 of the SSAR, the role of the intact CMT is nurumal. ,
It is not responsible for the ADS actuation signals, and provides very little makeup inventory to the RCS. The failure of the intact CMT does not have a significant impact on the accident
' progression. No MAAP4 analyses are performed for category OK8.
l l
l l
l l
a .
Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:1b-061997 l
l
l 6-66 i Table 6.1.8-1 Success Category OK8 (Sorted by Descending Frequency)
~
Equipment Assumptions Success Frequency Path CI CMT" Acc ADS-4 ADS 2,3 (per year) silb17 Yes 0 1 4 4 7.6E-8 silb18 Yes 0 1 4 2,3 1.9E-8 silb20 Yes 0 1 3 4 1.8E-10 silbl9 Yes 0 1 4 0,1 1.7E-10 silb44 No 0 1 4 4 8.8E-11 silb21 Yes 0 1 3 0-3 4.0E-11 silb4S No 0 : 4 0-3 2.0E-11 silb46 No 0 1 2,35 0-4 2.0E-13 TOTAL 9.6E-8 Note:
(1) Although no CMT injection to the RCS is credited, ADS actuation occurs from the faulted CMT blowing down through the break.
(2) This success path includes the failure of more stage 4 ADS than defined by category OK8. The inclusion of additional equipment failures in this path is of negligible importance because of the low frequency of the path.
l l
l:
l l
l l
i l
l 9l ,
Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:1W1997
L l 6-67 6.1.9 Category OK9 Category OK9 consists of scenarios that require manual ADS actuation because both CMTs
! fail. However, only initiating events with relatively small breaks are included within this category. The significance of the small break area is that inventory loss is relatively slow, and the operator has sufficient time to open the ADS lines before much RCS inventory is lost.
The initiating events within category OK9 are transients, SLOCA, and SGTR. Larger breaks, l with the same conditions of both CMTs failing, have less operator action time and are -
classified within UC categories.
The additional requirements for this category are intended to be 3 stage 4 ADS if the l containment is isolated, and 4 stage 4 if the containment is not isolated. However, when l . 2 CMTs fail, the expanded event trees only differentiate one more failure. Therefore, some of the success paths listed in Table 6.1.9-1 include the possibility of more stage 4 ADS line l failures. The frequencies of these paths are small, and the effect of including them within !
this category is negligible and does not impact the definition of this category. '
I It is also worth noting that this category includes success scenarios with and without PRHR.
- l. It is questionable whether some of the very small break scenarios with PRHR actually need ADS to achieve successful core cooling. However, the need for ADS has been conservatively
assu nption is maintained in the expanded event trees for TlH uncertainty evaluation.
Av.dyses to demonstrate the accident progression for the OK9 category are provided in Figures 6.1.9-1 to 6.1.9-1S. The analyses are performed with the MAAP4 code, which has been benchmarked against the NOTRUMP code (Ref. 2). Results are presented for the following small breaks with the loss of both CMTs: 1-inch SLOCA, SGTR, and a loss-of-feedwater transient. The equipment assumptions that are consistent in all the analyses are:
! failure of both CMTs, I accumulator,1 path in 1 line for IRWST gravity injection, and j operator action required to open stage 4 ADS. The operator action for these initiating events is credited 30 minutes after the failed CMT actuation signal for the small LOCAs, including l SGTR. For transients, there are other operator cues, such as loss of PRHR and low SG level, l
that would be the operator's first indication that manual depressurization is needed. In the l MAAP4 analyses, the manual opening of ADS is modeled 30 minutes after the SGs empty. ;
l The number of ADS valves modeled depends on the containment isolation assumption. j l When the containment is isolated,3 stage 4 ADS valves are modeled, while all stage 4 ADS valves are modeled when cornplete containment isolation fails.
For each case, the following output parameters are provided as a function of time: RCS i
pressure, accumulator inventory, IRWST injection, pressurizer water inventory, RCS water inventory, and vessel mixture level. The mixture level remains well above the top of the core
- O in all the OK9 cases.
Categorization of Success Patiis for Short-Term Cooling June 1997 o:\3661w.vyf:H>061997 L. . - . , , . - . _ . . ,_ - , - . _ - - -
6-68 1
1
< Table 6.1.9-1 Success Category OK9 (Sorted by De scending Frequency)
Equipment Assumptions Success l Frequency Path CI CMT Acc ADS 4 ADS 2,3 (per year) i 1
sgtrw34 Yes 0 2 4 4 6.3E-7 sgtrw35 Yes 0 2 4 0-3 1.6E-7 slocwo34 Yes 0 2 4 4 2.8E-8 tran34 Yes 0 2 4 4 2.8E-8 slocaw34 Yes 0 2 4 4 1.7E-8 slocwo35 Yes 0 2 4 0-3 7.1E-9 l
tran35 Yes 0 2 4 0-3 6.0E-9 j sgtrw38 Yes 0 1 2-4* 04 5.3E-9 slocaw35 Yes 0 2 4 0-3 4.3E-9 sgtrw36 Yes 0 2 2,3 0-4 1.5E-9 sgtrw60 No 0 1,:t 24' 0-4 7.2E-10 slocwo38 Yes 0 1 2-4' 0-4 2.4E-10 slocaw38 Yes 0 1 2-4* 0-4 1.4E-10 tran38 Yes 0 1 2-4' 0-4 9.8E-11 slocwo36 Yes 0 2 2,3' 0-4 6.7E-11 sgtrwo34 Yes 0 2 4 4 6.5E-11 tran36 Yes 0 2 2,3' 0-4 6.0E-11 slocaw36 Yes 0 2 2,3' 0-4 4.0E-11
,locwo60 No 0 1,2 2-4* 04 3.2E-11 tran60 No 0 1,2 2-4* 0-4 2.5E-11 slocaw60 No 0 1,2 2-4' 0-4 1.9E-11 sgtrwo35 Yes 0 2 4 0-3 1.4E-11 sgtrwo38 Yes 0 1 2-4' L 04 2.3E-13 sgtrwo36 Yes 0 2 2,3' 0-4 1.4E-13 sgtavo60 No 0 1,2 2-4* 0-4 5.9E-14 TOTAL 8.8E-7 1
Note: I l
These success paths include accident scenarios with more failures than defined by category OK2. The inclusion of additional equipment failures in these paths is of negligible importance because of the low frequency of the paths.
Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:1b-061997
l 6-69 g .
Figure 6.1.9-1 RCS Pressure For 1.0 Inch Break in Category-0K9 l Co n t a i nme n t 'I s o l'a t e d . 3 Stage 4 ADS Containment Not i sola t ed. -4 Stage 4 ADS L
3000 :
h
, 2500 -- i l -
m _
o en 2000 -- . . -
a -
O v c) 1500 -
k_
- o _
( cn _
ca 1000 --
a) - '
u -
~
l
- l. ~
\
l 5 0 0 -- -
t' - l l - I i
\
t t i i t i t i I I I I
- r-- + -.-H J t-0 1 I I
- -i - w -. -i-I n_
0 1000 2000 3000 4000 5000 Time (S)
I lO Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf;1b-061997
6-70 0
Figure 6.1.9-2 Accumulator Water For 1.0 Inch Break in Category OK9 Containment isolated. 3 Stage 4 ADS Containment Not Isolated. 4 Stage 4 ADS 120000 100000 -- l 1
^ l E 1 o 1
- 80000 -- i v i a
M I
I W
60000 -- 1 25E t l
' i o 40000 -- i
\
_ i N 1 1
20000 -- ,
i i
1 0 l l l l
' i_
0 1000 2000 3000 4000 5000 Time (S)
O Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:1b-061997
6-71 r,
- C Figure 6.1.9-3 IRWST Injection
- For 1.0 Inch Break in Category OK9 l Containment isolated. 3 Stage 4 ADS Containment Not Isolated. 4 Stage 4 ADS 120 n
m x 100 -- ,-o E
n -
,\ ',
i
" II 80 -- l l
- 4 U
\
/
~
cu l pr p :
o 60 -- y I
oc l se q\
o I
_. 40 -- j ;
W I cn I m
O 20 -- I l
2 ~
1 l
I
- 0 l l ' -l '
l ' ' '
1000 2000 0 3000 4000 500 0 Time (s) i
~$
L' Categorization of Success Paths for Short-Term Cooling June 1997 c:\3661w.wpf:1b41997
sn O
Figure 6.1 ')-4 RCS Coolant Inventory For 1.0 Inch Break in Category OK9 Centainment isolated. 3 Stage 4 ADS Containment Not isolated. 4 Stage 4 ADS 350000 _
300000 --
250000 -2 n -
E o
- 200000 --
- g v -
m 150000 -- ,
l w -
1 o _
- lE _
100000 -- _
R N #
50000 -- _
~
0 0 10'00 20'00 30'00 40'00 5000 Time (S)
O Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:1t>O61997
6-73 l
l l
Figure 6.1.9-5 Vessel Mixture Level For 1.0 Inch Break in Category OK9 Containment isolated. 3 Stage 4 ADS Containment Not Isolated. 4 Stage 4 ADS 4- - - - T o p of Core 30 26 --
m _
~ 22 --
? (Ol v _
l =._._. ; ._. l ._. l ._._.4_._. l ._._ +._._. ; . _ . _ + _ . _ .+ _ . _ . l l c ' 18 -- -
~
cn -
C -
a2 14 --
10 --
1 _
L 0 i , i i i e i i e ii ii i i i i i i i i i i i t i i i i 0 1000 2000 3000 4000 5000 Time (s)
,_)'
! Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf-1b-061997
6-74 O
Figure 6.1.9-6 RCS Pressure For SGTR in Category OK9 Containment isolated. 3 Stage 4 ADS Containment Not isolated. 4 Stage 4 ADS 3000 2500 --
m _
o m 2000 --
o_ -
- s. ..
l g 1500 --
u 3 5 m _
}
m 1000 --
a) -
u _
Q_ -
500 -- I
_ l
_ l
\
' ' ' ' ' ' ' ' ' ' T '
0 l l r ' -' - ~ ~ ; - ~ ~ - ' - '
0 1000 2000 3000 4000 5000 Time (s)
O Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:lt41997
6-75 l
oO Figure 6.1.9-7 Accumulator Water For SGTR in Category OK9 Contoinment isolated. 3 Stage 4 ADS Containment Not isolated. 4 Stage 4 ADS 120000 100000 --
\
m E
_a 1
- 80000 -- l (O/ cn j
[ 60000 --
1 \
_ 1 L I o 40000 -- I
. -. , i o I y -
1 1
20000 -- i i
_ i 1
0
'l ' ' ' '
l
' ' b' ' ' ' ' ' ' ' ' ' '
0 1000 2000 30'00 40'00 5000 Time (S)
LO i
Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:1b41997
6-76 I
Figure 6.1.9-8 i
IRWST Injection For SGTR in Category OK9 Containment Isolated. 3 Stage 4 ADS ,
Containment Not Isolated. 4 Stage 4 ADS l
120
( 100 --
E
.a -
80 -- '
lb A N[F W c3 h
. V F o 60 -- fi cr Y i) l
- .p 40-- 4 l![h)l m
h' i
20 --
1
' ' ' ' ' ' ' ' ' ' ' ' !'''''i 0 l 0 1000 2000 30'00 40'00 5000 Iime (s)
O 6tegorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:1b-061997
l l
s-n !
t l -O t 1 i
I i
i Figure 6.1.9-9 !
L l RCS Coolant inventory l For SGTR in Category OK9 Containment Isolated. 3 Stage 4 ADS Containment Not isolated. 4 Stage 4 ADS l 350000 1 l
j l
I 300000 -- - l 1
1
~
250000 -- -
n
- E l
l t]'
_a
- 200000 --
v i
m 150000 --
m -
a ~
1 _
100000 --
! 50000 --
? -
l -
! i e i iii iii i i
! O i i iii,iiiiiiiii, 0 1000 2000 3000 4000 5000 Time (s)
O Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:11>&l997 I
6-78 i
l 9
Figure 6.1.9-10 Vessel Mixture Level For SGTR in Category OK9 Contoinment Isolated. 3 Stage 4 ADS
' Containment Not isolated. 4 Stage 4 ADS
+---Top of Core 30 26 --
n -
~ 22 --
+
v g
=._._. ; . _ . ; . _ . ; . _ . _ . 4_ . _ . ; . _ . _4. _ . _ . ; . _ . _4 _ . _ .4 _ . _ . ;
y 18 --
cn -
C -
cu 14 --
l 10 -- I
_ 1
' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' i i ' ' i 6 i i i i l
0 1000 2000 3000 4000 5000 Time (S) 1 91 Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:1t>M1997
6-79 l f^
k Figure 6.1.9-11 1 RCS Pressure For Transienis (Loss of FW) in Category OK9 l Containment isolated. 3 Stage 4 ADS l
- ---- Co n t a i nme n t Not isolated. 4 Stage 4 ADS 3000 l
l 2500 -- l
,- 1
^ o 2 O -
m 2000 --
l a -
V 1
, 1500 -
m _
m
! m 1000 - 5 l
e _
u _
a- -
1 i
500 -- l i
- l
- \
' ' ' ' ' ' ' ' ' ' ' ' ' ' '5-'-+--
0 l l 'l -
0 1000 2000 3000 40'00 5000 Iime (S) 4 i 4
)
Categorization of Success Paths for Short-Tenn Cooling June 1997 o:\3661w.wph1b-061997
l l 5 80 O
l Figure 6.1.9-12 Accumulator Water '
For Transienis (Loss of FW) in Category OK9 Containment Isolated. 3 Stage 4 ADS Containment Not Isolated. 4 Stage 4 ADS 120000 1
100000 -- l l i
E 1 l
- 80000 -- I i
v I
m i i
60000 -- i l 2 l
- 1 !
L i O I
~
40000 -- t o -
i 3:: 1 i
20000 -- t i
_ i
\
0 l 1000 l
2000
l 3000
' ' i 4000 h'ie i 0 5000 Time (S) l O
Categorization of Success Paths for Short-Term Cooling June ~.99 o:\3661w.wpf:1b41997
6-81 l
b~s ,
1 t
i- Figure 6.1.9-13
! IRWST Injeetion l For Transients (Loss of FW) in Category OK9 j l Containment isolated. 3 Stage 4 ADS l l
Containment Not isolated. 4 Stage 4 ADS 120 l
m m
x 100 --
E
~
d
, iIgd 80 - -
/ '
'l /
e - I p
o 60 - -
/
oc I
- I w I o I
__ 40 - -
w l
- I m l g 20 -- i E I g
0 l l 'l 0 1000 2000 3000 4000 5000 Time (s)
.O l
Categorization of Success Paths for Short-Term Cooling J = 1997 c:\3661w.wpf:1M)61997
6-82 O
Figure 6.1.9-14 RCS Coolant Inventory For Transienis (Loss of FW) in Category OK9 Containment isolated. 3 Stage 4 ADS
Containment Not isolated. 4 Stage 4 ADS 350000 _
300000 -- _
~
250000 --
m _
E :
_a 200000 --
g v -
m 150000 --
m -
o I
- lE : I 100000 -- -
s l s-
~
50000 -- -
\
_ 1 i
~
0 l 1000 l l l 0 2000 3000 4000 5000 Time (s)
O Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:1W1997
r 6-83
-y M
l Figure 6.1.9-15 Vessei Mixture Level For Transients (Loss of FW) in Category OK9 Containment isolated. 3 Stage 4 ADS
Co n t a i nme n t Not Isolated. 4 Stage 4 ADS
-t- - - - T o p of Core l 30 l _
26 --
n -
~ 22 -- l
! [}
'~
v
. _ . ; . _ . _ 4. _ . _ . j . _ . _ + _ . _ + _ . _ . ;
- ._. ; ._. l . _. . _ . j y -
en -
C -
e 14 --
_a _
10 --
6 i i i i 0 1000 2000 3000 4000 5000 Time (S) l l
l i
lO i
Categorization of Success Paths for Short-Term Cooling June 1997 o \3661w.wpf:1b-061997
6-85 6.2 UC CATEGORIES OF LOW-MARGIN ACCIDENT SCENARIOS l
O UC categories are comprised of accident sequences that result in core uncovery, and are L therefore defined as low-margin accident scenarios. Accident progressions that include core l uncovery based on nominal plant calculations have the Icwest margin to the acceptance criteria, and thus are the most likely to have an influence on the PRA results when TE uncertainty is considered.
l .
l " Low margin" is defined as a scenario that results in core uncovery. Core uncovery occurs l when the predicted coolant two-phase mixture level falls below the top of the active fuel.
l The occurrence of core uncovery is used only as a screening criterion for an accident scenario to be considered further within the TH uncertainty evaluation process. The acceptance criterion by which an accident scenario leads to successful core cooling in the PRA is that the p peak cladding temperature (PCT) should remain below 2200 F.
The process of identifymg the types of core uncovery extends from the same process that was l used to develop the PRA Phenomena Identification and Rankmg Tables (PIRTs) to support
! the MAAP4NOTRUMP benchmarking effort in Ref. 2. To develop the PIRTs, a spectrum i of PRA scenarios was examined by a group of experts with experience in AP600 systems
! design, small-break LOCA analyses, PRA, and PIRTs. Key thermal-hydraulic phenomena L that could impact challenges to core coolant inventory were identified. These same i
challenges can also be defined in terms of the equipment loss that causes them to occur.
This process led to the definition of categories UCI tiuough UC5.
- l. Categories UC6 through UC9 were developed with a different emphasis. These UC categories include accident scenarios that cannot be supported by current analyses, and are therefore assumed to result in core uncovery in the categorization process. Rather than
! perform additional analyses to determine whether the core remains covered, the information from the expanded event trees permits a risk-informed decision to be made on whether additional analyses are needed.
l Table 6.2-1 provides an overview of the ten UC categories and the impact on the Focused
! PRA if these categories were counted as core damage rather than successful core cooling.
L The impact is provided in terms of the change in the Focused PRA CDF and LRF, if the i accident led to core damage rather than successful core cooling.
i Sections 6.2.1 to 6.2.9 contain discussions of each of the UC categories and why the l
l specified equipment failures may result in a period of core uncovery. The basis for each i
- UC category may reference ex Sng analyses, such as those documented in Ref. 2, the l MAAP4NOTRUMP benchmarking report. However, no new analyses are performed for I
. UC categories unless the category is determined to be PRA-important. The deternunation of PRA importance is documented in Section 6.3.
Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:1b 061997
. . _ . . _ _ _ ._ _ . . _ _ , _ . ~_ _ _,
6-86 l
Table 6.2-1 Summary of UC Categories if counted as core damage, increase to Focused PRA Defining Initiating Equipment ACDF ALRF Number Description Event Conditions Uyear) Uyear)
UC1 No makeup inventory NLOCA 0 CMTs L4E-7 8.3E-9 l if RCS pressure is DVI LB greater than 700 psig UC2A 1 accumulator depletes MLOCA 0 CMTs 1.0E-9 8.0E-11 prior to operator CMT LB 1 accumulator ,
intervention l l
UC2B 2 accumulators deplete MLOCA 0 CMTs 1.2E-7 7.5E-9 prior to operator CMT LB 2 accumulators intervention UC3 No rapid inventory MLOCA 0 accumulators 2.2E-8 1.3E-9 makeup during CMTLB blowdown UC4 Reduced inventory LLOCA 1 accumulator 1.1E-6 6.8E-8 makeup during LLOCA reflood UC5 No makeup when ADS NLOCA 0 accumulators 7.2E-7 7.6E-8 is actuated at higher DVI LB pressure SLOCA SGTR Transients UC6 Reduced ADS-4 All 2 stage 4 ADS 3.3E-7 7.5E-8 Cont. isolation UC7 No ADS-1 LLOCA 0 stage 4 ADS 32E-9 1.9E-10 Cont. isolation UC8 No containment LLOCA CI failure 4.1E-10 4.1E-10 isolation s 3 stage 4 ADS 2 accumulators UC9 No containment All except CI failure 1.6E-9 1.6E-9 isolation LLOCA < DBA ADS Reduced ADS Refer to Section 6.3.1 for LRF estimate basis.
O Categorization of Success Paths for Short-Term Cooling Jum 1997 o:\3661w.wpf:1t>41997
. . . _ _ m _ . _ _ _ _ . . . _ . . _ . _ _ _ - . _ ._ _ __ __ _ _ . _ .
6-87 6.2.1 Category 'UC1 O
V Category UC1 contains scenarios with the failure of both CMTs. Without CMTs, operator action is the only means of opening ADS lines to depressurize the RCS to achieve IRWST j gravity injection. Prior to operator intervention, the only source of makeup water is the accumulators. However, accumulators can inject only after the RCS pressure falls below ;
l 700 psig. For LOCA break sizes that do not depressurize below this point, there is the l potential for core uncovery due to the lack of makeup water.
The potential for this type of core uncovery is also impacted by operator action time. The -
- question to be considered is whether core uncovery occurs before the break depressurizes the RCS below 700 psig and before the operator manually opens ADS lines. With operator action times of 20 or 30 minutes credited in the PRA success criteria, the core uncovers prior to accumulator injection for breaks between approximately 2 and 6 inches, as shown in j Figure 6.2.1-1. For break sizes at the upper end of the NLOCA spectrum, accumulator i injection starts shortly after the core uncovers, but the RCS depressurization rate is not sufficient to provide rapid accumulator injection to recover the core. For all break sizes within the NLOCA spectrum, the perioc' of core uncovery ends when the operator opens ADS lines, allowing the accumulators to inject rapidly.
The LOCA break sizes that lead to this type of core uncovery correspond to the intermediate LOCA (NLOCA) and DVIline break initiating events. Smaller break sizes lose inventory at a slow enough rate that the coolant inventory is not challenged prior to operator action; they are classified in category OK9 Larger breaks depressurize so that the accumulator (s) can inject prior to core uncovery, and are classified in categories UC2A and UC2B.
I Table 6.2.1-1 shows the applicable success paths, and the impact on the Focused PRA CDF and LRF if the scenario were counted as core damage.
LO Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:ll>461997
6-88 Table 6.2.1-1 Success Category UC1 (Sorted by Descending Frequency)
Equipment Assumptions If counted as core l damage, increase to l Focused PRA Success ADS Frequency l Path CI CMT Acc ADS-4 2,3 (per year) A CDF A LRF
- nloca34 Yes 0 2 4 4 9.2E-8 9.2E-8 5.5E-9 nloca35 Yes ,0 2 4 0-3 2.3E-8 2.3E-8 1.4E-9 l silb28 Yes 0 1 4 4 1.6E-8 1.6E-8 9.6E-10 silb29 Yes 0 1 4 0-3 4.2E-9 4.2E-9 2.5E-10 1
nloca38 Yes 0 1 2-4 0-4 7.8E-10 7.8E-10 4.7E-11 nloca36 Yes 0 2 2,3 0-4 2.3E-10 2.3E-10 1.4E-11 nloca60 No 0 1 2-4 0-4 1.1E-10 1.1E-10 1.1E-10 silb30 Yes 0 1 2,3 0-4 3.9E-11 3.9E-11 2.3E-12 silb50 No 0 1 2-4 G-4 1.9E-11 1.9E-11 1.9E-11 TOTAL 1.4E-7 1.4E-7 8.3E-9 Note:
(1) LRF for scenarios with containment isolation is estimated at 6% of core damage. Scenarios without containment isolation increase the LRF by 100% of the core damage frequency. Refer to Section 6.3.1 for LRF estimate basis.
i d
1 e
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6-89 i
(~')
! v Figure 6.2.1-1 Effect of Break Size and Accumulator injection on Time of Core Uncovery (1 Acc, No CMT. No ADS)
= = Co r e Uncovers 30 .
s
\ g
\ \
\ \
~
\ \
~
\ Accumulator \
\ \
g Injection Staris \
m -
g \
m -
g \
e 20 -- -
g \
~ \
,e \
>)
D s
\
' c- : \
s
\ \
E ~
\ \
- \
s ,#'s s e \
_ Accumulator E 10 -- s Empties
_ s s
s s
~~,
SLOCA NLOCA MLOCA 0 l l l l l l l l 0 1 2 3 4 5 6 7 8 9 l
l Break ID (inch)
C)
\v Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:1t>O61997
6-91 j 6.2.2 Category UC2A and UC2B l /~T '
l O j Like category UC1, categories UC2A and UC2B address the failure of both CMTs. Without CMTs, operator action is the only means of opening ADS lines to depressurize the RCS to achieve IRWST gravity injection. Prior to operator intervention, the only source of makeup !
water is the accumulators. For relatively large breaks, accumulator inventory may deplete prior to operator action to open ADS. This can create a period of core uncovery after ,
l accumulators empty and prior to operator intervention. This type of core uncovery applies to breaks from approximately 7 to 9 inches in diameter, as was shown in Figure 6.2.1-1. The corresponding initiating events are medium LOCAs (MLOCAs) and CMT line breaks. Larger breaks do not rely on ADS lines opening to achieve gravity injection since the break will depressurize the RCS to IRWST injection. Furthermore, the PRA event trees count failure of both CMTs as leading to core damage for larger breaks.
l The distinction between category UC2A and category UC2B is the number of accumulators
- available for injection to the RCS. The depth and duration of core uncovery is greater when
- there is only one accumulator (category UC2A). With two accumulators, the operator has l more time to take action to open ADS before core uncovery would occur. For the largest i j ' breaks in catepty UC2B, analyses have not been done to determine whether core uncovery occurs with two accumulators, and thus, the sequences are conservatively grouped into a UC category.
O Tables 6.2.2-1 and 6.2.2-2 show the applicable success paths and the impact on the Focused ]
I PRA CDF and LRF if the scenarios were counted as core damage. l l
L L .
O 1
Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:1b.061997
)
.e T--
6-92 Table 6.2.2-1 Success Category UC2A (Sorted by Descending Frequency)
Equipment Assumptions If counted as core damage, increase to Focused PRA Success Frequency Path CI CMT Acc ADS.4 ADS 2,3 (per year) A CDF A LRF
- cmtib28 Yes 0 1 4 4 6.7E-10 6.7E-10 4.0E-11 cmtib29 Yes 0 1 4 0-3 1.6E-10 L6E-10 9.6E-12 mloca38 Yes 0 1 2-4 0-4 1.5E-10 1.5E-10 9.0E-12 mloca60 No 0 1 2-4 0-4 2.1E-11 2.1E-11 2.1E-11 cmtib30 Yes 0 1 2,3 0-4 1.6E-12 1.6E-12 9.6E-14 cwtib50 No 0 1 2-4 0-4 7.6E-13 7.6E-13 7.6E-13 TOTAL 1.0E-9 1.0E-9 5.0E-11 Note:
(1) LRF for scenarios with containment isolation is estimated at 6% of core damage. Scenarios without containment isolation increase the LRF by 100% of the core damage frequency. Refer to Section 6.3.1 for LRF estimate basis.
O I
i G
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l 6-93 l
l ('S
\
Table 6.2.2-2 Success Category UC2B (Sorted by Descending Frequency)
Equipment Assumptions If counted as core damage, increase to Focused PRA Success Frequency Path CI CMT Ace AD%1 ADS 2,3 (per year) A CDF A LRF "'
cmtib21 Yes 0 2 4 4 8.0E-8 8.0E-8 4.8E-9 cmtib22 Yes 0 2 4 2,3 2.0E-8 2.0E-8 1.2E-9 i
miocaM Yes 0 2 4 4 1.8E-8 1.8E-8 1.1E-9 mioca35 Yes 0 2 4 0-3 4.6E-9 4.6E-9 2.8E-10 cmtlb24 Yes 0 2 3 4 1.9E-10 1.9E-10 1.1E-11 cmtlb23 Yes 0 2 2,3 0-4 1.8E-10 1.8E-10 1.1E-11 cmtlb46 No 0 2 2,3 0-4 9.2E-11 9.2E-11 9.2E-11 I mloca36 Yes 0 2 2,3 0-4 4.5E-11 4.5E-11 2.7E-12 cmtib25 Yes 0 2 2,3 0-4 4.1E-11 4.1E-11 2.5E-12 cmtlb47 No 0 2 2,3 0-4 2.0E-11 2.0E-11 2.0E-11 cmtib26 Yes 0 2 2,3 0-4 6.5E-12 6.5E-12 3.9E-13 cmtib48 No 0 2 2-4 0-4 2.0E-13 2.0E-13 2.0E-13 TOTAL 1.2E-7 1.2E-7 7.5E-9 Note:
(1) LRF for scenarios with containment isolation is estimated at 6% of core damage. Scenarios without containment isolation increase the LRF by 100% of the core damage frequency. Refer to Section 6.3.1 for LRF estimate basis.
(
l v
)
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-- - _ - . . .. - . - - -.. -. - .~. .. - - - . . - - . .
l 6-95
!=
l 6.2.3 Category UC3 A
\)
Category UC3 is a type of core uncovery that occurs in scenarios with the failure of both accumulators. The rapid makeup capability of the accumulators is essential for large breaks, and the failure of both accumulators is counted as core damage in the PRA LLOCA event tree. However, for breaks smaller than a LLOCA, the PRA success paths do not require any accumulators if at least 1 CMT functions. The CMT, although a similarly sized large tank of water, does not provide rapid makeup capability. Therefore, core uncovery can occur for breaks a little smaller than LLOCA The corresponding initiating events are MLOCA and CMT line break. As shown in the MAAP4NOTRUMP benchmarking case 4 (Ref. 2), the l depth and duration of this type of core uncovery do not challenge core cooling. For smaller i break sizes, inventory loss through the break is at a slower rate, and the CMT can perform an
! inventory makeup function in time to prevent this type of core uncovery.
Table 6.2.3-1 shows the applicable success paths, and the impact on the Focused PRA CDF and LRF if the scenarios were counted as core damage.
r
,k iO l
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1 6-96 Table 6.2.3-1 Success Category UC3 (Sorted by Descending Frecyecy)
Equipment Assumptions If counted as core damage, increase to Focused PRA Success ADS Frequency Path CI CMT Acc ADS-4 2,3 (per year) ACDF A LRF '"
mloca17 Yes 2 0 4 4 1.1E-8 1.1E-8 6.7E-10 cmtib17 Yes 1 0 4 4 6.2E-9 6.2E-9 3.7E-10 mioca18 Yes 2 0 4 0-3 2.8E-9 2.8E-9 1.7E-10 cmtlb18 Yes 1 0 4 0-3 1.6E-9 1.6E-9 9.3E-11 mioca19 Yes 2 0 2,3 0-4 2.7E-11 2.7E-11 1.6E-12 1
mloca32 Yes 1 0 2-4 0-4 1.7E-11 1.7E-11 1.0E-12 1
cmtibl9 Yes 1 0 2,3 0-4 1.3E-11 1.3E-11 8.0E-13 mloca52 No 2 0 2-4 0-4 1.3E-11 1.3E-11 1.3E-11 nloca58 No 1 0 2-4 0-4 1.2E 1.2E-11 1.2E-11 I 1
cmtib44 No 1 0 2-4 0-4 6.0E-12 6.0E-12 6.0E-12 mloca58 No 1 0 2-4 0-4 2.3E-12 2.3E-12 2.3E-12 TOTAL 2.2E-8 2.2E-8 1.3E-9 Note:
(1) LRF for scenarios with containment isolation is estimated at 6% of core damage. Scenarios without containment isolation increase the LRF by 100% of the core damage frequency. Refer to Section 6.3.1 for LRF estimate basis.
O Categorization of Success Paths for Short-Terrn Cooling June 1997 o:\3661w.wpf:1b-061997
. _.____.m _ _ _ . _ . _ _ . _ _ _ . - _ _ _ . _ _ . . . . . _ _ _ _ . _ . _ _ _ _ . _ . _ . _ _ _ .
L 6-97
- i. 6.2.4 Category UC4
- i. T The fourth type of core uncovery occurs in LLOCAs with 1 accumulator due to the high rate p of inventory loss from the break. Large-break LOCA is a design basis accident analyzed and l documented in Chapter 13 of the SSAR. The DBA scenario includes 2 accumulators, and core
- uncovery occurs due to the large inventory loss through the break. The success of this j - accident scenario has been demonstrated, including conservative assumptions, and is not subject to further investigation in this TlH uncertainty evaluation process. However, the
! LLOCA success criterion for the PRA only requires 1 accumulator. The failu e of an accumulator could impact the PCT during reflood.
l Table 6.2.4-1 shows the applicable success paths, and the impact on the Focused PRA CDF ~
l and LRF if the scenarios were counted as core damage.
l l
I t
i i
i i
i r
i-l l
I l
i.
- O Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:1t> 061997
6-98 Table 6.2.4-1 Success Category UC4 (Sorted by Descending Frequency)
Equipment Assumptions if counted as core
~~
damage, increase to Focused PRA Success ADS Frequency Path CI CMT Acc ADS 4 2,3 (per year) A CDF A LRF
- lloca10 Yes 2 1 4 4 8.9E-7 8.9E-7 5.3E-8 Ilocall Yes 2 1 4 2,3 2.2E-7 2.2E-7 1.3E-8 lloca13 Yes 2 1 3 4 2.1E-9 2.1E-9 1.3E-10 lloca12 Yes 2 1 4 0,1 2.1E-9 2.1E-9 1.3E-10 lloca25 Yes 1 1 4 4 1.3E-9 1.3E-9 7.8E-11 lloca39 No 2 1 4 4 1.1E-9 1.1E-9 1.1E-9 Iloca14 Yes 2 1 3 0-3 5.0E-10 5.0E-10 3.0E-11 lloca26 Yes 1 1 4 03 3.2E-10 3.2E-10 1.9E-11 lloca40 No 2 1 4 0-3 2.6E-10 2.6E-10 2.6E-10 I Iloca15 Yes 2 1 2 0-4 2.0E-10 2.0E-10 1.2E-11 lloca16 Yes 2 1 0,1 0-4 2.7E-11 2.7E-11 1.6E-12 lloca27 Yes 1 1 2,3 0-4 3.2E-13 3.2E-13 1.9E-13 lloca41 No 2 1 2,3 0-4 2.7E-13 2.7E-13 2.7E-13 i lloca50 No 1 1 2-4 0-4 8.2E-13 8.2E-13 8.2E-13 lloca28 Yes 1 1 0,1 0-4 3.3E-14 3.3E-14 2.0E-15 lloca42 No 2 1 0,1 0-4 7.6E-15 7.6E-15 7.6E-15 lloca51 No 1 1 0,1 0-4 0.0 0.0 0.0 TOTAL 1.1E-6 1.1E-6 6.8E-8 Note:
(1) LRF for scenarios with containment isolation is estimated at 6% of core damage. Scenarios without containment isolation increase the LRF by 100% of the core damage frequency. Refer to Section 6.3.1 for LRF estimate basis.
O Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf-1b.061997
l i 6-99 I
6.2.5 Category UC5 l O Category UC5 is a type of core uncovery also caused by the loss of accumulators. Categories UC3 and UC4 were associated with the acciunulators and their ability to provide rapid makeup for medium and large breaks. Category UC5 completes the examination of the effect of losing accumt:lators for the remaining initiating events. -
The initiating events to be considered are all those with breaks smaller than MLOCA (6 inches), including transients with loss of heat removal that can result in loss of inventory through the pressurizer safety valves. The accumulator cannot function until the RCS pressure is less than 700 psig, which happens when ADS lines are opened. The RCS pressure is relatively high (betmen 700 psig and 2500 psig) when ADS is opened, and the mass lost through the ADS is 5.qh. Accumulators provide rapid inventory makeup for this condition.
The cold accumulator water can also keep the downcomer subcooled, reducing the l downcomer pressure and making IRWST gravity injection easier to achieve. However, if both accumulators fail, analyses in the MAAP4NOTRUMP benchmarking report (Ref. 2) show that core uncovery can occur. This type of core uncovery applies to NLOCA, SLOCA, SGTR, and transients.
Table 6.2.5-1 shows the applicable success paths, and the impact on the Focused PRA CDF and LRF if the scenarios were counted as core damage. !
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! Categorization of Succ-ss Paths for Short-Term Cooling June 1997 j o:\3661w.wpf:1b-061997 l
l 6-100 Table 6.2.5-1 Success Category UC5 (Sorted by Descending Frequency)
Equipment Assumptions If counted as core damage, increase to Focused PRA Success ADS Frequency Path C1 CNfr Acc ADS 4 2,3 (per year) A CDF A LRF "'
silb10 Yes 1 0 4 4 .t.4p .7
. 4.4E-7 2.6E-8 silbli Yes 1 0 4 2,3 1.1E-7 1.1E-7 6.6E-9 nloca17 Yes 2 0 4 4 5.6E-8 5.6E-8 3.4E-9 sgtrwl7 Yes 2 0 4 4 2.8E-8 2.8E-8 2.8E-8 tran17 Yes 2 0 4 4 1.8E-8 1.8E-8 1.1E-9 slocwo17 Yes 2 0 4 4 1.7E-8 1.7E-8 1.0E-9 nloca18 Yes 2 0 4 0-3 1.4E-8 1.4E-8 8.4E-10 slocawl7 Yes 2 0 4 4 1.0E-8 1.0E-8 6.0E-10 sgtrwl8 Yes 2 0 4 0-3 7.0E-9 7.0E-9 7.0E-9 slocwo18 Yes 2 0 4 0-3 4.4E-9 4.4E-9 2.6E-10 tran18 Yes 2 0 4 0-3 3.6E-9 3.6E-9 2.2E-10 slocawl8 Yes 2 0 4 0-3 2.6E-9 2.6E-9 1.6E-10 silb13 Yes 1 0 3 4 1.0E-9 1.0E-9 6.1E-11 silb12 Yes 1 0 4 0,1 1.0E-9 1.0E-9 6.1E-11 silb40 No 1 0 4 4 5.1E-10 5.1E-10 5.1E-10 silb24 Yes 0* 0 4 4 3.2E-10 3.2E-10 1.9E-11 silbl4 Yes 1 0 3 0-3 2.5E-10 2.5E-10 1.5E-11 nloca19 Yes 2 0 2,3 0-4 1.4E-10 1.4E-10 8.3E-12 silb41 No 1 0 4 0-3 1.2E-10 1.2E-10 1.2E-10 nloca32 Yes 1 0 2-4 0-4 8.5E-11 8.5E-11 5.1E-12 silb25 Yes 0* 0 4 0-3 7.8E-11 7.8E-11 4.7E-12 nloca52 No 2 0 2-4 0-4 6.5E-11 6.5E-11 6.5E-11 sgtrw19 Yes 2 0 2,3 0-4 6.1E-11 6.1E-11 6.1E-11
! silbl5 Yes 1 0 2 0-4 4.1E-11 4.1E-11 2.5E-12 I slocwo19 Yes 2,3 2 0 0-4 4.0E-11 4.0E-11 2.4E-12 sgtrwo17 Yes 2 0 4 4 3.9E-11 3.9E-11 3.9E-11 sgtrw32 Yes 1 0 2-4 0-4 3.7E-11 3.7E-11 3.7E-11 i Categorization of Success Paths for Short-Term Cooling June 1997 J.\3661w.wpf:1t>G1997 l
6-101 n s.m Table 6.2.5-1 Success Category UC5 (Sc.rted by Descending Frequency) t.g (cont.)
Equipment Assumptions If counted as core damage, increase to Focused PRA Success ADS Frequency Path CI CMT Acc ADS-4 2,3 (per year) A CDF A LRF
- tran19 Yes 2 0 2,3 0-4 2.9E-11 2.9E-11 1.7E-12 sgtrwS2 No 2 0 2-4 0-4 2.8E-11 2.8E-11. 2.8E-11 tran32 Yes 1 0 2-4 0-4 2.6E-11 2.6E-11 1.6E-12 slocwo32 Yes 1 0 2-4 0-4 2.5E-11 2.5E-11 1.5E-12 slocaw19 Yes 2 0 2,3 0-4 2.3E-11 2.3E-11 1.4E-12 slocwoS2 No 2 0 2-4 0-4 1.9E-11 1.9E-11 1.9E-11 slocaw32 Yes 1 0 2-4 0-4 1.4E-11 1.4E-11 8.4E-13 nloca58 No 1 0-1 2-4 0-4 1.2E-11 1.2E-11 1.2E-11 tran52 No 2 0 2-4 0-4 1.2E-11 1.2E-11 1.2E-11 slocawS2 No 2 0 2-4 0-4 1.0E-11 1.0E-11 1.0E-11 sgtrwo18 Yes 2 0 4 0-3 7.8E-12 7.8E-12 7.8E-12 sgtrw58 No 1 0 2-4 0-4 5.8E-12 5.8E-12 5.8E-12 tran58 No 1 0 2-4 0-4 2.9E-12 2.9E-12 2.9E-12 slocwoS8 No 1 0 2-4 0-4 2.4E-12 2.4E-12 2.4E-12 slocaw58 No 1 0 2-4 04 2.2E-12 2.2E-12 2.2E-12 silb42 No 1 0 2,3 0-4 1.2E-12 1.2E-12 1.2E-12 silb26 Yes 0m 0 2,3 0-4 7.6E-13 7.6E-13 4.6E-14 silb48 No 0* 0 2-4 0-4 3.7E-13 3.7E-13 3.7E-13 sgtrwo19 Yes 2 0 2,3 0-4 6.3E-14 6.3E-14 6.3E-14 sgtrwo32 Yes 1 0 2-4 0-4 5.8E-14 5.8E-14 5.8E-14 sgtrwoS2 No 2 0 2-4 0-4 2.7E-14 2.7E-14 2.7E-14 sgtrwoS8 No 1 0 2-4 0-4 6.5E-15 6.5E-15 6.5E-15 TOTAL 7.2E-7 7.2E-7 7.6E-8 Notes:
(1) LRF for scenarios with containment isolation is estimated at 6% of core damage. SGTRs and scenarios without containment isolation increase the LRF by 100% of the core damage frequency. Refer to Section 6.3.1 for LRF estimate basis.
(2) Although no CMT injection to the RCS is credited, ADS actuation occurs from the faulted CMT blowing down through the break.
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Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf;1t41997
- . . . - ~ . - . - . - - . - - . - . _ . . - . - . - . - . - . - . . ~ . - . . - . - . .
l l 6-103 6.2.6 Category UC6 .
]
Category UC6 contains accident scenarios from all initiating events with 2 stage 4 ADS and successful containment isolation. The concern for this category is whether 2 stage 4 ADS l valves provide adequate venting to achieve and maintain IRWST gravity injection when the containment is isolated.
1 There are no current analyses that support this accident scenario. Preliminary MAAP4 l analyses were performed with 2 stage 4 ADS. However, the MAAP4NOTRUMP j
. benchmarking effort (Ref. 2) determined that the ADS stage 4 input in MAAP4 had not adequately accounted for the line resistances. Subsequently, benchmarking cases were modified to model the more probable condition of 3 stage 4 ADS, although the pessimism of :
no containment isolation was maintained. !
i Because of the lack of analytical support, all initiating events are assumed to result in core uncovery when there are 2 stage 4 ADS. Table 6.2.6-1 shows the applicable success paths, and the impact on the Focused PRA CDF and LRF if the scenarios were counted as core
' damage.
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6-104 Table 6.2.6-1 Success Category UC6 (Sorted by Descending Frequency) '
Equipment Assumptions If counted as core
- damage, increase to l Focused PRA l Success ADS Frequency l Path CI CMT Ace ADS-4 2,3 (per year) A CDF A LRF
- nloca08 Yes 2 2 2 0-3 6.6E-8 6.6E-8 4.0E-9 nloca07 Yes 2 2 2 4 5.0E-8 5.0E-8 3.0E-9 sgtrw08 Yer. 2 2 2 0-3 3.3E-8 3.3E-8 3.3E-8 i sgtrw07 Yes 2 2 2 4 2.5E-8 2.5E-8 2.5E-8 l slocwo08 Yes 2 2 2 0-3 2.0E-8 2.0E-8 1.2E-9 Iloca08 Yes 2 2 2 0-3 1.9E-8 1.9E-8 1.1E-9 tran08 Yes 2 2 2 0-3 1.9E-8 1.9E-8 1.1E-9 tran07 Yes 2 2 2 4 1.6E-8 1.6E-8 9.6E-10 slocwo07 Yes 2 2 2 4 1.5E-8 1.5E-8 9.2E-10 mloca08 Yes 2 2 2 0-3 1.3E-8 1.3E-8 7.8E-10 slocaw08 Yes 2 2 2 0-3 1.2E-8 1.2E-8 7.3E-10 mloca07 Yes 2 2 2 4 9.9E-9 9.9E-9 5.9E-10 lloca07 Yes 2 2 2 4 9.9E-9 9.9E-9 5.9E-10 slocaw07 Yes 2 2 2 4 9.2E-9 9.2E-9 5.5E-10 cmtibO8 Yes 1 2 2 0-3 7.2E-9 7.2E-9 4.3E-10 silbO7 Yes 1 1 2 4 6.4E-9 6.4E-9 3.8E-10 cmtlbO7 Yes 1 2 2 4 5.5E-9 5.5E-9 3.3E-10 silbO8 Yes 1 1 2 0-3 5.0E-9 5.0E-9 3.0E-10 nloca15 Yes 2 1 2 0-4 8.6E-10 8.6E-10 5.1E-11 sgtrw15 Yes 2 1 2 0-4 3.7E-10 3.7E-10 3.7E-10 l
slocwo15 Yes 2 1 2 0-4 2.5E-10 2.5E-10 1.5E-11 mioca15 Yes 2 1 2 0-4 1.6E-10 1.6E-10 9.3E-12 l
nloca26 Yes 1 2 2 0-4 1.6E-10 1.6E-10 9.3E-12 1 1
slocaw15 Yes 2 1 2 0-4 1.4E-10 1.4E-10 8.3E-12 tran15 Yes 2 1 2 0-4 1.2E-10 1.2E-10 7.3E-12 cmtibl5 Yes 1 1 2 0-4 7.7E-11 7.7E-11 4.6E-12
_ sgtrw26 Yes 1 2 2 0-4 5.4E-11 5.4E-11 5.4E-11 Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf.1b-061997
6-105
]
'v-Table 6.2.6-1 (cont.)
Success Category UC6 (Sorted by Descending Frequency)
Equipment Assumptions if counted as core damage, increase to Focused PRA Success ADS Frequency Path CI CMT Acc ADS 4 2,3 (per year) A CDF A LRF
- sgtrwo08 Yes 2 2 2 0-3 4.0E-11 4.0E-11 4.0E-11 sgtrwo07 Yes 2 2 2 4 3.5E-11 3.5E-11 3.5E-11 lloca23 Yes 1 2 2 0-4 3.2E-11 32E-11 2.0E-12 mioca26 Yes 1 2 2 04 3.1E-11 3.1E-11 1.8E-12 tran26 Yes 1 2 2 0-4 2.1E-11 2.1E-11 1.3E-12 slocaw26 Yes 1 2 2 0-4 2.0E-11 2.0E-11 1.2E-12 silb22 Yes 0* 1 2 04 7.1E-12 7.1E-12 4.3E-13 sgtrwo15 Yes 2 1 2 0-4 2.7E-13 2.7E-13 2.7E-13 sgtrwo26 Yes 1 2 2 0-4 4.6E-14 4.6E-14 4.6E-14 j TOTAL 3.3E-7 3.3E-7 7.5E-8 f)
G Notes:
(1) LRF for scenarios with containment isolation is estimated at 6% of core damage. SGTRs increase the LRF by 100% of the core damage frequency. Refer to Section 6.3.1 for LRF estimate basis.
(2) Although no CMT injection to the RCS is credited, ADS actuation occurs from the faulted CMT blowing ,
down through the break. l l
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I (V Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:1b-061997 1
6-107 1
m 6.2.7 Category UC7 i Category UC7 addresses the scenario of a large LOCA without any ADS, but with the I success of containtnent isolation. Large LOCA is the only PRA initiating event that credits IRWST gravity injection without the actuation of any ADS. The size of the LOCA break is defined to be large enough to provide the needed venting for IRWST gravity injection when the containment is isolated. However, analyses to support this are not current.
Table 6.2.7-1 shows the applicable success paths, and the impact on the Focused PRA CDF and LRF if the scenarios were counted as core damage. Note that although the desire is to
- separately consider the impact of no ADS, the expansion of the LLOCA event tree is not refined to the point that this option can be fully isolated. For this reason, the estimated numerical values for the frequency of this category err on the high side, although the frequency of the category is still relatively small.
l l
Table 6.2.7-1 Success Category UC7 (Sorted by Descending Frequency) l
! Equipment Assumptions If counted as core damage, increase to Focused PRA
/~s Success ADS Frequency j( Path CI CMT Acc ADS-4 2,3 (per year) A CDF A LRF "'
lloca09 Yes 2 2 0,1 0-4 3.2E-9 3.2E-9 1.9E-10 l Iloca24 Yes 1 2 0,1 0-4 4.6E-12 4.6E-12 2.7E-13 TOTAL 3.2E-9 3.2E-9 1.9E-10 Note:
l (1) LRF for scenarios with containment isolation is estimated at 6% of core damage. Refer to Section 6.3.1 for LRF estimate basis.
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Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:1b41997
l l 6-109 6.2.8 Category UC8
,f) iV l Category UC8 is comprised of LLOCA sequences with success of both accumulators, failure of containment isolation, and failure of 1 or rnore stage 4 ADS valves. There are no existing l analyses that demonstrate the effect of loss of containment isolation, along with the possible l loss of ADS valves, on the LLOCA initiating event.
Table 6.2.8-1 shows the applicable success paths, and the impact on the Focused PRA CDF and LRF if the sequences were counted as core damage.
Table 6.2.8-1 Success Category UC8 (Sorted by Descending Frequency)
Equipment Assumptions If counted as core damage, increase to l Success ADS Frequency Path CI CMT Acc ADS 4 2,3 (per year) A CDF A LRF ")
lloca34 No 2 2 3 4 3.1E-10 3.1E-10 3.1E-10 lloca35 No 2 2 3 0-3 6.9E-11 6.9E-11 6.9E-11 lloca36 No 2 2 2 0-4 2.4E-11 2.4E-11 2.4E-11
(> lloca37 No 2 2 0,1 0-4 1.9E-12 1.9E-12 1.9E-12 lloca47 No 1 2 2,3 0-4 4.5E-13 4.5E-13 4.5E-13 lloca48 No 1 2 0,1 0-4 2.4E-15 2.4E-15 2.4E-15 1
TOTAL 4.1E-10 4.1E-10 4.1E-10 l 1
Note:
l (1) Scenarios without containment isolation increase the LRF by 100% of the core damage frequency.
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6-111
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l 6.2.9 ' Category UC9
'(; \
Category UC9 is defined as the loss of containment isolation along with ADS losses that '
l reduce the ADS venting capacity below that assumed in design basis conditions. This category is defined to encompass all initiating events except LLOCA. It includes the most limiting success paths (i.e., ones with the most failures) on all the event trees.
l Although preliminary MAAP4 analyses had been done to support most of the success paths
- applicable to this category, no analyses have been done since the MAAP4 code was benchmarked. Therefore, no attempt is made to draw distinctions between which of the l initiating events and break sizes would result in core uncovery. They are all pessimistically
[ assumed to result in core uncovery. Table 6.2.9-1 lists the success paths, and the impact on I
the Focused PRA CDF and LRF if the scenarios were counted as core damage. l l
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6-112 Table 6.2.9-1 Success Category UC9 (Sorted by Descending Frequency)
Equipment Assumptions If counted as core damage, increase to ,
Focused PRA Success ADS Frequency Path CI CMT Acc ADS-4 2,3 (per year) A CDF A LRF
- nloca45 No 2 2 3 0-3 5.7E-10 5.7E-10 5.7E-10 sgtrw45 No 2 2 3 0-3 2.4E-10 2.4E-10 2.4E-10 slocwo45 No 2 2 3 0-3 1.6E-10 1.6E-10 1.6E-10 nloca46 No 2 2 2 0-4 1.2E-10 1.2E-10 1.2E-10 mioca45 No 2 2 3 0-3 1.1E-10 1.1E-10 1.1E-10 tran45 No 2 2 3 0-3 9.8E-11 9.8E-11 9.8E-11 slocaw45 No 2 2 3 0-3 9.0E-11 9.0E-11 9.GE-11 silb37 No 1 1 3 0-3 6.2E-11 6.2E-11 6.2E-11 cmtlb37 No 1 2 3 0-3 5.3E-11 5.3E-11 5.3E-11 )
sgtrw46 No 2 2 2 0-4 4.1E-11 4.1E-11 4.1E-11 slocwM6 No 2 2 2 0-4 2.9E-11 2.9E-11 2.9E-11 mloca46 No 2 2 2 0-4 2.3E-11 2.3E-11 2.3E-11 slocaw46 No 2 2 2 0-4 1.5E-11 1.5E-11 1.5E-11 tran46 No 2 2 2 0-4 1.4E-11 1.4E-11 1.4E-11 silb38 No 1 1 2 0-4 8.5E-12 8.5E-12 8.5E-12 cmtib38 No 1 2 2 0-4 7.9E-12 7.9E-12 7.9E-12 sgtrwo45 No 2 2 3 0-3 2.2E-13 2.2E-13 2.2E-13 sgtrwM6 No 2 2 2 0-4 3.1E-14 3.1E-14 3.1E-14 TOTAL 1.6E-9 1.6E-9 1.6E-9 j Note. l l
(1) Scenarios without containment isolation increase the LRF by 100% of the core damage frequency.
O Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:1b-061997
._,m ._. - _ _ _ _ . _ _ _ . - . _ _ _ _ . _ _ _ _ _ . - _ _ . . _ _ _ _ . _ . . _
{ 6-113 6.3 POTENTIALLY RISK-SIGNIFICANT SCENARIOS FOR SHORT-TERM COOLING-l The section identifies the AP600 accident scenarios that are both potentially risk-significant and result in core uncovery during the phases of the accident up to the establishment of
! IRWST gravity injection. Section 6.3.1 summarizes the quantification results from the UC categories and identifies which categories are potentially risk-significant. Section 6.3.2 l
, documents the selection of the limiting cases for low-margin, potentially risk-significant
{- categories. !
l 6.3.1 Definition of Potentially Risk-Signi6 cant Categories !
l Section 6.2 identifies the basis for grouping low-margin success paths from the expanded i
event trees into UC categories. Within Section 6.2, tables contain information on the increase to the Focused PRA CDF and LRF if the success paths were counted as core damage. It l should be emphasized that these are success paths in the Baseline and Focused PRAs.
l- However, the PRA T/H uncertainty evaluation process considers the possibility that the path l . is incorrectly categorized as success, and instead should be counted as core damage. This
. allows a ~ determination of the PRA importance of each path, based on the Focused PRA and
! . Baseline PRA impacts. The terms "PRA-important" and "potentially risk-significant" are used interchangeably within this report.
If a success path is counted as core damage, the increase to the CDF is the addition of the l frequency of that path to the Focused PRA CDF The impact on the LRF is estimated based l on the following rationale. The cases of no containment isolation and SGTR scenarios are straightforward, since all core damage is assumed to result in a large release to the enviromnent. Thus, the increase to the LRF is the same as the increase to the CDF. If the containment is isolated, however, only a fraction of the core damage accidents result in a large release to the environment. The deternunation of this fraction is done by binning core l
damage accidents into an appropriate PRA accident class, and the sequence frequency is multiplied by the containment matrix for the accident class to determine the contribution to the large release frequency. Most of the accidents being considered in this T/H uncertainty evaluation process, if they resulted in core damage, would have mmimal core damage that would neither relocate debris to the lower head nor generate significant hydrogen. Based l on Level 2 Baseline PRA work, it is estimated that 6 percent of the core damage scenarios with containment isolation could lead to a large release.
The impact of counting success paths as core damage was considered for each category.
l Individual success paths are treated as described above with respect to the determination of LRF, but the entire category is considered as a unit when determmmg potential risk i significance. In other words, the total CDF and LRF impacts for a category are used to Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wphlb-061997
_ . , _= _ - - _ _ . . _ --__ , _ _ _ _ _ _
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6-114 determine if the category is potentially risk-significant. This is because the UC categories are defined around a specific issue that is common to all the success paths that fit that category.
Therefore, if it were incorrect to credit successful core cooling in one success path, this would likewise apply to the other success paths with the same conditions defined by the category.
This is a conservative method of defining potential risk significance, since the binning process captures some accident scenarios that do not result in core uncovery. For example, core uncovery may happen for a 2-inch break, but core uncovery may be avoided with the same equipment assumptions if the break is 5 inches. However, both 2-inch and 5-inch breaks are modeled in the NLOCA event tree, and thus both are pessimistically assumed to result in core uncovery for the determination of potential risk significance.
Potential risk significance for the TIH uncertainty evaluation process is defined as increasing the Focused PRA CDF or LDF by at least 1 percent if the success category were counted as core damage. In addition, if a category includes DVI line break or LLOCA initiating event, the impact on the Baseline PRA is estimated, as discussed in Section 4.3.
Table 6.3.1-1 summarizes the UC categories and whether they are potentially risk-significant.
The PRA-important categories are further discussed in Section 6.3.2, which provides more details on the success paths that cause the category to be defined as PRA-important.
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6-115 l
p Table 6.3.1-1 Potential Risk Significance of UC Categories v ---
If counted as core damage, increase to Defining Focused PRA Potentially Equipment Risk Category Initiating Event Conditions ACDF ALRF Significant?'"
UC1 NLOCA 0 CMTs 1.4E-7 8.3E-9 Yes DVI Line Break UC2A MLOCA 0 CMTs 1.0E-9 8.0E-11 No CMT Line Break UC2B MLOCA 0 CMTs 1.2E-7 7.5E-9 Yes l CMT Line Break UC3 MLOCA 0 accumulators 2.2E-8 1.3E-9 No
- CMTLB UC4 LLOCA 1 accumulator 1.1E-6 6.8E-8 Yes l
UC5 N1OCA 0 accumulators 7.2E-7 7.6E-8 Yes DVI Line Break SLOCA l SGTR l Transients l O UC6 All 2 stage 4 ADS 3.3E-7 7.5E-8 Yes lV Cont. isolation UC7 LLOCA 0 stage 4 ADS 3.2E-9 1.9E-10 Yes* I Cont. isolation UC8 LLOCA CI failure 4.1E-10 4.1E-10 Yeso l
UC9 All CI failure 1.6E-9 1.6E-9 No l
Notes:
I I
(1) Potential risk significance is primarily based on the Focused PRA impact being greater than 1% of l
CDF or LRF. Exceptions are noted.
l (2) Categories (JC7 and UC8 are potentially risk-significant based only on the Baseline PRA impact.
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l 6-117 i
6.3.2 Definition of Low-Margin, Potentially Risk-Significant Cases f3 l
LJ There are five UC categories that are potentially risk significant based on the impact to the
! Focused PRA if the accident type leads to core damage rather than su :cessful core cooling.
- These categories are
- UC1, UC2B, UC4, UC5, and UC6. When the impact of LLOCA and DVI line break on the Baseline PRA is considered, two more categories (UC7 and UC8) are
, defined as potentially risk-significant. Table 6.3.2-1 is a comprehensive summary of each of l the potentially risk-significant categories. The dominant accident sequences for each potentially risk-significant UC category are defined in terms of:
The success path on the expanded event trees The equipment assumptions
. The increase to the Focused PRA CDF and LRF The increase to the Baseline PRA CDF and LRF for DVI line break and LLOCA A dominant eccident sequence is defined as one that contributes to the category CDF or LRF exceeding 1 percent of the PRA CDF or LRF. The residual effect of all scenarios not identified as dominant for a given category adds up to less than 1 percent of the PRA CDF or LRF.
l lq Limiting cases for each of the potentially risk-significant UC categories are summarized in l () Table 6.3.2-2. The basis for the selection of the cases is provided in Sections 6.3.2.1 tluough l 6.3.2.6. Note, however, that there is no case identified for category UC8. This is because the dominant sequence for this category is bounded by case UC42, defined to address category I UC4. T/H analyses for the NOTRUMP/LOCTA cases are presented in Section 9.1. T/H i analyses for the }VCOBRA/ FRAC cases are presented in Section 9.2. l l
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, og Table 63.11 Dominant'" Accident Sequences for Low-Margin, Potentially Risk-Significant Categones CD EO h if counted as core damage, increase to If counted as core damage, increase to g& Equipment Assumptions Focused PRA Baseline PRA h Success ADS ACDF ALRF ACDF ALRF ACDF ALRF ACDF ALRF
~E Category rath CI CMT Acc ADS-4 2,3 Vyear) Vyear) (%) (%) Vyear) Vyear) (%) (%)
km k UC1 nloca34 Yes 0 2 4 4 9.2E-8 5.5E-9 1.2% 1.0% - - - -
8 !
E silb28,29 Yes 0 1 4 0-4 - - - -
2.0E-8 1.2E-9 11.8 % 6.7%
'o UC2B cmttb21 Yes 0 2 4 4 8.0E-8 4.8E-9 1.0% 0.9% - - - -
UC4 Iloca10,11 Yes 2 1 4 2-4 1.1E-6 6.6E-8 14 3 % 12.0 % 1.1E-6 6.6E4 >100% >100%
y lloca12 Yes 2 1 4 0,1 - - - -
2.1E-9 1.2E-10 1.2% 0.7%
o
@ Ikra13 Yes 2 1 3 4 - - - -
2.1E-9 1.2E-10 1.2% 0.7%
W Iloca25 Yes 1 1 4 4 - - - -- 13E-9 8.0E-11 0.8% 0.4%
g O Iloca39,40 No 2 1 4 0-4 - - - -
1.4E-9 1.4E-9 0.8% 7.8%
8 .
@~ UC5 silb10.11 Yes 1 0 4 2-4 5.5E-7 33E4 7.1% 6.0% 53E-7 33E-8 >100% >100%
og silb12 Yes 1 0 4 0,1 - - - -
1.0E-9 6.0E-11 0.6% 03%
silb13 Yes 1 0 3 4 - - - -
1.0E-9 6.0E-11 0.6% 0.3%
silb40,41 No 1 0 4 0-4 - - - - 63E-10 63E-10 0.4% 3.5%
nloca17 Yes 2 0 4 4 5.6E-8 3.4E-9 0.7% 0.6% - - - -
sgtrwl7,18 Yes 2 0 4 0-4 3.5E-8 3.5E-8 05% 6.4% - - - -
tran17 Yes 2 0 4 4 1.8E-8 1.1E-9 0.2% 0.2% - - - -
y O -- - - -
O - - - - - - - - - - - -- -- - - - - -
O
O O O on
/u gg Table 6.3.2-1 Dominant"' Accident Sequences for Low-Margin, Potentially Risk-Significant Categories Q . 6 (cont.)
m If counted as core damage, increase to If counted as core damage, increase to Equipment Assumptions Focused PRA Baseline PRA gA Success Acc ADS 2,3 ACDF Uyear)
ALRF Uyear)
ACDF ALRF ACDF Uyeart ALRF Uyear)
ACDF
(%)
ALRF
(%)
N[ Category Fath Cl OIT A DS-4 (%) (%)
n 8 UC6 niva07,08 Yes 2 2 2 0-4 1.2E-7 7.0E-9 1.6% 1.3% - - - -
y sgtrw07,08 Yes 2 2 2 0-4 5.8E-8 5.8E-8 0.8% 10.5 % - - - -
slocwo7,8 Yes 2 2 2 1-4 35E-8 2.1E-9 0.5% 0.4% - - - -
o
" tran07,08 Yes 2 2 2 1-4 3.5E-8 2.1E-9 0.5% 0.4% - - - -
m D'
S Ikra07,08 Yes 2 2 2 04 2.9E-8 1.7E-9 0.4% 0.3% 2.9E-8 1.7E-9 17 % 9.4%
7 M mloca08 Yes 2 2 2 0-3 13E-8 7.8E-10 0.2% 0.2% - - - -
h silbO7,08 Yes 1 1 2 0-4 - - - -
1.1E-8 6.8E-10 65% 3.8%
O b UC7 Iloca09 Yes 2 2 0,1 0-4 - - - -
3.2E 4 1.9E-10 1.9% 1.1%
09 UC8 Iloca34 No 2 2 3 4 - - - - 3.1E-10 3.1E-10 <0.1% 1.7%
Notes-(1) Dominant scenarios are defined as ones that contribute to the category CDF or LRF exceeding 1% of the PRA CDF or LRF. The residual effect of all scenarios not identified as dominant for a given category adds up to less than 1% of the PRA CDF or LRF. For the Focused PRA, all initiating events defined in Section 6.2 for a specific category are considered. For the Baseline PRA, only DVI line breaks and large LOCA, if applicable to the category, are considered (refer to Section 4.3).
(2) Percentage impact on Focused PRA CDF and LRF is based on at-power values of 7.7E-6/ year CDF and 55E-// year LRF.
(3) Percentage impact on Baseline PRA CDF and LRF is based on at-power values of 1.7E-7/ year CDF and 1.8E-8/ year LRF.
I w
E a P 5 0 e
s
>Q i
- s Table 6.3.2-2 Cases for Analysis with Detailed T/H Codes U g%
y -
Jd g E. Break Size and Equipment Assumptions Case Location Code CI CMT Acc ADS 2,3 ADS-4 IRWST
{8
-o
@G UCI 3.25" Hot Leg NOTRUMP/LOCTA Yes 0 1 0 4 1 line,1 path e
UC2B Largest CMT LB NOTRUMP/LOCTA Yes 0 2 0 4 1 line,1 path y UC41 Large-Break LOCA WCOBRA/ TRAC Yes 1 1 0 3 1 line,1 path UC42 Large-Break LOCA WCOBRA/ TRAC No 2 1 0 4 1 line,1 path m UCS DVI LB NOTRUMP/LOCTA No 1 0 0 3 1 line, I path
?
2 UC61 DVI LB NOTRUMP/LOCTA Yes 1 1 0 2 1 line,1 path H
l UC62 2" Hot Leg NOTRUMP/LOCTA Yes 1 1 1 st. 3 2 1 line,1 path
{5 UC7 9" Hot Leg NOTRUMP/LOCTA Yes 2 2 0 0 1 line,1 path m
I 1
6 O - - - - -
O O
6-121 6.3.2.1 Selection of Limiting Case for Category UC1 O
Category UC1 represents core uncovery that occurs when there is no short-term makeup inventory because the RCS pressure is greater than 715 psia and both CMTs have failed. The break must be large enough to lose sufficient inventory prior to operator intervention to open ADS, but the break must be small enough to prevent significant accumulator injection.
MAAP4/NOTRUMP benchmarking case 5 in Ref. 2 demonstrates this type of core uncovery prior to ADS actuation.
According to Table 6.3.2-1, the only dominant initiating event based on the Focused PRA impact is an NLOCA, which covers a break spectrum from 2- to 6-inch diameter. However, a DVI line break is also important to the Baseline PRA. Therefore, the case to be analyzed is defined based on the most limiting aspects of the NLOCA and DVIline success paths that are identified in Table 6.3.2-1.
The MAAP4 code was used to analyze a spectrum of break sizes and locations with the following limiting equipment based on the dominant success paths: )
l
= Containment isolated !
- No CMTs !
q = 1 accumulator i
()
- No stage 1,2, or 3 ADS 4 stage 4 ADS (based on operator action 20 minutes after the failed CMT actuation signal)
J
=
1 line, I path for IRWST gravity injection The MAAP4 analysis method and thermallhydraulic assumptions are consistent with those used in Ref. 2, including best-estimate decay heat. Minimum vessel mixture level results i from the MAAP4 analyses are summarized in Figure 6.3.2-1. The deepest core uncovery occurs for a 3.25-inch hot-leg break. At this break size, the RCS pressure prevents accumulator injection until ADS is about to actuate. The core recovers due to the rapid l accumulator injection when ADS actuation depressurizes the RCS. There is no further challenge to core cooling, because all stage 4 ADS lines are open, providing ample venting capability to keep the RCS depressurized to provide IRWST gravity injection.
Case UC1 for NOTRUMPILOCTA analysis is defined based on these results. The equipment assumptiore are summarized in Table 6.3.2-2, and the NOTRUMPILOCTA analysis results are discussed in Section 9.1.2.1.
d A
Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.v p61M61997
6 122 O
Figure 6.3.2.1-1 Minimum Vessel Mixture Leyel for Co tego ry UC1 6
v _
3_ CoId Leg e
e ~
_.J g 0- - - - - - - ----- ---------- - _o,p T _of core m
x DVI Line O'
_3 __
e _ Hot Leg
[ -
o _
E i 2 - 1 E -
I 1
C l
E ' ' ' ' ' ' ' ' ' ' '
-12 ' ' ' ' l i i i ,
2 3 4 5 6 l Break ID (inch) .
O1 Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:1M61997
- _ _ . _ _ , . . _ _ . _ _ _ _ .. _ ._ .. _ _ _ _ . . _ _ . . _ . _ _ . . -____._m_
1 l 6-123 6.3.2.2 Selection of Limiting Case for Category UC2B l
Category UC2B represents core uncovery that occurs when there is no short-term makeup
! inventory because both CMTs have failed and accumulators have emptied prior to operator invention. The break must be large enough to drain both accumulators prior to operator l . intervention. MAAP4/NOTRUMP benchmarking case 7 in Ref. 2 is an example of an accident with this type of core uncovery, except only one accumulator was modeled. When both accumulators are credited, core uncovery may be prevented, although this has not been demonstrated through analyses and thus is considered via category UC2B.
According to Table 6.3.2-1, the only dominant initiating event based on the Focused PRA impact is a CMT line break. There are no further sequences to consider due to Baseline PRA -
considerations. A CMT line break is defined for the PRA as a break that occurs in the CMT L balance line or CMT injection line up to the check valves that prevent reverse flow from the l DVI line. Some break locations on the CMT line could result in the CMT draining, but this has been pessimistically ignored for the PRA. Manual ADS is required based on the
, assumption that neither CMT drains.
l Case UC2B for NOTRUMPlLOCTA analysis can be directly defined based on the dominant l success path for this category, without supporting MAAP4 analyses. The limiting break size l for this category is the largest that can occur due to the higher rate of accumulator draining.
Q The equipment is:
- Containment isolated a No CMTs l
- 2 accumulators a No stage 1,2, or 3 ADS l
4 stage 4 ADS (based on operator action 20 minutes after the failed CMT actuation signal)
=
1 line,1 path for IRWST gravity injection The NOTRUMP/LOCTA analysis results are discussed in Section 9.1.2.2. '
l r
6.3.2.3 Selection of Limiting Case for Category UC4 Category UC4 represents core uncovery that occurs in a large LOCA when there is only one accumulator. The accident scenario is similar to the SSAR Chapter 1S large-break LOCA, with the exception of only one accumulator instead of two.
1 According to Table 6.32-1, the dommant accident sequences based on the Focused PRA are paths 10 and 11 on the LLOCA expanded event tree in Section 4.4. The equipment failures l'
Categorization of Success Paths for Short-Term Cooling June 1997 c:\3661w.wpf.Itr061997
[
6-124 j are 1 accumulator and possibly some stage 2 and 3 ADS lines. Due to Baseline PRA considerations, additional equipment failures become potentially risk-significant, based on the -
definition of 1 percent impact on CDF or LRF. The additional equipment failures that are important in the Baseline PRA are loss of I stage 4 ADS, loss of 1 CMT, and loss of containment isolation.
The dominant accident sequences for category UC4 were grouped into two scenarios to define the cases for further TlH analysis: with containment isolation and without contaimnent isolation. Case UC41 is defined with the following equipment to bound the sequences with containment isolation in Table 6.3.2-1:
- Containment isolated a 1CMT
- 1 accumulator a No stage 1,2, or 3 ADS
- 3 stage 4 ADS
- 1 line,1 path for IRWST gravity injection Case UC42 is defined with the following equipment based on the category UC4 sequence with no containment isolation:
- Containment not isolated a 2 CMTs a 1 accumulator a No stage 1,2, or 3 ADS 4 stage 4 ADS 1 line,1 path for IRWST gravity injection The }yCOBRAffRAC methodology and analysis rsults for these cases are discussed in Section 9.2.
I l
O Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:1b-061997 l
i l 6-125 I l
[ 6.3.2.4 Selection of Limiting Case for Category UC5
' Category UC5 represente core uncovery that can occur when there are no accumulators to provide rapid, subcooled makeup inventory when ADS Os actuated. Many of the MAAP4I' i l
NOTRUMP benchmarking cases in Ref. 2 demonstrate accident scenarios that fall withm this j type of core uncovery. .l According to Table 6.3.2-1,'the SI line break is the most important initiating ever.t, based on
{
the Focused PRA and Baseline PRA impacts if the accident were to result in core damage ;
l PRHR, or transient with loss of PRHR could also be risk-significant if the accident resulted in I core damage.
To define a limiting case for further T/H analyses, the accident sequences were separated
[ into DVI line breaks and non-DVI line breaks. The limiting equipment to bound the DVI line accident sequences on Table 6.3.2-1 is:
. Containment not isolated a 1CMT. l
. No accumulator 1
,
- No stage 1,2, or 3 ADS
- 3 stage 4 ADS
=
1 line,1 path for IRWST gravity injection MAAP4/NOTRUMP benchmarking case 8 and case 8b in Ref. 2 analyze this scenario, with the exception of the IRWST gravity injection path. The benchmarking cases credit two paths -
on one injection line, effectively providing a lower line resistance than the DVI line break scenario above. The difference between benchmarking case 8 and case 8b is whether the CMT on the faulted loop is modeled to spill out the break, causing an earlier ADS actuation signal. Ref. 2 shows that it is more limiting to ignore the faulted CMT and wait for the ADS actuation signal from the intact CMT low-low level (benchmarking case 8).
No additional MAAP4 analyses are performed for the DVI line break scenario for category UC5. The results from benchmarking case 8 show that core uncovery occurs between 30 and 40 minutes after reactor trip, and the minimum mixture level is 3.7 feet below the top of the core. The total duration of core uncovery is 600 seconds with 2 paths on 1 IRWST injection line. With only 1 path on 1 IRWST injection line, the duration of core uncovery is likely to increase, but the minimum mixture level would not be significantly impacted.
1
' b/
Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:11.-061997 j
l l
6-126 For non-DVI line break scenarios, the MAAP4 code was used to perform scoping analyses.
The limiting equipment to bound the non-DVI line break scenarios on Table 63.2-1 is:
- Containment isolated 4
. ICMT
- No accumulator
. No stage 1,2, or 3 ADS
- 4 stage 4 ADS
- 1 line,1 path for IRWST gravity injection The MAAP4 analysis method and thermallhydraulic assumptions are consistent with those used in Ref. 2, including best-estimate decay heat. The non-DVI line break initiating events to be considered are NLOCA (2 to 6 inches), SGTR with PRHR, and transients with loss of PRHR. Minimum vessel mixture level results a' Tom the non-DVI line break MAAP4 analyses are summarized in Figure 6.3.2.4-1. All the non-DVI line break cases are less limiting than the DVIline break.
Case UC5 for NOTRUMP/LOCTA analysi is defined as the DVI line break scenario because it is the most limiting. The equipment assumptions are summarized in Table 6.3.2-2, and the NOTRUMPILOCTA analysis results are discussed in Section 9.1.2.3.
O 1
9 i Categorization of Success Paths for Short-Tenn Cooling June 1997 o:\3661wapf;1W1997
I i 1
6-127 l
O Figure 6.3.2.4-1 )
Minimum VesseI Mixture LeveI !
for Non-DVI Line Breaks in Category UC5 ;
A 6 i
SGTR f .
v _
3--
! o
/
Cold Leg o -
_J o_ _____.________ _ _ _ _ _ _ _ _ I 9_ P_ .g f_ _C_o r e_ _ _ _ _ q i e <
.y 3
~
l0
> \
X
-3__ Hot Leg E
['-6--
o -
\
L E a _g__
E -
l c -
E i i , i i i i i i i
-12 , , i, , ,
0 1 2 3 4 5 6 Break ID (inch)
- O l Categorization of Success Paths for Short-Term Cooling June 1997 o
- \3661w.wpf:1b-061997 l
l l
- . ~ - , . -- .-~ ~ . - - . . ~ - - - . - . - . . . - . . - . - - . .
t 6-129 6.3.2.5 Selection of Limiting Case for Category UC6 i
O Category UC6 contains sequences from all the initiating events with only 2 stage 4 ADS valves and successful containment isolation. According to Table 6.3.2-1, the dominant ,
accident sequences in this category encompass most of the initiating events. The initiating l
l events that are most important to the PRA are:
i-l SGTR, with an increase of 11 percent to the Focused PRA LRF if core damage occurs LLOCA, with an increase of 17 percent to the Baseline PRA CDF if core damage occurs DVI line break, with an increase of 7 percent to the Baseline PRA CDF if core damage l occurs NLOCA, with an increase of 2 percent to the Focused PRA CDF if core damage occurs The other initiating events that are not as important, but still classified as dominant accident sequences, are SLOCA, transients, and MLOCA.
l To define limiting cases for further TlH analyses to support category UC6, the initiating events with dominant accident sequences in this category were grouped based on similarity in the plant response. The initiatirg events will be discussed in the following groups:
I - - -
- 1. LLOCA and MLOCA (O.
yj 2. Transients, SLOCA, and SGTR
- 3. NLOCA and DVIline breaks 1
The LLOCA and MLOCA initiating events are the least restrictive in terms of the plant response to the actuation of 2 stage 4 ADS valves. Depressurization of the RCS is aided by the break area, and therefore the venting capacity requirements from the ADS valves is not as great as for smaller break sizes. The plant response from the NLOCA initiating event, which is discussed later in' this section, bounds the MLOCA and LLOCA response. Note that the dominant sequences include the success of 2 CMTs and 2 accumulators, and therefore the
. issue for these success paths is only one of adequate venting from stage 4 ADS. l The transients, SLOCA, and SGTR initiating events are on the other end of the break spectrum. These are high-pressure accident scenarios, and the success criterion requires the actuation of 1 stage 2 or 3 ADS valve in addition to the stage 4 ADS valves. This requirement is to reduce the RCS pressure below the stage 4 ADS interlock pressure. These high-pressure accidents are the same as illustrated in Section 6.1.1 for Category OK1, except l with the failure of several ADS valves. Therefore, the plant response has already been shown up to the time of ADS actuation. ADS actuation for the high-pressure events typically occurs several hours after reactor trip, when the decay heat is relatively low. Low decay heat makes it easier to depressurize the system, even if there is little or no venting capacity from a break l
ICategorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:lt461997
1 1
6-130 in the system. Therefore, the high-pressure accidents are bounded by the analyses presented below, which credit 1 stage 3 ADS plus 2 stage 4 ADS lines.
The final initiating eventa in category UC6 are NLOCA and DVI line break. The MAAP4 code was used to analyze a spectrum of break sizes and locations with the following limiting equipment based on the dominant sequences in Table 6.3.2-1:
. Containment isolated
. ICMT
= 1 accumulator
. No stage 1,2, or 3 ADS
= 2 stage 4 ADS
= 1 line,1 path for IRWST gravity injection The MAAP4 analysis method and thermalthydraulic assumptions are consistent with those used in Ref. 2, including best-estimate decay heat. Minimum vessel mixture level results from the MAAP4 analyses are summarized in Figure 6.3.2.5-1. Although the depth of core uncovery is within an acceptable range, the duration of core uncovery is too long at the lower end of the break spectrum, as shown in Figure 6.3.2.5-2. Break sizes between 2 inches and approximately 4 inches are not adequately depressurized with 2 stage 4 ADS valves to allow IRWST gravity injection to recover the core in a timely fashion. The PRA impact of this finding is addressed in Section 11. However,2 stage 4 ADS valves provide adequate venting for breaks 4 inches and larger. The 4-inch DVI line break and the 4-inch hot-leg break exhibit similar plant responses. A DVI line break was selected as Case UC61 for further analysis with NOTRUMP/LOCTA. The equipment assumptions are consistent with those defined above, which represent the limiting equipment for the DVI line break dominant sequences for category UC6. These assumptions for case UC61 are summarized in Table 6.3.2-2.
I Further MAAP4 analyses were done to define the number of ADS valves that must open at ]
the lower end of the NLOCA break spectrum. Cases were run that credit 1 stage 3 ADS i valve in addition to the 2 stage 4 ADS valves. Results of minimum vessel mixture level l
(Figure 6.3.2.5-3) and duration of core uncovery (Figure 6.3.2.5-4) support the conclusion of successful core cooling. The limiting break size is at the small end of the spectrum. Case ;
UC62 for further analysis with NOTRUMPILOCTA is defined based on these results. The equipment assumptions are summarized in Table 6.3.2-2. l Results from the NOTRUMPILOCTA analysis of case UC61 and case UC62 are presented in l Sections 9.1.2.4 and 9.1.2.5. l i
G Categorization of Success Paths for Short-Term Cooling June 1997 l o:\3661w.wpf:1b-061997 l
l 6-131 l-I I
o G
1 l Figure 6.3.2.5-1 l
Minimum Vessel Mixture LeyeI for Category UC6 with 2 s t'a g e 4 ADS 1 6 j
! ^
v . 3--
a) -
> Top of Core cu 0- - - - - - - - - - - - - - - - - - - - - ---------------
._J -
l f3 Q a>. -
a ~3~~ DVI Line Break l W x l i
t ..-
( OE Hot Leg Break i
l E -
l m E -
- e -
- s
\
l -12 '
l l
l 2 3 4 5 6 l Break ID (inch) k Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wphib&l997
6-132 _.
1 O
Figure 6.3.2.5-2 Duration of Core Uncovery for Cotegory UC6 with 2 stage 4 ADS 2000 i o _
en v _
x -
1500 --
e O _
o C -
e 1000 - _ Hot Leg Break O
o _
o -
C 500 -- DVI Line Break o _
O _
L D -
o 0 i , , , , ,
i i i 2 3 4 5 6 Break ID (inch) l l
l 9
Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf-1W1997 l
l
l 6-133 t
l lO iv
- i l
l Figure 6.3.2.5-3 l
Minimum Vessel Mixture Level i for Potegory UC6 with 1 stage 3 and 2 stage 4 ADS l
6- , -
l _CoId Leg
~~~
l ,
Breok f v
3-- \/ /
- /
_ /
.e /
> Top of Core ca 0-- - - - - r/ - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
/
J '
( e -
.s m _3 _ _
~^ .
l X
2 Hot Leg Break I E _
m E -
c_ -
1
-12 l- l l l
2 3 4 5 6 Break ID-(inch) l Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:1M)615f7
6-134 O
Figure 6.3.2.5-4 Duration of Core Uncovery for Cotegory UC6 with 1 stage 3 and 2 stage 4 ADS 2000 o -
! e -
en v _
x -
1500 --
e O _
o c -
D _
g e 1000 --
u o
o , Hot Leg Break o _
c 500 --
o _
'~ !
!~~~ _ Cold Leg Break a -
s !
m s
~3 -
g a o, i s, , , , ,
i i i 2 3 4 5 6 Break ID (inch)
O Categorization of Success Paths for Short-Term Cooling June 1997 o:\3e61w.wpf:1b-061997
6-135 6.3.2.6 Selection of Limiting Case for Category UC7:
lb '
l Category UC7 consists of the large LOCA initiating event with failure of all ADS, but with success of containment isolation. The definition of the LLOCA initiating event in the PRA is based on a break size that is large enough to achieve IRWST gravity injection without ADS l actuation. The lower end of the LLOCA break spectrum would be the most challenged by l the loss of all ADS since the break itself provides venting to keep the RCS depressurized.
I According to Table 6.3.2-1, this category is potentially risk-significant due to the impact on ,
the Baseline PRA. Also, as noted in Section 6.2.7, the frequency of this category is . l overestimated because the LLOCA' expanded event tree does not fully isolate the possibility of no ADS actuation. Had the event tree been more refined, this category may have fallen below the potentially risk-significant cut-off. Nevertheless, TIH analyses are performed that not only support this UC category, but provide further defense of the PRA LOCA initiating event definitions.
Case UC7 can be directly defined based on the dominant success path for this category, without scoping MAAP4 analyses. The limiting break size is 9-inch diameter, which is the I smallest in the LLOCA spectrum. This is close to break sizes that have been analyzed with the NOTRUMP code, and thus the combination of NOTRUMP/LOCTA is used. The equipment assumptions are- l l
. Containment isolated j
. 2 CMTs
. . No stage 1,2, or 3 ADS
- No stage 4 ADS i
= 1 line,1 path for IRWST gravity injection The NOTRUMPILOCTA analysis results are discussed in Section 9.1.2.6.
l O
Categorization of Success Paths for Short-Term Cooling June 1997 o:\3661w.wpf:1b41997
I 7-1 1 7 CATEGORIZATION OF SUCCESS PATHS FOR LONG-TERM !
O t.] RECIRCULATION COOLING The approach used for the long-term recirculation cooling evaluation parallels that used for the short-term cooling evaluation. This involves identifying PRA success sequences that could be potentially risk-significant if the basis for success were doubtful due to TE l
uncertainty; collecting these into groups based on similarities in available hardware and thermallhydraulic conditions; and then analyzing the behavior of a sufficient number of sequences to confum successful plant response. ;
l The Focused PRA event tree expansion as described in Section 4 provides the success paths and frequencies for both short-term and long-term cooling scenarios. The Focused PRA models credit only safety-related systems for mitigation of an initiating event, and are therefore more dependent on passive-only systems than the Baseline PRA models. Thus, the Focused PRA provides the basis for the assessment of long-term cooling success criteria and uncertainty.
The following paragraphs describe the process used to identify potentially risk-important ,
sequences. This information is then used to define the necessary combinations of hardware I and TM conditions to be analyzed in order to establish that the effects of TE uncertainty on the PRA are sufficiently small that the PRA conclusions and insights are not significantly affected.
7.1 GROUPING OF SUCCESS SCENARIOS FOR LONG-TERM RECIRCULATION l COOLING A summary of factors potentially important to long-term cooling success was presented in Section 5.3 These factors have been used in combining the success sequences into groups with sufficiently similar characteristics in the long term so that a manageable yet sufficiently complete TM analysis can be performed. The manner in which each of the parameters summanzed in Table 5-1 is addressed in grouping the success sequences for the long-term cooling TM analysis is indicated in Table 7.1-1.
Based on the information in Table 7.1-1, the equipment and initiating event combinations by which the expanded sequences for long-tenn cooling are grouped can be summarized as follows:
O C'
Categorization of Success Paths for Long-Term Recirculation Cooling June 1997 c:\3661w.wpf:1b-061897
7-2 l
]
. Containment isolated or not isolated (not isolated results in reduced sump water level);
DVI LOCA initiating event (for which high decay heat level, low sump water level are O' "
assumed), or all other initiating events;
. Number of ADS valves open.
The relative importances of the number of open recirculation flow paths, and of the number of CMTs and accumulators injecting, are evaluated; a single condition is selected for each that limits the potential uncertainty from these parameters. The acmal grouping of sequences, and the bases for the groupings, are further discussed in Section 7.2.
1 O
9, Categorization of Success Paths for Long-Term Recirculation Cooling June 1997 o:\3661w.wpf;1b-061897
l 7-3 Table 7.1-1 4
, Summary of Manner in Which Parameters Important to Long-Term Cooling are 5
Addressed in Grouping of Sequences Manner Addressed in Grouping Sequences for Parameter (per Table 5-1) TH Analysis Height of Sump Water This is a function of several parameters, including the number of CMTs and accumulators that inject into the RCS, the success or failure of containment isolation, and whether or not sump watir is diverted into the normally dry valve compartments.
The effect of the number of CMTs and accumulators injecting into the RCS is evaluated, but this parameter is not used as a sequence grouping criterion. See Section 7.2.4 for additional discussion of this j topic.
The effect of the success or failure of containment isolation is evaluated, and tlus parameter is used as a sequence grouping criterion.
. The effect of the diversion of water from the sump into a valve compartment is ;
evaluated. This parameter is used as a sequence grouping criterion, by assigning
/D all DVI LOCAs to a category in which the V valve compartment with the broken DVI i
line is flooded by the IRWST, and groupmg !
events in terms of DVI LOCA or non-DVI I LOCA events. l RCS Steam Venting Capability This is a function of the number of ADS valves open and, potentially, a function of RCS break size and location.
- As a conservatism, the LTC TM analysis l generally does not credit break venting. ,
The effect of the number of available ADS '
valves is evaluated, and this parameter is used as a sequence grouping criterion.
Resistance of R@culation Flow Paths This is a function of the number of available '
flow paths and the maximum alowable (per ITAACs) resistance per line.
Maximum allowable resistances are modeled (conservatively high) in the LTC TH analysis (see Section 10).
- The effect of the number of available recirculation flow paths is evaluated, but this parameter is not used as a sequence grouping criterion. See Section 7.2.4 for additional discussion of this topic.
A N._]
Categorization of Success Paths for Long-Term Recirculation Cooling June 1997 oA3661w.wpf:llA61897
7-4 Table 7.1-1 Summary of Modeling of Parameters Important to Long-Term Cooling (cot.t.)
Manner Addressed in Grouping Sequences for Parameter (per Table 51) T/H Analysis Containment Pressure This is a function of success or failure of containment isolation, and also a function of success or failure of the passive containment cooling system (PCS).
. The effect of the success or failure of containment i<olation is evaluated, and this parameter is used as a sequence grouping criterion.
. The effect of the success or failure of PCS is evaluated, but this parameter is not used as a sequence grouping criterion. See Section 7.2.4 for additional discussion of this topic.
The effect of failure of containment isolation on available sump inventory is addressed in the LTC T/H analysis for scenarios in which containment isolation fails.
Decay Heat Level at Onset of Recirculation This is a function of the type of initiating event (e.g., relatively low decay heat at time of recirculation for transients and small LOCAs, relatively high decay heat at time of recirculation for large LOCAs and some DVI line breaks).
. Decay heat levelis ensidered in the LTC --- ~
TlH analyses (Section 10) so that events with high decay heat and events with lower decay heat at the time of recirculation are covered by the analysis.
The effect of decay heat level is evaluated.
This parameter is implicitly used as a sequence grouping criterion, by assigning all DVI LOCAs to a high decay heat category (relatively early onset of recirculation, assuming that the IRWST spills into the normally dry compartment with the broken line) and grouping events l in terms of DVI LOCAs or non-DVI LOCAs.
O Categorization of Success Paths for Long-Term Recirculatior Niing June 1997 o:\3661w.wpf:lt>.061897
l l
l 7-5 m 7.2 PRA-IMPORTANT SUCCESS SEQUENCE GROUPS FOR I.ONG-TERM lV 1 RECIRCULATION COOLING The sequence grouping begins with the list of expanded success paths developed in Section 4. All success paths are considered initially, whether the designation is OK or UC.
l As explained in Section 5.3, this is necessary because, for long-term recirculation cooling, there is no pre-existing set of TlH analyses for use in defining " low-margin" scenarios.
The set of sequences that is the starting point for the long-term recirculation TM analysis therefore consists of all sequences listed in the sequence tables in Section 6.1 (the "OK" sequences) and in the sequence tables in Section 6.2 (the "UC" sequences). This set includes all success paths on the expanded Focused PRA event trees.
In order to define a manageable set of cases for thermallhydraulic analysis, it is necessary to group the success sequences according to characteristics described in Table 7.1-1, then examine the risk significance of each group. The main groups to be defined are:
Sequences already addressed by the design basis analysis Sequences with successful containment isolation DVI line breaks
) -
other events P.
Sequences with failure of containment isolation DVI line breaks other events 7.2.1 Sequences Already Covered by Design Basis Analyses Included in the set of all success sequences are those sequences covered by the design basis accident (DBA) analysis as presented in AP600 SSAR Chapter 15 (Reference 4). Because the design basis accident analysis includes consider.uon of TH uncertainty, sequences covered by the DBA need not be further considered in this LTC TIH uncertainty analysis.
The sequences of interest are those that have equipment availability equivalent to or better than that asse ned in the long-term recirculation cooling DBA. This is defined here to include sequences with better than or equal to design basis ADS capacity, and with up to two failures of CMTs or accumulators (since CMTs and accumulators have only a small effect l on sump level, as explained in Section 7.2.4). These generally consist of those sequences in l the "OK1," "OK2," and "OK7" categories as defined in Section 6.2.
- (V7 l
Categorization of Success Paths for Long-Terrn Recirculation Cooling June 1997 o:\3661w.wpf:lb-061897
7-6 Table 7.2.1-1 lists those sequences that fall into the DBA or higher ADS capacity categories, as defined above.
The subsequent groupings are performed on the set of all success sequences except those included in Table 7.2.1-1.
9 I
l l
O Categorization of Success Paths for Long-Term Recirculation Cooling June 1997 o:\3661w.wpf:ll>O61897
7-7
(~]
v Table 7.2.1-1 Summary of Sequences with DBA (or Better than DBA) Conditions Equipment Assumptions Category Success Path CI CMT Acc ADS-4 ADS 2,3 Frequency (per year)
OK1 sgtr01 Yes 2 2 4 4 5.5E-03 OK1 nloca01 Yes 2 2 4 4 5.9E-M l l
OK1 trant01 Yes 2 2 4 4 1.9E-04 OK1 stoct01 Yes 2 2 4 4 1.8E-04 OK1 mioca01 Yes 2 2 4 4 1.2E-04 OK1 sloca01 Yes 2 2 4 4 1.1E-04 I OK1 lloca01 Yes 2 2 4 4 7.6E-05 OK1 cmtib01 Yes 1 2 4 4 6.5E-05 OK7 lloca02 Yes 2 2 4 2,3 2.7E-05 OK2 nloca10 Yes 2 1 4 4 6.9E-06 OK2 sgtr10 Yes 2 1 4 4 3.4E-06 OK2 trant10 Yes 2 1 4 4 2.2E-06 p OK2 sloct10 Yes 2 1 4 4 2.1E-06 OK2 nloca04 Yes 2 2 3 4 1.9E-06 OK2 mloca10 Yes 2 1 4 4 1.4E-06 OK2 sloca10 Yes 2 1 4 4 1.3E-06
- OK2 nloca21 Yes 1 2 4 4 1.2E-06 OK2 sgtrN Yes 2 2 3 4 9.3E-07 OK2 cmtib10 Yes 1 1 4 4 7.6E-07 OK2 trant04 Yes 2 2 3 4 6.1E-07 OK2 sgtr21 Yes 1 2 4 4 6.1E-07 OK2 sloct04 Yes 2 2 3 4 5.8E-07 OK1 sgtt01 Yes 2 2 4 4 4.2E-07 OK2 trant21 Yes 1 2 4 4 3.9E-07 OK2 sloct21 Yes 1 2 4 4 3.SE-07 OK2 mioca04 Yes 2 2 3 4 3.8E-07 OK2 sloca04 Yes 2 2 3 .4 3.5E-07 p OK7 lloca03 Yes 2 2 4 0,1 2.5E-07 h
Categorization of Success Paths for Long-Term Recirculation Cooling June 1997 o:\3661w.wpf:1b-061897 a
l
7-8 Table 7.2.11 Summary of Sequences with DBA (or Better than DBA) Conditions (cont.)
Equipment Assumptions Category Success Path CI CMT Ace ADS 4 ADS 2,3 Frequency (per year)
OK2 mioca21 Yes 1 2 4 4 2.5E-07 OK7 Iloca04 Yes 2 2 3 4 2.5E-07 OK2 sloca21 Yes 1 2 4 4 2.3E4)7 OK2 cmtib04 Yes 1 2 3 4 2.1E-07 OK7 Iloca18 Yes 1 2 4 4 1.6E-07 OK7 Iloca05 Yes 2 2 3 2,3 6.4E-08 OK7 lloca19 Yes 1 2 4 2,3 4.0E-08 OK2 nloca13 Yes 2 1 3 4 1.6E-08 OK2 nloca28 Yes 1 1 4 4 1.0E-08 OK2 sgtr13 Yes 2 1 3 4 7.9E-09 OK2 sgtr28 Yes 1 1 4 4 5.1E-09 OK2 sloct13 Yes 2 1 3 4 4.9E-09 OK2 sgtt10 Yes 2 1 4 4 4.9E-09 OK2 trant13 Yes 2 1 3 4 4.8E-09 OK2 sloct28 Yes 1 1 4 4 3.2E-09 OK2 mioca13 Yes 2 1 3 4 3.2E-09 OK2 trant28 Yes 1 1 4 4 3.0E-09 OK2 sloca13 Yes 2 1 3 4 3.0E-09 l i
OK2 nloca24 Yes 1 2 3 4 2.9E-09 OK2 mloca28 Yes 1 1 4 4 2.1E-09 OK2 sloca28 Yes 1 1 4 4 1.9E-09 OK2 cmtib13 Yes 1 1 3 4 1.8E-09 OK2 sgtr24 Yes 1 2 3 4 1.4E-09 OK2 sgttG1 Yes 2 2 3 4 1.3E-09 J
OK2 sloct24 Yes 1 2 3 4 8.8E-10 OK2 sgtt21 Yes 1 2 4 4 8.7E-10 OK2 trant24 Yes 1 2 3 4 8.2E-10 l OK2 mloca24 Yes 1 2 3 ! 4 5.7E-10 Categorization of Success Paths for Long-Term Recirculation Cooling June 1997 c:\3661w.wpf:lt>o61897 l
l l
- ~ . - _ . - . _ , .. -_. .-.
7-9 l
Table 7.2.11 Sununary of Sequences with DBA (or Better than DBA) Conditions !
Q (cont.) j Equipment Assumptions Category Success Path CI CMT Acc ADS 4 ADS 2,3 Frequency (per year)
OK7 lloca% Yes 2 2 3 0,1 5.6E-10 OK2 sloca24 Yes 1 2 3 4 5.3E-10 OK7 Iloca21 Yes 1 2 3 4 3.7E-10 OK7 Iloca20 Yes 1 2 4 0,1 3.6E-10 OK7 lloca22 Yes 1 2 3 0-3 8.0E-11 OK2 nloca30 Yes 1 1 2,3 0-4 2.5E-11 OK2 sgtr30 Yes 1 1 2,3 0-4 1.2E-11 l
OK2 sgtt13 Yes 2 1 3 4 1.1E-11 OK2 trant30 Yes 1 1 2,3 0-4 7.0E-12 OK2 sgtt28 Yes 1 1 4 4 6.6E-12 OK2 sloct30 Yes 1 1 2,3 0- .'. 5.9E-12 OK2 rnloca30 Yes 1 1 2,3 0-4 4.9E-12 r#~\
V OK2 sloca30 Yes 1 1 2,3 0-4 4.5E-12 OK2 sgtt24 Yes 1 2 3 4 1.8E-12 OK2 sgtt3C Yes 1 1 2,3 OU 1.5E-14 i
l l
l
/^\
O Categorization of Success Paths for Long-Term Recirculation Cooling June 1997 o:\3661w.wpf;1b-061897
7-11 l
l 7.2.2 Containment Isolation Status
! Once the DBA sequences are segregated, the remainig sequences are grouped with respect
[ to containment isolation status. Failure of containment isolation has an important effect on j sump water level. Sump level is important because of its effect on the driving head for l recirculation. The subset of non-DBA sequences for which containment isolation is successful l consists of those sequences listed in the tables of Sections 6.1 and 6.2 with "Yes"in the CI column, minus the DBA sequences shown in Table 7.2.1-1. The subset of sequences for l which containment isolation fails consists of those sequences listed in the tables of Sections 6.1 and 6.2 with "No" in the CI column.
7.2.3 DVI Break versus Non-DVI Break Once the sequences are segregated by containment isolation status, they are further sd.xlivided with respect to whether the initiating event is a DVI line break. DVI line breaks luve the potential to drain IRWST water into a normally dry valve compartment, if the DVI inet valves associated with the broken DVI line open. This reduces the overall sump water leve: (since the available water fills a larger total containment volume in this case), leaving a lower driving head for recirculation. It also results in earlier draining of the IRWST into the sump (relative to most other events), so that there is a higher decay heat level at the onset of recirculation. Table 7.2.3-1 lists the DVI line break sequences with successful containment isolation, and Table 7.2.3-2 lists the DVI line break sequences with failed containment isolation. Similarly, Table 7.2.3-3 lists sequences other than DVI line break with successful containment isolation, and Table 7.2.3-4 lists sequences other than DVI line break with failed containment isolation. Note that the sequences in these tables were sorted according to similarities in equipment availability. Thus, the frequencies are not monotonically decreasing from top to bottom of the table, although the highest-frequency sequences tend to be near the top of the list.
l l
l
- O Categorization of Success Paths for Long-Term Recirculation Cooling June 1997 c
- \3661w.wpf:1b-061897
7-12 um -
Table 7.2.3-1 DVI Line Break Success Paths with Successful Containment Isolation U counted as core damage, increase Equipment Assumptions to Focused PRA Success Core Damage Large Release Path CI CMf'l Acc(*) ADS-48 ADS 2,3* Frequencylyr Frequencytyr silbO2 Yes 1 1 4 2,3 2.6E-05 1.6E-06 silbO3 Yes 1 1 4 0,1 2.5E-07 1.5E-08 silb05 Yes 1 1 3 2,3 6.3E-08 3.8E-09 silb06 Yes 1 1 3 0,1 5.5E-10 3.3E-11 silbO7 Yes 1 1 2 4 6.4E-09 3.8E-10 silbO8 Yes 1 1 2 0-3 5.0E-09 3.0E-10 silb10 Yes 1 0 4 4 4.4E-07 2.6E-08 silbli Yes 1 0 4 2,3 1.1E-07 6.7E-09 silb12 Yes 1 0 4 0,1 1.0E-09 6.1E-11 silb13 Yes 1 0 3 4 1.0E-09 6.1E-11 silbl4 Yes 1 0 3 0-3 2.5E-10 1.5E-11 silbl5 Yes 1 0 2 0-4 4.1E-11 2.5E-12 silb17 Yes 0 1 4 4 7.6E-08 4.6E-09 silb18 Yes 0 1 4 2,3 1.9E-08 1.2E-09 silbl9 Yes 0 1 4 0,1 1.7E-10 1.0E-11 silb20 Yes 0 1 3 4 1.8E-10 1.1E-11 silb21 Yes 0 1 3 0-3 4.0E-11 2.4E-12 silb22 Yes 0 1 2 0-4 7.1E-12 4.3E-13 silb24 Yes 0 0 4 4 3.2E-10 1.9E-11 silb25 Yes 0 0 4 0-3 7.8E-11 4.7E 12 silb26 Yes 0 0 2,3 0-4 7.6E-13 4.6E-14 silb28 Yes 0 1 4 4 1.6E-08 9.8E-10 silb29 Yes 0 1 4 0-3 4.2E-09 2.5E-10 silb30 Yes 0 1 2,3 0-4 3.9E-11 2.3E-12 Notes:
(a) For DVI line break, only the intact-loop CMT and accumulator status is addressed in the expanded event tree sequences, since the failed-loop components are not available for injection for short-term cooling. However,if the failed loop components spill into the DVI compartment, as expected, that additional inventory contributes to the sump level available for recirculation cooling.
(b) The ADS notation is as follows: where a single number is shown, that number of valves is available (e.g., "4" means that 4 valves are available); where two different numbers are shown, the group includes that range of possibilities (e g., "O,4" means that sequences may include 0,1,2,3, or 4 valves).
Categorization of Success Paths for Long-Term Recirculation Cooling June 1997 o:\3661w.wpf:1t>.061897
l l 7-13 i
l A Table 7.2.3-2 DVI Line Break Success Paths with Failed Containment Isolation l
b If counted as core damage, increase to Equipment Assumptions Focused PRA Success Core Damage Large Release Path CI CMY") Acc(*) ADS-4N ADS 2,3(b) Frequencylyr Frequency /yr l silb33 No 1 1 4 4 1.2E-07 1.2E-07 silb34 No 1 1 4 2,3 3.0E-08 3.0E-08 silb35 No 1 1 4 0,1 2.7E-10 2.7E-10 silb36 No 1 1 3 4 2.8E-10 2.8E-10 silb37 No 1 1 3 0-3 6.2E-11 6.2E-11 silb38 No 1 1 2 0-1 8.5E-12 8.5E-12 silb40 No 1 0 4 4 5.1E-10 5.1E-10 silb41 No 1 0 4 0-4 1.2E-10 1.2E-10 silb42 No 1 0 2,3 0-4 1.2E-12 1.2E-12 silb44 No 0 1 4 4 8.8E-11 8.8E-11 silMS No 0 1 4 0-3 2.0E-11 2.0E-11
,-s
/\ silb46 No 0 1 2,3 0-4 2.0E-13 2.0E-13 V
silMS No 0 0 2,4 0-4 3.7E-13 3.7E-13 silb50 No 0 1 2,4 , 0-4 1.9E-11 1.9E-11 Notes:
(a) For DVI line break, only the intact-loop CMT and accumulator status is addressed in the expanded event tree sequences, since the failed-loop components are not available for injection for short term cooling. However, if the failed loop components spill into the DVI compartment, as expected, that additional inventory contributes to the sump level available for recirculation cooling.
(b) The ADS notation is as follows: where a single number is shown, that number of valves is available (e.g., "4" means that 4 valves are available), where two different numbers are shown, the group includes that range of possibilities (e.g., "O,4" or "0-4" means that sequences may include 0,1,2,3, or 4 valves).
l 3
(O Categorization of Success Paths for Long-Term Recirculation Cooling June 1997 o:\3661w.wpf:1b-061897 1
7-14 I
Table 7.2.3-3 Success Paths for Events Other Than DVI Line Breaks, with Successful Containment Isolation If counted as core damage, increase to Equipment Assumptions Focused PRA Success Core Damage Large Release Path CI CMT Acc ADS 4(*) ADS 2,3(*) Frequency /yr Frequency /yr nloca02 Y 2 2 4 2,3 2.1E-04 1.2E-05 sgtr02 Y 2 2 4 2,3 1.0E-04 1.0E-04 trant02 Y 2 2 4 2,3 6.6E-05 4.0E-06 sloct02 Y 2 2 4 2,3 6.3E-05 3.8E-06 mioca02 Y 2 2 4 2,3 4.1E-05 2.5E-06 sloca02 Y 2 2 4 2,3 3.8E-05 2.3E-06 sgtt02 Y 2 2 4 2,3 1.5E-07 1.5E-07 nloca03 Y 2 2 4 0,1 1.9E-06 1.2E-07 sgtr03 Y 2 2 4 0,1 9.5E-07 9.5E-07 mioca03 Y 2 2 4 0,1 3.9E-07 2.3E-08 sloca03 Y 2 2 4 0,1 3.6E-07 2.2E-08 trant03 Y 2 2 4 0,1 3.1E-07 1.9E-08 sloct03 Y 2 2 4 0,1 2.8E-07 1.7E-08 sgtt03 Y 2 2 4 0,1 6.4E-10 6.4E-10 nloca05 Y 2 2 3 2,3 5.0E-07 3.0E-08 sgtr05 Y 2 2 3 2,3 2.4E-07 2.4E-07 trant05 Y 2 2 3 2,3 1.5E-07 9.3E-09 I sloct05 Y 2 2 3 2,3 1.5E-07 9.1E-09 mioca05 Y 2 2 3 2,3 9.8E-08 5.9E-09 sloca05 Y 2 2 3 2,3 9.2E-08 5.5E-09 sgtt05 Y 2 2 3 2,3 3.4E-10 3.4E-10 nloca06 Y 2 2 3 0,1 4.4E-09 2.7E-10 sgtr06 Y 2 2 3 0,1 2.1E-09 2.1E-09 mloca06 Y 2 2 3 0,1 8.8E-10 5.3E-11
)
sloca06 Y 2 2 3 0,1 8.1E-10 4.8E-11 O
Categorization of Success Paths for Long-Term Recirculation Cooling June 1997 o:\3661w.wpf.lb 061897 l
l
l l
i l 7-15 i
r Table 7.2.3-3 Success Paths for Events Other Than DVI Line Breaks, with Successful l 'y]/ (cont.) Containment Isolation j If counted as core damage, increase to Equipment Assumptions Focused PRA Success Core Damage Large Relears Path CI CMT Acc ADS-4(*) ADS 2,3(') Frequencylyr Frequencylyr trant06 Y 2 2 3 0,1 6.5E-10 3.9E-11 sloct06 Y 2 2 3 0,1 6.5E-10 3.9E-11 sgtt06 Y 2 2 3 0,1 1.4E-12 1.4E-12 nloca07 Y 2 2 2 4 5.0E-08 3.0E-09 sgtr07 Y 2 2 2 4 2.5E-08 2.5E-08 i trant07 Y 2 2 2 4 1.6E-08 9.6E-10 sloct07 Y 2 2 2 4 1.5E-08 9.2E-10 mioca07 Y 2 2 2 4 9.9E-09 5.9E-10 lloca07 Y 2 2 2 4 9.9E-09 5.9E-10 sloca07 Y 2 2 2 4 9.2E-09 5.5E-10 g sgtt07 Y 2 2 2 4 3.5E-11 3.5E-11
- a L/ nloca08 Y 2 2 2 0-3 6.6E-08 4.0E-09 sgtr08 Y 2 2 2 0-3 3.3E-08 3.3E-08 sloct08 Y 2 2 2 63 2.0E-08 1.2E-09 Iloca08 Y 2 2 2 3-3 1.9E-08 1.1E-09 trant08 Y 2 2 2 0-3 1.9E-08 1.1E-09 mioca08 Y 2 2 2 0-3 1.3E-08 7.8E-10 sloca08 Y 2 2 2 0-3 1 J-08 7.3E-10 l sgtt08 Y 2 2 2 0-3 4.0E-11 4.0E-11 lloca09 Y 2 2 0,1 0-4 3.2E-09 1.9E-10 lloca10 Y 2 1 4 4 8.9E-07 5.3E-08 nlocall Y 2 1 4 2,3 1.7E-06 1.0E-07 sgtr11 Y 2 1 4 2,3 8.6E-07 8.6E-07 trant11 Y 2 1 4 2,3 5.5E-07 3.3E-08 f
(
Categorization of Success Paths for Long-Term Recirculation Cooling June 1997 o:\3661w.wpf:1b-061897
7 16 Table 7.2.3-3 Succesa Paths for Events Other "Ihan DVI Line Breaks, with Successful Containment (cont.) Isolation Success Equipment Assumptions If counted as core damage, increase to Path Focused PRA Core Damage Large Release CI CMT Acc A DS-4(*) ADS 2,3(*) Frequencylyr Frequencylyr sloct11 Y 2 1 4 2,3 5.3E-07 3.2E-08 mlocall Y 2 1 4 2,3 3.5E-07 2.1E-08 slocall Y 2 1 4 2,3 3.2E-07 1.9E-08 Ilocall Y 2 1 4 2,3 2.2E-07 1.3E-08 sgttil Y 2 1 4 2,3 1.2E-09 1.2E-09 nloca12 Y 2 1 4 0,1 1.6E-08 9.7E-10 sgtr12 Y 2 1 4 0,1 7.9E-09 7.9E-09 mloca12 Y 2 1 4 0,1 3.2E-09 1.9E-10 sloca12 Y 2 1 4 0,1 3.0E-09 1.8E-10 trant12 Y 2 1 4 0,1 2.4E-09 1.4E-10 sloct12 Y 2 1 4 0,1 2.4E-09 1.4E-10 lloca12 Y 2 1 4 0,1 2.1E-09 1.2E-10 sgtt12 Y 2 1 4 0,1 5.0E-12 5.0E-12 l
Iloca13 Y 2 1 3 4 2.1E 09 1.2E 10 l nloca14 Y 2 1 3 0-3 4.0E-09 2.4E-10 sgtr14 Y 2 1 3 03 1.9E-09 1.9E-09 i sloct14 Y 2 1 3 43 1.28-09 7.3E-11 trant14 Y 2 1 3 0-3 1,1E-09 6.5E-11 mioca14 Y 2 1 3 0-3 7.9E-10 4.8E-11 sloca14 Y 2 1 3 0-3 7.2E-10 4.3E-11 lloca14 Y 2 1 3 0-3 5.0E-10 3.0E-11 sgtt14 Y 2 1 3 0-3 2.4E-12 2.4E-12 nloca15 Y 2 1 2 0-4 8.6E-10 5.1E-11 sgtr15 Y 2 1 2 0-4 3.7E-10 3.7E-10 0
Categorization of Success Paths for Long-Term Recirculation Cooling June 1997 o:\3661w.wpf:1b-061897
7-17
, A Table 7.2.3-3 Success Paths for Events Other Than DVI Line Breaks, with Successful Containment l (cont.) Isolation If counted as core damage, increase to Equipment Assumptions Focused PRA Success Core Damage Large Release Path CI CMT Acc ADS 4(*) ADS 2,3(*) Frequency /yr Frequency /yr sloct15 Y 2 1 2 0-4 2.5E-10 1.5E-11 11oca15 Y 2 1 2 0-4 2.1E-10 1.2E-11 mioca15 Y 2 1 2 0-4 1.6E-10 9.3E-12 sloca15 Y 2 1 2 0-4 1.4E-10 8.3E-12 trant15 Y 2 1 2 0-4 1.2E-10 7.3E-12 sgtt15 Y 2 1 2 0-4 2.7E-13 2.7E-13 lloca16 Y 2 1 0,1 0-4 2.7E-11 1.6E-12 nloca17 Y 2 0 4 4 5.6E-08 3.4E-09 sgtr17 Y 2 0 4- 4 2.8E-08 2.8E-08 l trant17 Y 2 0 4 4 1.8E-08 1.1E-09 sloct17 Y 2 0 4 4 1.7E-08 1.0E-09 O mloca17 Y 2 0 4 4 1.1E-08 6.7E-10 sloca17 Y 2 0 4 4 1.0E-08 6.3E-10 sgtt17 Y 2 0 4 4 3.9E-11 3.9E-11 nloca18 Y 2 0 4 0-3 1.4E-08 8.6E-10 sgtr18 Y 2 0 4 0-3 7.0E-09 7.0E-09 sloct18 Y 2 0 4 0-3 4.4E-09 2.6E-10 trant18 Y 2 0 4 0-3 3.6E-09 2.2E-10 mioca18 Y 2 0 4 0-3 2.8E-09 1.7E-10 sloca18 Y 2 0 4 0-3 2.6E-09 1.6E-10 sgtt18 Y 2 0 4 0-3 7.8E-12 7.8E-12 nloca19 Y 2 0 2,3 0-4 1.4E-10 8.3E-12 sgtr19 Y 2 0 2,3 0-4 6.1E-11 6.1E-11 sloct19 Y 2 0 2,3 0-4 4.0E-11 2.4E-12 trant19 Y 2 0 2,3 0-4 2.9E-11 1.7E-12 mloca19 Y 2 0 2,3 0-4 2.7E-11 1.6E-12 i
'(
(
Categorization of Success Paths for Long-Term Recirculation Cooling June 1997 o:\3661w.wpf:1t>061897
7-18 Table 7.2.3-3 Success Paths for Events Other Than DVI Line Breaks, with Successful Containment (cont.) Isolation If counted as core damage, increase to Equipment Assumptions Focused PRA Success Core Damage Large Release Path CI CMT Ace ADS-4(') ADS 2,3(*) Frequency /yr Frequency /yr sloca19 Y 2 0 2,3 0-4 23E-11 1.4E-12 sgtt19 Y 2 0 2,3 0-4 6.3E-14 6.3E-14 cmtlbO2 Y 1 2 4 2,3 2.3E-05 1.4E-06 nloca22 Y 1 2 4 2,3 3.1E-07 1.9E-08 sgtr22 Y 1 2 4 2,3 1.5E-07 1.5E-07 trant22 Y 1 2 4 2,3 9.8E-08 5.9E-09 sloct22 Y 1 2 4 2,3 9.5E-08 5.7E-09 mloca22 Y 1 2 4 2,3 6.2E-08 3.7E-09 sloca22 Y 1 2 4 2,3 5.8E-08 3.5E-09
)
sgtt22 Y 1 2 4 2,3 2.2E-10 2.2E-10 cmtlbO3 Y 1 2 4 0,1 2.1E-07 1.3E-08 nloc423 Y 1 2 4 0,1 2.9E-09 1.7E-10 st tr23 Y 1 2 4 0,1 1.4E-09 1.4E-09 mioca23 Y 1 2 4 0,1 5.7E-10 3.4E-11 sloca23 Y 1 2 4 0,1 5.2E-10 3.1E-11 sloct23 Y 1 2 4 0,1 4.2E-10 2.5E-11 trant23 Y 1 2 4 0,1 4.1E-10 2.5E-11 sgtt23 Y 1 2 4 0,1 8.5E-13 8.5E-13 cmtlb05 Y 1 2 3 2,3 5.4E-08 3.3E-09 nloca25 Y 1 2 3 0-3 7.4E-10 4.5E-11 sgtr25 Y 1 2 3 0-3 3.1E-10 3.1E-10 sloct25 Y 1 2 3 0-3 2.1E-10 1.3E-11 trant25 Y 1 2 3 0-3 1.8E-10 1.1E-11 mloca25 Y 1 2 3 0-3 1.5E-10 8.8E-12 sloca25 Y 1 2 3 0-3 1.2E-10 6.9E-12 O
Categorization of Success Paths for Long-Term Recirculation Cooling June 1997 o:\3661w.wpf:lt41897
. - . - . a 7-19
(~'
Table 7.2.3-3 Success Paths for Events Other Than DVI Line Breaks, with Successful Containment (cont.) Isolation If counted as core damage, increase to Equipment Assumptions Focused PRA Success Core Darnage Large Release Path Cl CMT Ace ADS 4(') ADS 2,3(') Frequency /yr Frequency /yr sgtt25 Y 1 2 3 0-3 4.1E-13 4.1E-13 cmtib06 Y 1 2 3 0,1 4.8E-10 2.9E-11 cmtibO7 Y 1 2 2 4 5.5E-09 3.3E-10
~
nloca26 Y 1 2 2 0-4 1.6E-10 9.3E-12 sgtr26 Y 1 2 2 0-4 5.4E-11 5.4E-11 sloct26 Y 1 2 2 0-4 4.1E-11 2.5E-12 Iloca23 Y 1 2 2 0-4 3.3E-11 2.0E-12 mioca26 Y 1 2 2 0-4 3.1E-11 1.8E-12 trant26 Y 1 2 2 0-4 2.1E-11 1.3E-12 sloca26 Y I 2 2 0-4 2.0E-11 1.2E-12 sgtt26 Y 1 2 2 0-4 4.6E-14 4.6E-14 b cmtibO8 Y 1 2 2 0-3 7.2E-09 4.3E-10 lloca24 Y I 2 0,1 0-4 4.6E-12 2.7E-13 lloca25 Y 1 1 4 4 1.3E-09 8.0E-11 cmtlbli Y 1 1 4 2,3 1.9E-07 1.2E-08 nloca29 Y 1 1 4 0-3 2.6E-09 1.6E-10 sgtr29 Y 1 1 4 0-3 1.2E-09 1.2E-09 sloct29 Y 1 1 4 0-3 7.8E-10 4.7E-11 trant29 Y 1 1 4 0-3 6.8E-10 4.1E-11 mioca29 Y 1 1 4 0-3 5.0E-10 3.0E-11 sloca29 Y 1 1 4 0-3 4.6E-10 2.8E-11 lloca26 Y 1 1 4 0-3 3.2E-10 1.9E-11 sgtt29 Y 1 1 4 0-3 1.5E-12 1.5E-12 cmtlb12 Y 1 1 4 0,1 1.8E-09 1.1E-10 cmtibl4 Y 1 1 3 0-3 4.2E-10 2.5E-11 f
l O
, U Categorization of Success Paths for Long-Term Recirculation Cooling June 1997 o:\3661w.wpf:ltHM1897
7-20 Table 7.2 3-3 Success Paths for Events Other Than DVI Line Breaks, with Successful Containment (cont.) Isolation if counted as core damage, increase to Equipment Assumptions Focused PRA Success Core Damage Large Release Path CI CMT Ace ADS-4(*) ADS 2,3) Frequencylyr Frequencylyr lloca27 Y 1 1 2,3 0-4 3.2E-12 1.9E-13 a
I cmtibl5 Y 1 1 2 0-4 7.7E-11 4.6E-12 lloca28 Y 1 1 0,1 0-4 3.3E-14 2.0E-15 cmtib17 Y 1 0 4 4 6.2E-09 3.7E-10 cmtib18 Y 1 0 4 0-3 1.6E-09 9.3E-11 nloca32 Y 1 0 2,4 0-4 8.5E-11 5.1E-12 sgtr32 Y 1 0 2,4 0-4 3.7E-11 3.7E-11 trant32 Y 1 0 2,4 0-4 !.6E-11 1.6E-12 sloct32 Y 1 0 2,4 0-4 2.5E-11 1.5E-12 mloca32 Y 1 0 2,4 0-4 1.7E-11 1.0E-12 sloca32 Y 1 0 2,4 0-4 1.4E-11 8.4E-13 sgtt32 Y 1 0 2,4 0-4 5.8E-14 5.8E-14 cmtibl9 Y 1 0 2,3 0-4 1.3E-11 8.0E-13 sgtr34 Y 0 2 4 4 6.3E-07 6.3E-07 nloca34 Y 0 2 4 4 9.2E-08 5.5E-09 cn db21 Y 0 2 4 4 8.0E-08 4.8E-09 sloct34 Y 0 2 4 4 2.8E-08 1.7E-09 trant34 Y 0 2 4 4 2.8E-08 1.7E-09 mioca34 Y 0 2 4 4 1.8E-08 1.1E-09 sloca34 Y 0 2 4 4 1.7E-08 1.0E-09 sgtt34 Y 0 2 4 4 6.5E-11 6.5E-11 cmtib22 Y 0 2 4 2,3 2.0E-08 1.2E-09 sgtr35 Y 0 2 4 0-3 1.6E-07 1.6E-07 nloca35 Y 0 2 4 0-3 2.3E-08 1.4E-09 sloct35 Y 0 2 4 0-3 7.1E-09 4.3E-10 trant35 Y 0 2 4 0-3 6.0E-09 3.6E-10 Categorization of Success Paths for Long-Term Recirculation Cooling June 1997 o:\3661w.wpf lb-061897
I i
l l 7 21 1
,q Table 7.2.3-3 Success Paths for Events Other Than DVI Line Breaks, with Successful Containment I () (cont.) Isolation if counted as core damage, increase to Equipment Assumptions Focused PRA Success Core Damage Large Release Path CI CMT Acc ADM*) ADS 2,3(*) Frequency /yr frequencylyr mioca35 Y 0 2 4 0-3 4.6E-09 2.8E !
sloca35 Y 0 2 4 0-3 4.3E-09 2.6E-10 sgtt35 Y 0 2 4 0-3 1.4E-11 1.4E-11 cmtib23 Y 0 2 4 0,1 1.8E-10 1.1E-11 i l
cmtlb24 Y 0 2 3 4 1.9E-10 1.1E-11 cmtib25 Y 0 2 3 0-3 4.1E-11 2.5E-12 sgtr36 Y 0 2 2,3 04 1.5E-09 1.5E-09 nloca36 Y 0 2 2,3 0-4 2.3E-10 1.4E-11 sloct36 Y 0 2 2,3 0-4 6.7E-11 4.0E-12 trant36 Y 0 2 2,3 0-4 6.0E-11 3.6E-12 mioca36 Y 0 2 2,3 0-4 4.5E-11 2.7E-12 O sloca36 Y 0 2 2,3 0-4 4.0E- 2.4E-12 sgtt36 Y 0 2 2,3 0-4 1.4E-13 1.4E-13 cmtlb26 Y 0 2 2 0-4 6.5E-12 3.9E-13 cmtlb28 Y 0 1 4 4 6.7E-10 4.0E-11 cmtib29 Y 0 1 4 0-3 1.6E-10 9.5E-12 sgtr38 Y 0 1 2,4 0-4 5.3E-09 5.3E-09 nloca38 Y 0 1 2,4 0-4 7.8E-10 4.7E-11 sloct38 Y 0 1 2,4 0-4 2.4E-10 1.4E-11 mloca38 Y 0 1 2,4 0-4 1.5E-10 9.2E 12 sloca38 Y 0 1 2,4 0-4 1.4E-10 8.6E-12 trant38 Y 0 1 2,4 0-4 9.8E-11 5.9E-12 sgtt38 Y 0 1 2,4 0-4 2.3E-13 2.3E-13 cmtib30 Y 0 1 2,3 0-4 1.6E-12 9.5E-14 Note:
(a) The ADS notation is as follows: where a single number is shown, that number of valves is available (e.g., "4" means that 4 valves are available); where two different numbers are shown, the group includes that range of possibilities (e.g., "O,4" or "0-4' means that sequences may include 0,1,2,3, or 4 valves).
- O Categorization of Success Paths for Long-Tern Recirculation Cooling June 1997 l o:\3661w.wpf:lt41897
7-23 i
I
()
\v u Table 7.2.3-4 Success Paths for Other Than DVI Line Breaks, with Failed Containment Isolation If counted as core damage, increase to Equipment Assumptions Focused PRA Success Path CI CMT Acc ADS-4(*) ADS 2,3(*)
Core Damage Large Release )
Frequencylyr Frequencylyr nloca41 N 2 2 4 4 9.5E-07 9.5E-07 ;
1 sgir41 N 2 2 4 4 4.6E-07 4.6E-07 trant41 N 2 2 4 4 3.0E-07 3.0E-07 l sloct41 N 2 2 4 4 2.9E-07 2.9E-07 l mloca41 N 2 2 4 4 1.9E-07 1.9E-07 sloca41 N 2 2 4 4 1.8E-07 1.8E-07 lloca31 N 2 2 4 4 1.3E-07 1.3E-07 sgtt41 N 2 2 4 4 6.6E-10 6.6E-10 rloca42 N 2 2 4 2,3 2.4E-07 2.4E-07 sgtr42 N 2 2 4 2,3 1.2E-07 1.2E-07 I l
trant42 N 2 2 4 2,3 7.4E-08 7.4E-03 l sloct42 N 2 2 4 2,3 7.3E-08 7.3E-08 mioca42 N 2 2 4 2,3 4.7E-08 4.7E-08 sloca42 N 2 2 4 2,3 4.4E-08 4.4E-08 )
lloca32 N 2 2 4 2,3 3.4E-08 3.4E-08 sgtt42 N 2 2 4 2,3 1.6E-10 1.6E-10 nloca43 N 2 2 4 0,1 2.2E-09 2.2E-09 sgtr43 N 2 2 4 0,1 1.1E-09 1.1E-09 mloca43 N 2 2 4 0,1 4.3E-10 43E-10 sloca43 N 2 2 4 0,1 3.9E-10 3.9E-10 sloct43 N 2 2 4 0,1 32E-10 3.2E-10 lloca33 N 2 2 4 0,1 3.0E-10 3.0E-10 trant43 N 2 2 4 0,1 2.8E-10 2.8E-10 sgtt43 N 2 2 4 0,1 5.8E-13 5.8E-13 l nloca44 N 2 2 3 4 2.2E-09 22E-09 l sgtr44 N 2 2 3 4 1.1E-09 1.1E-09
( T sloct44 N 2 2 3 4 6.7E-10 6.7E-10
'w)
Categorization of Success Paths for Long-Term Recirculation Cooling June 1997 o:\3661w.wpf:1b 061997
7-24 Table 7.2.3-4 Success Paths for Other Than DVI Line Breaks, with Failed Containment Isolation (cont.)
If counted as core damage, increase to Equipment Assumptions Focused PRA Success Core Damage Large Release Path CI CMT Acc ADS-4(*) ADS 2,3(*) Frequency /yr Frequency!yr trant44 N 2 2 3 4 5.6E-10 5.6E-10 mloca44 N 2 2 3 4 4.4E-10 4.4E-10 sloca44 N 2 2 3 4 4.1E-10 4.1E-10
~11oca34 N 2 2 3 4 3.1E-10 3.1E-10 sgtt44 N 2 2 3 4 1.2E-12 1.2E-12 nloca45 N 2 2 3 0-3 5.7E-10 5.7E-10 sgtr45 N 2 2 3 0-3 2.4E-10 2.4E-10 sloct45 N 2 2 3 0-3 1.6E-10 1.6E-10 mioca45 N 2 2 3 0-3 1.1E-10 1.1E-10 trant45 N 2 2 3 0-3 9.8E-11 9.8E-11 stoca45 N 2 2 3 0-3 9.0E-11 9.0E-11 lloca35 N 2 2 3 0-3 6.9E-11 6.9E-11 sgtt45 N 2 2 3 0-3 2.2E-13 2.2E-13 nloca46 N 2 2 2 0-4 1.2E-10 1.2E-10 sgtr46 N 2 2 2 0-4 4.1E-11 4.1E-11 sloct46 N 2 2 2 0-4 2.9E-11 2.9E-11 lloca36 N 2 2 2 0-4 2.4E-11 2.4E-11 mioca46 N 2 2 2 0-4 2.3E-11 2.3E-11 sloca46 N 2 2 2 0-1 1.5E-11 1.5E-11 trant46 N 2 2 2 0-4 1.4E-11 1.4E-11 sgtt46 N 2 2 2 0-4 3.1E-14 3.1E-14 Iloca37 N 2 2 0,1 0-4 1.9E-12 1.9E-12 nloca48 N 2 ,
1 4 4 8.0E-09 8.0E-09 sgtr48 N 2 1 4 4 3.9E-09 3.9E-09 l
sloct48 N 2 1 4 4 2.5E-09 2.5E-09 trant48 N 2 1 4 4 2.3E-09 2.3E-09 u .__
Categorization of Success Paths for Long-Term Recirculation Cooling June 1997 o:\3661w.wpt:1b-061997 1
7-25 i i
[)
V Table 7.2.3-4 Success Paths for Other Than DVI Line Breaks, with Failed Containment Isolation (cont.) !
If counted as core damage, increase to Em ment Assumptions Focused PRA Success Core Damage Large Release Path CI CMT Ace ADS 4(*) ADS 2,3(*) Frequency /yr Frequencylyr mloca48 N 2 1 4 4 1.6E-09 1.6E-09 sloca48 N 2 1 4 4 1.5E-09 1.5E-09 lloca39 N 2 1 4 4 1.1E-09 1.1E-09 sgtt48 N 2 1 4 4 5.0E-12 5.0E-12 nloca49 N 2 1 4 0-3 2.0E-09 2.0E-09 sgtr49 N 2 1 4 0-3 9.2E-10 9.2E-10 sloct49 N 2 1 4 0-3 6.0E-10 6.0E-10 trant49 N 2 1 4 0-3 4.4E-10 4.4E-10 i i
mioca49 N 2 1 4 0-3 3.8E-10 3.8E-10 sloca49 N 2 1 4 0-3 3.5E-10 3.5E-10
(] Iloca40 N 2 1 4 0-3 2.6E-10 2.6E-10 l sgtt49 N 2 1 4 0-3 9.6E-13 9.6E-13 nloca50 N 2 1 2-3 0-4 1.9E-11 1.9E-11 sgtr50 N 2 1 2,3 0-4 9.2E-12 9.2E-12 trant50 N 2 1 2,3 0-4 4.5E-12 4.5E-12 mloca50 N 2 1 2,3 0-4 3.8E-12 3.8E-12 sloca50 N 2 1 2,3 0-4 3.4E-12 3.4E-12 sloctSO N 2 1 2,3 0-4 3.1E-12 3.1E-12 lloca41 N 2 1 2,3 0-4 2.7E-12 2.7E-12 sgtt50 N 2 1 2,3 0-4 9.9E-15 9.9E-15 lloca42 N 2 1 0,1 0-4 7.6E-15 7.6E-15 nloca52 N 2 0 2,4 0-4 6.5E-11 6.5E-11 sgtr52 N 2 0 2,4 0-4 2.8E-11 2.8E-11 l sloct52 N 2 0 2,4 0-4 1.9E-11 1.9E-11 mioca52 N 2 0 2,4 0-4 1.3E-11 1.3E-11 (m trant52 N 2 0 2,4 0-4 1.2E-11 1.2E-11 Q)
Categorization of Success Paths for Long-Term Recirculation Cooling June 1997 o:\3661w.wpf-1b-061997
7-26 Table 7.2.3-4 Success Paths for Other Than DVI Line Breaks, with Failed Containment Isolation (cont.)
If counted as core damage, increase to Equipment Assumptions Focused PRA Success Core Damage Large Release Path CI CMT Acc ADS 4(*) ADS 2,3(*) Frequency /yr Frequencylyr sloca52 N 2 0 2,4 0-4 1.0E-11 1.0E-11 sgttS2 N 2 0 2,4 0-4 2.7E-14 2.7E-14 cmtIb33 N 1 2 4 4 1.0E-07 1.0E-07 nloca54 N 1 2 4 4 1.4E-09 1.4E-09 sgtr54 N 1 2 4 4 7.0E-10 7.0E-10 sloct34 N 1 2 4 4 4.4E-10 4.4E-10 trantS4 N 1 2 4 4 3.5E-10 3.5E-10 mioca54 N 1 2 4 4 2.8E-10 2.8E-10 sloca54 N 1 2 4 4 2.6E-10 2.6E-10 lloca45 N 1 2 4 4 2.0E-10 2.0E-10 sgttS4 N 1 2 4 4 7.6E-13 7.6E-13 cmtib34 N 1 2 4 2,3 2.6E-08 2.6E-08 nloca55 N 1 2 4 0-4 3.6E-10 3.6E-10 i sgtr55 N 1 2 4 0-4 1.6E-10 1.6E-10 sloctSS N 1 2 4 04 1.0E-10 1.0E-10 l
mloca55 N 1 2 4 0-4 7.2E-11 7.2E-11 l
trant55 N 1 2 4 0-4 6.2E-11 6.2E-11 sloca55 N 1 2 4 0-4 5.8E-11 5.8E-11 sgtt55 N 1 2 4 0-4 1.4E-13 1.4E-13 lloca46 N 1 2 4 0-3 4.4E-11 4.4E-11 cmtib35 N 1 2 4 0,1 2.3E-10 2.3E-10 cmtib36 N 1 2 3 4 2.4E-10 2.4E-10 cmtlb37 N 1 2 3 03 5.3E-11 5.3E-11 nloca56 N 1 2 2,3 0-4 3.4E-12 3.4E-12 sr,tr56 N 1 2 2,3 N 1.6E-12 1.6E-12 sloctS6 N 1 2 2,3 0-4 8.3E-13 8.3E-13 Categorization of Success Paths for Long-Term Recirculation Cooling June 1997 o:\3661w.wp61b-061997
l 7-27 i
Table 7.2.3-4 (V) (cont.)
Success Paths for Other Than DVI Line Breaks, with Failed Containment Isolation If counted as core damage, increase to Equipment Assumptions Focused PRA Success Core Damage Large Release Path CI CMT Acc ADS-4(*) ADS 2,3(*) Frequencylyr Frequencytyr mioca56 N 1 2 2,3 0-4 6.5E-13 6.5E-13 trant56 N 1 2 2,3 0-4 6.3E-13 6.3E-13 sloca56 N 1 2 2,3 0-4 5.9E-13 5.9E-13
'lloca47 N 1 2 2,3 0-4 4.5E-13 4.5E-13 sgttS6 N 1 2 2,3 0-4 1.4E-15 1.4E-15 cmtib38 N 1 2 2 0-4 7.9E-12 7.9E-12 Iloca48 N 1 2 0,1 0-4 2.4E-15 2.4E-15 I cmtib40 N 1 1 4 4 8.7E-10 8.7E-10 cmtib41 N 1 1 4 0-3 2.0E-10 2.0E-10 lloca50 N 1 1 2,4 0-4 8.2E-13 8.2E-13
(%
i cmtib42 N 1 1 2,3 0-4 2.0E-12 2.0E-12 nloca58 N 1 0 _
2,4 0-4 1.2E-11 1.2E-11 cmtib44 N 1 0 2,4 N 6.0E-12 6.0E-12 sgtr58 N 1 0 2,4 0-4 5.8E-12 5.8E-12 trant58 N 1 0 2,4 0-4 2.9E-12 2.9E-12 sloctS8 N 1 0 2,4 0-4 2.4E-12 2.4E-12 mioca58 N 1 0 2,4 0-4 2.3E-12 2.3E-12 sloca58 N 1 0 2,4 0-4 2.2E-12 2.2E-12 sgttS8 N 1 0 2,4 0-4 6.5E-15 6.5E-15 cmttb46 N 0 2 4 4 9.2E-11 9.2E-11 cmtlb47 N 0 2 23 0-4 2.0E-11 2.0E-11 cmtlb48 N 0 2 2,3 0-4 2.0E-13 2.0E-13 sgtr60 N 0 2 2,4 0-4 7.2E-10 7.2E-10 nloca60 N 0 1 2,4 0-4 1.1E-10 1.1E-10 l
N sloct60 0 1 2,4 0-4 3.3E-11 3.3E-11 n trant60 N 0 1 2,4 0-4 2.5E-11 2.5E-11 Categorization of Success Paths for Long-Term Recirculation Cooling June 1997 o:\3661w.wpf-1Mki1997 e
7-28 Table 7.2.3-4 Success Paths for Other 'Ihan DVI Line Breaks, with Failed Containtnent isolation
- (cont.)
If counted as core damage, increase to Equipment Assumption.s Focused PRA Success Core Damage Large Release Path CI CMT Acc ADS-4(*) ADS 2,3(*3 Frequency /yr Frequencylyr mioca60 N 0 1 2,4 0-4 2.1E-11 2.1E-11 slo a60 N 0 1 2,4 0-4 1.9E-11 1.9E-11 cmtib50 N 0 1 2,4 0-4 7.6E-13 7.6E-13 sgtt60 N 0 1 2,4 0-4 5.9E-14 5.9E-14 Note:
(a) The ADS notation is as follows: s here a single number is shown, that number of valves is available (e.g., "4" means that 4 valves are available); where two different numbers are shown, the group includes that range of possibilities (e.g., "O,4" or "0-4" means that sequences may include 0,1, 2, 3, or 4 valves).
O O
Categorization of Success Paths for Long-Term Recirculation Cooling June 1997 o:\3661w.wpf:1b-061997
7-29 7.2.4 Fourth Grouping: ADS Capacity For the sets of sequences defined in the third grouping (i.e., Tables 7.2.3-1 through 7.2.3-4) it is necessary to examine each group to determme available relief (i.e., ADS valve) capacity, since this is an important factor in the ability to achieve recirculation cooling. It is possible to subdivide each group in terms of number of available ADS valves that meet the PRA cuccess criteria (e.g.,4 ADS stage 4 valves available,3 ADS stage 4 valves available,2 ADS stage 4 valves available, combinations of stage 4 and stages 1-3, and so forth), and then perform analyses for each set. However, to limit the T/H analyses to a manageable number of cases, the ADS subcategorization is done only in terms of number of available stage 4 valves.
The frequencies, and percentage contributions, for each of the groups defined to this point are summarized in n hic 7.3-1, which is further discussed in Section 7.3, after the discussion of other considerations m Section 7.2.5.
7.2.5 Additional Long-Term Recirculation Cooling-Specific Expanded Event Tree Sequence Considerations Each expanded event tree scenario defined in Section 4 and grouped in this section includes the initiating event frequency, and the status of the safety-related (i.e., passive) systems p important to long-term cooling. However, there are also several considerations specific to d long-term cooling that are not addressed in the short-term TlH uncertainty analysis, and that can affect the success or failure of long-term recirculation. These include:
Ine impact of passive residual heat removal (PRHR) operation on success for transient events as modeled in the focused PRA The knowledge of how many paths are available for recirculation, given that one or more paths is available a
The success or failure of passive containment cooling system (PCS)
The knowledge of how many CMTs and accumulators empty into the sump, and how many ADS stage 2 and 3 valves open i
The first consideration arises primarily as a result of the focused PRA "groundrules," which do not allow mitigation credit for nonsafety-related systems. The second consideration deals with resolving the relative importance of various numbers of flow paths for recirculation, and the associated impact on requirements for demonstrating sequence ruccess via the long-term recirculation TlH analyses. The third consideration deals with the relative importance of PCS operation to sequence success; that is, assuming that PCS operation is important to the 4
Categorization of Success Paths for Long-Term Recirculation Cooling June 1997 o:\3661w.wpf:ltW1897
7-30 1
analyses, what is the effect of PCS failure on the PRA results. The fourth consideration deals with resolving the relative importance of various numbers of successfully actuated CMTs and accumulators, and ADS stage 2 and 3 valves.
7.2.5.1 Relative Risk Importance of Passive RHR to Long-Term Cooling The AP600 design includes several means of decay heat removal that would normally be expected to function following a transient. However, some of these are active, nonsafety-related systems such as main and startup feedwater, which, given the Focused PRA assumptions, would not be available following transients (which, as a group, have the highest initiating event frequencies). Thus, for such events in the Focused PRA, passive RHR operation provides the only safety-related means of decay heat removal that can be credited without requiring feed-and-bleed cooling. Feed-and-bleed for AP600 involves actuation of ADS; without credit for normal RHR (RNS), which is a nonsafety-related system, actuation of ADS would eventually lead to the need for IRWST injection and long-term recirculation cooling.
The FRA models credit PRHR operation as able to provide decay heat removal sufficient to preclude the need for RCS depressurization with IRWST injection and long-term recirculation cooling. That is, in any event sequence in which PRHR is successful and in which ADS and IRWST injection actuation are not otherwise actuated, long-term recirculation cooling is not required. This is consistent with the PRA success criterion for PRHR, which requires that PRHR be able to remove decay heat for a sufficiently long time to prevent the need for h
IRWST injection and recirculation cooling (Reference 3, Chapter 6).
l If PRHR were not able to perform this function, then, in the Focused PRA, long-terrn recirculation cooling would be required for the relatively high-frequency transient events. !
This would affect the relative importance of transient scenarios to long-term cooling success. l That is, unless PRHR can provide long-term cooling, sequences with higher initiating event I frequencies (i.e., transients) would require recirculation cooling, so that the T/H uncertainty I analysis would need to show success for lower-probability scenarios (i.e., more equipment j failures).
For the purposes of this long term cooling T/H uncertainty evaluation, the ability of PRHR ;
to remove decay heat and preclude the need for IRWST injection and recirculation cooling, l consistent with the modeling in the focused PRA event trees, is a key factor in defining the necessary analysis scope. This PRHR capability has been assured, within the reliability of the associated equipment, with the recent design change that makes the IRWST gutter and isolation valve system safety related. Per SSAR subsection 6.3.2.1.1 (Revision 13), the valves in these gutters will close on a PMS or DAS PRHR actuation signal so that, as PRHR heats up the IRWST and water evaporates into containment, a sufficient amount is condensed cn the containment shell and returned, by the gutter system, to the IRWST. This provides Categorization of Success Paths for Long-Term Recirculation Cooling June 1997 o:\3661w.wpf:lt461897
- - - - - -_- ..- . . -.. ,.- -~.
7-31 l.
I. - sufficient PRHR capability to allow continuous operation for long term cooling without the I
need for depressurization and IRWST injection. Incorporation of this change into the design ,
! validates the PRA success criteria requiring PRHR to provide long term cooling capability.
l Therefore, it is appropriate for the PRA, and in particular, the focused PRA,6 credit PRHR operation as able to prevent the need for long term recirculation' cooling.
7.2.5.2 Relative Risk Importance of Number of Recirculation Paths The expanded event tree success paths do not distinguish among the number of IRWST injection and recirculation flow paths available for a given success sequence. As long as at least one path is available to allow both injection and subsequent recirculation, the sequence is defined as successful, subject to the requirements for other systems such as ADS, CMTs, l and so on. This is consistent with the PRA success criteria for IRWST injection and l recirculation, which also require only one flow path for success (Reference 3, Chapter 6). l However, in terms of definition of conditions for which long-term recirculation TlH analysed are necessary in order to demonstrate successful cooling capability, the requirement for success with only one path is quite stringent, and is expected to be unjustified based on %
significance. That is, accepting the criterion as is would require that the long-term cochng T/H analyses show that recirculation cooling works with ody one path, for all events, when
- in fact it is possible that the probability of having only one path open is small compered to the probabilities of having two, three, or four paths. As a result, sequence expansions beyond the IRWST injection and recirculation path possibilities considered in Section 4 have been performed, to help define the risk significance of numbers of flow paths.
The relative probabilities of having a given number of recirculation paths can be defined in ;
terms of an expanded event tree similar to but more limited in scope than those shown in l Section 4. This is shown in Figure 7.2.5-1. Each expanded event tree sequence from Section 4 includes the probability that all four recirculation paths did not fail, which is the same as the probability that one or more of the four paths opeed. Thus, each previou.dv expanded sequence can be " transferred-in" to (i.e., continued with) the logic in Figure 7.1.5-1 j to continue the expansion of recirculation paths. A recirculation expansion similar to the
- expansions shown for stage 4 ADS valves on the expanded event trees in Section 4 was <
performed for this case, and the results are shown at the end paths in this figure.
l This expansion, after the expansion shown in Section 4, is valid because there are no i significant common-cause contributions among the top events in success paths. That is, given that at least minimum success is achieved for ADS, CMTs, or accumulators, IRWST injection, and recirculation (which must be the case for a success path), there are no significant faults that would preclude better-than-minimum success. The results are the same as would be obtained had this expansion been incorporated directly into the expanded event trees in Section 4.
Categorization of Success Paths for Long-Term Recirew. ion Cooline, June 1997 o:\3661w.wptib-061897 v- -
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l l
l l
l Path l Probability Success of 4 paths 0.937 Success of 3 (P4) or 4 paths Success of 2, 3, or 4 paths Success of 1, 2, 3, or 4 paths Success of only 3 paths (P3 ) 6.2E-2 Success of only 2 paths (P2) 1. l E-3 Success of only 1 path 2.8E-4 (P3 )
P1 = Probability of failure of 3 paths, given that at least 1 path is available.
P2= Probability of failure of 2 paths, given that at least 2 paths are available.
P3 = Probability of failure of 1 path, given that 3 or 4 paths are available.
P4 = Probability that no paths fail.
l l
Note that each end path probability is the product of the success and failure probabilities for each branch along the path. For example, the end path probability with 3 paths successful is P = (1 - P3 ) x (1 - P2 ) x (P3) '
l l
l l
Figure 7.2.5-1 Expansion of Recirculation Branch Showing Probabilities of Success for Each '
Possible Number of Open Paths Categorization of Success Paths for Long-Term Recirculation Cooling June 1997 o:\3661w.wpf:1b-061897 l
. _ . _ . _ _ _ - _ . . __ _ _ . ._ .~. _ _.-. _ _ _ _ . . ._. . ___
7-33 l
L An expansion of the IRWST injection path possibilities would be expected to provide a L; / similar set of results, at least for the non-DVI cases, since the configuration is similar to that j for recirculation.' Thus, there is only an insignificant probability that only one IRWST
! _ injection path will be available for these cases. For the DVI cases, injection may not be l possible via the broken DVI line, so the success paths may be limited to one path open which would have a probability similar to that of P 3on Figure 7.2.S-1 or two paths open which
- would have a probability similar to that of P on 4 Figure 7.2.5-1.
l . Figure 7.2.5-1 shows that there is only a small probability that, for any successful event l sequence, only one recirculation path will be available. That is, the probability that there will be more than one recirculation path available for a given success sequence is nearly 1.0c Applying these results, for example, to the DVI cases with containment isolated as listed in Table 7.3-1, the frequency of the sequence group with 2 ADS-4 valves open and only one l
~ recirculation path is: 1.14E-8 x 2.8E-4 = 3.2E-12; the frequency for this group with two recirculation paths is: 1.14E-8 x 1.1E-3 = 1.3E-11; and the frequency for this group with three recirculation paths is 1.14E-8 x 6.2E-2 = 7.1E-10 These values are all insignificant with respect to the Focused PRA CDF and LRr. Thus, for the 2 ADS-4 DVI case with containment ;
isolated, only the condition with all recirculation paths available is potentially risk-significant.
Similarly, for the other sequences, it is not necessary to show success for cases with only one recirculation path available, since the potential contributions to CDF or LRF from such paths, if they were unsuccessful, are very small. The recirculation expansion results apply to non-DVI line break cases as well as to DVI cases. Once the sump is flooded, the water level is above the recirculation inlets, and flow paths can be established whereby sump water enters either recirculation line and flows either directly into the RCS via the associated DVI line, or flows through the IRWS'l and into the RCS through the opposite DVI line (Ref. 3, Chapter 6).
Thus, any recirculation pata can work with any injection path.
This evaluation provides a sufficient basis for specifying conditions for the analyses as two recirculation paths rather than one.
7.2.5.3 Relative Risk Importance of Operation of Passive Containment Cooling System The expanded event tree success paths do not distinguish whether or not the passive containment cooling system is successful. PCS operation affects the heat transfer rate t' hrough the containment shell, and therefore affects containment pressure, which in tum affects recirculation capability. The specific impacts of PCS operation or failure on the long-term cooling TlH analyses are described in Section 10, and have also been addressed l previously in Chapter 40 of the PRA (Reference 3). Since it is most likely that the PCS will l operate, it is important to include'the effects of PCS operation in the long-term recirculation H
T'H analyses. However, since it is possible that the PCS will not operate, it is also necessary to show that the potential impact of PCS failure on risk significance of sequences is small.
This is discussed in the following paragraphs.
- Categorization of Success Paths for Long-Term Recirculation Cooling June 1997 l on3661w.wpf
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Since PCS was not addressed in the expanded event tree sequences, it is necessary to check for independence of faults that can cause PCS failure from faults modeled in other systems in the event sequences (i.e., ADS, CMT, accumulators, RWST, recirculation). Such faults would I have to affect the PCS without resulting in failure of tre other systems, since the success paths are of interest. A PCS fault tree had not been de" eloped for the Focused PRA model. I Review of the Baseline PRA PCS failure model showed that the only fault with the potential i to affect other systems modeled in the PRA is common cause failure of containment pressure transmitters modeled for system actuation. This common-cause failure is also modeled as a contributor, along with diverse actuation system (DAS) failures, in the baseline model, to j failure of containment isolation actuation.
Therefore, for sequences with successful containment isolation, PCS operation is independent of other events in the sequences. For such sequences, there is only a very small probability that PCS will not operate: in the Baseline PRA, PCS failure probability is approximately 1E-4; it is estimated to be 7E-4 using the baseline model but taking no credit for DAS actuation and l
without assuming fail-safe actuation of the PCS air-operated valves on loss of air; and it is '
estimated to be 1E-4 without DAS but with the assumption of fail-safe actuation on loss of air, consistent with the Focused PRA modeling assumptions. Applying either of these probabilities (i.e.,1E-4 or 7E-4) to the frequencies listed for containment isolation in i Table 7.3-1, and assuming that PCS failure adversely affects long-term recirculation cooling, i results in insignificant potential PRA impacts, relative to the Focused PRA, for the cases with ,
any failures of ADS stage 4. For cases with all ADS stage 4 available, or for the design basis cases, the sequence group frequencies with PCS failure are potentially significant relative to i the Focused PRA CDF and LRF. However, the analysis presented in Chapter 40 of the PRA shows that failure of PCS results in higher containment pressure, which is a benefit to decay heat removal capability during long-term circulation, with only a small probability (IE-4) of containment failure due to the higher (above design basis) containment pressure. Therefore, it is expected that long-term circulation cooling would be successful even without PCS water for sequences with containment isolation.
For cases in which containment isolation has failed, failure of PCS could result in a large loss of containment inventory due to the relatively high differential pressure across the unisolated containment penetration. If this condition lasted long enough, there could be insufficient water level in the sump to support recirculation cooling. For the Table 7.3-1 sequence groups with failure of containment isolation, the frequencies for groups with less than 4 ADS stage 4 valves are already sufficiently small that uncertainty regarding the status of PCS, or of thermallhydraulic performance generally, cannot have a large impact on either Focused PRA or Baseline PRA results and conclusions.
There are two sets of potential impacts to consider for sequence groups with failure of containment isolation and all ADS stage 4 valves available: potential Baseline PRA impact due to DVI line breaks and large LOCA, and potential Focused PRA impact due to all Categorization of Success Paths for Long-Term Recirculation CooPng June 1997 o:\3661w.wpf:lt>-061897
7-35 initiating events. For the Baseline PRA, the PCS failure probability of ~1E-4 can be applied to f]
U the DVI line break and large LOCA sequence group frequencies, since, in the baseline cases, credit is taken for DAS and associated operator actions. The potential baseline PRA impact of PCS failure is therefore not significant, even with failure of containment isolation.
For the Focused PRA, it is important to assume consistency with the Focused PRA groundrules, one of which is that the necessary safety-related valves assume their fail safe positions on loss of s"nnmt systems (nonsafety-related air and electrical power). In this case, the impact of PCS failure would be similar to that noted above for the Baseline PRA,i.e.,
multiplying the Table 7.3-1 frequencies by ~1E-4, with a resulting insignificant impact. The assumption that the PCS valves will go to their fail-safe (open) positions in time for recirculation cooling, given Focused PRA conditions (i.e., without support systems) is reasonable because there is a relatively long period of time available before recirculation cooling is required. During this time, the IRWST will be emptying through the RCS into the containment sump. Sump level would be expected to continue to rise during approximately the first 10 hours1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br /> after the event, even with failed PCS and failed containment isolation, to a level that would support natural recirculation. It is unlikely that the air supply to hold the valves closed would last longer than this. Thus, even with failure of the actuation signal, PCS actuation is anticipated, so that PCS failure is effectively independent of containment isolation failure, from a Focused PRA perspective. (Note that the contribution of the common containment pressure sensors to failure of containment isolation is approximately
('} 29 percent of the total conta*nent isolation failure probability, using the Baseline PRA model, which includes actuawn faults, per PRA Section 24), so that only 29 percent of the frequencies shown in Table 7.3-1 could be subject to any common-cause consideration.)
The conclusion of this evaluation is that PCS failure to operate does not have a significant impact on the PRA importance of the sequence groups.
7.2.5.4 Relative importance of Numbers of CMTs, Accumulators, and ADS Stage 2 and 3 Valves As noted in the Table 7.3-1 entries, the various sequence groups each contain sequences that have different numbers of CMTs, accumulators, and ADS stage 2 and 3 valves. Per the FRA success criteria (in PRA Chapter 6), there must always be at least 1 CMT or accumulator, so there can be from 1 to 4 of these available in the success sequence groups. Success can be defined for some events, however, without operation of ADS stages 2 and 3, so there can be from 0 to 4 of these valves available in the success sequence groups. The numbers 01 CMTs, accumulators, and ADS stage 2 and 3 valves are indicated for each sequence in the tables in Section 7.2.3. Thus,it is possible to obtain the relative contributions of various numbers of available devices. In general, ADS stage 2 and 3 valves will not be modeled in the T/H uncertainty analysis (i.e., no credit for these valves), in order to simplify the modeling.
Therefore, the rest of this discussion deals only wnh sailability of CMTs and accumulators.
Categorization of Success Paths for Long-Term Recirculation Cooling June 1997 o:\3661w.wpf:1b-061897 i
7-36 Failures of CMTs and accumulators to inject may affect recirculation cooling by reducing the sump water level. Because the containment cross-sectional area is large, however, failure of individual CMTs or accumulators has only a smali effect (estimated to be on the order of one-tenth of a foot) on sump level. For non-DVI line break cases with successful containment isolation, this effect is not important to the T/H analyses. The effect is somewhat more important for DVI line break cases with successful containment isolation, assuming that the DVI break results in flooding of a normally dry valve compartment, and slightly more important than that for cases with failure of containment isolation, with the largest impact being for DVI line breaks without contairunent isolation.
For DVI line breaks with failed containment isolation, the sequence frequencies indicate that there is an insignificant contribution from sequences with only 1 CMT or accumulator, regardless of the number of open ADS stage 4 valves; for these cases, the T/H analyses can assume that the sump contains the inventory from 2 CMTslaccumulators.
For other events with failed containment isolation, there is no significant contribution from sequences with less than 2 CMTs or accumult. tors, for cases with either 3 or 4 ADS stage 4 valves available. For cases with only 2 ADS stage 4 valves available, the total frequency of sequences with only 1 CMT or accumulator available is relatively more important to the group total; however, per the values shown in Table 7.3-1, the entire group contribution is not a significant percentage of the Focused PRA large release frequency, so it is not potentially risk-significant.
h For DVI line break cases with containment isolated, the PRA sequences consider only the possibility of 1 or 2 CMTslaccumulators inje.Mg, since the PRA models for these systems were based on requirements for short-term injection. For a DVI line break, it is possible that the water from the CMT and accumulator in the broken loop will spill into the valve compartment and not inject into the RCS. However, this spilled inventory willlater be available for recirculation. For the successful containment isolation DVI line break sequences as listed, more than 99 percent of the CDF is associated with sequences with 2 CMTslaccumulators. A calculation of the probabilities of having 3 or 4 CMTslaccumulators would be expected to result in numbers similar to those described earlier for recirculation paths, i.e., the most likely case would be that with 4 devices spilling into the sump.
l i For other events with containment isolation, the contributions of sequences with at least l 3 CMTs and accumulators account for approximately 95 percent of the group totals for cases l with either 2 or 3 ADS stage 4 valves, and approximately 85 percent of the total for the group with 4 ADS-4 valves. This indicates, using the values from Table 7.3-1, that having only 2 CMTslaccumulators for the 2 ADS stage 4 valve case would have an insignificant potential risk impact (i.e.,5 percent of 3.1E-7 = 1.6E-8, or unly about 0.2 percent of Focused PRA CDF, and a similarly small percentage of Focused PRA LRF). This is also true (i.e., less than 1 percent potential impact) for the 3 ADS stage 4 valve case. The potential impact for Categorization of Success Paths for Long-Term Recirculation Cooling June 1997 o:\3661w.wpf:1b-061897
7-37 i
L the 4 ADS stage 4 valve case is somewhat higher, but the T/H advantage of having the RCS
(~~ venting capacity from all stage 4 valves open would outweigh the relatively small reduction
)
in sump level from a CMT or accumulator. If the T/H analyses for this group are sensitive to having 2 versus 3 CMTs/ accumulators, any resultant impact will be addressed in Section 11.
l 1
l i
O I
s l
l l
l l
t s
lO Categorization of Success Paths for Long-Term Recirculation Cooling June 1997 o:\3661w.wpf:IMI61897 t
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l l 7.3
SUMMARY
OF LTC RISK IMPORTANCE GROUPINGS AND SELECTION OF l[]
N>
CASES FOR TlH ANALYSIS Table 7.3-1 summarizes the total success path frequencies corresponding to the various numbers of ADS stage 4 valves available, for each of the previously defined groups. The numbers of CMTs and accumulators, ADS stage 1-3 valves, and recirculation paths indicate the range of available equipment for the sequences within each group.
The information in Table 7.3-1 illustrates the expected result, that sequences with the least l equipment available have the lowest potential impact. The table also provides the means for i defining a set of cases for which TlH analyses should be performed so that there is only
! small potential impact on the Focused PRA and Baseline PRA results due to TIH uncertainty, For example, for the cases with failed containment isolation, there is no potential impact of any significance on either the Focused PRA or Baseline PRA from sequences with only 2 ADS 4 valves available, and only a very small potential impact (just over 1 percent of Focused PRA LRF for non-DVI break cases, about 2 percent Baseline PRA LRF for DVI cases) l with 3 ADS-4 valves available. As another example, for DVI line breaks with containment i isolated, the case of 2 ADS-4 valves available has a relatively insignificant potential impact on the Focused PRA results. There is also a potential impact for this case on the Baseline PRA A results, however, since the DVI line break event sequences are the same for Baseline and
() Focused PRA. In this case, the potential impact on the baseline results is not insignificant, but is small.
With the sequence groupings shown in Table 7.3-1 and the evaluations provided in ;
Section 7.2, the following conclusions can be made regarding the conditions to be addressed in the TlH analyses for long-term recirculation cooling,
- a. The analyses will not address sequences identified as design basis scenarios, since these are already analyzed and shown to be successful in the design basis analyses.
- b. The analyses need to address the potential sump level reduction caused by failure of containment isolation.
- c. The analyses need to address the potential sump level reduction caused by valve compartment flooding for some DVI line breaks.
! n
\.
Categorization of Success Paths for Long-Term Recirculation Cooling June 1997 o:\3661w.wpf:1b-061897
on
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L g ni o g .
Table 73-1 Success Frequencies for Sequence Groups, Sorted by Containment Isolation Status and ADS Stage 4 Valve Availability, for DVI Line Break and Non-DVI Line Break Events 2 cr.
$ Total Expanded
[hR k Equipment Available During Recirculation Focused PRA Event Tree Core If counted as core damage, increase to Focused PRA")
If counted as core damage, increase to Baseline PRA"I g Damage Sequence
$ ADS Frequency (yr)
? CMTs Stage ADS Over All 7 & 4 2/ 3 Recire. Sequences in the g Description Accum. Valves Valves Paths (b) Group ACDF ALRF"I ACDF ALRF
[ CONTAINMENT ISCLATED o
DBA Sequences 4 3-4 0-4 1-4 6.9E-03 >>100 % >>100 % (d) (d)
@ DVI Line Break 1-4 (') 4 0-4 1-4 2.7E-05 >100 % >100 % >>100 % >>100 %
k W
1-4 (') 3 0-4 1-4 65E-08 1% 1% 38 % 22 %
{ 1-4(3) 2 0-4 1-4 1.1E-08 -0% ~0% 7% 4%
( Large LOCA 2-4 4 0-4 1-4 1.1E-06 15 % 12 % >100 % >100 %
{ 3 3 0-4 1-4 2.6E-09 0% 0% 2% 1%
[ 2-4 2 0-4 1-4 3.2E-08 ~0% ~0% 19 % 11 %
2-4 0-1(f) 0-4 1-4 3.2E-09 ~0 % --O % 2 % (f) 1 % (f)
Other Than DVI Line 1-4 4 0-4 1-4 5.5E-04 >>100 % >>100 % (d) (d)
Break and Large LOCA 1-4 3 0-4 1-4 13E-06 17 % 56 % (d) (d) 1-4 2 0-4 1-4 3.1E-07 4% 14 % (d) (a}
O -
O - - - - -- - - -
O --
3 g Ol
- k. Table 7.3-1 Success Frequencies for Sequence Groups, Sorted by Containment Isolation Status and ADS Stage 4 Valve Availability, for y$ (cont.) DVI Line Break and Non-DVI Line Break Events bh C$ Total Expanded Focused PRA If counted as core dama e, if counted as core dama e, Equipment Available During
$E Recirculation Event Tree Core increase to Focused PRA d increase to Baseline PRA d g Damage Sequence
@ ADS Frequency ( yr)
- Over All CMTs Stage ADS
= & 4 2/ 3 Recire. Sequences in the k Description Accum. Valves Valves Paths (b) Group ACDF ALRF(d ACDF ALRF E'
CONTAINMENT NOT ISOLATED
, DVI Line Break 1-4(*) 4 0-4 1-4 15E-07 2% 28 % 89 % >100 %
M 1-4(a) 3 0-4 1-4 3.4 E-10 0% -0 % <1 % 2%
0 x 1-4 (*) 2 0-4 1-4 2.9E-11 0% 0% 0% -0 %
B g Large LOCA 3-4 4 0-4 1-4 1.7E-07 2% 31 % 100 % >>100 %
$ 4 3 0-4 1-4 3.8E-10 0% ~0% ~0% 2%
O g 2-4 2 0-4 1-4 3.0E-11 0% 0% 0% ~0%
o g 2-4 0-1 (f) 0-4 1-4 1.89E-12 0% 0% 0 % (f) 0 % (f)
Other 'Ihan DVI Line 1-4 4 0-4 1-4 3.1E-06 41 % > 100 % (d) (d)
Break and Large LOCA 1-4 3 0-4 1-4 6.9E-09 -0% 1% (d) (d) 1-4 2 0-4 1-4 1.4E-09 0% ~0% (d)' (d)
I
9O
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Notes to Table 7.3-1 N A
g' mE N (a) The event trees model only the possibility of I or 2 CMTs/ accumulators injecting for DVI line break, to cover ini-ction conditions. For recirculation. if the CMT and/or 3k accumulator in the broken DVI line spill, the water ends up in the sump and is useful for recirculation cooling. The sequence fn=quencies have been calculated on the dh basis of I of 1 intact-line CMT or 1 of ', intact-line accumulator injecting, so that the resulting success frequencies are lower than would be expected if the CMT and Cy accumulator success criteria wen cada 1 of 2. Further, the effect on sump water level of additional CMT/ accumulators is small relative to other effects (as discussed in h3 g O (b)
Section 7.25). Therefore, it is reaso..at le to use the sequences as defined. Specific consideration of the relative prababilities of each condition is provided in Section 7.25.
The event trees model only the possibility of I recirculation hne (with one of two paths in the line required to open), even though the design of the IRWST and 4m recirculation lines is such that, once the sump is flooded, all 4 recirculation paths in the two lines would be available (PRA success criteria in Ref. 3, Chapter 6). Specific E consideration of the relative probabilities of exh condition is provided in Section 7.25.
@ (c) Large release frequency values are estimates. Contributions from SCTR sequences, and from sequences with failed containment isolation, are equal to the CDF for those m sequences. Contributions for all other sequences are estimated as the average percentage of the CDP that was obtained in the Focused PRA (i.e, LRF = 6 % CDF for non-2 failed containment /non-bypass sequences).
g (d) Percentage of Baseline PRA values are not relevant for these categories. The corresponding Baseline PRA sequences for these categories include active, nonsafety-related
, systems whose effects are not present in the Focused PRA sequences used for this analysis.
o (e) Potential impacts greater than 100% are indicated as "> 100 %" when the magnitude is between 100% and 900% (i.e., between a factor of 2 and 10 increase), and
">> 100 %" when the magnitude is greater than 900% (i.e., more than a factor of 10 increase). All percentages are rounded to the nearest percent.
3 (f) The PRA success criterion for large LOCA is 2 ADS-4 valves required if containment is not isclated and the break is smaller than a cutoff area determined in the analyses 0? supporting the success criteria. If containment is isolated, or if the break size is a greater than this cutoff, the success criterion is O ADS 4 valves required. If, in the long-p term recirculation cooling T/fl analyses, the break does not provide RCS venting capability, which is the most probable condition for a large LOCA, then the case of 0 g ADS-4 valves would not represent success. Note that although the sequences contributing to this category were not expanded to distinguish between 0 ADS 4 valves and 1 ADS 4 valve available, there would be a higher probability of having 1 valve available rather than 0. Ilowever, given the small contribution from this category, T/fl e analysis cases will not be defined.
h a
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o D
O 8
m s
ea s
O O O _
7-43
. 'd. The analyses can assume that the passive containment cooling system operates, since e failure of PCS does not have a risk-important effect on the PRA results.
- e. The analyses need to cover each of the cases of ADS stage 4 with availability of 2 or more valves. It is expected that this can be accomplished without the need to explicitly analyze each case by analyzing cases with the most ADS failures first. Cases with fewer failures than a case shown to be successful would then be judged to be successful also, on the basis that additional ADS capacity results in additional system venting capacity and is beneficial to natural recirculation.
- f. The analyses similarly can cover all potentially risk-important cases of CMTlaccumulator availability by assuming that at least 1 CMT or accumulator has ,
failed to empty. For the cases with failed containment isolation, it is suggested that at least 2 CMTslaccumulators be assumed failed, since these cases may have lower sump level to begin with and may be more sensitive to the relatively small sump level effects of additional CMTlaccumulator failures.
- g. The analyses'can account for potentially risk-important conditions of recirculation path availability (i.e., available recirculation flow area) by assuming that 2 (of 4) recirculation flow paths are available.
- h. The analyses should apply conservatisms sufficient to bound, to the extent possible, parameters that can affect the analyses (e.g., decay heat levels, flow resistances, and so forth), in order to minimize uncertainty remaining after the analyses are completed.
- i. The analyses need not explicitly cover sequences whose potential risk contribution is sufficiently small that it can be addressed in terms of results uncertainty or, if necessary, modification to the PRA success criteria.
The above conclusions can be used as the bases for collapsing the set of sequence groups in Table 7.3-1 into a smaller set of TlH analysis cases, which are shown in Table 7.3-2.
The sequence collapsing process was as follows:
O Categorization of Success Paths for Long-Term Recirculation Cooling June 1997 o:\3661w.wpf:1tH)61897
7-44 Table 7.3-2 Case / Disposition Sequence Group from Table 7.3-1 for LTC TIH Analysis Design Basis Sequences Not analyzed, per item a '
Containment Isolated DVI Line Break with 4 ADS-4 Covered by case 3 per item 3 DVI Line Break with 3 ADS-4 Case 3 DVI Line Break with 2 ADS-4 Not analyzed, per item i Large LOCA with 3 ADS-4 Covered by case 2a or 2b, per item e Large LOCA with 3 ADS-4 Case 2a or 2b Large LOCA with 2 ADS-4 Not analyzed, per item i Large LOCA with 0,1 ADS-4 Not analyzed, per item i Other with 4 ADS-4 Covered by case 2a or 2b, per item e Other with 3 ADS-4 Case 2a or 2b Other with 2 ADS-4 Not analyzed, per item i Containment Not Isolated DVI Line Break with 4 ADS-4 Case 4 DVI Line Break with 3 ADS-4 Not analyzed, per item i DVI Line Break with 2 ADS-4 Not analyzed, per item i Large LOCA with 3 ADS-4 Covered by case 4, per item e Large LOCA with 3 ADS-4 Not analyzed, per item i Large LOCA with 2 ADS-4 Not analyzed, per item i Large LOCA with 0,1 ADS-4 Not analyzed, per item i Other with 4 ADS-4 Covered by case 4, per item e Other with 3 ADS-4 Not analyzed, per item i Other with 2 ADS-4 Not analyzed, per item i Given this information, the cases in Table 7.3-2 are identified for the TlH analyses. These are the cases for which successful long-term recirculation core cooling with bounding T/H conditions will demonstrate minimalimpact of T/H uncertainty on the PRA. Additional explanation of conditions selected for the analyses, and justifications as to the bounding nature of these cases and conditions, is provided in Section 10, along with the results of the analyses.
O Categorization of Success Paths for Long-Term Recirculation Cooling June 1997 c:\3661w.wpf:1b-061897
(x /N A b
en f ,E, Table 7.3-2 Summary of Cases Representing Potentially Risk-Important Conditions mimmuummesummusummmmmmmmmmmuseum ----
g&
it Case Containment Isolation Type of Initiating Number of Number of Available Availab PCS Notes 3 !! Successful (Yes/No) Event ADS Stage 4 ADS Stage 2/3 CMTs and/or le Successful Valves Available Valves Accumulators Recircu
{$
- 9., Available (Max. = 4) lation (Yes/No) 4E Paths R (Max. =
h 4) m I Yes Non-DVI 2 0 3 2 Yes (a),(b) 5 2A Yes Non-DVI 3 0 3 2 Yes (a) g 2B 2 2
{
- s
" 3 Yes DVI Break 3 0 3 2 Yes (c) 4 No DVI Break 4 0 2 2 Yes (d)
$ Notes:
O.
b E (a) He case with 2 ADS stage 4 valves represents the case as modeled in the PRA, and the case selected as a result of the sequence groupings.
Information obtained from initial 2(COBRA / TRAC analyses indicates that this is a difficult case for which to demonstrate success. If success cannot
[
n be demonstrated for this case with the inclusion of bounding T/H conditions, success for the case of 3 ADS stage 4 or 2 ADS stage 4 plus 2 ADS 8 stage 2/3 valves, with bounding T/H conditions, should be shown. Any resulting effect on the PRA will be addressed in Section 11.
5 (b) His case addresses Baseline PRA long-tenn recirculation cooling success criteria for ADS following LLOCA (potential impacts of ~19% Baseline PRA CDF, ~10% Baseline PP.A LRF)
(c) His case represents relatively small potential Focused PRA impacts, but potentia!!y significant Baseline PRA impacts, if not successful. This case is being run primarily to support the basis for Baseline PRA success criteria; T/H conditions are similar to the DVI line break analyzed for DBA.
(d) This case represents potentially risk-important impacts for both the Focused and Baseline PRA. He DVI break without containment isolation case is chosen to bound the non-DVI line breaks without containment isolation.
I.
a
~ .
8-1 I 8 COMPARISON OF SHORT-TERM COOLING AND LONG-TERM
) COOLING CASE DEFINITIONS As identified in Section 3, there are two parallel processes to arrive at TlH uncertainty l analysis cases for short-term and long-term cooling. The case definitions for short-term l
cooling are documented in Section 6, while the case definitions for long-term cooling are documented in Section 7. The purpose of this section is to compare the results of these separate categorization efforts. The comparison of the short-term cooling and long-term cooling case definitions is done to confirm the completeness of the parallel processes, and to explain the similarities and differences in the case definitions. The case definitions include some similarities, because both processes identify potentially risk-significant scenarios using the same expanded success paths in Section 4. However, there are variations due to the different factors that influence successful core cooling in the short term and in the long term.
There are also differences in the cases that need to be analyzed because of differences in the existing analysis basis for short-term cooling versus long-term cooling.
To perform the comparison of cases, the major groupings defined for long-term cooling are used. The two primary sorting criteria used for long-term cooling are whether the containment is isolated, and whether the initiating event is a DVI line break or another initiating event. This produces four groups that are discussed in the following sections:
q l bl . Non-DVI line break with containment isolation
= DVI line break with containment isolation
. Non-DVI line break without containment isolation a DVI line break without containment isolation l
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i 8-2 I
l l
8.1 SHORT-TERM AND LONG-TERM COOLING CASES FOR NON-DVI LINE BREAKS WITII CO!iTAINMENT ISOLATION h
For long-term cooling, the equipment specification corresponding to the group of non-DVI line breaks with containment isolation is:
CMTs/ Accumulators: 3 ADS: 2 stage 4 (Note that, if this is not successful, add another stage 4 or 2 stage 2G)
Recirculation: 2 paths PCS: Successful This group is the highest-frequency group of accident sequences not addressed by DBA analyses. It encompasses most of the cases that are defined for short-term cooling analyses.
The four equipment specifications above are discussed in the following paragraphs.
CMTSIACCUMULATORS For the short-term analyses, the number of CMTs and accumulators can determine whether core uncovery occurs. The loss of 2 CMTs or 2 accumulators often leads to core uncovery, and these expanded event tree sequences are grouped into UC categories. The potentially risk-significant UC categories based on the loss of both CMTs or both accumulators are summarized in Table 8-1. Note, however, that the loss of I CMT and 1 accumulator is not a determining factor in whether core uncovery occurs, and these sequences are grouped based on other equipment successes and failures. The 1 CMT and 1 accumulator sequences with few other failures are generally grouped within OK categories, and the potential risk significance is not determined because core uncovery does not occur. The 1 CMT and 1 accumulator sequences with several other failures are generally grouped within UC categories, but are too low in frequency to be risk-significant.
The issues that are addressed by the short-term categories identified in Table 8-1 are not issues for the long-term analyses. For long-term cooling, the failure of CMTs or accumulators can impact the sump water elevation for natural recirculation. However, the amount of water in these tanks is relatively small compared to the amount of water in the IRWST, and thus the impact of CMT or accumulator fr.ilure on the sump water elevation is relatively small. Nevertheless, the possibility of up to 2 tanks failing is addressed for long-term cooling in the more limiting category of DVI line breaks without containment isolation.
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Comparison of PRA-Important Short-Term Scenarios to Long-Term Scenarios June 1997 oA3661w.wptib-061697
I 8-3 s
p Table 8-1 Potentially Risk-Significant Short-Term Cooling Categories for Loss of V CMTs/ Accumulators with Successful Containment Isolation Category Description Notes l UC1 2 CMTs fail for intermediate breaks DVI line break also falls within this and limited makeup inventory is category, but the case selected for analysis available until manual ADS is a non-DVIline break actuation UC2B 2 CMTs fail for medium breaks and l the accumulator inventory may l deplete prior to manual ADS actuation UC4 1 accumulator fails for large breaks, A potentially risk-significant sequence )
which reduces the makeup within this category that includes failure of inventory during LOCA reflood containment isolation is addressed in a
, separate case.
UCS 2 accumulators fail so that there is DVI line breaks and non-DVI line breaks no makeup inventory when ADS is fall within this category; a bounding DVI actuated at higher pressure line break case is selected for analysis.
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8-4 ADS The loss of 2 stage 4 ADS has been shown to be potentially risk-significant for accident sequences in which tnere are limited additional failures. For both short-term and long-term cooling, the ADS lines provide the venting capacity to keep the RCS pressure low enough to maintain water injection from either gravity draining of the IRWST or natural recirculation of the sump water, i l
For short-term cooling, the loss of 2 stage 4 ADS is addressed via category UC6. Through scoping analyses performed with the MAAP4 code, it was determined that the remaining 2 stage 4 ADS valves are not sufficient for breaks between 2 and 4 inches in diameter without crediting at least 1 stage 2 or 3 ADS valve. Two analytical cases are defined to illustrate the ,
extra venting capacity needed for the 2-inch break, and the sufficiency of the existing success criterion with a 4-inch break. The resulting impact on the PRA is addressed in Section 11.
For long-term cooling, a case is also defined to address 2 stage 4 ADS. Since the break location is likely to be covered, the break is not credited to provide additional venting capacity. Because of this,it was recognized that alternatives were needed if 2 stage 4 proved to be insufficient. Cases to examine an additional stage 4 valve, or 2 additional stage 2G valves, were defined if needed, with the resulting impact on the PRA to be addressed in Section 11.
Based on the baseline PRA impact, the short-term cooling process also identifies a large O
LOCA with no ADS for analysis as Case UC7. For long-term cooling, there may be no venting for a large LOCA when all ADS fail since the break is likely to be covered with water. The resulting impact on the Baseline PRA is addressed in Section 11.
RECIRCULATION PATHS The number of injection / recirculation paths is defined differently for the short-term and long-term cooling analyses. In the short-term cooling process, the most restrictive possibility of only 1 path on 1 injection line is considered. This is based on the expanded event trees as presented in Section 4. For long-term cooling, additional PRA quantification work was performed to justify that only 1 path being available is very unlikely, as is the case of only 2 paths available. However, the case of 2 paths being available is selected for the LTC analyses.
PCS The success of the PCS is explicitly identified for long-term cooling case definitions because the failure of the system could have an impact on the LTC results, when containment is not isolated. The operation of the PCS is much more likely than the failure of PCS. The case Comparison of PRA-Irnportant Short-Tenn Scenarios to Long-Term Scenarios June 1997 o:\3661w.wpf:1b 061697
_ _ . . _ . . ---~ _ _ . _ - _ _
i 8-5 i
1 definitions for the short-term analyses do not explicitly identify the status of the PCS. The '
( analysis assumption of containment backpressure is conservatively low and addresses the most likely condition of PCS operation.
i 8.2 SHORT-TERM AND LONG-TERM COOLING CASES FOR DVI LINE BREAKS WITH CONTAINMENT ISOLATION For long-term cooling, the equipment specification corresponding to the group of DVI line breaks with containment isolation is:
CMTs/ Accumulators: 3 ADS: 3 stage 4 Recirculation: 2 paths PCS: Successful For short-term cooling, categories UC1, UC5, and UC6 include DVI line breaks. Categories UCI and UC5 address the loss of CMTs or accumulators, and are discussed in Section 8.1 1 along with non-DVI line breaks. Category UC6 includes a DVI line break that becomes I potentially risk-significant due to the impact on the Baseline PRA. The resulting analytical case definition for case UC62 is compared in Table 8-2 to the above specification for an LTC analytical case.
O !
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l 8-6 Table 8 2 Comparison of STC and LTC Speci6 cation of DVI Line Break with Containment Isolation Equipment STC LTC Reason for Difference CMTsl 2 3 In STC, the concern is the water inventory Accumulators from the tanks that enters the RCS. In LTC, the water inventory that is spilled l directly out the break is available through I the sump. l ADS 2 stage 4 3 stage 4 For STC, scoping MAAP4 analyses indicate that 2 stage 4 ADS provide adequate venting for a 4-inch DVIline break. For LTC, preliminary LVCOBRAffRAC analyses indicated that 2 stage 4 ADS would be inadequate venting, and the PRA impact is addressed in Section 11.
Recirculation! I path in 1 line 2 paths in same See discussion in Section 8.1. l Injection or different lines PCS Not specified Successful See discussion in Section 8.1.
O l l
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9 Comparison of PRA-Important Short-Term Scenarios to Long-Term Scenarios June 1997 o:\3661w.wpf:ltr061697
8-7 8.3 SHORT-TERM AND LONG-TERM COOLING CASES FOR NON-DVI LINE Is' BREAKS WITHOUT CONTAINMENT ISOLATION V
For long-term cooling, a DVI line break was chosen to bound the non-DVI line breaks without containment isolation. Therefore, no cases are defined for the group of non-DVI line i breaks without containment isolation. 1 i
i For short-term cooling, DBA analyses of small-break LOCAs do not credit any containment backpressure above atmospheric. Therefore, the highest-frequency events with loss of containment isolation are already bounded by DBA analyses, are grouped in OK categories, and the potential risk significance is not determine d. The only exception is for large LOCA, where DBA analyses model containment pressuriiation. Based solely on the Baseline PRA impact, sequences lloca34, lloca39, and lloca40 are defined as potentially risk-significant.
These sequence:, fall within category UC8 and UC4, and are addressed by case UC42.
8.4 SHORT-TERM AND LONG-TERM COOLING CASES FOR DVI LINE BREAKS WITHOUT CONTAINMENT ISOLATION For long-term cooling, the equipment specification corresponding to the group of DVI line breaks without containment isolation is:
CMTsIAccumulators: 2 ADS: 4 stage 4 Recirculation: 2 paths PCS: Successful The definition of this case is based on success sequences silb40 and silb41 on the expanded event trees in Section 4. These paths are potentially risk-significant based only on the Baseline PRA impact. The additional specification of 2 recirculation paths and successful PCS l are based on the same justification summarized in Section 8.1.
l For short-term cooling, a DVI line break without containment isolation is analyzed as j case UCS. The equipment specification for this case is more limiting than identified for the
[ corresponding LTC case, because the short-term case also bounds other potentially risk- l sipificant accident sequences with neither accumulator injecting into the RCS. !
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9-1 9 TIH UNCERTAINTY ANALYSES FOR SHORT-TERM COOLING
.a O
Section 9 documents the thermalthydraulic analyses performed to support the low-margin, PRA-important accident scenarios defined in Section 6.3. The scope of these analyses is short-term cooling, from the initiation of the event until IRWST gravity injection is ,
established. The analysis methodology is consistent with design basis methods, codes, and l assumptions. The conservative assumptions used in the analyses bound the T/H l uncertainties identified in Section 2, providing a robust basis for the success criteria that have l been credited in the AP600 PRA. Section 9.1 documents the small LOCA analyses performed j with the NOTRUMP and LOCTA codes. Section 9.2 documents the large LOCA analyses performed with the WCOBRA/ TRAC code. Details of the analysis methodologies used are provided within each subsection. I 9.1 NOTRUMPILOCTA ANALYSES OF SMALL LOCAs i
i The potentially risk-significant accident scenarios identified in Section 6.3 were analyzed using the design basis NOTRUMP small LOCA analysis code and the LOCTA cladding heat-up code. Assumptions from Appendix K to 10CFR50 were used in both the NOTRUMP and LOCTA code calculations. Section 9.1.1 identifies the analysis methodology and Section 9.1.2 provides analysis results.
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'V TIH Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:1141897 I
9-2 1
l 9.1.1 NOTRUMPlLOCTA Analysis Methodology 9.1.1.1 NOTRUMP Analysis Methodology 9
The methodology presented in SSAR Section 15.6.5.4B (Reference 4) for the application of NOTRUMP to the AP600 design was used in TM uncertainty analyses with some exceptions, as follows:
- 1. Equipment failurcslassumptions were based on the potential for risk significance in the AP600 PRA, as defined in Section 63.
- a. The PRHR was not modeled in the TM uncertainty analyses.
- b. More than one single failure was considered in the TM uncertainty analyses.
- 2. The break discharge coefficient was either 0.7 or 1.0 based on consideration of conservatism for the case analyzed.
- 3. Credit for containment isolation was modeled in most cases. A containment backpressure of 25 psia was used in the containment isolation cases. This is the same value used in the SSAR small-break LOCA long-term cooling analyses (Section 15.6.5.4C of Ref. 4). When applied to short-term cooling, this pressure is conservatively low; the containment pressure is higher early in the accident progression, especially after Stage 4 ADS actuation.
- 4. The core quench model presented in Section 5.2 of Ref. 2 was also used in the thermalhydraulic uncertainty analyses.
The applicability of NOTRUMP to AP600 design basis accidents and PRA scenarios has already been presented in References 2 and 4.
9.1.1.2 LOCTA Cladding Heat-Up Methodology When a TM uncertainty case, as outlined in Section 6.3, results in noticeable core uncovery, a cladding heat-up analysis is performed. The cladding heat-up analysis is used to determine if adequate core cooling is maintained for the TM uncertainty scenario.
The Westinghouse small-break clad heat-up code (LOCTA) of Reference 6, as modified by Reference 7, is used to determme the peak cladding temperature of the lead rod. The cladding heat-up code of References 6 and 7 applies to the AP600 design because l
9 TlH Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:1b-061897 1
9-3
, 1. The AP600 uses the 17x17V5H fuel design already in use in conventional Westinghouse-designed PWRs. This fuel type lies within the assumptions and models employed in the code.
- 2. The low pressures seen in the AP600 small-break transients subsequent to ADS.
actuation are within the limits of the small-break heat-up code, since this code is a version of the Westinghouse large-break heat-up code, which must operate at low pressures.
- 3. The AP600 uses a 12-foot core design nd has peaking factors similar to current Westinghouse-designed operating reactors. Thus, the power shape used in the AP600
]
cladding heat-up calculation was taken from data for current core designs. The power shape based on current core designs, which are low-leakage-pattern designs with integral absorbers, while not representing the AP600 core design, bounds the AP600 core, which is a low-power-density design with less axial peaking.
l Additionally, the cladding heat-up analysis assumes a total core peaking factor (Fq ) of 2.60 l and an enthalpy rise peaking factor (Fm) of 1.65.
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TlH Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:1b-061897
9-4 9.1.2 NOTRUMPILOCTA Results The cases outlined in Table 6.3.2-2 are all LOCA scenarios, with breaks either in the RCS hot leg, CMT balance line, or the DVI line piping. The response of the AP600 plant to these events are presented in the following subsections.
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9-5 L 9.1.2.1 Case UC1 Results b
d Case UC1 is a 3.25-inch break in the RCS hot leg. Neither of the 2 CMTs is assumed to operate and therefore operator action to actuate the ADS must be assumed. Additional j assumptions are:
Credit for only 1 of 2 accumulators.
- ADS stages 1,2, and 3 ADS are assumed to be lost.
Credit for 4 out of 4 ADS stage 4 at 20 minutes (1200 seconds).
Only 1 of 2 IRWST lines is assumed available for injection. Further, failure of 1 of the 2 parallel paths in the available IRWST line is assumed.
i l Credit for contairunent isolation; containment pressure assumed to be 25 psia.
t l
l Figures 9.1.2.1-1 through 9.1.2.1-15 provide plots of the plant response and Table 9.1.2-1
- provides the sequence of key events. Figures 9.1.2.1-1 and 9.1.2.1-2 show the liquid and l steam break flow rates that lead to depressurization of the RCS, as seen in Figure 9.1.2.1-3, and draining of the RCS pressurizer (Figure 9.1.2.1-4). The 3.25-inch break size was selected
( as the largest break ci:.e that would not result in accumulator injection before the operator opens the ADS stage 4 valves at 20 minutes. Figure 9.1.2.1-3 shows the RCS pressure to be slightly above the accumulator cut-in pressure of 715 psia at 20 minutes. At 20 minutes, the operator opens all 4 ADS stage 4 valves (Figures 9.1.2.1-10 and -13), which results in rapid
! depressurization down to less than 50 psia. The accumulator injects as a result of the j depressurization (Figure 9.1.2.1-8), refilling the RCS downcomer (Figure 9.1.2.1-6), and recovering the core (Figure 9.1.2.1-12). The single accumulator runs dry at about j 1400 seconds and the IRWST begins to inject (Figure 9.1.2.1-14). Core uncovery occurs before operator action to open the ADS stage 4 valves (Figure 9.1.2.1-12), followed by a rapid '
- recovery of the core due to injection of the single accumulator. A minimum RCS mass of i 46,000 lbm occurs shortly after 1200 seconds (Figure 9.1.2.1-11), the time of maximum core uncovery.
A clad heat-up calculation for case UC1 (Figure 9.1.2.1-15) show a peak cladding temperature of 1157'F at 10.5 feet on the fuel rod occurring at 1200 seconds. These results are well below the 2200'F acceptance criterion.
I
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T/H Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:1b061897
9-6 r l
' .'able 9.1.2-1 UCI Sequence of Events (3.25-Inch flot-Leg Break)
Event Tune (sec)
Break Opens 0.0 Reactor Trip Signal 24 l
"S" Signal 30 l Steam Turbine Stop Valves Close 31 Main Feed Isolation Valves Begin to Close 31 ;
1 Reactor Coolant Pumps Stan Coastdown 46 I Top of Core Uncovers 990 ADS Stage 4 Opens (414 Valves) 1200 Accumulator Injection Starts (la) 1200 Top of Core Recovers 1205 IRWST Injection Starts 1405 Accumulator Empties (la) 1410 9
l I
l l
l l
l l
l 9
TlH Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf;16-061897
\
9-7 O
j Figure 9.1.2.1-1 l
Case UC1 Break Liquid Flow 3.25 inch Hot Leg Break /Woncol ADS /No Stage 1-2-3 ADS /No CMTs ,
l l
1000 l -
i 4
l m
- x 800 - -
E
_a l
I v
! I 600 -- l e ~
! ~
!(mJ o -
- 400 --
o
-t m
- 200 --
a 1 -
l l
0 0 5b0 10'00 15'00 20'00 25'00 3000 Time (S) iv o
- TlH Uncertainty Analyses for Short-Term Cooling June 1997 l o
- \3661w.wpf:1b-061897
9-8 O
Figure 9.1.2.1-2 Case UC1 Break Vapor Flow 3 25 Inch Hot Leg Break /Monual ADS /No Stage 1-2-3 ADS /No CMTs 100
^ _
cn x 80 --
E _
_a v _
6 0 .--
D _
w a -
in 40 --
o -
u_ _
m -
- 20 --
o
=E 0
0 5d0 10'00 15'00 20'00 25'00 3000 Time (s)
O TlH Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:1b41897
9-9 l
O l
l Figure 9.1.2.1-3 l
l l Case UC1 Pressurizer Pressure 3 25 inch Hot Leg Break /Wonual ADS /No Stage 1-2-3 ADS /No CMTs l
2500 l -
i 2000 - -
n o
- w -
- v
' 1500 --
O
~
- w -
l D
l >-
u a
m 1000 --
- m -
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! c_ -
i 500 --
1 -
l 0 'l '
O 500 1000 1500 2000 2500 300 0 Time (s)
U TlH Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:1M)61897
9-10 0
Figure 9.1.2.1-4 Case UC1 Pressurizer Levei 3.25 Inch Hot Leg Breck/Wonual ADS /No Stage 1-2-3 ADS /No CMTs 60 n
5 0 --
v a) cu 4 0 --
g
__J aa L._
a X
.__ 3 0 -- <
'::E _
I 20 l l l '} ' i !
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0 500 1000 1500 2000 2500 3000 IIme (S) )
O T/H Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:1b-061897
9-11
(~~\
G Figure 9.1.2.1-5 Case UC1 Core Makeup Tank Injection FIow 3.25 inch Hot Leg Break /Wonua ADS /No Stage 1-2-3 ADS /No CMTs 1
m u
a) _
(n x 5--
E _
_a
_J -
V 0
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3R:
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~
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.5-- l m j m -
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l
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l 'l l 0 500 1000 1500 2000 2500 3000 Time (s) r TlH Uncertainty Analyses for Short-Term Cooling June 1997 o;\3661w.wpf:1b-061897
9-12 O
Figure 9.1.2.1-6 Case UC1 Downcomer Mixture Level 3.25 inch Hot Leg Break /Wonual ADS /No Stage 1-2-3 ADS /No CMTs 35 30 --
m e -
v -
25 --
__ _ l CD -
a> 2 0 --
_.J -
- 1 CD -
u _
o 15 --
~ _
l x _
l 2 -
10 --
5 l l l l
l '
0 500 1000 1500 2000 2500 300 0 Ilme (S)
G T/H Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:1b-061897
9-13 l
l 1
O Figure 9.1.2.1 -7 Case UC1 Hot Leg To Pressurizer Mass F1 o w 3.25 Inch Hot Leg Break /Monual ADS /No StJge 1-2-3 ADS /No CMTs i 400 r
_ 1 l
]c) 200 --
~
\
m l
N -
E O -- o l
.a -
, J -
! v
- - 2 0 0 --
t o I cc
-4 0 0 -- I 3::
l o l -
l 1 -600-m m
, -800-l l
l -1000 i
l !'l '
l
! 0 500 1000 1500 2000 2500 300 0 Time (s)
O T/H Uncertainty Analyses for Short-Term Cooling Jee 1997 o:\3661w.wpf:1b-061897 l
9-14 l
O 1 Figure 9.1.2.1-8 Case UC1 AccumuIator Injection FIow 3.25 inch Hot Leg Breck/Monual ADS /No Stage 1-2-3 ADS /No CMTs 800 n -
cu - k c.n x 600 --
E
_a v
] 400__
G: _
3!: _
o u_
200 --
en en _
o zei -
0 l ''l l l l 0 500 1000 1500 2000 2500 3000 Time (s)
O TlH Uncertainty Analyses for Short-Term Cooling June 1997 o \3661w.wphlb-061897
9-15 l
c l0 Figure 9.1.2.1-9 Case UC1 First Through Third Stage ADS Vapor Flow 3.25 Inch Hot Leg Breck/Wonual ADS /No Stage 1-2-3 ADS /No CMTs l
1 1
- 1 m -
cn
~
N E 5-- l
_a '
v -
a) ~
+
o 0 K -
l
? % -
(
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0 500 1000 1500 2000 2500 3000 l Time (s) l l t i i V T/H Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpElb-061897 i
i
9-16 O11 Figure 9.1.2.1-10 Case UC1 4th Stage ADS Liquid Flow Through All Open Paths 3.25 Inch Hot Leg Breck/Monual ADS /No Stage 1-2-3 ADS /No CMTs 50
~
m o -
c) 40 --
W _
N ~
E a -
-J -
"30--
~
as
+ -
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o - l 2 -
Il k
' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' "' l 0 l l l '
'l l 0 500 1000 1500 2000 2500 300 0 Time (S) i l
l 9l T/H Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:1b-061897 l
1 9-17 ;
l
()
(>
Figure 9.1.2.1-11 Case UC1 Reactor System Coolant Inventory 3.25 inch Hot Leg Break /Wonual ADS /No Stage 1-2-3 ads /No CMTs m 400000 E _
a a _
v x
6 O
- 300000 --
C v -
C -
~
O O o
__ 200000 --
o -
O o -
E _
v m ~
x 100000 --
c.n u
O -
0 O
v
" 0
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0 5d0 10'00 15'00 20'00 25'00 300 0 Time (S) c Tai Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:1W1897
9-18 O
Figure 9.1.2.1 -12 Case UC1 Upper Plenum and Core Mixture Level 3 25 Inch Hot Leg Break /Wonual ADS /No Stage 1-2-3 ADS /No CWis 30 m
25 -- .
- -- -__ ~ r r ^
v
~
~
\
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G) -
L
~
o
~ _
X
._ 15 --
E _
i 10 '
l l l '
l 0 500 1000 1500 2000 2500 300 0 Time (s) I O
TIH Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:1b-061897
9-19 l
l (v3 l
i Figure 9.1.2.1-13 Case UC1 4th Stage ADS Vapor Flow 3 25 inch Hot Leg Break /Monual ADS /No Stage 1-2-3 ADS /No CMis 1200 l
~
m -
0 1000 --
D _
cn N -
- E -
800 --
v e ~
f')N L ~
600 --
a g
3: _
O
._. 400 --
- w -
m _
1 m
a 200--
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l l _
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0 i i
! 0 5d0 1000 1500 20'00 25'00 300 0 Iime (s)
+
f"%
TIH Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:1W1897 l
l
i 9-20 I l
O Figure 9.1.2.1-14 Case UC1 IRWST In eetion Flow 3.25 inch Hot Leg Break / Manual ADS /{o Stage 1-2-3 ADS /No CMTs 100 m ag o -
S 80 --
cn N -
E _
n 60 --
v -
a T -
, 40 --
O _
g _
t m
m 20 -- I o _
- E 0 l 'l l l l 0 500 1000 1500 2000 2500 3000 IIme (s)
G T/H Uncertainty Analyses for Short-Term Cooling June 1997 0:\3661w.wpf:1b-061897
l 9-21 1
O
- Figure 9.1.2.1-15 l
Case UC1 Peak Cladding l Temperature 3.25 inch Hot Leg Break /Wonual ADS /No Stage 1-2-3 ADS /No CMTs 1200 l 1000 --
m -
{
u_
v g 800 --
n - - l
's._/ o _
~
o -
$ 600 --
ct _
w E
o w _
400 --
200 '
l 'l ' ' '
'l ' '
l 500 1000 1500 2000 2500 300 0 Time (s) lO i
i T/H Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:1b-061897
9-23 9.1.2.2 Case UC2B Results
' O.d Case UC2B is a double-ended rupture of an 8.0-inch CMT balance line (inside diameter of 6.8 inches). This break is very much like a break in the RCS cold leg. Both CMTs are assumed to fail. In addition, the break is assumed to be in a location that prevents the faulted CMT from draining. Therefore, operation action to actuate the ADS must be assumed.
=
Credit for 2 out of 2 accumulators.
=
ADS stages 1,2, and 3 are assumed to be lost.
Credit for 4 out of 4 ADS stage 4 at 20 minutes (1200 seconds).
Only 1 of 2 IRWST lines is assumed to inject. Further, failure of 1 of the 2 parallel paths in an IRWST line to open is assumed.
Credit for containment isolation; containment pressure assumed to be at 25.0 psia.
Figures 9.1.2.2-1 through 9.1.2.2-14 provide plots of the plant response and Table 9.1.2-2 provides the sequence of key events. Figures 9.1.2.2-1 and 9.1.2.2-2 show the liquid and
()
steam break flow rates that lead to depressurization of the RCS, as seen in Figure 9.12.2-3, and draining of the RCS pressurizer (Figure 9.1.2.2-4). Due to the large size of the break and lack of CMT injection, the RCS rapidly depressurizes and accumulator injection (Figure 9.1.2.2-8) begins at around 150 seconds. Both accumulators continue to inject until around 1086 seconds, providing adequate injection to keep the core covered. At 20 minutes, the operator opens all 4 ADS stage 4 valves (Figures 9.1.2.2-10 and -13), which results in a further depressurization down to less than 50 psi. The depressurization brought on by the opening of ADS stage 4 is sufficient to allow for IRWST injection (Figure 9.1.2.2-14), which begins at 1388 seconds (188 seconds after opening ADS stage 4). The IRWST injection rate is sufficient to prevent core uncovery, stabilizing at about 90 lbm/sec, which matches the losses out of the break and ADS. Since core uncovery does not occur for case UC2B, the clad does not experience a heat-up, and a clad heat-up calculation is not performed.
l rh
/
l TIH Uncertainty Analyses for Short-Term Cooling June 1997 oM561w.wpf:1b-061897 i
9-24 Table 9.1.2-2 UC2B Sequence of Events (8-Inch CMT Balance Line) nummummuumummmmmmmmmmu Event Tune (sec)
Break Opens 0.0 Reactor Trip Signal 5 Steam Turbine Stop Valves Close 6 Main Feed Isolation Valves Begin to Close 6 "S" Signal 6 Reactor Coolant Pumps Start Coastdown 22 Accumulator Injection Starts (2/2) 150 Accumulators Empty (22) 1086 ADS Stage 4 Opens (44 Valves) 1200 IRWST Injection Starts 1388 9
O T/H Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:1t> 061897
l 9-25 i
O Figure 9.1.2.2-1 Case UC2B Break Liquid Flow 8 inch CMT Bolonce Line Break /Monual ADS /No Stoge 1-2-3 ADS /No CMTs 10000 M
w x 8000 - -
E -
_a v .
6000 - -
e D (m
v) "
a .
- 4000 - -
o 4
- k 2000 -
a
'=E l
' I " ' 4' ' ' ' ' ' ' ' ' ' ' ' ' '
0 l l
- O 1000 2000 3000 4000 Ilme (s) k.
\
[b T!H Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:1b061897
9-26 i
O Figure 9.1.2.2-2 Case UC2B Break Vapor Flow 8 inch CMT Balance Line Break /Wonual ADS /No Stage 1-2-3 ADS /No CMTs i
400 m _
m N ~
_a E 300 --
v .
$ ~
o 200 --
T -
O -
- u. -
m 100 --
m -
o \
s -
1 N gs s 0
0 1000 2000 30'00 4000 Time (s)
G T/H Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf 1b-061897
9-27 i
lO 1
l Figure 9.1.2.2-3 Case UC2B Pressurizer Pressure 8 Inch CMT Bolonce Line Break /Wonual ADS /No Stege 1-7-3 ADS /No CMTs 2500 2000 - -
~
m o ~~
m _
j 1500 - -
()
e ..
L
[ 1000 --
m -
v
' -{
Q- _
500 --
4-0 l ; ; t 0 1000 2000 3000 4000 l Time (S) l l
i O) r
\ !
T&I Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:1b-061897
9-28 O
Figure 9.1.2.2-4 Case UC2B Pressurizer Level B inch CMT Bolonce Line Break /Wanual ADS /No Stage 1-2-3 ADS /No CMTs 60 n
~
50 - -
v -
o g
o 40 - -
W e -
L
-+ ' _
x
- 30 - t
= 1 , j _ _= _n = _ _ . , , , nn 1
' ' ' ' ' ' ' ' i 20 l
! ! i i i , , , ,
0 1000 20'00 30'00 4000 IIme (s)
O T/H Uncertainty Analyses for Short-Term Cooling I"1997 o:\3661w.wpf:1b41897
9-29 l
O .
1 Figure 9.1.2.2-5 1
Case UC2B Core Makeup Tank injection Flow 8 inch CMT Bolonce Line Break /Wanual ADS /No Stage 1-2-3 ADS /No CMTs 1
i 1
1 m
o -
CD _
cn x .5--
E _
_a
._J -
v
<D -
\O e c 0 l
l cr -
5t:
o -
u_
.5--
m m -
o _
JE
-1 ' ' ' '
l l
l 0 1000 2000 3000 4000 Iime (S)
O T/H Uncertainty Analyses for Short-Term Cooling June 1997 c:\3661w.wpf;1W1897
)
9-30 0
Figure 9.1.2.2-6 Case UC2B Downcomer Mixture Level -
B inch CMT Bolonce Line Break /Wonual ADS /No Stage 1-2-3 ADS /No CMTs 35 m
~
30 --r v -
l 0
> _\ l a W
e 25 --
e u
_ I k I I I lk
~ -
I x
. _ _ 20 -- o
- E _
I
' ' ' , i ,
15 '
'l ' ' i i , , , , , ,
0 1000 20'00 30'00 4000 Iime (S)
G TlH Uncertainty Analyses for Short-Term Cooling June 1997 c:\3661w.wpf:1b-061897
9-31
/^\
l U Figure 9.1.2.2-7 Case UC2B Hot Leg To Pressurizer Mass Flow B Inch CMT Bolonce Line Greak/Wonual ADS /No Stage 1-2-3 ADS /No CWTs 2000 n
u -
0 1000 --
W _
N E
a -
__J _
0- F! l r e
~
C -
cr _
y -1000 - -
o -
m -20 0 0 - -
o ..
2 _
-3000 l l l 0 1000 2000 3000 4000 Time (S)
(
N l
T/H Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:1b41897
9-32 O
Figure 9.1.2.2-8 Case UC2B Accumulator injection Flow 8 inch CMT Bolonce Line Break /Wonual ADS /No Stage 1-2-3 ADS /No CWTs 500 I
n ,
o -
i
- 400 --
W _
N -
E
_a -
- 300 --
o A a
7 W :
3 200 -- "
q o -
LL. -
l m 1 m 100 --
o _
4 s _
0 l 0 1000 2000 3000 4000 Time (S)
G T/H Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:1b-061897
- 9-33 l
l
! /"N lU Figure 9.1.2.2-9 I Case UC2B First h Third Stage ADS Vapor Flow 8 inch CW) Bolonce LineT hBreak r o u g/Wo n u ADSa l /No Stage 1-2-3 ADS /No CMTs 1
~
A o
CJ _
(M
, x 5--
l E -
o g _
v, _
O C
- * ~
i o -
u_ -
.5--
i
- m -
o _
=E i j l _
_j i i . , , , i i i , , , , , , , , ,
0 10'00 20'00 30'00 400 0 Time (S) o
. (_)
T/H Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:1b41897 l
9-34 O
Figure 9.1.2.2-10 l Case UC2B 4th Stage ADS Liquid Flow Through All Open Poths 8 inch C64T Bolonce Line Areak/Wonual ADS /No Stage 1-2-3 ADS /No CMTs l
3000 1 o 2500 --
c) w _
N -
E -
-Q 2000 --
J _
U 1500 -
T _
3:
o -
__ 1000 --
u.
us -
en -
o 500 --
- aE
'~
0 0 10'00 20'00 3000 4000 Time (S)
O T/H Uncertainty Analyses for Short-Terrn Cooling June 1997 o:\3661w.wpf:1%1897
.. - . . .- -. -. . . _ = _ _ _ - - _
9-35 l l
l
/D l U <
Figure 9.1.2.2-11 Case UC2B Reactor System Coolant Inventory 8 Inch CWT Bolonce Line Greak/Wonual ADS /No Stage 1-2-3 ADS /No CMTs m 350000 l E -
.O -
a -
v
>, 3 0 0 0 0 0 - -
m _
o _
~
- =
~
e e
250000 -.-
v j 200000 --
o -
1 o -
l 0 - 1 E
e 150000 --
m _
x -
en o
100000 --
a o -
o -
e _
m ' ' ' ' '
50000 ' ' '
l l
0 1000 2000 3000 4000 Time (S)
O v
l T/H Uncertainty Analyses for Short-Term Cooling June 1997 l o:\3661 v.wpf:1b-061897 l
9-36 l
l l
O t
j Figure 9.1.2.2-12 Case UC2B Upper Plenum and Core Mixture Level 8 inch CMT Bolonce Line Break /Wonual ADS /No Stoge 1-2-3 ADS /No CMTs 28 l _
m 26--
v W '[h r -r ' 'I '
o I T
o 24 --
__J D l L -
a
-w -
x '
.__ 22 -- -
':lEE 20 l l 0 1000 2000 3000 400 0 IIme (s) l l
O T/H Uncertainty Ar.alyses for Short-Term Cooling June 1997 o:\3661w.w; 61b-06184/
9-37 O
i Figure 9.1.2.2-13 Case UC2B 4th Stage ADS Vapor Flow 8 inch CMT Bolonce Line Break /Wonval ADS /No Stage 1-2-3 ADS /No CMTs 120 l
m -
0 100 --
o ~
tn N -
E -
_J 80 --
v e
("}
" ^
60 --
l a
l
?
l O l __ 40 --
i u_ -
i
- 20 --
2 _
0 l l 0 1000 2000 3000 4000 Time (s)
O
' T/H Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:1b-061897
1 4-38 O
Figure 9.1.2.2-14 Case UC2B IRWST In'eetion Flow 8 inch CWT Bolonce Line Breck/Monual AD /No Stage 1-2-3 ADS /No CMTs 100
~
^
- ^-
- :L m _
O O 80 --
Cn N -
/
E _
f
_a 60--
c a
y 40--
o _
u -
m m 20 --
o _
2
' ' ' ' ' i , , , ,
i ! , , i , ,
0 l '
0 1000 2000 30'00 4000 I,lme (S)
O T/H Uncertainty Analyses for Short-Tenn Cooling June 1997 o:\3661w.wpf:1b-061897
. . . - - . - - . . - - . . . ~ . . - - - - . - . . - - _ - . - - ~ - - - . .
i~
l 9-39 l.
l i 9.1.2.3 Case UC5 Results O- '
- Case UC5 is a double-ended rupture of the DVI line piping. On the vessel side, the break is limited to 4 inches in diameter by an orifice. On the passive injection side, the break is -
limited by a 3.7-inch orifice. Additional assumptions are:
l~
Credit for the CMT on the intact loop. The CMT isolation valve on the faulted loop is assumed to fail closed.
! . Loss of both accumulators.
. ADS stages 1,2, and 3 are assumed to be lost. ,
c .-
Credit for 3 of 4 ADS stage 4, automatically actuated due to draining of the intact CMT.
i-Only 1 of 2 IRWST lines is assumed to inject. Further, failure of I of the 2 parallel l paths in an IRWST line to open is assumed.
Loss of containment isolation; containment pressure conservatively assumed to be l 14.7 psia.
Figures 9.1.2.3-1 through 9.1.2.3-15 provide plots of the plant response and Table 9.1.2-3 provides the sequence of key events. Figures 9.1.2.3-1 and 9.1.2.3-2 show the liquid and steam break flow rates on the vessel side of the broken DVI piping, which leads to depressurization of the RCS, as seen in Figure 9.1.2.3-3, and draining of the RCS pressurizer (Figure 9.1.2.3-4). The intact CMT begins to recirculate at about 40 seconds and injection occurs at 280 seconds. The intact CMT drains, resulting in ADS stage 4 actuation at l 1586 seconds (Figure 9.1.2.3-13). The actuation of the ADS stage 4 results in a depressurization down to less than 50 psia. The depressurization brought on by the opening of AD'.i stage 4 is sufficient to allow for IRWST injection (Figure 9.1.2.3-14), which begins at 2536 seconds (950 seconds after ADS stage 4 is opened). The IRWST injection rate is sufficient to recover the core, exceeding losses through the break and ADS stage 4 almost immediately after initialization at 2536 seconds.
A clad heat-up calculation for case UC5 (Figure 9.1.2.3-15) shows a peak cladding temperature of 1435 F at 11.25 feet on the fuel rod occurring at 2897 seconds. These results are well below the 2200*F acceptance criterion.
l-I O
^
TlH Uncertainty Analyses for Short-Term Cooling June 1997 oA3661w.wpf:1b461897
. . . ~=
9-40 Table 9.1.2-3 UC5 Sequence of Events (4-Inch DVI Line Break)
Event Tune (sec)
Break Opens 0.0 Reactor Trip Signal 11 "S" Signal 14 Steam Turbine Stop Valves Close 12 Main Feed Isolation Valves Begin to Close 12 Reactor Coolant Pumps Start Coastdown 30 ADS Stage 4 Opens (3/4 Valves) 1587 Intact-Loop CMT Empty (1/2) 1900 Top of Cover Uncovers 2360 IRWST Injection Starts 2536
)
Top of Core Recovers 3275 l
9' l
O TlH Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:1b&l897
9-41 I
O U
Figure 9.1.2.3-1 l Case UC5 Break Li FIow 40 IN DVI Breek/ Auto ADS. 1/2 CMTs. 0/2 Accums.NoqStoge uid 1-2-3 ADS. 3/4 Stage 4 2500
^
m x 2000 - -
E -
i a _
i
~
v l 1500 - i o
(_.)
2 a
oc
- 1000 - -
o u_
m -
- 500 --
o -
=E 0
0 10'00 20'00 30'00 4000 Time (s)
'O TlH Uncertainty Analyses for Short-Term Cooling June 1997 o \3661w.wpf:1W1897
4 9-42 O
Figure 9.1.2.3-2 Case UC5 Break Vapor Flow 40 IN DVI Brook / Auto ADS. 1/2 CWTs. 0/2 Accums. No Stoge 1-2-3 ADS, 3/4 Stage 4 150 m
en N
E
_a -
v 100 --
cu a -
O CE -
ii: -
o 50 --
u_
cn !
1 to _
o 2 _
l 1
l
' ! l I f I i
! ! ! I t I e i f e i t 0 1000 2000 3000 4000 Time (s)
O TlH Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf-1t>061897
9-43 !
I i
,i^%.
- v Figure 9.1.2.3-3 1
Case UC5 Pressurizer Pressure l 4.0 IN DVI Brook / Auto ADS. 1/2 CMTs. 0/2 Accums. No Stage 1-2-3 ADS. 3/4 Stage 4 2500 i l
2000 - -
~
m o -
m .
l v
" 1500 - -
- m U D a
m 1000 --
m -
D _
CL _
d 500 --
~
\
l 0 l ; i 0 1000 2000 3000 4000 Time (S)
O TlH Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:1bJJ61897 I
l
I
\
9-44 l
1 9ll Figure 9.1.2.3-4 Case UC5 Pressurizer Leve1 40 IN DVI Brook / Auto ADS. 1/2 CWTs. 0/2 Accums. No Stage 1-2-3 ADS. 3/4 Stage 4 60 n
50 - -
v e
e 40 - -
G J _
O L
a X
. 30 -
E _
20 ' '
l l
l 0 1000 2000 3000 4000 IIme (s)
O TlH Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:lt>-061897
l 9-45 l
n v
Figure 9.1.2.3-5 Case UC5 Core Makeup Tank injeetion Flow i 4.0 IN DVI Brook / Auto ADS. 1/2 CMTs. 0/2 Accums. No Stege 1-2-3 ADS. 3/4 Stoge 4 '
120
^ 10 0 --
O _
e w
N
~
E 80 --
_a -
l -
h w _ i 60 --
(~'
\ ~
o _
o _F cr 40 --
Sc o -
' 20 - -
j m
o I y 0- -
-20 l l l 0 1000 2000 3000 400 0 Iime (s) o v
T/H Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:1W1897
9-46 t l
O Figure 9.1.2.3-6 Case UC5 Downcomer Mixture Leve1 4.0 IN DVI Break / Auto ADS. 1/2 CMTs. D/2 Accums. No Stoge 1-2-3 ADS. 3/4 Stage 4 35 m 30 N
~ -
~ _
v _
_ L -
e _
o T
o 20 --
)
o -
)
~
.I $
- E 15 --
j
' ' ' ' ' ' i ' ' i 10 ' i i i ! , !
0 10'00 20'00 30'00 4000 Time (s)
O T/H Uncertainty Analyses for Short-Term Cooling jun,1997 o:\3661w.wpf:1b-061897
9-47 1
1 es U
1 1
i I Figure 9.1.2.3-7 l Case UC5 Hot Leg To Pressurizer Mass Flow 40 IN DVI Break / Auto ADS. 1/2 CWTo. 0/2 Accums. No Stage 1-2-3 ADS. 3/4 Stage 4 1
500 R 1
_ l g
e I
(M x 0- a = _ --
E
_a
_a v
(3 e G ~
c -500 - -
oc 3::
o u_
m
-1000 - -
m o -
CEE
-1500 ' ' '
l l
l 0 1000 2000 3000 4000 Time (s)
TlH Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:1b41897
9-48 O
Figure 9.1.2.3-8 Case UC5 Accumulator injtogeection Flow 40 IN DVI Break / Auto ADS. 1/2 CWis. D/2 Accums. No 1-2-3 ADS. 3/4 Stoge 4 1
m o
O _
W x .5--
E _
_o J
a) -
~
0 o
X -
3!::
o -
~
Lt.
.5--
en l (/J -
O _
2
-1 ' ' ' ' ' ' i
' i, i i , . , ,
l 0 10'00 2000 30'00 4000 Time (s)
O l T/H Uncertainty Analyses for Short-Term Cooling June 1997 c:\3661w.wpf:ll>&l897 i
i
9-19 O)
L l
I Figure 9.1.2.3-9 Case UC5 First Through Third Stage ADS Vapor Flow I 4.0 IN DVI Brook / Auto ADS. 1/2 CMTs. 0/2 Accums. No Stege 1-2-3 ADS. 3/4 Stage 4 l 1
i i
l m -
1 m i
\
E 5--
o \
i v _
as O
V
~
~
o 0 cr -
Sc _
o -
u- _
m .5--
m _
o
- !E -
-1 '
l l
l 0 1000 2000 3000 4000 '
, Iime (S) . I l
l l
l T/H Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:1W1897
j 9-50 l
O Figure 9.1.2.3-10 Case UC5 4th Stage ADS Li Flow Through All Open Paths 40 IN DVI Brook / Auto ADS. 1/2 CMT s .q0/2 u i dAccums. No Stage 1-2-3 ADS. 3/4 Stage 4 400
^
o a) -
CO x 300 --
E _
_a
-) ~
v -
D -
e a 200 --
Q: -
o _
1 100 --
m m -
U _
2 0 l l l 0 1000 2000 3000 4000 Time (s) l I
O TlH Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wptit>.061897
9-51
' f)
V Figure 9.1.2.3-11 Case UC5 Reactor S t inventory 40 IN DVI Brook / Auto ADS. 1/2 CMTe,y 0/2s Accums.
t e m C No o oStage l a n 1-2-3 A05. 3/4 Stage 4 m 400000 E _
- l J _
v x
6 O
~ 300000 -
C D -
C -
('")
C
_ 200000 --
o _
O o -
E _
D
- _ i m ('
x 100000 --
en
~
m I
o -
o -
o _
l CJ
- 0 l l l 0 1000 2000 3000 4000 Time (S)
/~h
)
T/H Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:114)61897
9-52 1
l O
Figure 9.1.2.3-12 Case UC5 U per Plenum and Core Mixture Level 4.0 IN DVI Break /AupoADS. 1/2 CWTs. 0/2 Accums. No Stogs 1-2-3 ADS. 3/4 Stage 4 30 n
25 --
v o
o 20 --
g
_.J e -
u W a -
~ -.
x h
._ 15 -- i s _
l l
10 l l l
O 1000 300 .9 00 4000 (S)
O T/H Uncertainty Analyses for Short-Term Cooling June 1993 o:\3661w.wpf.lb41897
! 9-53 I
i O
V Figure 9.1.2.3-13 l Case UC5 4th Stage ADS Va3or Flow l
4.0 IN DVI Break / Auto ADS. 1/2 CWTs. 0/2 Accums. No Stage '
2-3 ADS. 3/4 Stoge 4 200 m
o O _
m x 150 --
E _
_a
_ _s U
D tO V ~
o 100 --
QC -
se o _
u-50 --
en en -
o _ _
=E 0 i i '
0 1000 2000 3000 4000 Time (s) l
(}cs TlH Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf.It41897
9-54 O
Figure 9.1.2.3-14 Case UC5 IRWST i njeetion Flow 4.0 IN DVI Break / Auto ADS. 1/2 CMTs. 0/2 Accums. No Stoge 1-2-3 ADS. 3/4 Stoge 4 100 n
o S 80 --
cn N -
E _
f
_a
__i 60 --
o o
g Z -
3 40 --
o -
u-m m 20 --
o -
2E 0 l O 1000 2000 3000 4000 Time (s) i O
TIH Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661v.wpf:1W1897 l
l
9-55 l
O) 1 l
Figure 9.1.2.3-15 i Case UC5 Peak Cladding Temperature 40 IN DVI B r e c k / A u' t o A05. 1/2 CMTs. 0/2 Accums. No Stege 1-2-3 ADS. 3/4 Stage 4 1600 1400 --
n tu 1200 --
v _
- ' 1000 -- i (Q) a _
1 a 1 u 800 -- 1 o -
l 1
1 -
E -
o 600 --
H- -
400 --
t _
200 l l l l
2000 2500 3000 3500 4000 Time (s) l i
O T/H Uncertainty Analvses for Short-Term Cooling June 1997 o:\3661w.wpf:1b-061897
9-57 I
t
!- 9.1.2.4 Case UC61 Results l
Case UC61 is an double-ended rupture of the DVI line piping. On the vessel side, the break l is limited to 4 inches in diameter by an orifice. On the passive injection side, the break is limited by a 3.7-inch orifice. This case differs from case UC5 in that credit is given for an ;
accumulator, containment isolation and I less ADS stage 4 valve is assumed to open.
Additional assumptions are: ]
c j
1 l .
Credit for the CMT on the intact loop. The CMT isolation valve on the faulted loop is l assumed to fail closed. ,
1 1
Credit for 1 of 2 accumulators.
ADS stages 1,2, and 3 are assumed to be lost.
Credit for 2 of 4 ADS stage 4, automatically actuated due to draining of the intact CMT. !
l Gdy 1 of 2 IRWST lines is assumed to inject. Further, failure of 1 of the 2 parallel {
paths in an IRWST line to open is assumed.
l Credit for containment isolation; containment pressure assumed to be at 25.0 psia.
l l Figures 9.1.2.4-1 through 9.12.4-15 provide plots of the plant response and Table 9.1.2-4 i l provides the sequence of key events. Figures 9.1.2.4-1 and 9.1.2.4-2 show the liquid and I
{ steam break flow rates on the vessel side of the broken DVI piping, which leads to RCS l depressurization as seen in Figure 9.1.2.4-3, and draining of the RCS pressurizer l (Figure 9.1.2.4-4). The intact CMT begins to recirculate at about 40 seconds and injection occurs at 280 seconds. The intact CMT drains, resulting in ADS stage 4 actuation at 1608 seconds (Figure 9.1.2.4-13). The actuation of ADS stage 4 results in a depressurization
- down to less than 50 psia. The depressurization brought on by the opening of ADS stage 4 is sufficient to allow for IRWST injection (Figure 9.1.2.4-14), which begins at 3345 seconds (1737 seconds after ADS stage 4 opens). The IRWST injection rate is sufficient to recover the core, exceeding losses through the break and ADS stage 4 almost immediately after initialization at 3345 seconds. l A clad heat-up calculation for case UC61 (Figure 9.1.2.4-15) shows a peak dadding i temperature of 1235.3'F at 11.5 feet on the fuel rod occurring at 3803 seconds. These results j
, are well below the 2200 F acceptance criterion. )
!O
{ TlH Uncertainty Analyses for Short-Term Cooling June 1997
.,amm l
I -
9-58 l
l Table 9.1.2-4 UC61 Sequence of Events (4-Inch DVI Line Break)
Event Tune (sec) l Break Opens 0.0 Reactor Trip Signal 11 1
! "S" Signal 14 !
l !
l Steam Turbine St >p Valves Close 12 l Main Feed Isolation Valves Begin to Close 12 Reactor Coolant Pumps Start Coastdown 30 Accumulator Injection Starts (1/2) 680 ADS Stage 4 Opens (2/4 Valves) 1608 Accumulator Empties 1953 Intact-Loop CMT Empty (1/2) 2440 Top of Core Uncovers 3140 IRWST Injection Starts 3345 Top of Core Recovers 5200 l
l l
l O
Tai Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:lt41897
9-59 U
figure 9.1.2.4-1 Case UC61 Break Liquid Flow 4.0 Inch DVI Break / Automatic ADS /No Stage 1-2-3 ADS & 2/4 Stage 4 ADS 2500
^
m ,
x 2000 -- )
E -
.a .
~
1 v l 1500 - -
tO a ~
G) -
o ,
cc
^
l 1
3: 1000 - -
o w
m
- 500 --
O _
E lg
.Em 0 'l '
O 1000 2000 30'00 40'00 50'00 600 0 Time (s)
O T/H Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:1b-061897
9-60 9'
Figure 9.1.2.4-2 Case UC61 Break Vapor Flow 4.0 inch DVI Breck/ Automatic ADS /No Stage 1-2-3 ADS & 2/4 Stage 4 ADS 150 m
N E
_a -
v 100 --
a K -
3i: -
o 50 --
w m
m _
o OE _
0 l l 'l '
l 'l ' ' ' '
0 1000 2000 3000 4000 5000 6000 Time (s)
O' T/H Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:1b41897
i 9-61 i
e' Figure 9.1.2.4-3 Case UC61 Pressurizer Pressure 40 inch DVI Break / Automatic ADS /No Stage 1-2-3 ADS & 2/4 Stage 4 ADS 2500 2000 --
~
n o ~
m ss
" 1500 - -
(O%)
v m 1000 --
m -
D -
u _
Q- _
500 --
0 0 10'00 20'00 30'00 40'00 5000 600 0 Time (S)
O O
T/H Uncertainty Analyses for Short-Term Cooling June 1997 c:\3661w.wpf:lW1897
9-62 9
Figure 9.1.2.4-4 l Case UC61 Pressurizer Level 4.0 Inch DVI Break / Automatic ADS /No Stage 1-2-3 ADS & 2/4 Stage 4 ADS 60 n
~
50 - -
W ~
o o 40 -
g l
)
__; l cv -
u a
x .
.__ 30 - _ __
2 _
' ' ' ' ;i',ii,,ii,,,,,,,,,,
20 l 0 1000 2000 30'00 40'00 5000 6000 I,lme (s)
O TsH Uncertainty Analyses for Short-Term Cooling } " 1997 o:\3661w.wpf;1b-061897
l 9-63 r
L 4
. Figure 9.1.2.4-5 Case UC61 Core Makeup Tank Injection Flow 4.0 Inch DVI Breck/ Automatic ADS /No Stage 1-2-3 ADS & 2/4 Stage 4 ADS 12 0 ---
m -
u 100 --
D -
(.A N ~
E -
-Q
._.J 80 --
~
v
-s h
(%/ "
D a o0--
Of
_S 5 -
o
_ 40 --
LL. -
M i a 20 -- l
- lE i
0 O 1000 2000 3000 4000 5000 6000 IIme (s) i I
l l
- g~$ .
j V k@
TlH Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:1b41897 l l
l
9-64 91 Figure 9.1.2.4-6 Case UC61 Downcomer Mixture Leve1 :
4.D inch DVI Break /Actomatic ADS /No Stage 1-2-3 ADS & 2/4 Stage 4 ADS l 35 m30-w-v _
_L -
o D
h a 1 o 20 --
a -
X 2 15--
10 ' ' ' 'i''iiii>>iiii,,,,,,,
0 1000 20'00 30'00 40'00 50'00 6000 Iime (S)
G T/H Uncertainty Analyses for Short-Term Cooling I " 1997 o:\3661w.wpf It>&a1897
l l
1
-- 9-65 1
i n
( i w/
1 I
Figure 9.1.2.4-7 Case UC61 Hot Leg To Pressurizer Mass Flow 4.0 inch DVI Breck/ Automatic ADS /No Stage 1-2-3 ADS & 2/4 Stage 4 ADS )
500 l
l l
^ I o
e l m . Al l N 0 -
, i
~
E
_a
__i U
o (v) a -500 - -
cr -
3:
o _
en
-1000 - -
tn o
2
-1500 ' ' ' ' ' ' ' ''''''''
'l l l '
0 1000 2000 3000 4000 50'00 600 0 Time (s) l O
y/
TIH Uncertainty Analyses for Short-Term Cooling June 1997 o \3661w.wphlb-061897 l
l
1 9-66 O
Figure 9.1.2.4-8 Case UC61 Accumulator In'ection FI 4.0 Inch DVI Breck/ Automatic ADS /No Stage 1 ADS & 2/4 Stage DS 400 m
u -
G) _
cn N 300 --
E _
.a
_J e ..
$ 200 --
cr _
3::
o _
u_ -
100 -- '
m _
a - I
- A--
' ' t iiit , i,,i,,,,,,,,,
0 'l '
0 1000 2000 30'00 4000 50'00 600 0 l
IIme (S)
O T&l Uncertainty Analyses for Short-Term Cooling June 1997 0:\3661w.wpf:1b-061Sn7 l
l
i 9-67 1
l t
i Figure 9.1.2.4-9
! . Case UC61 First Through Third Stage ADS Vapor Flow l 4.0 Inch DVI Break / Automatic ADS /No Stage 1-2-3 ADS & 2/4 Stage 4 ADS 1
l
^ -
i l l w -
N E 5--
l
-Q v _
l rk D ~
l 1
Q) ~
o 0 cc I
in -
l O
u- _
m .5--
M _
o
!E l
-1 ' ' ' ' ' ' ' ' ' ie iiiiiiiiiii,i j 0 1000 20'00 30'00 40'00 5000 6000 IIme (S)
,r
(.
T/H Uncertainty Analyses for Short-Term Cooling g 3997 o:\3661w.wpf:ll>&l897
9-68 l
l O'
l l
Figure 9.1.2.4-10 Case UC61 4th Stage ADS uid Flow Through All Open Paths 4.0 inch DVI Breck/ Automatic Liq ADS /No Stage 1-2-3 ADS & 2/4 Stage 4 ADS 500 1
m o -
{
o 400 -- 1 Cn -
N -
E
_a -
__) ..
" 300 -- l
- l a -
o -
K _
g 200 --
o -
k _
m m 100 --
o -
2 -
t i I t i i i '
! I f I ! l t I i i l i i i 0 i l l
I i t e 1 e i i 4
0 1000 2000 3000 4000 5000 6000 Iime (S) 9 T/H Uncertainty Analyses for Short-Term Cooling June 1997 o \3661w.wpf:1W1897
9-69 O
~
Figure 9.1.2.4-11 Case UC61 Reactor System Coolant Inventory 4.0 inch DVI Breck/ Automatic ADS /No Stage 1-2-3 AOS & 2/4 Stage 4 ADS m 400000 E _
.o a -
v
~
x 6 .
O
~ 300000 -.
C e -
l c -
~
O _ 200000 -
O o _
E -
e m
x 100000 --
~
O -
a u -
0
~
0 0 'l l ''l '
l l 0 1000 2000 3000 4000 5000 600 0 IIme (s)
O T&I Uncertainty Analyses for Short-Term Coohng June 1997 o:\3661w.wpf:1b-061897
! 9-70 l
l 9
Figure 9.1.2.4-12 Case UC61 Upper Plenum and Core Mixture Level 4.0 inch DVI Break / Automatic ADS /No Stage 1-2-3 ADS & 2/4 Stage 4 ADS 28 1
26 --
m _
-+* _
U 24 --
ca 22 -- I s CD -
__J _
20 --
(o _
x 18 --
2 -
16 --
j4 i i i ! i i i i i iiiiiiiiiii! i i i i i i i 0 1000 2000 3000 4000 5000 6000 Time (s)
O TlH Uncertaint) Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:1W1897
9-71 l
O Figure 9.1.2.4-13 Case UC61 4th Stage ADS Vapor Flow 4.0 inch DVI Breck/ Automatic ADS /No Stage 1-2-3 ADS & 2/4 Stage 4 ADS 120 n _
o 100 --
o ~
l N -
E -
80 --
w
? P 1 l
T e i v .
a 60 --
cr -
3: _
o 40 --
[ _
h en a 20 --
E _
l 0 l 'l 'l 'l O 1000 2000 3000 4000 5000 600 0 Iime (S)
.O TIH Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:lt>O51897 I
l
9-72 O
Figure 9.1.2.4-14 Case UC61 IRWST Injection Flow 4.0 inch DVI Break / Automatic ADS /No Stage 1-2-3 ADS & 2/4 Stage 4 ADS 80 m -
o (v -
W N 60 --
E
_a -
v D
40 -
5 -
O l _
i Lt.
20 -- ]
en .
o 2 -
0 l 'l l ' ' '
'l O 1000 2000 3000 4000 5000 6000 Time (s) l T/H Uncertainty Analyses for Short-Term Cnoling June 1997 o:\3661w.wpf:1W1897
9-73 l
lQ l Figure 9.1.2.4-15 Case UC61 Peak Cladding Temaerature l
4.0 inch DVI Breck/ Automatic ADS /No Stage 1 2-3 ADS <t 2/4 Stage 4 ADS 1400 1200 --
n u_ _
1000 --
l i
e v -
' () j 800 --
o -
1 u _ l o _
Q.
E 600 --
m -
w _
i 1
400 --
l -
l _
l 200 l 'l 'l l l 3000 3500 4000 4500 5000 5500 6000 Time (s)
O U
T/H Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:1b-061897
9-75 9.1.2.5 Case UC62 Results Case UC62 is a 2-inch break in the RCS hot leg. Credit for one CMT was assumed and therefore automatic opening of the ADS was modeled. Additional assumptions are:
Credit for 1 of 2 accumulators.
One ADS stage 3 is assumed to open.
Credit for 2 out of 4 ADS stage 4.
Only 1 of 2 IRWST lines is assumed to inject. Further, failure of 1 of the 2 parallel paths in an IRWST line to open is assumed.
Credit for containment isolation, containment pressure assumed to be at 25.0 psia.
Figures 9.1.2.5-1 through 9.1.2.5-14 provide plots of the plant response and Table 9.1.2-5 provides the sequence of key events. Figures 9.1.2.5-1 and 9.1.2.5-2 show the liquid and steam break flow rates that lead to RCS depressurization, as seen in Figure 9.1.2.5-3, and draining of the RCS pressurizer (Figure 9.1.2.5-4). The RCS rapidly depressurizes until the '
RCS pressure approaches the steam generator secondary pressure (1100 psia). The RCS then stabilizes at this pressure as the steam generators still provide a necessary heat sink and CMT injection is maintaining RCS inventory (Figure 9.1.2.5-5). Due to the draining of the CMT, ADS stage 3 opens at 2020 seconds (Figure 9.1.2.5-9), starting a second depressurization of the RCS. ADS stage 3 provides sufficient depressurization to permit accumulator injection, which starts at 2120 seconds (Figure 9.1.2.5-8), with the accumulator emptying at 2912 seconds. Further depressurization due to ADS stage 3 and accumulato1 injection results in opening of 2 of 4 ADS stage 4 valves at 2715 seconds (Figure 9.1.2.5-10 and -13). By 3470 seconds, the CMT has completely drained and there is a period of no injection. During this period of no safety injection, the RCS continues to lose inventory and depressurize, leading to core uncovery at 4500 seconds (Figure 9.1.2.5-12). Prior to core uncovery, the IRWST begins to inject (Figure 9.1.2.5-14) at 4440 seconds, but at a rate initially too low to prevent core uncovery. A minimum RCS mass of 71,080 lbm occurs at 4570 seconds (Figure 9.1.2.5-11), the time of maximum core uncovery. However, the core uncovery is very slight (about 0.4 feet) and therefore, a significant heat-up of the cladding would not occur.
For this reason, a clad heat-up calculation was not performed.
O T/H Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf.lb.061897
. 9 76 l
! h-GI Table 9.1.2-5 UC62 Sequence of Events C-Inch Hot Leg Break) l l Event Tune (sec)
Break Opens ~ 0.0 Reactor Trip Signal 71 Steam Turbine Stop Valves Close 72 Main Feed Isolation Valves Begin to Close 72 "S" Signal 82 Reactor Coolant Pumps Start Coastdown 98 ADS Stege 3 Opens (12) 2020 Accumulator Injection Starts (1/2) 2120 ADS Stage 4 Opens (24 Valves) 2716 Accumulator Empties (12) 2912 IRWST Injection Starts 4440 l
_ CMT Empties $470 i
)
Top of Core Uncovers 4500 Top of Core Recovers l 4800 j l
l TlH Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wptib-061897
l 9-77 9
Figure 9.1.2.5-1 CASE UC62 Break Liquid FIow 2.0 inch Hot Leg Break / Automatic ADS /One Stage 3 ADS Volve & 2/4 Stage 4 ADS 400 n .
m
\
_a E 300_
v U O W
~
o 200 --
W -
o 1 w
~ L.
m 100 --
m _
o
- E -
t 'I l 1 l l I 1 l l ! I l l I t I i i e ' I t I 0 I i I
e l 0 1000 2000 3000 40'00 50'00 6000 ,
Time (s) 9 T/H Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:1b41897
I
\
9-78 m l U l Figure 9.1.2.5-2 CASE UC62 Break Vapor Flow 20 inch Hot Leg Break / Automatic ADS /0ne Stage 3 ADS Volve & 2/4 Stage 4 ADS 20 n
en N
_a E 15 --
v _
im a>
U -
o 10 --
~
ce -
3e -
o l u- _
en 5--
en _
\
o i
=E -
l l
^' ' ' ' ' ' ' ' ' ' ''' '
- 0 . . .
l 0 1000 2000 3000 40'00 50'00 6000 IIme (s) !
4 (v~)
j TlH Uncertainty Analyses for Short-Term Cooling June 1997
! o:\3661w.wpf:1W1897
i 9-79 l
O Figure 9.1.2.5-3 I l
CASE UC62 Pressurizer Pressure 1 2.0 Inch Hot Leg Break / Automatic ADS /0ne Stoge 3 ADS Volve & 2/4 Stage 4 ADS I 2500 l
2000 -. I o ~
Cn _
v
" 1500 --
- O; D _
i 6 -
m I I
m 1000 --
m -
D -
L o_ _
500 --
0 l 'l l '
i i 0 1000 2000 3000 4000 5000 6000 IIme (s) 9 T/H Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:1W1897
9-80 1
l Figure 9.1.2.5-4 CASE UC62 Pressurizer Leve1 2.0 Inch Hot Leg Break / Automatic ADS /0ne Stage 3 ADS Valve & 2/4 Stage 4 ADS 90 J l
.. 1 8 0 -- 1 l i
n
~
7 0 --
p e 6 0 --
V > '-
as
_J 5 0 -- <
ca L. -
2 -
x 4 0 --
.__ l
~
!aE _
30 --
' '''i'ii,'iii,,,ii,,,
20 0 10'00 20'00 30'00 40'00 50'00 600 0 IIme (S) l l
I
,f l v)
TlH Uncertainty Analyses for Short-Term Cooling g 3997 o:\3661w.wpf:1W1897
9-81 O
Figure 9.1.2.5-5 CASE UC62 Core Makeup Tank injection Flow 2.0 inch Hot Leg Breck/ Automatic ADS /One Stoge 3 ADS Valve & 2/4 Stage 4 ADS 100
^
o o 80 --
m N
E _
.a 60 -- \
" ~
\Y O o
Z -
, 40 --
o _
u_ -
_ t m f m 20 -- I o _
- E 0 l l 'l 'l l 0 1000 2000 3000 4000 5000 6000 Time (s)
O T/H Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf16061897
9-82 i
n U
Figure 9.1.2.5-6 l
CASE UC62 Downcomer Mixture Leve1 20 inch Hot Leg Break / Automatic ADS /One Stage 3 ADS Volve & 2/4 Stage 4 ADS i
35 l
m 30 --
~ -
l w flP' D
(3 >
U .
e -
_._J l e 20 --
D
~
~
x -
l .- -
l 2 15 --
l 10 ' ' ' ' ' ' ' ' ' '' ' ' ' ' ' ' ' ' ' ' '
l i 0 1000 2000 3000 4000 5000 600 0 Time (S)
/')
V TlH Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:1W1897
9-83 O
Figure 9.1.2.5-7 CASE UC62 Hot Leg To Pressurizer Mass Flow 2.0 inch Hot Leg Break / Automatic ADS /0ne Stage 3 ADS Volve & 2/4 Stage 4 ADS 600 n -
o 400 --
G) _
cn E -
-Q 200 --
v l [_
~
l_
0- ,- -
j o .
ic _
o
__ - 2 0 0 --
m m
o -400 --
2 -
l 1
-600 l l l l l 0 1000 2000 3000 4000 5000 6000 Time (S) i I
O i
Tai Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:1b-061897
9-84 l i t i y \
V !
l Figure 9.1.2.5-8 ;
1 l CASE UC62 Accumulator in ection Flow 20 inch Hot Leg Break / Automatic ADS /0ne Stage 3A Valve & 2/4 Stage 4 ADS 400' m
u -
o _
CO x 300 -- [
E _ 1
_a 1 a -
" _ l
( o -
~a 2 00 --
Q -
3: l o _
Y 100 --
m w -
o _
2 1
0
' '''' ' '''''''''- 1 I I i 0 10'00 20'00 3000 4000 5000 6000 Iime (S) l I
(~.,
i t)
TIH Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:1b441897
9-85 O
Figure 9.1.2.5-9 CASE UC62 First Through Third Stage ADS Vapor Flow 2.0 inch Hot Leg Break / Automatic ADS /One Stage 3 ADS Volve & 2/4 Stage 4 ADS 250
^ _
m x 200 --
E -
_a _
v 150 --
a; _
~
o
_ O, i
~
- 100 -- )
o -
1 1
~
l m _
50 --
7 0 l ;'l l r
0 1000 2000 3000 4000 5000 600 0 Ilme (S)
O T/H Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:1b-061897
9-86 O
Figure 9.1.2.5-10 1
l CASE UC62 4th Stage ADS Liquid Flow Through n: ' O n Poths 20 inch Hot Leg Breck/ Automatic ADS /0ne Stage 3 ADS Vo l ve & 4,p eStage 4 ADS l
100 1
? m
~
o o 80 --
m N -
E _
_a J
60 --
m w
(d o
cr -
g 40 --
o _
l t
u_ -
m m 20 --
o _
2 '
l 0
, , , , , , , , ,,,,, , , l,,,,,,,,,,,1 0 10'00 20'00 30'00 40'00 50'00 600 0 :
Time (s) 1 l
l t
I
- O TlH Uncertainty Analyses for Short-Term Cooling June 1997 o
- \3661w.wpf:1b-061897
9-87 O
Figure 9.1.2.5-11 CASE UC62 Reactor System Coolant Inventory 2.0 inch Hot Leg Breck/ Automatic ADS /One Stage 3 ADS Valve & 2/4 Stage 4 ADS
_ 350000 E
~
.c a
v .
x 300000 --
u _
O _
~
~
C o -
> 250000 --
c _
~ -
e _
200000 --
O -
O -
o _
E e 150000 --
m _
x -
u, O
100000 --
u a -
o _
e ' ' ' ' ' ' ' ' ' ' ' ' '
50000 'l l '
l '
l l 0 1000 2000 3000 4000 5000 600 0 Time (S)
O TIH Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:1b-061897 L
9-88 l
.O V
1 l Figure 9.1 2.5-12 CASE UC62 Upper Plenum and Core Mixture Level 2.0 inch Hot Leg Breck/ Automatic ADS /One Stage 3 ADS Volve & 2/4 Stage 4 ADS 28 m26- -
+ _
v -
24 --
D _
i r}s r
\ >
o -
J o 22 --
u
_3 x
m 20 --
l 0 1000 200b 3000 4000 5000 6000 Time (s) o V
l TlH Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:lbo61897
1 l
9-89 l
9 Figure 9.1.2.5-13 CASE UC62 4th Stage ADS Vapor Flow 2.0 inch Hot Leg Brook / Automatic ADS /0ne Stage 3 ADS Volve & 2/4 Stoge 4 ADS 100 n
o 0>
80 --
<.n N ~
E _
_a
_J -
60 --
O a
K _
g 40 --
o _
u.
m m 20 --
o _
E 0 ''l '''l ' ' ' '
l 0 1000 2000 3000 4000 5000 6000 Iime (S)
O T/H Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:1M61897
9-90 i
l
! r I.t t
l Figure 9.1.2.5-14 .
CASE UC62 IRWST injection Flow 20 inch Hot Leg Breck/ Automatic ADS /0ne Stage 3 ADS Volve & 2/4 Stage 4 ADS i 100 m
o -
J D 80 - -
f cn N -
E _
_a
_J -
60 - -
f% .
e .-
o M -
, 40 -- $
o _
u_
~
m m 20 - -
o _
=E
''''''*''i,- iii,iii 0
0 10'00 20'00 30'00 40'00 50'00 600 0 Time (S) l l
l TlH Uncertainty Analyses for Short-Term Cooling 3 3997 c:\3661w.wpf:1b41897
9-91 9.1.2.6 Case UC7 Results UC7 is a 9-inch-diameter hot-leg break with no credit for any of the ADS stages 1 through 4.
This break, on the boundary between MLOCA and LLOCA breaks, is expected to provide adequate depressurization via the break. A discharge coefficient of 1.0 was applied to the critical-flow calculation and a loss coefficient of 1.5 was used when the break was no longer critically limited. Other important assumptions are:
a Credit for 2 of 2 CMTs.
Credit for 2 of 2 accumulators.
=
Only 1 of 2 IRWST lines is assumed to inject. Further, failure of 1 of the 2 parallel paths in an IRWST line to open is assumed.
Credit for containment isolation; containment pressure assumed to be at 25.0 psia.
Figures 9.1.2.6-1 through 9.1.2.6-14 provide plots of the plant response and Table 9.1.2-6 provides the sequence of key events. Figures 9.1.2.6-1 and 9.1.2.6-2 show the liquid and steam break flow rates that lead to RCS depressurization, as seen in Figure 9.1.2.6-3, and draining of the RCS pressurizer (Figure 9.1.2.6-4). Due to the large size of the break, the RCS depressurizes rapidly and accumulator injection starts at 85 seconds (Figure 9.1.2.6-8). The CMTs cannot inject during the accumulator injection period (Figure 9.1.2.6-5) due to the common connection between the accumulator and CMT in the DVI piping network. This common connection remains at a pressure too high for CMT injection, which can only start after the accumulators have emptied at 473 seconds. The CMTs begin to inject and CMT injection continues to 1925 seconds. From 1925 to 2135 seconds, there is no injection.
However, the inventory injected by both accumulators and CMTs is adequate to prevent core uncovery until IRWST injection starts at 2135 seconds. The postulated 9-inch break can provide adequate venting so that the IRWST begins to inject at 2135 seconds and IRWST injection (Figure 9.1.2.6-14) rises rapidly to 50 lbm/sec, a flow rate that keeps the core covered (Figure 9.2.3.6-12). For this reason, a clad heat-up calculation was not performed.
Case UC7 was also analyzed using a break discharge coefficient of 0.7. The lower discharge coefficient restricted the break flow and resulted in a higher hydraulic resistance when the break was no longer critically limited. This case resulted in core uncovery and a core steam vapor temperature greater than 2200 F. The effect of this result on the PRA is addressed in Section 11.
O TlH Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:ll>051897
l 9-92 l
i O Table 9.1.2-6 UC7 Sequence of Events (9-Inch Hot-Leg Break)
- G
- Event Time (sec)
Break Opens ' O.0 Reactor Trip Signal 49 l
l Steam Turbine Stop Valves Close 50 l Main Feed Isolation Valves Begin to Close 50 "S" Signal 60 l Iwactor Coolant Pumpr Start Coastdown 76 l Accumulator Injection Starts (2/2) 85 Accumulator Empties (2/2) 473 CMTs Empty 1925 IRWST Injection Starts 2135 1
1 1
l i
1 l
l l
i l
Tiri Uncertainty Analyses for Short-Term Cooling June 1997
- o
- \3661w.wpf;1W1897
l 9-93
{
O Figure 9.1.2.6-1 ;
i Case UC7 Break Liquid Flow "
90 Inch Hot Leg Breck. 2/2 CWTs. 2/2 Accumulators. No Stage 1-2-3-4 ADS i
12000 l m
en 10000 --
N -
E -
D -
v 8000 - -
l l
1 0 !
~
j o 6000 -- )
Q: ..
I 1
~
3: l a - i 4000 - -
u_ +
en CD -
2000 -- l E -
i l
0 l
J 10'00 20'00 30'00 40'00 500 0 IIme (s) l O
TH Uncertainty Analyses for Short-Terrn Cooling June 1997 o:\3661w.wpf.lb-061897
)
l 9-94 l)
- V l
l Figure 9.1.2.6-2 l Case UC7 Break Vapor Flow
, 90 inch Hot Leg Break. 2/2 CMTs. 2/2 Accumulators. No Stoga 1-2-3-4 ADS l
l 500
^
en l x 400 --
! E -
.c _
l -
v 300 --
co _
( ~
1 O
K in 2 0 0 --
o l -
l LL. a i l %i
! i ,
l M l . I
! m 100 l -
o l 2 w ,- , .
_h hhA hm I I I I I I I f f I I i l l l t i t 0 I i i l t 1 i
I I
- 0 1000 2000 3000 4000 500 0 Time (s)
\
1 D
b
"~~
T/H Uncertainty Analyses for Short-Term Cooling june 1997 o:\0661w.wpf;1b41897 4
9-93 O
Figure 9.1.2.6-3 Case UC7 Pressurizer Pressure 9.0 inch Hot Leg Brack. 2/2 CMTs. 2/2 Accumulators. No Stage 1-2-3-4 Ab3 2500 2000 - -
a -
m .
v
" 1500 - -
a;
- O L
m 1000 -
w -
q) -
1 _
500 --
0 ! ; ; i 0 1000 2000 3000 4000 5000 :
Time (S) d!;
I 5If li certainty Analyses for Short-Term Cooling June 1997 o% zw.wpf:lb&>1897 I
9-96 n
V Figure 9.1.2.6-4 Case UC7 Pressurizer Level 90 Inch Hot Leg Break. 2/2 CMTs. 2/2 Accumulators. No Stage 1-2-3-4 ADS 60 m
50 - -
o O >
a> 40 - -
-J -
9 q)
L t
x
.__ 30 - t_. 1._
OE _
20 '
l l 0 1000 2000 30'00 40'00 5000 Iime (S)
O TlH Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:1b-061897
9-97 O
Figure 9.1.2.6-5 Case UC7 Core 9.0 inch Hot Leg Break. 2/2 M CMTs.
a k e u2 p/2Tank injection Flow Accumulators. No Stage 1-2-3-4 ADS 500 m
o o 400 --
W _
N E
_a -
J _
" 300 --
o e -
o -
T _
3 200 --
o -
L L- _
m m 100 --
o -
i 2 _
I ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' - -
O i . .
0 1000 2000 3000 40'00 5000 IIme (s)
O TlH Uncertainty Analyses for Short-Term Cooling Junetw7 o:\3661w.wpf:1W1897
9-98 O
i Figure 9.1.2.6-6 I
Case UC7 Downcomer Mixture Level 9.0 Inch Hot Leg Breck. 2/2 CMTs. 2/2 Accumulators. No Stage 1-2-3-4 ADS 35 i
~
i
)
s 30 -!
v l -
- o e iV _
l 1 o ~
i _J j e 20 --
u -
a _ g x _
I 2 15 -- !
l l -
I 10 l l l l
O 1000 2000 ,3000 4000 5000 l T.ime (s) i i
O !
TlH Uncertainty Analyses for Short-Term Cool.ing June 1997 o:\3661w.wpf:1b-061897 I
)
9 99 9
Figure 9.1.2.6-7 Case UC7 Hot Leg To Pressurizer Mass Flow 90 Inch Hot f.eg Break. 2/2 CWTs. 2/2 Actumulators. No Stage 1-2-3-4 ADS 500 n .
g 0- y . --
o _
cn -
N -
E -500 - -
~
_.J
-1000 -
+
o g >
o -
oc -
)
-1500 - -
l 3: ~
o ^
' -2000 - $ 1 1
m -
w -
o 2 -2500 - -
-3000 ' ' ' '
l-' ' '
'l ' ' ' ' ' ' ' ' '
O 1000 2000 3000 40'00 5000 Iime (s)
O T/H Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:1b 061897
l 9-100 l I l :
Figure 9.1.2.6-8 l Cose UC7 Accumulator injection Flow 9.0 Inch Hot Leg Break. 2/2 CMTs. 2/2 Accumulators. No Stage 1-2-3-4 ADS 1000 m l u -
S 800 -- l m L l N -
E _
_a
__J -
600 --
- e -
- s o
Z -
3 400 --
l O _
l u_ ~
m m 200 --
c l :llE l
l -
1
' ' ' ' ' ' ' ' ' ' ' ' ' iii!
0 i i i 0 1000 2000 3000 40'00 5000 Time (s)
+
- (m
< f(
TlH Uncertainty Analyses for Short-Term Cooling June 1997 oA3661w.wpf:1b4M1897
9-101 6
Figure 9.1.2.6-9 Case UC7 First Through Third Stage ADS Vapor Flow 9.0 Inch Hot Leg Brook. 2/2 CMTs. 2/2 Accumulators. No Stage 1-2-3-4 ADS 1
m _
m
~
N E 5--
_a v _
o _
~
o 0 Si: _
o -
Lt _
m .5--
m _
o
=E -
-1 ' ' '
l l
'l ' ' ' '
0 1000 2000. 3000 4000 5000 Time (s)
O T/H Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wptlb-061897
! 9-102 l O
!O Figure 9.1.2.6-10 Case UC7 4th Stage ADS Liquid Flow Throu 9.0 inch Hot Leg Break. 2/2 CMTs. 2/2 Acc umu l a t o r s .g hNo All Open Potha Stage 1-2-3-4 ADS i
1 l
L n
o a) -
cn x 5-- ,
l E _ !
l o l l
' v _
l l
(~~ 03 -
l
\, - !
0
- o l T -
l l 3 0 -
u_ -
.5--
m
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l O _
2 i
i
-1 ' ' ' '
i i
' ' ' iiiii'ii i i
- O 1000 2000 3000 4000 5000 l IIme (S) d
. .r
\%
T&l Uncertainty Analyt.es for Short Term Cooling June 1997
.; o:\3661w.wpf:1b-061897
l 9-103 Figure 9.1.2.6-11 Case UC7 Reactor System Coolant inventory 9.0 inch Hot Leg Break. 2/2 CWTs. 2/2 Accumulators. No Stage 1-2-3-4 ADS m 350000 E -
.a _
_a _
v x 300000 - -
u _
o _
~
C v
C 250000 -'-
C
_ 200000 --
o o
o E
e 150000 --
m x
w -
^
' 100000 --
o
_i
\ -
o -f o -
O -
x 50000 ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' '
l l 'l 0 1000 2000 3000 4000 500 0 Iime (s)
O
~
T/H Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:1b441897
9-101 i
I O
1 l Figure 9.1.2.6-12 l
Case UC7 Upper Plenum and Core Mixture Level 90 inch Hot Leg Break. 2/2 CMTs. 2/2 Accumulators. No Stage 1-2-3-4 ADS l
28 .
l i
4 n27- -
44 _
l l
1 l
- 26 - ;
! o
> .. i o ,
~
l
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)
o 25 --
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l l
23 l l 0 1000 2000 30'00 40'00 500 0 Time (S)
T/H Uncertainty Analyses for Short-Term Cooling l* M7 o:\3661w.wyttb-061897
9-105 9
Figure 9.1.2.6-13 Case UC7 4th Stage ADS Vaaor Flow 9.0 loch Hot Leg Breck. 2/2 CMTs. 2[2 Accumulators. >o Stage 1-2-3-4 ADS 1
m o -
CD _
V)
N 5--
E -
_o J -
v- ,
~
0 o
CE -
~
52 o _
LA
.5--
en en O _
2
' t i '
_j > t i t ! i i e iiiit i i i ! i i 0 1000 2000 3000 4000 5000 Time (s)
O T/H Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:1b 061897 m
l 9-106 l
iQ V l Figure 9.1.2.6-14 !
Case UC7 IRWST i njection Flow 9.0 inch Hot Leg Breck. 2/2 CMTs. 2/2 Accumulators. No Stage 1-2-3-4 ADS 80 l !
1 I
O y -
l M
N 60 -- 1 E l
, _ j d
~
v Q)
~
o 40 --
i K
1 3
l O l ,
' i 1
~
l 20 --
CO CD l -
I o 2 -
I I
0 I i i I
( 0 1000 2000 3000 4000 5000 IIme (s) i l
T.H Uncertainty Analyses for Short-Terrn Cooling June 1997 o:\3661w.wpf;1b-061897 i
9-107 9.2 .WCOBRAfrRAC ANALYSIS OF LARGE-BREAK LOCA Westinghouse applies the WCOBRA/ TRAC computer code to perform AP600 best-estimate large-break LOCA analyses in compliance with 10 CFR 50 (in the SSAR). The methodology used for the AP600 analysis is documented in WCAP-12945-P and WCAP-14171 (References 5 and 11).
Application of this methodology is conservatively simplified for AP600. The parameters important to the initial conditions and power distribution uncertainty components are set to bounding values establizied by sensitivity studies. The model uncertainty component is quantified in the same way as for three- and four-loop plants, with the other parameters set to those bounding values. The code uncertainty estimate based on direct comparisons with data, the uncertainty in the experimental data itself, is also considered in the overall uncertainty estimate. A discussion of the AP600 large-break LOCA uncertainty methodology is given in WCAP-14171 (Reference 11). A summary of the methodology is provided in Section 9.2.1, the plant response to the PRA TlH uncertainty cases in provided in Section 9.2.2, and the uncertainty evaluation for large LOCA is in Section 9.2.3.
9 l
l l
1 l
l l
O TlH Uncertainty Analyses for Short-Term Cooling June 1997 o \3/ '.1w.wpf:1b 061897
i i
l 9-108 9.2.1 WCOBRA/I'RAC Analysis Methodology O The thermalthydraulic computer code used to calculate realistic fluid conditions in the PWR during blowdo,wn and reflood of a postulated large-break LOCA is WCOBRAffRAC. This code is assessed against a variety of two-phase flow data from experiments that simulate important phenomena anticipated during postulated accidents and transients.
l These assessments demonstrate that WCOBRAffRAC is capable of modeling the following important phenomena occurring in a PWR during blowdown and reflood:
l =
Critical break flow Degraded pump performance e, Critical heat flux and dryout Fuel rod rewetting l Countercurrent flow-limiting phenomena in the vessel Multidimensional flow patterns in the reactor vessel
.Nonequilibrium heat transfer in the core and primary side of the steam generators Steamisubcooled water mixing phenomena Heat release from vessel internal structures j =
Temperature distribution and transient behavior in nuclea- fuel rods l The WCOBRATTRAC Code Qualification Document (Reference 5) contains a complete description of the models integrated into the code and justifies their applicability. The
, WCOBRAffRAC ability to mode! AP600 large-break LOCAs is discussed in detail in
)- Reference 11.
The beyond-DBA scenarios analyzed for the PRA TlH uncertainty evaluation do not involve !
any new phenomena are outside the scope of WCOBRAfrRAC applicability. {
t I
For the AP600 large-break LOCA TlH uncertainty analysis, the uncertainty methodology of the best-estimate LOCA analysis methodology in subsection 15.6.5.4A of the SSAR is applied.
The plant initial conditions for WCOBRAffRAC, including the RCS operating conditions and the core power parameters, are bounded in a conservative manner based on SSAR sensitivity studies investigating the range of AP600 possible values. Additional failures identified as important in PRA scenarios are assumed. i i The basis of the input decks for the beyond-DBA cases identified in Section 6.3 was adopted j from the most limiting split and guillotine break cases among the AP600 large-break LOCA
- spectrum.
i Hot assembly located under a guide tube Zero' percent steam generator tube plugging t ' T&{ Uncertainty Analyses for Short-Term Cooling - June 1997 4 o:\3661w.wpf:1b-061897 i-
.I
9-109 l
. PRHR fully operational High reactor coolant temperature - Tgt= 606.5 F
. Axial power shape no. 3 CD = 0.8, double-ended cold-leg break; CD = 1.0, split break
= Successful containment isolation The cases are analyzed through the limiting part of the accident - blowdown and reflood.
The parameters of principal interest are listed below, and are presented for each case in Section 9.2.2.
. PCT at any elevation for the five fuel rods modeled Hot rod cladding temperature transient at the limiting elevation for PCT Core fluid mass flows at top of core for hot assembly
. Core pressure
. Transient core and downcomer levels
. Break flow rates Cladding temperature at other elevations Hot assembly void fraction at several levels Accumulator water flow rate
. CMT flow rate 9
l l
l l
l l
O T/H Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:1b441897
110 i
9.2.2 .ECOBRAITRAC Results for Large-Break LOCA This section presents results for the MCOBRA/ TRAC analyses performed to address beyond- ,
DBA events for short-term cooling category UC4. Three cases are examined, and are '
. discussed in the following subsections:
A double-ended guillotine break for case UC41 A split break for case UC41
=
A double-ended guillotine break for case UC42 The uncertainty evaluation for the limiting case, which shows that the PCT remains below l 2200*F, is dccumented in Section 9.2.3.
9.2.2.1 HCOBRAfrRAC Results for Case UC41 DECLG Break Case Case UC41 is a double-ended cold-leg guillotine (DECLG) break. Based on the equipment specifications in Section 6.3, the following modifications were made to the limiting SSAR case (with CD = 0.8):
1 accumulator credited instead of 2 accumulators l 1 CMT credited instead of 2 CMTs iO The break was modeled to occur in one of the cold legs in the loop containing the CMTs.
l l Shortly after the break opens, the vessel rapidly depressurizes and the core flow quickly reverses. During the flow reversal, the hot assembly fuel rods dry out and begin to heat up (Figures 9.2.2.1-1 and 9.2.2.1-2).
i The steam generator secondary sides are assumd to be isolated immediately at the inception of the break to maximize their stored energy. The massive size of the break causes an immediate, rapid pressurization of the containment. At 1.2 seconds of the transient, credit is taken for receipt of an "S signal due to high-1 containment pressure. Applying the pertinent signal processing delay means that the valves isolating the CMTs from the DVI line begin to open at 2.4 seconds into the transient. Automatic reactor coolant pump trip occurs 17.4 seconds into the LOCA transient; until that time, the reactor coolant pumps are
! presumed to operate normally. Core shutdown occurs due to voiding. - No credit is taken for the control rod reactivity effect. l
!: - The system depressurizes rapidly (Figure 9.2.2.1-4) as the initial mass inventory is depleted i due to break flow. The pressurizer drains completely 7.5 seconds into the transient and
, accumulator injection commences at 14.9 seconds into the transient (Figure 9.2.2.1-5). The accumulator is modeled at nominal gas pressure (703 psig) and water volume (1700 cf)
I TlH Uncertainty Analyses for Short-Term Cooling June 1997
, o:\3661w.wpf:1b-061897 i
1
-. _ m.,, ,, . -.. .._,. ._, ,, , ,_, , . #_- , _ m.__,,.. ~ _ _ -, , , , , , ,,s=. 4
9-111 conditions. The CMT liquid level remains well above the ADS stage 1 actuation setpoint g during the blowdown phase of the CD = 0.8, DECLG LOCA transient. T The dynamics of the CD = 0.8 DECLG case are shown in terms of the flow rates of liquid, vapor, and entrained liquid at the top of the core (Figures 9.2.2.1-6 through 9.2.2.1-8) for the low-power periphery, open holelsupport column average power interior, and guide tube average power interior assemblies (the corresponding figure for the hot assembly is Figure 9.2.2.1-3). The cladding temperature transients are shown for the 6-foot,8.5-foot, and 10-foot elevations in Figures 9.2.2.1-9 through 9.2.2.1-11. Rod 1 refers to the hot rod at the maximum allowed linear heat rate, rod 2 represents the average rod in the hot assembly that contains the hot rod, rod 3 represents the open holeisupport column rod, rod 4 represents the guide tube rod, and rod 5 represents the low-power peripheral fuel assembly rod.
Figures 9.2.2.1-7 and 9.2.2.1-8 illustrate the impact of upper head drain through the guide tubes and upper support plate holes, respectively, on core flow. While liquid remains in the upper head above the top of the guide tubes, the guide tubes (Figure 9.2.2.1-8) are the preferred path for draining liquid into the upper plenum. Top-of-core flow is relatively stagnant for the first few seconds; once the upper head begins to flash, liquid drains directly down the guide tubes and that fraction that is able to penetrate into the core against continuous steam upflow does so, at flow rates exceeding 500 lb/sec of continuous liquid between 5 and 13 seconds.
Figure 92.2.1-7 presents the core flow behavior at the top of th. 13n hotelsupport column assembly. In contrast to the guide tubes, flow of liquid de.m into the core open holelsupport column locations does not become significant until about 6 seconds of the CD = 0.8 DECLG transient. There is a significant entrained liquid flow between 10 and 25 seconds exceeding 1000 lb/sec. After 7 seconds of transient, the downflow pattern in the open holeisupport column locations is established to the extent that vapor downflow is also predicted. In this time interval, vapor is flowing up out of the core in the guide tube locations.
Thus, there exists a good flow of liquid into the top of the core at these locations from before 10 seconds to almost 25 seconds. The flow in the open hole and guide tube assemblies is sufficient to quench the fuel in the assembly (rod 3 and rod 4, respectively) at the 6-foot, 8.5-foot, and 10-foot elevations as shown in Figures 9.2.2.1-10 through 9.2.2.1-11. !
Liquid downflow is delayed into the hot asserr bly. By 10 seconds into the transient, liquid that has built up in the global region above the upper core plate begins to flow through the plate at the hot assembly location and then proceeds into the core (Figure 9.2.2.1-3). i Significant flow of continuous and/or entrained droplet liquid into the hot assembly exists from 9 to 18 seconds. The liquid flow is not enough to quench the hot rod and hot assembly l rod at all elevations (Figure 9.2.2.1-1) although effective cooling is achieved. I TlH Uncertainty Analyses for Short-Term Cooling June 1997 v\3661w.wpf:1b-061897
k 9-112 Figure 9.2.2.1-6 demonstrates that liquid downflow exists through the top of ti.e peripheral Q~ core assemblies from the first fraction of a second through the end of blowdown in the CD = 0.8 DECLG transient. The low power of the fuel in this region leads to a small cladding temperature excursion for the peripheral rod, as shown in Figure 9.2.2.1-9. Some of the initial upper-plenum inventory passes through initially, cooling the fuel, and thereafter, liquid downflow proceeds continuously as that liquid draining from the upper head that does not pass directly into the core through open holeisupport column and/or guide tube channels passes via the global region above the upper core plate and is delivered into the low-power peripheral channel.
By 11 seconds into the transient, the entire length of the peripheral rods quench and remam so through the end of blowdown.
As the vessel depressurizes during blowdown, liquid inventory continues to be depleted and the hot assembly void fraction increases (Figure 9.2.2.1-12). Curve 1 of SSAR Figure 15.6.5A-61 is the void fraction at the bottom of the active fuel, curve 2 is at the core midplane, and curve 3 is at the top of the core. This results in reduced core flow and the i resulting cladding temperature excursion for the hot assembly; other regions of the core also undergo a cladding temperature excursion.
i 1
About 14.9 seconds into the transient, the accumulator begins to inject water into the upper l
. downcomer region, most of which is initially bypassed to the break. At approximately )
19 seconds, accumulator water begins to flow into the lower plenum. Lower plenum and downcomer liquid levels are plotted in Figures 9.2.2.1-13 and 9.2.2.1-14, and the hot assembly liquid level is shown in Figure 9.2.2.1-15. Break flow rates through the loop (Figure 9.2.2.1-16) arid vessel (Figure 9.2.2.1-17) sides of the break diminish as the transient progresses.
At approximately 65 seconds, the lower plenum fills to the point that water begins to reflood the core from below. The void fraction at the core bottom begins to decrease
~(Figure 9.2.2.1-12). As time passes, core cooling increases substantially and the cladding temperature begins to decrease as the core water level rises.
Simulating the availability of only 1 accumulator has the following effect on the development of the transient:
Due to the reduced net DVI injection, there is a delay of the momen' when liquid penetrates the core bottom. The bottom collapsed liquid level is recovered at 65 seconds instead of approximately 40 second.s as is the case of 2 accumulators available.
='
. The delay of the coolant penetration into the core results in an increase of the reflood PCT to 1773*F.
l l T&I Uncertainty Analyses for Short Term Cooling June 1997 o:\3661w.wpfho61897 l-l
. .-- , , - ~ . . ,
9-113 The quasi-steady state of the core being fully quenched is established 260 seconds after the break occurs, instead of around 120 seconds, as is in the case with 2 accumulators.
The hot assembly collapsed liquid level (Figure 9.22.1-15) reaches a quasi-steady plateau of approximately 5.0 feet, instead of 7.5 feet as in case of 2 accumulators.
The reduced net DVI injection in the period between 170 and 300 seconds into the transient does not affect the core cooling capabilities.
1 l
l l
0 i TlH Uncertainty Analyses for Short-Term Cooling % 3997 o:\3661w.wpf:1W1897 I
9-114
- s t
.:g l
- l Figure 9.2.2.1-1 l l
l Peak Cladding Temaeratures for Case UC41 Case UC41 (CD=0.8 DECLG Break /High RCS Temp)
PCT 1 0 0 PEAK CLADDING TEMP.
PCT 2 0 0 PEAK CLADDING TEMP.
PCT 3 0 0 PEAK CLADDING TEMP.
---PCT 4 0 0 PEAK CLADDING TEMP !
PCT 5 0 0 PEAK CLADDING TEMP 1
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t l LJ TlH Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:1b-061897
1 9-115 9
~
Figure 9.2.2.1-2 Hot Rod TULAD at Elevotion 9.11 Feet Case UC41 (CD=0.8 DECLG Break /High RCS Temp)
TCLAD 1 61 0 ELEV. 9.11 FT.
2000 _
~
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O 100 200 300 400 IIme (S) el 1 T/H Uncertainty Analyses for Short-Term Cooling June 1997 l o:'.3661w.wpf:1b-061897
9-116
,o V
~
Figure 9.2.2.1-3 Hot Assembly Top Flows Case UC41 (CD=0.8 DECLG Break /High RCS Temp)
FLM 27 15 0 L10 AXIAL MASS FLOW
FEM 27 15 0 ENT AXIAL MASS FLOW FCM 27 15 0 VAP AXlAL MASS FLOW 50 -
I
^ 40 --
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O 100 200 300 400 Time (s)
T/H Uncertainty Analyses for Short-Tenn Cooling June 1997 o:\3661w.wpf:1W1897
9-117 0
Figure 9.2.2.1-4a per Head Vessel Pressure Case UC41 Up(CD=0.8 DECLG Break /High RCS Temp)
P 77 2 0 PRESSURE 2500 2000 --
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1500 -
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O TM Uncertainty Analyses for Short-Term Cooling June 1997 oM661w.wpf:1W:897
9-118' l w
Figure 9.2.2.1-4b per Head Vessel Pressure Case UC41 Up(CD=0.8 DECLG Break /High RCS Temp)
P 77 2 0 PRESSURE 50 l
40 --
n o -
m _
CL 30 --
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0 100 200 300 400 Time (s) k lO T/H Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf;1b-061897
9-119 0
m Figure 9.2.2.1-5 Accumulator /CMT Injection Flows Case UC41 (CD=0.8 DECLG Break /High RCS Temp)
RMVM 30 2 0 ACC MASS FLOWRATE RMVM 32 5 0 CMT MASS FLOWRATE 1000
~
n CD -
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O TIH Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf IbG1897
l 9-120 l
O Figure 9.2.2.1-6 1
Peripheral Channel To Flows Case UC41 (CD=0.8 DECLG Break /p High RCS Temp) i FLM 24 15 0 L10 AXIAL MASS FLOW
FEM 24 15 0 ENT AXIAL MASS FLOW
FGM 24 15 0 VAP AXlAL MASS FLOW 1000 l ~
(
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-2000 ''''!''''l''''l''''
O 100 200 300 400 Time (s) l A
b T/H Uncertainty Analyses for Short-Term Cooling June 1997 0:\3661w.wpElb-061897 l
l l
9-121 O
Figure 9.2.2.1-7 Open Hole / Support Col. Channel Top Flows Case UC41 (CD=0.8 DECLG Break /High RCS Temp)
FLM 25 15 0 LIQ AXIAL MASS FLOW FEM 25 15 0 ENT AXIAL MASS FLOW
-- FGM 25 15 0 VAP AXlAL MASS FLOW 2000 m -
m ..
N E
-Q 1000 --
v m
1 G
o 0- - - - - - - - -- ~ ~ 3 4- J .,g ,d .j, y. [,,. (
vM_
d l
cr _
i l 1
l g _
o _
l I
-1000 --
w _
w ..
a
- E -
-2000 '''''''''''''''''iiii! iiiiiiii,i,,
0 1d0 2b0 3d0 400 Iime (S)
O TlH Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf 1b41897
9-122 r
L)
Figure 9.2.2.1-8 Guide Tube Channel To Flows Case UC41 (CC=0.8 DECLG Break /p High RCS Temp)
FLM 26 1' O L10 AXIAL MASS FLOW FEM 26 15 0 ENT AXIAL MASS FLOW FGM 26 15 0 VAP AXIAL MASS FLOW 2000
^
m N
E 1000 --
_a -
l..
v _
O -
o o-h-- ---- - --
M's. l c a . :'!.1,. ;:- ;c 1 l i
~
o -
cr _
g -1000 --
o -
- u. -
m m
-2 000 --
U _
s y
-3000 ''''''''''''''' ''''''''''
0 100 2b0 3b0 400 Time (s) l l i j
' r%
j A TlH Uncertainty Analyres for Short-Term Cooling June 1997 c:\3661w.wpf:Ib4)61897 l
l l __ _ . - . _ - - - _ -
9-123 0
Figure 9.2.2.1-9 Peripheral Channel Rod 5 TCLAD Case UC41 (CD=0.8 DECLG Break /High RCS Temp)
TCLAD 5 41 0 Elev. 6 ft TCLAD 5 57 0 Elev. 8 5 ft TCLAD 5 67 0 Elev. 10 ft 1200 1000 --
u.
v -
800--
o g
... W p
6
- +~' 600 - / 9' l'
, Ii
/ e
" ~ /, \
'i % i-tu -
/
o- 400 -- '
E - /
g
\
h,\
H
// I i' I
[
200 --
_ l l
0~''''l''''l''''l''''
100 O 200 300 400 l Time (s) l 9
TlH Uncertainty Analyses for Short-Tenn Cooling June 1997 o \3661w.wpf:1M61897
l l
9-124 O
Figure 9.2.2.1-10 Open Hole /Sup) ort Col. Rod 3 TCLAD Case UC41 (CD=0.8 DECLG Break /High RCS Temp)
TCLAD 3 41 0 Elev. 6 ft TCLAD 3 57 C Elev. 8.5 ft l TCLAD 3 67 0 Elev. 10 ft 1200
~
1000 -- / ~ ^ '.
./ t.
m ./ ~ ' g \.
La-.
v -
,, \ *;
l
// i T, l 800 - // i
(
O ~
-)j ,
l j'/
l 4
\a j 600 --i,1
// k l C /- 1 i
' ~
I 'l l / !3 0 ~
l / k i a- 400 -- / t i ij E -
3 j U -
( t _.
p 200 --
~
l 0 ''''l''''l''''l''''
0 100 200 300 400 l Iime (s) i i
i O
T/H Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wp01W1897
9-125 9
Figure 9.2 2.1-11 Guide Tube Rod 4 TCLAD Case UC41 (CD=0.8 DECLG Break /High RCS Temp)
TCLAD 4 41 0 Elev. 6 ft TCLAD 4 57 0 Elev. 8 5 ft
TCLAD 4 67 0 EIev. 10 ft 1200 1000 -- , , ,
m 4
I, f' ".
g ,r , N L, *
//
O
\
800 - f'i f, i i,.
fl // \ )
o .
- // i I
' Lt '/ l I j 600 -- I f i O l I u -
/ l a) -
! l jll cL 400 -- fj j i E -
r, !,
O 's F--
200 - -
0 '''l''''''''''''''l''''
O 100 200 300 400 Time (s)
O' T/H Uncertainty Analyses for Short-Terrn Cooling June 1997 o:\3661w.wp61b-061897 l
l l
9-126 lo
~
Figure 9.2.2.1-12 case Uc41 ([D=08 DECLG Break /High RCS Temp)
~~~
_.._._.2 1 p 1
ip. g i ,r-,
q . . r .y . t,. ., ,,i i ) i
'~
~l i f 1 hlf l
~ '
c l L lj l! . El l ll i
$ l I u d !' l u l i
);j
._ 1 i i O g ll li, 8-: j ,
j '(i
, l ll l ,,jl Nni ;h{;h4{Q ll [
is I i i i 2-- ,,,g p ll
, ,i
'-- +-- 6 0 'l 1 ;-
! 0 100 200 300 400 IIme (s) l O
m Unmtggalyses for Short-Term Cooling June 1997
I 9-127
)
G Figure 9.2.2.1-13 Lower Plenum Collapsed Li Level Case UC41 (CD=0.8 DECLG B r e a k /qu i dHigh RCS Temp)
LO-LEVEL 1 0 0 COLLAPSED L10 LEVEL 7
m - -
~ _
, 7 7 .._
- _ j v6- -
I
~
~
o 5- -
f O -
3
=
cr
. 3-~
O en 2--
f c 1 o _
-1__
o -
O 0 ''''l''''l''''l''''
100 0 200 300 400 Time (s) l I
TlH Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf;1b-061897
9-128 O i a
Figure 9.2.2.1-14 l Downcomer Colla) sed Liquid Level l Case UC41 (CD=0.8 DEC_G Break /High RCS Temp) l LQ-LEVEL 10 0 0 COLLAPSED L10 LEVEL J ,
30 I L
m
~
v 25 --
1 1
l e
[ 20 -I -
.__i Q
kj T o :
._J ~
i
~C 10 - - 1 l
D m _-
Q- -
l 5---
[
l 0 -
l O -
0 ''''l''''l''''l''''
0 100 200 300 400 Time (s) l l
i-f TlH Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf;1b-061897
9-129 9\
Figure 9.2.2.1-15 Hot Assembly Collapsed Li Level Case UC41 (CD=0.8 DECLG Break /quidHighRCS Temp)
LO-LEVEL 5 0 0 COLLAPSED L10 LEVEL 12-n -
+ _
10 --
o _
g 8--
u -
6--
r 9
g j l 5 :
A/tetp(fVf{ ,$9 ;(
y 4--
o -
I en -
Q. -
~
2- -
O -
O -l h '
0 ''l''''l''''l''''
0 100 200 300 400 Time (s)
O !
TlH Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf;1b41897 .
)
.=
9-130 b !
l .
I Figure 9.2.2.1-16 l
Loop Side Break Flow Case UC41 (CD=0.8 DECLG Break /High RCS Temp)
RMVM 60 4 0 MASS FLOWRATE 15000 n .
en N
E l .O -
v 10000 --
I O ~*
o l
Z -
)
3: -
! O i 5000 --(
x )
en tn -
C l
3 -
0 'l''''l''''l''''
0 100 200 300 400 IIme (S)
!O TIH Uncertainty Analyses for Short-Tenn Cooling June 1997 c:\3661w.wpf:1b-061897
1 9-131 h
i l
Figure 9.2.2.1-17 Vessel Side Break Flow '
~~
Case UC41 (CD=0.8 DECLG Break /High RCS Temp) [
RMVM 61 1 0 MASS FLOWRATE '
1 30000 '
(n 25000 ---
N E
_a v 2 0 0 0 0 --
~
O o 15000 --
OC -
3: -
O -
- 10000 - -)
u_ -
en -
gn _ l o 5000 -- !
s -
0 l' '''''l''''
, l 0 100 200 300 400 IIme (S) .
Ol TlH Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:Ib-061997 I
. - - . _ - _ . - . .. .. . . _~ ,- .. ., . - - . - . . . . - -. - ..
9-133 4 4 l
9.2.2.2 ECOBRA/ TRAC Results for Case UC41 Cold-Leg Split Break Case !
U This UC41 case has the same initial RCS conditions as the previous UC41, except that a cold-leg split break.is simulated with CD = 1.0. The set of figures prepared for this scenario
! (Figures 9.2.2.2-1 through 9.2.2.2-16) is the same as those for the DECLG break UC41 case, ,
! except that only the split break flow is shown in Figure 9.2.22-16.
p )
i
' Generally, the plant behavior is the same as for the DECLG case with the exception that the PCT during the reflood period reaches 1786'F - slightly higher than the DECLG break case. !
l 1 i
The vessel-bottom collapsed liquid level is recovered as fast as in the UC41 DECLG break i
. case. After steady CMT injection is established, the downcomer level (Figure 9.2.2.2-14) stays at around 15 feet, compared to 16 feet for the UC41 DECLG break case. The core collapsed I liquid level (Figure 9.2.2.2-15) is the same as for case UC41 (around 5 feet).
l (M
V .
1 b
(>
TlH Uncertainty Analyses for Short-Term Cooling June 1997 oA3661w.wpf:ll>O61997
9-134 I
l 9l 1
Figure 9.2.2.2-1 J 1
i Peak Claddin Temaeratures for Case UC41 '
Case UC41 (CD= 0 DECLS Break /High RCS Temp)
PCT l 1 0 0 PEAK CLADDING TEMP.
PCT 2 0 0 PEAK CLADDING TEMP ;
PCT 3 0 0 PEAK CLADDING TEMP.
PCT )
4 0 0 PEAK CLADDING TEMP PCT 5 0 0 PEAK CLADDING TEMP. I 2000 _
1800 -- _
m 1600 - <
' \, 's W : -
1400 -}
e 1200 -
- O u
" 1000 - : ,. p. ~ ~--ay C .// N.q D
800 - ej
~Q
,/
.//
46 a ;
,fy , , .
\g E 600 - :; ,il( ,j ,.- .. g) i 400 - \c', i B
A d- a_ai 200 --
0 ''''l+',,i,,i,,,,,,,,,,,,,,,,,,,
0 100 2b0 360 400 I,lme (S)
O T/H Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:1W1997
i 9-135 f
i Figure 9.2.2.2-2 Hot Rod TCLAD at Elevotion 9.11 Feet Case UC41 (CD=1 0 DECLS Break /High RCS Temp)
TCLAD 1 61 0 ELEV. 9.11 FT.
2000 -
f 800 -}-
1600 -- _
n _
u_ -
v 1400 --
e 1200 -I L
j 1000 - {
a -
g 800 - }-
Q. -
E
~
c) 600 - -
p _
l 400 -- -
_ U_- __
u __ -.
I 200 -_-
~
0 ''''l''''l''''l''''
100 0 200 300 400 Time (s)
O TlH Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf.1b4M1997
9-136 O ,
Figure 9.2.2.2-3 Hot Assembly Top Flows Case UC41 (CD=1.0 DECLS Break /High RCS Temp)
FLM 27 15 0 L10 AXIAL MASS FLOW FEM 27 15 0 ENT AXIAL MASS FLOW
FGM 27 15 0 VAP AXIAL MASS FLOW 50 _
~
^ 38 --
m N -
E 2 6 ---
_a -
~
v 14__ .
2- _ _. __
~~ l g . ..
, il v o - ~
i 3: - ; o - { - _ m -4 6 -- o ~
- !E - 5 8 -
~
-70 ''''l''''l''''l''''
0 100 200 300 400 Time (s) G T&l Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf.lb41997
l 9-137 l /~'N k_r l l Figure 9.2.2.2-4a l per Head Vessel Pressure Case UC41 Up(CD=1.0 DECLS Break /High RCS Temp) P 77 2 0 PRESSURE 2500 2000 -- o - m C1. l
,s., v 1500 ---
I t U D - g 1000 -- m D - L _ Q_ _ 500 -- 0 i 'l' ; O 100 200 300 400 l Time (s) V TlH Uncertainty Analyses for Short-Term Cooling June 1997 ( o:\3661w.wpf.It>061997 i l
9-138 9 Figure 9.2.2.2--4b per Head Vessel Pressure Case UC41 Up(CD=1.0 DECLS Break /High RCS Temp) P 77 2 0 PRESSURE 50 40 -- o - cn _ v "30-- a) _ [ 20 -- ~ cn a) - L _
)
Q_ _ 10 -- l
~
1 0 ''''l''''l''''lii! ' ' ' l 0 100 200 300 400 IIme (S) O T!H Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:Ib-061997
9-139 j o %) 1 Figure 9.2.2.2-5 Case UC41 Accumulator /CMT Injection Flows (CD=1 0 DECLS Break /High RCS Temp) RMVM 30 2 0 ACC MASS FLOWRATE J RMVM 32 5 0 CMT MASS FLOWRATE I 1000 I m j cn - i N 800 -- E _a - v 600 -- O,A D
~
c - T - 3: 400 -- o _ Lt. cn cn 200 -- a -
,3....
p- __, I
' ' ~
0 ''!''''l- ~l'''' 0 100 200 300 400 Ilme (S) o a T/H Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:1b-061997
9-140 0 Figure 9.2.2.2-6 Peripheral Channel To Flows Case UC41 (C0=1.0 DECLS Break /p High RCS Temp) FLM 24 15 0 L10 AXIAL MASS FLOW
----FEM 24 15 0 ENT AXIAL MASS FLOW FGM 24 15 0 VAP AXIAL MASS FLOW 1000 n e en -
N E _a ^ v ' ' - - - - ' ' - - ' 0-
'i H -
I - ' ' F , d < e
' i[' '-
l i i l I' i 4 I g
- _ i I i o ' '
cr I 3: f
-1000 --
1 _ en _ en a _ 2
-2000 ''''l''''l''''l''''
0 100 200 300 400 Time (S) l 1 l TIH Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:Ib41997 t
l 9-141 l l I - ,73 V l Figure 9.2.2.2-7 l Open Hole / Support Col. Channel Top Flows 1 Case UC41 (CD=1.0 DECLS Break /High RCS Temp) FLM 25 15 0 L10 AXIAL MASS FLOW FEM 25 15 0 ENT AXIAL MASS FLOW
----FGM 25 15 0 VAP AXlAL MASS FLOW 2000 l
n - m - 1 E - c 1250 - - v O d e o 500 - {t 3 cr _g g _ 4-g o -i _ . t u _ _. . _. _ ._ ~ .g . -3. w-- i 1 : . ,,a,;, p ,, L g g }gJ. ,ii n 1 I l u_ _%,T~ i i ,i
-250 - i , I w -i. I m / I
- i o i,t
':lE - il
_(
-1000 ''''l''''l''''l''''
0 100 200 300 400 l Time (S) l TlH Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:1b-061997 l l l
9-142 i O' Figure 9.2.2.2-8 Guide Tube Channel To Flows Case UC41 (CD=1.0 DECLS Break /p High RCS Temp) FLM 26 15 0 L10 AXIAL MASS FLOW FEM 26 15 0 ENT AXIAL MASS FLOW FGM 26 15 0 VAP AXlAL MASS FLOW 2000
^
m
~
en \ E 1500 -- O - 1000 - h l C ' QC 3: 500 - - O k. d l LL l. l I,1 i r l C 0- n-- d "' '- '~;^'*' ~ ~:r?N I-) 1 e
}ll ,
I -
-500 il''''l''''l''''
O 100 200 300 400 Iime (S) O TlH Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf;1t>.061997
9-143 1 Figure 9.2.2.2-9 , Peripheral Channel Rod 5 TCLAD Case UC41 (CD=1.0 DECLS Break /High RCS Temp) TCLAD 5 41 0 Elev. 6 ft TCLAD 5 57 0 Elev- 8.5 ft TCLAD 5 67 0 Elev. 10 ft 1200 1000 --
~
n W ~ v - 800 -- O e u j . ~.g 3 600 -
,,90 ', f a // 1 .
u -
, (i ,
O ~
'/
I i o- 400 -- < s E - / i i e \ \ g_. I(! I ik N.m __ ~- j _ 200 -- 0
''''l''''l''''li'ii'i 100 0 200 300 400 Iime (s)
(~~ TlH Uncertainty Analyses for Short-Term Cooling g 3997 o:\3661w.wpf.lb&l997
9-144 l Figure 9.2.2.2-10 Open Hole / Support Col. Rod 3 TCLAb Case UC41 (CD=1.0 DECLS Break /High RCS Temp) TCLAD 3 41 0 Elev. 6 ft TCLAD 3 57 0 Elev. 8 5 ft TCLAD 3 67 0 Elev 10 ft 1200 - 1000 - - W ~
/^' \
,/N ,
ff L
\
is / ./ f lg 800 -p / ./ I -g a; ! /f/ i i
$ i. // i t.
_ 600 - it / 1,
/
a .
/ l j
O -
/ I ct 400 -- t/ li h E -
d i l i O 1
- ( =_-
200 -- 0 '''l''''l''''l'''' 0 100 200 300 400 Time (s) O. T/H Uncertainty Analyses for Short-Term Cooling June 1397 o:\3661w.wpf:1b-061997
l 9-145 O G l Figure 9.2.2.2-11 l l Guide Tube Rod 4.TCLAD Case UC41 (CD=1.0 DECLS Break /High RCS Temp) l TCLAD 4 41 0 Elev. 6 't
---- TCLAD 4 57 0 Elev. 8 ,e ft l
---- TCLAD 4 67 0 Elev. 10 ft 1200 i
l 1000 -- _. l m
/
.-
- s. \
w
,/ ' N i v /- ] %
800 - t' \ , p 'r; llj 1 f.t
\.
\ @
' g ik /
/ I
/ 1 jii 3 600 - ,' !
I i C /j i ( j i I O - j l I o- 400 -- f / 'g i E -
! i b ,
( O _ t ' l-- _ 200 -- 1 0 ''''l'''''''''''''''''''''''' 0 100 200 300 400
- Time (s) t.
l l l I r\ !b r l T&i Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:lb061997 l i
9-146 O Figure 9.2.2.2-12 Case Uc41 (C[=1.[*DECLS Break /High RCS Temp) AL 27 2 0 Bottom AL 27 7 0 Midplane AL 27 15 0 Top I t . f.r ---<-r,
;, 1.
ja .. m l h l l = ; .
,l (l lll all ll ll-fli l 9 e=
e 1ain i,!, i i ll ( n ,, iu i in i l i i i, g'glm I I / 1 s,, i 4 - "
'!},l l p;
,o{'l,
.? l l!! Shllj,,!Ik,lc! S 'il]h,",!l,qfi
'y'l('y dg y ll I!I 2-
,,,9 ol1l :,
i
- 3 :
I 0 lb0 2b0 3b0 400 Time (s) G TIH certainty lyses for Short-Term Cooling June 1997 i
\ 9-147 (" ( Figure 9.2.2.2-13 Lower Plenum Collapsed Liquid Level Case UC41- (CD=1.0 DECLS Break /High RCS Temp) LO-LEVEL 1 0 0 COLLAPSED L10 LEVEL 7
} -
v6-- i c) 5-- i c) - J $ lO .- c 4-3 - o3-- l J : l o - a> 2 -- - en C-O ._ 1__ [ o _ o - 0 ''''l''''l''''l'''' 0- 100 200 300 400 Time (s) I l-TlH Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:1W1997
9-148 9 m Figure 9.2.2.2-14 Downcomer Colla) sed Liquid LeveI Case UC41 (CD=1.0 DEC.S Break /High RCS Temp) LO-LEVEL 10 0 0 COLLAPSED L10 LEVEL S 25 --
~
c) [ 20 -- a _~ m : e ] 15 -- J _ J _ y 10 --
~
a> ~ cn - c_ 5-O _ O 0 '''''''''''''''''''''iiii! 'iii ' 0 lb0 2d0 3d0 400 IIme (S) O' T/H Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:1b-061997 l
l l 9-149 (, t
~
l Figure 9.2.2.2-15 Hot Assembly Collapsed Li Level Case UC41 (CD=1.0 DECLS Break / quid High RCS Temp) LO-LEVEL 5 0 0 COLLAPSED L10 LEVEL l l 12 m -
+ .
10 -- O _ g 8--
~
J
~
' ((j ) '- O _
\
6-- A If 1
- E sl \ y 6 yn! p j
-.J l
)
o D cn C1. 4- ~ [ fI i l 2- - o 0 '''''''!''''l'''' 0 100 200 300 400 Time (S) l l
/3 l '%)
TlH Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf.lb-06137
I 9-150 0 Figure 9.2.2.2-16 Split Break Flow Case UC41 (CD=1.0 DECLS Break /High RCS Temp) RMVM 61 6 0 MASS FLOWRATE 40000
^
v2 N - f 30000 - - v 2 - O o 20000 -- . T _ 1 3: - l o _ w - g 10000 -- en - C _ 2 0
'l' " l''''l''''
0 100 200 300 400 Iime (S) O T/H Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:1W1997
_ _ - . _ . . . . -_. _ __.. _.._ _ __ _ _.___ _ _ _ .=_. _ ._ _ .. _ __._ _ _ .._.. _ 9-151 l 9.2.2.3.lTCOBRAfrRAC Results for Case UC42 . NJ
~
\
l Scenario UC42 is the same as UC41, except that the containment is not fully isolated, i.e., l l atmospheric pressure is assumed in the containment equal to 14.7 psia, and 2 CMTs are available. The set of figures prepared for case UC42 (Figures 9.2.2.3-1 through 9.2.2.3-17) is the same as those for case UC41. The only difference is that the injection of the second l - available CMT also appears in Figure 9.2.2.3-5. Generally, the plant behavior is the same as for case UC41 with the exception that, because the second CMT is injectmg more coolant, the water inventory is recovered faster and the PCT during the reflood period does not exceed 1681*F. l I i l- The vessel-bottom collapsed liquid level is recovered as fast as in case UC41. The second ! CMT has a more pronounced effect on the downcomer and core collapsed liquid levels.
- After steady CMT injection is established, the downcomer collapsed liquid level (Figure 9.2.2.3-14) remains above 20 feet, compared to 15 feet for the UC41 case. The core 1 L collapsed liquid level (Figure 9.2.2.3-15) is 5.5 feet instead of 5 feet as for case UC41.
l t l' l l I l-l l iO i
. T/H Uncertainty Analyses for Short-Term Cooling June 1997 c:\3661w.wpf:lt>&l997 l-i I
9-152 O Figure 9.2.2.3-1 Peak Cladding Temperatures for Case UC42 Case UC42 (CD=0.8 DECLG Break /High RCS Temp) PCT 1 0 0 PEAK CLADDING TEMP.
---- PCT 2 0 0 PEAK CLADDING TEMP PCT 3 0 0 PEAK CLADDING TEMP.
PCT 4 0 0 PEAK CLADDING TEMP PCT 5 0 0 PEAK CLADDING TEMP. 2000 _ 1800 -- m 1600 -~ s s w _
,~,
" ~ 1400 - o 1200 - [- ~ 1000 -h o - w// p.=w,.,* g.
' 800 - -h .d #
o : // , a- ggg _ .// , ,.
~
'r~.,, si E 4 ,/ '
o s' f l\t\ H 400 - ~ _\,r/ ,. .-
' . , ,I 'li
/
t, 5 -l
-.w .h -
u 200 -_ _
~
0 ''''i''''''''''''''l'''' 0 100 200 300 400 IIme (s) Oi; T/H Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:1b 061997 l l l
l l l 9-153 i ' \ lO l l Figure 9.2.2.3-2 l Hot Rod TCLAD at Elevation 9.11 Feet Case UC42 (CD=0.8 DECLG Break /High RCS Temp) TCLAD 1 61 0 ELEV. 9 11 FT. l 2000 .
~
1800 --
~
1600 -- m _ u_ v 1400 - l 1200 - { lO ~ l j 1000 -}- o - o 800 - o_ - E 600 - o _ , H - l _
.400 - -
l : L __ i 200-0 '''''''''''''''''''''''''''''''''' l 0 lb0 2d0 300 400 , I I'm e (s) i 4 i O ; i T/H Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf;1t>&l997 l
l l 9-154 l I e I Figure 9.2.2.3-3 Hot Assembly Top Flows Case UC42 (CD=0.8 DECLG Br'eak/High RCS Temp) FLM 27 15 0 L10 AXlAL MASS FLOW
---- FEM 27 15 0 ENT AXIAL MASS FLOW
---- FGM 27 15 0 VAP AX1AL MASS FLOW 50 _
~
- 4 3. 5 -- m ~ N - E 37 -- _o -
~
C 30. 5 -- 24 -- a) - ~ o 17.5 - Z 1 3: 11 -- ' o l l _,_ -1 i i t
- 4. 5 - p 4
g I l p ,_.mu___._ M m . .1 L . h _ _ i k, d l J ll UYV cn ' 1 q' m ; ' '
,1 f,'d n o i l i l
1 -8. 5 -_ _
\
~
-15 ''''l''''l''''l''''
0 100 200 300 400 Time (s) ; O1 TlH Uncertainty Analyses for Sbart-Term Cooling June 1997 o:\3661w.wp61b-061997 l i
l 9-155 ( \ t U l-l Figure 9.2.2.3-4a per Head Vessel Pressure
. Case UC42 Up(CD=0.8 DECLG Break /High RCS Temp)
P 77 2 0 PRESSURE 2500
~
2000 -- n Q .. m i $ 1500 - - ! I a) L _ [ 1000 -- w - a) - u _
- a _
500 -- 1
' ~
0 i ; i 0 100 200 300 400 l Time (s) t l l TlH Uncertainty Analyses for Short Term Cooling June 1997 c:\3661w.wpf:1b-061997
i 9-156 l 9 Figure 9.2.2.3-4b per Head Vessel Pressure Case UC42 Up(CD=0.8 DECLG Break /High RCS Temp) P 77 2 0 PRESSURE 50 40 -- n O - W _ c_ 3 0 --
- O o _
g 20 -- u (d' Q- _ 10 -- _ l l 0 ''''l'! ! t ii! ii,i,,,,,,,,,,,,, 1 0 100 200 3d0 400 i Iime (S) O1 TlH Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:1W1997
J a%am..-.A- J4h--. Mm.4e .-A++.--.a.ma,, -- s ,4 m a 4m 4 a _ m ._
-4 * -4Aa_ 4se a- - aav. a_4J_a h AmaA--3a- 4-a.A 4 4 m 9-157 O
V Figure 9.2.2.3-5 l Accumulator /CMT Injection Flows i Case UC42 (CD=0.8 DECLG Break /High RCS Temp) l RMVM 30 2 0 ACC MASS FLOWRATE RMVM 32 5 0 CMT-A MASS FLOWRATE t -
. - - RMVM 72 4 0 CMT-B MASS FLOWRATE l
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.. . - - =- . .- _ _. . _ . ..
9-158 O Figure 9.2.2.3-6 Peripheral Channel To Flows Case UC42 (CD=0.8 DECLG Break /p High RCS Temp) FLM 24 15 0 L10 AX1AL MASS FLOW FEM 24 15 0 ENT AXIAL MASS FLOW FGM 24 15 0 VAP AX1AL MASS FLOW 1000 n g N E 4 - 0-. L
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9-159 lO l V Figure 9.2.2.3-7 l Open Hole / Support Col. Channel Top Flows l Case UC42 (CD=0.8 DECLG Breok/High RCS Temp) FLM 25 15 0 LIO AXIAL MASS FLOW
----FEM 25 15 0 ENT AX1AL MASS FLOW FGM 25 15 0 VAP AXlAL MASS FLOW 2000 m _
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9-160
$1 Figure 9.2 2.3-8 '
1 Guide Tube Channel To Flows l Case UC42 (CD=0.8 DECLG Break /p High RCS Temp) FEM 26 15 0 L10 AXIAL MASS FLOW l FEM 26 15 0 ENT AXlAL MASS FLOW
----FGM 26 15 0 VAP AXIAL MASS FLOW 2000 m
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9-161 l
)
C\ V l l Figure 9.2.2.3-9 Peripheral Channel Rod 5 TCLAD ! Case UC42 (CD=0.8 DECLG Break /High RCS Temp) l TCLAD 5 41 0 Elev. 6 ft TCLAD 5 57 0 Elev 8 5 ft TCLAD 5 67 0 Elev. 10 ft ! 1200
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9-162 O l l Figure 9.2.2.3-10 Open Hole / Support Col. Rod 3 TCLAD Case UC42 (CD=0.8 DECLG Break /High RCS Temp) TCLAD 3 41 0 Elev. 6 ft
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---- TCLAD 3 67 0 Elev. 10 ft 1200 1000 --
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4 9-163 l i i O) i
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i Figure 9.2.2.3-11 Guide Tube Rod 4 TCLAD Case UC42 (CD=0.8.DECLG Break /High RCS Temp) TCLAD 4 41 0 Elev. 6 ft
----TCLAD 4 57 0 Elev. 8.5 ft TCLAD 4 67 0 EIev. 10 ft i 1200 ;
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9-164 O Figure 9.2.2.3-12 Case UC42 (CD=0.8 DECLG Break /High RCS Temp)
~-~-
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9-165 jG t.a1 I Figure 9.2.2.3-13 l l 1 Lower Plenum Collapsed Licuid Level ! l Case UC42 (CD=0.8 DECLG Break /Kigh RCS Temp) i l LO-LEVEL 1 0 0 COLLAPSED L10 LEVEL l i l , 7 ' m [ T'l~~r
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9-166 O Figure 9.2.2.3-14 Downcomer Collaased Liquid Level Case UC42 (CD=0.8 DEC_G Break /High RCS Temp) LQ-LEVEL 10 0 0 COLLAPSED L10 LEVEL 30 L ~ 25 -- ___ 1 o [ 20 -- a : m g ] 15 - T o- : / -J [ y 10 --
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l 9-167 l l L) l - Figure 9.2.2.3-15 Hot Assembly Collapsed Li Level Case UC42 (CD=0.8 DECLG Break /quidHigh RCS Temp) LO-LEVEL 5 0 0 COLLAPSED L10 LEVEL 12 m -
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9-168 O Figure 9.2.2.3-16 Loop Side Break Flow Case UC42 (CD=0.8 DECLG Break /High RCS Temp) RMVM 60 4 0 MASS FLOWRATE 15000 n - en N E _a v 10000 -- o Z - g _ O 5000 --{ u_ ) cn (n - 0 2 - 0 l''''l'''''''''''''' O 100 200 300 400 Iime (S) O TlH Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf-It>O61997
l
. 9-169 1
r\ ' Figure 9.2.2.3-17 i Vessel Side Break Flow ! Case UC42 (CD=0.8 DECLG Break /High RCS Temp) . RMVM 61 1 0 MASS FLOWRATE 30000 l \
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9-171 1 9.2.3 Uncertainty Evaluation for Large-Break LOCA Analysis HOTSPOT runs were performed, as in the AP600 SSAR Large-Break LOCA Analysis, to obtain a local paumeter uncertainty evaluation assessment for the limiting split break for the AP600 UC41 scenario. HOTSPOT indicates that the hot rod PCT is 1767 F for the nominal calculation. A Monte Carlo simulation for the determination of the 95th-percentile PCT is presented in SSAR Table 15.6.5-9. The PCT-based code uncertainty correction in the SSAR agrees with the data-based code uncertainty. As discussed in Reference 12, uncertainty is applied to the PCT computed for the limiting split-break UC41 case. The PCT adder to obtain the 95th-percentile PCF to cover the }VCOBRA/ TRAC and data PCT-based uncertainty is 244*F for reflood PCT. This gives a result with uncertainty addressed of less than 2020 F for the limiting UC41 scenario limiting split-break case. The calculations performed provide confidence that, for the limiting scenarios analyzed, the PCT does not exceed 2200 F. The emergency core cooling system maintains the core temperature at an acceptably low value and decay heat is removed for an extended period of time required by the long-lived radioactivity remaining in the core. WCOBRAfrRAC cases presented in this section predict full-core quench, and the calculations are run well past PCT turnaround. O T/H Uncertainty Analyses for Short-Term Cooling June 1997 o:\3661w.wpf:1M41997
i 10-1 10 T/H UNCERTAINTY ANALYSIS FOR LONG-TERM COOLING 0 Section 10 documents the thermallhydraulic analyses performed to support the PRA-important accident scenarios defined in Section 7.3. The scope of these analyses is long-term cooling, starting with the end of IRWST injection, the transition to sump recirculation, and the long-term natural circulation from the sump. The analysis methodology is consistent with design basis methods, codes, and assumptions. The conservative assumptions used in the analyses bound the MI uncertainties identified in Section 2, providing a robust basis for the success criteria that have been credited in the AP600 PRA. Details of the analysis methodology are provided in Section 10.1. Results of the analyses are provided in Section 10.2. 10.1 LONG-TERM COOLING ANALYSIS MODELING AND ASSUMPTIONS The objective of the analyses is to bound the thermalthydraulic uncertainties associated with the success criteria for core cooling by long-term recirculation. The probabilistic basis for selection of the specific scenarios for analysis is discussed in Section 7. Two classes of analyces are considered: LOCAs for which the containment is isolated, and small-break for which the containment is not isolated. As discussed in SSAR Chapter 15, for a large-break LOCA, the sump level is certain to be above the level of the break. Thus, there will be a continuous supply of water with a positive head to drive injection via the break and DVI O(3 lines. Since the cases reported herein do not consider the break as' an injection path, these calculations are sufficient to bound large-break LOCAs. The breaks analyzed are a 2-inch cold-leg break (containment isolated), and a DVI line break (containment isolated and not isolated). For both classes of analyses, the assumptions and methodology of the calculations remain essentially the same. Conservative boundary and liial conditions are established along with bounding scenarios to ensure that the thermal / hydraulic uncertainties contained within the success criteria are bounded. 10.1.1 WCOBRAffRAC Mc& ling Methodology The analyses are performed using the WCOBRAfrRAC code (Ref. 5) in the window mode of analysis as validated by the Oregon State University (OSU) Tests (Reference 8) The window mode method allows analysis of long transients within reasonable computer resources. In the window mode of analysis, the calculations can be initiated from a set of initial conditions and proceed to a quasi-steady state that represents the time window of interest. As shown in the model validation, the calculation may proceed from an arbitrary set of initial conditions, but conservative initial conditions based on short-term cooling calculations are used. Two time windows are analyzed that cover the end of IRWST injection and the begmnmg of sump injection. The time window at the end of IRWST injection provides an ending point for initial long-term cooling and an initial state for the sump injection time window. TlH Uncertainty Analysis for Long-Term Cooling June 1997 o43661w.wpf:1b-061897
10-2 One of the key assumptions that apply to all analyses presented in Section 10 relates to the behavior of the break during long-term recirculation. It is assumed that the liquid level in
+ u compartment where the break occurs covers the break by the time the sump squib valves operate. With the break covered, the break no longer provides a path to vent the reactor I coolant system. Although there are cases where the break can provide a path for I recirculation injection (for example, a double-ended DVI line break in the passive core cooling system (PXS) valve vault), these analyses take no credit for a break as an injection path. Taking no credit for the break conservatively elimmates the break as both a vent path and an injection path, l It is assumed that the liquid in the sump is at the saturation temperature for the containment pressure. Realistically, some subcooling will be provided by the passive containment cooling system (PCS). To assume saturated sump conditions bounds the uncertainty in the actual temperature of the sumps, and other uncertainties that may be associated with the sump.
The temperature of the liquid in the IRWST is assumed to be the same as in the DBA analyses in SSAR Chapter 15 (Ref. 4). The analyses presented here also assume failure of ADS stages 1,2, and 3, in which case the IRWST liquid temperature would not rise above its pre-LOCA temperature. The higher value used in the DBA analyses bounds uncertainties associated with the IRWST boundary condition. In all cases,10 CFR 50 Appendix K decay heat is assumed. Decay heat is also coupled to the assumed time of entry into long-term cooling. The enty time is assumed to be the same as in the DBA analyses. It is expected that the failures of ADS valves and DVI valves associated with the multiple-failure cases being analyzed would lead to a slower rate of depressurization and hence a lower injection rate. Thus, entry into long-tenn cooling is expected later than is modeled for this study, with the associated lower decay heat levels. The early entry assumption provides an additional margin to bound uncertainties in the analyses. The above assumptions are summarized in Table 10.1-1. This set of conservative assumptions bounds the thermallhydraulic uncertainties needed to ensure that a given analysis that predicts success represents actual r uccess. The scenarios selected in Section 7 identify the potentially risk-significant scemaios. The combined thermallhydraulic assumptions allow the analyses to be used to bound scenarios other than the breaks analyzed. Since no credit is taken for the break, the analyses may be applied to other scenarios where the entry time into long-term recirculation is later than assumed and bounded by the assumed equipment availability. This could include transients and other breaks. The WCOBRAffRAC model for the analysis of thermallhydraulic uncertainties in long-term cooling uses the same models as used in the DBA analyses described in the AP600 Standard Safety Analysis Report (SSAR). The objective is to analyze those cases that thermal-hydraulically bound the PRA-important scenarios in the Focused PRA. TIH Uncertainty Analysis for Long-Term Cooling June 1997 o:\3661w.wpf:1b-061897
10-3 { Table 10.1-1 Common Assumptions Bounding TM Uncertainties Parameter Assumption
~
Break No credit for venting or injecting Sump Temperature Saturation temperature for containment pressure IRWST Temperature Same as DBA analyses in SSAR Chapter 15 Decay Heat 10 CFR 50 Appendix K Time of Entry into Long-Tenn Cooling Same as DBA analyses In SSAR Chapter 15 PCS Operating RNS Off f ( TH Uncertainty Analysis for Long-Term Cooling June 1997 o:\3661w.wpf.lW1897
10-4 10.1.2 Modeling and Boundary Conditions for Cases with Containment Isolated In general, breaks and transients will enter into long-term recirculation with similar conditions. The IRWST and sump levels will be similar from case to case. For an isolated containment, the containment pressure, and hence the sump temperature, will vary somewhat from case to case. Note that Section 10.1.3 covers unisolated-containment low-pressure cases, which can be used to bound low-pressure isolated-containment cases. Decay heat will vary from case to case depending on the time of entry into long-term recirculation. Cc.nsistent with the objective of obtaining the maximum amount of information from the fewest possible computer calculations, two cases of potential risk signifiance are identified in Chapter 7. These two cases include a non-DVI line break and a DVIline break. The non-DVI break is modeled as a 2-inch cold-leg break, which is predicted to enter into long-term recirculation significantly later than a double-ended DVI line break. These two cases bound the spectrum of scenarios entering long-term cooling with containment pressures of approximately 25 psia, and long-term recirculation entry times greater than approximately 17,000 seconds, per SSAR Chapter 15. For the 2-inch cold-leg break, the desired bounding case is one in which depressurization is accomplished with only 2 of the 4 ADS stage 4 paths operable. The analysis showed that successfu? depressurization could not be achieved with 2 ADS stage 4 valves, so the depressuri2ation capacity was increased to include 3 ADS stage 4 valves.1 As discussed in Section 10.2.1, this case is shown to be successful. g T The DVI line break is assumed to be either double- or single-ended. The double-ended DVI line break allows the IRWST to spill into the sump through the PXS valve vault. This empties the IRWST earlier than in other scenarios, which results in a higher decay heat load and potentially higher core steaming rate. The single-ended DVI break requires that the break be between the injection valves and the vessel, and that the two injection paths in the broken line fail. This prevents spilling of the IRWST into the sump via the PXS valve vault. Both of these cases are bounding as will be explained in the following paragraphs. To bound the potentially risk-significant scenarios, only 2 of the 4 possible IRWST injection paths are assumed to be open. With two injection paths open, three possible valve alignments could exist: (a) one path open in the intact DVI line and one path open in the broken line, (b) two paths open in the intact line, and (c) two paths open in the broken line. 1 Recirculation begins after the pressurizer is empty, and the total area of one bank of stage 1-3 paths is close to the area of 1 ADS stage 4 path. With the pressurizer empty, nearly all outflow through the bank of ADS stage 1-3 valves would be steam, and the performance would be similar to or better than 1 ADS stage 4, since the ADS stage 4 valves are predicted to receive significant liquid. Thus, a calculation with 3 ADS stage 4 paths is equivalent to or bounds 2 ADS stage 4 with I bank of ADS stages 1-3. T/H Uncertainty Analysis for Long-Term Cooling June 1997 o:\3661w.wpf.It>-061897
l 10 _5. Case (a) allows the IRWST to drain into the sump through the PXS valve vault, and the ( vessel to depressurize through the break. Case (a) will be called a double-ended break of the DVI line.' Case (b) prevents draining of the IRWST through the broken line, but allows the vessel to depressurize through the break. Case (b) will be called a single-ended break Case ; (c) prevents DVI injection through the intact line prior to initiation of long-term recirculation.
~
Case (c) is a failure case and is not considered further For a doubk-ended DVI line break, at least 1 of the 2 open IRWST injection paths must be open in each lir,e. With any 2 paths available, if both injection paths were open in the broken DVI line, then none would be open j in the intact line, and there would be no injection before long-term recirculation, resulting in a short-term failure case. The bounding success path double-ended DVI line break during - i IRWST injection is 1 IRWST injection path open in each of the DVI lines. Once long-term I recirculation commences with opening of the sump valves, the sump will equalize the level ! in the PXS valve vault. When the sump valves open and deliver to the PXS valve vault, the i levels equalize, injection through the broken DVI line can occur, and two parallel paths for injection become available. The double-ended DVI break is bounding for IRWST injection, but not for sump injection. 1 i With credit for only two of four injection paths, the single-ended break allows two IRWST injection paths to be open in the intact line, and none open in the broken line. This is a l higher-resistance flow path than the parallel combination of the intact DVI and broken DVI ) L. lines. Thus for long-term recirculation, the single-ended DVI line break provides the highest- l l resistance flow path. However, since the IRWST is prevented from spilling into the sump, j j through the PXS valve vault, the entry time into long-term recirculation would be later than j the double-ended DVI line break, and the decay heat would be lower for the single-ended l ' break. The counter-balancing effects of decay heat and line resistance suggest that the single- ; ended DVI line break may not be bounding. For this reason, and to limit the analysis to a single bounding calculation, the long-term sump recirculation was modeled with a single-ended DVI line break with entry into long-term cooling at me time a double-ended break is predicted to enter into long-term recirculation. Although this approach does not provide a realistic prediction of the plant response to a .cing!c-ended DVI line break during sump injection, it does provide bounding results fr,r DVI line breaks during sump injection. Table 10.1.2-1 summarizes the four cases considered for isolated-containment scenarios.
- 10.1.2.1 Non-DVI LOCA with 3 ADS Stage 4 Valves; IRWST Injection Phase i
Initial calculations assuming 2 ACS s4. age 4 valves open as the only depressurization paths did not demonstrate continuous, positive core cooling. For this reason, alternative , depressurization scenarios were evaluated. The next-worst cases are to assume 3 ADS stage j 4 valves open, or 2 ADS stage 4 valves with one group of ADS stages 1-3 valves open. these two cases provide similar flow areas for depressurization. The flow area of one bank of ADS >g stages 1 -3 is about 23 percent greater than 1 ADS stage 4 valve. Thus, in long-tenn ; TM Uncertainty Analysis for Long-Term Cooling June 1997 c:\3661w.wpf:1N061897
10-6 l l recirculation,3 ADS stage 4 valves make a more limiting case than 2 ADS stage 4 valves with gl 1 group of ADS stages 1-3. The 3 ADS stage 4 case is documented in this report. W This subsection describes the boundary conditions that define the small-break LOCA with ADS stage 4 single failure, DVI valve failures, and failure of ADS stages 1,2, and 3. Long-term cooling behavior is discussed for the last portion of the IRWST injection time window and the first portion of sump recirculation. The break modeled is a 2-inch-diameter cold-leg split break at the bottom of a horizontal section of one of the cold legs in the non-PRHR loop. The long-term cooling phase begins when IRWST injection is established following opening of the squib valves in the IRWST DVI lines. The starting time for the calculation is 33,500 seconds after the initial break. At this time, the IRWST is drained to the low-low level setpoint, which activates sump injection. This first time window considers the last time period of the IRWST injection. It is assumed that 1 ADS stage 4 valve fails to open in the non-PRHR loop, and both banks of ADS stages 1,2, and 3 fail, thereby generating the minimum venting capability. Failure of the IRWST injection valves in the non-PRHR loop is assumed, and one IRWST injection valve is assumed to open in the other DVI line. 'Ihe initial conditions used for the calculation of this window are consistent with the NOTRUMP 2-inch-diameter small-break LOCA calculation reported in SSAR subsection 15.6.5.4B.3.3 and are consistent with the OSU long-term cooling test simulations. The window is a continuation of the identified case C 2-inch-diameter break of subsection 15.6.5.4B.3.3. , The initial RCS liquid inventory and temperatures are determined from the SSAR Chapter 15 l NOTRUMP calculation. This equates to a full lower plenum and downcomer, a core collapsed liquid level of 9 feet (relative to the bottom of the heated length), and a collapsed level of 4 feet in the upper plenum. It is conservatively assumed that the loops contain only saturated vapor. The temperature of the injection of liquid from the bottom of the IRWST is set to 165*F and is kept constant during the transient. The PRHR loop was not modeled for the OSU test; therefore, the PRHR is not included in the current model. Instead, the PRHR inlet pipe is only modeled to connect ADS stage 4. The initial temperature of the metal components is determined from the NOTRUMP reference calculation. The initial fuel rod temperature is specified as saturation temperature throughout both fuel rods used to represent the core: the core hot rod and the average power rod. Although the cladding temperatures are correct, the fuel centerline temperature and the heat fluxes are low initially, but readjust quickly within the time frame of the window. This approximation does not affect the calculated results after the early portion of the window is complete. The core decay heat is prescribed according to 10CFR50, Appendix K. The containment pressure is assumed to be 25 psia, which is consistent with the SSAR WGOTHIC analysis of the 2-inch-diameter cold-leg break. Both steam generators secondary T/H Uncertainty Analysis for Long-Term Cooling June 1997 o \3661w.wpf:1b-061897
i l 10 7 i 'q sides are isolatect, and the conditions are taken from the NOTRUMP reference calculation. Q The reactor coolant pumps are tripped and not rotating. j i The boundary. conditions for the 2-inch cold-leg break are summarized in Table 10.1.2-2. i Other 2-inch cold-leg break cases were also evaluated using these boundary conditions. The additional cases varied assumed equipment failures, and provide additional insight to the success criteria. For example, one case considers that only 2 of the 4 ADS stage 4 valves operate. The calculation cases are summarized in Table 10.1.2-3. 10.1.2.2 Non-DVI LOCA with 3 ADS Stage 4 Valves Available; Sump Recirculation Phase This subsection describes the boundary conditions that define the small-break LOCA with I ADS stage 4 single failure, DVI valve failures, and failure of ADS stages 1,2, and 3. Long- l term cooling behavior is discussed for the sump injection (recirculation) phase time window. The initial conditions for the sump injection phase time window are obtained by restarting the simulation from the end of the IRWST injection phase time window and opening one sump squib valve on the non-PRHR loop DVI line. Dunng sump injection with one DVI line having open flow paths (active DVI line), there are still three possible arrangements for recirculation with only 2 recirculation valves open. The possibilities are: 2 recirculation a valves open on the active DVI line,1 valve opens in each line, or 2 sump valves open on the inactive DVI line. The last case requires recirculation flow through the IRWST and into the active DVI line. This is the highest-resistance flow path, and is assumed for the calculations reported, except as otherwise noted. The boundary conditions for sump injection are shown in Table 10.1.2-4. The calculation cases are shown in Table 10.1.2-5. 10.1.2.3 DVI LOCA with 3 ADS Stage 4 Valves Available; IRWST Injection Phase This subsection describes the boundary conditions that define the DVI LOCA with ADS stage 4 single failure and ADS stage 1,2, and 3 failure during the IRWST injection phase time window. The break modeled is a double-ended break of the DVI line in the non-PRHR loop. It is assumed the breaks occur between the injection valve headers and the reactor vessel within the PXS valve vault. The long-term cooling phase begins when IRWST injection is l established following opening of the squib valves in the IRWST DVI lines. For a double-i ended break, it is assumed that one injection path in'the broken DVI line operates, l
- allowing the IRWST to spill into the PXS valve vault. The starting time for the calculation is !
! 17,150 seconds after the initial break. It is assumed that 1 ADS stage 4 valve fails to open in I the non-PRHR loop, both banks of ADS stage 1,2, and 3 valves fail to open, and one T&I Uncertainty Analysis for Long-Term Cooling June 1997 o:\3661w.wpf:1b.061897 l l l
10-8 IRWST injection path operates. It is further assumed that the level in the PXS valve vault is sufficient to prevent venting of the reactor vessel through the break, and insufficient to cause injection through the break. Thus, no credit is taken for the break. The window continues until a quasi-steady state is reached. Equipment conditions for the double-ended DVI line break are summarized in Table 10.1.2-6. The initial conditions, including the RCS liquid inventory and temperatures, temperatures of metal components, and fuel rod temperatures, were taken from the DBA analysis of the double-ended DVI line break described in Chapter 15 of the SSAR. As with the 2-inch cold-leg break, the PRHR loop is not modeled. The containment pressure is assumed to be 24 psia, and the IRWST liquid temperature is assumed to be 139 F. The boundary conditions for the double-ended DVI line break during IRWST injection are summarized in Table 10.1.2-7. 10.1.2.4 DVI LOCA with 3 ADS Stage 4 Valves, Recirculation Phase This subsection describes the boundary conditions that define the DVI LOCA with ADS stage 4 single failure and ADS stage 1,2, and 3 failure during the sump recirculation time window. The break modeled is a single-ended break of the DVI line in the non-PRHR loop. The difference between this case and the double-ended DVI line break described in 10.1.2.3 is the assumed failure of both IRWST injection valves in the broken DVI line. Both IRWST injection valves in the intact DVI line are assumed to operate. Although the time of entry into long-term recirculation would be greater than 17,150 seconds, it is assumed that long-term cooling begins at 17,150 seconds. This provides a case that bounds both the double-ended and single-ended DVI line breaks for sump recirculation. Since the IRWST does not spill in+o the PXS valve vault, the level in the vault cannot be sufficient to proside injection, and it assumed that the level in the PXS valve vault reaches a level sufficiett to prevent ventirg of the reactor vessel. Thus, no benefit for the break is taken in the cale tlation. Equipment conditions for the single-ended DVI line break are summarized in Table 10.1.2-8. An initial IRWST window is calculated assuming a single-ended DVI break using the same initial and boundary conditions in which both IRWST injection valves open in the intact DVI line. The initial conditions for the sump recirculation time window are a continuation of the IRWST window. Both sump valves on the broken DVI line are assumed to open. Sump flow is through the IRWST, and sump injection is modeled as described in subsection 10.1.2.2. The boundary conditions for the double-ended DVI line break during sump injection are summarized in Table 10.1.2-9. O TIH Uncertainty Analysis for Long-Term Cooling June 1997 o:\3661w.wpf:1t>-061897
10-9 Table 10.1.2-1 Summary of Isolated-Containment Cases Sump Injection Case IRWST Injection (Recirculation) i 2-inch Cold-Leg Break Analyzed Analyzed l Double-Ended DVI Line Break Analyzed Not analyzed because not l (Bounding analysis) bounding Single-Ended DVI Line Break Not analyzed because not Analyzed bounding (Bounding analysis) l Table 10.1.2-2 Boundary Conditions for 2-inch Cold-Leg Break during IRWST Injection Parameter Boundary Condition Containment Pressure 25 psia IRWST Level 107 ft , 2 in. l i IRWST Temperature 165'F O Table 10.1.2-3 Summary of 2 Inch Cold-Leg Break Calculations during IRWST Injection Case Number of ADS Stage 4 Number of ADS Stage 1-3 Number of Injection Paths No. Paths Open Banks Open Open 1 3 0 1 2 2 0 2 3 2 1 2 t 7Y . k 4 Table 10.1.2-4 Boundary Conditions for 2-Inch Cold-Leg Break with Isolated Cor .ainment during j Sump Injection (Recirculation) f Parameter Boundary Condition Contaimnent Pressure 25 psia 3 i Sump Level 107 ft ,2 in. 4 Sump Temperature 212 F l i TlH Uncertainty Analysis for Long-Term Cooling June 1997 i o:%1661v.wpf:ltr061897 4
i l l 10-10 ; 1 Table 10.1.2-5 Summary of 2-Inch Cold-Leg Break Calculations during Sump Injection Case Number of ADS Stage 4 Number of ADS Stage 1-3 Number of Recirculation No. Paths Open Banks Open Paths Open l l 1 3 0 1 l l 2 2 0 2 1 1 3 2 1 2 1 Table 10.1.2-6 Equipment Available for Double-Ended DVI Line Break during IRWST Injection Equipment Assumed Condition Intact DVI Line One open injection path Broken DVI Line One open injection path to PXS valve vault ADS Stages 1-3 All valves in both banks fail to open ADS Stage 4 3 of 4 Containment Isolation Isolated i Table 10.1.2-7 Boundary Conditions for Double-Ended DVI Line Break with Isolated Containment during IRWST Injection ! Parameter Boundary Condition Containment Pressure 24 psia IRWST Level IRWST window: 107 ft,6.6 in. IRWST Temperature 139 F l l 1 O T&I Uncertainty Analysis for Long-Term Cooling June 1997 o:\3661w.wpf:1t>&l897
1 10-11 Table 10.1.2-8 Equipment Available for Single-Ended DVI Line Break with Isolated Containment during Sump Injection i Equipment Aesumed Condition Intact DVI Line Two open injection paths Broken DVI Line Two open recirculation paths ADS Stages 1-3 All valves in both banks fail to open ] ADS Stage 4 3 of 4 Containment Isolation Isolated l Table 10.1.2-9 Boundary Conditions for Single-Ended DVI Line Break with Isolated Containment t during Sump Inketion Parameter Boundary Condition
- Containment Pressure 24 psia i Sump Level Sump window: 107 ft,2 ht 1 (O d Sump Temperature 239'F 1
1 i 4 1 l TlH Uncertainty Analysis for Long-Term Cooling June 1997 o:\3661w.wptitW1897
10-12 l 10.1.3 Modeling and Boundary Conditions for Cases with Failure to Isolate Containment l The AP600 containment purge system is composed of two 18-inch supply and return air lines, each with two aireperated valves in series. Failure of these valves to close would result in the loss of cooling water as steam through the open purge system. Loss of steam through the purge system would reduce the available head in the AP600 sump, affecting long-term cooling performance. The MAAP4 computer code (Reference 9) was used to calculate both the loss of containment inventory through the failed purge system and the resulting long-term sump liquid elevation. The MAAP4 computer code allows the containment to be divided into compartments. The compartment model has a feature that allows the volume versus elevation changes within the containment to be modeled. For application to the AP600 design, the AP600 containment has been divided into 11 different compartments. There are individual compartments for the containment steam generator rooms, which also contain the sump, the IRWST, reactor vessel cavity, lower compartments, and valve vault. Modeling these regions as separate compartments allows MAAP4 to predict the elevation of the liquid in each region. The liquid elevation in the steam generator rooms provides the head needed for long-term recirculation. Calculation of the inventory lost through the unisolated purge system requires that the MAAP4 primary system model calculate reasonable mass and energy release rates to the containment and that the MAAP4 containment model be capable of calculating the containment pressure and flow rate through the purge system. Chapter 40 of the AP600 PRA (Reference 3) compares results from both MAAP4 and WGOTHIC (Reference 10) containment calculations where identical mass and energy releases were used in each code. The results show the MAAP4 containment pressure calculation is reasonable when compared to EGOTHIC. Reference 2 compares results between MAAP4 and NOTRUMP for calculation of the AP600 primary response to various loss-of-coolant transients. The conclusion of Reference 2 is that MAAP4 reasonably predicts the loss of primary inventory over a range of break sizes and with various equipment failures analyzed. The results of the work performed in References 2 l and 3 demonstrate that MAAP4 can predict the interaction between the AP600 primary l system, AP600 passive systems, containment, and containment systems. The MAAP4 model of the containment purge system is a simple flow path model capable of calculating critically limited flow conditions at high containment pressure and using a loss coefficient when flow is no longer critical. Further, the MAAP4 flow path allows for both forward (containment to outside atmosphere) and reverse flow (outside atmosphere to l containment). Depending upon flow direction, the flow may consist of a mixture of steam TlH Uncertainty Analysis for Long-Term Cooling June 1997 o:\3661w.wpf:1b-061897
1 10-13 I and air or be air only. The MAAP4 containment model has been designed to perform ig calculations for mixtures of steam, air, hydrogen, and gaseous releases from a failed core. Therefore, the MAAP4 calculation for failure to isolate the containment purge system with adequate core cooling falls well within the capabilities of MAAP4. Additional assumptions employed in the MAAP4 analyses were: 102 percent of core power Appendix K decay heat Initial inside and outside air temperature set at 120 F PCS water tank at 120 F IRWST water temperature at 120*F These assumptions are conservative with respect to expected nominal plant operating conditions. These conservative assumptions were applied as a means to bound thermall i hydraulic uncertainties associated with the calculation of containment conditions. f Other conditions for the analysis are selected consistent with the potentially PRA-important long-term core cooling scenarios identified in Chapter 7. The case analyzed is a postulated break in the DVI piping with failure of the containment to isolate, no credit for ADS ' stage 1-3,4 of 4 ADS stage 4 and 1 IRWST line injecting, and 1 IRWST line spilling to l; containment. The DVI break was further postulated to occur in one of the PXS valve vaults, which are generally assumed to be dry. The DVI break in a PXS valve vault would result in the break and the spilling IRWST line filling the valve' vault. Thus, less inventory would be available to the containment sump with a lower sump level during long-term sump reciredation. Additional inventory is lost out of the unisolated containment purge system, as a result of containment pressurization during the early part of the postulated LOCA, due to the mass and energy released out of the break. Later, actuation of the stage 4 ADS will continue to pressurize the containment resulting in steam flow out of the failed containment isolation system. These losses, together with filling the PXS valve vault, reduce the liquid level in the sump during the long-term recirculation period. However, once the condensation of steam by the PCS exceeds the steam generation by decay heat, the containment pressure equalizes with the outside atmospheric pressure, ending the long-term loss of containment inventory. Generally, cases with containment isolation and all PXS equipment functioning will result in a containment sump feet level of 108.3 feet for long-term sump recirculation. l The DVI break with contamment isolation failure resulted in a long-term sump level greater ; than 105.5 feet. The loss of almost 3 feet of head can be attributed to filling of the valve i vault and losses through the unisolated containment purge system. For the loss of
, containment isolation case, with a break in the DVI piping, the containment sump level varied from 107.4 feet at 17,500 seconds down to 105.6 feet at 72 hours. Therefore, use of a sump level of 105.4 feet in the analysis presented in Section 10.2.2 represents a ccrnservative
- estimate of the long-term sump level.
T&i Uncertainty Analysis for Long-Term Cooling June 1997 oA3661w.wpf:1t> 061897
10-14 10.1.3.1 DVI Line Break with 4 ADS Stage 4 Valves, IRWST Injection Phase This subsection describes the boundary conditions that define the DVI LOCA with failure to isolate containment, DVI IRWST injection valve failure, and failure of ADS stages 1,2, and 3. Long-term cooling behavior is discussed for the IRWST injection phase time window. With two injection paths open, three possible valve alignments could exist: (a) one path open in the intact DVI line and one path open in the broken line, (b) two paths open in the intact line, and (c) two paths open in the broken line. Case (a) allows the IRWST to drain into the sump through the PXS valve vault, and the vessel to depressurize through the break. Case (a) will be called a double-ended break of the DVIline. Case (b) prevents draining of the IRWST through the broken line, but allows the vessel to depressurize through the break. Case (b) will be called a single-ended break. Case (c) prevents DVI injection through the intact line prior to initiation of long-term recirculation. Case (c) is a failure case and is not considered further. The break modeled is a double-ended break of the non-PRHR loop DVI line as described in subsection 10.1.2.3. In this case, it is assumed that one 18-inch containment purge line is open,4 ADS stage 4 valves open, both banks of ADS stage 1,2, and 3 valves fail, and one IRWST injection valve in the intact DVI line fails. The initial conditions for the primary coolant system are as established for the DBA analysis, as described in subsection 10.1.2.3. Boundary conditions for the failure to isolate containment case are derived from the MAAP4 calculation described above. In order to maintain conservatism, the IRWST and sump levels are assumed to be lower than the MAAP4 predictions. The IRWST level is assumed to be 106.3 feet during the IRWST time window. Containment pressure is assumed to be 14.7 psia, consistent with the MAAP4 calculations. Other boundary conditions are derived from the DBA analysis, and are summarized in Table 10.1.3-1. The equipment assumed to be available for the analysis is shown in Table 10.1.3-2. T/H Uncertainty Analysis for Long-Term Cooling June 1997 o;\3661w.wpf:1b-061897
l { 10-15 l l ! Table 10.13-1 Boundary Conditions for Double-Ended DVI Line Break with Failure to Isolate i \ Containment during IRWST Injection Time Window Parameter Boundary Condition Containment Pressure 14.7 psia , IRWST Level 106 ft,3 in. Decay Heat Appendix K l i l Table 10.13-2 Equipment Conditions for Double-Ended DVI Line Break with Failure to Isolate Containment during IRWST Injection Time Window Equipment Assumed Condition ! l l Intact DVI Line One open injection path Broken DVI Line No open injection paths ADS Stages 1-3 All valves in both banks fail to open ADS Stage 4 4 of 4 Containment Isolation 18-inch purge line open l l l l l l f TIH Uncertainty Analysis for Long-Term Cooling June 1997 c:\3661w.wpf lt@l897
i l 10-16 1 10.1.3.2 DVI Line Break with 4 ADS Stage 4 Valves, Recirculation Phase ; l This subsection describes the boundary conditions that define the small-break LOCA with DVI line failure and ADS 1,2, and 3 failure. Long-term cooling behavior is discussed for the sump injection phase time window. The sump injection time window is initiated fram a restart of a previous IRWST injection window for a single-ended DVI line break. It is assumed that 2 sump valves open in the sump with the broken DVI line. As described in Section 10.1.1, this requires flow from the sump through the IRWST and is the highest-resistance path for sump recirculation. For the base-case analysis, the sump level is assumed to be 105.9 feet, less than the 107.4-feet level predicted by MAAP4 at 17,500 seconds. To gain insight into the effects of sump level uncertainties, sensitivity calculations at sump levels of 105.4 feet and 104 feet were performed. The equipment assumed to be available for the sump injection phase is shown in Table 10.1.3-3. The boundary conditions are shown in Table 10.1.3-4. O O T/H Uncertainty Analysis for Long-Term Cooling June 1997 o:\3661w.wpf:1bo61897
1 l l \ 10-17 l
\
l Table 10.1.3-3 Equipment Conditions for Double Ended DVI Line Break with Failure to Isolate ! Containment during Samp Injection Tune Window l Equipment Assumed Condition Intact DVI Line Two open IRWST injection path Broken DVI Line Two open sump recirculation paths ADS Stages 1-3 All valves in both banks fail to open ADS Stage 4 4 of 4 Containment Isolation 18-inch purge line open l Table 10.1.3-4 Boundary Conditions for Double-Ended DVI Line Break with Failure to Isolate Containment during Sump Injection Time Window Parameter Boundary Condition Containment Pressure 14.7 psia Sump Level 105 ft,9 in. i .( l l 1 l l l
\
4 T/H Uncertalaty Analysis for Long-Term Cooling June 1997 o:\3661w.wpf;1b4M1897
10-19 10.2 LONG-TERM COOLING RESULTS 10.2.1 LTC Results with Containment Isolated 10.2.1.1 Small-Break LOCA with 3 ADS Stage 4 Valves; IRWST Injection Phase This subsection provides an analysis of the small-break LOCA with ADS stage 4 single failure, DVI line valve failure, and failure of ADS stages 1,2, and 3. Long-term cooling results are discussed for the IRWST injection phase time window. This subsection analyzes a 2-inch-diameter cold-leg break at the close of the IRWST injection phase, using the window mode of analysis. Initial conditions at the start of the window are prescribed to allow a calculation to begin at an intermediate time in the small-break long-term cooling transient and proceed until a quasi-steady state is achieved. At tids time, it can be assumed that the predicted results are independent of the assumed initial anditions. This approach enables extremely long transients to be analyzed in an acceptable amount of computer time. This calculation begins with the boundary conditions described in subsection 10.1.2.A. The IRWST level, which at the beguunng of the simulation is set to the low-low level, is simulated as constant during the transient. The calculation is then carried out to 3000 seconds and a quasi-steady-state condition is established. In this calculation, the IRWST provides a head sufficient to drive water into the downcomer through the operable DVI nozzle. The water introduced into the downcomer flows down the downcomer and up through the core, into the upper plenum. Steam produced in the core entrains liquid and flows out the RCS via the ADS stage 4 valves. The venting provided by the ADS paths enables liquid to flow through the core to maintain core cooling. Approximately 1800 seconds of transient are required to establish the quasi-steady-state condition, so this time is ignored in the following discussion. In this case, the venting path provided by the 3 ADS stage e valves produces continuous positive safety injection. In the following, average flow rates have been evaluated by integration of the flow rates over the last 1000 seconds of the tilne window to calculate quasi-steady-state values. The head of water in the IRWST causes a flow of subcooled water into the downcomer at an approximate average rate of about 49 lb/sec through the operable DVI nozzle. The downcomer level reached at the end of the time window is about 19.4 feet (Figure 10.2.1.1-1). All of the IRWST injection water flows down the downcomer and up through the core (Figure 10.2.1.1-2). Pressure spikes produced by boiling in the core can cause the mass flow into the bottom of the core to reverse momentarily, but the core flow is predonunantly upward. The accumulators have been fully discharged before the start of the time window considered and do not contribute to the DVI flow. TlH Uncertainty Analysis for Long-Term Cooling June 1997 o;\3661w.wpf:1b-061897
10-20 Boiling in the core produces steam and a two-phase mixture that flows out of the core, into the upper plenum. The core is 12-feet high and the core collapsed liquid level (Figure 102.1.1-3) is greater than 9 feet for the time period of interest and drops I intermittently to not less than, about 8 feet, while liquid is present at all elevations in the core. The boiling process causes a variable rate of steam production and consequent pressure ) spikes, which in turn cause oscillations in the liquid flow rate at the bottom of the core and also variations in the core collapsed level and the flow rates of liquid, entrained droplets, and vapor out through the top of the core. In the ECOBRAffRAC noding, the core is divided into two axial levels, each 6-feet long. The void fractions in the two levels are shown as Figures 10.2.1.1-4 and -5. It can be seen that the core void fraction is low for the bottom cell. The top core node void fraction is less than 0.6 in the time period of 2000 to 3000 seconds. Subcooled boiling is predicted in the middle levels of the rods and nucleate boiling in the uppermost level. The peak cladding temperature does not rise appreciably Dove the saturation temperature (Figure 10.2.1.1-6). The flow through the core and out of the itCS is more than sufficient to provide adequate flushing to preclude concentration of the boric acid solution. Some of the water canied out of the top of the core falls back into the core in the form of liquid and droplets. The mass flow rates at the top of the core are given as Figures 10.2.1.1-7 through -9, for vapor, liquid, and droplets. The average steam flow rate out of the core during the last 1000 seconds of the time window is 16 lb/sec. The liquid Q ilow rate out of the core shows wide band variations (Figure 10.2.1.1-8) but is upward-oriented for most of the time. Liquid collects above the upper core plate in the upper plenum, where the average collapsed liquid level is about 3.5 feet for the period 2000 to 3000 seconds (Figure 10.2.1.1-10). The variation in the flow rates out of the core causes the observed variation in the liquid levels in the upper plenum and the hot legs. The vapor and entrained liquid mixture flows from the upper plenum into both hot legs. The hot legs receive a two-phase mixture, which discharges through the open ADS stage 4 paths (Figures 102.1.1-11 and .-12). The mass flow rate out of the ADS stage 4 pipes at the top of the hot legs shows oscillations indicating intermittent discharge of liquid along with the vapor. The variation in discharge quality is caused by the variation of the void fraction at the top of the hot leg (Figures 10.2.1.1-13 and -14). The pressure drop across ADS stage 4 a in the intact loop is about 1 psi. The horizontal sections of the hot legs are each modeled as l COBRA channels to permit the formation of a pool in the hot legs, between the vessel and the upward slope to the steam generators. Inspection of the void fractions and velocities predicted by ECOBRATTRAC shows that at the bottom of the pipe is a pool of stagnant liquid, and at the top of the pipe there is mainly vapor flow toward the ADS stage 4 valves. At the interface region between the liquid and vapor is a mixture with an average void fraction of about 0.6 where vapor rises toward the ADS valves with entrained droplets TlH Uncertainty Analysis for Long-Term Cooling June 1997 o:\3661w.wpf:1b.061897 i I
*my*-
10-21 and liquid falls back into the pool. The collapsed liquid level in the intact hot leg ranges from 0.3 to 1.5 feet. The hot leg is about 50 percent full, on average. The hot leg in the broken loop receives two-phase mixture from the upper plenum, all of which discharges through the single, open ADS stage 4 valve. The pressure drop across ADS stage 4 in the broken loop is about 1 psi. As in the intact loop, the unsteady nature of the flow shows the venting of steam from the top of the hot leg, together with the occasional carry-out of liquid. The total discharge from all ADS stage 4 valves is about 49 lb/sec. Venting the core of steam and water ensures that there is adequate flow through the core to cool it and to prevent boron precipitation. Inspection of the void fractions and axial velocities predicted by .WCOBRAITRAC shows that at the bottom of the hot leg in the broken loop is a pool of stagnant liquid, and at the top of the pipe is mainly vapor flow toward the ADS stage 4 valve. At the interface region between the liquid and vapor is a mixture with an average void fraction of about 0.7, where vapor with entrained droplets rises toward the ADS valve and liquid falls back into the pool. The collapsed liquid level in the hot leg of the broken loop ranges from 0 to 1.5 feet. The hot leg is about 50 percent full, on average. The pressure in the upper plenum is shown in Figure 10.2.1.1-15. The upper plenum pressurization that occurs in some time periods is due to the ADS stage 4 water discharged, as previously discussed. A negligible pressure drop is calculated across the g vessel (Figure 10.2.1.1-16), and the injection rate through the DVI line into the vessel is showTt W in Figure 10.2.1.1-17. The analysis demonstrates that adequate core cooling is provided throughout the time window. O TlH Uncertainty Analysis for Long-Tenn Cooling June 1997 o:\3661w.wpf:1W1897
l I 10-22 l O i l l l Figure 10.2.1.1-1 l Downcomer Collapsed Liquid Levei 2 in CLB with 3 ADS Stage 4 paths IRWST window with one injection path 1
~
22 _ _ l ~ 21 -: e - l
- >20-: '
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=
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" 15 0 10'00 2000 300 0 Iime (s) i T&l Uncertainty Analysis for Long-Term Cooling June 1997 "W1W.wpf.lb@l897
10-23 0 Figure 10.2.1.1-2 Liquid mass fIow rate into core 2 in CLB with 3 ADS Stage 4 paths IRWST window with one injection path m 4000 _ EE I 3000 -~ v 2000 - :
- Ol o 1000 - -
ce:
$ 0- MM rlN i q l l N ih8dMh b E :
m -1000 -: ~ m - 1 o -
~
- E ' ' ' ' ' ' ' ' ' '
.-2000 l 0 1000 2000 300 0 Time (s)
O TH Uncertainty Analysis for Long-Term Cooling June 1997 o:\3661w.wpf:lt41997
1 10-24 U l Figure 10.2.1.1-3 l Core collapsed liquid level l 2 i n CLB with 3 ADS Stage 4 paths IRWST window with one injection path 12 _ i C : li
~ 11 -
- 10 --
o . -
~
f '
$YW Y c
.?
a 8-i t I l T 7-: , a : 6-_2 O - i 5 0 1000 2000 300 0 l Time (s) ., bi
\ vl i
TIH Uncertainty Analysis for Long-Ten Cooling June 1997 o:\3661w.wpf-Ib&l997 1
l 10-25 ! l 1 O 1 l
\
l l l l Figure 10.2.1.1-4 Void fraction Iower half of core
- 2. ,I n CL8 with 3 ADS Stage 4 paths IRWST window with one injection path !
1
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~ g.6-} $ u - u_ - 4-- o -
~
, 2- - O
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- :-u -
21 u 0 1000 20'00 3000 IIme (S) O
~
T&I Uncertainty Analysis for Long-Term Cooling June 1997 o:\3661w.wpf:1b41997
I l 10-26 1 i i l \ ! V l t Figure 10.2.1.1-5 l Void fraction upper half of core 2 in CLB with 3 ADS Stage 4 paths IRWST window with one injection path 1 C o *B. :.
/
.6-o -
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-l l
$Wf f $ $$
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l , i.
' ' ' ' ' ' ' ' i i 0 l l 0 1000 2000 300 0 Time Is) l C
d T&f Uncertainty Analysis for Long-Term Cooling June 1997 o:\3661w.wpf-Ib-061997
10-27 9' Figure 10.2.1.1-6 Peak cladding temperoture 2 in CLB with 3 ADS Stage 4 paths
-IRWST window with one injection path 260
~
m L 5 v _ 255 -- I ), 3 250 -- O _ L _ D - a_ 2 4 5 -- E - D F-240 l l 0 1000 2000 3000 Time (s) G TM Uncertainty Analysis for Long-Term Cooling June 1997 o:\3661w.wpf;1W1997
l 10-28 l l l Figure 10.2.1.1-7 l l Core exit vapor moss flow rate l CLB with 3 ADS Stage 4 paths l 2 in IRWST window with one injection path
, 50 i m - 1 N -
E 40 -} _
)
v : l 30 --
' ~
%% 9%W44* w m _
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-10 'l ' '
l 0 1000 2000 300 0 Time (S) i l l O TlH Uncertainty Analysis for Long-Tenn Cooling Jime 1997 o:\3661w.wpf:1b-061997
4 10-29 O Figure 10.2.1.1-8 Core exit liquid mass flow rate 2 in CLB with 3 ADS Stage 4 paths IRWST window with one injection path m 3000 _ m - N - E 2000 -- l v : - 1000 -- gl EM M r I h ohl Hh 0- --- 4 , M ' Il '
-t
$ -1000 - : -
- u. :
m -2000 -:
=s ~
-3000 ' ' ' '
l l 0 1000 2000 300 0 Time (s) O T/H Uncertainty Analysis for Long-Term Cooling June 1997 o:\3661w.wpf:1b-061997
- j. .,
10-30 1 O 4 x Figure 10.2.1.1-9 l Core exit droplet mass flow rate 2 in CLB with 3 ADS Stage 4 paths IRWST window with one injection path m 200 _ m : Y
.O 100 - i v
0 e
. - 10 0 - i
-200-
= :
o :
-300 - -
u :
,m -400 - i c o :
i
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l l O 1000 2000 3000 Ilme (s) T/H Uncertainty Analysis for Long-Term Cooling o:\3661w.wp611>461997 June 1997
10-31 9 Figure 10.2.1.1-10 Upper plenum collapsed liquid level 2 in CLB with 3 ADS Stage 4 paths IRWST window with one injection path
;5 _
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h 5 : v e E. o 1 --- _- ~ o _ o0 ' ' ' l 0 1000 20'00 3000 Iime (S) i l l 9 TIH Uncertainty Analysis for Long-Term Cooling 9 ,3997 o:\3661w.wphib 061997
) I 10-32 i
- O i
4 i 1 l Figure 10.2.1.1-11
- PRHR Loop ADS Stage 4 mass flow rate
- 2- in CLB with 3 ADS Stage 4 paths j IRWST window with one injection path
. _ 200 w -
- l x -
- E -
- .c _
- 150 --
l y O 1000 2000 3000
- Time (s) l l
i 10 TlH Uncertainty Analysis for Long-Term Cooling June 1997 o:\3661w.wp01b-061997 i
10-33 Figure 10.2.1.1-12 Non-PRHR Loop ADS Stage 4 mass flow rate 2 in CLB with 3 ADS Stage 4 paths IRWST window with one injection path m 500 _ m _ N - E 400 - _a - v : 300 -- ~
- 9 o 200 -
m : a : o 100 -- 0-
$ I' '
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im l_ n d c~ m ~ m _ O -
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-100 l l 0 1000 2000 3000 Ilme (s)
O TlH Uncert.dnty Analysis for Long-Term Cooling June 1997 o:\3661w wpf:ll>.061997
10-34 !O i 4 4 ! Figure 10.2.1.1-13 i PRHR Loop hot leg collapsed liquid level j 2 in CLB with 3 ADS Stage 4 paths IRWST window with one injection poth i _2 ~ i C _ l 1 5-- O
}
l-E f, f I l ,, 5-- l ? : ( i : - 1 i 0 0 I O 10'0 ') 20'00 3000 ! Time (s) i l 4 5 4 iO ": TlH Uncertainty Analysis for Long-Term Cooling June 1997 j o:\3661w.wpf:1ba1997 i i
10-35 0 Figure 10.2.1.1-14 Non-PRHR Loop hot leg collapsed liquid leve1 2 in CLB with 3 ADS Stage 4 paths IRWST window with one injection path C _ C -
~
f if $
. i
.5- -
l I : o -
" 0 l l 0 1000 2000 3000 Time (S) l l
9 T& certainty Analysis for Long-Term Cooling jun,1997
10-36 0 l 1 l Figure 10.2.1.1-15 Ua3er 3 enum aressure 2 in CLB with 3 ADS Stage 4 paths IRWST window with one injection path 32 _
^ :
o 31 _:; m : a_ 3 0 -- 29 -; a) u 28 - : o : m 27 - m I 26 - : I o_ ig i 25 l l 0 1000 2000 3000 Time (S) i I 4
%.)
i TlH Uncertainty Analysis for Long-Term Cooling June 1997 o:\3661w.wpElb-061997
10-37 O Figure 10.2.1.1-16 Pressure difference across vessel 2.in CLB with 3 ADS Stage 4 paths IRWST window with one injeetion path 6 _
.4-{ -
0- , r.h 5 m .4- ; m : os .6-L - CL
.8-3
-1 ' ' '
1000 2000 3000 Time (s) ! i O TH Uncertainty Analysis for Long-Term Cochng I"" I"7 o:\3661w.wpf 1M)61997
l l 10-38 ?,)- il. I 1 Figure 10.2.1.1-17 DVI injection mass flow rate 2 in CLB with 3 ADS Stage 4 paths IRWST window with one injection path m 80 _ m _ N 6, iT v 4 0 -- ( O(3
- 20 -- ,
a 0-l ~ a _ C - _.. - 2 0 - - w : a
, -4 0 -}
e -
- s
~
-60 l l O 1000 2000 3000 IIme (s) lO T/H Uncertainty Analysis for Long-Term Cooling June 1997 o:\3661w.wpf:1b-061997
10-39 10.2.1.2 Small-Break LOCA with 3 ADS Stage 4 Valves, Sump Recirculation Phase This subsection provides an analysis of the small-break LOCA with ADS stage 4 single failure, DVI line valve failure, and failure of ADS stages 1,2, and 3. Long-term cooling l results are discussed for the sump injection phase time window. This subsection analyzes a 2-inch-diameter cold-leg break during the sump injection, using the window mode of analysis. Conditions at the start of the window are created by restarting from the previous IRWST injection time window. The sump is turned on at restart cud about 2000 seconds are required to transition to a new quasi-steady-state solution that is independent of the initial conditions. The sump level is simulated as constant at 107.2 feet during the window while the sump liquid temperature is set at the saturation condition (240*F) at the containment pressure (25 psia) computed by WGOTHIC for conservatism for the 2-inch cold-leg-break DBA analysis presented in the SSAR. In this calculation, the sump provides a head sufficient to drive water into the downcomer through the DVI nozzles. The water introduced into the downcomer flows down the downcomer and up through the core, into the upper plenum. Steam produced in the core entrains liquid droplets and flows out of the RCS via the ADS stage 4 valves. The DVI flow and the venting provided by the ADS paths provide a high flow through the core, for it to remain cool. Approximately 2000 seconds of transient time are required to reach a new quasi-steady state. The venting path provided by the 3 ADS stage 4 valves provides continuous positive safety injection. In the following discussion, average flow rates have been determined by integration over the last 500 seconds of the time included to calculate quasi-steady-state conditions. The DVI flow rate is shown in Figure 10.2.1.2-17. The average DVI flow rate is 43 lb/sec. The DVI injection variations are due to variation of quality at the ADS stage 4 valves. When more water is entrained from the hot legs, the upper plenum pressure increases and, in turn, the injection flow rate decreases. In this case, the injection flow is always positive. The downcomer collapsed liquid level (Figure 10.2.1.2-1) decreases during the transition to a quasi-steady-state level of about 19 feet, on average. All of the sump injection water flows down the downcomer and up through the core (Figure 10.2.1.2-2). Pressure spikes produced by boiling in the core can cause the mass flow into the bottom of the core to reverse momentarily, but the core flow is predominant.y upward. Boiling in the core produces steam and a two-phase mixture that flows out of the core, into g the upper plenum. The core collapsed liquid level (Figure 10.2.1.2-3) maintains a mean level W T&I Uncertainty Analysis for Long-Term Cooling June 1997 oA3661w wpf;1b-061897
.- _m m. _ _ _ __ _ _ _ _ _ _ _ _ _ . - _ _ . _ -
l \ l 10-40 p of approximately 8.6 feet. The increased steaming rate in the core,18 lb/sec during sump
- ( -
. reci rcul a ti on versus 16 lb/sec during the IRWST time window, is a result of introducing l saturated (for containment pressure) liquid at the DVI nozzle. The increased steaming causes L
the collapsed liquid level to decrease. The boiling process causes pressure variations, which in turn cause variations in the liquid flow rate at the bottom of the core and in the core collapsed level and the flow rates of liquid, entrained droplets, and vapor out of the top I of the core. In the WCOBRAITRAC noding, the core is divided into two axial levels, l- each 6-feet long. The void fraction in the top level is shown in Figure 102.1.2-5, while Figure 10.2.12-4 shows the small void fraction that exists at the bottom level. Subcooled boiling is predicted in the middle levels of the rods. Nucleate boiling is predicted in the uppermost level of the rods. The peak cladding temperature does not rise appreciably above the saturation temperature of 240 F (Figure 10.2.1.2-6). The flow through the core and out of the RCS is more than sufficient to provide adequat" flushing to preclude concentration of the boric acid solution. Some of the water carried out of the top of the core falls back into the core in the form of liquid and droplets. The mass flow rates at the top of the core are given as Figures 10.2.1.2-7 through -9, for vapor, liquid, and droplets. The average production of steam during sump injection is 18 lb/sec. The liquid flow rate out of the core shows wide band variations (Figure 10.2.1.2-8) but is upward-oriented for most of the time. Liquid collects above the upper core plate in the upper plenum, where the average collapsed liquid level is 3.3 feet. l The vapor and entrained liquid mixture flows from the upper plenum into both hot legs. The hot legs receive a two-phase mixture, which discharges through the open ADS stage 4 paths (Figure 10.2.1.2-11). The mass flow rate out of the ADS stage 4 pipes at the top of the hot legs shows oscillations indicating intermittent discharge of liquid along.with the vapor. The variation in discharge quality is caused by the variation of the void fraction at the top of the hot leg (Figure 10.2.1.2-13). The pressure drop across ADS stage 4 in the intact loop is, on average, approximately 1.5 psi. The horizontal sections of the hot legs are each modeled [ as COBRA channels, as described in the SSAR, to permit the formation of a pool in the hot legs, between the vessel and the upward slope to the steam generators. Inspection of the , L void fractions and velocities predicted by WCOBRAITRAC shows that at the bottom of the l , pipe is a pool of stagnant liquid, and at the top of the pipe there is mainly vapor flow . l toward the ADS stage 4 valves. At the interface region between the liquid and vapor is a l mixture with an average void fraction of about 0.6 where vapor rises toward the ADS valves with entrained droplets and liquid falls back into the pool. The collapsed liquid level in the intact hot leg averages about 1.1 feet. The hot leg is, on average, more than 45 percent full. I
- The hot leg in the broken loop receives two-phase mixture from the upper plenum, all of which discharges through the single, open ADS stage 4 valve (Figure 10.12.2-12). The c pressure drop across ADS stage 4 in the broken loop is, on average, about 1 psi. As in the l intact loop, the unsteady nature of the flow shows the venting of steam from the top of the TIH Uncertainty Analysis for Long-Term Cooling June 1997 o
- \3661w.wplib-061897
10-41 1 hot leg, together with the occasional carry-out of liquid. Venting the core of steam and water g ensures that there is adequate flow through the core to cool it and to prevent boron W precipitation. Inspection of the void fractions and axial velocities predicted by WCOBRA/ TRAC shows that at the bottom of the hot leg in the broken loop is a pool of l stagnant liquid, and at the top of the pipe is mainly vapor flow toward the ADS stage 4 valve. At the interface region between the liquid and vapor is a mixture with an average void fraction of about 0.8 where vapor with entrained droplets rises toward the ADS valve and liquid falls back into the pool. The collapsed liquid level in the hot leg of the broken loop is, on average, about 1.2 feet (Figure 10.1.2.2-14). The hot leg averages more than 45 percent full. The pressure in the upper plenum is shown in Figure 10.2.1.2-15. The upper plenurn pressurization that occurs in some time periods is due to the ADS stage 4 water discharged as previously discussed. A negligible pressure drop is calculated across the vessel (Figure 10.2.1.2-16), and the injection rate through the DVI line into the vessel is shown in Figure 10.2.1.2-17. The analysis demonstrates that adequate core cooling is provided throughout the time window. O 1 l l l O TlH Uncertamty Analysis for Long-Term Cooling June 1997 o:\3661w.wpf:1b-061897
l l 1 0 -12 1 f~~h. L) i l Figure 10.2.1.2-1 Downcomer Collapsed Liquid Leve1 2 i n CLB with 3 ADS Stage 4 aaths Sump window with two injection and recirculat on paths m 25 -
~
_ 23 -- - o j - (c s o 21 -- 19 - "' W aq'qg o -
= _
m
- a. 1 7 -- l a -
O - a ' ' ' ' ' ' ' ' ' ' ' ' 15 l 3000 4000 5000 6000 Time (s) l l l /T
%Y TlH Uncertainty Analysis for Long-Term Cooling June 1997 o:\3661w.wpf.1b-061897
i i 10-43 l
- l
- Figure 10.2.1.2-2 Liquid mass flow rate into core l 2 in CLB with 3 ADS Stage 4 3aths Sump window with two injection and recirculot on paths m 1500 E5
- 1000 --
e -
&1 ll l ld l
$ I o _
2 ' ' ' ' ' ' ' ' '
-500 ' ' ' ' '
3000 40'00 50'00 6000 I i in 6 (S) I 4 wgggya--e-c- , ,- 1
l t 10-44 l
,e x 's l
i l l Figure 10.2.1.2-3 e Core collapsed liquid leve1 2 in CLB with 3 ADS Stage 4 aaths Sump window with two injection and recirculot on paths _ 15 l l p <> - l C "o 11 --
~~
o \ 1 o- -
\
M r^d.'((,[,", ] 4 ~7'-;y;' _ 2 ,_4 -
;_ 9 i o -
~
m a 7-- o - o - 5 ' ' ' ' ' ' ' 1 I 3000 4000 5000 6000 Iime (s) f l TlH Uncertainty Analysis for Long-Term Cooling June 1997 o:\3661w.wpf:1b-061897 i
10-45 0 Figure 10.2.1.2-4 Void fraction Iower half of core 2 in CLB with 3 ADS Stage 4 3aths Sump window with two injection and recirculat on paths 1
.8-e O
o 6-- u - Lt. 4-- o -
> *2--
-i^-- = "
0 C '
" -- ' ~
- M i U C '* 2 I' 0 ----i=
3000 4000 5000 6000 Time (S) O TlH Uncertainty Analysis for Long-Term Cooling June 1997 c:\3661w.wpf:1b4161897
10-46 l l \ (~~'s l V l l l l Figure 10.2 1.2-5 Void f.r a c t i o n upper half of core 2 in CLB with 3 ADS Stage 4 aaths Sump window with two injection and recirculot on paths 1 I I
~
c-g 8- - e - _ l ()s o o 6--
, h M, E
M/hd'F'.n'.N Nht'Aih 4-- o - I 1 o
)
y 2--
~
i
' ' ' ' i i i , , , , , ,
0 3000 40'00 50'00 6000 I,lme (S) ' l A i T/H Uncertainty Analysis for Long-Term Cooling June 1997 o:\3661w.wpf;1t>sig97 l l
1047 I 1 Figure 10.2.1.2-6 Peak cladding temperoture 2 in CLB with 3 ADS Stage 4 aaths Sump window with two injection and recirculat on paths 256.5 _ . u- 256 -3 255.5 -f a : g 253 - ' ' ' ' l l 3000 4000 5000 6000 Iime (s) l l 9 T/H Uncertainty Analysis for Long-Term Cooling June 1997 o:\3661w.wph1MM1897
i i 10-48 O i l
- Figure 10.21.2-7 4
- Core exit vapor mass flow rate
. 2 in CLB with 3 ADS Stage 4 aaths Sump window with two injection and recirculot on paths j m 25 m - N - E o _ a:
,10--
o _
~
5-- m - m -
~
O
" 0
~
' ' ' ' ' ' i i i i i i i i 3000 40'00 50'00 6000 Ilme (S)
O TlH Uncertainty Analysis for 1 ong-Term Cooling June 1997 c:\3661w.wpf:1b-061897
l 1049 I G Figure 10.2.1.2-8 Core exit liquid mass flow rate 2 in CLB with 3 ADS Stage 4 oaths Sump window with two injection and recirculat on paths _ 2000 _ m : N 1500 -; E :
.o -
1000 -: 500 -: g
% 0
~ '
I J I ' I I I l I l
' I'U l l Ilh l ' 'I l li- - L - II "
z
- 1 I l
r 'r i,J r' l l i r i- 'q i r I y 91 a -500-
'~
u_ - 1 0 0 0 - t
" -1500 --
o : 2 -
-2000 ' ' ' '
l l i < _,i i 3000 4000 5000 6000 Iime (S) O T/H Uncertainty Analysis for Long-Term Cooling June 1997 o:\3661w.wpf:1b-061897
10-50 O v Figure 10.2.1.2-9
. Core exit droplet mass flow rote 2 in CLB with 3 ADS Stage 4 paths Sump window with two injection and recirculotson poths m 8E-01 m -
N _ 1 E o -
. 6 E-01 --
O - 1 o 4 E-01 -- m - o . u 2 E-01 -- m m 2 '- ~' "- 0 3000 4000 50'00 6000 Iime (S) o O TlH Uncertainty Analysis for Long-Term Coolin$ June 1997 o:\3661w.wpf:1b-061897
r i 10-51 1 01, l 1 l l l 1 Figure 10.2.1.2-10 Upper plenum collapsed liquid leve1 2 in CL8 with 3 ADS Stage 4 aaths Sump window with two injection and recircula< ion paths 5 4--
=
C :)l$ & ' W f p ysy r gg. -}p,,,w 4 o 3-- h
=
O- -
"-2-- -
m - m O
- o. 1 -- i O -
0 ! !
3000 4000 5000 6000 I I rn e (S) 1 O TlH Uncertainty Analysis for Long-Term Coolutg June 1997 o:\3661w.wpf:1M61897
10-52 O l Figure 10.2.1.2-11 PRHR Loop ADS Stage 4 mass flow rate 2 in CLB with 3 ADS Stage 4 paths Sump window with two injection and recirculation paths _ 140 120 -} f - v 100 -{
- 80 -
60 -{ l
~
40 --
- 20 -~ >
~
o -
~
2 ' ' ' ' ' ' ' ' ' ' ' ' 0 ' l ! 3000 4000 5000 600 0 ! ! Time (s) l ! l i t i lo T/H certain alysis for Long-Term Cooling June 1997
1 1 10-53 0 l 1 i Figure 10.2.1.2--12 l Non-PRHR Loop ADS Stage 4 mass flow rate 2 in CLB with 3 ADS Stage 4 aaths Sump window with two injection and recircuiotion paths m 500 _ m - N - E 400 - .c - v - 300 -- o 9 o 200 -- - Q: -
~
3 - o 100 -- - d o .u . I . L li i i l9pf l. . al J . ll,. 21bdidA >LI ' ' 9A n HL in+ 1.ltillLAm M =11 m 0-- - m - o -
~
2 ' ' ' ' ' ' ' ' ' ' ' '
-100 l l 3000 4000 5000 6000 IIme (S)
O TlH Uncertainty Analysis for Long-Term Cooling June 1997 o:\3661w.wpf.lb-061897
i 10-54
'O O
l Figure 10.2.1 2-13 PRHR Loop hot leg collapsed liquid level l 2 in CLB with 3 ADS Stage 4 30ths l Sump window with two injection and recircu'ation paths m 2 2 lj O f,__i q I g ln 4 ggk.hyggly
.5 ~
m - 5- - 2 : o - O ' ' ' ' ' ' ' ' ' ' 0, ' ' ' ' 3000 4000 5000 6000 IIme (S) l l TlH Uncertainty Analysis for Long-Term Cooling June 1997 o:\3661w.wpf;1b-061897
l 10-55 0 Figure 10.2.1.2-14 Non-PRHR Loop hot leg collapsed liquid levei 2 in CLB with 3 ADS Stage 4 paths Sump window with two injection and recirculation paths - 2 2 1 1 .5-h .? a 1-- i
~
f hfN0'f*k)V U$ e o : o - ! 5--
- o. -
l o : I 0 ' 3000 40'00 5000 6000 Iime (s) I l l 1 TlH Uncertainty Analysis for Long-Term Cooling June 1997 o:\W1w.wpf:1b41897
i . 10-56 i O ' i ! l i Figure 10.2.1.2-15 l 1 1 U33er enum a aressure in CLB with 3 ADS Stage 4 aaths 2 2
- Sump window with two injection and recirculot on paths i
i 27.4
- m :
! a 27.2 -: ) . _ . - l ca 27 - i a : ! co - 26 - 1 25.8 ' ' ' l l 3000 4000 5000 600 0
- Iime (s)
? i l l I
!O
, TlH UncertTinty Analysis for Long-Term Cooling June 1997
- o
- \3661w.wpf:ltH)61897
10-57 0 Figure 10.2.1.2-16 Pressure difference across vessel 2 in CLB with 3 ADS Stage 4 aoths Sump window with two injection and recirculat on paths
.4 _
~
^
.2--
en - v.
" 02 O ' '
L _. 2 - a _ m 4 -h e _
$ .6 -}
l :
.8 i i i i i i , , i i , , , ,
3000 40'00 50'00 6000 Time (s) e Tai Uncertainty Analysis for Long-Term Cooling I W 1997 o:\3661w.wpf:ltW1897
10-58 (G
%.)
Figure 10.2.1.2-17 DVI injection mass flow rate 2 in CLB with 3 ADS Stage 4 aaths Sump window with two injection and recirculat on paths m 60 _ d E 55 -} - v 50 -- Os e : i - m 35 -- m o ..
" 30 ~
l l - ' 3000 4000 5000 6000 Time (s) O TlH Uncertainty Analysis for Long-Term Cooling o:\3661w.wptib-061897 June 1997
10-59 10.2.1.3 DVI LOCA with 3 ADS Stage 4 Valve, IRWST Injection Phase This subsection provides an ana ysis of the DVI LOCA with ADS stage 4 single failure and failure of ADS stages 1,2, and 3. Long-term cooling results are discussed for the IRWST injection phase time window. This subsection analyzes a double-ended DVI line break in the PXS valve vault at the close of the IRWST injection phase, using the window mode of analysis. Conditions at the start of the window are prescribed to allow a calculation to begin at an intermediate time in the small-break long-term cooling transient and proceed until a quasi-steady state is achieved. At this time, it can be assumed that the predicted results are independent of the assumed initial conditions. This approach enables extremely long transients to be analyzed in an acceptable amount of computer time. This calculation begins with the boundary conditions described in subsection 10.1.2.1. The IRWST level, which at the begmning of the simulation is set to the low-low level, is simulated as constant during the transient. The calculation is then carried out for 2000 seconds and a quasi-steady-state condition is established. In this calculation, the IRWST provides a head sufficient to drive water into the downcomer through the operable DVI nozzle. The water introduced into the downcomer flows down the downcomer and up through the core, into the upper plenum. Steam produced in the core entrains liquid and flows out the RCS via the ADS stage 4 valves. The venting provided by the ADS paths enables liquid to flow through the core to maintain core cooling. , Approximately 1000 seconds of transient are required to establish the quasi-steady-state ) condition, so this time is ignored in the following discussion. In this case, the venting path provided by the 3 ADS stage 4 valves produces continuous positive safety injection. In the following, average flow rates have been evaluated by integration of the flow rates over the last 1000 seconds of the time window to calculate quasi-steady-state values. The head of water in the IRWST causes a flow of subcooled water into the downcomer at an approximate average rate of 37 lb/see through the operable DVI nozzle. The downcomer level reached at the end of the time wMdow is about 18.7 feet (Figure 10.2.1.3-1). All of the IRWST injection water flows down the downcomer and up through the core (Figure 10.2.1.3-2). Pressure spikes produced by boiling in the core can cause the mass flow into the bottom of the core to reverse momentarily, but the core flow is predominantly upward. The accumulators have been fully discharged before the start of the time window considered and do not contribute to the DVI flow. Boiling in the core produces steam and a two-phase mixture that flows out of the core, into the upper plenum. The core is 12-feet high and the core collapsed liquid level g (Figure 10.2.1.3-3) is greater than 8 feet once quasi-steady state is reached, while liquid is W 1 TlH Uncertainty Analysis for Long-Term Cooling June 1997 o:\3661w.wpf-lb-061897
10-60 73 present at all elevations in the core. The boiling process causes a variable rate of steam
! ) production and consequent pressure spikes, which in turn cause oscillations in the liquid flow rate at the bottom of the core and also variations in the core collapsed level and the flow rates of li_ quid, entrained droplets, and vapor out the top of the core. In the WCOBRAll'RAC noding, the core is divided into two axial levels, each 6-feet long. The void fractions in the two levels are shown as Figures 10.2.1.3-4 and -5. It can be seen that the care void fraction is low for the bottom cell. The top core node void fraction is less than 0.6 in the time period of 1000 to 2000 seconds. Subcooled boiling is predicted in the middle levels of the rods and nucleate boiling in the uppermost level. The peak cladding temperature does not rise appreciably above the saturation temperature (Figure 10.3.2.3-6). The flow through the core and out of the RCS is more than sufficient to provide adequate flushing to preclude concentration of the boric acid solution. ,
l Some of the water carried out of the top of the core falls back into the core in the form of I liquid and droplets. The mass flow rates at the top of the core are given as Figures 10.2.1.3-7 through -9, for vapor, liquid, and droplets. The average steam flow rate out of the core during the last 1000 seconds of the time window is approximately 18 lb/sec. The liquid flow rate out of the core shows wide band variations (Figure 10.2.1.3-8) but is upward-oriented for most of the time. l l Liquid collects above the upper core plate in the upper plenum, where the average collapsed y/ liquid level is about 3.2 feet for the period of 1000 to 2000 seconds (Figure 10.2.1.3-10). The : variation in the flow rates out of the core causes the observed variation in the liquid levels in the upper plenum and the hot legs. 1 The vapor and entrained liquid mixture flows from the upper plenum into both hot legs. ! The hot legs receive a two-phase mixture, which discharges through the open ADS stage 4 l paths (Figures 10.2.1.3-11 and -12). The mass flow rate out of the ADS stage 4 pipes at the 1 l top of the hot legs shows oscillations indicating intermittent discharge of liquid along with the vapor. The variation in discharge quality is caused by the variation of the void fraction l at the top of the hot leg (Figures 10.2.1.3-13 and -14). The pressure drop across ADS stage 4 i in the intact loop is about 1.4 psi. The horizontal sections of the hot legs are each modeled as COBRA channels to permit the formation of a pool in the hot legs, between the vessel and ) i the upward slope to the steam generators. Inspection of the void fractions and velocities predicted by WCOBRAll'RAC shows that at the bottom of the pipe is a pool of stagnant l liquid, and at the top of the pipe there is mainly vapor flow toward the ADS stage 4 valves. At the interface region between the liquid and vapor is a mixture with an average void fraction of about 0.6, where vapor rises toward the nos valves with entrained droplets and liquid falls back into the pool. The collapsed liquid level in the intact hot leg averages 1.1 feet. The hot leg is about 40 percent full, on average. o
.~s TlH Uncertainty Analysis for Long-Term Cooling June 1997 o:\3661w.wphlt41897
10-61 The hot leg in the broken loop receives two-phase mixture from the upper plenum, all of which discharges through the single, open ADS stage 4 valve. The pressure drop across ADS stage 4 in the broken loop is about 1.4 psi. As in the intact loop, the unsteady nature of the flow shows the venting of steam from the top of the hot leg, together with the occasional carry-out of liquid. The total discharge from all ADS stage 4 valves is 37 lblsec. Venting the core of steam and water ensures that there is adequate flow through the core to cool it and to prevent boron precipitation. Inspection of the void fractions and axial velocities predicted by WCOBRAITRAC shows that at the bottom of the hot leg in the broken loop is a pool of stagnant liquid, and at the top of the pipe is mainly vapor flow toward the ADS stage 4 valve. There is a sharp interface between the liquid and vapor as the liquid pool transitions to a region with an average void fraction of about 0.9, and fewer liquid droplets rise toward the ADS valve and less liquid falls back into the pool. The collapsed liquid level in the hot leg of the broken loop is 1.2 feet. The hot leg is about 45 percent full, on average. The pressure in the upper plenum is shown in Figure 10.2.1.3-15. The upper plenum pressurization that occurs in some time periods is due to the ADS stage 4 water discharged, as previously discussed. A negligible pressure drop is calculated across the vessel (Figure 10.2.1.3-16), and the injection rate through the DVI line into the vessel is shown in Figure 10.2.1.3-17. The analysis demonstrates that adequate core cooling is provided throughout the time window. O l l l l O' 1 TIH Uncertainty Analysis for Long-Term Cooling June 1997 o:\3661w.wpf:1W1897
10-62 O 1 l Figure 10.2.1.3-1 1 Downcomer Collapsed Li uid Level Double ended D,VI break with isolated containment IRWST window with one injection path i ! 19.5 l l - E 19 -- , l
- 18.5 -- \
fYf f1 l ' . 2 18 -- i 0$ l
.T -
[ 17. 5 - f l l ? 17 - - l
' ' ' ''''''iiiii
" 16.5 0 5b0 10'00 15'00 2000 Time (s) l I
I, O d TlH Uncertainty Analysis for Long-Term Cooling Jtme 1997 c:\3661w.wpf:Ib-061897
1 10-63 h Figure 10.2.1.3-2 Liquid mass flow rate into core Double ended DVI break with
' isolated containment IRWST window with one injection path
- 2000 _
m - N - E 1500 -~ - 1000 -~
~
~ ~
o 500 - - 0- d 1 1' ' l l {igh. l l l l i 1 j u_ _
~
m -500 -
~
o m -1000 ~ l l l 0 500 1000 1500 200 0 IIme (s) l l T&l Uncertainty Analysis for Long-Term Cooling June 1997 o:\3661w.wpf:1b-061897
I 10-64 1 In iU Figure 10.2.1.3-3 Core collapsed Iiquid level Double ended DVI breok with isolated contoinment 1RWST window with one injection path 12 11 - 2 - ')p . 3 l' .n 'ig 3 10 -- o o 7 - g- -
]. f y gh crMN
- o. 8-O _
o _
"7 'l ' ' ' '
l l i i ' i 0 500 1000 1500 2000 Time (s) i l l l
- O i
d TlH Uncertainty Analysis for Long-Term Cooling June 1997 c:\3661w.wpf:1b 061897
1 10-65 0 Figure 10.2.1.3-4 Void fraction Iower half of core Double ended DVI break with isolated containment IRWST window with one injection path 1 c 8-- o _ ~ u a
.6- 5 hi u -
u_ - 1
.4-- 1 o -
o - > 2-- l 0- " " ' " ' " " "" h #" h W h~' ; ' # " A ~^ ^ ' ~ 2 " ! C -- 0 5b0 10'00 15'00 2000 ; Time (S) l O TIH Uncertainty Analysis for Long-Term Cooling June 1997 o.\3661w.wpElb-061897
l 10-66 l l O v l l . l l Figure 10.2.1.3-5
- Void fraction u p,p e r half of core l Double ended DVI break with isolated containment l- IRWST window with one injection path 1
c 8-- o _
+ _
w Q Lu -
,4 ..I o
~~
_) f
> 2- \[
-ja,l;
~
1 0 0 500 1000 1500 2000 Time (S) l l 1\ TlH Uncertainty Analysis for Long-Term Cooling June 1997 o:\3661w.wpf:1b4E1897 l
l 10-67 i O Figure 10.2.1.3-6 Peak cladding temperoture Double ended DVI break with isolated containment IRWST window with one injection path 255 _ La._ _ v 250 --h@ h' 245 - - s 1 e -
~
240 -- e : O- - E 235 -- W e :
~
230 ' ' ' ' l 0 500 1000 1500 200 0 IIme (s) 1 O T/H Uncertainty Analysis for Long-Term Cooling June 1997 o:\3661w.wpf:lt> 061897 l
1 1 10-68 l q , V l
. i l
1 Figure 10.2.1.3-7 Core exit vapor mass flow rate Double ended DVI break with isolated containment . IRWST window with one injection path m 35 _ 4 m : i e
)n 30 -2: ' ; 25 -2 3 4
- 1 o [ q {b l l
1 l ll h l ll pg((
- o 15 -
5 I i a 10 - o : 5-: j u_
$ 0-5 o :
=E -
-5 l l 0 500 1000 1500 200 0 IIme (s)
O TIH Uncertainty Analysis for Long-Term Cooling June 1997 o:\3662w.wpf:ll>O61897
l 10-69 I O Figure 10.2.1.3-8 Core exit liquid mass flow rate Double ended DVI break with isolated containment IRWST window with one injection path m 2500 _ m : N 2000 - E : .c - 1500 - 1000 -~ g o 500 - : ce : 8 ' ' ' ' id hI iil ,l . I I I ,1.'il L ;l ill i l 0- p'u.pi
. i s::
h[11[ - t j , t
-500 -i $ -1000 -2 o :
2 ~
-1500 ' ' ' '
l l l 0 500 1000 1500 200 0 Time (s) )l l l l l S l TlH Uncertainty Analysis for Long-Term Cooling June 1997 o:\3661w.wpf:1tA1897 l
I 10-70 l C\
'\j l
Figure 10.2.1.3-9 i Core exit droplet mass flow rate l Double ended DVI break with isolated containment IRWST window with one injection path I l m 5E-02 _ l m _ l N _ E - o . 4 E-0 2 -- _ v -
'O ~
. 3 E-0 2 - l o _
a: _ a 2 E-0 2 - _
.1 E-0 2 --
f i l Yh1h lflhlhhM m - m - o -
~
2 ' ' ' ' ' '
'l '
0 l l ' ' ' 0 500 1000 1500 2000 Time (s) l l l I ! l l
? s N)
TlH Uncertainty Analysis for Long-Term Cooling June 1997 o:\3661w.wpf:1W1897
l l l 10-71 l O l l Figure 10.2.1.3-10 Upper plenum collaased liquid level Double ended DVI break with isolated containment IRWST window with one injection path m 4 ~ u&!sm&s,P" M'+ O
\ ;; 2--
er - -
. j ,
l o - l l O 1-r 1 m o. O
~
o _ [I 0 l l i 0 500 1000 1500 200 0 Time (s) l l l l l l O' TlH Uncertainty Analysis for Long-Term Cooling June 1997 c.\3661w.wpf:1b4)61897
l 10-72 l O L Figure 10.2.1.3-11 PRHR Loop ADS Stage 4 mass flow rate Double ended DVI break with
' isolated containment IRWST window with one injection path m 160 _
m - NE 140 -: -
.c -
l 120 -- O o -i o 80 -: c: : an o 60 -[-
~
l m 0- k l 0 '''iiiiiii 0 5d0 10'00 15'00 200 0 l Time (s) t l T/H Uncertainty Analysis for Long-Term Cooling I" I o:\3661w.wpf;1b-061897
a A
-c - -
10-73 0 Figure 10.2.1.3-12 Non-PRHR Loop ADS Stage 4 mass flow rate Double ended DVI break with isolated containment IRWST window with one injection path 60 _ I m _ N - j 50 -~ v : 40 -- ~ a>
- W o 30 --
s : o 20 -- u_ .. m 10 -- ihh Mgg HQ, InhN g,J j gl g ; o
' ' ' ' i i , , ,
O 0 5$0 10'00 1500 2000 T,me i (s) O TIH Uncertainty Analysis for Long-Term Cooling June 1997 a\3661w.wpf:Im1397
i 10-74 i n U Figure 10.2.1.3-13 i PRHR Loop hot leg collapsed liquid leveI ! Double ended DVI break with isolated containment IRWST window with one injection path m 1.6 _
~ _
v 1. 4 -- T 1. 2 -_ - (~ 1-~ - l b1hhYN)+f'0Y f Y0 3 Vl.l,;2, 3 l y _
~
T 8-er _ a 6- _ m -
.4-~ f
- a. _
O _ 2- _
' ' ' ' ' ' ! i i , i i i , , , ,
0 l 0 500 10'00 15'00 200 0 IIme (S) { l l TH Uncertainty Analysis for Long-Tenn Cooling g 3997 a: .3661w.wpf:Ib-061897
10-75 0 Figure 10.2.1.3-14 i l Non-PRHR Loop hot leg collapsed liquid level i Double ended DVI break with isolated containment j IRWST window with one injection path i 1.6 _ ~ . O 1. 4 - l) - 1. 2 - j gp ggg phpjg g499 a 1-- ] o : I ';; .8-- '~ w :
~
6-4-: m o 2-: $ 0 l l l 0 500 1000 1500 2000 IIme (s) O Tai Uncertainty Analysis for Long-Term Cooling June 1997 o:\3661w.wpf:1b4>1897
L 10-76 (~\ U Figure 10.2.1.3-15 U33er Double ended DVI a enum break with 3ress$re isolated containment l lRWST window with one injection path 31
- I m -
- l. o 30 -3 i m :
a 29 --
- t ' 3 28 - -
ca : l- u 27 -: 2 . 26 -3
' 25 - : ^""
Q- I O 24 l l ' ' l 0 500 1000 1500 200 0 ! Time (s) i 4 i
\d l
l TlH Uncertainty Analysis for Long-Term Cooling June 1997 l o:\3661w.wpf:1b-061897 i
10-] l . i O 1 1 d
- Figure 10.2.1.3-16 Pressure difference across vessel Double ended DVI break with isoleted contoinment IRWST window with one injection path 4
~
^
2--
= :
" 0- ' . A La v r' jPmi
* ~
.2-- I
.4-o _
L _ a.6-- ~
, , i
_,3 ,
. .. i
, i i i i , , , , , , , i 0 500 1000 1500 2000 Iime (S)
O T/H Uncertainty Analysis for Long-Term Cooling jun,1997 o:\3661w.wpf:1b41897 1
b 10-78 O v Figure 10.2.1.3-17 . DVI injection mass flow rate Double ended DVI break with isololed containment IRWST window with one injection path m 60 m N - E _o 40 - - v - O ., 20- - o - Cl". -
, 0- - 1 o -
u_ -
-2 0 --
m - m _ o 2 ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' '
-40 l l l 0 500 1000 1500 200 0 Time (s) i l
l i O !l TlH Uncertainty Analysis for Long-Terrn Cooling June:997 l o:\3661w.wpf:1M61897 !
10-79 10.2.1.4 DVI LOCA with 3 ADS Stage 4 Valves, Recirculation Phase This subsection provides an analysis of the DVI LOCA with ADS stage 4 single failure, DVI line valve failure, and failure of ADS stages 1,2, and 3. Long-term cooling results are discussed for the sump injection phase time window. This subsection analyzes a single-ended DVI line break in the PXS valve vault during the sump injection, using the window mode of analysis. Conditions at the start of the window are created by restarting from a previous IRWST injection time window. The sump is turned on at restart and about 1800 seconds are required to transition to a new quasi-steady-state solution that is independent of the initial conditions. The sump levelis simulated as constant at 107.55 feet during the window, while the sump liquid temperature is set at the saturation condition (239'F) at the containment pressure (24 psia). In this calculation, the sump provides a head sufficient to drive water into the downcomer through the DVI nozzles. The water introduced into the downcomer flows down the downcomer and up through the core, into the upper plenum. Steam produced in the core entrains liquid droplets and flows out of the RCS via the ADS stage 4 valves. The DVI flow and the venting provided by the ADS paths provide a high flow through the core, for it to remain cool. Quasi-steady state is reached at about 3800 seconds. Averages for the last 1000 seconds are computed by integration. The following discussion relates to the quasi-steady-state time window. The downcomer collapsed liquid level (Figure 10.2.1.4-1) decreases during the transition to a quasi-steady-state average level of 17.4 feet. The level decreases from 2000 seconds to 3800 seconds as a result of shifting injection to the saturated sump. All of the sump injection water flows down the downcomer and up through the core (Figure 10.2.1.4-2). Pressure spikes produced by boiling in the core can cause the mass flow into the bottom of the core to reverse momentarily, but the core flow is predominantly upward. Boiling in the core produces steam and a two-phase mixture that flows out of the core, into the upper plenum. The core collapsed liquid level (Figure 10.2.1.4-3) maintains a quasi-steady-state mean level of approximately 7.9 feet after 4000 seconds. The boiling process causes pressure variations, which in turn cause variations in the liquid flow rate at the bottom of the core and in the core collapsed level and the flow rates of liquid, entrained droplets, and vapor out of the top of the core. In the ECOBRA/ TRAC noding, the core is divided into two axial levels, each 6-feet long. The void fraction in the top level is shown in Figure 10.2.1.4-5, while Figure 10.2.1.4-4 shows the small void fraction that exists at the bottom level. Subcooled boiling is predicted in the middle levels of the rods. Nucleate , boiling is predicted in the uppermost level of the rods. The peak cladding temperature does TIH Uncertainty Analysis for Long-Term Cooling June 1997 o:\3661w.wpf.lb-061897 l
.__sa aemacJum3Ed58 i
.10-80 ,
, not rise appreciably above the saturation temperature of 240 F (Figure 10.2.1.4-6). The flow
\ through the core and out of the RCS is more than sufficient to provide adequate flushing to ,
preclude concentration of the boric acid solution.
~
Some of the water carried out of the top of the core falls back into the core in the form of liquid and droplets. The mass flow rates at the top of the core are given as Figures 10.2.1.4-7 through -9, for vapor, liquid, and droplets. The average production of steam during sump injection is 21 lb/sec. The liquid flow rate out of the core shows wide band variations (Figure 10.2.1.4-8) but is upward-oriented for most of the time. Liquid
. collects above the upper core plate in the upper plenum, where the average collapsed liquid -
level is 3.0 feet (Figure 10.2.1.4-10). The vapor and entrained liquid mixture flows from the upper plenum into both hot legs. The hot legs receive a two-phase mixture, which discharges through the open ADS stage 4 paths (Figure 10.2.1.4-11). The mass flow rate out of the ADS s+ age 4 pipes at the top of the hot legs shows oscillations indicating intermittent discharge of liquid along with the vapor.. The variation in discharge quality is caused by the variation of the void fraction at the top of the hot leg (Figure 10.2.1.4-13). The pressure drop across ADS stage 4 in the intact loop is, on average, approximately 2 psi. The horizontal sections of the hot legs are each modeled as i COBRA channels, as described in the SSAR, to permit the formation of a pool in the hot legs, between the vessel and the upward slope to the steam generators. Inspection of the void fractions and velocities predicted by ECOBRAfrRAC shows that at the bottom of the pipe is a pool of stagnant liquid, and at the top of the pipe there is mainly vapor flow toward the ADS stage 4 valves. At the interface region between the liquid and vapor is a mixture with an average void fraction of about 0.6, where vapor rises toward the ADS valves with entrained droplets and liquid falls back into the pool. The collapsed liquid level in the
- intact hot leg is, on average, about 0.9 foot. The hot leg is approximately 35 percent full, on average.
3-
- . The hot leg in the broken loop receives two-phase mixture from the upper plenum, all of which discharges through the single, open ADS stage 4 valve (Figure 10.1.2.4-12). The pressure drop across ADS stage 4 in the broken loop is, on average, about 2 psi. As in the ,
intact loop, the unsteady nature of the flow shows the venting of steam from the top of the ' hot leg, together with the occasional carry-out of liquid. Venting the core of steam and water 4
- ensures that there is adequate flow through the core to cool it and to prevent boron precipitation. Inspection of the void fractions and axial velocities predicted by ECOBRA/ TRAC shows that at the bottom of the hot leg in the broken loop is a pool of l stagnant liquid, and at the top of the pipe is mainly vapor flow toward the ADS stage 4 )
valve. There is sharp interface between the stagnant pool and the region where vapor with entrained droplets rises toward the ADS valve and liquid falls back into the pool. The 1 collapsed liquid level in the hot leg of the broken loop is, on average, about 1.1 feet (Figure 10.1.2.4-14). The hot leg is approximately 42 percent full, on average. TlH Uncertainty . Analysis for Long-Term Cooling June 1997 o:\3661w.wpf:1t>061897 t \
,,_,;. _ - - - , "-- ' ^ ' I
10-81 The pressure in the upper plenum is shown in Figure 10.2.1.4-15. The upper plenum g pressurization that occurs in some time periods is due to the ADS stage 4 water W discharged, as previously discussed. A negligible pressure drop is calculated across the vessel (Figure .10.2.1.4-16), and the injection rate of 42 lb/sec through the DVI line into the vessel is shown in Figure 10.2.1.4-17. The analysis demonstrates that adequate core cooling is provided throughout the time window. 9 O T/H Uncertainty Analysis for Long-Term Cooling June 1997 o:\3661w.wpf:1W1897
10-82 i O . e i Figure 10.2.1.4-1 Downcomer ColIapsed Liquid Level Single ended DVI break with isolated containment i Sump window with two injection & two recirculation paths 19.5 l
~
19 - f[/ b l ] 18. 5 - ! b7 , m - l
';; 18 -
j ._ b 17.5 -~
@ 17 -: -
" b ' '
- 16 5 ' ' ' ' i i . , , , , ,
- 2000 3000 40'00 5000 l Time (s) l O
T/H Uncertainty Analysis for Long-Term Cooling I*' IM o:\3661w.wpf;1b-061897
10-83 0 Figure 10.2.1.4-2 l Liquid mass flow rate into core ! Sump w ndow w th two inject n & two recirculation oths ;
, 1500 _
1000 -2 o 500 -- h i 0- d i lb i l E :
~
-500 -- I
~
=s ' ' ' ' ' ' ' ' ' ' ' '
-1000 l I l 2000 3000 4000 5000 Time (S) i TlH Uncertain
- Analysis for Long-Term Cooling June 1997 l
10-84 m
- V
] l Figure 10.2.1.4-3 4 Core collapsed Iiquid leveI
! Si.ngle ended DVI break with isolated containment
- Sump window with two injection & two recirculation paths 9.5 -
~
} i k_h W4.L l Li 4 - l e 8. 5 -- ' 1FIfi 9 7.5-: i e _ 4 m _
- a _
7~~ i
~
' ' ' i i , , ,
6.5 2000 30'00 4000 5000 T,ime (s) O T/H Uncertainty Analysis for Long-Term Coolin8 Jtme 1997 0:\3661w.wPf :ll>&l897
10-85 O l Figure 10.21.4-4 1 Void fraction lower half of core ' Single ended DVI break with isolated contoinment Sump window with two injection & two recirculation paths 1 i 1 l c 8-- o ~ g' o .6-- o - w - u_ -
.4-- !
o - o > 2--
. . , _ .__. _ m....- m . ..a. a.m a.u um a ~ .=m a .i-2ttu m - -. +
0 , 2000 3000 4000 5000 IIme (S) i 1 l i O T&I Uncertainty Analysis for Long-Term Cooling June 1997 o:\3661w.wpf:1W1*97 I
1 i 10-86 l l O l l Figure 10.2.1.4-5 l Void fraction up3er half of core l Single ended DVI break w th isolated containment Sump window with two injection & two recirculation paths l 1 1 C .8-- l o _ i _ o .6-- H u_ Y-
.4--
,:a I ._
o - y 2-- 0 l l 2000 3000 4000 500 0 T me (s) T/H Uncertainty Analysis for Long-Term Cooling - June 1997 o:\3661w.wpf:Ib-061897
10-87 l Figure 10.2.1.4-6 Peak cladding temperature Sump w ndow w th two injection & tw recircu ation oths 255 _
' 254.5 -
252 5 -
~
252 ' l 2000 3000 4000 5000 Time (s) O TlH Uncertainty Analysis for Long-Term Cooling June 1997
10-88 !O, i
- Figure 10.2.1.4-7
- Core exit vapor mass flow rate i Single ended DVI break with isolated containment j Sump window with two injection & two recirculation paths l m 35
! m _
- N _
! E - o 30 - v _
=
I O
~
2 ' ' ' ' ' ' ' i 10 l l
- 2000 3000 4000 5000
) Iime (S) i j ! TlH Uncertainty Analysis for Long-Term Cooling June 1997 o:\3661w.wpf:1W1897 i i
l 10-89 I O-Figure 10.2.1.4-8 Core exit Iiquid mass flow rate Single ended DVI break with isolated containment Sump window with two injection & two recTrculation paths m 2000 _ E - o 1000 -- I L y f { h- h; 0-bdd 6 r T I 1 b l e ' ' l I ' 4 ~ l i l o cr
) , -1000 --
o _
-2000 -
m - m - 0
~
=s
-3000 ' ' ' '
l 2000 3000 4000 5000 Time (s) O TlH Uncertainty Analysis for Long-Term Cooling June 1997 o:\3661w.wpE1W1897
4 10-90 4 !C i 4 l l Figure 10.2.1.4-9 Core exit droplet mass flow rate . Single ended-DVI break with isolated containment ! Sump window with two injection & two recirculation paths I t m 100 _ m : l N 0
.o E :
-100 -: _
t -200 -:
\ e : i1 a _
I o -300 -: I m :
- \
I g -4 00 -- 1 o : ; u_ - 5 0 0 - j v3 - m -600 -: o - s~-700 ' ' ' ' ' ' ' ' ' ' ' i i i 2000 30'00 40'00 5000 T-ime (S) U TlH Uncertainty Analysis for Long-Term Cooling June 1997 o:\3661w.wpf:1b-061897
10-91 O Figure 10.2.1.4-10 Upper plenum collapsed liquid level Single ended DVI break with isolated containment Sump window with two injection & two recirculation paths m 3.6 _ 3.4-jlhW L.L aa
- 3. 2 - I f
3-- ' i l
, l
=>
- l i
.5 2 . 8 -- i a :
? 2. 6 -1 1 :
. 2. 4 -2
; I
~
22 'l ' ' ' ' ' ' ' ' 2000 3000 4000 5000 Time (S) O T/H Uncertainty Analysis for Long-Term Cooling June 1997 c:\3661w.wpf;1W1897
1 i
- 10-92 i
1 lO i j 4 4 4 J ,! Figure 10.2.1.4-11 i j PRHR Loop ADS Stage 4 mass flow rate 4 Single ended DVI break with isolated containment l Sump window with two injection & two recirculation paths l l l _ 140 i m i ' N i E 120 '
.o i
v 100 !
- B0 a
i a -
- i ..
l 60 3 II 1 o 1 - 40 l u-i ! m 20 m O 2 ' ' ' ' g i t ! I ' 0 i
! 3000 40'00 50'00
!, Time (s) i ) i i 1 !O TlH Uncertainty Analysis for Long-Term Cooling June 1997 o:\3661w.wpf:1b-061897 4
l 10-93 0 Figure 10.2.1.4-12 Non-PRHR Loop ADS Stage 4 mass flow rate Single ended DVI break with isolated containment Sump window with two injection & two recirculation paths _ 35 _ ( E 30 _} v 25 - I o 2 0 -- cr o 15 -- f
~
)(
l d ll I h I L I , f.$ J Ill ' k' i 5 l l ' ' ' ' 2000 3000 4000 5000 Time (s) O TIH Uncertainty Analysis for Long-Term Cooling June 1997 o:\3661w.wpf:IM61897
10-94 I O i l l l Figure 10.2.1.4-13 !' PRHR Loop hot leg collapsed liquid level Single ended DVI break with isolated containment , Sump window with two injection & two recirculation paths m 1.6 ~ i C -
- 1. 4 --
4 _
$12-~ -
l- I N I h ; j )
~
.h -
8-f i
- m 1 ,
6-f
; o _
o ,4 - i i i i , , , i i , , i i 2000 30'00 40'00 5000 IIme (S) O TlH Uncertainty Analysis for Long-Term Cooling June 1997 o-\3661w.wpf:1W1897
10-95 0 Figure 10.2.1.4-14 Non-PRHR Loop hot leg collapsed liquid level Sump w ndow wfth two inject $n & tw recirculotio aths 1.4 C l I ll l l Il g'
;; 1__
.T - m -
. 8 -- ?
c; ' ' ' ' ' ' ' ' 6 l l 2000 3000 4000 5000 Time (S) O m une ignalysis for tong-Term cooling June 1997
- l l
10-96 l i ! O i
~
l l l l l Figure 10.2.1.4-15 l U33er plenum aressure Single ended DVI break with isolated containment Sump window with two injection & two recirculation paths ! I j 26.6 _ ! m i o 26.4 -~ 6-u 25.8 - l l " 2 5. 6 -j i e - i ' 25.4 -~ - i o_ : 25.2 ' ' ' l l l 2000 3000 4000 5000 l Time (s) l l I i i i lO j TlH Uncertainty Analysis for Long-Term Cooling June 1997 j o:\3661w.wpf:1b461897
10-97 O Figure 10.2.1.4-16 S n e e ded DVI break wi h i oloted co to nment Sump window with two injection & two recirculation poths
.5 _
4-
}
.3 i i i , ,
2000 30'00 4000 500 0 I , IIT16 (S) O [fd,"$*[1$33plysis for Long-Term Cooling
i 10-98 O l l Figure 10.2.1.4-17 DVI in'eetion mass flow rate Single ende DVI break with isolated containment Sump window with two injection & two recirculation paths _ 60 _
~
s 55 -- v - e 50 - -
}
o
~
k )l l; l f l l l l ( l 0
~
l 2 ' ' ' ' ' ' ' ' ' ' ' ' 35 l l 2000 3000 4000 500 0 Iime (S) D J Ta ai Analysis for Long-Term Cooling June 1997
J - 10-99 10.2.2 Results with Failure to Isolate Containment 10.2.2.1 DVI LOCA with Failure of ADS Stages 1,2, and 3 and Containment Isolation Failure This subsection provides an analysis of the DVI LOCA with failure of ADS stages 1,2, and 3, and failure to isolate contamment. Long-term cooling results are discussed for the IRWST injection phase time window. This subsection analyzes a double-ended DVI line break in the PXS valve vault at the close of the IRWST injection phase, using the window mode of analysis. In this analysis, it is assumed that both banks of ADS stages 1,2, and 3 fail, and that one 18-inch containment purge line remains open. All four ADS stage 4 valves are assumed to operate to provide the vent path. Conditions at the start of the window are prescribed to allow a calculation to begin at an intermediate time in the small-break long-term cooling transient and proceed until a quasi-steady state is achieved. At this time, it can be assumed that the predicted results are independent of the assumed initial conditions. This approach enables extremely long transients to be analyzed in an acceptable amount of computer time. This calculation begins with the boundary conditions described in Section 10.1.3. The IRWST level, which at the begnuung of the simulation is set to the low-low level, is simulated as constant during the transient. The calculation is then carried out for 2000 seconds and a quasi-steady-state condition is established. In this calculation, the IRWST provides a head sufficient to drive water into the downcomer through the operable DVI nozzle. The water introduced into the downcomer flows down the downcomer and up through the core, into the upper plenum. Steam produced in the core entrains liquid and flows out the RCS via the ADS stage 4 valves. The venting provided by the ADS paths enables liquid to flow through the core to maintain core cooling. Approximately 300 seconds of transient are required to establish the quasi-steady-state condition, so this period is ignored in the following discussion. In this case, the venting path provided by the ADS stage 4 valves produces continuous oositive safety injection. In the following, average flow rates have been evaluated by integration of the flow rates over the last 1000 seconds of the time window to calculate quasi-steady-state values. The head of water in the IRWST causes a flow of subcooled water into the downcomer at an approximate average rate of 40 lb/sec through the operable DVI nozzle. The downcomer level reached at the end of the time window is about 15.9 feet (Figure 10.2.2.1-1). All of g the IRWST injection water flows down the downcomer and up through the core W TlH Uncertainty Analysis for Long-Term Cooling June 1997 o:\3661w.wpf It461897
--- - .. - - . ~ . . - ~ .- - . . - - - - - - - - . - - -
I 10-100 n- (Figure 10.2.2.1-2). Pressure spikes produced by boiling in the core can cause the mass
- d. '
flow into the bottom of the core to reverse momentarily, but the core flow is predominantly ! upward. The accumulators have been fully discharged before the start of the time window considered and do not contribute to the DVI flow. Boiling in the core produces steam and a two-phase mixture that flows out of the core, into the upper plenum. The core is 12-feet long and the core collapsed liquid leve) (Figure 10.22.1-3) is, on average, approximately 7.5 feet once quasi-steady state is reached,
- while liquid is present at all elevations in the core. The boiling process causes a variable rate I of steam production and consequent pressure spikes, which in turn cause oscillations in the liquid flow rate at the bottom of the core and also variations in the core collapsed level and the flow rates of liquid, entrained droplets, and vapor out the top of the core. In the -
WCOBRAITRAC noding, the core is divided into two axial levels, each 6-feet long. The void l fractions in the two levels are shown as Figures 10.2.2.1-4 and -5. It can be seen that the core j void fraction is low for the bottom cell. The top core node void fraction is about 0.7, on average. Subcooled boiling is predicted in the middle levels of the rods and nucleate boiling in the uppermost level. The peak cladding temperature does not rise appreciably above the ; saturation temperature (Figure 10.2.2.1-6).- The flow through the core and out of the RCS is 1 more than sufficient to provide adequate flushing to preclude concentration of the boric acid solution. I Some of the water carried out of the top of the core falls back into the core in the j form of liquid and droplets. The mass flow rates at the top of the core are given as j Figures 10.2.2.1-7 through -9, for vapor, liquid, and droplets. The average steam flow rate l out of the core during the last 1000 seconds of the time window is approximately 19 lb/sec. l- The liquid flow rate out of the core shows wide band variations (Figure 10.2.2.1-8) but is upward-oriented for most of the time. Liquid collects above the upper core plate in the upper plenum, where the average collapsed liquid level is about 1.4 feet (Figure 10.2.2.1-10). The variation in the flow rates out of the i core causes_ the observed variation in the liquid levels in the upper plenum and the hot legs. The vapor and entrained liquid mixture flows from the upper plenum into both hot legs. The hot legs receive a two-phase mixture, which discharges through the open ADS stage 4 L paths (Figures 10.2.2.1-11 and -12). The mass flow rate out of the ADS stage 4 pipes at the l top of the hot legs shows oscillations indicating intermittent discharge of liquid along with the vapor. The variation in discharge quality is caused by the variation of the void fraction at the top of the hot leg (Figures 10.2.2.1-13 and -14). The pressure drop across ADS stage 4 , in the intact loop is about 0.8 psi. l The horizontal sections of the hot legs are each modeled as COBRA channels to permit the formation of a pool in the hot legs, between the vessel and the upward slope to the steam ? T/H Uncertainty Analysis for Long-Term Cooling June 1997 o:\3661w.wpf:1b.061897 I - ..
10-101 generators. Inspection of the void fractions and velocities predicted by WCOBRA/ TRAC shows that at the bottom of the pipe is a pool of stagnant liquid, and at the top of the pipe there is mainly vapor flow toward the ADS stage 4 valves. At the interface region between the liquid and vapor is a mixtme with an average void fraction of about 0.6, where vapor rises toward the ADS valves with entrained droplets and liquid falls back into the pool. The collapsed liquid level in the intact hot leg averages 0.9 feet. The hot leg is about 35 percent full, on average. The hot leg in the broken loop receives two-phase mixture from the upper plenum, all of which discharges through the single, open ADS stage 4 valve. The pressure drop across ADS stage 4 in the broken loop is about 0.8 psi. As in the intact loop, the unsteady nature of the flow shows the venting of steam from the top of the hot leg, together with the occasional carry-out of liquid. Venting the core of steam and water ensures that there is adequate flow through the core to cool it and to prevent boron precipitation. Inspection of the void fractions and axial velocities predicted by WCOBRA/ TRAC shows that at the bottom of the hot leg in the broken loop is a pool of stagnant liquid, and at the top of the pipe is mainly vapor flow toward the ADS stage 4 valve. There is a sharp interface between the liquid and vapor as the liquid pool transitions to a region with an average void fraction of about 0.9, fewer liquid droplets rise toward the ADS valve, and less liquid falls back into the pool. The collapsed liquid level in the hot leg of the broken loop is 0.9 feet. The hot leg is about 35 percent full, on average. The pressure in the upper plenum ic shown in Figure 10.2.2.1-15. The upper plenum pressurization that occurs in some time periods is due to the ADS stage 4 water discharged, as previously discossed. A negligible pressure drop is calculated across the vessel (Figure 10.2.2.1-16), and the injection rate through the DVI line into the vessel is shown in Figure 10.2.2.1-17. The analysis demonstrates that adequate core cooling is provided i throughout the time window. l l l l l l 9 l TlH Uncertainty Analysis for Long-Term Cc,oling June 1997 o:\3661w.wpf:1b-061897
10-102 l O l l
~
l l Figure 10.2.2.1-1 Downcomer Collapsed Liquid Levei Double ended DVI break with unisolated contoinment IRWST window with one injection path _ 20
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_ 19 - _ o . C "'8- '
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\.
i l i T/H Uncertainty Analysis for Long-Te:m Cooling June 1997 o:\3661w.wpf:ll>461897
10-103 I Figure 10.2.2.1-2 Liquid mass flow rate into core fRWS ndo w t$ o e fec$ posh _ 3000 _ 2000 -I
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0 500 1000 1500 2000 IIme (S) O Ta u certain atysis for Long-Tenn cooling jun, m7
10-104 O l
~
l Figure 10.2.2.1-3 Core collapsed Iiquid levei Double ended DVI break with unisolated contoinment IRWST window with one injection path 9_ C - 8.5-
~ ^
'1 1 7.5- l 7-m -
? 6. 5 -
$ 6 u 5b0 10'00 15'00 2000 Iime (s) l l
l I O TlH Unc in lysis for Long-Term Cooling Junei s
10-105 l 1 e; i! l l l Figure 10.2.2.1-4 Void fraction lower half of core ; Double ended DVI break with unisolcted containment l lRWST window with one injection path 1 C
.8-- ,
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. . __ ... . - - - . ~ . . . . - .
10-106 1 O l l Figure 10.2.2.1-5 Void fraction upper half of core Double ended DVI break with unisolated containment IRWST window with one injection path 1 l _
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l 0 0 500 10'00 15'00 2000 I I fn e (S) l 1
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W ain lysis for Long-Term Cooling
10-107 0 Figure 10.2.2.1-6 Peak cladding temperature Double ended DVI break with unisolated containment IRWST window with one injection path 245 _ ^ : u_ v 240 - - i-
$ 235 -
a _ ~ - l [ 230 -~ 225 - . k H :
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10-108 l O l Figure 10.2.2.1-7 Core exit vapor mass flow rate Double ended DVI break with unisolated containment ! IRWST window with one injection path m 50 _
$E 5 40 - }
30 -
- Ik ij l o 10 - :
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10-109 1 9 4 Figure 10.2.2.1-8 Core exit liquid mass flow rate Double ended DVI break with unisolated contoinment i IRWST window with one injection path _ 3000 _
~
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, 0- , i i pf i ; j l l i
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i
- 10-110 o
V j Figure 10.2.2.1-9 Core exit droplet mass flow rate
- Double ended DVI break with unisolated containment IRWST window with one injection path
_ 600 _ m _ N - E 400 --
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T/H Uncertainty Analysis for Long-Term Cooling June 1997 o:\3661w.wpf:1b-061897
10-111 O
. l Figure 10.2.2.1-10 ,
Upper plenum collapsed liquid level I Double ended DVI break with unisolated containment ! IRWST window with one injection path i 2 C _ 1 f -
\
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l 10-112 l l Figure 10.2.2.1-11 PRHR Loop ADS Stage 4 mass flow rate Double ended DVI break with unisolated contoinment IRWST window with one injection path ! l _ 100 , E 80-- l ; l 60-- l'\ ~ c3 ? l o 40 - e:
~
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! l i l 0 500 1000 1500 200 0 Time (s)
, C) TIl inty lysis for Long-Term Cooling June 1997
l _ 10-113 1 Ol l Figure 10.2.2.1-12 Non-PRHR Loop ADS Stage 4 mass flow rate Double ended DVI break with unisolated containment IRWST window with one injection path m 300 _ en - N - E 250 -} v 200 -
~
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0 500 1000 1500 2000 Iime (s) O TlH Uncertainty Analysis for Long-Term Cooling June 1997 o:\3661w.wpf:1b-061897
10-114 l lO j 1 l l Figure 10.2.2.1-13 PRHR Loop hot leg collapsed liquid level Doeb:e ended DVI break with unisolated containment IRWST window with one injection path { 1 l 1.4 - -
~ 1 l
r
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)
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l ' '
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l 10-115__ O 1 i I l Figure 10.2.2.1-14 Non-PRHR Loop hot leg collapsed liquid level Double ended DVI break with unisolated containment i IRWST window with one injection path l _ 1.4 _ l
# I
- r l
~ 1. 2 - -
r i
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l 10-116 (~)\ i . Figure 10.2.2.1-15 U33er p enum aressure Double ended DVI' break with unisolated containment IRWST window with one injection path 32 _ _
^30-:
o :
] 28 -3 v c 26 --
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i 10-117 0 Figure 10.2.2.1-16 Pressure difference across vessel Double ended DVI break with unisolated containment IRWST window with one injection path
.6 _
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l l l 0 500 1000 1500 200 0 Time (s) l l 9 l :==gy,,,, ,,, mg_ c., ,_ _
10-118 l I ~ l Figure 10.2.2.1-17 l- DVI i njection mass flow rate Double ended DVI break with unisolated containment IRWST window with one injection path _ 50 _ 40 ---
- 30 -.-
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10-119 10.2.2.2 Small-Break LOCA with ADS Stage 4 Single Failure, DVI Line Valve Failure, and Failure of ADS Stages 1,2, and 3 This subsection provides an analysis of the small-break LOCA with ADS stage 4 single failure, DVI line failure, and failure of ADS stages 1,2, and 3. Long-term cooling results are discussed for the sump injection phase time window. This subsection analyzes a single-ended DVI line break in the PXS valve vault during the sump injection, using the window mode of analysis. Conditions at the start of the window are created by restarting from a previous IRWST injection time window. The calculation assumes 2 sump valves open in the broken DVI line, and that 2 injection paths are open in the intact DVI line. Recirculation flow is from the sump through the IRWST to the intact DVI line and then to the vessel through the intact DVI nozzle. The sump is turned on at restart and 500 seconds are required to transition to a new quasi-steady-state solution that is independent of the initial conditions. Average flows are computed by integration over the last 1000 seconds of the time window. The sump level is simulated as constant at 105.9 feet during the window while the sump liquid temperature is set at the saturation condition (212*F) at the containment pressure (14.7 psia). In this calculation, the sump provides a head sufficient to drive water into the downcomer through the DVI nozzles. The water introduced into the downcomer flows down the downcomer and up through the core,into the upper plenum. Steam produced in the core entrains liquid droplets and flows out of the RCS via the ADS stage 4 valves. The DVI flow and the venting provided by the ADS paths provide a high flow through the core for it to remain cool. The DVI flow rate is shown in Figure 10.2.2.2-17. The injection flow rate ranges between l 35 lb/sec and 65 lb/sec, and is into the vessel throughout the calculation. The variations in DVI injection are a result of intermittent pressurization in the upper plenum of the reactor l vessel. The intermittent pressurization of the upper plenum results from boiling in the core. l The average injection rate is 48 lb/sec. The downcomer collapsed liquid level (Figure 102.2.2-1) decreases during the transition to a quasi-steady-state average level of 16.1 feet. All of the sump injection water flows down the downcomer and up through the core (Figure 10.2.2.2-2). Pressure spikes produced by boiling in the core can cause the mass flow into the bottom of the core to reverse momentarily, but the core flow is predominantly upward. Boiling in the core produces steam and a two phase mixture that flows out of the core, into the upper plenum. The core collapsed liquid level (Figure 10.2.2.2-3) maintains a quasi-steady-state mean level of approximately 7.2 feet. The boiling process causes pressure variations, which in turn cause variations in the liquid flow rate at the bottom of the core and TlH Uncertainty Analysis for Long-Term Cooling June 1997 o:\3661w.wpf:1b-061897
10-120 lp ' in the core collapsed level and the flow rates of liquid, entrained droplets, and vapor out of j;' the top of the core. In the ECOBRAITRAC noding, the core is divided into two axial levels, each 6-feet long. The void fraction of 0.76 in the top level is shown in Figure 10.2.2.2-5, while Figure 10.2.2.2-4 shows the small void fraction that exists at the bottom level.- Subcooled boiling is predicted in the middle levels of the rods. Nucleate boiling is predicted in the 1 uppermost level of the rods. The peak cladding temperature does not rise appreciably above the saturation temperature of 212 F (Figure 10.2.2.2-6). The flow through the core and out of the RCS is more than sufficient to provide adequate flushing to preclude concentration of the boric acid solution. Some of the water carried out of the top of the core falls back into the core in the form of liquid and droplets. The mass flow rates at the top of the core are given as Figures 10.2.2.2-7 through -9, for vapor, liquid, and droplets. The average production of steam during sump injection is 21 lb/sec. The liquid flow rate out of the core shows wide band variations l (Figure 10.2.2.2-8) but is upward-oriented for most of the time. Liquid collects above the upper core plate in the upper plenum, where the average collapsed liquid level is 1.4 feet. The vapor and entrained liquid mixture flows from the upper plenum into both hot legs. The hot legs receive a two-phase mixture, which discharges through the open ADS stage 4 paths (Figure 10.2.2.2-11). The mass flow rate out of the ADS stage 4 pipes at the top of the hot legs shows oscillations indicating intermittent discharge of liquid along with the vapor. The variation in discharge quality is caused by the variation of the void fraction at the top of the hot leg (Figure 10.2.2.2-13). The pressure drop across ADS stage 4 in the intact loop is,
~on average, approximately 1.1 psi. The horizontal sections of the hot legs are each modeled l as COBRA channels, as described in the SSAR, to permit the formation of a pool in the hot legs between the vessel and the upward slope to the steam generators. Inspection of the void L fractions and velocities predicted by ECOBRA/rRAC shows that at the bottom of the pipe is a pool of stagnant liquid, and at the top of the pipe there is mainly vapor flow toward the ADS stage 4 valves. At the interface region between the liquid and vapor is a mixture with an average void fraction of about 0.6, where vapor rises toward the ADS valves with entrained droplets and liquid falls back into the pool. The collapsed liquid level in the intact hot leg is, on average, about 0.8 foot. The hot leg is approximately 33 percent full, on
- average.
i The l'at leg in the broken loop receives two-phase mixture from the upper plenum, all of , which discharges through the single, open ADS stage 4 valve (Figure 10.2.2.2-12). The pressure drop across ADS stage 4 in the broken loop is, on average, about 1.1 psi. As in the intact loop, the unsteady nature of the flow shows the venting of steam from the top of the , hot leg, together with the occasional carry-out of liquid. Thus, the total discharge from all L -ADS stage 4 valves is about 48 lb/sec. Venting the core of steam and water ensures that
- there is adequate flow through the core to cool it and to prevent boron precipitation.
! Inspection of the void fractions and axial velocities predicted by ECOBRA/ TRAC shows that i-TH Uncertainty Analysis for Long-Term Cooling June 1997 o:\3661w.wpf:1b 061897
10-121 at the bottom of the hot leg in the broken loop is a pool of stagnant liquid, and at the top of I the pipe is mainly vapor flow toward the ADS stage 4 valve. There is sharp interface between the stagnant pool and the region where vapor with entrained droplets rises toward the ADS valve,and liquid falls back into the pool. The collapsed liquid level in the hot leg of the broken loop is, on average, about 0.9 foot (Figure 10.2.2.2-14). The hot leg is approximately 35 percent full, on average. The pressure in the upper plenum is shown in Figure 10.2.2.2-15. The upper plenum pressurization that occurs in some time periods is due to the ADS stage 4 water discharged, as previously discussed. A negligible pressure drop is calculated across the vessel (Figure 10.2.2.2-16), and the injection rate through the DVI line into the vessel is shown in Figure 10.2.2.2-17. The analysis demonstrates that adequate core cooling is provided throughout the time window. O O TIH Uncertainty Analysis for Long-Term Cooling ,7une 1997 o:\3661w.wpf:1W1897
1 10-122 l l A V , l Figure 10.2.2.2-1 Downcomer Collapsed Liquid Levei Single ended DVI Break with unisolated containment Sump window with two injection and recirculation paths C :
~
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15 l l 2100 2600 3100 36'00 4100 Time (s) i g T aignalysis for Long-Term cooling jun, im l
)
. . _ . _ _ _ . . . . . _ _ _ _ _ _ . _ . _ _ . _ _ _ _ _ _ _ . _ . _ . . _ . _ _ _ _ . . _ . _ . - . _ . _ _ . - ~ . . _ _ . _ . . _ . . . _ . _ _ . _ . _ _ _ _ . . _ . . _ _ _ _ _ _ _ _ _ _
I 10-123 Figure 10.2.2.2-2 Liquid mass flow rate into core Sin le ended DVI Break with unisolated containment Sum window with two injection and recirculation paths m 2000 _ m :
)
1500 -3 C ! 1000 -{ j 500 -- 0-
-500 ; i
-1000 1 1 o 3
=E ' ' ' ' ' ' ' ' ' ' ' ' ' ' '
-1500 l 21r0 ~.' 2600 3100 l
3600 l 4100 Time (s) I O T/H Uncer in Analysis for Long-Term Cooling June tw _ _ _ . _ _ _ _ . _ _ . _ _ - - .- __.__ _ _ _ _ . _ _ _ _ _ m _ _ _ _ - - - r---
. - _ - . . . . . - - . - . . .-.~ - . ..
L 10-124 0 Figure 10.2.2.2-3 Core colIapsed liquid leveI Single ended DVI Sump window with Break with unisolated two injection and recirculation containment paths 9_ C :
" 8.5 :
8-h:M- Mpsyk 76.5-3 1 : 61 - 5.5 2100 l l ' ' ' ' l 2600 3100 3600 410 0 Time (s) l l Tai Uncertain alysis for Long-Term cooling Junes s
10-125 0 Figure 10.2.2.2-4 Void fraction Iower haif of core Single ended DVI Break with unisolated containment S u m p' window with two injection and recirculation paths l l 1
'~ 8--
g _
~
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4-- a - O
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0 2100 2600 3100 3600 4100 Time (s) O T/H Uncertainty Analysis for Long-Term Cooling June 1997 o:\3661w.wpf:lt>4M1897
10-126 , 1 l O Figure 10.2.2.2-5 Void fraction upaer half of core I Single ended DVI Break with unisolated containment Sump window with two injection and racirculation paths 1
~ 1
$l l
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kk if I ql kl A o 6-- V o u w - 4-- o - o -
> 2--
' ' ' ' ' ' ' ' ' ie i , i , ,
0 2100 26'00 31'00 36'00 4100 IIme (S) l l 1 m unceruin atysis for 'ang-Term cooling %, m, 1 l
10-127 0 Figure 10.2.2.2-6 Peak cladding temperature Single ended DVI Break with unisolated containment Sump window with two injection and recirculation paths 230 _ m : g 229 - syW 228 - g 3 p l
- c. :
b 225 -[ 224 - ' ' ' ' l l l 2100 2600 3100 3600 4100 Time (s) O T/H Uncertain lysis for Long-Term Cooling June 1997
10-128 O 1 Figure 10.2.2.2-7 Core exit v a p"o r mass fIow rate i d ' " " ' ' * ' '" "* lum"p' 'w'r n'a"o w' N i Eh two inje on n recireufa"i n paths m 40 _ m :
)o 35 -3 C 3 0 _:
5 -
, 10 -j 5 5 l
l l 2100 2600 3100 3600 4100 Time (s) l l l O TIH i Analysis for Long-Term Cooling June 1997
10-129 9 Figure 10.2.2.2-8 i Core exit Iiquid mass flow rate ump window i h two injec on and recircufotion poths m 2000 _ 1500 -! 1000 -- 500 - . g 0-
]
i [ i j n q u l p s: -500 - . u_ - 10 0 0 -2 ] m -1500 -
" -2000 ~
l ! l 2100 2600 3100 3600 4100 Time (s) TlH Uncertain alysis for Long-Term Cooling June 15
10-130 i lvO i - l Figure 10.2.2.2-9 Core exit droplet mass flow rate Single ended DVI Break with unisolated contoinment Sump window with two injection and recirculation paths m 600 m - l
- x !
l E 400 - -
- _a _
v _ 200 -- : O o .. (._) l i 1 o 0 L- 'd '- - - '. ' - I' a:: - ! s: ' o -200 -- -
- 1
_ 1 m -400 -- l m I o
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~
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- Iime (S) 1 i
TIH Uncertainty Analysis for Long-Term Cooling June 1997 c:\3661w.wpf:1W1897 l l l
10-131 9' Figure 10.2.2.2-10 ; i Upper plenum collapsed liquid leveI i Single ended DVI Break with unisolated containment ' Sump window with two injection and recirculation paths m 2.2 _
~
2 --
- 1. 8 -
e
- 1. 6 - I h 1.4- l l
g 1. 1 i t ) % 1 2 -- I j( E :
. 1 --
$ 8
~
l l l 2100 2600 3100 3600 4100 Time (s) I I O TM U certamy Analysis for Long-Term Cooling June 1997
j 10-132 iO ! l i l ) Figure 10.2.2.2-11 i PRHR Loop ADS Stage 4 mass flow rate ump window i h two injec on and recircufation paths ! m 80 1 6 0 -- 2
$ 0 ' ' ' '
' 2100 2600 3100 3600 4100 Ilme (S) 1 io TlH Uncertain l alysis for Long-Term Cooling June 1997
10-133 0 Figure 10.2.2.2-12 Non-PRHR Looa ADS Stage 4 mass flow rate Single ended DV Break with unisolated containment Sump window with two injection and recirculation paths m 300 _ m :
) 250 -3 f E v 2 0 0 --
150 -- h m m 0-- d J i bu l i LILhd I o -
=s ~
-50 l l
l 2100 2600 3100 3600 4100 IIme (s)
O TIH Uncertainty Analysis for Long-Tenn Cooling June 1997 o:\3661w.wpf:1b-061897
- - _ - . _ _ _ - - = _. - - . -
10-134 f l l l4v Figure 10.2.2.2-13 PRHR Loop hot leg collapsed liquid levei Single ended DVI Break with unisolated contoinment Sump window with two injection and recirculation paths
,_,, 1 4 -
12-
- I l
$ ~h h bi dl k I
J f l l U~. = : l,/ Ml .4 ) , v
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1 10-135 l 9' Figure 10.2.2.2-14 Non-PRHR Leop hot leg collapsed liquid level Single eneed DVI Break with unisolated contoinment Sump window w!th two injection and recirculation paths 1.4 _ C _ "12- J j
. [ 'D M Qg fQ '
I i 1 . .r
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~ . . - . . . . . - - . - - . . . . - . . - - _ . - . - . - . . . . . - . . . . . . - . - . . . _ . . . . .
10-136 9 2 Figure 10.2.2.2-15 i l i U33er 3 enum aressure Single ended DV! Break with unisolated containment l Sump window with two injection and recirculation paths j 17
^ -
l c _ j - 16 . 5 -- , v2 1 $ f
~_
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'''l ' ' ' '
2100 2600 3100 3600 410(I Time (s) O
~ ~ ~
TlH Weemin Analysis for Long-Term Cooling Junei s
10-137 O Figure 10.2.2.2-16 Pressure difference across vesseI fum"p window Nih two inject on and recircufotion poths 6 m 4: m 2 5 o_ . w - Cl- .6-
.8 ' ' '
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10-138 l i , o
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l Figure 10.2.2.2-17 DVI i njeetion mass flow rate Single ended DVI Break with unisolated containment Sump window with two injection and recirculation paths m 60 _ m - N - E 55 - j. i i l i l l \ 50 -- ] j l I
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1 10-139 I 10.2.2.3 Sensitivity Calculations on Sump Level for DVI Break with Failure to Isolate Containment This section analyzes level sensitivity calculations for a single ended DVI line break with failure to isolate containment during a sump injection time window. The initial conditions used are the same as in the calculation described in subsection 10.2.2.2. The calculations are initiated as a restart after the base calculation modeling a sump level of 105.9 feet has reached quasi-steady state, and represent a perturbation from the quasi-steady-state conditions. The calculations are run for 1000 seconds, a time window suficient to determine the effect of sump level uncertainties. With the sump level assumed to be at 105.4 feet, the sump provides sufficient hydraulic head to drive water into the downcomer through the DVI nozzles. The water introduced into the downcomer flows down the downcomer and up through the core, into the upper plenum. Steam produced in the core entrains liquid droplets and flows out of the RCS via the ADS stage 4 valves. The DVI flow and the venting provided by the ADS paths provide a high flow through the core for it to remain cool. The collapsed liquid level in the downcomer decreases from 16.1 feet in the base case to 16 feet (Figure 10.2.2.3-1), and the core collapsed liquid level remains about 7.2 feet (Figure 10.2.2.3-2). As in the base case, the peak cladding temperature does not rise significantly above the saturation temperature (Figure 10.2.2.3-3). Some of the water carried out of the top of the core falls back into the core in the form of liquid and droplets. The vapor mass flow rate at the top of the core is given as Figure 102.2.3-4. The average production of steam during sump injection is 21 lbisec, as with the base case, and the DVI injection mass flow rate averages approximately 47 lb/sec (Figure 10.2.2.3-5). It can be concluded that the solution obtained for this case is insensitive to a sump level variation of 0.5 feet. Further, Section 10.1.3 has provided justification that 105.4 feet is a conservative lower level. If the sump levelis assumed to be 104 feet and the calculation performed as described above, the hydraulic head provided by the sump is insufficient to drive water into the dowmcomer through the DVI nozzle. The rate at which steam is produced in the core remains at about 21 lb/sec (Figure 10.2.2.3-6), while the DVI injection rate drops to about 8 lb/sec (Figure 10.2.2.3-7). In a sensitivity case for a single-ended DVI break in which only one injection and one recirculation path were assumed to be open in the intact DVI line, instead of two paths each, the sump head of 105.9 feet was insufficient to maintain core cooling. TlH Uncertainty Analysis for Long-Term Cooling June 1997 o:\3661w.wpf:ll>461897
l l 10-140 O . l l Figure 10.2.2.3-1 Downcomer collopsed liquid level. Sump window Single ended DVI break with unisolated containment Sump window with sump level = 105.4 feet m 17.5 - i
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10-141 O Figure 10.2.2.3-2 Core collapsed liquid leve1. Sump window Single ended DVI break with unisolated contoinment Sump window with sump level = 105.4 feet m 8.5 - w - 8_-
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J 10-142 O v 1 Figure 10.2.2.3-3 Peak cladding temperature. Sump window Single ended DVI break with unisolated containment Sump window with sump level = 105.4 feet i 230 _ I u_ _ Y v 229 -- _
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i 10-143 i O i i l Figure 10.2.2.3-4 ; l Core exit vapor flow. Sump window ! Single ended DVI break with unisolated containment Sump window with sump level = 105.4 feet i _ 45 _ m : )_a40 -3 - v 35 -:
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10-144 3 (G l Figure 10.2.2.3-5 DVI i n'ection, Sum window Single ended DVI break with unisolated containment Sump window with sump level = 105.4 feet m 60 _ m :
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10-145 0 Figure 10.2.2.3-6 Core exi: va30r ow Single ended DVI break with unisoloted contoinment i Sump window with sump level = 104 feet m 45 _ m : Y 40 -3 v 35 -i 30 - O o : 2 25 -I 1 l
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O T/H Uncertainty Analysis for Long-Term Cooling June 1997 o:\3661w.wpf:1W1897
l' i 10-146 O ; i l l l Figdre 10.2.2.3-7
- JV ended DVI break w i' t i n'ec: i on h unisol'ated containment Single Sump window with sump level = 104 feet l
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11-1 p 11
SUMMARY
OF RESULTS !d This section discusses the potential effects on the AP600 PRA due to issues identified during the TH analyses documented in Sections 9 and 10. The TE analyses were performed for accident sequences with a high enough frequency to be potentially risk-significant if core damage, rather than successful core cooling, were predicted. The TE analyses were performed with conservative TH assumptions, which bound the TH uncertainty rather than quantifying it. This section is organized with a discussion in Section 11.1 of the issues that were identified from the TH analyses, and a discussion of the effect of these issues on the Focused PRA and Baseline PRA in Sections 11.2 and 11.3. Section 11.4 concludes with a summary of the potential effect of the residual sequences excluded by the 1 percent screening criterion used to determine the cases chosen for TM analyses. 11.1
SUMMARY
OF ISSUES IDENTIFIED FROM TM ANALYSES The TH uncertainty evaluation process was designed to provide a set of conservative l analyses that gives higher confidence in the success criteria defined for the AP600 PRA. Most of the TE analytical cases result in successful core cooling, and therefore demonstrate p that the corresponding AP600 PRA success criteria are valid even with more restrictive TE ( assumptions. However, there are a few instances of TM analyses that do not result in a prediction of successful core cooling (i.e., the PCT may be greater than 2200*F). Due to the process of bounding the TH uncertainty rather than quantifying it, exceeding 2200 F in a conservative analysis does not necessarily provide information on why the case failed. For example, the reason for exceeding 2200 F could be due to an assumption such as the decay heat, or could be due to a system lirnitation. A system limitation, such as line resistance or valve flow area, could be physically based or due to overly conservative input. The process used in this report does not usually include further analytical assessments to determine whether the same set of equipment would provide successful core cooling,if the TE assumptions were less conservative. Instead, alternate cases were analyzed with more quipment, while maintaining the conservative analysis assumptions, to show successful core cooling. Therefore, the end product of a case exceeding 1200'F PCT is the definition of a set of equipment for which it is unknown whether successful core coeling wili scur under less restrictive, or nominal, conditions. The only findings from the TH analyses are relative to the number of ADS valves that are j needed for successful core cooling, given the conservative analysis assumptions. The cuccess l criteria in the AP600 PRA require 2 stage 4 ADS lines to open to achieve IRWST gravity
- injection, and subsequently long-term sump recirculation. There are two exceptions in the l
Summary of Results June 1997 o:\3661w.wpf:1b-061897
11-2 current success criteria: 1) LOCAs smaller than 2 inches, and transients with loss of PRHR, require an additional stage 2 or 3 ADS line to reduce the RCS pressure below the stage 4 { ADS interlock pressure, and 2) LOCAs larger than 9 inches do not require any ADS, if the { containment is isolated. The first finding from the TlH analyses is that 2 stage 4 ADS may not always be adequate to provide the necessary venting of the RCS to maintain passive injection from the IRWST and sump recirculation. In the short-term cooling phase of the accident, a conservative NOTRUMP analysis shows that 2 stage 4 ADS is adequate for a 4 inch DVI line break. Because venting from the break can help keep the RCS depressurized in the short term, this case is used as an illustration of successful core cooling with 2 stage 4 ADS for breaks that I are at least 4 inches. For a break with less than a 4-inch diameter, a conservative NOTRUMP analysis shows that an additional stage 2 or 3 ADS line is adequate to depressurize the RCS for IRWST gravity injection. The conservative long-term cooling analyses also show that 2 ' stage 4 ADS lines are not adequate venting to maintain sump recirculation. Alternate LTC cases demonstrate that successful core cooling occurs if 1 bank of stage 1,2, and 3 ADS is credited, or if another stage 4 ADS line is credited. This finding is bounded by exanurung l the effect on the PRA of requiring 3 stage 4 ADS lines for any condition where 2 stage 4 ADS l lines are currently required. I The second finding from the T/H analyses is that a LLOCA may not adequately depressurize g without the actuation of ADS. In the short-term cooling NOTRUMP analysis, the results for W a 9-inch break were found to be sensitive to the discharge coefficient assumed. A sensitivity to the discharge coefficient is the same thing as a sensitivity to the break size that defines the lower end of the LLOCA initiating event. The PRA modeling of the LLOCA event tree with no ADS has further implications for long-term cooling. Because the break location may be covered with water during sump recirculation, venting is only available through ADS. The structure of the LLOCA event tree is based primarily on the early phase of the accident progression, and does not consider ADS requirements for the recirculation phase of the accident. Finally, it should be noted that the long-term cooling analyses are performed not only to bound TlH uncertainty, but also to provide the basis for the success criteria during this phase of the accident. Unlike short-term cooling, there were no pre-existing analyses to show sump recirculation for the multiple failure accidents credited as successful core cooling in the PRA. The information from the expanded event trees in Section 4 was used to make risk-informed decisions to concentrate long-term cooling analysis efforts on accident sequences that have the most significance to the PRA. Through this process, and technical interactions between analysts, AP600 designers, and PRA engineers, observations were made about the long-term cooling phase of the accident relative to how it has been modeled in the PRA. The lack of ADS modeling for LLOCA, discussed above, is one of these observations. Another Summary of Results June 1997 o:\3661w.wpf:1141897
i 1 11-3 O observation is that the SI line break event tree does not n odel the need to open recirculation 4 g paths; recirculation through the break had been assumed, but is not always possible. The effect of these issues on the PRA is addressed in Section 11.2 for the Focused PRA and in Section 11.3 for the Baseline PRA. i 11.2 EFFECT OF TlH UNCERTAINTY RESUL'IS ON FOCUSED PRA This section addresses the effect on t' he Focused PRA due to the following three issues: A change to the success criteria of 3 stage 4 ADS lines rather than 2 stage 4 ADS g . . Adding a recirculation top event (requiring 2 of 4 paths) to the SI line break event tree a No ADS top events are asked in the LLOCA event tree, if the containment is isolated The Focused PRA models were examined to estimate the effect of changing success criteria to address the first two issues (ADS success criteria and SI line break event tree structure). The j results of this analysis show that the AP600 Focused PRA CDF for the at power internal ! initiating events increases from 7.7E-6/ year to approximately 8.0E-6/ year. The LRF for the Focused PRA at power internal initiating events increases from 5.5E-7/ year to approximately l_ 6.5E-7/ year. Almost all of the increase is due to the change in ADS success criteria. The Focused PRA total core damage frequency and large release frequency remain within the goals established in SECY-94-84. The small increase in CDF and LRF does not affect existing conclusions or insights from the Focused PRA. i The third item is addressed based on the following: i a For short-term cooling, no ADS are needed when the containment is isolated. Case UC7 demonstrates this, but also identifies that the results can be sensitive to the break size at the lower end of the LLOCA break spectrum. However, as shown in Section 6.3, the potential impact on the Focused PRA CDF or LRF is < 0.1 pcreent. This potential < impact is based on expanded event tree sequences that not only consider the failure of all ADS but also include the possibility of 1 stage 4 ADS line succeeding. Therefore the impact, that is already r.egligible, is overestimated. > a For long-term cooling, the ADS is needed, but the number of lines required is 4-undefined. As mentioned above, the potential Focused PRA CDFILRF impact of not succeeding with 0 or 1 stage 4 line is < 0.1 percent. Using the information presented in Table 7.3-1, if 2 stage 4 ADS is not adequate, the impact on the Focused PRA CDF and LRF is estimated to be 0.4 percent. O Summary of Results June 1997 o:\3661w.wpf:lt41897
11-4 This evaluation demonstrates that the effect of the identified success criteria changes on the Focused PRA are small, and do not change the conclusions or insights gained from the Focused PRA. 11.3 EFFECT OF TIH UNCERTAINTY RESULTS ON BASELINE PRA This section addresses the effect on the Baseline PRA due to the same issues that were addressed in the previous section: A change to the success criteria of 3 stage 4 ADS lines rather than 2 stage 4 ADS Adding a recirculation top event (requiring 2 of 4 paths) to the SI line break event tree
=
No ADS top events are asked in the LLOCA event tree,if the containment is isolated The potential effect of the first issue (ADS success criteria) on the baseline PRA has already been evaluated and presented in Chapter 50.5.6 of the PRA. The potential effect of the second issue (change to the SI line break event tree) is expected to be small, because the probability of failure of 2 recirculation lines was shown, in Section 7, to be small. The incremental CDFILRF due to this change would therefore be only a small fraction of the existing SI line break contribution to the baseline results. This expectation is supported by the results of the Focused PRA evaluation discussed in Section 112, in which the change to the SI line break event tree had very little effect on the results. The third item is addressed based on the following: I
=
For short-term cooling, the PRA model does not require ADS for large LOCA when the containment is isolated. Case UC7 demonstrates this, but also identifies that the results 1 can be sensitive to the break size at the lower end of the LLOCA break spectrum. I Redefining the break size cutoff between large and medium LOCAs in the FRA would not be expected to have a significant effect on the PRA results, because the conditional core damage probabilities (that is, the event CDF divided by the event initiation frequericy) are similar for both of these events. For long-term cooling, ADS would be needed for the passive cooling scenarios. However, in the Baseline PRA, the RNS can be credited as a means of providing recirculatica without the need for passive sump recirculation. RNS is not currently modeled in the LLOCA event tree, because of the rapid accident progression early in the event; there may not be time for the operator to align the RNS. However, it is expected that there would be adequate time to actuate RNS for long-term cooling, because it takes several hours for the IRWST to drain. Because there is a relatively high probability (i.e., approximately 94 percent, based on results from the Baseline PRA) that RNS is available for this scenario, but has not been factored into the frequency because Summary of Results June 1997 o:\3661w.wpf:IM161897
l l i 1 i 11-5 l I f- it was not modeled in the FRA, any effect on the results of the Baseline PRA is judged to be small, on the order of 1 percent or less CDF or LRF. ' This evaluation demonstrates that the effect of the identified success criteria changes on the Baseline PRA is small, and does not change the conclusions or insights gained from the
- Baseline PRA.
l 11.4 OTHER RESULTS l , 3 .. l This analysis examined, in a bounding manner, the ability to successfully cool the core under adverse configurations modeled (explicitly or implicitly) in the PRA. In defining the cases to l be analyzed, the relative risk importance of various sequence groups was used as one criterion for limiting the number of analyses to be performed. Thus, there is the potential that there is some residual frequency currently assigned to success sequences in the PRA for which analyses have not been performed, either in this TE uncertainty analysis or in the other analyses that have already been performed to support the success criteria. However, the following discussion shows that this residualis small. For the short-term cooling analysis, although a criterion of 1 percent of the Focused PRA CDF was used to define cases for conservative TM analyses, the analysis cases were defined in a bounding manner, so that sequences with frequencies below the criterion were captured in other sequence groups for which analyses were performed. Further, a portion of the sequences with frequencies below the criterion involves equipment failures for which the TM effects are bounded by other failures that are evaluated in one or more cases. Finally, a substantial additional analytical basis beyond the conservative TM analyses performed in this study, exists to support success for short-term cooling cases. As a result, any residual ; frequency unsupported by short-term cooling TM analyses is judged to be significantly less than 1 percent of the Focused PRA CDF. For the long-term cooling analysis, a probabilistic argument regarding the number of recirculation paths was used to narrow the set of groups for which analyses were needed. The number of recirculation paths was specified to be 2 of 4 for success in Section 7. However, the conservative analyses described in Section 10 show' successful core cooling for cases with 1 of 4 recirculation paths, except for the DVI line breaks. The Focused PRA results in Section 11.2 account for 2 of 4 recirculation paths for the DVIline initiating event, which is supported by TM analyses in Section 10. Section 7 also specified that the TM analyses could credit 3 of 4 CMTslaccumulators, because the probability of having fewer devices spilling into the sump is relatively small. The effect of failure of additional CMTs or accumulators has been evaluated in the TN analyses described in Section 10, through the sump level sensitivity and through the analyses iO Summary of Results June 1997 o:\3661w.wpf:1b-061897
11-6 of DVIline break with failed containment isolation. Thus, there is no significant residual g impact as a result of this assumption. W Given the resuJts above, and considering the conservative, bounding nature of the TM analyses performed, any residual frequency unsupported by long-term cooling TM analyses is judged to be significantly less than 1 percent of the Focused PRA CDF. 9 O Summary of Results June 1997 a\3661w.wpf:lb-061897
12-1 12 CONCLUSION The T/H uncertainty evaluation process to determine the potential impact of TlH uncertainty ort the AP600 PRA has been completed, and is documented within this report. The process encompassed a thorough evaluation of the passive-only success sequences in the AP600 PRA. Both short-term and long-term phases of the accident progression were considered. The comprel ensive process undertaken to address the potential impact of T/H uncertainty on the AP6C0 PRA provides a considerable basis for the claims of successful core cooling for multiple-failure accidents. The result of the process is confirmation that the majority of the success criteria specified in the AP600 PRA for passive-only accident sequences lead to successful core cooling, even when conservatisms consistent with design basis methodology are applied. For multiple-failure accident sequences that exceed the 2200 F PCT core cooling criterion using conservative assumptions, the effect on both the Focused PRA and the Baseline PRA was determined. The effect on tl.- PRA is small, and the Focused PRA total core damage frequency and large release frequenef remain within the goals established in SECY-94-84. More importantly, the conclusions and insights drawn from the PRA results are not affected. O O \ Conclusion June 1997 o:\3661w.wpf:1b-061897
)
l
i 13-1 13 REFERENCES
- 1. NSD-NRC-96-4796/DCPINRC0576, Letter from Brian McIntyre (Westinghouse) to T. R. Quay (NRC) on "AP600 Passive System Reliability Roadmap," August 9,1996.
- 2. WCAP-14869, MAAP4NOTRUMP Benchmarking to Support the Use ofMAAP4for AP600 PRA Success Criteria Analyses, April 1997.
- 3. AP600 Probabilistic Risk Assessment, Revision 8, September 30,1996
- 4. AP600 Standard Safety Analysis Report, Rev.13, May 30,1996.
- 5. WCAP-12945, Code Quahfication Documentfor Best Estimate Analysis, Volumes 1 through 5, Revision 1 (Westinghouse Proprietary).
6. Bordelon, F. M., D. L. Burman, et al., WCAP-8301, LOCTA-IV Program, Loss-of-Coolant Transient Analysis, June 1974 (Westinghouse Proprietary). 7. Lee, N., et al., WCAP-10054-P-A, Westinghouse Small Break ECCS Evaluation Model Using the NOTRUMP Code, August 1985 (Westinghouse Proprietary). A Q 8. Gamer, D. C., et al, WCAP-14776, WCOBRAERAC OSU Long-Term Cooling Final Validation Report, November 1996 (Westinghouse Proprietary).
- 9. MAAP4, Modular Accident Analysis Program, User's Manual, Rev 0, May 1994.
- 10. WCAP-14382, WGOTHIC Code Description and Validation, May 1995 (Westinghouse Proprietary).
- 11. Hochreiter, L.E., et al., WCAP-14171, ECOBRAERAC Applicability to AP600 Large-Break Loss-of-Coolant Accident, Revision 1, October 1996 (Westinghouse Proprietary).
- 12. NTD-NRC-96-4629, Westinghouse Letter, " Confirmatory Items Related to Review of WCAP-12945-P," January 24,1996, Attachment 2, pages 6-8.
O References June 1997 o:\3661w.wpf:ll>461897 ____-_____}}