ML20137X772
| ML20137X772 | |
| Person / Time | |
|---|---|
| Site: | 05200003 |
| Issue date: | 04/16/1997 |
| From: | Gresham J, Ohkawa D WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP. |
| To: | |
| Shared Package | |
| ML20137X744 | List: |
| References | |
| WCAP-14869, WCAP-14869-R, WCAP-14869-R00, NUDOCS 9704220159 | |
| Download: ML20137X772 (456) | |
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1 i i i i MAAP4/NOTRUMP - - 4 I Benchmar<ing to - L Support the Use of , l MAAP4 for AP600 PRA O Success Criteria Analyses l
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I AP600 DOCUMENT COVER SHEET TDC: IDS: 1 S Form 58202G(5/94)[t:\xxxx.wpf:1x) AP600 CENTRAL FILE USE ONLY: 0058.FRM RFS#: RFS ITEM #: AP600 DOCUME44T NO. REVsSION NO. ASSIGNED TO RA-GSR-006 0 Page 1 of 1 ALTERNATE DOCUMENT NUMBER: WCAP-14869 WORK BREAKDOWN #: 3.2.4 DESIGN AGENT ORGANIZATION: Westinghouse TITLE: MAAP4/NOTRUMP Benchmarking to Support the Use of MAAP4 for AP600 PRA Success Criteria Analyses ATTACHMENTS: DCP #/REV. INCORPORATED IN THIS DOCUMENT REVISION: 1 CALCULATION / ANALYSIS
REFERENCE:
ELECTRONIC FILENAME ELECTRONIC FILE FORMAT ELECTRONIC FILE DESCRIPTION S (C) WESTINGHOUSE ELECTRIC CORPORATION 1995. O WESTINGHOUSE PROPRIETARY CLASS 2 g This document contains information proprietary to Westinghouse Electnc Corporation: It is subm4tted in confidence and is to be used solely for the 1 I purpose for which it is fumished and returned upon request. This document and such information is not to be reproduced, transmitted, disclosed V or used otherwise in whole or in part without prior written authorization of Westinghouse Electre Corporation, Energy Systems Business Unit, subject to the legends contained hereof. O WESTINGHOUSE PROPRIETARY CLASS 2C This document is the property of and contains Proprietary information owned by Westinghouse Electric Corporation and/or its subcontractors and suppliers. It is transmitted to you in confidence and trust, and you agree to treat this document in stnct accordance with the terms and conditions of the agreement under which it was provided to you.
@ WESTINGHOUSE CLASS 3 (NON PROPRIETARY)
COMPLETE 1 IF WORK PERFORMED UNDER DESIGN CERTIFICATION gg COMPLETE 2 IF WORK PERFORMED UNDER FOAKE. 1 @ DOE DESIGN CERTIFICATION PROGRAM - GOVERNMENT LIMITED RIGHTS STATEMENT [See page 2] Copynght statement: A license is reserved to the U.S. Govemment under contract DE ACO3-90SF18495. O DOE CONTRACT DELIVERABLES (DELIVERED DATA) Sutaect to specified exceptions, disclosure of this data is restncted until September 30.1995 or Design Certification under DOE contract DE-ACO3-90SFt B495, whichever is later. EPRI CONFIDENTIAL: NOTICE: 1 0 2 3 4 5 CATEGORY: A 3 8 C D E F0 i 2 O ARC FOAKE PROGRAM ARC LIMITED RIGHTS STATEMENT [See page 2) Copynght statement: A lecente is reserved to the U.S Government under contract DE-FCO2-NE34267 and subcontract ARC-93-3-SC-001. O ARC CONTRACT DELIVERABLES (CONTRACT DATA) Subject to specified exceptions, disclosure of this data is restricted under ARC Subcontract ARC 93 3-SC-001, GINATOR SIGNQUgE/DATE
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JJ%i Qhtaun 4lI&7 AP600 RESPONSIBLE MANAGER SI UR 'f APPR VA DATE
- A A. G= nam
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' Approve of the responsible manager signifies document is complete, all required reviews are complete, electronec file is attached and document is released for use.
AP600 DOCUMENT COVER SHEET PJge 2 l Form 58202G(5/94) LIMITED RIGHTS STATEMENTS DOE GOVERNMENT UMITED RIGHTS STATEMENT (A) These data are submitted with limited rights under govemment contract Nu DE ACO3-90SF18495. These data may be reproduced and used by the govemment with the express hmitation that they will not, without wntten permission of the contractor, be used for purposes of manufacturer nor disclosed outside the govemment, except that the govemment may disclose these data outside the govemment ] for the fonowing purposes, if any, provided that the govemment makes such disclosure subject to prohibition against further use and i disclosure: (l) This 'Propnetary Data' may be disclosed for evaluation pu poses under the restnetions above. (II) The 'Propnetary Data' may be oisclosed to the Electnc Power Research institute (EPRI), electnc utility representatives and their - direct consultants, excluding direct commercial competitors, and the DOE National Laboratones under the prohibitions and l restnctions above. (B) Tnis notice shalt be marked on any reproduction of these data, in whole or in part. ARC UMiTED RIGHTS STATE'AENT: This propdetary data, fumished under Subcontract Number ARC-93-3-SC-001 with ARC may be duphcated and used by the govemment and ARC, sutrect to the hmitations of Article H-17.F. of that subcontract, with the express hmitations that the propnetary data may not be disclosed outside tf.e goverrament or ARC, or ARC's Class 1 & 3 members or EPRI or be used for purposes of manufacture without pnor permission of tha Subcontractor, except that further disclosure or use may be made solely for the following purposes: This proprietary data may be disclosed to other than commercial competitors of Subcontractor for evaluat on purposes of this subcontract under
- the resinction that.the propnetary data be retained in confidence and not be further disclosed, and subl ect to the terms of a non-disclosure cgreernent between the Subcontractor and that organization, excluding DOE and its contractors.
DEFINITIONS CONTRACT /DEUVERED DATA - Consists of documents (e.g. specifications, drawings, repotts) which are g:;nerated under the DOE or ARC contracts which contain no background proprietary data, EPRI CONFIDENTIALITY / OBLIGATION NOTICES N <TICE 1: The data in this document is subject to n'o confidentiality obhgations. NOTICE 2: The data in this document is propnetary and confidential to Westinghouse Electric Corporation and/or its Contractors. It is forwarded to recipient under an obhgation of Confidence and Trust for hmated purposes only. Any use, disclosure to unauthorized persons, or copying of this document or parts thereof is prohibited except as agreed to in advance by the Electnc Power Research Institute (EPRI) and Westinghouse Electnc Corporabon. Recipient of this oata has a duty to inquire of EPRI and/or Westinghouse as to the uses of the information contained herein th:t are perm:tted. NOTICE 3: The data in this document is propnetary and confidential to Westinghouse Electnc Cc sorat on and/or its Contractors. It is forwarded to recipient under an obhcation of Confidence and Trust for use only in evaluation tasks specifically authorized by the Electric Power Research Institute (EPRI). Any use, disclosure to unauthonzed persons, or copying this document or parts thereof is prohibited except as agreed to in advance by EPRI and Westinghouse Electric Corporation. Recipient of this data has a duty to inquire of EPRI and/or Westinghouse as to the uses of the information contained herein that aie permitted. This document and any copies or excerpts thereof that may have been generated tra to be retumed to Westinghouse, directly or through EPRI, when requested to do so. NOTICE 4: The data in this document is propnetary and confidential to Westinghouse Electric Corporation and/or its Contractors. It is being rIvealed in confidence and trust only to Employees of EPRI and to certain contractors of EPRI for hmited evaluation tasks authonzed by EPRI. Any use, disclosure to unauthon2ed persons, or copying of this document or parts thereof is prohibited. This Document and any copies or cacerpts thereof that may have been generated are to be retumed to Westinghouse, directly or through EPRI, when requested to do so. NOTICE 5: The data in this document is propnetary and confidential to Westinghouse Electric Corporation and/or its Contractors. Access to this data is given in Confidence and Trust only at Westinghouse facihties for limited evaluation tasks assigned by EPRt. Any use, disclosure to unauthonzed persons, or copying of this document or parts thereof is prohibited. Neither this document nor any excerpts therefrom are to be removed from Westinghouse facihties. EPRI CONFIDENTIALITY / OBLIGATION CATEGORIES CATEGORY "A"- (See Delivered Data) Consists of CONTRACTOR Foreground Data that is contained in an issued reported. CATEGORY "B"- (See Delivered Data) Consists of CONTRACTOR Foreground Data that is not contained in an issued report, except for computer programs. CATEGORY "C"- Consists of CONTRACTOR Dackground Data except for computer programs. CATEGORY "D"- Consists of computer programs developed in the course of performing the Work. CATEGORY T - Consists of computer programs developed pnor to the Effective Date or after the Effe::tive Date but outside the scope of the Work. CATEGORY T*- Consists of administrative plans and admannstrative reports. O
WESTINGHOUSE NON-PROPRIETARY CLASS 3 l WCAP-14869 V I MAAP4/NOTRUMP Benchmarking to Support the Use of i MAAP4 for AP600 PRA Success Criteria Analyses l l l April 1997 O V i Westinghouse Electric Corporation Energy System Business Unit P.O. Box 355 Pittsburgh, PA 15230-0355 gG, C 1997 Westinghouse Electric Corporation ( ,/ All Rights Reserved c:\newprt42\3603w.wpf.It@l497
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# TABLE OF CONTENTS : l h, 4: )
U ~ LIST OF TAB LES '. . . . . . . . . . :. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v
~i LIST OF FIGURES . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii i 4 . j
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- LIST OF ACRONYMS ...................................................... xi - -l 1
EXECimVE S UMMARY . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . 1 I l 1 1- INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1 ; 1.1 : ; Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . ~. . . . . . . . . . . . . . . . . . . . . . . . . 1-1 , f 1.2 - Scope......................................................1-1~ ; 1.3 . Relationship to T/H Uncertainty Resolution . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2 .I 1
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- 2 THE MAAP4 CODE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1 i, Overview of Major Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 2.1. 1 2.1.1 Primary System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2 .;
2.1.2 Core Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-5 l
.2.1.3 AP600-Specific Models . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . 2-6 4 2.2 MAAP4 Simplifications Potentially Impacting Success Criteria Analyses . . . . . . . 2 .
2.2.1 Effect of Homogeneous Two-Phase Flow . . . . . . . . . . . . . . . . . . . . . . . 2-9
- 2.2.2 Effect of Downcomer Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-10 2.2.3 Effect of Core Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .' 2-10 2.2.4 Effect of CMT Simplifications . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . 2-11 t
(^ 3 PRA PHENOMENA IDENTIFICATION RANKING. TABLES (PIRTs) . . . . . . ...... 3-1 3.1 Overview of Multiple-Failure Accident Scenarios . . . . . . . . . . . . . . . . . . . . . . . 3-1 3.2 Development of PRA PIRTs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-14 4 BENCHMARKING CASES . . . . . . . . . .. . . . . . . . . .. . . . . , . . . . . . . . . . . . . . . . . . . 4-1 l i 4.1 - Equipment Modelled . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . _ 4-1 ! 4.2 Primary Benchmarking Cases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-7 4.3 Sensitivity Benchmarking Cases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-11 3 4 a 4 l, 5 ANALYS IS METHOD . . . -. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 p 5.1 Analysis Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1 5.1.1 Decay Heat .................................... ...... 5-2 . 5.1.2 ' Initial Conditions and Line Resistances . . . . . , . . , . . . . . . . . . . . . . . . 5-2 I i 5.1.3 Containment Pressee . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-3 5.1.4 Actuation Logic and Delays . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . 5-3
-5.1.5 Break Discharge Coefficient . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4 , . 5.2 NOTRUMP Applicability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-8 l 5.3 Comparison Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-10 j i
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y iv i l 1 TABLE OF CONTENTS (cont.) i 6 RESULTS OF PRIMARY CASES . . . . . . . . . . . .............. ........... 6-1 6.1 0.5 Inch Break with Automatic ADS (Case 1) . . . . . . . . . . . . . . . . . . . . . . . . 6-1 j 6.2 2.0 Inch Break with Automatic ADS . . . . . . . . . . . . . .. ............. 6-35 6.3. 5.0 Inch Break with Automatic ADS .................... ........ 6-63 6.4 S.75 Inch Break with Automatic ADS .......................... .. 6-91 ; 6.5 3.5 Inch Break with Manual ADS . . . . . . . . . . . . . . . . . . . . . . ... . . . . 6-120 6.6 6.0 Inch Break with Manual ADS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-144 l 6.7 8.75 Inch Break with Manual ADS ............ . . . . . . . . . . . . . . . . . 6- 169 ! 7 RESULTS OF SENSITIVITY CASES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1 7.1 Break Location .............................................. 7-1 7.2 Number of CMTs and Accumulators . . . . . . . . . . . . . . . . . . . . .... . . . . 7-41 : 1 7.3 Number of ADS ............................................ 7-61 ' 7.4 Partial Depressurization for RNS Injection . . . . . . . . . . . . . . . . . ......... 7-97 7.5 IRWST Injection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-112 8 LOCTA PCT RESULTS . . . . . . . . . . ............................. .. . 8-1 9 EVALUATION OF RESULTS . . . . . . . . . . . . ................ ........... 9-1 9.1 Assessment of High Importance Models/ Phenomena . . . . . . . . . . . . . . . . . . . . . 9-1 9.1.1 B reak Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-4 ! i 9.1.2 Interfacial Condensation on CMT Water Surface . . . . . . ........... 9-8 l 9.1.3 Core Cooling / Vessel Mixtun: Level . . . . . . . . . . . . . . . . . . . . . . . . . . 9-11 < 9.1.4 Downcomer . . . . . . . . . . . . . . . . . . . . . . . . . . ...............9-17 9.1.5 ADS-4 ............................ .............. . 9-19 9.1.6 ADS 1 to 3 ......... ........... ................ . 9-24 l 9.1.7 IRWST . . . . . . . . . . . . . . . ............................. 9-27 9.1.8 Accumulator ....... .................................9-29 9.2 Assessment of High Interest Models/ Phenomena . . . . . . . . . . . . . . . . . . . . . 9-31 10 CONCLUS ION S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-1 11 REFEREN CES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1 - 1 O ofwwwpro3N603w.wpf.lt>4*H 4V7 Rev. O, Apre 1997
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- LIST OF TABLES ;
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' Table No. ' Title 'Page ,
3.1-l . Summary of PRA Event Trees Related to MAAP4 Benchmarking . . . . . . . . . . . 3 l 3-2' PIRT for PRA Scenarios with CMT (No Accumulators) . . . . . . . . . . . . . . . . 3-15. 1 3-3 PIRT for PRA Scenarios without CMTs (With Accumulators) . . . . . . . . . . . . . 3-22 4-1 . List of MAAP4/NOTRUMP Benchmarking Cases . . . . . . . . . . . . . . . . . . . . . . 4-3 ; i 4-2L Equipment Defimition and Risk Significance of Benchmarking Cases . . . . . . . . . 4-4 ; 5.1-1 Actuation Signals and Delays for MAAP4/NOTRUM" Benchmarking . . . . , . . . '5-5 ) i 5.1-2 Effective Break ID (inches) for Benchmarking Cases . . . . . . . . . . . . . . . . . . . . 5-6 i [5.3-1 Parameters Compared for Primary Cases (Case 1 to 7) . . . . . . . . . . . . . . . . . . 5-13 6.1-1 Summary of Events for Benchmarking Case 1 - 0.5" Hot Leg Break with 1 CMT (seconds) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-5 6.2-1 Summary of Events for Benchmarking Case 2 - 2.0" Hot Leg Break with 1 CMT (seconds) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-38 6.3-1 Summary of Events for Benchmarking Case 3 - 5.0" Hot Leg Break with 1 CMT (seconds) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-66 6.4 Summary of Events for Benchmarking Case 4 - 8.75" Hot Leg Break with 1 CMT (seconds) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-95 6.5-1 Summary of Events for Benchmarking Case 5 - 3.5" Hot Leg Break with 1 Accumulator (seconds) ......................... ... 6-123 6.6-1 Summary of Events for Benchmarking Case 6 - 6.0" Hot Leg
- 3. ak with 1 Accumulator (seconds) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6- 14 8 6.7-1 Summary of Events for Benchmarking Case 7 - 8.75" Hot Leg Break with 1 Accumulator (seconds) . . . . . . . . . . . . . . . . . . . . . . . . . . . , . 6- 172 8-1 Core Cooling Information for Benchmarking Cases With Core Uncovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-3 i
l 9-1 Code Comparison Plots for High Importance Phenomena from PRA PIRTs . . . . . 9-3 j i i onnewpropueu3w.wpuumwi . Rev. o. AjiMTM7 > i i 1
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. LIST OF FIGURES -
[, , { Figure No.. Title ~ Page .j
.i 2-1 -;- MAAP4 PWR Primary System Gas Nodalization . . . . . . . . . . . . . . . . . . . . . . . ' 2-4 -l l
2-2 MAAP4 PWR Primary System Water Pool Nadalir=* ion . . . . . . . . . . . . . . . . . . 2'-8 !
'i; 31 Sketch of CMT & DVI Lines ' . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 ;
3-2: - 3-6 j through through .! 3-9 Provide mfonnation for SGTR Response . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . 3-13 .
.4 l' . Minimum Vessel Mixture Level for Automatic ADS Cases :
MAAP4 Results, No Accumulators, Containment Isolation Failure Modelled . . . 4-9 ! 4 2' Minimum Vessel Mixture Level for Manual ADS Cases 5 MAAP4 Results, No CMTs. Containment Isolation Failure Modelled . . . . . . . . 4-10 i i 5-1 ' First 100 Seconds of 1979 Best Estimate Decay Heat : c -- for MAAP4/NOTRUMP Benchmarking . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-7 j g 5-2'. Longterm 1979 Best Estimate Decay Heat for ; MAAP4/NOTRUMP Benchmarking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-7 .l 6.1-1 6-6 )
- through ' through 6.1-29 Provide information for Case 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-34 1 1
1 6.2-1 6-39
- through through 6.2-24 Provide information for Case 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-62 6.3 1 6-67 through ' through 6.3-24 Provide information for Case 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-90
. 6.4-1 6-%
through ' through 6.4-24 Prcvide information for Case 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-119 ,
- 6.5-1 6-124
' through - through j 6.5-20 Provide information for Case 5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-143 1 i
- 6.61 6 149 ;
O : through _ through ! L 6.6 20 Pmvide information for Case 6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-168 !
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viii LIST OF FIGURES (cont.) Figure No. Title O Page 6.7-1 6-173 through through 6.7-20 Provide information for Case 7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6- 1 92 7.1 1 7-6 through through 7.1 35 Provide information for Cases 8 and 9 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-40 7.2-1 7-44 through through 7.2-17 Provide information for Cases 10 and 11 ...... . ................. 7-60 7.3 1 7-66 through through 7.3 31 Provide information for Case 12 . . . . . . . . . . . . . . . . . .......... 7-96 7.4-1 7-99 through through 7.4 13 Provide information for Case 13 . . ............. ...............7-111 7.5-1 7-115 through through 7.5-17 Provide information for Cases 14,15 and 16 . . . . . . . . . . . . .... . . . . . . 7-131 8-1 LOCTA Peak Cir.d Temperature for Case 1,0.5 inch Break with 1 CMT . . . .................. ................ ... 8-4 ; 8-2 LOCTA Peak Clad Temperature for Case 2,2.0 inch ; Break with 1 CMT . . . . . . . . . . . . . . . . . . . . . . . .................. . 8-5 ; 8-3 LOCTA Peak Clad Temperature for Case 5,3.5 inch ' Break with 1 Accumulator ...................................... 8-6 ; 8-4 LOCTA Peak Clad Temperature for Case 12b,2.0 inch Break with 2 Stage 4 ADS . . . . . . . . . . ....................... ... 8-7 ; 9 la Integrated Break Inventon Loss at Time of ADS Actuation . ............. 9-6 l 9 Ib RCS Pressure at Time of ADS Actuation . . . . . .... ................. 9-7 9-2a Time CMT Draining Starts - Overview . . . . . . . . . . . . . . . . . . . .. . . . . . 9-12 9-2b Tirue CMT Draining Starts - Detailed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-13 9-3a Minimum Vessel Mixture Level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-14 9-3b Duration of Core Uncovery . . . .................... . . . . . . . . . . 9-15 9-3c Shutdown Time When Core Starts to Uncover . . . . . . . . . . . . . . . . . . . . . . . . 9-16 9-4 Duration of daarried Conditions in the Downcomer after ADS Actuation . . . . . .................................... 9-18 9-Sa Integratn ADS 4 Inventoy Loss for 1000 Seconds after Wives Open ......... ................. ........... ... 9-21 9 5b Time Delay from ADS 4 Acruation Until IRWST Injection Starts . . . . . . . . . . . 9-22 9-5c Mot Leg Level at Time of ADS Actuation . . . ..... ................. 9-23 9-6 .'ntegrated ADS 1 to 3 Inventory Loss for 100 Seconds . . . . . . . . . . . . . . . . . . 9-26 9-7 h tegrated IRWST Injection for 1000 Seconds . . . . . . . . . . . . . . . . . . . . . . . . 9-28 9-8 Duration of Accumulator Injection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-30 O o.\newprojlO603w.wptib-041397 Rev. O, Apnl 1957
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ix 2[r LIST OF ACRONYMS n , ADS ~ Automatic depressurization system-
'ANS American Nuclear Society ;
ATWS Anticipated transient without scram '] BWR- Boiling water reactor ; CCFL- Counter-current flow limited CCW Component cooling water ! CDF Core damage frequency . j
~ CI - Containment isolation _3 CL Cold leg l CVCS Chemical and.. volume control system .i'
- CMT' Core makeup tank '
' DBA'. Design basis accident
' DVI ' Direct vessel injection ECCS Emergency core cooling system
; EPRI Electric Power Research Institute HL- Hot leg IRWST In-containment refueling water storage tank LRF. Large release frequency LLOCA Large loss-of-coolant accident
- LOCA. Loss-of-coolant accident MAAP Modular Accident Analysis Program MFW Main feedwater MLOCA Medium loss-of-coolant accident MSIV ' Main steam isolation valve NLOCA Intennediate loss-of-coolant accident PBL Primary balance line PCS Passive containment cooling system PCT Peak clad temperature PIRT Phenomena identification ranking tables PRA- Probabilistic risk assessment PRHR Passive msidual heat removal system PWR Pressurized water reactor RCP Reactor coolant pump RCS. Reactor coolant system RNS Normal residual heat removal system SBLOCA Small-break loss-of-coolant accident SO Steam generator SOTR Steam generator tube rupture SLB Steam line break SLOCA Small loss-of-coolant accident SSAR Standard Safety Analysis Report l SV- Safety valve l SWS Service water system l T/H Thermal /hydrauhc :
4 i 1 O V , o.Wnrpo)AMMUw.wp0lb-041397 , Rev. O. Apnl 195U w - . . - . _. . . . . -. . .
1 EXECUTIVE
SUMMARY
p Westinghouse undertook an extensive effort to analyze the thermal / hydraulic response of AP600 to support claims of successful core cooling for multiple failure accidents in the AP600 Probabalistic Risk Assessment (PRA). MAAP4 was chosen as the code for this task because of its flexibility and ease of use. The code is fast-running, making it feasible to analyze a large number of scenarios, , variations of the scenarios, and sensitivities. However, concerns have been raised on the suitability of MAAP4 models for assessing successful core cooling, particularly for plants with passive safety systems. l Berefore, as documented within this report, MAAP4 was benchmarked against the more detailed models in NOTRUMP, the Westinghouse-validated code for AP600 small-break LOCAs. A total of nineteen benchmarking cases were analyzed with both MAAP4 and NOTRUMP. He first seven cases were chosen at limiting break sizes across the spectrum of the break sizes analyzed with MAAP4, as I discussed in Section 4.2 of this report. Hey demonstrate the basic phenomena that are identified in the PRA Phenomena Identification Ranking Tables (PIRTs) in Section 3.2. The remaining cases are sensitivities that demonstrate the capability of MAAP4 to predict trends for different break locations, different number of core make-up tanks (CMTs) or accumulators, different number of automatic depressurization system (ADS) lines, and different parameters affecting in-containment refueling water storage tank (IRWST) gravity injection. O ( j There is excellent agreement in the trends predicted by the two codes for most of the benchmarking cases. Sections 6.0 and 7.0 of this benchmarking report show detailed output from each case, comparing the prediction of specific parameters for different components and systems within the plant. Section 9.0 provides code comparison plots for issues identified as highly important through the PIRT process. Core uncovery of limited depth and duration occurs in approximately half of the benchmarking cases, with similar trends predicted by both MAAP4 and NOTRUMP. For each case, the reason that the core uncovers is understood, and both codes predict similar system actuations and timing leading to the core uncovery. Both codes also predict similar accident progressions for scenarios that do not include core uncovery. However, the MAAP4 / NOTRUMP benchmarking effort identified one accident scenario where MAAP4 did not adequately predict the vessel mixture level, which is used to determine whether core uncovery occurs. He difference is due to a limitation of the MAAP4 code that may impact cases that credit stage 1,2 and 3 ADS, as explained within Section 7.3 of this report. Here are some accident scenarios that credit ADS stage 1,2 and 3 for which MAAP4 is adequate, while there are others that credit ADS stage 1,2 and 3 for which MAAP4 is not adequate. The caution to the AP600 MAAP4 user is that if MAAP4 does not predict water drawn into the pressurizer when ADS stage 1,2 or 3 valves open, the code may overpredict the resulting RCS depressurization; the conclusions of the MAAP4 analysis should not be used without further justification. This limitation does not seriously n restrict MAAP4% applicability to PRA success criteria analyses, since stage 1,2 and 3 ADS play a ( ) minimal role in success criteria definitions. v onnewpro) abo 3w.wptit>MI av7 Kev. O. Apnl IW7
2 The benchmarking of MAAP4 against NOTRUMP illustrates not only the capabilities of the MAAP4 code, but the adequacy of the input modelling used for AP600. The benchmarking effort shows that the MAAP4 parameter file and input decks previously developed for AP600.ae accurate, with one exception. The input modelling of ADS line resistances in MAAP4 had t.:. ce corrected, which impacted the RCS depressurization prediction. The modelling is explained within Section 4.1 of this report. The' result is that it takes 3 stage 4 ADS valves to achieve the same plant response that was attributed to 2 stage 4 ADS valves in previous MAAP4 analyses. Although the ADS success criteria in the PRA is based on 2 stage 4 ADS valves for full depressurization, most of the benchmarking cases are analyzed with 3 stage 4 ADS valves. The update of Appendix A of the PRA, which documents the MAAP4 success criteria ant. lyses, will address any PRA impact of the ADS-4 line resistance modelling change. De conclusions of the MAAP4/NOTRUMP benchmarking effon are as follows.
- 1. The thermal-hydraulic models in the MAAP4 code can model the key thermal-hydraulic phenomena with sufficient accuracy that it can be used as a screening tool to detennine whether core uncovery occurs. The use of MAAP4 is subject to the limitation identified above, and the potential impact of the code simplifications discussed within Sections 2.1 and 2.2 of this report.
1
- 2. If core uncovery occurs, MAAP4 predicts the depth and duration of uncovery well enough for an assessment of successful core cooling to be justified, if the depth and duration of uncovery are similar to that demonstrated within this report. The assessment of core cooling for core l uncovery cases is based on the NOTRUMP/LOCTA peak clad temperature (PCT) results remaining well below 2200*F for the benchmarking cases, as shown in Section 8.0 of this report.
- 3. MAAP4 can be used to estimate operator action times for the'PRA. The accident progression predicted by MAAP4 generally has similar timing compared to the NOTRUMP calculation.
The benchmarking of MAAP4 against the more detailed models in NOTRUMP has demonstrated that MAAP4 is an adequate, useful tool to support the AP600 PRA claims of successful core cooling in mul3ple-failure accident scenados. Because the running time of MAAP4 is tens of minutes while more detailed codes such as NOTRUMP run for multiple days, it is feasible to consider many combinations of equipment failures with MAAP4 analyses. He ease of using MAAP4 leads to a thorough understanding of the integral AP600 plant response to multiple failure accident scenarios. O oMcwprojN603w.wpt.1b-041397 Rev. O. Apnl 1997
l 1-1
/3 1 INTRODUCTION i \
V The purpose of a PRA is to quantify core-damage frequency (CDF) and large-release frequency (LRF), l while gaining insights into any risk-significant vulnerabilities of the plant. One of the elements in l performing .a PRA is to define success criteria, which refer to minimum sets of equipment needed to I prevent core damage. The MAAP4 code is used to support the AP600 PRA success criteria def'mitions. An extensive set of MAAP4 analyses address the plant response to different initiating events and different sets of operating equipment. This is docuanented in Appendix A of the PRA, which was submitted to the NRC in January 1995 (Ref.1). ] MAAP4 was chosen as the code to support the PRA success criteria because of its flexibility and ease of use. The code is fast-running, making it feasible to analyze a large number of scenarios, variations of the scenarios, and sensitivities. The purpose of this document is to demonstrate the validity of the thermal-hydraulics (TSI) models used in MAAP4 code for assessing the AP600 plant response to various multiple-failure accidents. The assessment is performed by comparing MAAP4 results to results from the more detailed models in NOTRUMP, the Westinghouse-validated code for AP600 small-break LOCAs (Ref 2). Appendix A of the PRA is being revised, based on the benchmarked version of MAAP4, upon the completion of this MAAP4/NOTRUMP benchmarldng report. 1.1 Purpose () / The purpose of the MAAP4/NOTRUMP benchmarking is to demonstrate: l
- 1. that the thermal-hydraulic models in the MAAP4 code can model the key thermal-hydraulic phenomena with sufficient accuracy that it can be used as a screening tool to determine whether core uncovery occurs,
- 2. that when core uncovery occurs
- a. MAAP4 adequately predicts the depth z. i duration of uncovery to assess whether successful core cooling can be credited in the PRA; this assessment is based on
- b. the NOTRUMP/LOCTA-calculated peak clad temperature (PCT) for the benchmarking cases is less than 2200*F,
- 3. that MAAP4 can also be used to estimate operator action timing for the PRA.
1.2 Scope
'lhe benchmarking cases are divided into seven primary cases and twelve sensitivity cases. The (m benchmarking cases are identified and discussed in Section 4.0. The primary cases examine different k
Introduction Rev. O, April 1997 o bewproj2\%03w.wpf:1b-041497
1-2 break sizes for two types of PRA sceaarios: automatic ADS (with CMTs) and manual ADS (without CMTs). The cases were chosen to eihibit the range of thermal / hydraulic phenomena that can occur in j the multiple-failure PRA accident scenarios, as defined in the PRA PIRTs (Section 3.0). In addition, there are a dozen sensitivity cases that demonstrate the impact of adding equipment, different break locations, and different boundary conditions for the analysis. The MAAP4/NOTRUMP benchmarking cases examine the plant response from accident initiation, through short-term injection from the CMTs and/or accumulators, and are terminated when IRWST gravity injection has replenished and stabilized the RCS inventory. The benchmarking cases are some of the most restrictive accident scenarios that have been credited as successful core cooling in the PRA. Results of the primary cases are discussed in Section 6.0, while the sensitivity results are documented in Section 7.0. Many analysis assumptions are based on nominal plant conditions and best estimate decay heat. This is for consistency with the PRA, which 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, allowir.g one to obtain the most accurate insights on any risk vulnerabilities of the plant. More information on the analysis assumptions is provided in Section 5.1. Sections 5.2 and 5.3 provide information on the NOTRUMP code, and the process that is used to compare MAAP4 and NOTRUMP. The peak clad temperature for the most limiting cases is calculated with the LOCTA code, and results l are presented in Section 8.0. Sections 9.0 and 10.0 provide a summary of the results from all the cases, and conclusions on the O l range of applicability and limitations of the MAAP4 code. Key models of the MAAP4 code are also discussed in Section 2.0. 1.3 Relationship to T/H Uncertainty Resolution l Because of the nominal thermal-hydraulic assumptions in the analyses that support the PRA, there is a l separate AP600 T/H uncertainty resolution program to address the impact of other than nominal ] assumptions. The T/H uncertainty resolution program is based on a concern that uncertainties in predicting small changes in the /.P600 plant conditions could lead to different conclusions on the success of core cooling. This concern is due to the passive nature of the safety-related systems in AP600, and links to another program addressing passive system reliability issues for AP600 (Ref. 3). He T/H uncertainty resolution process identifies a set of low-margin, risk-significant accident scenarios, and shows acceptatie thermal-hydraulic performance when the uncertainties are bounded. The MAAP4/NOTRUMP benchmarking and T/H uncertainty resolution program are two separate work scopes. He purpose of the MAAP4/NOTRUMP benchmarking is to show that MAAP4 has sufficient thennal-hydraulic models to predict major trends in the AP600 plant behavior to suppoit the AP600 PRA success criteria. The T/H uncertainty resolution program addresses the potential impact on the PRA if thermal-hydraulic uncertainty is considered. Benchmarking is performed with nominal input Introduction Rev. o. April 1997 o%ewproj2\3603w wpf:lt@l197
1-3 assumptions. Analyses for TM uncertainty resolution use conservative assumptions. Benchmarking i ) cases are chosen to be some of the most limiting cases credited as successful core cooling in the PRA. T/H uncertainty resolution cases are chosen based on their potential adverse impact on the PRA results ; if they actually resulted in core damage rather than successful core cooling. { Although separate work scopes, the similarity of MAAP4/NOTRUMP benchmarking and T/H l uncertainty resolution program is that they are both related to the PRA and the AP600 plant response l to multiple-failure accidents. Both programs focus on core uncovery, although core uncovery is not necessarily anticipated in the majority of multiple-failure accidents. Both programs include the use of NOTRUMP and MAAP4 to assess the integral plant system response to loss-of-coolant accidents. The relationship of the analyses performed for the benchmarking program to the T/H uncenainty resolution ! process is funher explained below. ) l The benchmarking analyses demonstrate the expected plant response, and this information is used l within the T/H uncertainty resolution program. To select the T/H uncertainty cases for analysis, all successful core cooling PRA scenarios are grouped into categories based on the plant response. The key to the T/H uncenainty resolution categorization is an understanding of what equipment failures are responsible for core uncovery. A corollary to this is an understanding of what equipment successes are responsible for maintaining the coolant inventory above the top of the core. These elements of I understanding AP600 core uncovery for multiple-failure accidents are demonstrated in the MAAP4/NOTRUMP benchmarking process. U The MAAP4/NOTRUMP benchmarking cases are not used to resolve the thermal-hydraulic uncenainty concerns; the benchmarking cases only demonstrate an understanding of the plant behavior for nominal thermal-hydraulic conditions. Additional analyses are performeri for risk-significant accident scenarios that include core uncovery, yet have been credited as successful core cooling in the PRA. The additional analyses are performed with bounding assumptions and SSAR Chapter 15 accident analysis codes, and are documented in a separate T/H uncenainty resolution report. It is noted several places within this report that the benchmarking cases include too many equipment failures to be risk significant. 'Ihe term " risk significant" is used to refer to an accident, or a group of similar accidents, with a high enough frequency of occurrence to have an impact on the PRA core damage frequency or large release frequency. Within this report, the term is applied to scenarios that are credited as successful core cooling, that would have an ad"erse impact on the PRA results if they actually resulted in core damage. Because the benchmarking cases include too many failures to be risk significant, the benchmarking cases are not the same as the risk-significant cases analyzed in the T/H uncenainty resolution report. However, there can be similarities between benchmarking cases and T/H uncertainty cases. A benchmarking case can represent a type of core uncovery that is related to certain thermal-hydraulic phenomena or the loss of specific equipment. For example, the loss of both accumulators can lead to core uncovery in many accidents. If all other equipment functions, core n uncovery may still occur with the loss of both accumulators. Therefore, the loss of both accumulators () can be risk significant, and is examined in the T/H uncertainty resolution analyses. There are also introduction Rev. O. April 1997 o:\newpiojh3603npfho41197
1-4 benchmarking cases that do not credit either accumulator, and therefore core uncovery occurs. The difference is that the benchmarking cases also have other failures that may further challenge the plant response Section 4.0, while defining the benchmarking cases, provides infonnation on how each case
- relates to the risk-significance determined in the T/H uncertainty resolution process.
O O Introduction " ' ' owwproj20603w.wpf.lb-c41497
2-1
, 2 THE MAAP4 CODE
[v The Modular Accident Analysis Program 4.0 (MAAP4)is a computer code that simulates the transient response of light water reactor systems to different initiating events. It was originally developed to investigate the physical phenomena that may occur in the event of a severe (core damage) accident. I Although the emphasis in the code development has been on the severe fuel damage phase of the ! accident, the code can also be used to determine the thermal-hydraulic behavior prior to core damage. MAAP4 is a fully integrated, systems accident code and includes models for important thermal-hydraulic and fission product phenomena that are predicted to occur during a postulated accident in a ! pressurized water reactor plant. Version 4.0.2 of MAAP4 is used for these analyses. Ref. 4 provides ! details of the code models and user's guidance. MAAP4 includes the necessary models to simulate the passive safety systems in the AP600 plant, including the core makeup tanks (CMTs), in-containment refueling water storage tank (IRWST), and the passive containment cooling system (PCS). MAAP and its individual models have been continually compared to major experimental results; a table of such benchmarks is given in Volume 1 of the User's Manual (Ref. 4). Moreover, a dynamic benchmarking program has been implemented by the MAAP User's Group and the results of the various integral plant analyses and individual phenomenon comparisons are given in Volume 3 of the User's Manual. r% 3 C/ MAAP4 was chosen as the code to support the Level 1 PRA success criteria because of its flexibility, case of use, and ability to model, in an integrated fashion, both the primary reactor coolant system and the containment. MAAP4 calculates the thermal-hydraulics of the primary system, the secondary system, and the containment. The code is also fast-running, making it feasible to analyze a large number of scenarios, variations of the scenarios, and sensitivities. The flexibility of the code includes the capability to model a wide range of initiating events and the capability to model operator intervention based on times or " trigger" events. When applied to pre-core damage success criteria analyses, MAAP4 has limitations due to the model simplifications that make MAAP4 a fast-running code. An overview of the code's major models is pmvided in Section 2.1; the model simplifications that may impact the PRA success criteria analyses are summarized in Section 2.2. 2.1 Overview of Major Models There are two versions of MAAP 4.0.2 released by EPRI: one for PWRs and one for BWRs. The MAAP4 version for PWRs includes subroutines to model the components of the AP600 plant. The following sections provide an overview of the PWR MAAP4 code. Section 2.1.1 is an overview of the primary system: Section 2.1.2 is an overview of the core model; Section 2.1.3 summarizes the A AP600-specific features in the PWR version of MAAP4. The MAAP4 Code Rev. O. Apnl 1997 o'mewproj2\3603w.wpf.Itro41197
2-2 l 2.1.1 Primary System 4 The MAAP4 reactor coolant system model calculates the primary system thermodynamics, i.e., state and properties of water pools and gas space, the water and gas transport within the reactor coolant l system such as forced and natural circulation, the water and gas transport to/from the pressurizer and containment, the response of the reactor coolant system heat sinks, and the heat transfer to/from the heat sinks. ) The primary system model represents the reactor vessel and downcomer, the hot legs, the cold legs, and the primary side of the steam generators. The pressurizer and the core region are treated as ; I distinct, separate regions. The primary system models two reactor coolant loops, one for the broken loop, and the other for the rest of the unbroken loops. The user may select which loop has the pressurizer connected to it. Both reactor coolant loops are nodalized into fourteen (14) gas nodes and six (6) water pools. A schematic of the gas nodalization is provided in Figure 2-1, and a schematic of i the water pool nodalization is provided in Figure 2-2. A water pool may encompass several gas nodes. Each gas node has its own gas temperature and gas constituent species. Both the gas temperature and gas composition along with source / loss terms are used for calculating the gas transport around the reactor coolant system loop. Similarly, each water pool has its own water pool temperature and volume vs. elevation relationship which are used in calculating the water transport. The user has the ability to specify a break location in any one of the gas nodes in the broken loop and selected gas nodes in the unbroken loop. Generalized openings are provided between the primary system and the containment in addition to normal breaks used in LOCA sequences. For AP600, a generalized opening is used to model stage-4 ADS valves. The primary system is assumed to have a spatially constant, homogeneous void fraction until phase separation occurs. Note that the use of the term " primary system" is defined above, and does not include components such as the pressurizer or AP600 CMTs. The homogeneous void fraction exists when the reactor coolant pumps are running or when the primary system void fraction is smaller than the user-specified phase separation void fraction (VFSEP). When the primary system is in single-phase or two-phase natural circulation mode, MAAP4 does not calculate an actual natural circulation flow rate but uses a simple heat transfer calculation between the primary system and the steam generator based on the user input heat transfer coefficient. When the primary side is in two-phase natural circulation mode, the primary system models are in the equilibrium thermal hydraulic calculation mode where the water pools and the gas space equilibrate at the same temperature. When the loss of coolant invemo., has dropped sufficiently to interrupt homogeneous natmal circulation, the water and gas phases am separated. The primary system models are in non-equilibrium thermal hydraulic calculation mode when the water pools temperatures and the gas space temperatures are tracked separately. Note that the water pools may separate and consequently will have its own mass and temperature. 'Ihe flow rates between the water pools are then calculated using quasi-steady state manometric balance. The nodal gas temperature is determined from the total system gas energy, The MAAP4 Code Rev. O. Apnl 1997 cAnewprojN603w wpf;1b-041197
2-3
, masses, and pressure. The pressure is defm' ed at the gas region (top of the water pool) and the I hydrostatic head of water is applied whenever applicable.
(u.J The downcomer and core water pool models in MAAP4 use a simple control volume approach and have their own masses and energies. Once the phases are separated in the primary system, the flow rate between the downcomer and the core is calculated based on the hydrostatic head difference. The downcomer water pool is assumed to have no void but does exchange heat with the reactor vessel heat sinks including the lower head and the outer surface core barrel. On the other hand, the core pool tracks the two-phase level based on steaming rate in the core and exchanges heat with the fuel rods and the inner surface of the core barrel. The two-phase level in the core is calculated using the drift flux model using the steaming rate created in the core and in the lower head.
%e MAAP4 code has the models to add water to the primary system by engineered safeguard injection systems, makeup flow, and pressurizer sprays. Water may be lost from the primary system by letdown flow, breaks, and generalized openings. Flows through breaks and generalized openings may consist of water, two-phase, or gas flow.
he reactor coolant system heat sinks and heat transfers are an important part of the primary system model. Water, gas, or debris interfaces at the heat sink boundary and heat transfer including radiation may heat up or cool down the heat sinks including the heat losses to the containment. For instance, the core barrel heat sink interfaces between the com region and the downcomer region and can allow q Q heat transfer from the core region to the downcomer water pool. The two-dimensional nodalization scheme is employed to describe the temperature distribution in the primary system heat sinks. A total of seventeen (17) heat sinks are modelled in the primary system. Energy is transferred by natural convection from the various water pools in the primary system to the heat sinks in the primary system that are partially or completely submerged in those pools. V The MAAP4 Code Rey, o, April 1997 cAnewproj206o3w.wpf.lbe41497 l
'i
,.g 5 -
$?
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- f Cold Leg Hot Leg Hot Leg Cold Leg j Steam Generator Steam Generator Tubes Tubes Shell Shell o Pressurizerg ube -
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P . 3. Figure 2-1 MAAP4 PWR Primary System Gas Nodalization 9 O O
l l 2-5 2.1.2 Core Model (3 / iU The reactor core model in MAAP4 is represented by the thermal hydraulic subroutine HEATUP which ; calculates the thermal response of the reactor core. The AP600 reactor core model represents the reactor core divided into seven radial rings and seventeen axial rows. The number, length, and mass of the non fuel nodes with predetermined materials (SS and Zr), the locations of the upper gas plenum, the lower gas plenum, and the support plate, and the fraction of area for each radial ring can be specified. The AP600 core is modelled with two non-fueled rows: one at the bottom representing the ; core support plate, lower tie plate, and lower gas plenum; and one at the top representing the upper gas plenum and upper tie plate. The rest of the core rows, with equal axial lengths, are the active fuel , region. i Each core node in the PWR MAAP4 code contains four components: fuel, clad, control / water rod, l and coolant. Each of these components has its own mass and temperature. For possible material composition, the fuel contains UO2 , the clad contains Zr, ZrO2, SS, SSO, and a U-Zr-O mixture, the control / water rods contain Ag-In-Cd, B4 C, SS, SSO, Zr and ZrO 2, and the coolant contains hydrogen, i steam and water. Since the uranium can dissolve into the clad to form the U-Zr-O mixture, decay heat can also be generated in the clad directly. The heat transfer from the core to the primary system consists of two parts: covered and uncovered core to primary system fluid heat transfer. The covered part consists of the core under two-phase mixture level. First, the metal-water reaction is computed for oxidation of Zr and SS. Next, the intra- i
^
node heat transfer including conduction, convection, and radiation, heat transfer area, heat source / sink, and heat capacity among the six components of the core node just previously described results in a l 6x6 matrix to solve for the net heat transfer rates. For the AP600 application, the heat transfer modes of interest are the heat transfer prior to core damage, which includes forced convection, natural convection, nucleate boiling, and critical heat flux (CHF), all of which are represented in the MAAP4 code. When the primary system is in single-phase or two-phase natural circulation mode, the core is covered and the mixture level in the core is not calculated. Once the water and gas phases are separated based on the phase separation void fraction VFSEP, distinct water levels in the downcomer and in the core are calculated. For a given collapsed water level in the core, two-phase mixture level is calculated based on a steaming rate in the core and a void fraction model which is a semi-analytical relationship l for the vapor volume flux from a swollen pool for a churn turbulert flow regime using the drift flux model. The void fraction model calculates an average void fraction for a given steaming rate in the core assuming that the vapor generation at each elevation is proportional to the liquid content and liquid superficial velocity can be neglected.
/
'Ite MAAP4 Code Rev. O. Apil 1907 ohwpro}N603w.wpf;1b-o41497
I 2-6 I I 2.1.3 AP600-Specific Models ! AP600-specific models that are used in the PRA success criteria analyses and this benchmarking report O' are the CMT, IRWST, and ADS. There is also an AP600-specific PRHR that is not used in the l benchmarking cases, and thus is not discussed within this section. l The core makeup tank (CMT) model in MAAP4 calculates the thermodynamic properties and response of the AP600 core makeup tanks. Up to two core makeup tanks can be modeled through user input. The MAAP4 code models the CMT as a single control volume. It can have different gas space and water pool temperatures. However, the whole water volume is modelled as one node with one temperature. The top of the CMT is connected to the primary system cold leg by the cold leg balance line. The gas is allowed to flow in either direction between the cold leg and the CMT, and the water is only allowed to flow from the cold leg to the CMT. The bottom of the CMT is connected to the downcomer, and the water is only allowed to flow from the CMT to the downcomer depending on the available water head when the isolation valve on this line is open. The CMT is initially solid or full of water. If the CMT is solid, the pressure of the CMT is set to the pressure of the primary system. If :he CMT is not solid and has a gas space, the pressure of the CMT is calculated. CMT water flow is calculated when the CMT actuation signal opens the valve (s) on the connecting CMT lines. Water flow calculations are divided into several parts depending on the state of the CMT using simple quasi-steady state momentum equation by equating the frictional pressure drop to the pressure head difference including density head. If the CMT is solid, natural circulation is allowed with equal volumetric flow only if there is enough head in the primary system to push the water up the balance line or when there is sufficient water density difference between the CMT and the downcomer. Equal volumetric flow rate will keep the CMT solid when there is a stratified CMT water pool. Since the MAAP4 CMT model treats the water pool as a single node, an adjustment is made on the cold leg balance line flow rate to keep the CMT solid. If the CMT is not solid or when there is not enough head in the primary system to push water up the balance line to satisfy the condition of equal volumetric flow, the water flow rates in the CMT line to the downcomer and in the cold leg balance line are calculated independently based upon the pressure and water head differences. When equal volumetric flow stops, inflow can be less than the outflow which will result in a void in the CMT. The IRWST in AP600 is modeled as a generalized containment node in MAAP4. The IRWST node has its own pressure and temperatures for water and gas and is connected to the rest of the containment through openings (junctions). The water pool in the IRWST is modeled as one control volume and has a single temperature. The ADS stages I through 3 and relief valve flows from the pressurizer are released into the IRWST water pool through the spargers. The heat transfer between the released flow and the water pool and condensation of steam are considered. The gravity driven The MAAP4 Code Rev. O. Apnl 1997 oAnewproj20603w.wpf;1b-o41497
2-7 water injection from the IRWST into the reactor coolant system is modeled by using generalized [q 3 openings with a user-specified discharge coefficient. G' he ADS stages 1 through 3 are modeled by using the pressurizer relief valve model. Based on the ADS actuation signal, the area of the relief valve from the pressurizer to the IRWST is adjusted. In the pressurizer, steam can be generated due to the heat added by quenching of steam from the primary system or by depressurization when the relief valve is open. Steam evolution within the water pool directly influences the effective boiled-up water level and, therefore, the character of the mixture entering the relief valve. Both mass and volumetric flows are significantly influenced when a two-phase mixture enters a relief valve. Modeling of these processes is panicularly important when there is a large relief flow such as the opening of the ADS in AP600. A new pressurizer model was developed for MAAP4 to handle conditions of a relatively small volume, almost filled with water with large mass flow rates into and out of the pressurizer. The new model has a level swell model to determine when the two-phase mixture reaches the top of the pressurizer. The relief flow is calculated by the Henry-Fauske correlation using the void fraction at the top of the two-phase pool with user-specified discharge coefficient. De new pressurizer model had been benchmarked against numerous I high pressure blowdown experiments and agreed well with the experimental data. The ADS stage 4 is modeled using a gen.:ralized opening between the primary system and the containment. Similar to the ADS stages 1 through 3, the flow through the ADS stage 4 is calculated by the Henry-Fauske correlation with user input discharge coefficient. To model the line resistance coirectly, the discharge coefficient is adjusted based on whether or not the flow is choked. l l l I 1 l I l l
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Vl , l Re MAAP4 Code Rev. o. April 1997 j obewproj20603w.wpf:lt@l497
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)
! " Unbroken" Loops " Broken" Loop i ( I l CR-Com i 4 BT - Broken Loop Steam Generator Tubes BIL- Broken Loop Intermediate Leg DC- Downcomer { UIL- Unbroken Loop Intermediate Leg j UT - Unbroken Loop Steam Generator Tubes maannnnar m M Frota Volume II of Ref. 4 Figum 2-2 MAAP4 PWR Primary System Water Pool Nodalization De MAAP4 Code Rev. O April 1997 o:bprojA3603w.wpf:ll>o41397 i
y 1 l 2-9 ! 2.2 MAAP4 Simplifications Potentially Irppacting Success Criteria Analyses. O l V MAAP4 is a fast running code. Results from MAAP4 can be seen within tens of minutes, while the results from the more-detailed NOTRUMP code take multiple days for the same accident scenario. The fast running time of MAAP4 is due to simplifications in the code. The MAAP4/NOTRUMP benchmarking demonstrates that the MAAP4 simplifications do not impact the conclusions drawn from the analyses, as long as the simplifications and limitations of the code are understood. His section discusses the simplifications in context of how they can potentially impact the AP600 success cdteria analyses. The impact of simplifications in the two-phase flow model, the downcomer model and the core model are discussed. 2.2.1 Effect of Homogeneous Two-Phase Flow The MAAP4 simplification of the homogeneous versus stratified two-phase model being controlled by the user input of VFSEP potentially impacts the break flow calculation and the transition of the CMT from recirculation to draining. l The break flow rate in MAAP4 is determined by considering the pressure difference across the break, , the fluid properties, and the void fraction entering the break. When the break location is totally ! submerged, the void fraction is based on the RCS void fraction. Before the user-specified input of VFSEP is itached, the homogeneous natural circulation is assumed within MAAP4, and a void '( fraction is predicted at all locations within the primary system. Therefore, the coolant inventory at the break includes both steam and water regardless of the break location. When the RCS void fraction reaches the user-specified value of VFSEP and the coolant inventory separates, break locations such as the hot leg are usually submerged in water. Therefore, the break flow becomes all water. When the break location begins to uncover, the MAAP4 model considers :he entrainment of the liquid into the e overlying gas. However, the entrainment model is limited to only considedng the entrainment of liquid that is contained within the break node. The limitations of the homogeneous VFSEP model on the break flow prediction are well understood. The instantaneous break flowrate and composition of water versus steam may differ from codes calculating the two-phase response using more detailed models. MAAP4 should not be used to determine the rate of inventory loss over a time period on the order of tens of seconds. However, the integrated inventory loss predicted from the break is reasonable for the longer time frame studied for PRA success criteria. The reasonableness of the predictions are shown within this MAAP4/NOTRUMP benchmarking report. He second impact of the two-phase modelling in MAAP4 is that it influences the transition of the CMT from recirculation to draining. While there is a homogeneous two-phase mixture circulating through the RCS, MAAP4 does not predict any vapor flow from the cold line through the CMT balance line. Once an average RCS void fraction of 0.6 is reached, the geometry of the AP600 is such I that the separated water level will be below the cold leg. (The VFSEP value of 0.6 is used in the The MAAP4 Code Rev. O. Apnl 1997 o:\newprojAbO3w.wpf.Ib-041397
2-10 AP600 analyses and was originally selected based on the recommended value in Ref. 5). Therefore, when the RCS void fraction reaches the VFSEP input value of 0.6, the cold leg fills with steam and vapor flow goes into the CMT balance line. This causes the CMT to start draining. The start of CMT draining occurs shortly after VFSEP is reached because of the input value that is used. However, if the VFSEP input value is changed, the relationship between VFSEP and the transition to CMT draining is not necessarily maintained. For exarr.ple, if VFSEP is set to 0.3, the MAAP4 model switches from the homogeneous two-phase mixture to a steam-over-water assumption much sooner; the timing impact is based on the rate of void formation in the core and the inventory loss from the break. But with only 30% of the RCS voided, the separated water level is above the cold leg, not below it. Therefore, the code switches two-phase assumptions, but this does not cause the CMT to drain. Conversely, if VFSEP is set higher than 0.6, the transition to CMT draining may be 6elayed. However, the RCS vaid fraction is typically increasing at a very fast rate when the void fraction is this high. Therefore, a higher value of VFSEP would not significantly delay the transition to CMT draining. Although MAAP4's transition to CMT draining is related to its VFSEP model, the VFSEP parameter is not a tuning parameter that would allow the analyst to significantly alter MAAP4's predictions. The VFSEP value of 0.6 used for AP600 analyses usually provides a similar transition time from CMT recirculation to CMT draining as predicted by the detailed models in NOTRUMP. In benchmarking cases where the transition timing is not the same, altering the VFSEP input would not correct the i timing mismatch. 2.2.2 Effect of Downcomer Model As was discussed in the primary system description in Section 2.1.1, MAAP4 has a simple downcomer model. The water pool in the downcomer hcs its own mass and energy, and has a uniform temperature. Steaming in the water pool is calculated when the water becomes super-heated. Unlike l the core water pool, the water level in the downcomer is a collapsed level. Neglecting the two-phase water pool in the downcomer may have an effect in the initial stage of blowdown and may have an effect on the initiation of the IRWST injection. Once the injection starts, the water will become subcooled and void in the pool will be collapsed. The downcomer pressure is not calculated separately and is assumed to be the same as the overall primary system pressure. This assumption of equal pressure anywhere in the primary system gas region will lead to some error only when there is a significant pressure drop across the steam generator. 2.2.3 Effect of Core Model i
'Ihe core model within MAAP4 is described in Section 2.1.2. The AP600 core model is disided into seven radial rings and seventeen axial rows, with radial and axial peaking factors applied. The radial The MAAP4 Code Rev. O. Apnl 1997 owwproj20603w.wpf 1tsO41397
n j 2-11 j; and axial power shapes applied for AP600 are more limiting than typical beginning oflife, middle of ' l: g life, and end of life power shapes. De center nodes are a solid. cylirider shape, while all outer nodes f are toroidal shaped (like a donut). He r, ore noding technique was developed to model the core melt l progression in severe accidents, allowing the core to melt like a candle. - Detailed heat transfer'- ; calculations are performed for each node. The fuel, clad, control rod and coolant for a given node are~ l representative of that node, with the given radial and axial peaking factors. De MAAP4 output - ] variable TCRHOT is the maximum core temperature from any of the core nodes. The core temperature is an average of the fuel, control rod and clad temperatures, weighted by mass. Since .
] ;
these core components are within tens of degrees of each other after reactor shutdown, TCRHOT is a l reasonable estimate of the clad temperature. i However, the maximum core temperature from MAAP4 is not the peak clad temperature (PCT) that is reported for SSAR Chapter 15 LOCA analyses. De PCT is the peak temperature from the peak rod
] i
' in the peak fuel assembly. MAAP4's TCRHOT is the maximum temperature from the hottest toroidal- !
- shaped node in the core, not from a specific rod m a specific assembly.
- 3. The criterion for successful core cooling in the PRA is that the fuel cladding temperature remains below 2200'F (Ref. 6). Ref. 6 further defines the maximum fuel cladding temperature based on "any .
node of the core " With this vague definition, the historical presence of SSAR Chapter 15 analyses - < leads towards a strict interpretation. If the maximum fuel cladding temperature is defined as the peak . rod in the peak fuel assembly, the MAAP4 TCRHOT prediction lacks precision. Although the t TCRHOT output will accurately predict trends of increasing and decreasing clad temperature, the [] . accuracy of the numerical value for comparison to the 2200*F criterion has been questioned. Derefore, MAAP4 output of the maximum core temperature is not used to determine whether there is successful core cooling for PRA multiple-failure accident scenarios. Instead, the minimum mixture level in the core, the duration of core uncovery, and the level of decay heat at core uncovery is used to e assess whether successful core cooling occurs. De assessment is based on results presented within i this report, specifically the LOCTA calculations in Section 8.0. E 2.2.4 Effect of CMT Simplifications F In the AP600 plant, there is a phenomenon of interfacial condensation on the CMT water surface, which is break size deparvient. For small breaks, the CMT liquid heats during the recirculation of the -
- CMT such that the interfacial condensation is very small. As the break size increases, the recirculation i'
time for the CMT decreases such that the CMT liquid stays cold and the interfacial condensation will ). occur. De impact of the condensation is to reduce the pressure at the top of the CMT such that the l. CMT drain flow is reduced. i L MAAP4's CMT model does not include the ability to model the interfacial condensation on the CMT
. water smface. De impact of this model deficiency is seen in breaks with diameters of approximately 5" rad larger. In the early part of a LOCA, MAAP4 predicts too early of a transition from CMT g
- 'Ihe MAAP4 Code Rev. 0, April 1997 oNewproj2\3603w.wpf:ltM1397 y t 5ee-- -
e- *- +y y q Tf w W - m ,
2 12 recirculation to CMT draining. MAAP4's prediction of early CMT draining provides make-up inventory sooner than would actually occur. When there are no accumulators for rapid make-up inventory, the lack of the interfacial condensation capability in MAAP4 results in an overprediction of the vessel mixture level. The magnitude of the effect is discussed in Section 6.4 and Section 9.1.2. I I l l
)
O' O The MAAP4 Code Rev. 0, April 1997 ohwpmjA%03w.wpf.lb-o41397
l 3-1 3 PRA PHENOMENA IDENTIFICATION RANKING TABLES
.q b (PIRTs) 1 i
To focus the MAAP4/NOTRUMP benchmarking effort on areas of greatest concern, phenomena l identification ranking tables (PIRTs) have been developed for the PRA scenanos. ; 1 The key phenomena in the PRA PIRTs are based on accident scenarios that include actuation of ADS to mitigate the accident. A loss of primary coolant inventory causes the CMTs to drain, which results in ADS actuation from a low CMT level signal. The loss of inventory can be due to a "oreak within
)
1 the RCS, or it can be due to the opening of the pressurizer safety valves in a loss-of-heat-sink accident. The range of accident scenarios considered for the PRA PIRT development is based on the accident scenarios for which MAAP4 analyses are done to support the PRA. His section first j discusses the accidents that are considered for the PRA PIRTs, and then the development of the PRA l PIRTs is aiscussed. i 3.1 Overview of Multiple-Failure Accident Scenarios In the PRA, loss-of-coolant-accidents (LOCAs) are sub-divided into different initiating event categories based prirnarily on the bicak size, and sometimes the break location. Transient events (non-LOCAs) are also considered separately based on the initiating equipment failure. The different initiating events
/~'N for LOCAs and transients are defined and are modelled in individual event trees. An event tree contains paths of accidents with different sets of equipment failures and successes considered. Sets of equipment successes that lead to successful core cooling are defined as " success criteria." MAAP4 is used to analyze multiple-failure accident scenarios for the PRA that include ADS actuation as part of l the success criteria. The PRA event trees that are relative to MAAP4 benchmarking are summarized I in Table 3-1. Table 3-1 also includes a list of the related benchmarking cases, which are discussed in Section 4.0.
The largest LOCA initiating event is modelled in the large LOCA (LLOCA) event tree, and is for breaks with a diameter greater than 9". This category of LOCAs is distinguished by the break size being large enough to depressurize the RCS to achieve IRWST gravity injection without ADS actuation. This LLOCA category is not analyzed with MAAP4 due to limitations of the MAAP4 code. He accident progression of a LLOCA is not considered for the PRA PIRT development. De tut LOCA initiating event is modelled in the medium LOCA (MLOCA) event tree, and is for breaks with a diameter between 6.0" and 9.0". This initiating event category is defined based on the break being large enough to depressurize the RCS below the RNS shut-off head (175 psia) without ADS actuation. The large end of the MLOCA break spectrum provides the greatest challenge to core cooling. He relatively high rate of inventory im can result in core uncovery if there are no l accumulators to provide immediate make-up injection. Also, the high rate of inventorj loss can result ( PRA Phenomena Identification Ranking Tables (PIRTs) Rev. O. Apnl 1997 c:\newproj2\3603w.wpf:lt441397
3-2 in core uncovery if both CMTs fail and the accumulator (s) empty before the operator can manually actuate the ADS valves. Another PRA initiating event is a CMT line break. It is defined as any break in the CMT balance line or CMT injection line up to the check valves (that prevent reverse flow from the DVI une). The CMT line break is very similar to a MLOCA on the cold leg, except the faulted CMT is assumed to be unavailable for core cooling. Both accumulators are still available, since there is a check-valve between the postulated break location and the accumulator tee. Since the MAAP4 analyses to support the PRA typically assume only one CMT, there are no special phenomenological concerns for the CMT line break that are not addressed by the MLOCA event. The next smallest LOCA initiating event is modelled in the intermediate LOCA (NLOC,A) event tree, and is for breaks with a diameter between 2.0" and 6 0" This initiating event category is defined based on the break being large enough to depressurize the RCS below the ADS-4 interlock pressure (-1200 psia) without actuation of ADS stages 1,2 or 3. This range of break sizes produces the most limiting accident scenarios that are analyzed with MAAP4 and credited as successful core cooling in the AP600 PRA. Core uncovery can happen both before and after ADS actuation when both CMTs fail, and core uncovery can happen after ADS actuation when both accumulators fail. (Trends of core uncovery are shown and discussed in Section 4.0.) A break in the direct vessel injection (DVI) line is modelled in an event tree labeled "SI-break." The I DVI line is an 8" pipe, but the effective break area depends on the location of the break. For all locations, the initial break area cannot be greater than 4" because there is a flow restrictor in the DVI line where it connects to the reactor vessel downcomer. For a double-ended break, a second pathway can be created after the CMT isolation valve is opened. The second pathway can be equivalent to a 3.7" or 8" break depending on the location (refer to Figure 3-1). The second pathway allows coolant ; loss from the RCS via the cold leg and CMT. The overall plant response of a DVI line break is similar to the NLOCA initiating event. j l The smallest LOCA initiating events are modelled in the small LOCA (SLOCA) event tree and the RCS leak event tree. The RCS leak evem encompasses all breaks in the RCS up to 3/8", which is the largest size for which the CVCS can compensate for the lost inventory. Although the RCS Leak event addresses smaller breaks than the SLOCA event, the system response is similar if the CVCS is not providing injection. Therefore, if the CVCS faila, or if the operator fails to take actions that will keep the CVCS injecting, the RCS Leak progrusses the same as a small LOCA. SLOCAs are breaks up to 2.0" that are too small to depressurize the RCS below the ADS-4 interlock pressure. To depressurize below the ADS-4 interlock pressure, one of the following success criteria is needed: a stage 2 or stage 3 ADS valve opening, or the operation of the PRHR. Note that PRHR operation is not credited in the LOCA initiating events for heat removal beyond the ability to depressurize the RCS below 1200 psia. In the PRA, the PRHR is credited for SLOCAs as performing
)
PRA Phenomena Identification Ranking Tables (PIRTs) Rev. O, Apnl 1997 o%ewproj2\3603w wpf.It@l197
3-3 i the same depressurization function as a stage 2 or 3 ADS valve. MAAP4 analyses focus on the more Od limiting condition of not crediting any heat removal from the PRHR. He most inmiting SLOCAs are too small to remove the core decay heat, and thus the steam generators play a role in the accident progression. When the secondary side steam generator inventory is gone, the primary side pressurizes until the pressurizer safety valves are actuated. The inventory loss through the pressurizer safety valves is greater than the inventory loss from the break. At this point, , the accident progression accelerates, and is similar to a larger initiating event LOCA. The differences are the high pressure of the RCS when ADS is actuated, and the benefit of a lower decay heat due to j the slow rate of inventory loss early in the transient. Specialized small LOCAs are modelled in the PRHR tube rupture and SG tube rupture event trees. The PRHR tube rupture is considered as a separate event tree, since it is feasible for the operator to i terminate the event by isclating the break. In addition, the operation of the CVCS could reduce the l net loss from the break. If the break is not isolated, the PRHR tube rupture progresses the same as a j SLOCA. l De steam generator tube mpture (SGTR) initiating event is also a specialized small LOCA. It is modelled in a PRA event tree that considers three phases of the accident progression. The first and second phases are scenarios where non-safety systems, operator actions, and automatic isolation of the faulted SG are credited. These scenarios are not analyzed with the MAAP4 code. The third phase, ! O when the actuation of ADS valves is needed to prevent core damzge, is addressed with MAAP4 analyses. The accident progression of the third phase of a SGTR event is very similar to the SLOCA accident progression. The major difference is the break location. For the SLOCA, the water that goes through ! the break is " lost" to the containment. For the SGTR, the break flow goes to the faulted SG, where j the water keeps the SG tubes covered for a longer period of time. This provides a continued mechanism for removing decay heat through the steam generators, turning the break water into steam. Although the rupture in the SG tube creates concerns of large releases directly to the environment if there is core damage, the location also makes it easier to prevent core damage. The AP600 rnponse to a SGTR is compared to an equivalent sized SLOCA in Figures 3-2 to 3-9. He thermal / hydraulic phenomena, relative to preventing core damage, are the same for a SGTR and a SLOCA. Loss of primary coolant inventory can also occur with transient initiating events, such as a loss of feedwater. With failure of passive residual heat removal and startup feedwater, the steam generators remove decay heat until the secondary side empties. With no removal of decay heat, the RCS pressurizes until the pressurizer safety valves open. The inventory loss through the safety valves ! causes the CMTs to recirculate and eventually drain, actuating ADS to mitigate the event. The accident progression is very similar to the SLOCA initiating event. He heat-up events, including
- SLOCA and transient initiating events, are considemd in the development of the PRA PIRTs. His is t evidenced by steam generator, pressurizer and ADS 1 to 3 phenomena inclusion in the PIRTs.
PRA Phenomena identification Ranking Tables (PIRTS) Rev. O. Apnl 1997 oWwproj20603w.wpf.Itwo41197
3-4 l Table 3-1 Summary of PRA Event Trees Related to MAAP4 Benchmarking Benchmarking Cases PRA Event Trees Break Size Primary Sensitivity MLOCA 6.0" - 9.J" 4,6,7 - CMT Line Break NLOCA 2.0" - 6.0" 2,3,5 8,8b,9,10,11,12, DVI Line Break 12a,12b,13,14, 15 SLOCA < 2.0" 1 - RCS leak PRHR Tube Rupture SGTR Transients:
- Loss of MFW to both SGs - Loss of Offsite Power - Loss of Compressed Air - Loss of CCW/SWS - Loss of Condenser - Loss of MFW to 1 SG - Loss of Reactor Coolant Flow - Power Excursion Event Tree - SLB Downstream of MSIVs - SLB Upstream of MSIVs - Stuck-open Secondary Side SV - Transients with MFW - ATWS O
PRA Phenomena identification Rarking Tables (PIRTs) Rev. O. April 1997 owproj2\3603w wpf.lb-041397
3-5 i TN Figure 3-1 V Sketch of. CMT & DVI Lines , DVI Une and CMT Unes are 8 inch Pipe ' 4 h t CMT Bolonce une i CMT i i
, ,g .O isolation Volve CMT injection Une i
Cold Leg ) l Downcomer 2 l Chet.k Volves ;
- -*-- RNS Injection j
" -*-3.7" CMT Orifice 4.0" Flow Restricter _ ; _
i
-*-- IRWST Injection ACADs718 j PRA Phenomena Identification Ranking Tat'.es (PIRTs) Rev. O. April 1997 l o Wwproj20603w.wpf:1bo41197 .
i
3-6 l i O l 4 Figure 3-2 RCS P r e s s u r e MAAP4 SGTR to SLOCA Comporison 0.6 inch, 1 CMT, Auto ADS SLOCA SGTR m 3000 - c - m 2400 -- l
- c. i v a '
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f 1 Figure 3-3 Break i n.t e.g r a t e d Water SGTR. to SLOCA Comparison MAAP4 0.6- i n c h ,. 1- CMT, Auto A D S' SLOCA
----SGTR'
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PRA Phenomena identification Ranking Tables (PIRTs) . Rev. O. Apnl 1997 o'wwwproj20603w.wpCIb441197 .; i. jf. {3 .;
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3-8 I O Figure 3-4 Break Integrated Vapor ]i MAAP4 SGTR to SLOCA Comporison 0.6 inch, 1 CMT, Auto ADS
}
SLOCA SGTR 25000 ~ s
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3-9 :
/ ~,. 8 ,
V i t a a Figure 3 SG Moss inventory ! MAAP4 SGTR to SLOCA Comparison 0.6 i n c h .- 1 CMT, Auto ADS . SLOCA Either Loop
---- SGTR Broken Loop
+ ---SGTR Intact. Loop 120000
- v~..
^ '
96000- - ra. _+(+s E - ' Q o -
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C 72000-~ '+s. , Ns m 48000 - ,
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3-10
~
9 Figure 3-6 CMT Water inventory MAAP4 SGTR to SLOCA Comporison 0.6 inch, 1 CMT, Auto ADS SLOCA SGTR 14 0000
~
l l 112000 - ' E _a - 84000 --
's g;
O : ', _ s m 56000 -- \ w -
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I l I i d Figure 3-7 ! l
.lRWST Integrated i n j e c:t i o n :
' MAAP4 SGTR to SLOCA-. Comparison l 0'. 6 inch, 1 C M T .. Auto ADS :
. SLOCA .j [ SGTR. . 3.00000 -- 1 i .
. .I m:240000 - -
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i is i i PRA Phenomena Identification Ranking Tables (PIRTs) , Rev. O. April 1997 f. ( c:Wrwproj20603w.wpf:lt441197
, , . . . . . , . . , _ , , , , ,._~-s
3 12 O Figure 3-8 RCS Mass Inventory MAAP4 SGTR to SLOCA Comparison 0.6 inch, 1 CMT. Auto ADS SLOCA SGTR 350000
^
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m 280000 -1 E : _a
- 210000 --
_ s g
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m 140000 -- 1 in - 5 C [ Nj ' - _ . 2 70000 - - 0? l l l 0 5000 10000 15000 2000 0 Time (S) l 9 PRA Phenomena Identification Ranking Tables (PIRTS) Rev. O, Apnl 1997 CWwproj20603wspf.lbeel197
.3-13'-
I i Figure 3-9 C o'r.e Mixture Level MAAP4 SGTR to SLOCA Comparison. : 0.6 i n c h.... 1 CMT, A'u t o A.D S L SLOCA. l 1
---- SGTR !
-t :- - - T o p of Core ;
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++++: : : : : +++++: : : :u{-)::::
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. ohwproi?\3603w.wpf;1b4 Mil 97 -
l 3-14 i 1 3.2 Development of PRA PIRTs The development of the PRA PIRTs started with the small break LOCA PIRT (Ref. 7) and includes O modificaticns as needed for the PRA cases to reflect the effects of the loss of additional equipment. ) Since the PRA scenarios of interest are very close to the small break LOCA design basis, the PRA l PIRTs are similar to the small break LOCA PIRT. Also, since the PRA PIRT is very similar to the j small break LOCA PIRT, the validation which has been performed on the small break LOCA PIRT l for the NOTRUMP code also applies to the PRA PIRT. I A group of experts from within Westinghouse were assembled who have experience in AP600 systems design, small-break LOCA, PRA and PIRTs. The different accidents (summarized in Section 3.1) which are used to describe the plant performance for beyond design basis accidents were reviewed and contrasted to the AP600 small-break LOCA. The focus of discussion was the role of different !
. equipment for preventing and mitigating core uncovery. The discussion also included how MAAP4 does the calculations relative to NOTRUMP. The PRA scenarios were categorized to develop two PIRTs: scenarios with CMTs and no accumulators, and scenarios with accumulators and no CMTs. ]
The small-break LOCA PIRT was the starting point to identify the high ranked phenomena for the PRA scena-ios. The nomenclature for the ranking of the phenomena in the PRA PIRTs is as follows: l H liigh Importance: Has controlling influence on minimum vessel inventory; high accuracy l needed on prediction. A bold H indicates that the phenomenon was not identified as high importance in the SBLOCA PIRT. I High Interest: Phenomenon that is unique to AP600 and/or PRA scenarios that should be examined, but moderate differences in the predictions are not expected to have controlling influence on the minimum vessel inventory. Most of these phenomena were identified as high importance on the Chapter 15 SBLOCA PIRT. A bold I indicates that the phenomenon was not identified as high importance in the SBLOCA PIRT. (Dash): Neither a high importance nor a high interest item for benchmarking. O Qmitted: Same as Dash, but it was a high importance item on the Chapter 15 SBLOCA PIRT. The phenomena that are rated as high importance or high interest are grouped into categories that are related to the code models. For each category, parameters are identified for the MAAP4/NOTRUMP comparison that will allow an assessment of the identified phenomena. The PRA PIRT for scenarios with CMTs (and no accumulators) is provided in Table 3-2, and the PRA PIRT for scenarios without CMTs (but with accumulators) is provided in Table 3-3. O PRA Phenomena identification Ranking Tables (PIRTs) Rev. 0. Apnl 1997 oAnewprti2\3603w.wpf:Ibest397
s \ f* U nm IN Table 3-2 PIRT for PRA Scenarios with CMTs (No Accumulators) G mW hS Nat. ADS IRWST hh Blow- Circe- B3ew- Gravity 89 C- -
./,.Thenomens down lation down Drain Discussion of High Importance and High Interest Items Benchmarking Focus u$ Break Break Integrated break water
{g Critical Flow H H H - The tweak now rate determmes the rate of inventory loss, the system depressurization, and the tirrung of the accident Integrated break vapor R3 pressure - :n progression. For larger breaks. the prediction of break now
- So{ and depressurization is most important during the blowdown phase becaese it can impact coolant inventory in the core g regiert For nrnaller breaks, L-.is in break flow g predictions may have a conmhtive effect. impacting the g tirning of the accident progression.
H
- g. Subsonic Flow - - - - - -
5" [ m Line Resistance - - - - - -
$ Descharge CoefficierW - - - - - -
Y CMT Recirculation OtT Ruois;- CMT water injection now rate Natural circulation of 1 I - - CMT secirculation consists of cold water being injected to Balance line water How rate CMT and CL balance leg the a,-u through the DVI line, and hot water CMT water mass invernory returning to the CMT via the cold leg and balance line. This resuhs in a small net injection to the RCS. CMT recirculation occurs for a long period of time in sman.cr breaks. controlling the timing of the acciders progression. liquid mixing of CL I I - - Thermal mixing and stratification was observed in CMT temperature balance leg, condensate. experiments, but code numerical diffusion is not expected to and CMT liquid have a significant ingmet on the overall accirculating and draining behavior. Flashing effests of hot - - - - - - CMT liquid layer CM1~ wall heat transfer - - - - - -
- o h
.o k w w u
o *C' \" f@ Table 3-2 PIRT for PRA Scenarios with CMTs (No Accumulators) E 3@ (cont.) 33 h Nat. ADS IRWST sE Q Blow- Clttu- Blow. Gravity
.g s* Component / Phenomena down lation down Drain Discussion of High importance and Illah Interest Items Benchmarking Focsis m~
OtT Balance Lines OtT Transitroen to Drainine Balance line water flow rate Si Pressure Drop - I I - The do-.- in the balance lines and cold legs determine Balance line vapor (Iow rate
~g 3 when vapor will enter the balance Ime, ending the GtT level
- g. I%w Composition -
I I - recirculanon period of the OtT. Pluise separation indrcates Time recirculation ends a when tie CMT starts to drain. Draining of the OtT initiates f ADS. These Sm me.- are unique to t.se AP600 plant, and
- p. C PB
'd jo-Cold le8Tee hm the f ces f Mns and analyses. no.w.
I I _ 5- differences in the pre Jiction of the transition from g,, -
, _ y g _
rectrculation to draining do not haw: a controlling influence r, on core cooling. E o y Flashing - - - - - - m
% Stored Energy Release - - - - - -
a-l O CMT Draining Effects GtT Drainine GtT water injection flow rate
'Ihermal stratification and -
I I - These du-.m- are related to the deterrnination of the OtT mass inventory mixing of warmer pressure at the top of the OtT, which controls the draining OtT level condensate with colder rate of the CMT. The impact of the interfacial condensation CMT temperature oft water is to reduce the pressure at the top of the GtT such that the Time draining starts GtT drain flow is reduced; this is more important for larger Interfacial condensation - - II - breaks. The overall draining rate of the CMT is important on OtT water surface since it determines the time of ADS actuation. Condensation on cold - - - - - - thick steel arfaces Transient conduction in - - - - - - oft walls Dynarnic effects of steam - - O - This is only a possible effect for the larger breaks; the GtT - injection and nexing with diffusor helps to mitigate this effect. OtT liquid and
.o 3.
w O O O
f3 y
\
V 1 [m L/ t v
)-
nm
!I$ Table 3-2 FIRT for PRA Scenarios with CMTs (No Accumulators)
T7 (cont) h8 IRWST h$ Blow. Nat. Ciren. ADS Blow- Gravity N down Drain Discussion of High I..yas and High Interest Items Benchrearking Focus {a @8* o. Compenent.Thenomens down lation S Upper IIcad "I@ DMning Effects - - - - - - bO Flashing g. W Mature level in the upper plenum is consi& red below;
@ Mixture Ixvel O O O O -
E mixture level in the upper head is not a conant 5$ g EnrrammentrDe. - - - - - - entrainment 8~ o Ugper Plenum - - - - - - 3 Drainmg Effects W
$ Flashing - - - - - -
Entrainment/De- - - - - - - entrainment Mixture Izvel 11 II H H Core Cooline RCS mass inventory 1hese A-ue are ranked high since the two@ drift Vessel mass invernory flux and mixture level models determine the distribution of a Core mixture level
'**-phase mixture, which determines if the core would Com collapsed level Vesselrore uncovered and experme a claf temperatm heat Mixture level / Mass H H H H up. These are the key phenomena for PRA success criteria.
inventory Decay Heat II H H H The decay heat to be removed is a sensitive boundary condition. Forced Convection - - - - - - Flashing - - - - - - Natural Circulation Flow - - - - - j7 and IIcat Transfer
.O w
$ b
o *U w I$ Table 3-2 PIRT for PRA Scenarios with CMTs (No Accumulators) h fy (cont.) da ADS IRWST $y Nat. Orce- Gravity 7n Blow. Blow- . 4E Component /rhenomene down tarion down Drale Disemanlon of High insportance and High Interest items Benchesarking Focus p S~ Vessel Core (cont) gE Mass How - - - - - - -D 3QC. Flow Resistance - - - - - - O Wall Stored Energy - - H H Downcomer Downcomer Pressure W The stored energy in the vessel wall can impact the pressure of Downcomer Temperature the RCS dormg the IRWST gravity injection phase. The stored Downcomer Mass lawntory energy is a potential source of addnional steam generation. { % g,,,,, H which may provide additional challenges to RCS venting 90 Stored Energy - - H j Release /Besimg C*P**I' cr Level H H This is highly ranked since it provides the gravity driving head Downtomer 12 ret { - - for flow into the core. It is specifically of gnatest interest 3 during the IRWST injection period. W Hashing - - [ - - - - tenp Asymmetry Fifects - - - - - - Hotlegs C .. ... ~.; I' low - - - - - - Entrainment - - - - - - Hashing - - - - - - liorironral Hvid - - II II A DS-4 Intgrated ADS-4 water Strarification ADS 4 is a key component for the PRA success criteria. The Integwed ADS-4 vapor reduced venting capacity (compared to DB A) is the reason for RCS pressure Phase Separation in Tees - - II H the increased unportance. The flow regime in the bot leg Hoe leg water level (Row Region) determines the mixture that is eturained into the ADS stage 4 , lines. The ADS stage 4 lines are the primary venting path to ADS 4 reduce system pressure to achieveAnaintain IRWST gravity Crus. cal Row - - H 11 g Subsonic Flow - - - Il Two-Phaw Pressure Drop - - - Il
? .o 3_
meg O O O
ps s V d d eo
$ Tak 3-2 PIRT for PRA Scenarios with CMTs (No Accumulators)
Ji (cont.) +g ,.m y Nat. ADS IRWST 8E Q Blow. Circu- Blow. Gravity
- t,Thenocnena down lation down Drain Discussion of Hizb Importance and Illgh Interest Items Benchmarking Focus
.,g .-- -C, _ ADS Stages I - 3 ADS I 3 Integrated ADS l-3 water _Q Critical Row O O II - In PRA full depressurization scenanos (to IRWST gravity Integrated ADS I-3 vapor "g
% injection). ADS stage I to 3 are only used in high pressure RCS pressure g Two-Phase Pressure Drop - - I -
scenarios to seduce the pressure below the 4th stage a interlock. ADS I - 3 do not have a comrolling influence on W Valve less Coefraciens - - O - the enna progression. E h Single-Phase Pressure - - - - - -
,g Drop p
E I' 1RWST IRWST IRWST flow rate E Pool level - - - 11 The IRWST injectica pmvides core cooling. The pool level IRWST level Q is a boundary condition that provides the elevation head to IRWST temperature
% Gravity Draining - - - 11 drive the inventory injection. Gravity draining also depends RCS pressure j on the primary system pressure, pressure drops in the wns Temperature - - -
11 patts, and line tesistances in the injection lines. DVI Line Pressuve Drop - - - - - - (Flow Resistance) Discharge Line Flashing - - - - - - Flow and Ternperature - - - - - - Distribution in PRilR Bundle Region Vapor Condensation - - - - - - M
?
P E _ v
$ E
om = w h Table 3-2 PIRT for PRA Scenarios with CMTs (No Accumulators) $$ 9! (cont.) 0 h Nat. ADS IRH3T .E Blow- Circu- Blow- Grasity Discussion of Iligh Importance and liigh Interest Items Benchmarking Focus {[@ ~ Component,Thenomena down lation down Drain {@g5 Pressunzer Surge IJne Pressere Drop - - - - - -
- n E. Flooding /CCIL - 1 I -
Pressurizer Pressurizer level O The guessurizer of high interest tecause it can irrpact the Pressurizer muss inventory
,g Pressurizer Ilashing I - - -
redistribution of mass in the RCS. 3 C' g Irvel (Inventory) - I I - Isvel Swell - I I - X CCFt - - - - - - m g r_;.___ -.st)e. - - - - - -_- j entrainment v Stored Energy Release - - - - - - Vapor Space Behavior - - - - - - Steam Generator Stearn Genersor SG Mass Inventory 20 Natural Circulation I I - - The steam generators are the only source of energy removal SG 11 eat Transfer excegt tie CMTs and the break flow. For breaks too srnall to remove the decay heat, the steam generators play a ro*e in Secondary Mass I I - - the timing of the event. Inventory Steam Generator ficat - - - - - - Transfer Secondary Conditions - - - - - - U-tube Condemaion - - - - - - Secondary Pressure - - - - - - to y Steam Generator Tube - - - - - - p Draining i 1 E I O O O
_ . _ - . . . . . . _. . . . . . . . .m.. . . _ . . . . . _ . _ . _ . . _ _ . . _ &
%)
\ l s
om f$ Table 3-2 FIRT for PRA Scenarios with CMTs (No Accumulators) pdE (co.o hh Blow-Nat. Circe-ADS Blow. IRWST Gravity
.8! @
~{ $ Component /T" ._.-
. down tation down Drain Discussion of liigh I- , n s.s amt Illgh Interest items Benchmarking Focus
[E.k
". RCP c oow,
_g _ _ _ _ _ _ 3 8- Flow Resistance - - o
- s W >
tr. E d a
>=4 50 H
O l r i b
- 3. y 3 e
i w l- om fh " Table 3-3 PIRT for PRA Scenarios without CMTs (With Accumulators) b I@ l $ Nat. ADS IRWST I g' g Blow. Circa. Blow- Gravity sE Component / Phenomena down latten down Drain Discussion of Hhth Importance and fligh Interest Items Benchmarkkg Focus E Break Break Integrated tweak we H H H The break flow rate determines the rate of inventory k ss, the Integrated break vapor {$ Critical Flote - system depressurization, and the timing of the accident RCS pressure
.5 jQ progression. fir larger breaks. the predKtion of break flow
@ and depressurization is snost important during the blowdown D phase because it can impact coolant inventory in the core f region. For smaller lxcaks, lim a. in tweak flow g predictions may have a cunwlative effect, impacting tia g timing of the accident gvogression.
j Subsonic Flew - - - - - - E 2 Une Resistar,ce - - - - - - 9 g Discharge Coefficient - - - - - - H O Accunndators Ano..J An Accunmlata injecticn flowrate Injection Flow Rate II H II - The accumulators provide the only source of reactor coolant Accumulator mass inventory make-up prior to ADS actuation. The rate of delivery can play a key role in the primary inventory status. Noncondensible Gas - - - - - - Entrainment Upper Head Draining Effects - - - - - - Flashing Mixture level O O O O Mixture level in the upper plenum is considered telow; - mixture level in the upper head is not a conenn Entrainment/ - - - - -- - De-entrainment M
?
p b w
& O O
\
I )
%) ^ j N.
om if M> Table 3-3 PIRT for PRA Scenarios without CMTs (With Accumulators)
@ (cont.)
E h Nat. ADS IRWST
? Blow- Orcu- Blow. Gravity
{[E C_anyonent!Phenernena down lation down Drain Discussion of High Importance and High Interest Items Benchmarking Focus
~ $*
[g uprer Fienum - - - - - - i -m Draining E!Tects bO
- g. Fiashme _ _ - - - __
- s W Entrainment/De- - - - - - -
E entramnuma ec
- s
** Mixture Level H H H H Core Cooline RCS mass inventory j These pie- . are ranked high since the two-phase dnft Vessel snass inventory E flux and mixture level models determine the distribution of a Core mixture level mM nuxture, wM Menmnes if tk core mtd Core collapsed level Vessel 0nre 3' Mixture LeveWlass 11 II H H d **P""*"C' *
- W ""
g,, up. These are the Ley p- --- ---- for PRA success criteria. O Decay liest H I! H II De decay hear to be removed is a sensitive boundary condition. Forecd Convection - - - - - - Flashing - - - - - - Natural Orculation Flow - - - - - and IIca Transfer Mass Flow - - - - -- -- Flow Resistance - - - - - - n
?
p i > 1 ' l - s v" w l l l i i _ - . . . .m _ _ _ _ _ _ . . . . . _ _ _ _ _ _ _ _ . _ _ _ . . _ _ _ _ _ _ _ _ _ __ _ . _ . _ _ ..___m._ - _ . _ . _ _ _ _ _ _ _ _ . . . . _ _ _ _ _ _ _ _ . _ _ _ _ _ _ _ _ _ _ . _ _ _ _ _ . _ _ . _ _ _ __.________________._.____________m
- T \**
T fh 1; Table 3-3 (co.o PIRT for PRA Scenarios without CMTs (With Accumulators) ga Nat. ADS IRWST , h Blow-9 Blow- Circo- Gravity Drain Discussion et High importance and High Interest items Benchmarking Focus { Q,* C % thenomens down latlen down o. a$ Vessel Core (cont.) {s 30g-Wan Stored rurgy
- - Il 11 Downcomer The stored energy in the vessel wall can impact the pressure r- A..s Pressure Oce.-m. Temperature of the RCS during the IRWST gravity injecten phase. The Dee,wm. Mass inventory 3 Dse. isAnwer Plenurn stored energy is a poternial source of aihtsonal stearn g Stored Energy - -
II II generation. which may provide additional challenges to RCS Release / Boiling venting capacity. 4 E This is highly ranked since it pnmdes the gravity driving Downcomer level um level - - 11 11 p head for flow into the core. It is specifically of giratest 5[ interest during the IRWST injection period. 3 q nashing - - - - - - 5 g Loop Asymmetry Effects - - - - - - O Ild Irgs C a.a.ma Flow - - - - - Entrainment - - - - Flashing - - - - - llorizontal Fluid - - 11 11 ADS-4 Integrated ADS-4 water Struttfication ADS-4 is a key component for the PRA success critesia. Integrated ADS-4 vapor The reduced ventmg capacity (compared to DBA) is the RCS pressure Phase Separation in Tees - - II II reason for the increased iWm The flow regime in the flot leg water level (Row Region) hot leg deter nmes the mixture that is entrained into the ADS stage 4 lines. The ADS stage 4 lines are the primary venting AD Path to reduce system pressure to AR.C..intain IRWST
- - H H. gravity niection.
Subsome Flow - - - 11 Two-Phase Pressure Drop - - - 11 w P k O O O
a n -
. \
nm Ih Table 3-3 PIRT for PRA Scenarios without CMTs (With Accumulators) (cont.) f@E {h o m
? Blow.
Nat. Circu-ADS Blow-IRWST Gravity
" lation down Drain Discunion of High Importance and Iligh Interest items Benchmarking Focus
{@ u o. Componest/Phenomens down ADS I 3 Integrated ADS l-3 water {S
= Ei ADS Stages I - 3 Critical Flow O O H - In PRA full & pressurization scenanos (to IRWST gravity Integrated ADS l-3 vapor
'S U injection) ADS stage I to 3 are only used in high pessure RCS pressure
$- Two-Phase Pressure Drop - - 1 -
scenanos to rede the pessure below the 4th stage interlock. ADS I - 3 do not have a controtting influence on g Valve Loss Coefficient - - O - the event progression. W 5' to Single-Phase Pressure - - - - - - p Drop z 3 IRWST IRWST IRWST flow rate g Poollevel - - - 11 De IRWST injection povides core cooling. The pool level IRWST level is a boundary corxfirion that provides the elevation leaf to IRWST temperature
% Gravity Draining 11 drive the inventory injectiort Gravity draining also depends RCS pressu.e
.-] - - -
v on the primary system pessure, pressure drops in the vent Temperature - - - 11 paths, and line resistances in the ingtion lines. DVI Line Pressure Drop - - - - - - (Flow Resistance) Discharge line Flashing - - - - - - Flow and Temperature - - - - - - Distribution in PRiiR Bundle Region Vapor Condensation - - - - - - l W
?
p 1 w ' 5 S l _-2 _______.._______-..____.-_____ . _ _ _ _ - - _ _ - _ s._ _ _ __m_ _m + __ _ _ _
om y fs Table 3-3 (cont.) PIRT for PRA Scenarios without CMTs (With Accumulators) $ 3M @3 hh W* Blow-Nat. Circu-4DS Blow. IRWST Gravity CompM----- --a down latten down Drain Discussion of High Importance and High Interest Items Benchmarking Focus u o. Presswizer Surge une {$ _. 5 Presswe Drop - - - - -- -- n g
* $. Flooding /CCFL -
I I - Pressurizer Pressurizer level 8 The pressurizer of high interest because it can impact the Pressurizer mass inventory lc Pressurizer redistribution of mass in the RCS. g Flashing I - - - c I y level (Inventory) - 1 - Irvel Swell - 1 I - o~
= CCFL - - - - - -
9 Entrainment/ H De<ntrainment
?
Stored Energy Release - - - - - - Vapor Space Behavior - - - - - - Steam Generator $1gm Gene.arer SG Mass inventory 24 Natural Circulation' I - - - T1n steam generatas are the only source of energy removal SG l{ cat Transfer carept the break flow. Since the actuation of ADS is controlled by operator action, the SGs play a smaller role in Secondary Mass I - - - the timing of the erect. Inverwory Steam Generator Heat - - - - - - Transfer Secondary Conditions - - - - - - U-tube Condensation - - - - - - Secondary Pressure - - - - - - F Sicam Generator Tube - - - - - - [o Draining k w O O
O O o ._ . g* Table 3-3 PIRT for PRA Scenarios without CMTs (Hith Accumulators)
@ (cont) --
Q - o mh Nat. ADS IRM3T
?9 Blow Circu- Blow- Gravity k" , Cg h down lation down Drain Disassion of High Importwee and Illah laterest Items Benchmarking Focus "k RCP
[-mE. Coast Down - - - - - 50g- mw nes% _ _ - - _ _- p to
?
s
- 90 z
3 i
- o Y
4
.O m
b
- - - - .____-w--
4 - , 1 4-1~ f
~4 BENCHMARKING CASES '
- O I
. His section defines the benchmarking cases and explains wh'y they were chosen. There is a total of nineteen cases. De first seven cases are primary cases to demonstrate the basic phenomena that are 4 identified in the PRA PIRTs (Section 3.0). De remaining cases are sensitivities that demonstrate the 1 capability of MAAP4 to predict trends for different break locations, different numbers of CMTs or j
- accumulators, different number of ADS valves, and different parameters affecting IRWST injection. .
Dere are two tables that summarize the benchmarking cases. . De first table, Table 4-1, provides a l brief description of the case, and the general purpose of the case. De second table, Table 4-2, is a more detailed listing of the equipment that is assumed to function in each case. Table 4-2 also summarizes what type of core uncovery is exhibited by each benchmarking case, and whether this core uncovery is risk significant. Note that the frequency of each of the benchmarking cases is less than j IE-10/ year, and therefore no benchmarking case by itself is risk significant (i.e., impacts t'ie results 1'
' and conclusions of the PRA). .
t l ' De following sections provide more details on the general equipment assumptions made in the i benchmarking cases, the selection of the primary benchmarking cases, and the selection of the l sensitivity benchmarking cases.
- Y n 4.1 Equipnient Modelled Most of the benchmarking cases have basic equipment assumptions that are consistent from case to ,
case. This section identifies and discusses the equipment assumptions that are generally applicable to j the majority of the benchmarking cases. Case by case differences are identified in Table 4.2. A single success path in the AP600 PRA represents many combinations of equipment failures and i' successes. Success criteria analyses to support the claim of successful core cooling for a given success ;
- . path are typically based on the most pessimistic set of functioning equipment for that path. Minimum
- . functionmg equipment leads to the most limiting accident progression. The benchmarking cases are defined similar to success criteria analysis cases, with the most limiting set of equipment credited as successful core cooling in the PRA. The benchmarking sensitivity cases may deviate from this
- philosophy, since the purpose of some of the sensitivity cases is to show the impact of additional equipment.
Minimum equipment availability throughout most of the benchmarking cases includes: ) i
* ' no PRHR, i a
no feedwater to the ' steam generators after reactor trip, l either one CMT or one accumulator, I
- . ' no stage 1,2 or 3 ADS valves,.
l Benchmarking Cases - Rev.O. AprH 1997 onnewpoj20603w.wpf.lb041497 . i [- - - - I
4-2 l
. one DVI line for IRWST injection, and e no containment isolation.
The equipment availability assumptions of no PRHR and no feedwater to the SGs after reactor trip are bounding because this restricts how decay heat is removed. The PRHR removes decay heat, lowers the RCS pressure, and can have a positive benefit of delaying the accident progression. Without the PRHR, the system pressure remains higher, putting a greater challenge on the ADS valves to depressurize the system when the decay heat is higher. The assumptions of either one CMT or one accumulator and one DVI line for IRWST injection are straight-forward, because they are the limiting conditions defined for the success criteria. The assumption of no containment isolation is a conservatism in the analyses that is not explicitly identified on the PRA event trees. The method of modelling the assumed equipment failure in the containment isolation system is discussed in Section 5.1.3. The final equipment assumption to be explained is the number of ADS valves credited. In the Baseline and Focused PRAs, the ADS success criterion to achieve successful core cooling with passive IRWST gravity injection is based on the number of stage 4 ADS valves needed to open. The question of how many stage 1,2 and 3 ADS valves open is not asked (unless the event is a high pressure scenario). Therefore, for any given success path, it is not known how many of the stage 1,2 and 3 l ADS valves may be open. For the success criteria analyses, the bounding assumption of no stage 1,2 and 3 ADS is generally made. This produces the most limiting thermal / hydraulic plant response in regard to core cooling. l In the early phases of the MAAP4/NOTRUMP benchmarking effort, it was discovered that the input model for MAAP4 did not adequately account for resistances in the ADS stage 4 piping. The line resistances have a minor impact on the flowrate through the ADS-4 valves when the flow is choked, but they have a large impact at low pressures when the flow through the valve is unchoked. When a better input model of the stage 4 piping resistances was developed for MAAP4, the prediction of RCS depressurization was impacted. The result was that it takes 3 stage 4 ADS valves to achieve approximately the same plant response as was previously attributed to 2 stage 4 ADS valves. Therefore, although the ADS success critena in the current PRA are based on 2 stage 4 ADS valves , for full depressurization, most of the benchmarking cases are analyzed with 3 stage 4 ADS valves. l The update of Appendix A of the PRA, which documents the MAAP4 success criteria analyses, will l address any PRA impact of the ADS-4 line resistance finding. t O I Benchmarking Cases Rev. O. April 1997 ohwpmjh3603w.wpf:lb.041497
4-3 Table 41 List of MAAP4/NOTRUMP Benchmarking Cases
/]
D Case Case Summary Purpose 1 0.5" HL break with I CMT Primary cases chosen to represent different phenomena in PRA cases with CMTs (automatic 2 2.0" HL break with 1 CMT ADS) 3 5.0" HL break with 1 CMT 4 8.75" HL break with 1 CMT 5 3.5" HL break with I accumulator Primary cases chosen to represent different phenomena in PRA cases withou, CMTs (manual 6 6.0" HL break with 1 accumulator ADS) 7 8.75" HL break with I accumulator 3 DVI line break with I CMT injecting To demonstrate the capability of MAAP4 to model 8b DVI line break with I CMT spilling, I CMT injecting 9 5" CL with I CMT 10 5" HL with I CMT, I accumulator To demonstrate no adverse system interaction issues and to support basic element in the categorization i1 5" HL with 2 CMTs,2 accumulators f r T/H uncertainty resolution that I or 2 tanks result in similar accident progression 12 2" HL with 3 stage 4, all stage 1,2,3 To demonstrate no adverse system interaction issues with more ADS; to demonstrate the effect of stage 12a 2" HL with 4 stage 4, all stafe 1,2,3 4 versus stages 1,2,3. 12b 2" HL with 2 stage 4, all stage 1,2,3 13 2" CL with I stage 3 for RNS injection To demonstrate the depressurization effect from I stage 3 ADS 14 2" HL with cont. pressure of 30 psia To demonstrate the m:gnitude of impact of factors 15- 2" HL with higher IRWST temperature 16 2" HL with 21RWST lines l l c) Benchmarking Cases Rev. O. April 1997 oAnewproj20603w.wpf.It@l497
5 f fR:r Table 4 2 Equipment Definition and Risi Significance of Benchmarking Cases 2 Relattenship to T/II LWertainty Resolution Categorization N Case Equipment Definition
- E T!Et y& Sire and Uncertainty kn
~3 R No. location CI ChfT Ace ADS 1-3 ADS-4 Category Ream for Core Uncovery Risk Significance I 03" Hot Leg No 1 0 I 3 UC5 No accumulators when ADS is actuated. This category is risk significant, but the h dominant scenanos include a&fitional I 3 2 2.0" Hot Irg No I O O 3 gim such as containment isolmion
^ '
3 5.0" flot leg No 1 0 0 3 4 8.75" Hot leg No 1 0 0 3 UC3 No accumulators duriirg initial break This category is not risk significant. blowdown. 5 3.5* Hot trg - No 0 I O 3 UCI !) Before ADS, there is no injection This category is risk sigraficant, but the because the RCS remams above dominant scenanos inclu& adthtional accumulator pressure. equipment, such as m.i_:. ._.a isolation
- 2) After ADS. &,m vnw. boiling and a&litionni ADS. The additional delays IRWST gravity injection equipment will minimize the impact of, or eliminste, the second core uncovery.
6 6.0" Hot leg No 0 1 0 3 UCI Dis break size is grouped within a core His category is risk significars, but the uncovery category, although accumulaton limiting break size is smaller, and the stop net inventory loss prior to core dominant scenanos include addniorial uncovery The top of the core almost equipment. uncovers. 7 8.75* Hot leg No 0 1 0 3 UC2A Core uncovery occurs as a result of the This category is not aisk significant. accumulator inventory depleting prior to the operator manually actuating ADS. 8 DVI Une No I O O 3 UC5 No accumulators when ADS is actuated. This category is risk significant, but the dominars scenarios include ad&tional 8h DVI line No 2* O O 3 UC5 No accumulators when ADS is actuated. equipment, such as containment isolation
^ '
l9 5" Cold leg No I O O 3 UC5 No accumulators when ADS is actuated.
- e h
p O O O
7.- x V / (s t v e tn k Table 4-2 Equipment Definition and Risk Significance of Benchmarking Cases
.@ (cont.)
g:I Equipment Definition
- Reistionship to T/H Uacertainty Resolution Categorization
.g Case s g
- O Till <
)k* Size and Uncertainty New location C1 CMT Acc ADS 1-3 ADS-4 Category Reason for Core Uncovery Risk Significance @ 10 $*IIctLeg No I I O 3 UC9 This scenano is pessimistically assunrd This category is net tisk signifrant. to result in core uncovery, tecause it has failure of containment isolation, and less than DBA ADS. Ilomever, this case 11 $* 110s leg No 2 2 0 3 UCS sinws t: ! accumulator in a&htmn to I CMi' ma core uncovery, even with containment isolation failure. 12 2* Itat leg No 1 0 all 3 UC5 No accumulators wten ADS is actuated. His category is risk significant, and case 12a is the nest similar to dominant scenanos of a.ny of the benchmarking cases. 12a 2" Het leg No 1 0 all 4 UC5 Howewr, the dominant scenano includes successful containment isolation. 12b 2* Hot irg No 1 0 all 2 UC5 No accumulators when ADS is actuated is His category is risk signirmant, but the the reason attributed for core uncovery. dominant scenarios include altitional
%e contribution of reduced ADS-4 is not equipment, such as more ADS 4 and explicitly idernified for this set of successful w,C. ._.; isolation.
equipment failures. If there were at least one accuumlator and successful containment isolation, this would be category UC6. UC6 is a risk significant category, and therefore the impact of 2 stage 4 ADS is addressed. 13 2* Cold Irg No 1 0 1 0 - - This case illust.e cooling from pumped RNS injectien. De risk significance of this case has not been determined, because it is a scenario that includes active systems. P 1 5 Y w u
. _ . _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __...____...__________m______ _ _ _ _ _ _ _ _ . _ _ _ _ _ , ,- _ _ _ . _ _ _ _ _ . _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ . _ . _ _
o tn m p g" ,R Table 4-2 Equipment Definition and Risk Significance of Benchmarking Cases e 3$ (cont.) L/ Rr 5' Case Equipment Definitien
- Relattenst ip to T/H Lhicertainty Resolution Categertration E **
~O 4 T/II b Size and Uncertainty {* No. location CI OIT Ace ADS 1-3 ADS 4 Category Rea en for Core Uncovery Rhk Significance 3 I4 2' Hot irg Yes I O O 3 UC5 No accumularon when ADS is actuated. His csegory is risk significant, but the dommart scenarios in the category have all ADS fundioning. 15 2* Ilot leg No I O O 3 UCS No accumulaton when ADS is actuated. Tins case is a sensitivity study to a higher IRWST k.,W,..wwhich could occur from the operation of ADS stages I to 3 or FRHR operation. This category is risk significant, but the dominant scenanos I include additional equipment, such as containment isolation and more ADS. 16 2" Ilot leg No 1 0 0 3 UC5 No accumulators when ADS is araared. His case is a sensitivity to 2 DVI lines for IRWST injection rather than 1. An increase in the number of DVI knes does not prevent core umg. This category is risk significant, but the donunant scenanos include additional equipment, such as containment isolation and more ADS. Notes: (t) All cases, except case 16. model only I DVI kne for IRWST injection. (2) He faulted CMT is modelled, which opens a second pathway to lose RCS hventcry (from the co!d leg. through the CMT) out the DVI line break. Case Eb also takes credit for ADS actuation on the faulted OIT signal. De imentory from the faulteel OTT is lost out the break. U
.O O O O
. 4-7 'l 4.2 Primary Benchmarking Cases o The primary benchmarking cases are selected to be close to the limiting break Ozes across the spectrum of the break sizes analyzed with MAAP4. Figures 4-l' and 4-2 show the minimum vessel"
{ mixture level as a function of break size for automatic ADS cases and manual ADS cases,- respectively. The hot leg is approximately 5 feet above the tc p of the core, and no level'above this t elevation is shown (i.e.,5 feet on the figures means "at least 5 feet" above the top of the core.)'. Figures 4-1 and 4-2 also distinguish between the minimum mixture level that is predicted before ADS is actuated, and the minimum level that is predicted after ADS is actuated.' he break sizes that are ! selected for the primary benchmarking cases are indicated on Figures 4-1 and 4-2. l here are three basic groups of break sizes, as discussed in Section 3.1 and summarized in Table 31: ! SLOCA, NLOCA, and MLOCA. The SLOCA can result in core uncovery because the RCS pressure ! is high when ADS is actuated, and there is a very large depresmrization needed to achieve IRWST ! gravity injection. Without accumulators, core uncovery can oc:ur. His is illustrated with case 1, which is a 0.5" hot leg break. Manual ADS SLOCAs (Figure 4 2) are not challenging because they ; credit an accumulator, and operator action to open ADS is credited }.rior to substantial RCS inventory loss. De NLOCA break spectrum, starting at 2.0", can experience core uncovery for several reasons. In automatic ADS cases with CMTs and no accumulators, core uncovery can occur after ADS actuation as a result of no accumulators. Cases 2 and 3 illustrate this with 2.0" and 5.0" breaks. For manual ADS cases with an accumulator but no CMTs, core uncovery can occur twice. De first core uncovery can occur prior to ADS actuation because the RCS pressure is above the accumulator back pressure of 700 psig, and therefore there is no available injection to make-up the inventory lost through the break. The most limiting break size for this core uncovery is approximately 3.5", since this is 24 largest break size that remains above the accumulator pressure until operator action at 20 minutes after the failed CMT actuation signal. This is demonstrated with benchmadcing case 5. As long as the secaario is defined by failure of both CMTs, there is nothing that can be done to prevent this core accovery, other than the operator taking action to open ADS. Benchmarking case 5 also shows core uncovery after ADS. This core uncovery occurs because the , i
.downcomer water saturates after the accumulator empties, which stops the RCS depressurization, and delays IRWST injection until after the top of the core uncovers. Since the RCS pressure is very low when the downcomer boils, and IRWST injection is almost able to start, there are several changes to
- the scenario that would prevent the core uncovery after ADS. If both accumulators were credited, the downcomer would remain subcooled for a longer period of time, allowing IRWST injection to start a' before the core uncovers. In addition, a containment back pressure above atmospheric would provide sufficient AP from the top of the IRWST (which is open to containment) to the RCS to allow IRWST gravity injection prior to the downcomer boiling. And finally, venting through an additional ADS j
' stage 4 is likely to provide the extra depressurization needed to achieve IRWST injection prior to t Ldowncomer boiling. .s L Benchmarking Cases . Rev. O. April 1997 cAnewproi2\3603w.wpf;1W41197 1
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48 l The largest break sizes analyzed with MAAP4, the' MLOCA breaks, start at 6.0". Primary benchmarking cases 4,6 and 7 demonstrate the plant response for 6.0" and 8.75" breaks. The large end of the break spectrum is more limiting, due to the higher rate of inventory loss through the break. For cases without either accumulator, core uncovery can occur because the CMT is not able to provide the rapid inventory make-up that the accumulators do. This is illustrated in case 4. With the failure of both CMTs, core uncovery can happen because the accumulators empty when the RCS pressure is approximately 100 psia, while IRWST injection does not start until the pressure is below 30 psia. This period of no injection lead to core uncovery.
- De break location for all the primary cases is chosen at the bottom of the hot leg. The water in the -
hot leg is less dense than the water in the cold leg, and less inventory is initially lost from the hot leg break than from an equivalent cold leg break. However, the hot leg connects to the AP600 reactor vessel at an elevation approximately 1.7 feet lower than the cold leg. Therefore, water inventory continues to be lest from the hot leg after an equivalent cold leg break location uncovers and transitions to vapor-only break flow. The hot leg break results in a lower vessel inventory when ADS is actuated, causing the system response to be slightly more limiting than a cold leg break. The effect of the break location is an interesting thermal-hydraulic issue, but does not impact the PRA success criteria definitions. He plant response to different break locations is similar enough to define the same set of equipment needed to achieve successful core cooling. Nevertheless, sensitivity cases for MAAP4/NOTRUMP benchmarking demonstrate the effect of different break locations. J Ol l l l l 4 I O1 i
~
Benchmarking Cases Rev. O, Aprd 1997 l ohwprti2\3603w.wpf Ib 041197 I
i
.4-9: l 1
1' 10' 4 Figure 41
' Minimum Vessel Mixture Level for Automatic ADS Cases MAAP4 Resuks, No A'ccumulators Containment Isolation Failure Modelled I
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- O 1 2 3 4 5 6 7 8 9
)s - Break Diameter (inen) O Before ADS + After ADS g Automatic ADS includes I stage 3 and 3 stage 4 ADS for breaks < 2" Automatic ADS is only 3 stage 4 ADS for breaks 22 " This figure is based on MAAP4 analyses done early in the MAAP4 / NOTRUMP benchmarking 1 process.- The input and assumptions are similar to the benchmarking cases, except there is a difference in the containment back pressure Failure of the largest penetration in the contalament isolation (Cl) system is modelled for these cases, rather than a constant atmospheric containment pressure assumed for the benchmarking cases. With the CI failure modd in MAAP4, a limited
. containment pressurization occurs due to the break and ADS-4 actuation.
i ' D 'i. V' l.
' ilenchmarking Cases . Rev. 0, Apnl 1997 c:Vwwproj20603w.wpf;t b-041197 -
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4-10 Figure 4-2 Minimum Vessel Mixture Level for Manual ADS Cases MAAP4 Results, No CMTs Containment Isolation Failure Modelled 6
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_11 - Case 5 Case 6 Case 7
-12 O 1 2 3 4 5 6 7 8 9 Break Diameter (inch) o Before ADS A After ADS Manual ADS at 30 minutes after failed CMT actuation signal for breaks < 2" Manual ADS at 20 minutes after failed CMT actuation signal for breaks 22 "
This figure is based on MAAP4 analyses done early in the MAAP4 / NOTRUMP benchmarking process. The input and assumptions are similar to the benchmarking cases, except there is a difference in the containment back pressure. Failun: of the largest penetration in the containment isoidion (CI) system is modelled for these cases, rather than a constant atmospheric containment pressure assumed for the benchmarking cases. With the CI failure model in MAAP4, a limited containment pressurization occurs due to the break and ADS-4 ac2uation. O Benchmarking Cases Rev o, Apnl 1997 oh.srproj2V603w wpf:lt@l197
, - - ~ . . - . . . . - - - . - - - -.. - - - - _.-.--.-
4 11 4.3 Sensitivity Benchmarking Cases - The first set of sensitivity cases for MAAP4/NOTRUMP benchmarking demonstrates the effect of different break locations. One cold leg break and two DVI line breaks are analyzed. For the DVI line break, two separate scenarios are considered. The first scenario (case 8) assumes that the CMT isolation valves on the faulted DVI line fail to open. Therefore, the RCS " sees" only one side of the DVI line break, and the 4" flow mstrictor at the reactor vessel limits the break size. The intact CMT provides the ADS actuation signal. The second scenario (case 8b) takes credit for the blow-down of - the faulted CMT through the break, which provides an earlier ADS actuation signal. De blow-down of the faulted CMT also creates a second pathway for RCS inventory loss via the cold leg and the balance line. The e!.fective break area of the second pathway is 3.7" (refer to Figure 3-1). The equipment assumpdons that are different for case 8b when compared to a design basis DVI line break scenario is tnat case 8b does not credit an accumulator nor any stage 1,2, or 3 ADS valves. A 5" cold leg break is analyzed as case 9. He analysis and equipment assumptions are identical to benchmarking case 3, except the location of the break. The results of the sensitivities to break location are presented in Section 7.1. Also note that case 13 is a 2" cold leg break, but it is analyzed to demonstrate the resuhs of a scenario that relies on RNS pumped injection rather than IRWST gravity injection. The second type of sensitivity analyses is to the number of CMTs and accumulators credited. The
, primary benchmarking cases credit either one CMT or one accumulator. - Accumulators are designed for rapid inventory make-up when the RCS pressure falls below 700 psig. CMTs are able to provide inventory make-up at higher pressures, but cannot inject as rapidly as accumulators. When both CMTs or both accumulators are lost, there is the potential for core uncovery because the function of the lost tanks is unfulfilled. De first sensitivity to the number of tanks is case 10, which credits 1 CMT and I accumulator for a 5" hot leg break. This case, compared to case 3 without an accumulator, demonstrates that the accumulator makes the difference of whether core uncovery occurs. De break size of 5" is chosen because it is a size for which it is not intuitively obvious that the accumulator would prevent core uncovery. It is cicar that small breaks at a high RCS pressure when ADS is actuated would benefit from the rapid inventory injection of an accumulator. Likewise, larger breaks would experience the benefit of an accumulator early in the event. Therefore, the intermediate size of 5" was chosen.
The second sensitivity to the number of tanks is case 11, which is the same 5" break as case 10 with 2 CMTs and 2 accumulators. This case is selected to demonstrate that the accident progression for 1 CMT and 1 accumulator is similar to 2 CMTs and 2 accumulators. This similarity is used in the T/H uncertainty resolution process to help group accident scenarios into categories. Resuhs from the sensitivities to the number of tanks are documented in Section 7.2. ( 1 Benchmarking Cases Rev, o. Apnl 1997 o%ewprof?J603w.wpf:IMMil97
4 12 The third type of sensitivity is to the number of ADS valves that are credited. A 2" break was selected for these cases, because this break size produces the most limiting core uncovery. The first l ADS sensitivity case is the same as primary case 2, except that all stage 1,2,3 ADS valves are credited. This is case 12, and is similar to the design basis accident scenario, except no accumulators are credited. The purpose of this case is to show that there is no adverse impact on core cooling due to the additional inventory loss that occurs from more ADS valves opn. The next sensitivity, case 12a, credits all ADS, which is an additional stage 4 valve than case 12. He purpose of this case is also to show whether more ADS valves open can cause an adverse impact. The final ADS sensitivity is case 12b, with only 2 stage 4 ADS in addition to all stages 1,2, and 3. This case shows the importance of stage 4 ADS relative to the other stages of ADS. De results of the ADS sensitivities are documented in Section 7.3. Section 7.4 contains the results of a single sensitivity. All the other benchmarking cases conclude with stage 4 ADS actuation to achieve IRWST gravity injection. Case 13 is a 2" cold leg break in which only I stage 3 ADS is actuated. This case represents a type of case within the PRA known as i " partial depressurization." which credits pumped RNS injection for core cooling. The break location ) on the cold leg was chosen because the hot leg is more likely to be filled with water when ADS is actuated, and therefore there is more likely to be an in-surge of water into the pressurizer. An insurge of water into the pressurizer can adversely impact the depressurization of the RCS. , 1 The final benchmarking sensitivities examine the impact of boundary conditions impacting IRWST injection. Case 14 shows the benefit of a higher containment pressure. The higher containment pressure could be due to the containment being isolated, or a nare realistic modelling of a containment isolation failure. Case 15 shows the impact of a higher IRWST temperature. The higher temperature could be due to the operation of the PRHR heat exchaigers, or the outlet of hot vapor and water from stages 1,2, and 3 ADS. An IRWST water temperature of 200*F is selected for the sensitivity. Case 16 is a sensitivity to crediting both DVI lines as injection paths for the IRWST gravity injection. All other benchmarking cases demonstrate injection through only 1 DVI line. These IRWST sensitivities an: documented in Section 7.5. i I i O Benchmarking Cases Rev. O, April 1997 l oWwproj20603w.wpf.It>&l197
5-1 5 ANALYSIS METHOD U The MAAP4 code is benchmarked against the NOTRUMP code. In this context, benchmarking refers to a comparison of results for the same transient case from two separate computer codes with models of the AP600 plant. He NOTRUMP and MAAP4 input decks and modelling methods have been developed and used for the AP600 design cer+1rication program over a period of many years. The benchmarking of MAAP4 is not used te tune" MAAP4 user-selected input to match NOTRUMP output. Rather, the benchmarking of MAAP4 is to validate the thermal-hydraulic model adequacy of the MAAP4 code for the purposes for which it is used. This section addresses the analysis assumptions that are made in both MAAP4 and NOTRUMP analyses, provides the basis for the use of NOTRUMP as the comparison tool, and describes the process that is used to compare the two codes. 5.1 Analysis Assumptions It is acceptable for analysis assumptions for the MAAP4/NOTRUMP benchmarking effort to be based on nominal performance of the plant. This is because MAAP4 is used to support the AP600 PRA. The philosophy of the AP600 PRA, which is consistent witii industry-wide PRA practices, is to model the nominal performance of the plant. The purpose of nominal assumptions is to maintain the PRA p) ( plant model as close to reality as possible, allowing one to obtain the most accurate insights on ary risk vulnerabilities of the plant. De impact of uncertainties on the PRA successful core cooling cases is addressed separately through PRA sensitivity studies and a T/H uncertainty resolution program for ; AP600 passive system reliability. l Although it is acceptable for all analysis assumptions to be nominal, many of the assumptions for the MAAP4/NOTRUMP benchmarking effort are consistent with the assumptions used in the Chapter 15 SSAR analyses. For exenple, line resistances for injection paths such as the CMTs, accumulators and 1 DVI line are maximized. Ilowever, the most important assumption is the decay heat level, for which nominal values are used with no uncertainty applied. Although difficult to fully separate, an attempt is made to distinguish analysis assumptions from the l equipment that is assumed to function. The functioning or failure of equipment defines the accident scenario, and is specified within Section 4.0 for each benchmarking case. The analysis assumptions , defined in this section are of a general nature, and are applicable to the majority of the MAAP4/NOTRUMP benchmarking cases. To the extent possible, the input boundary conditions of the benchmark analyses are consistent for both the MAAP4 and NOTRUMP calculations for a specific case. He comparisons between the MAAP4 and NOTRUMP results indicate only the difference in l the thermal-hydraulic models. , l O) i V l Analysis Method Rev. O. April 1997 o%ewpmj2\3603w.wpf.Ib-o41197
5-2 5.1.1 Decay Heat Decay heat is the most important boundary condition that must be consistent in the MAAP4 and O NOTRUMP analyses. For nominal predicdon of the plant perfonnance after reactor trip, best estimate ANS 1979 decay heat is used, without uncertainty (Ref. 8). Although MAAP4 has an internal calculation of decay heat based on user-specified parameters such as irradiation time and fuel enrichment, the MAAP4 calculation does not include residual fissions, which can significantly impact the core heat within the first 100 seconds after reactor trip. Although the fizit 100 seconds are not critical to the accident scenarios of interest for the PRA, the rd.ual fissiens are included for several reasons. To include the residual fissions is consistent with the general philosophy of modelling the plant response as close to reality as possible. Secondly, the inclusion of the residual fissions is a method to conclusively show that they do not adversely impact the conclusion of successful core cooling. And finally, to include the residual fissions requires that the decay heat be specified in MAAP4 as an input table. Therefore both MAAP4 and NOTRUMP can use identical decay heat input tables, ensuring that this important boundary condition is identical. Figure 5-1 and Figure 5-2 show the decay heat with residual fissions used for MAAP4/ NOTRUMP benchmarking compared to the intemal MAAP4 calculation of decay heat. The first figure shows this comparison for the first 100 seconds, when there is a significant difference. The second figure shows that over the longer time period of interest for most of the benchmarking cases, the decay heat input for benchmarking is similar to the internal MAAP4 calculation. 5.1.2 Initial Conditions and Line Resistances The initial plant conditions associated with the primary and secondary systems are generally assumed at nominal conditions. Nominal initial conditions include:
- 100% power, or 1933 MWt
- 2250 psia RCS pressure
- 37% pressurizer level (minimum nominal level)
- 110,700 lbm initial SG inventory Iritial conditions associated with the temperature of make-up water tanks are set to the Tech Spec maximum values:
- 120'F CMT temperature
= 120 F IRWST temperature O
Analysis Method Rev. O, Apnl 1997 o%ewproj2\360h wpf Ib-o41197
5-3 i Hydraulic resistances associated with the passive ECCS equipment are assumed consistent with the - .; SSAR Chapter 15 LOCA analyses. Maximum resistances to achieve minimum flow are assumed for. ,
- CMT injection line !
- DVIinjection line to the IRWST j
- Accumulator injection line
- ADS l' through 3 discharge line
- ADS 4 ' discharge line l
5.1.3 Containment Pressure !
- ne limiting multiple-failure analyses that are selected for MAAP4/NOTRUMP benchmarking include failure of the containment isolation system. In the PRA, this refers to the failure of the largest f penetration, which is 254 in2. The opening within the containment isolation system limits the containment pressurization, so that the RCS must further depressurize to achieve the needed AP from '{
1 the top of the IRWST to the RCS to allow IRWST gravity injection to begin. Although CI failure limits the containment pi ssurircon,it does not keep the containment from pressurizing at all. In , particular, the steam released from stage 4 ADS to the containment causes the containment to
]
pressurize at a time that is beneficial to achieving IRWST gravity injection. i he benchmarking cases, however, do not take credit for any containment pressure throughout the entire accident progression, nis assumption is made for consistency of boundary conditions between MAAP4 and NOTRUMP. NOTRUMP requires the containment pressure as an input, which is specified as a single value throughout the analysis. De MAAP4 model generated for AP600 includes the containment, and it is difficult to maintain a constant pressure throughout the analysis, unless that pressure is atmospheric. Atmospheric containment pressure is modelled in MAAP4 by assuming an unrealistically large hole in the containment. The effect of the benchmarking case assumption of atmospheric containment pressure is deeper and longer duradon core uncovery than occurs if CI failure, as defined for the PRA, is modelled. i 5.1.4 Actuation Logic and Delays Actuation setpoints and delays are typically consistent with SSAR Chapter 15 assumptions. Table 5.1-I lists the signals, setpoints, delays and valve opening times that are assumed for MAAP4/NOTRUMP benchmarking. De MAAP4 and NOTRUMP input assumptions are the same, except MAAP4 does not model valve opening times. Instead, the MAAP4 delay is increased to encompass the valve ; opening time. ! ( !
- Analysis Method Rev. 0, April 1997 o%ewproj7060)w.wpf;1beel197 ]
i
l 5-4 5.1.5 Break Discharge Coefficient The break discharge coefficient is a multiplier on the break area to compensate for the head loss across O , the break opening. The value of the discharge coefficient usually varies from 0.6 for a sharp-edged l outlet to 1.0 for a well-rounded outlet (Ref. 9). It is not possible to pre-determine the actual j discharge coefficient that a break will have, since a break could either be " clean" or could result in l jagged edges at the opening. A discharge coefficient less than 1.0 has the effect of reducing the inventory loss from the break, and reducing the rate of depressurization. For the MAAP4/NOTRUMP benchmarking, the break discharge coefficient is set at 0.7. This discharge coefficient is at the lower l end of the expected range (0.6 to 1.0), and is also the value recommended in Ref.10. The effect of the break discharge coefficient is to change the effective break area. Table 5.1-2 shows I the effective break diameter that is modelled for tne break sizes analyzed in the MAAP4/NOTRUMP benchmarking cases. Since analyses are performed over a range of break sizes, the thermal-hydraulic significance of the assumed discharge coefficient is addressed. ! l The assumed breal, discharge coefficient can also impact the PRA. The initiating event frequency for l each of the LOC /. categories is based on the depressurization of the RCS to certain levels. For example, a MLOCA break must be large enough to depressurize the RCS below the RNS pump shut-off head (-17's psia). If the RCS does not depressurize due to the inventory lost from the break, then more equiptrent such as ADS is needed. Since more equipment must operate to achieve successful core coolint orf a smaller break, a smaller discharge coefficient is conservative with respect to the initiating e"ent frequency calculation and the overall estimate of core damage frequency in the PRA. Thus the value of 0.7 is used. O Analysis Method Rev. O. April 1997 ohwprojA%03wspf.lb-041197
1 5-5 l I I Q) Table 5.1 1 Actuation Signals and Delays for MAAP4/NOTRUMP Benchmarking Valve Opening Item Signal Setpoint De!ay (sec) Time "' Reactor Trip low Pressurizer Preeg 1800 psia 2.4 - CMT Actuation Low Pressurizer Pe .,uw 1700 psia 20.0 1.0 l 1 Accumulator Back - 715 psia - - l Pressure ADS Stage 1 Low CMT Level 67.5 % 80 30 ADS Stage 2 Low CMT Level 67.5 % 150 80 ADS Stage 3 Low CMT Level 67.5 % 270 80 ADS Stage 4
- Low-low CMT Level 20% 90 30 Low CMT Level 67.5 % 390 30 i l
IRWST valve Low low CMT Level Signal 20% - - opening i Notes l (1) MAAP4 does not separately model the valve open'ng times; the delay input is increased to encompass the valve opening time.
'd (2) There is also an ADS Sage 4 ir.t: dock that requires the RCS pressure to be below 1200 psia for l ADS-4 actuation.
(l u Analysis Method Rev. O. Apnl 1997 ohwproj2\3603w.wpf:ltWil97
5-6 Table 5.12 Effective Break ID (inches) for Benchmarking Cases Assumed Break Diameter Effective Break Diameter
- 0.50 0.42 2.00 1.67 3.00 2.51 3.50 2.93 4.00 3.35 5.00 4.18 6.00 5.02 8.75 7.32 The benchmarking documentation identifies the assumed break diameter (left column) for each case. A discharge coefficient of 0.7 is applied, and the effective break diameter is shown in the right column.
9 1 O Analysis Method Rev. O. Apri; 1997 chpuj20t43wspf Ib-041197
5-7 I i m Figure 5-1 O First 100 Secon'd's o' f '1979 Best' Estimate Decay-Heat for MAAP4 / NOTRUMP Benchmarking
, input wi'th Residual Fissions (Used in Benchmarking)
----Internal WAAP4 Calculation
. 25 _i
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- i
. 15 - g,g
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. 5 E-01 -- --
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l 0 20 40 60 80 100 Time (s) O rigure s-2 Longterm 1979 Best Estimate Decay Heat . for MAAP4 / NOTRUMP Benchmarking ! Input with Residual Fissions (Used in Benchmarking) i Internal MAAP4 Calculation
- 6E-01 a 5 E 2 . 4 E . 3 E _
- 2 E ~
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- 5. 0
= ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' '
i i . 0 2000 4000 6000 80'00 1000 0 Iime (S) _O, Analysis Method Rev, D April 1997 c:%ewproj2\3603w.wpf;1t441197
5-8 1 5.2 NOTRUMP Applicability I G The applicability of the NOTP. UMP computer code to the analysis of design basis small-break loss-of-coolant accident (LOCA) for the AP600 design has previously been validated by Reference 11. The Reference 11 version of NOTRUMP has been applied to the PRA benchmark cases identified in Reference 12. In order to show the applicability of NOTRUMP to the PRA benchmark cases, a PRA Phenomena Identification and Ranking Table (PIRT) was developed (Chapter 2.0). The PRA PIRT l table was compared to Table 1.3-1 of Reference 11 to determine if any new phenomena have been l introduced by the PRA scenarios or if some phenomena are now more important. Phenomena introduced or ofincreased importance as a result of PRA scenarios were:
- 1. Core Uncovery (Tv/o-Phase : Addressed in Reference 11 Level Swell) Chapter 4 l
- 2. Vessel Metal Heat, Downcomer Boiling: Addressed in original NOTRUMP model i (References 13 and 14) and Reference 11 Chapter 4 ;
- 3. ADS 4 flow during IRWST gravity: Addressed in Reference 11 )
injection - Critical Flow, non-critically Chapter 7 limited single and two-phase flow j
- 4. IRWST Temperature: Sensitivity study in this WCAP
- 5. Pressurizer surge line flooding /CCFL,: Addressed in Reference 11 Pressurizer level and inventory Chapters 3.2,4.2, & 7
- 6. Primary System Natural Circulation: Addressed in Reference 11 Chapter 7
- 7. Core Node Heat Transfer Model: Developed in original NOTRUMP model, Reference 13 Chapter 7 AP600 NOTRUMP code used in the PRA benchmark slightly modified this model as discussed below.
The phenomena listed above ere a natural outcome of the larger number of equipment failures considered in the PRA when compared to the Design Basis Accidents (DBA). These additional failures lead to periods of no safety injection which result in downcomer boiling and core uncovery. While some of these phenomena may not be observed in the DBA, the NOTRUMP code still has the necessary models to calculate the effects of these phenomena, as shown in the listing above. O. Analysis Method Rev. o. April 1997 o \nrwproj20603w wpf.!b-o41197
. . . - - - - - . - - . - - . _ . - . - - . . ~_ ~ - - .-.. - .-
l 5-9 Item 7 above,
- Core Node Heat Transfer Model," has been modified from the model described in Reference 13, Chapter 7. De model described in Reference 13 would determine the amount of stored j energy in the fuel rod covered by the advancing mixture level. The stored energy from the movement ;
1- of the mixture level was combined with the stored energy of that portion of the fuel rod which was ! below the mixture level in the previous time step. His combining of the energies results in an i increase in the temperature of the fuel rod below the mixture level. While this method conserved [ j energy, it also resuhed in an increase in the fuel rod temperature ant the heat transfer between the l portion of the rod below the mixture level and the associated fluid node. De increased heat transfer i below the mixture level increased the void fraction, which swelled the mixture, forcing the mixtme l' 1 level higher. This process of coupling the mixture level and the fuel rod temperature could feedback upon itself resulting in a rapid increase in the mixture level to a height above the active fuel, i f particularly at low pressure. When the mixture level rises above the top of the active fuel, the coupling between the mixture level and fuel temperature no longer exists and NOTRUMP's drift flux, bubble rise, and mixture level tracking models allow the mixture level to fall back to an appropriate level within the core. The tendency for the mixture level to spike to a height above the active fuel was corrected by requiring the energy removed from the core node at the mixture interface to generate : I , steam at the mixture interface, instead of increasing the fuel rod temperature below the mixture level. His approach more closely models the effects of fuel rod quenching and corrects the previous models , 1 tendency to swell the mixture and force the mixture level upwards in situations where an uncovered core was recovering. De NOTRUMP code with the modification described above has been shown to be capable of d modeling the phenomena introduced by the PRA transients. The validation effort of Reference 11 l provides assurance that NOTRUMP is capable of modeling the AP600 PRA transients. k a O I Analysis Method Rev. O. Apnl 1997 c:\newpml?.3603w wpf.lb-041397 1
- 1 l
5-10 5.3 Comparison Process 1 Results from MAAP4 are compared to NOTRUMP results using three methods. The first method is to i compare transient plots of output parameters from each code. The second method is to compare the sequence of event actuation times. The final method is to develop code comparison plots of key output pammeters. The results from all of these comparisons are used to develop final assessments of the MAAP4 thermal-hydraulic models, capabilities, and limitations, discussed in Section 9.0. Further details on each of the comparison elements are provided below. PLOTS OF TRANSIENT RESULTS The largest comparison effort is focused on how well the MAAP4 transient prediction matches NOTRUMP's prediction. A comprehensive set of output parameters identified in the PRA PIRTs is examined for each of the primary cases. An effort was made to present a consistent set of parameters for each case. However, plots are not provided for systems that are not modelled in a specific case. For example, cases 2 through 7 do not model any stage I through 3 ADS and therefore there are no corresponding plots. In addition, plots of IRWST level and water temperature are of little interest when there is no stage 1 through 3 ADS and no PRHR. Therefore, these are also not shown for cases 2 through 7; the initial part of the case I transient is adequate to illustrate the IRWST boundary conditions assumM in MAAP4 and NOTRUMP for all primary cases. The parameters that are compared for each case are summarized in Table 5.31. This table also includes further information about the codes'icpresentation of the parameter that is plotted. For example, there are some parameters that could not be captured in exactly the same manner from the two codes, and therefore ) differences in the plotted output are anticipated. The comparison of MAAP4 output to NOTRUMP I output is documented in Section 6.0 for the primary cases. I Code results for the sensitivity cases (8 to 16) are documented in Section 7.0. Most of the sensitivity , case results are presented as a comparison to a previous case; NOTRUMP to NOTRUMP results are shown, and MAAP4 to MAAP4 results are shown. For example, case 9 is a 5" cold leg break, and it ' is compared to the results from a 5" hot leg break (case 3) to show the impact of changing break location. Each figure includes an "a" plot and a "b" plot, presented on one page. The top "a" plot l shows NOTRUMP results, and the bottom "b" plot shows MAAP4 results for the same parameter. l This method is used to illustrate that both codes show the same thermal-hydraulic behavior for a j specific change to the accident scenario or analysis assumption. This plot format allows one to focus on both the effect of the sensitivity, and differences in the codes' predictions that have previously been identified and discussed. For example, many of the sensitivities are based on a 2" break. which has j timing differences between the two codes of approximately 10 minutes. The timing differences are l discussed in detail in Section 6.0, and are also seen in the sensitivity results. Therefore, the l NOTRUMP to NOTRUMP and MAAP4 to MAAP4 comparison is used for the sensitivity cases ) wherever possible. O Analysis Method Rev. O. Apn! 1997 owwprojA3603w.wpf Ib-o41197
5-11 i There are some sensitivity cases for which there is no previous case to make a clear comparison. For ! example, case 8 is a 4" DVl line break. There is no primary case with the same break size or the same break location. For this sensitivity case, MAAP4 results are compared directly to NOTRUMP results, similar to the method used for the primary cases. Direct comparisons between the codes is also done for case 13, which demonstrates the ability of a single stage 3 ADS valve to depressurize the RCS to achieve pumped RNS injection. The plotted output parameters that are selected for all the sensitivity cases are based or, the issue being demonstrated. The parameters for the sensitivity cases are selected from the parameters used for the primary cases (listed in Table 5:3-1), and are usually presented in the same order. The final parameter shown for every case is the vessel mixture level, because it is the focus of the benchmarking effort. SEQUENCE OF EVENTS The second comparison method used to document the results from MAAP4 and NOTRUMP is to develop summary of event tables for the primary cases. The summary of events includes the key system actuations that mark the accident progression. Timing items included within the summary table of events are:
- reactor trip,
- CMT actuation,
. accumulator draining starts,
(
- CMT transition from recirculation to draining,
- ADS 1 setpoint reached (although not actuated),
- ADS-4 opening, e core starts to uncover, e core fully recovers,
- CMT emptie*,
e accumulator empties,
- IRWST injection starts.
Tables of the summary of events are included within Section 6.0. CODE COMPARISON PLOTS The final method used to compare MAAP4 results to NOTRUMP results is to develop code comparison plots for key variables. Code comparison plots summarize how well the two codes predict a single item for multiple cases. MAAP4% results are presented on the x-axis, and NOTRUMP's results are on the y-axis. A perfect match between the codes' results yields data points in a straight, 45' line. Tae choice of the specific variables examined through code comparison plots is discussed in Section 9.1. 'O Analysis Method Rev. 4. April 1997 o%ewproj20603w.wpf:Ib-o41497 l
5-12 Other general assessments are made in Section 9.2 of MAAP4's capabilities to model the high int.ge.g phenomena in the PRA PIRTs, but the development of code comparison plots is focused on the issues that have the greatest potential to influence final conclusions drawn from MAAP4 analyses. O O Analysis Method g,,,g, Ap,,,,997 o%ewprojN60.1w wpf.ib 041497
,m . ,m (m) s (v) l I
i l V. V
- l. P>
- 5. ' Table 5.3-1 Parameters Compared for Primary Cases (Case 1 to 7)
! $5 Figure Number j 2g j $2 .-
- .a
- Cases Further Information About the l A Case 1 Cases 2,3,4 5,6,7 Parameter Related Item from PIRT Codes' Repnsentation of Parameter i :-
h I i 1 RCS pressure Break Pressure in the pressurizer j ADS I - 3 ADS-4 2 2 2 Integrated break water Break Integrated inventory loss at treak location 3 3 3 Integrated break vapor Break j 4 4 4 SG heat transfer Steam generator From RCS to both SGs 5 5 5 SG mass inventory Steam generator Mass for one SG 6 6 - CMT water injection flowrate CMT recirculation Flow rate from CMT to DVI line CMT draining 7 7 - Balance line water flowrate CMT recirculation Flow rate from cold leg to CMT CMT transition to draining 8 8 - Balance line vapor flowrate CMT transition to draining 9 9 - CMT water mass inventory CMT recirculation Illustrates the integrated impact of the , CMT draining injection and balance line flow rates 10 10 - CMT level CMT transition ta draining Mixture level CMT draining 5 h 1 m
- > '?
h g. Table 5.3-1 (cont.) Parameters Compared for Primary Cases (Case I to 7) E }dK $g Figure Number k Cases Further Information About the Case 1 Cases 2,3,4 5,6,7 syrameter Related Item from PIRT Codes' Representation of Parameter 5 II 11 - CMT temperature CMT recirculation De top and botto:n CMT nyJes from CMT draining NOTRUMP are compared to the single node from MAAP4. 6 Accumulator injection flow rate Accumulator Flow rate from accumulator to DVI line
-- - 7 Accumulator inventory Accumulator Water mass inventory in I accumulator 12 - -
Pressurizer level Pressurizer Pressurizer water level 13 12 8 Pressurizer mass inventory Pressurizer Water mass within the pressurizer; vapor mass is not included 14 - - ADS I - 3 integrated water ADS 1 - 3 Flow rate from top of pressurizer to IRWST. In MAAP4, these output parameters also include the pressurizer safety valve discharge. 15 - - ADS I - 3 integrated vapor ADS I - 3 Derefore, the pressurizer safety valve output from NOTRUMP was added to the ADS output for comparison. 16 13 9 ADS-4 integrated water ADS-4 Flow rate fro'm hot leg to containment 17 14 10 ADS-4 integrated vapor ADS-4 il' 1 5a O O O
~g a p Table 5.3-1 Parameters Compared for Primary Cases (Case I to 7) 15 (cont.)
UK $g Figure Number Further Information About the k Cases 2,3,4 Cases 5,6,7 Parameter Related Item from PIRT Codes' Representation of Parameter Case 1 j' 18 15 II Hot leg water level ADS-4 The MAAP4 hot leg water level is for a node that includes the hot side of the SG tubes. MAAP4 s calculation of the broken and unbroken loop level is performed separately, but the results are similar and only one is plotted. To match the definition of MAAP4h hot leg water level, the stacked mixture level from NOTRUMP is used, which extends to the bottom of the hot leg. The plot is shown with the y-axis sized to show to show the hot leg level relative to the bottom of the reactor vessel. The top of the hot leg is at an elevation of 26.2 feet, and the bottom is at an elevation of 23.6 feet. 19 16 12 Downcomer mass inventory Downcomer MAAP4% downcomer fluid node also includes the lower plenum and the cold legs. To provide a more consistent comparison basis, NOTRUMPs lower plenum and cold leg inventory is added to its downcomer inventory. m P t.n I N
. - . m 9 ?
l E h> Talise 5.3-1 Parameters Compared for Primary Cases (Case 1 to 7)
- g. (cont.)
K ma Figure Number o Further Informrtion About the k Cases 2,3,4 Cases 5,6,7 Parameter Related Item frem FIRT Codes' Representation of Parameter Case 1 5 20 17 13 Dawncomer level Downcomer Downcomer mixture level in NOTRUMP; downcomer collapsed level in MAAP4 21 18 14 RCS Void Fraction - The global RCS void fraction predicted by MAAP4 is provided, and is compared to the MAAP4 input VFSEP that controls the two-phase modelling in the RCS. This information helps to explain an irregularity in MAAP4 s downcomer inventory prediction. No information from NOTRUMP is included on this plot. 22a,22b 19a,19b 15a,15b Downcomer temperature Downcomer Output from the two codes is pre cnted in separate figures, with the downcomer water temperature
; compared to the saturation temperature. For NOTRUMP, the saturation temperature is estimated as the temperature of the pressurizer water. For MAAP4, the saturation temperature is a direct output of the g code.
E'
.O '53 O O O
~
(d3 G s l'~'s b o>
- 2. Table 5.3-1 Parameters Compared for Primary Cases (Case I to 7) 3 (cont.)
K { Figure Number k Cases 5,6,7 Further Information About the Case 1 Cases 2,3,4 Parameter Related Ittm from PIRT Codes' Representation of Parameter j 23 20 16 Downcemer pressure Downcomer MAAP4 does not capture an explicit IRWST downcomer pressure calculatien, and the pressure from the pressurizer is used to show the trend; the value for NOTRUMP is fmm the downcomer. In the figures, the maximum y-axis value is usually 50 psia to focus on the pressure around the time that IRWST injection starts. 24 21 17 IRWST Integrated Injection IRWST Integrated inventory from the IRWST to the RCS via time DVI line. 25 - -- IRWST level IRWST The IRWST water level ts referenced to the bottom of the reactor vessel. 26 - - IRWST temperature IRWST 7he top and bottom IRWST nodes from NOTRUMP are compared to the single node from MAAP4. 27 22 18 RCS mass inventory Core cooling Tb- RCS inventory includes water and vapor from the RCS, including the pressurizer. CMTs and accumulators are excluded. x
.o E.
C ?
$ G
> Y
$. Table 5.3.I Parameters Compared for Primary Cases (Case I to 7) U l (cont.)
lg.3: l 7g Figure Number i k Cases Further Information About the Case 1 Cases 2,3,4 5,6,7 Parameter Related Item from PIRT Codes' Representation of Parameter j 28 23 19 Vessel mass inventory Core cooling The vessel inventory is the water mass from the downcomer, lower plenum, core region, upper plenum and upper head. In MAAP4, there are only six water pools (refer to Figure 2-2), and it is not possible to isolate the vessel inventory when the system is full of water. Therefore,
- Sc initial MAAP4 " vessel" inventory is too high. He vessel inventory is meaningful when the primary side of the steam generators empty.
29 24 20 Core mixture level Core cooling He core mixture level is referenced to the bottom of the reactor vessel. In MAAP4, the output is truncated at the hot leg elevation, so that levels above the hot leg are not provided. l 5 f k 1 O O O . L _ _ . _- ----_- . _ _ _ . _ - - - _ - _ - - - _ _ _ _ - _ _ _ _ _ _ - _ _ - . _ _ _ _ - . - _ - - - - _ . - _ _
6-1 6 RESULTS OF PRIMARY CASES V The following sections discuss the results for the seven primary MAAP4/NOTRUMP benchmarking i cases. Each section contains information on the accident scenario, the plant response, and a comparison of the codes' predictions. Analysis results for each case are presented in plots of important parameters versus time, and in a sequence of events table. 6.1 0.5 Inch Break with Automatic ADS (Case 1) ACCIDENT SCENARIO . Case 1 is a 0.5" diameter hot leg break with the loss of PRHR and start-up feedwater. De break is assumed to occur at the bottom of the hot leg pipe. The main feedwater is also assumed to stop at the time of reactor trip, with no coast-dovm of the main feedwater pumps. The feedwater modelling is chosen to provide the earliest SG dry-out time. The SG safety valves open at pressures of 1100,1130 and 1155 psia with a flowrnte of 1.54 x 10 6lbm/hr per valve. On the primary side, the pressurizer safety valves open at a pressure of 2500 psia with a flowrate of 375,000 lbm/hr per valve. Only one CMT is assumed to function, and na accumulators are credited. Based on a low CMT level signal, I stage 3 ADS valve is credited to open, followed by 3 stage 4 ADS valves after the low-low CMT level is reached. _ One stage 2 or 3 ADS is needed to depressurize the RCS below approximately O 1200 psia, which is the stage 4 interlock pressure. Stage 3 ADS is modelled rather than stage 2 ADS because uage 3 has a longer time delay, and opens when there is less RCS inventory. One DVI line is assumed available for IRWST injection. De containment is conservatively assumed to remain at atmospheric pressure throughout the accident progression.
SUMMARY
OF PLANT RESPONSE Case 1 demonttrates the plant response to a loss-of-heat-sink event. Although the initiating event is a SLOCA, the break is too small to remove the decay heat produced in the core. As a result, the steam generators remove a significant fraction of the decay heat until the secondary side inventory is boiled away. When the steam generators can no longer provide a heat sink, the RCS pressure increases until the pressurizer safety valves open. The rate of inventoy loss through the pressurizer safety valves is greater than the rate of inventory loss from the break in the hot leg. He CMT, which was actuated early in the event and operated in a recirculation mode for thousands of seconds, starts to drain when vapor enters the CMT balance line. He decrease in CMT level provides the actuation signals for ADS. The RCS pressure is above 2500 psia when stage 3 ADS opens The opening of stage 3 ADS empties the pressurizer water inventory, reduces the RCS pressure, and increases the IRWST level and temperature slightly. Stage 3 ADS reduces the RCS pressure to below 500 psia by the time stage 4 fG ADS is actuated on a low-low CMT level signal. Within 300 seconds after stage 4 ADS is opened. Resuhs of Primary Caiu Rev. O. April 1997 c:hewproj2\3603w.l.wpf;1b-o41197 s
6-2 the RCS pressure is low enough to achieve IRWST gravity injection. However, the core uncovers prior to IRWST injection because there is no make-up from the accumulators as the systern depressurizes from a very high pressure. He duration of core uncovery is on the order of 10 minutes, at a time when the core decay heat is low. IRWST gravity injection is established to maintain successful core cooling for this accident scenario. DETAILED PLANT RESPONSE Re MAAP4 prediction of this accident progression shows the same trends as the NOTRUMP code predictions. De summary of events for this case is listed in Table 6.1-1 for both NOTRUMP and MAAP4. Transient plots of key parameters are provided in Figures 6.1-1 to 6.1-28. The following paragraphs provide more details of N plant response, highlighting similarities and differences in the codes' predictions. MAAP4 and NOTRUMP predict the same RCS pressure (Figure 6.1-1) trend. The RCS begins an immediate depressurization as a result of the break. The break flow (Figures 6.1-2 and 6.1-3) is relatively low due to the small size of the break. Although both codes predict similar break flow trends, MAAP4 predicts less water loss and more vapor loss than NOTRUMP due to the simplified homogenous fluid modelling in MAAP4 (see Sections 2.1.1 and 2.2.1). Reactor trip occurs on low pressurizer pressure approximately 30 minutes after the break occurs. Reactor trip causes a small inflection in the RCS pressure transient due to the increase in hot leg subcooling and the loss of enthalpy rise in the core. De system continues to depressurize until about 3600 seconds, when the RCS pressure is controlled by primary to secondary heat transfer as the principal means of removing decay heat. The two codes predict similar SG heat transfer rates (Figure 6.1-4). This results in a stable RCS pressure of about 1200 psia until the secondary side of the steam generators dry out around 8000 seconds (Figure 6.1-5). Although MAAP4 predicts a more gradual rate of mass loss when the SGs are almost empty, this does not have a large impact on the heat transfer to the SGs or the overall RG pressure response. He CMT actuation signal occurs on a %w-low pressurizer pressure signal shortly after reactor trip. His signal also results in Reactor Coolant Pump (RCP) trip, and the loss of the RCP head allows RCS pressures to readjust such that the head of water in the CMT is able to inject against the RCS pressure. Only one CMT is assumed to function in this accident scenario. Since the RCS is in a single phase liquid condition, water flows from the cold leg through the CMT balance line (Figure 6.1-7) in response to the flow from the CMT to the DVI line (Figure 6.1-6). His is referred to as the recitrulation period, which lasts approximately 10,000 seconds in both the MAAP4 and NOTRUMP prediction. The NOTRUMP model shows some large flow changes during this period which are not seen in the more empirical MAAP4 CMT model. The first sudden reduction in the NOTRUMP recirculation flow occurs at approximately 3600 seconds due to a small amount of flashing in the upper plenum that disrupts the pressure distribution, causing the flow to decrease. Once the flashing stops the pressures redistribute and the recirculation flow increases back to a value dictated by the Results of Primary Cases Rev. O, Aprd 1997 oAnewproj20603w.impf:lb-o41197
4 j 6-3 1 static head in the CMT. De upperpienum flashes again after 6100 seconds and the process repeats , . except this time the upper plenum remains two-phase and flow is reduced until draining starts with the arrival of steam at the top of the CMT at 9150 seconds.' The differences in MAAP4's and
- NOTRUMP's prediction of the CMT injection and balance line flowrates during the CMT recirculation phase does not significantly impact the CMT water inventory (Figure 6.1-9) nor the CMT level (Figure j- 6'.1-10) piedictions.
[ The end of CMT recirculation occurs when steam flows from the cold les up the balance line, breaking the siphon (Figure 6.1-8). De transition from CMT recirculation to CMT injection is more l- : distinct in MAAP4 than in NOTRUMP. The MAAP4 transition occurs as a result of the switch from the homogenous two-phase flow model to a separated model (see Section 2.1.1 and 2.2.1). De
. NOTRUMP transition is more gradual, as steam flow in the balance line slowly increases.
The final CMT output parameter to be discussed is the CMT temperature (Figure 6.1-11). Both
- MAAP4 and NOTRUMP predict an increase in the CMT temperature through the recirculation phase,
- and a decrease in the temperature to tne RCS cold leg temperature when the CMT empties. The MAAP4 single node temperature is approximately the average of the NOTRUMP top and bottom node temperatures.
l Le MAAP4 and NOTRUMP predictions of pressurizer level (Figure 6.1-12) and pressurizer inventory (Figure 6.1 13) show the same trends. Both codes show the p essurizer emptying within the first 2000 i secondso' f the event, and refilling when the secondary side of the SGs empty. Both codes also show that the pressurizer empties when stage 3 ADS is opened. Minor differences in the predictions are due to differences in the pressurizer geometry modelling, and the surge line resistance in MAAP4 leads to ! a faster refill after the loss of the secondary heat sink. f The pressurizer safety valve and ADS 3 water (Figure 6.1-14) and vapor (Figure 6.1-15) flowrates are combined because MAAP4 has a sing'le output parameter for the flowrate from these valves. De predictions of water and vapor from the pressurizer safety valves are similar for MAAP4 and NOTRUMP. - When ADS-3 opens, MAAP4 predicts a spike of water flow through the ADS-3 valve when the pressurizer is full, but predicts the remaining flow through stage 3 ADS as vapor. NOTRUMP entrains more liquid in the two-phase flow through stage .4, reducing the pressurizer j 7 inventory faster. E ) [y The inventory loss from the stage 4 ADS valves is similar in the two codes' predictions. Neither code predicts water loss through ADS-4 (Figure 6.1-16) until after IRWST injection has begun and the I l
' water inventory in the hot legs is restored (Figure 6.1-18). Vapor loss through ADS-4 (Figure 6.1-17) '
; is similar, with MAAP4 predicting the opening of the stage 4 ADS valves later than NOTRUMP, due
- to small differences in the timing of CMT transition from recirculation to draining.
.l 1
F MAAP4 and NOTRUMP's downcomer results have the largest deviations of the output parameters j
'; examined. De initial MAAP4 downcomer inventory (Figure 6.1-19) is 10,000 lbm lower than l l l R Resuhs of Primary Cases Rev. o. April 1997 o%ewproj20603w-l.wpf:lt441197
. I
+
e y e .y. , ysi ,, - u
6-4 NOTRUMP's due to a smaller volume and higher cold leg temperature in MAAP4. MAAP4 shows more of a decrease in downcomer inventory, due to the homogeneous two-phase model. When the MAAP4 RCS void fraction (Figure 6.1-21) reaches the user-input value of 0.6, the phases in the RCS separate, and the downcomer inventory suddenly increases at approximately 12,000 seconds. The d' uncomer level (Figure 6.1-20) closely corresponds to the mass relationship, as expected. The downcomer temperature prediction from MAAP4 and NOTRUMP are shown separately and are compared to the saturation temperature. In NOTRUMP (Figure 6.1-22a), the downcomer begins to flash shortly after opening of the stage 3 ADS. Flashing occurs between 12,800 seconds and 13,400 seconds, stage 3 ADS opened at 12,679 and the RCS pressure fell below the RCS saturation pressure at 12,800 seconds. The flashing / boiling is terminated shortly after initiation of IRWST injection at 13,300 seconds. The downcomer water temperature in MAAP4 (Figure 6.1-22b) shows the same trend as NOTRUMP after ADS actuation. IRWST gravity injection is the final phase of the accident progression that is examined for this analysis. IRWST gravity injection occurs when the downcomer pressure is within approximately I bar (15 psia) of the pressure at the top of the IRWST. The downcomer pressure (Figure 6.1-23) is reduced below 500 psia by stage 3 ADS, and stage 4 ADS reduces the pressure to allow IRWST injection. The MAAP4 pressure does not go as low as the NOTRUMP pressure, but both codes stabilize at pressures between 20 psia and 25 psia, allowing the IRWST to easily inject , (Figure 6.1-24). l The IRWST level (Figure 6.1-25) is similar for the two codes, with a slight increase when the stage 3 j ADS valve opens, and a decrease when IRWST injection starts. However, the IRWST contains more than ten times the RCS initial inventory, so that large mass changes must occur in the IRWST before 1 the level is affected. The IRWST temperature (Figure 6.1-26) prediction by MAAP4 and NOTRUMP l is also similar, showing an increase in temperature when the stage 3 ADS valves are opened.
'Ibe conclusions from the accident analysis are drawn from the RCS mass inventory (Figure 6.1-27),
the vessel mass inventory (Figure 6.1-28) and the core mixture level (Figure 6.1-29). 'Ihe overall trends for this parameters are consistent between MAAP4 and NOT' UMP, with NOTRUMP predicting more limiting minimum inventories and core mixture level. Mion 8.0 provides the basis for the clad temperature response remaining below 2200 F. The same conclusion of successful core cooling is drawn from either MAAP4 or NOTRUMP results. O Results of Primary Cases Rev. O. Apnl 1997 oAnewprop0603w-1.wpf Ib411197
6-5
/ Table 6.1 1 Summary of Events for Benchmarking Case 1 0.5" Hot 14g Break with 1 CMT
( (seconds) NOTRUMP MAAP4
- Break occurs 0 0 Reactor trips on low pressurizer pressure 1666 1983 CMT actuation signal on low pressurizer pressure 1785 2123 SCs Empty 8000 10,400 CMT draining begins (recirculation ends) 11,900 12,830 ADS-1 setpoint reached (no actuation) 12,489 13,342 ADS-3 opens 12,679 13,582 Top of core uncovers (Few seconds) 13,050 13,830 ADS-4 opens 13,088 13,914 Top of core uncovers 13,180 13,940 CMT empties 13,250 14,100 IRWST injection starts 13,300 14,229
( Top of core recovers 13,850 14,520 i O Results of Primary Cases Rev. O. Apnl 1997 ohwpmA%03w.l.wpf it@l197
6-6 O Figure 6.1-1 RCS Pressure for casel 0.5 Inch HL Break, 1 CMT, Auto ADS NOTRUMP MAAP4 3000 _ o ~
.__ 2500 - - , ~ e g ,n.'a ,
m _ v " 2000 - _ s. s
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Results of Primary Cases Rev. O. Apnl 1997 v:Wwproj20601w.l wpf:Ib 4til97
6-7: l
- n
' \j .
t 6 Figure 6.1-2 : 1
.8reak Integrated Water for case 1 '
05 Inch HL B r e.a k , 1.CMT, Auto ADS NOTRUMP i
---MAAP4
'400000 _
350000 -E. !
.m
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O
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__ 250000 -; - 200000 -2 m 150000 -; -~~ m : C 100000 -; 2 :
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6-8 O Figure 6.1-3 Break Integrated Vapor for case 1 0.5 inch HL Break, 1 CMT, Auto ADS NOTRUMP
---- MAAP4 120000 _
100000 -I E : 4 80000 -- g v W 60000 -{ m : m 40000 -- o - 2 - 20000 - _
~
0 , , , , , 0 2500 5000 7500 10000 12500 15000 Time (S) O Results of Primary Cases gev. o, Apni 1997 o wwproj2\3603w.t.wpf.It>(Mil 97
l t 6-9 l l i I
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f x : j Figure .6.1 -4. f SG Heat Transfer ' f o re case 1 0.5 1.nc'h HL-Break, - 1-CMT, Auto ADS , NOTRUMP
- ---MAAP4 i
-+- - - - D e c a y Heat 100000 ,
= :
- l ;
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I, 3- 80000 - - l m - I r ; i
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-\.p ' I Results of Primary Cases nev. o, April 1997 ;
chwproj20603w-l.wpf:lbal197 ! 4 1 e , , . , --,g -y v- ,y ., , .._ . , . - , , _ - , . . . . , -
6 ____ O Figure 6.1-5 SG Mass Inventory for casel 0.5 Inch HL Break, 1 CMT, Auto ADS NOTRUMP
---- MAAP4 120000 _
\
100000 -- 1 m - s E : ' s o 80000 -- s 1 1 ',s I v _ s 60000 -- ' s s en : ' u,. 40000 -- s o : ' s 2 - N 20000 -- s s s s
% _l f i ! Q %
0 ' 0 25'00 5000 75'00 10b00 12$00 1500 0 Time (s) O Results of Pnmary Cases Rev. O. Apnl 1997 ovewpioj20603w-l.wpf:lb-041197
. , .. . ~ . . _ . . _ _ _ -. ._
7 _ l 6-11-L
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i l
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Figure 6.1 ' CMT Water I n.j e c t i o n for casel : O.5 Inch HL Break, 1 CMT, Auto AD.S . NOTRUMP MAAP4
)
m 120 _ ) . N , E 100 -_ -
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1 1 1 J) .. O i Results of Primary Cases Rev. O, Apnl 1997
. ohwproj2\3603w.l.wpClb-041197
6-12 O Figure 6.1-7 B a.l a n c e Line Water Flowrote for case 1 0.5 Inch HL Break, 1 CMT, Auto ADS NOTRUMP
----MAAP4
_ 120 _ m . \ .. E 100 - - v _ 80 --
- : 9, t
I o 60 -- eI I x - ll S 40 -~ -
- l
% , % I) j,
~~~
~
' ' ' ' ' ~ ~ ' " ' ~
m 20 -- ' ll ti
- l e */vy ww 1 ll !
0 l l l l ' l i 0 2500 5000 7500 10000 12500 1500 0 l Time (s) O Results of Primary Cases Rev. 0. Apnl 1997 chwproj2\M03w l.wpf:lb-Gil197
6-13 j i y .- 1 t- . j l l Figure 6.1-8 Balance Line Vapor Flowrate for casel : 0.5 -Inch HL B r e'a k . '1 CMT-, Auto ADS l NOTRUMP ]
----MAAP4
. ;_ 50 i i
.x a
~
ll
.I g E -
? 0
~
^-- A N Y : ,.
- _ f.i , !
es _ { p
~
..:J . l g o -3 0 -- I i
. o: _
o I I _ l t -100 -- I m _ , m . o _ l 3 -150 l
'l l l l !
0 2500 5000 7500 10000 12500 1500 0 ! Iime (S) g ..: l d l Results of Primary Cases nev.o,Apni1997 ohwprol2\3603w l.wp(.lb441197
i 6-14 0 Figure 6.1-9 CMT Water Inventory f o r. casel 0.5 inch HL Break, 1 CMT, Auto ADS NOTRUMP MAAP4 140000 _ 120000 -- E 100000 -: _ _ , _ o 80000 -- s ' 1 g
- i m 60000 -- \
w _ \ C ' 40000 - s 2 : g 20000 - i
- \
0
~
l l l l l 0 2500 5000 7500 10000 1'500 1500 0 Time (s) O Results of Primary Cases Rev. O. Apnl 1997 c:\nempro320603w l.w;4:Ibellt97
1 6-15 Figure 6.1-10 CMT Level for casel 0 . ' 5' i nch HL Break, 1 CMT, A u-t o ADS . NOTRUMP
---MAAP4 i
25 -
~
m20- ------------------------ --
\
~ : \
\
~
' (O9
- 15 - -
\
\
- : \
r \ e 10 -~
\
\
w - I i
- r. 5- t
* \
t 0 0 25'00 50'00 75'00 10000 12$00 1500 0 < Iime (S) l i y g, . $. j - Results of Primary Casc5 Rev. O, April 1997 c:Wewproj2\3603w-l.wpf:lb-041197 e- - r wr- s - ~ e
6-16 _. O Figure 6.1-11 CMT Temperature for casel 0.5 Inch HL Break, 1 CMT, Auto ADS NOTRUMP Top Node
----MAAP4 Single Node
-} - - - - NOTRUMP Bottom Node 700 1
v 600 -: , , . -~ ' t
,.'~ \ j 500 -; - t as
[ 400 -i
.-+-
, .' # \
w - , < ~ : - , I a 300 -: /
,+, . _ . s i u : f . \_
o 200 -i /,'
" : } l' E 100 __
o : 0 l l l ! l 0 2500 5000 7500 10000 12500 1500 0 Ilme (s) O Results of Primary Cases Rev. O. Apnl Ibh thwproj20603w.1,wpf;lt>041197
- 1
'6-17 .-
i n U l i
- a i
/
l Figure 6.1. . t
. Pressurizer LeveI for. casel 0.5 inch HL Break 1 CMT, Auto ADS-NOTRUMP j 1
----MAAP4 40 ,
1
, J
- i
.a ~ ;
.a 30 - -
i I s .b(^) v : ,
' t
')'
I 20 -- /
/
\
a 1 _c e
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\ / 1
*-.10-- s / t o -
s 1- - . s ,' -
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k
~
0 t .I L' I t t 0 25'00 50'00 75'00 10b00 12500 1500 0 Time (s)
!i i
f ~. a f. l Results o' f Primary Cases Rev,0, Apnl 1997 oMewprep\3603w 13pf;1bal197 i
6-18 i I Figure 6.1-13 l Pressurizer inventory for casel 0.5 Inch HL Break, 1 CMT, Auto ADS
- NOTRUMP MAAP4 70000 i 60000 -: .l-
^
- i *. ,
E 50000 -5 - i _c :
- / i v 40000 - ,
- e i 1
- / i !
30000 -- f g i m : / ., Cn / a 20000 -: /
/
I
\ l 2 / \s l 10000 -2 - s i
~
s '
- i 0 '-l l ~ l l l l 0 2500 5000 7500 10000 12500 1500 0 i Time (s) l l
l i Results of Primary Cases Rev. O. Apnl 1997 e: ohwproj20603w 1.wpf.lb-681197 l
A J-4,JA J' 4 .ab.. .a+4A . A -L &4. .s s 3 aees s -4 e - - 6-19 i l l h i Figure ~ 6.1 -14 ' P S .V and ADS-3 1.ntegrated Water for c a s e-1. ) 0.:5 ' l-n c h HL Break, 1 CMT, Auto ADS
-NOTRUMP
---- MAAP4 175000 _
15 0 0 0 0~ - - f m _ E 125000 -- L _a : ! I
.1 0 0 0 0 0 -
v : cn 75000 -! ,/--- cn : t 2 O 50000 - j _ l I 25000 -- ,8
- I {
0- l l l l l 0 2500 5000 7500 10000 12500 1500 0 ! Time (s) i j l
-l l
b
\ !
Results of Primary Cases .. Rev. 0, Apnl 1997 ohwproj2\3603w-l.wp01b-Ni!97 I
+-D w y 7- r- -
6 O f Figure 6.1-15 PSV and ADS-3 integrated Vapor for case 1 0.5 Inch HL Break, 1 CMT, Auto ADS NOTRULP-
---- MAAP4 175000 ._
150000 -i - E 125000 -- l
-_o
- 100000 -3 g
- I I
m 75000 -2 I m : ' C 50000 -: I E :
- l 25000 -i I
~
)/
0 l l l l ' - t 0 2500 5000 7500 10000 12500 1500 0 Time (S) O Results of Pnmary Cases Rev. 0. Apnl 1997 c:Wwpro;N603w l.wpf.lb-041197
L; .i:t -, g ,. , i
,)
p 4 t Figure 6.1-16 lA D S 4' .l n t e g r a t'e d Water- for ease 1- l; 0 '. 5 Inch HL 8reak, 1 'CMT. Aut.o ADS NOTRUMP I _._.MAAP4 100000 -
~
80000 - ; m. E -
- o D -
\ -
60000 - - v _
~
m 40000 - - m - o
'2 20000 - - o I
l
~
A 0 l l l l l 0 2500 5000 7500 10000 12500 1500 0 Time (s) b(D i
. Results of Pnmary Cases Rev, O. April 1997 chwproi2\3603w.l.wpf:lWI197
6e-- O Figure 6.1-17 ADS-4 Integroted Vapor for casel 0.5 Inch HL Break, 1 CMT, Auto ADS
-- NOTRUMP
----MAAP4 125000 _
~
m 100000 -- E : e : 75000 -- m 50000 - , m : /
/
o _ 2 25000 -{ [
~
~
l
' I '
0 l l l l 0 2500 5000 7500 10000 12500 15000 IIme (S) l l I O Results of Primary Cases Rev. O, Apnl 1997 o:\newproj20603w-1.wpf:Ib441197
6-23
,l .
. /
Figure 6.1-18 Hot Leg Water Level for case 1 _ 0.5 Inch HL Break, 1 .CMT, Auto ADS . NOTRUMP Unbroken Loop
---- MAAP4 Both Loops
-t- - - - N O T R U M P Broken Loop 30- 3.,
L _ l' I
^28-- l
~ i i Q
~
I i JN "26- -
! ' , ' ill i ,
- j. 1
.l il
.c j i ;
.m 24 - g-a>
r 22 -- < 20 l l l l l 0 2500 5000 7500 10000 12500 1500 0 Time (S) a
'A *
[ Results of Primary Cases . Rev, O. Apnl 1997 chmiroj20603w l.wpf;1b441197 L
24 O Figure 6.1-19 Downcomer and Lower Plenum Inventory for case 1 0.5 inch HL Break. 1 CMT. Auto ADS NOTRUMP
---- MAAP4 80000 v
s 60000 - ---- ---- E -
~~ '
-=
.o _
~
~
_ 's s
, i
/
40000 -- '
- v" - I t I s / l (n \ 1 m
_ , } sl o - i 22 20000 -- \ 0 l l l l l 0 2500 5000 7500 10000 12500 1500 0 IIme (S) e Results of Primary Cases Rev. O. Apn! 1997 c:Wwproj20603w.l.wpf;1b 041197 m
6-25 O-U Figure 6.1-20
. Downcomer Level = for case 1 0.5 Inch HL Break, 1 CMT, Auto-ADS NOTRUMP
---MAAP4 35 _
0- j___________ __
~ ~~
25 -; -----.,
< - : ii 20 - h i g
- : 1, , i ,
r 15- t,
/
b 1, k#
- si e 10 - -
c : 5-3
~
0 'l l l l l 0 2500 5000 7500 10000 12500 1500 0 Time (S) f
'T Q)
Results of Primary Cases nev.o,Apn11997 c.W20603w.l.wpf.lb-041197
.O
____________._____.__m _
6-26 O Figure 6.1-21 RCS Void Fraction for case 1 0.5 inch HL Break, 1 CMT, Auto ADS MAAP4 Input of VFSEP MAAP4 Void Iraction 1 C ..
/* N g
~ .8-- , y 0 - I
~
I L ,g ,- w - I
- I y -
._ 4-- ' I
~
O _ I l 2-- --- I en .
~~
C) - t I '" " Q t t 0 0 25'00 50'00 75'00 10$00 12$00 1500 0 i T.ime (s) O Results of Pnmary Cases nev. o. Apni 1997 c:'Jwwproi20603*-1 wpf.1b-041197
6 27 - I Figure 6.1-22a ,
'NOTRUMP Downcomer Temperature for casel 0.5 Inch-HL Break, 1 CMT, Auto ADS NOTRUMP Downcomer Water Temperature
-t- - - - R C S Saturation Temperature
_ 700 ._ j w - v 600 -y_li_ _ _ _ _ _ _ _ 4 _ _f -- o 500.-2
." 400 -E '
o . o 300 -:: -. i o.200 -:: e o -
~ =' '
100 l l l l l 1500 0 0 2500 5000 7500 10000 12500 i Ti'me (s)
,V Figure 6.1-22b-MAAP4.Downcomer Temperature for casel 0.5 Inch HL Break, 1 CMT, Auto ADS MAAP4 Downcomer Water Temperature j 4- - - - R C S Saturation Temperature
_ 700 . , , b 600 -h' _
'4+_, ,
500 -2 ; o : o 400.-E __
% 300 -E l
- o. : !
E S 200 -E i
~ ~' ' ' '
.100 l l l l . l 0 2500 5000 7500 10000 12500 1500 0 l Time (s) l Results of Primary Cases Rev. O. Apr01997 owproj2\3603w.I.mpr:IbNil97 r-
6-23 O Figure 6.1-23 Detoiled Downcomer Pressure for casel 0.5 Inch HL Break, 1 CMT, Auto ADS NOTRUMP Downcomer
----MAAP4 RCS 500 i n : \
o : i w 400 -- I Q- [ l 300 -{ i i h o : i 200 -- \ D ~
\
! M $ \ w - e L 100 - - ( \ , a_ -
~
~
! O l l l l 13000 13500 14000 14500 1500 0 Time (S) l O Results of Pnmary Cases Rev. O, Apnl 1997 oWwpoj2\3603w l.wptib4 Mil 97
='
6 29 ~ z.[ { 4 Figure 6.1-24 lRWST Integrated I n j e c t'i o n - for case 1' O. 5 l-n c h HL B r e.a k , 1 C M T., Auto ~ ADS NOTRUMP MAAP4 150000 _ 120000 - 7. E o i
~
f)-- ( _ 90000 - m ' m 60000 -- ~ I o l 2 : 1 30000 - - I-
- I
~
_ /
~
0' l l l l. l 0 2500 5000 7500 10000 12500 1500 0 Time (s) l' Results of Primary Cases Rev. O. Apnl 1997 owwproj2\3603w-l.wpf:lb-041197
I 6-30 O l Figure 6.1-25 IRWST Level for casel 0.5 Inch HL Break, 1 CMT, Auto ADS NOTRUMP MAAP4 60 _ 50 -i
~
40 -2
^
v
$< 1 l
30 -- ! c; : ) [ 20 - I a _ 10 -: -
~
0 l l l l l 0 2500 5000 7500 10000 12500 1500 0 IIme (s) O Results of Primary Cases e, c o, Apnl 1997 oWwproj20603w.l.wpf:Ib-041197
m, tib jt, . 3 6-31 !
. 1 '.
b
. v:
O ! 3: t Figure 6.1-26 . IRWST Tempera'ture 'f o r casel 0.5 inch HL Break, 1 CMT, Auto ADS ' NOTRUMP Top' Node
---- MAAP4 Single Node
. . _ -f- -+- N O T R U M P Botiom Node i
--s 200 _
i
- u. -
v . 150 - - fr - V * ~
; ; ._. 2+ -
j 100 -2 _. l o _ t u _
.g _
a 50 - - l l E - 1 o - H ~, , , . , , , , , ., i 0 0 25'00 50'00 75'00 10b00 12$00 1500 0 IIme (S) i 1
.g-. . %Y. l Rev. O. Apnl 1997 Resuks of Primary Cases o:Wj20603w.l.wpf;1t>.041197
( . j
6-32 i O Figure 6.1-27 RCS Mass inventory for casel 0.5 Inch HL Break, 1 CMT, Auto ADS l NOTRUMP MAAP4 350000
!\ ~
300000 -~ m : _ i E 250000 -- _a 200000 -3 g g v _ cn 150000 - I
\
en 25 C 100000 -3 -
\ /
/
- g/
50000 -- 0 l l l l l 0 2500 5000 7500 10000 12500 1500 0 Time (s) e Results of Primary Cases Rev. O. Apnl 1997 o dmewptt42\3603w l.wpf;1 boll 197
6 :
)
r~i
.()-
I i Figure 6.1-28 1-n v e n t o r.y for -case 1
~
.Vesse1 Mass 1
0.5 inch HL . Break, 1 CMT, Auto ADS i NOTRUMP ;
---MAAP4 .i i
100000 t I I , if I 80000 - I I I m
- I l l E -
i s _a .. v 1 _._ 60000 - - t ; ^
.v i f
\g
~
- 4 g
M 40000 - - l m - C - 2 20000 - f
~, , , . .,, . , ,, . , ,
0 0 25'00 50'00 75'00 10600 12500 1500 0 Time (s)
'4
- (
\~J Results of Primary Cases . Rev. O, Apnl 1997 chwproj20603w l.wpf:Ib 04tl97
. =
6-34 :. O 9 Figure 6.1-29 Core Mixture LeveI for casel
- 0.5 Inch HL Break, 1 CMT, Auto ADS I NOTRUMP l ----MAAP4 l -t- - - - T o p of Core m 30 _
~ _
A C 26-- N 22 -- ~ i I i o \ I g )g. -- l -+-+-+-+--l l l - + - + -+ - l +-+- -- , -
" : gi
~
o 14-- il u _ m - l
~x 10- _
~
- E ' ' ' ' ' '
6 0 25'00 50'00 75'00 10000 12500 1500 0 (s) IIme i l l O Results of Pnmary Cases Itev. O. Apnl 1997 cWwproj2\3603* 1.wpf:1boti197
6-35 6.2 2.0 Inch Break with Automatic ADS p,)
'd' ACCIDENT SCENARIO Case 2 is a 2.0" diameter hot leg break with the loss of both accumulators and 1 CMT. No PRHR nor start.up feedwater is credited. Based on a low-low CMT level signal,3 stage 4 ADS lines are assumed to open, with all other ADS failing. One DVI line is assumed available for IRWST injection.
The containment is conservatively assumed to remain at atmospheric pressure throughout the accident progression.
SUMMARY
OF PLANT RESPONSE Case 2 demonstrates one of the most limiting multiple-failure scenarios that is credited as successful core cooling in the PRA. The 2.0" break is the small end of the Intermediate LOCA (NLOCA) initiating event in the PRA. It is the smallest break size that does not require the actuation of a stage 2 or 3 ADS valve prior to stage 4 actuation. During the first 30 minutes of the 2.0" break accident, the steam generators play a role in removing a high percentage of the decay heat. A quasi-steady state condition is reached, where the RCS pressure is at the same pressure as the SG safety valve setpoint. The steam generators lose approximately one-third of their inventory, but do not come close to boiling away the secondary side inventory. The thermal-hydraulic coupling between the primary and secondary side continues until ADS is actuated. (v) The CMT, which is actuated early in the event and operates in a recirculation mode for approximately one thousand seconds, starts to drain when vapor enters the CMT balance line. The decrease in CMT level provides the actuation signals for ADS. Within 10 minutes after stage 4 ADS is opened, the RCS pressure is low enough to achieve IRWST gravity injection. However, the core tincovers prior to IRWST injection because there was no make-up from the accumulators as the system depressurizes from a high pressure. The core uncovery is a result of no accumulators when ADS is opened. The duration of core uncovery is approximately 1000 seconds. Peak clad temperature results for this case ; l are provided in Section 8.0, and are shown to irmain well belc w 2200 F. Sensitivity cases in Section 7.3 show that the core uncovery cannot be avoided for this 2" break by opening more ADS. l i i DETAILED PLANT RESPONSE l MAAP4 and NOTRUMP prediction of this transient show similar trends. The summary of important events are listed in Table 6.2-1 for both MAAP4 and NOTRUMP. Transient plots of key parameters l i are provided in Figures 6.2-1 to 6.2-24. The following paragraphs provide a more detailed discussion of the plant response as calculated by MAAP4 and NOTRUMP, with emphasis on similarities and differences between the predictions of the two codes. a
%l l
Results of Primary Cases Rev. O. April 1997 o%ewpetj2\3603w 2 wpf:Ib-o41197
6-36 MAAP4 and NOTRUMP predict the same RCS pressure (Figure 6.2-1) trend. The RCS begins an immediate depressurization as a result of the break. Within the first 100 seconds in NOTRUMP and the first 140 seconds in MAAP4, the reactor trips on a low pressurizer pressure signal and a CMT actuation signal is generated. Water is lost from the break (Figure 6.2-2) at a relatively slow rate. MAAP4 predicts a slour rate of water loss than NOTRUMP. The differences in the rate of inventory loss for this' break size are the largest seen in any of the benchmarking cases. The difference in break flowrate also contributes to the largest differences seen between MAAP4 and NOTRUMP in the accident progression timing for the benchmarking cases. The vaper lost from the break (Figure 6.2-3) is overpredicted by MAAP4 due to the simplified homogenous fluid modelling (see Sections 2.1.1 and 2.2.1). Most of the decay heat generated in the core is removed through the break. However, the steam generators also transfer some of the heat from the primary side (Figure 6.2-4). The heat transfer rate is gradually reduced over a 2000 second period of time. The instantaneous heat transfer rate predicted by MAAP4 is oscillatory, and may vary from the NOTRUMP calculated heat transfer rate at any given point in time. However, the net result is similar, with the same amount of water in the secondary side of the steam generators (Figure 6.2-5) boiling off through the steam generator safety valves. CMT water injection (Figure 6.2-6) starts within the first two to three minutes of the break initiation. At first, there is a period of CMT recirculation, where water enters the CMT balance line (Figure 6.2-7) from the cold leg. The water entering the CMT is approximately equal to the water , leaving the CMT, so there is little net effect on the CMT inventory. When vapor enters the balance line (Figure 6.2-8), the CMT transitions from a recirculation phase to a draining phase. The CMT water inventory (Figure 6.2-9) decreases, as does the CMT level (Figure 6.2-10). The net effect of the MAAP4 CMT calculations is similar to the NOTRUMP calculation. However, there is a delay of I approximately 600 seconds in the MAAP4 timing of the accident progression. The difference in the I timing is due to the simplified homogeneous two-phase flow modelling in MAAP4, as explained in Section 2.2.1. l 1 Both MAAP4 and NOTRUMP predict an increase in the CMT temperature (Figure 6.2-11) through the CMT recirculation phase, and a decrease in the temperature to the RCS cold leg temperature when the CMT empties. The single node in the MAAP4 model is horter than the bottom node in NOTRUMP, but is much cooler than the top node in NOTRUMP. The single node model simplification and the CMT water temperature differences do not significantly impact the accident progression. The pressurizer (Figure 6.2-12) empties early in the event, and does not play a role in the remainder of the accident progression. Both codes predict that the pressurizer empties within the first 100 seconds of the event. De timing difference of the CMT transition from recirculation to draining impacts the timing of ADS actuation. He 600 second difference in the timing of the event remains relatively constant through the remainder of the event. He ADS-4 valves are automatically actuated approximately 1250 seconds Results of Primary Cases Rev. O, April 1997 oWwpro;IG603w.2.wpf:lb-Nil 97
- .. . . - ~ -- . . -. .-.- -.---- . . ,.
6-37 i l after CMT draining starts. The integrated vapor loss through ADS-4 (Figure 6.2-14) is very similar 1 between NOTRUMP and MAAP4, with the exception of the timing shift.
/
. Although both codes predict the hot leg water level (Figure 6.215) at the bottom of the hot leg when the' ADS valves are opened, NOTRUMP predicts water entrainment through stage 4 ADS ;
. (Figure 6.2-i3). MAAP4 does not predict any water relief through stage 4 ADS. The difference is '
due to the water inventory that is predicted to be in the system at the time ADS valves are opened. Although MAAP4 predicted a slower rate of inventory loss from the break, the timing difference of
-600 seconds results in a greater net loss at the time of ADS actuation. In MAAP4, the vessel mixture level is several feet below the hot leg elevation when ADS valves open. In NOTRUMP, the vessel mixture level is high enough that liquid is entrained into the ADS-4 blowdown. However, the water loss is not significant, and this does not create any further differences in the MAAP4 and NOTRUMP resuks.
De MAAP4 and NOTRUMP downcomer inventory and level results (Figures 6.2-16 and 6.2-17) show differences very early in the event while MAAP4 is using the homogeneous two-phase model. When the MAAP4 RCS void fraction (Figure 6.218) reaches the user-input VFSEP value of 0.6, the ' phases in the RCS separate, and the downcomer inventory suddenly increases. De MAAP4 prediction of mass distribution in the RCS is more accurate after VFSEP is reached. The MAAP4 downcomer level shows the same trend as the downcomer mass, because the downcomer is a collapsed water pool in MAAP4. In NOTRUMP, the downcomer level is a mixture level, and shows a deviation from the downcomer inventory trend when ADS valves are opened.. Flashing is predicted by both codes in the downcomer when ADS valves are opened, as evidenced by the downcomer water temperature reaching j saturated conditions (Figures 6.219a and 6.2-19b). ! I 1 IRWST gravity injection is the f' al m phase of the accident progression that is examined for this i analysis. ' IRWST gravity injection occurs when the downcomer pressure is within approximately I bar (15 psia) of the pressure at the top of the IRWST De downcomer pressure (Figure 6.2-20) is quickly reduced with the opening of stage 4 ADS valves. Both codes predict the start of IRWST injection
- (Figure 6.2-21) approximately 600 seconds after ADS actuation.
1 The overall progression of the accident is demonstrated through the RCS mass inventory (Figure 6.2-22) and the vessel mass inventory (Figure 6.2-23) transients. Both MAAP4 and
'NOTRUMP predict similar trends. The conclusions of the analysis are based on the vessel mixture I level (Figure 6.2-24). Both codes predict a minimum vessel mixture level approximately 4.8 feet below the top of the core. De duration of core uncovery is predicted by MAAP4 to be close to 1200 seconds, while NOTRUMP predicts a little under 900 seconds.
I Section 8.0 shows that the peak clad temperature remains well below 2200*F during the period of core I uncovery. Despite the timing differences, the overall trends for this accident scenario are consistent between MAAP4 and NOTRUMP. The same conclusion of successful core cooling can be drawn j
- from either MAAP4 or NOTRUMP results. j j
Results of Primary Cases Rev. O. April 1997 ! ohrwprojN603w,2.wpf.lb 041197 i l
l
. 6-38 Table 6.21 Summary of Events for Benchinarking Case 2 - 2.0" Hot Leg Break with 1 CMT (seconds)
NOTRUMP MAAP4 Break occurs 0 0 Reactor trips on low pressurizer pressure 83 116 CMT actuation signal on low pressurizer pressure 99 138 CMT draining begins (recirculation ends) 1100 1785
^
ADS-1 setpoint reached (no actuation) 1615 2302 ADS-4 opens 2370 3031 CMT empties 2700 3308 Top of core uncovers 2800 3337 IRWST injection starts 3000 3617 Top of core recovers 3675 4531 O l I l l 9 Results of Primary Cases Rev. O. April 1997 ob rop T 0603w-2 wpf.lbottl97
l- 6-39 i i
'f 4 U. -
Figure . 6.2-1 RCS Pressure for- case 2 i 2.0 . Inch H L- Breok, 1 CMT, Auto ADS. 1 NOTRUMP MAAP4 . I 2500 ~ m o 2000 - , cn :
/ ,) v
- c. :\
_.i I V 1500 - - t o h1 - - - - - - - - - ~ _ _ _ _ _ _
' 1000 -- I
- s -
i Co I ; en - g e 500 -- , u _ g
~
Q- \ i i t i 1 1 1 1 I I f f 1 '5 a ' ' ' ' ' ' ' 0 0 10'00 20'00 30'00 40'00 500 0 Time (S) n V. Results of Primary Cases Rev. O. April 1997 owwproj20603w 2.wpf.1b-041197 I.' ,
6 40 0 Figure 6.2-2 Break Integrated Water for case 2 2.0 Inch HL Break, 1 CMT, Auto ADS NOTRUMP MAAP4 400000 _ 350000 -E - 5 , g 300000 -- ,- _a 250000 -E
/ &
w j v : / 200000 -E ' m 150000 -2 O 100000 - - s : 50000 -2,' _ 0 ''''''''''''''''''' 0 10'00 20'00 30'00 40'00 5000 IimG (S) Results of Primary Ca5C5 Rev. O. Apnl 1997 e ohwpmjA%0)w-2.wpf:Ib-041197
- l' 6-41 i.
l O 1 ; Figure 6.2-3 i Break Integrated Vapor for case 2 ! 2 . 0' inch HL Break, 1 CMT, Auto ADS NOTRUMP !
----MAAP4 120000 _
~
100000 -- ! m -
-E :
/7 c 80000 - - V v ~ 60000 - - _ 4 m _ m -40000 -- ! o : i E 20000 - -
/
~
' -1 " - ' - ' ' ' ' ' " ' '
0 ' e i 0 1000 2000 3000 40'00 5000 Time (s) , O ;
- Results of Primary Cases Rev. O, Apd 1997 ohnproj2\3603w 2.wpf.It@l197
6 42 l O I Figure 6.2-4 SG Heat Transfer for case 2 2.0 Inch HL Break, 1 CMT, Auto ADS NOTRUMP
----MAAP4
-t- - - - D e c a y Heat
_ 100000 - i
. g D 80000 --: I
; g m -
g
; 60000 -[
t
. 40000 -
- t i
s .9 {Ll i i
~
j
~
~~~ ~ ~ * ~ ^
$WS f '
o -
;I
~
z -20000 ' ' ' ' ' ' ' ' ' '
''''l l 0 1000 2000 3000 4000 5000 Time (s)
O Results of IMmary Cases Rev. O, Apnl 1997 owwproj2\3603w 2.wpf:lt> 081197
6-43: f i 1
- Q,h - l
. -i Figure 6.2-5
- SG Mass Inventory for case 2 : 2.0. Inch HL Break, 1 C M T ,. Auto ADS l [ -NOTRUMP !
----MAAP4 ,
i
~120000 _
i 100000 - - ', j n - - - , E :- * o 80000 - - s, , v _ ~ 60000 - - , m _ , m. 40000 -- o- : , , s - 20000 - _ ' ~ 0 0 10'00 20'00 30'00 40'00 500 0 Time (s) F ?\ Results of Pnmary Cases Rev, O. April 1997 ' owwyroj2\Moh 2.wpf.Ib441197 ,
w e Figure 6.2-6 CMT Water Injection for case 2 2.0 Inch HL Break, 1 CMT, Auto ADS NOTRUMP
----MAAP4 m 120 _ = _
N _ E 100 -- l's 80 -- - I
's s L s a> l s . _- s o 6 0 --- - ( s i__ _
e' ' 3 D - o 40 --l - l __ I L - 7 l .. 20 - - np I w - i o I' l l
- s 0
~ I" ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' '
l l 0 1000 2000 3000 4000 5000 Ilme (S) O Results of Primary Cases Rev. O. Apnl 1997 o wwproj20603w 2 wpf:Ibe41197
1 6 i r
- O ;
t y'
; Figure 6.2-7 Balonce Line W a.t e r Flowrote for case 2 .
2.0 inch HL Break, 1 CMT, Auto ADS j NOTRUMP
----MAAP4 m 120 , ,
m - N [ ! ! E 100.-- , l
- i
~ n - 8 - g il IIi o 60 - - If x - e,' p
^
40- - (%[< ~ g a - t 9 o , i ^ m 20- - gI g M il I
" ~ I' ' ' ' ' 8' ' 'L ' ' ' ' ' ' ' ' ' ' '
0 1 l 'l l 1000 2000 3000 4000 0 500 0 Time (S) 4 g \' V Results of Primary Cases Rev. O, Apnl 1997 - chewproj29603w 2.wptlMM1197
6-46 0 Figure 6.2-8 Balance Line Vapor Flowrote for case 2 2.0 Inch HL Break, 1 CMT, Auto ADS NOTRUMP
----MAAP4 m 50 m -
s - E -
.o _
r - - - ' - -- - - M p '~ ^U 'i p" ' 0 ~ _ I g e - I I I W l o -5 0 - - i I x .
- \
D - \
\
f [ -10 0 - - l i j m - l m _ l o -
" -150 ' ' ' ' ' ' ' ' ' ' ' ' ' '
l l 'l O 1000 2000 3000 4000 5000 Time (s) I 1 i l Results of Pnmary Cases Rev. O. Apnl 1997 9 cNewprojh3603w 2.wpf;lb441197
.. 6-47 l c-Figure 6.2-9: :
i CMTlWoter. l n v e n t o r y' f:o'r- case 2 ;
- 2.0 Inch HL-Break, 1 CMT, Auto ADS i L.-
NOTRUMP f 1 ----
"MAAP4 ,
4
..140000 i
120000 -- - m -
's \
l t, E 100000 -.:
-Q
, . N. ! v 80000 - -
-\ !
- . N
_ s 60000 -- m ~ N ~ \
\
- 0 40000 -- N i 2 : A s
- 20000 -- s s
l
~
s j' . 0 - '''' i i i
' ' ' ' i I
t- 0 1000 2000 3000 4000 . 500 0 1 ! Time (s) i i Results of Primary Cases :- _ Rev. O, Apnl 1997
,.o. %ewproj20603w 2.wpf:llWil97 - ;
1 l
6-48 ._ 1 O Figure 6.2-10 CMT Level for case 2 2.0 Inch HL Break, 1 CMT, Auto ADS NOTRUMP MAAP4 25 _
~
m 20 - ------ s ---
\
~ _ \
% \ ;
\ l
" 15 - _ \
- N
.C - \
en 10 -- x :
\ 4 l
s c.) s , I 5- - s _ s _ \
~ t I t I i t i t I t t t I t t i I t i 1 1 0 t, ,i , ,
0 1000 2000 3000 4000 500 0 i Iime (S) , 1 l l l l Results of Pnmary Cases Rev. 0. Apnl 1997 ohwproj2\3603w 2 wpf:Ib-Ni l97 I
,i p
I..f,' ~' I o i C u e l 1 1 Figure 6.2-11 j
.CMT-Temperature for case 2- !
2.:0 . inch.HL Break. 1 CMT, Auto ADS 1 NOTRUMP Top Node 1
----MAAP4 Single Node 4.--- NOTRUMP Bottom Node .I i
^
.700
- u. :
v 600 -- _ O 500 -2 I l O e E l 400 -: l m :. ____ i o.300 -:- , ,,_,_, g . - A u e 200 -2 s
' --- l ct ' /
E 100 __
---+,
e : H : ' ' ' ' ' ' ' ' ' i iiiiiie i i , , 0 0 10'00 20'00 30'00 40'00 5000 Time ('s) O v Results of Primary Cases nev.o Apni1997 owproj2\3603w-2.wpf:lbe41197 ~
6 50 0 Figure 6.2-12
'P r e s s u r i z e r Inventory for case 2 2.0 Inch HL Break. 1 CMT, Auto ADS NOTRUMP MAAP4 30000 _
25000 -: ^ : E - v o 20000 - { h l 15000 -- m : m 10000 o -
- E : i 5000 ; g
- 1 0 ' I" ' ' '
l-
""l 'l' ' '
'l ' ' ' '
O 1000 2000 3000 4000 5000 Time (S) O Results of Primary Cases Rev. O. Apn! 1997 chwpmj20603w-2 wptIb-041197
6-51 d Figure 6.2-13 ! ADS-4 Integrated Water. for case 2 2.0 Inch HL Break, 1 CMT, Auto ADS i NOTRUMP i MAAP4 100000 m 80000 - 1 D E : qQ. _
'V -
v 60000 - - m 40000 - m f . o 2 20000 - f
~
0 0 10'00 20'00 30'00 40'00 500 0 Time (s) W Results of Primary Cases Rev. O. Apnl 1997
, owwproj2\3603w-2 wpf;lb441197
6-52 ~ O Figure 6.2-14 ADS-4 Integrated Vapor for case 2 2.0 Inch HL Break, 1 CMT, Auto ADS NOTRUMP MAAP4 125000 _ m 100000 - _ E - v o 75000 --
~
i m 50000 - f m _ f O / CE 25000 - - I
~_ l
- 1
~
0 l l l' 'l 0 1000 2000 3000 4000 5000 ' Iime (S) ! l l I
-l O
Results of Pnmary Cases Rev. O. Apnl 1997 cAnewproj2\360)w 2 wpf;Ib-041197
6-53 (} Figure 6,2-15 Ho;t Leg Water L e v.e l for case 2 ' 2 . ' 0. Inch HL Break, 1 CMT, Auto ADS NOTRUMP Unbroken ~ Loop
----MAAP4-Both Loops
-t- - - - N O T R U M P Broken Loop 30 I.
): If il p/I
^28- -
i b "26-- ( s f
- 5. 24 ~
t:n
~
~
W\' -+- P c.. 4:::-4-.-. 3.f- - -
.>i9 i c) r 22 --
20 l 'l l 0 1000 2000 3000 4000 500 0 Time (S) O Rev. O, Apnl 1997 Results of Pnmary Cases o:\newprol20603w-2.wpf:1t4MII97
s-sa O Figure 6.2-16 Downcomer and Lower Plenum Inventory for cose2 2.0 inch HL Break. 1 CMT, Auto ADS NOTRUMP
----MAAP4 80000 1
^ 60000 - s 1 N s s i s
. O 40000 --
s I s i 1 - m s s _
, s ,
m - s o - s
- E 20000 --
0 .
l l 'l '
l 0 1000 2000 3000 4000 5000 Iime (S) e Results of Primary Cases Rev. O, Apnl 1997 c:Vrwproj20603w.2.wpf:1 bell 197
6 . k m U . a Figure 6.2-17 ! Downcomer Level for. case 2-2.0 Inch HL Break, 1 CMT. Auto ADS , NOTRUMP MAAP4 r 35 _ 30 -2
^
~
"'s 25 -: '~. rs O
- v
~
's N
; s
\
~2 s l .... -g c 15 -:
en
's s I i
N s,-~- e 10- - I : 5-2 0
~' ' ' ' ' ' ' ' '
0 1000 2000 3000 4000 500 0 Time (S)
.n-U Results of Pnmary Cases Rev. O. Apnl 1997 owwproj2\3603w-2.wpf.lb-041197
i 6-56 l l 9 Figure 6.2-18 RCS Void Fraction for case 2 2.0 Inch HL Break, 1 CMT, Auto ADS MAAP4 Input of VFSEP MAAP4 Void fraction 1 c- _ O -
~~--- ~
_, .8-- f
----s u ,
~
.6- -
u _
/
/
D -
/
.-- 4- - o /
~
> _ / 2-- ' D - i o -
~
0 l ! 'l l 0 1000 2000 3000 4000 500 0 Time (S) l 9; Results of Primary Cases Rev. O, Apnl 1997 l owwproJ20603w 2.wptib 041197 l
6-57
/~' Figure 6.2-19a
()s NOTRUMP Downcomer Temperature for case 2 2.0 Inch HL Break, 1 CMT, Auto ADS NoTRUMP Downcomer Water Temperature 4- - - - R C S Saturation Temperature w 700 _
- u. e
- 600 -:\
3~- I e 500 -E i
." 400 -E i O :
' 300 -:
~
a e 200 _
--+____+
e :
~ -' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' '
100 l 'l l O 1000 2000 3000 4000 .5000 Time (s) O Figure 6.2-19b MAAP4 Downcomer Temperature for case 2 2.0 inch HL Break, 1 CMT. Auto ADS MAAP4 Downcomer Water Temperature
-f- - - - R C S Soturation Temperature
_ 700 _
- u. c v 600 -:J4 - ' *
- 1 500 - i
-O 400 -:
300 -E o. E 200 - g 5
- - --t- -.-t- -
- 100 ' ' ' '
l l O 1000 2000 30'00 40'00 500 0 Time (s)
'C,-
Results of Primary Cases Rev. O. Apnl 1997 owwproj20603w-2.wpf.lbe41197 s--
6-58 O Figure 6.2-20 Detoiled Downcomer Pressure for case 2 2.0 Inch HL Break, 1 CMT, Auto ADS NOTRUMP Downcomer
----MAAP4 RCS 50 m i \
O 45 -i t w - o_ 40 -2 { 35 -- 5 si G , t O l u 30 -- 5 U I e y Wisr%e t m 25 -3 s._ 20 -: c_ : 15 - ' ' ' ' ' ' ' ' ' ' ' '''''' l l 0 1000 2000 3000 4000 500 0 Time (S) O Results of Pnmary Cases Rev. O, April 1997 otwwproj20603w-2.wpf.lb441197
6-59' ' l t
-(') - l v - -
i Figure 6.2-21 l lRWST Integrated injection for case 2 2.0 Inch HL Break, 1 CMT, Auto ADS ' NOTRUWP l
----MAAP4 150000'
- )
m. 120000 - -
.0 =E : >
- 90000 --
* : /
60000 - -
/
i M / O -
/
- . =E /
30000 - - 0 , 0 1000 2000 3000 4000 500 0 Time (s)
. srh Results of Primary Cases . Rev. O. Apnl 1997 oNwwprojA%03w 2.w1 4:1b-041197 1
r 6-60 i O1 Figure 6.2-22 RCS Mass inventory for case 2 2.0 Inch HL Break, 1 CMT, Auto ADS NOTRUMP MAAP4 350000 300000 -: . s 4 E 250000 -: _ s s g 200000 --!
's s
- s m 150000 -: _
s m : 's
's OE 0 100000 -_: __
50000 - s______ 0
~' ';iii,,,,,,,,,,,,,,,, ,
0 1000 2000 30'00 40'00 5000 Time (s) O Resnits of Primary Cases Rev. O. Apnl 1997 0 %)2\3603w-2.wpf.lb-041197
6-61 a
, s
?
Figure 6.2-23 Vessel Moss Invent.ory for' case 2 2.0 Inch HL Break. 1 CMT.. Auto ADS NOTRUMP l MAAP4 l 100000 ,s , si s s ;
\ !
4 m 80000 - - s- , 1 E - 1
/
i
-O .a
__ 60000 -
\
\
/
/
v s _- s _
~
s/ , U2 40000 -- l co o -
=E -
20000 -- _
~
0 l l l l O 1000 2000 3000 4000 500 0 - Time (s) i 1 Results of Primary Cases Rev. O. Apnl 1997 o:%ewproj20603w-2.wpf ll>o41197 P i,- ,- ..w , , , -
6-62. O Figure 6.2-24 Core Mixture Level for case 2 2.0 Inch HL Break, 1 CMT, Auto ADS NOTRUMP
----MAAP4
-f- - - - T o p of Core m 30 _
~ . C 26-1 ! 11 - 22 -- ~
,g /
e \ ! e 18 --.._._. ; . _ . _ . _ 4 . _ . _ . _ . ; . _ . _ . ; . _ . _ _ _4 . _ . N ; . _ . . _ . _ _4_. _ . z . _4_ _ . _ s a -
- s -
e 14 -- m - jo__ x _ " 6 i i i i 0 1000 2000 3000 4000 5000 Time (s) G; Results of Pnmary Cases Rev. O. Apnl 1997 l ohwprojh3603w-2.wpf it@l197 I i l
i 6 _63 6.3 5.0 Inch Break with Automatic ADS ACCIDENT SCENARIO Case 3 is a 5.0" diameter hot leg break with the loss of both accumulators and 1 CMT. No PRHR nor start-up feedwater is credited. Based on a low-low CMT level signal,3 stage 4 ADS valves are assumed to open, with all other ADS failing. One DVI line is assumed available for IRWST injection. The containment is conservatively assumed to remain at atmospheric pressure throughout the accident progression. His case has exactly the same equipmem failures as case 2; the only difference is the size of the break.
SUMMARY
OF PLANT RESPONSE Case 3 demonstrates that a 5.0* break results in a less limiting accident progression than a smaller break. It is used to demonstrate the ability of MAAP4 to correctly determine the trend of the plant response as the break size changes. The steam generators remove heat in this case for only the first few hundred seconds. The CMT, which operates in a recirculation mode at first, starts to drain at approximately 300 seconds. This is when approximately three-quarters of the RCS inventory has been lost out the break. The decrease in CMT level provides the actuation signals for ADS. Approximately 10 minutes after stage 4 ADS is opened, the RCS pressure is low enough to achieve IRWST gravity injection. However, the core uncovers prior to IRWST injection because no accumulators are credited. Accumulator (s) would provide make-up inventory as the system depressurizes from a high pressure during the ADS blowdown. Furthermore, an accumulator would keep the downcomer subcooled. Sensitivity cases in Section 7.3 show that the core uncovery can be avoided for this 5" break when an accumulator is available. The duration of core uncovery for case 3, without accumulators, is approximately 400 seconds. DETAILED PLANT RESPONSE MAAP4 and NOTRUMP prediction of this transient show similar trends. He summary of important events are listed in Table 6.3-1 for both MAAP4 and NOTRUMP. Transient plots of key parameters are provided in Figures 6.31 to 6.3-24. The following paragraphs provide a more detailed discussion of the plant response as calculated by MAAP4 and NOTRUMP, with emphasis on similarities and differences between the predictions of the two codes. MAAP4 and NOTRUMP predict the same RCS pressure (Figure 6.3-1) trend. The RCS begins an immediate depressurization as a result of the break. Within the first 25 seconds, the reactor trips on a low pressurizer pressure signal, and a CMT actuation signal is generated. The break flow (Figures 6.3-2 and 6.3-3) is fairly rapid. When the break location uncovers, both codes predict that h,m the water loss from the break stops, while the vapor loss increases. The two codes show the same Results of Primary Cases Rev. O, Apnl 1997 c:bewprojAD3*-3.wpf:lb-041197
6-64 trend of inventory loss from the break, with MAAP4 predicting slightly higher water loss from the break while the CMT is injecting. De break is large enough that steam generator heat transfer does not play a significant role in the accident progression. There is heat transfer from the primary side to the steam generators (Figure 6.34) during the first 300 seconds of the accident. There is only a slight loss of steam generator secondary side inventory (Figure 6.3-5) through the steam generator safety valves. CMT water injection (Figure 6.3-6) starts within 45 seconds of the break initiation. At first, there is a period of CMT recirculation, where water enters the CMT balance line (Figure 6.3-7) from the cold leg. The water entering the CMT is approximately equal to the water leaving the CMT, so theie is little net effect on the CMT inventory. When vapor enters the balance line (Figure 6.3-8), the CMT transitions from a recirculation phase to a draining phase. The CMT water inventory (Figure 6.3-9) decreases, as does the CMT level (Figure 6.3-10). The temperature (Figure 6.3-11) of the single node in the MAAP4 CMT model never increases more than approximately 40'F during this transient. This is because the recirculation period is short, and there is no appreciable vapor flow through the balance line. NOTRUMP shows that the top CMT node (out of four nodes) increases over 400 F by the time the CMT starts to drain. The bottom NOTRUMP node reinains closer to the MAAP4 single node prediction. Dere is not a large impact on the accident progression because of the difference in the CMT modelling and temperature prediction. , However, the downcomer in MAAP4 stays cooler than in NOTRUMP, due partially to the CMT simplification. The pressurizer (Figure 6.3-12) empties early in the event, and does not play a role in the remainder of l the accident progression. Both codes predict that the pressurizer empties within the first 100 seconds of the event. ADS-4 valves are automatically actuated approximately 1500 seconds after the event initiation. Neither code predicts any water relief (Figure 6.3-13) through the valves because the hot legs (Figure 6.3-15) are empty. The trend of the ADS-4 vapor relief (Figure 6.3-14) is the same for both codes, although MAAP4 underpredicts the integrated loss. The MAAP4 and NOTRUMP downcomer inventory and level results (Figures 6.3-16 and 6.3-17) show differences very early in the event while MAAP4 is using the homogeneous two-phase model. When the MAAP4 RCS void fraction (Figure 6.3-18) reaches the user-input VFSEP value of 0.6, the phases in the RCS separate, and the downcomer inventory suddenly increases. De MAAP4 prediction of mass distribution in the RCS is more accurate after VFSEP is reached. ne MAAP4 downcomer level shows the same trend as the downcomer mass, because the downcomer is a collapsed water pool in MAAP4. In NOTRUMP, the downcomer level is a mixture level, and shows a deviation from the downcomer inventory trend when ADS valves are opened. Flashing / boiling is predicted by NOTRUMP in the downcomer when ADS vr.lves are opened, as evidenced by the downcomer water Results of Primary Cases Rev. O. April 1997 o \newpeqh)603w.3mp0Ibel1197
6 65 ~ !
; temperature reaching saturated conditions (Figure 6.3-19a). MAAP4 predicts that the downcomer ,
- reaches saturated conditions after NOTRUMP (Figure 6.3-196).
{
~ IRWST gravity injection is the final phase of the accident progression that is examined for this analysis. IRWST gravity injection occurs when the downcomer pressure is within approximately I bar j
. (15 psia) of the pressure at the top of the IRWST. De downcomer pressure (Figure 6.3-20) is quickly -
reduced with the opening of stage 4 ADS valves. NOTRUMP predicts the start of IRWST injection . l (Figure 6.3-21) approximately 675 seconds after ADS actuation. MAAP4 predicts a slightly longer , delay of 840 seconds. ! De overall progression of the accident is demonstrated through the RCS mass inventory , (Figure 6.3-22) and the vessel mass inventory (Figure 6.3-23) transients. Both MAAP4 and ; NOTRUMP predict similar trends of decreasing inventory. However while the CMT is draining, j
' MAAP4 predicts a levelling off of the system inventory while NOTRUMP predicts upward trends in j
- the system inventory. His is due to the void fraction modelling within MAAP4. As identified in ,
Section 2.1.2, the MAAP4 core void fraction model calculates an average void fraction for a given l steaming rate in the core. NOTRUMP calculates no void fraction within the core if thermal hydraulic conditions permit. Dus as the CMT water enters the core region, NOTRUMP calculates no void , l fraction in the bottom nodes of the core. His results in NOTRUMP being able to store more inventory within the vessel. MAAP4, on the other hand, predicts more water loss from the break. The conclusions of the analysis are based on the vessel mixture level (Figure 6.3-24). Both codes ! predict a minimum vessel mixture level approximately 2 feet below the top of the core. The duration ; of core uncovery is also predicted by both codes to bc a little longer than 400 seconds. l Section 8.0 shows that the temperatures in the core are not challenging during core uncovery, and this l case results in successful core cooling. The overall trends for this accident scenario are consistent j between MAAP4 and NOTRUMP. He same conclusion of successful core cooling can be drawn from -) either MAAP4 or NOTRUMP results. l l 1
- Results of Primary Cases - Rev. O, April 1997 j chempropWiO3w.3.wpf.lb-041197 !
1
t 6-66 Table 6.3-1 Summary of Events for Benchmarking Case 3 - 5.0" Hot Leg Break with 1 CMT (seconds) NOTRUMP MAAP4 Break occurs 0 0 Reactor trips on low pressurizer pressure 12 18 CMT actuation signal on low pressurizer pressure 15 23 CMT draining begins (recirculation ends) 310 280 ADS-1 setpoint reached (no actuation) 763 783 ADS-4 opens 1477 1515 CMT empties 1780 1818 Top of core uncovers 2200 2217 IRWST injection starts 2220 2356 Top cf core recovers 2625 2626 O l 9.l Results of Primary Cases Rev. O, Apr01997 j o:inewproj2\3603w-3.wpf:lt441197
67' : 1 1 1 O 1-i 1
-y d
"h Figure 6.3-1 1
- RCS P r e s s u r-e- for . case 3 1
.-5..0 Inch HL Break, t-CMT, Auto-ADS ;
NOTRUMP' l
- - - - . M A A P 4.
i
\
2500 - 1 m - a - 1 2000 - - us. -
, c.- :
( v .
+
-1500 -.' r
.L.
e: , n-
1000 -.
3 s i D \ m - e 500 - --
'''''('-
u ____ 1 : ' ' ' ' ' '
-0 '
O 500 10'00 15'00 20'00 25'00 3000 Iime ( S_)
.l
-l
-i i
F , 1 i
- . J
\g 1 Results of Primary Cases . Rev. O. Apnl 1997 i
~L 0:W3w-3.wp0It>-041197 p G- q - w n -4 r q n- w ~ we -w -
r- e an,- m ---,-vr w ww -w - --=w-----v - or - -
I 6 68 O Figure 6.3-2 Break Integrated Water for case 3 5.0 Inch HL Break, 1 CMT, Auto ADS NOTRUMP MAAP4 400000 _ 350000 -[ _ ^E300000 -: - --- ------- - - 250000 -: - -~ v : / 200000 -: /
/
m 150000 -!'f
- f 100000 - /
50000 - 0 'l 'l 'l 0 500 1000 1500 2000 2500 300 0 Time (S) O Results of Primary Cases Rev. 0. Apnl 1997 owwproj70603w 3 wpf:lb-041197
.I
6-69 (a~s ., e Figure 6.3-3 ; Break Integrated Vapor for c:ase3
.5 . 0-I n'c h -H L .B r e a k ,- 1 CMT, Auto ADS NOTRUMP i MAAP4 120000
~
100000 - - i E :- o-. 80000 - -
~ \ ~
v _ - 60000 -- - m : m 40000 -- e o _
/
E - 20000 - _
~
0 ''l O 500 1000 1500 20'00 25'00 3000 - Time (S) Resuks of Primary Cases Rev. 0. Apnl 1997 . ohwpeq2\)603w-)*p(;l(>.04l197
6-70 0 Figure 6.3-4 SG Heat Transfer for case 3 5.0 Inch HL Break, 1 CMT, Auto ADS NOTRUMP MAAP4
-+- - - - D e c o y Heat m 100000 g th -
% t
~
5 m 80000 - \ n a 60000 -3 \.
- 1 's h
e '~.4,_ m 40000 - _-4 . 4
= :t , ._-+---._._._+_._._._._4._.__
E 20000 - i l o _ si
- _ i
,1 0-- _
,,,,,,,,y n ,,,,,,,,.. y _ _
. ~
z -20000 ''
'l 'l l 'l 'l 0 500 1000 1500 2000 2500 3000 Time (s)
O Results of Primary Cases Rev. o, Apl 199Y o:Wewpro3N603w-3mpf:lb-041197
6-71
]
Figure 6.3-5 SG Mass i n v e.n-t o r y for case 3-5.0 1-n c h H L. B r e a k..- 1 CMT, A u-t o ADS
'NOTRUMP MAAP4 120000
,, 100000-- k ________..._ E : o 80000 -_- L v : 60000 - - m :
- m 40000 - -
o _ OE - 20000 - - 0 'l' 'l 'l 0 500 1000 1500 2000 2500 3000 Time (S) i l 2 i
+
Results.of Primary Cases . Rev. O, Apnl 199'
. ohnp:oj20601w 3.wpCibe41197
6-72 O Figure 6.3-6 CMT Water injection for case 3 5.0 Inch HL Break, 1 CMT, Auto ADS NOTRUMP
----MAAP4 m 120 _
m N _ E 100 - _ I s _ ~ s
- I ~
s g 80 -- ,
's s a> _
- _ /
s o 60 -- / 's a: ~ j., - , g, J t o 40 - -l [' I 1
~
1 L- j g m 20 -1 - i m i
. I 0 '''''''''l l 0 500 1000 1500 2000 2500 3000 Time (S)
O Results of himary Cases Rev. O, Apnl 1997 owwprojN603w.3 wpf:lbeti t97
6-73 .
-1 I
1 f}x u 1 1 1 . Figure 6.3-7 Balance Line Water Flowrote for case 3 5.0 Inch HL B r e a k', 1- CMT, Auto ADS
- NOTRUMP 'l
- -- - - M A AP 4 m 120 -
. m - N _ E - 10 0 - _ l A 80 - - i l-LU m : dl o 60 -- I ce I 40 --I hI
,. :et o i
- I, I i
' -i I; i )
m 20 --i l i W m -j i ! o I 0 T'I i i 0 500 1000 1500 2000 2500 3000 Ilme S I f*g' V
' Results of Primary Cases Rev. O. Apnl 1997
- ohwproi2\3603w 3.wpf:lb 041197 i
l
i 6-74 l O i 1 Figure 6.3-8 Balance Line Vapor Flowrote for case 3 5.0 Inch HL Break, 1 CMT, Auto ADS NOTRUMP
----MAAP4
_ 50 m N - E - _a - 0--
- - - v -'-- T '11gr - -
I e o -5 0 -- e _
~
o -
~~
-100 --
m _ m _ o _ s -150 ' ' ' ' ' ' '
l '''l 'l 'l 0 500 1000 1500 2000 2500 3000 Time (s)
O Results of Pnmary Cases Rev. 0, April 1997 ohwproj20603w-3.wpf:Ibel1197
h 6-75' Q U i l Figure '6.3-9 , CMT Water- l-n v e n t o r y for case 3 , 5.0- - 1.n c h .H L Break, 1 CMT, Auto ADS ' NOTRUMP
----MAAP4' -!
'40000 1
120000 - - ' m s s E 100000 -:
/_)
'V
.c -
80000 -
.m 60000 --
m : o 40000 - 2 : 20000 - 0 'l 'l 'l l 0 500 1000 1500 2000 2500 300 0 Time (s) g Results of Pr4 mary Cases Rev. O, April 1997
'chwproj2\360)w-3.wpf.lbolil97 -
- .5 .
)
6-76 1 O Figure 6.3-10 CMT Level for case 3 5.0 Inch HL Break, 1 CMT, Auto ADS NOTRUMP MAAP4 25 _ m 20 -- s_ - : s
\
15 - _
\
s - : s s .c- _ cn 10 -- .__ : s s cu -
's C 5- -
's s
~ ' '
'l ' ' ' '
0 l l l 'l 0 500 1000 1500 2000 2500 3000 Time (S) 9 Results of Prunary Cases Rev. 0, Apnl 1997 o wwproj2\3603w.3 wpElb-Odi197
x 6-77 - t (n x_) i Figure' 6.3-11 CMT Temperature for case 3 5.0 . Inch HL-Break, 1 CMT, Auto ADS- : NOTRUMP Top Node- ; MAAP4.SingIe Node :
- -t - - - N O T R U M P Botiom Node !
700
^- : ,
w : : v 600 -: i i p) 500~-E l j
'c400 -2: l i
a 300 -E l u : , j i . e 200 -2 4-... +---+---+ - a ,--- ----------------- 2-+',. E e-100 _ : 0 0 500 10'00 15'00 20'00 25'00 300 0 Time (s) i I
~ - -
\,j i
' Results of Primary Cases Rev. o. Apro 1997 onmewpros2060.)w.3.wpf:!b.041197 l
6-78 9 Figure 6.3-12 Pressurizer inventory for case 3 5.0 inch HL Break, 1 CMT, Auto ADS NOTRUMP MAAP4 30000 _ 25000 -2 ^ : E - 4 20000 - g 15000 - m : m 10000 - : o - 5000 -. _ 0 ''!'l '''''''''''''' 0 500 1000 1500 2000 2500 3000 I i rn e (s) O Results of Primary Cases Rev. O. Apnl 1997 owprojN603w.3,wpf lbo41197 i
' 6-79 !
p V ' i J 1
-l 1
1 1 Figure 6.3-13 ADS-4 Integrated Water for cas.e3 5.0 Inch HL Break, 1 CMT., Auto ADS N0; RUMP ; MAAP4 ; 100000 -
~
m 80000 -- -
.E ! .(\ D - l v
60000 -- _ l m 40000 - f m - o l
- E 20000 - - >
l 0 0 5$0 10'00 15'00 20'00 25'00 3000 Time (S) i i Results of Primary Cases nev.o. Apn11997 oWwproj2\3603w 3.wpf:lbe41197__ g % _ _ _ _ _ _ _ . -- ^ ' ' '
6-80 Figure 6.3-14 ADS-4 Integrated Vapor for case 3 5.0 Inch HL Brerk, ' CMT, Auto ADS NOTRUMP MAAP4 125000 _
~
. -.,, 1 0 0 0 0 0 -- E : _a 75000 - g m 50000 - _ w _ , o - 2 25000 -- ,
- i
~
0 'l 'l ' ' ' ' ' ' ' ' l 0 .500 1000 1500 2000 2500 3000 Time (s) O Results of Primary Cases Rey,0, Apnl 1997 owwproj70603w-3 wpf.1b-041197 j l I
,~ .. _
o 6-81 ; y- . t ... t y 4 4 Figure 6.3 H o.t- Leg Wo.ter Level for case 3- 3 5.0 Inch HL Break, 1 CMT, A'u t o ADS 1 NOTRUMP. Unbroken' Loop.
--- MAAP4 Both Loops
- -t- - - N 0 T R U M P B r o k e n Loop i 30 -
I,! . l
- i 1
I ^ 2 8 .- -
.(-
"26- - I i
4
~
s c 24 - - i. _ _ _ _ _ _ _ _ _ _ _ _ ,-_ _ _ _ _ _ _ _ _ _ ______
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- c) l I- 22 - -
20 ' ' ' ' '''''''''''''''''''' 0 500 1000 1500 2000 2500 300 0 Iime (S) 1-
-\d.
Results of Primary Cases . Rev. O, April 1997 o:W*proj20603w-3.wpf:lb-041197 p .
6-82 -- O Figure 6.3-16 Downcomer and Lower Plenum inventory for case 3 5.0 inch HL Break, 1 CMT. Auto ADS NOTRUMP
---- MAAP4 80000 ^ 60000 ,
E
.c
_\ _s _\ g 40000 - '\ lo
~~ g , -
co si . _
~
cn \1 r a _ E 20000-- ) _ 0 l
l 'l '''l 0 500 1000 1500 2000 2500 300 0 IIm8 (S)
O Eults of Pnmary Cases Rev. O, Apnl 1997 oAnewproj20603w-3.wpf:lbo41197
b i. i 6 1 C ,
]
s 4 l Figure 6.3-17 l fo.r case 3 ' ~ Downcomer L'evel : 5.0 1.nch HL Break, 1 CMT, A u t o- ADS NO, TRUMP ]
----MAAp4
' 3 5 -- -
q i 30 -b - i V 25 -b i
' (J~ ~ : .
- L 1
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- , J 0
- Wewpoj20603w 3 w#1beel197
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6-84 O! i Figure 6.3-18 RCS Void Fraction for case 3 5.0 Inch HL Break, 1 CMT, Auto ADS MAAP& input of VFSEP MAAP4 Void Fraction 1 c _ O - 8- -- O
- l u_
O
.6
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I 7-(n - I C) -I cr -l 0 ''i; iii,,,,,,,,,,,,,, 0 500 1000 15'00 20'00 25'00 3000 Time (S) e Results of Primary Cases Rev. O. Apnl 1997 ohwptt:320603w.3.wpf:Ib-041]v7
m - , -,s - w a n.n as_ a +-o . . . - 6 85 Figure 6.3-19a , NOTRUMP Downcomer Temperature,for case 3 5.0 Inch HL Break, 1 CMT, Auto ADS
^NoTRuMP-Downcomer Water Temperature
-t- - - - R C S Saturation Temperature
_ 700 _ . . l u_ . p
- 600 -i e 500 --:
~%
s,
-4' -+---+,
l' 400 -i o : s 300 -:: s
=
- .W i W~
=
200 -5 - I 100 l '''l l '!' 0 500 1000 1500 2000 2500 3000 Time (s) pU Figure 6.3-19b l i MAAP4 Downcomer Temperature for case 3 ) 5.0 inch HL Break. 1 CMT, Auto ADS ; MAAP4 Downcomer Water Temperature !
-t- - - - R C S Saturation Temperature l
_ 700 _ u.
- 600 -i_ : s
- 500 -i 4.
f 400 - h ~ ~ ~
- +t 300 -! _
s E 200 - !
" ~' ' '
100 'l ' ' ' ' ''''''''''''''' 0 500 10'00 15'00 20'00 25'00 30'00 Time (s) Resuhs of Pnmary Cases Rev. O, Apnl 1997 owwproj20603w.3.wpf:ltWil97
6-86 O Figure 6.3-20 Detoiled Downcomer Pressure for case 3 5.0 Inch HL Break, 1 CMT, Auto ADS NOTRUMP Downcomer
----MAAP4 RCS 50 -
.i
- m. : i o 45-:
cn i a_ 4 0 -3 3 \ 35 -: _
's c) : ,_ 30 -: ,^ % ,
3
% i 'M 25 - l' ' N cn : N'.u c2 :
u 20 -- o_ : 15 'l 'l ''''l 'l I 0 500 1000 1500 2000 2500 300 0 l Time (s) ! I 1
~
O Resulis of Primary Cases nev, o, Apni sc97 s:Wwproj2\3603w 3 wpf.lb Ost 197
7 w s 1 i
\
e e L - Figure 6.3-21 .
. .,1 IRWST I n t-e g r a t e.d Injection- for. case 3
, 5. 0 Inch HL'Breok, 1 CMT, Auto ADS- .. ~ NOTRUMP
----MAAP4 ,
.150000 _
4 ; n 120000 -! - 1
;r E -
.o .
~
.'k.)_/ _ 90000 -- w - m 60000 -: m : o - 2 -
/
30000 - -
- /
- ,/
0 0 5d0 10'00 15'00 20'00 25'00 3000
- Time (s) t
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Results of Primary Cases Kev. o, Apre 1997 .t oWwyso320603w 3.wyf:lb 041197 ;
.'t
-..,,a . . . . , ,,- - ~ n,
6 88 O Figure 6.3-22 RCS Mass Inventory for case 3 5.0 inch HL Break, 1 CMT, Auto ADS NOTRUMP MAAP4 350000 300000 - m v E 250000 -: 200000 -: E, s e s
\
m 150000 -i 1 m : s $ ' 0 0 0'0 0 ~ ~~__=_______ 50000 -- 0 'l' l l 'l 0 500 1000 1500 2000 2500 300 0 Time (s) ' l l 9 Results of Pnmary Cases Rev. O. April 1997 l 0 4aewpro3 2 V603w-3 wpf:lb&l197
...a...
6-89 ) n L) - l Figure. 6.3-23 ) Vessel Mass Inventory. for ca.se3 , 5.0 Inch HL Break, 1 CMT,, Auto ADS NOTRUMP l MAAP4 ! 1
]
100000 1 4 80000 -- 1
,C }
o
~~
------s___
's
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's ,-
\
m' 40000 - - l m - _ a -
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5 90 0 Figure 6.3-24 Core Mixture Level for case 3 5.0 Inch HL Break, 1 CMT, Auto ADS NOTRUMP
----MAAP4
+ - - - Top of Core m 30 _
~ _
C 26 -k l 5-- - -- _- k , ,- g
's s 22 -- ,
' w i e l c$ 18 - -~-'!'~~~~ !'--~~~+-~~~~+~~ '~~
~ ~ -~ I I a :
m 14 -- s_ -
~
x 10 -- , l
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. .I I 1 1
0 500 1000 1500 2000 2500 3000 IIme (S) O' Re$ults of Pnmary CnSCS Rev. O And 1997 owwproj20603w~3 wpf:lb-041197
6-91 6.4 8.75 Inch Break with Automatic ADS ACCIDENT SCENARIO Case 4 is an 8.75" diameter hot leg break with the loss of both accumulators and 1 CMT. No PRHR nor start-up feedwater is credited. Based on a low-low CMT level signal,3 stage 4 ADS lines are assumed to open, with all other ADS failing. One DVI line is assumed available for IRWST injection. The containment is conservatively assumed to remain at atmospheric pressure throughout the accident progression. This case has exactly the same equipment failures as cases 2 and 3; the only difference is the size of the break.
SUMMARY
OF PLANT RESPONSE ? Case 4 demonstrates the plant response of the largest break size that is analyzed with MAAP4. This break size is at the upper end of the break size spectrum for the PRA MLOCA event tree. This means that this break size readily depressurizes below the RNS shut-off head (-175 psia) without ADS actuation. Ilowever, it is not large enough to depressurize to allow IRWST injection without ADS actuation. The inventory loss from the break D at a rapid rate, causing the vessel mixture level to fall below the hot legs within the first 200 seconds. The RCS depressurization is likewise rapid, but with both Q accumulators assumed to fail, there is no immediate inventory make-up available. One CMT is assumed available, and it provides make-up injection within the first few hundred seconds, but soon enough to prevent the top of the core from uncovering. The ADS actuation signals are generated from the low and low-low CMT level signals plus time delays. With the faiLire of stage 1,2 and 3 ADS and the time delays in the ADS actuation logic, no ADS valves open until after 1300 seconds. This is very close to the same time frame that operator action is credited in the manual actuation cases when the CMT actuation signal fails. The opening of ADS-4 valves causes the RCS pressure to decrease, allowing IRWST injection to start within 5 minutes. Both MAAP4 and NOTRUMP show that IRWST injection increases the RCS and vessel mass. The core mixture level is maintained at or above the hot leg elevation after ADS actuation. Core cooling is not challenged. DETAfLED PLANT RESPONSE MAAP4 and NOTRUMP prediction of this transient show similar trends. 'Ihe summary of important events are listed in Table 6.4-1 for both MAAP4 and NOTRUMP. Transient plots of key parameters are provided in Figures 6.4-1 to 6.4-24. The following paragraphs provide a more detailed discussion of the plant response as calculated by MAAP4 and NOTRUMP with emphasis on similarities and differences between the predictions of the two codes. 7 t U Results of Primary Cases Rev. O. April 1997 o%ewpmj20603w-4.wpf:ll>o41397
6 92 'Ihe opening of a 8.75 diameter break in the RCS hot leg results in a rapid loss of RCS inventoy with a corresponding decrease in RCS pressure (Figure 6.4-1). As long as the RCS in:entory remlins subcooled with respect to the current pressure, both MAAP4 and NOTRUMP calcuiate a!most exact water inventory losses (Figure 6.4-2). Between 10 and 20 secends the RCS pressure decreases below the saturation pressure and flashing occurs. MAAP4, using a hornagenous model, calculates both steam and liquid out the break, while NOTRUMP with mu!dple nodes and flow paths having drift flux models can allow for slip between the phases (Figure 6.4-3). Therefore MAAF4 initially hangs up in pressure, while NOTRUMP continues to depressurize. MAAP4 shifts to a separated model for the two-phase composition at approximately 80 seconds. This sudden shift in MAAP4 modelling assumptions results in a more rapid depressuriza: ion for MAAP4, and by 120 seconds the MAAP4 pressure is less than seen in NOTRUMP. Because of the large size of the break, and the rapid blowdown of RCS inventory, primary to steam generator seconday heat transfer is lost quickly (Figure 6.4-4) with a very slight loss of steam generator secondary side mass (Figure 6.4-5). The steam generator heat transfer does not play a role in the accident progression. CMT water injection (Figure 6.4-6) starts within 30 seconds of the break initiation. At first, there is a period of CMT recirculation, where water enters the CMT balance line (Figure 6.4-7) from the cold leg. For this relatively large break, the period of CMT recirculation is extremely brief. Furthermore, MAAP4 underpredicts the period of recirculation flow due to not modeling the interfacial condensation l on the water surface of the CMT, as identified in Section 2.2.4. For breaks within this size range, the short recirculation time for the CMT causes the CMT liquid to stay cola and interfacial condensation occuls. The impact of the condensation is to reduce the pressure at the top of the CMT such that the CMT drain flow is reduced. MAAP4 predicts too early of a transition from CMT recirculation to CMT draining. MAAP4's prediction of early CMT draining provides make-up inventory (Figure 6.4-
- 9) sooner than would actually occur. The CMT level (Figure 6.4-10) starts to decrease sooner in MAAP4 than in NOTRUMP.
The temperature (Figure 6.411) of the single node in the MAAP4 CMT model never increases more than approximately 10*F during this transient. This is because the recirculation period was so short, and there is no appreciable vapor flow through the balance line (Figure 6.4-8). NOTRUMP shows that the top CMT node (out of four nodes) increases over 300"F within approximately 200 seconds. The bottom NOTRUMP node remains much colder. There is not a large impact on the accider.t progression because of the difference in the CMT modelling and temperature prediction. However, the downcomer in MAAP4 stays cooler than in NOTRUMP, due partially to the CMT simplification. The pressuriter (Figure 6.4-12) empties early in the event, and does not play a role in the remainder of the xcident progression. Both codes predict that the pressurizer empties within the first 50 seconds of the event. O Results of Pnmary Cases Rev. O, Arn! 1997 o \newproj2\3603w-4 wpf it>448197 ! l
a 6-93 ADS-4 valves are automatically actuated approximately 1300 seconds into the accident. Neither code (G predicts any water relief (Figure 6.4-13) through the valves because the hot legs (Figure 6.4-15) are empty. De trend of the ADS-4 vapor relief (Figure 6.4-14) is the same for both codes, although MAAP4 underpredicts the integrated loss. The MAAP4 and NOTRUMP downcomer inventory and level results (Figures 6.4-16 and 6.4-17) show differences very early in the event while MAAP4 is using the homogeneous two-phase model. When the MAAP4 RCS void fraction (Figure 6.4-18) reaches the user-input VFSEP value of 0.6, the phases in the RCS separate, and the downcomer inventory suddenly increases. However, this is during a period of rapid inventory loss from the break, and the MAAP4 downcomer inventory resumes a rapid decrease. De MAAP4 downcomer level shows the same trend as the downcomer mass, because the downcomer is a collapsed water pool in MAAP4. In NOTRUMP, the downcomer level is a mixture level, and shows a deviation from the downcomer inventory trend when ADS valves are opened. Flashing / boiling is predicted by NOTRUMP in the downcomer when ADS valves are opened, as evidenced by the downcomer water temperature reaching saturated conditions (Figure 6.4-19a). MAAP4 predicts that the downcomer remains subcooled (Figure 6.4-19b). IRWST gravity injection is the final phase of the accident progression that is examined for this analysis. IRWCT gravity injection occurs when the downcomer pressure is within approximately I bar (15 psia) of the pressure at the top of the IRWST. The downcomer pressure (Figure 6.4-20) is quickly () reduced with the opening of stage 4 ADS valves. IRWST injection (Figure 6.4-21) stans approximately 250 seconds after ADS actuation. MAAP4 predicts exceptionally good agree.aent with NOTRUMP on the RCS depressurization rate, the start of IRWST injection, and the average rate of IRWST injection after it begins. The overall progression of the accident is demonstrated through the RCS mass inventory (Figure 6.4-
- 22) and the vessel mass inventory (Figure 6.4-23) transients. Both MAAP4 and NOTRUMP predict similar trends of decreasing inventory. However, at approximately 700 seconds MAAP4 predicts a levelling off of the system inventory, while NOTRUMP predicts upward trends in the system inventory. His is due to the void fraction modelling within MAAP4. As identified in Section 2.1.2, the MAAP4 core void fraction model calculates an average void fraction for a given steaming rate in the con:. NOTRUMP calculates no void fraction within the core if thermal hydraulic conditions permit. Bus as the CMT water enters the core region, NOTRUMP calculates no void fraction in the bottom nodes of the core. This results in NOTRUMP being able to store inventory within the vessel.
MAAP4, on the other hand, predicts more water loss from the break. The conclusions of the analysis are based on the vessel mixture level (Figure 6.4-24). NOTRUMP predicts a core uncovery of limited depth and duration within the first 10 minutes of the accident. MAAP4 predicts the vessel mixture level decreasing to within one foot of the top of the core, but the core is predicted to remain covered. This slight nonconservatism in MAAP4 is due to the la:k of an interfacial condensation model in the CMT. This is a limitation of MAAP4 that was identified during the development of the PRA PIRTs, and is discussed in Section 2.2.4. Results of Pnmary Cases Rev. O. Apnf 1997 ohwprojh3603w.4.wpf lbest 197
l 6-94 Section 8.0 shows that the temperatures in the core are not challenging during core uncovery, and this case results in successful core cooling. The overall trends for this accident scenario are consistent , between MAAP4 and NOTRUMP. 'Ihe same conclusion of successful core cooling can be drawn from I either MAAP4 or NO'IRUMP results. 4 4 i l l 1 l O Results of Prirnry Cases g,y,g,gpn3i997 j ohwinj2\3603w-44pf:Ib-04i L97 .
6-95 l ' ,e] Table 6.41 Summary of Events for Benchmarking Case 4 - 8.75" Hot Leg Break with 1 CMT ,g, (seconds) NOTRUMP MAAP4 Break occurs 0 0 Reactor trips on low pressurizer pressure 3 6 CMT actuation signal on low pressurizer pressure 6 8 CMT draining begins (recirculation ends) 200 50 Top of core uncovers 320 -- Top of core recovers 518 -- ADS-1 setpoint reached (no actuation) 628 593 ADS-4 opens 1334 1325 IRWST injection starts 1550 1605 CMT empties 1640 1622 O I l Results of Primary Cases Rev. O. Apnl 1997 o \rewprojn3603w 4 wpf Ib-041197
6-96 O; 1 1 l l Figure 6.4-1 RCS Pressure for case 4 8.75 inch HL Break, 1 CMT, Auto ADS NOTRUMP MAAP4 2500 m : o - 2000 - - m - ct 1500 -- - e s 1000 - s - m :_\I m e 500 - - t u : \ s 1 0 0 5$0 10'00 15'00 20'00 25'00 3000 Time (S) O h Results of Pnmary Cases Rev. O, Apnl 1997 oWwpnsN603* 4 wpf:1b-041197
1 6-97~ 0 . Figure 6.4-2 Break I n t e g r a.t e d Water for case 4
-8.75 l-nch HL Break. 1 CMT, Auto ADS NOTRUMP
----MAAP4 400000 _
350000 -5 _ - 7.a300000 -f _ O 250000 -s,----- v : 200000 -E m m-150000 -E - 100000 -~
":2 .
50000 -i
~' '1' '''''''''
0 l ''l 0 500 1000 1500 20'00 25'00 3000 Iime (S)
. Results of Primary Cases . Rev. o. Apna 1997 o wwpro)2\3603 4 wpf:1b&I197
6-98 O Figure 6.4-3 8reak Integrated Vapor for case 4 8.75 Inch HL Break, 1 CMT, Auto ADS NOTRUMP MAAP4 120000 - 100000 -- , E : ' c 80000 -- - w 60000 --
~
/
s'
- /
m m 40000 -
~
,' 1 i
f C / ) 2 - / I 20000 - - f 0 'l 'l 'l 'l ) 0 500 1000 1500 2000 2500 3000 ; Iime (S) l l O Results of Primary Cases Rev. 0. Apnl 1997 o \newprojN603w-4 wpf:lwI197 ) l
f f 6-99' ; J
;. A i '
'l Figure G.4-4.
SG Heat Transfer. for case 4 t 8.75. Inch.HL Break, 1 CMT, Auto ADS NOTRUMP i l MAAP4 4- - - - D e c o y Heot ; I l
. ,100000 a, -6 >
% '\\.
2
- 80000 ---il'
= -
. - -i t.
3 60000 - \. l
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=
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, --t- - . . _ . _ . _ + - - - ,-.-._.l._
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= - o
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O. Sb0 1000 1500 2000 2500 300 0 Time (s) l
,-< i I
Results of Pnmuy Cases -. . Rev. 0. Apnl 1997 o wwwsw20603wa spr.Ibo 1197 w
6-100 Figure 6.4-5 SG Mass Inventory for case 4 8.75 inch HL Break, 1 CMT, Auto ADS tt0 TRUMP MAAP4 120000 _ r_ _ _ _ _ _ _ _ __ _ _. _ _ _. _ _ _ _ __ _ _ _ _ _ _ _ _ _ _ _ _ _ 100000 -I E : v c 80000 -- g 60000 -- _ m : m 40000 -- o '.
- lE -
20000 -- _
~
0 'l 'l l 'l 'l 0 500 1000 1500 2000 2500 3000 Iime (S) O Results of Pnmary Cases Rev. O. Apnl 1997 o Wwproj2\)603w-4 m pf:1b-Os t 197
i 16-101.'
- l J
of'\ U - l Figure 6.4-6 . CMT Water- I n j e c t-i o n for case 4 ) 8.75 Inch HL Break, 1 CMT, Auto ADS-NOTRUMP M A A P 4' ) i _ - 12 0 '
= _
N _ E 100-- l' - s
-i ~
~
-.s, s,
_ s
- _r 's J o 60 --i 's
.o -t 1
l o 4 0 '-J i i
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0- 500 10'00 15'00 20'00 25'00 3<00 0 Iime (S) , j i i l l . .\ i
-]
- Results of Primary Cases: Rev,0. Apnl 1997 otwwproj2\3603* 4 wpf:!b-041197 i
.s. ,
4 j
6.'02 l i Ol l Figure 6.4-7 Balance Line Water Flowrote for case 4 8.75 Inch HL Break, 1 CMT, Auto ADS NOTRUMP
----MAAP4 m 120 -
m ~ N _ E 100 - - w - 80 - _ e - o 60 -- x - o -~ 1 o 40 -ll '
- il W 1l m 20 -4 -
m ; o a '
- s ' ' '
0 ''''''l 'l '''' 0 500 1000 1500 2000 2500 300 0 Time (S) i i I O Results of Pnmary Cases Rev 0, Apnl 1997 o M projN603*-4 wpf. Ib-04 L 197
6-103
,q U -
1 Figure 6.4-8 Balance Line Vapor Flowrote for case 4 8.75 Inch HL Break, 1 CMT, Auto-ADS NOTRUMP
----MAAP4 50 g ,\
E -
.o _
0- y
.* - - + ,, . - r re v - - - - - - - - - - - - - - - - --
O .
.=>
O -5 0 - - e -
~
o [ -10 0 -_ - m _ m _ O '
" -150 ''''''''''''''''''''''''
0 500 1000 1500 2000 2500 3000 Time (S) O ^ Results of Pnmary Cases Rev. O. Apnl 1997 o:Wewproj2\3603w al wpf lb-041197 -
a h-104 I l Q Figure 6.4-9 CMT Water inventory for cose4 8.75 Inch HL Break, 1 CMT, Auto ADS NOTRUMP MAAP4 140000
~
120000 -7 s
- ,s s
E 100000 -: _a 80000 -- s s h v : s s cn 60000 -; s cn - s o ' 40000 - s =E - s
- s 20000 -- s
~
s s 0 'l ' '
l l 'l 0 500 1000 1500 2000 2500 300 0 Iime (S)
O Results of Pnmary Cases Rev. O. Apni 1997 o bewpro;N603w-4 wpf.%Stl 197
.- - . .- . . - - .. . . . . . . - . . . .~ . .
6-105-j(s) -
= ,
Figure 6.4-10 CMT Level 'for case 4- l 8.75 Inch'HL Break, 1 CMT, Auto ADS. P
-NOTRUMP
-- - - - M A A P 4 25 _
1 m .2 0 -_ s- A'
-- - s \
s O v. 15- :
~
- s
~
's s
.c en 10 --
- 's s s
* ~
s C 5- N
~
0 0 500 10'00 15'00 20'00 25'00 3000 Time (S) n As Results of Primary Cases Rev. O. Apnl 1997 u Wepro;N603=-4 mp0lboti197
r 6-!% O, Figure 6.4-11 CMT Temperature for case 4 8.75 Inch HL Break, 1 CMT, Auto ADS NOTRUMP Top Node MAAP4 Single Node
-t- - - - N O T R U M P Bottom Node 700 -
vu_ 6 0 0 -: 500 -E o :
' 400 -:
o :
~
a 300 -: u 3 Y i o 200 -: ! ' a_ g
. ...+ ..+._._._+._._._+._._.I E 100 -
o : H 0 :'3 - ''''''''''''''''''' 0 580 10'00 15'00 20'00 25'00 3000 Iime (S) O Results of Primary Cases Rev. O. Apnl 1997 chwpre>N603w-4 mpf 1b-041197
au .. 6 107
'f a
j F Figure '6.4-12 Pressurizer I.n y e n t o r y f o r. co'se'4
- 8 . : 7. 5 -
Inch HL 8 r.e o k , 1:CMT, Auto ADS NOTRUMP.
- - - -: 'MAAP4-30000- ..
25000 - x . E : c 3 20000 -- O -
.v.
.15000'-~
en . . ro 10000 - -
.o ;-
2 :~ 5000'- -
, j 0
1' ' '
l ' ' ' ' l ' '''l ''''
0 500 1000 1500 2000 2500 3000 I-ime (S)
,..I.
M Results of Pnmary Cases Rev 0 Apal1997
- c:%roprep20603w4wpf:Ib4LI197 1' s,
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6-108 O Figure 6.4-13 ADS-4 Integrated Water for case 4 8.75 Inch HL Break, 1 CMT, Auto ADS NOTRUMP MAAP4 100000 m 80000 -- - E _
.c g 00000 -5 W v _
m 40000 - o . 2 20000 - - 0 '''''''''''''''''''''''' 0 580 10'00 15'00 20'00 25'00 3000 Time (s) e Results of Primary Cases nev.o,Apnl1997 oWwpro3N603w4 wpf:It>o41197
6-109 O-9 . Figure 14-14
- . ADS-4 Integrated Vapor for case 4 8.75 Inch HL-Break,- 1 CMT, A u't o ADS No. TRUMP MAAP4' 125000 _
m 100000 -{ E - A _ o -
.d -
-75000 -
cn 50000 - 2 25000'-{ 0- '!'l l' l 'l O 500 1000 1500 2000 2500 3000 Time (s)
.O .E .
Results of Primary Cases Rev. 0, Apnl 1997 cWwprolh3603w.4 wp( Ib-04t l97 s
6-110 l 01 i 1
~
l! I l Figure 6.4-15 i l Hot Leg Water Level for case 4 . ! 8.75 Inch HL Break, 1 CMT, Auto ADS NOTRUMP Unbroken Loop MAAP4 Both Loops
-t-.- - - H 0 T R U M P Broken Loop 30 t
i ,l)
^ 28 - 'I I
~'
i ,
" l ,
26 - 11 3 i i l l
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e _c 22 -- 20 '''l l 'l l 0 500 1000 1500 2000 2500 3000 Time (s) P O Results of Primary Cases Rev. O. Apn! 1997 o Wwpro)N603w.4 wpf:1b-041197
6-111 r\ . LJ Figure 6.4-16
. Downcomer and Lower-Plenum Inventor'y for case 4 ;
8.75 Inch HL Break, 1 CMT, Auto ADS NOTRUMP MAAP4 i 80000 l 4
^ 60000 -r
- E r '
4 (~N _ o ,; 41 'hw i [ 40000 - t( - l m _tI - m 11 , a \ \ E 20000 -- i 0 ' ' ' ''''''''''''''''' I O 500 10'00 15'00 20'00 2500 3000 Time (s) i i l i O l Rewits of Pnmary Cases Rev. 0. Apnt 1997 , c:\newpro32 \3003w-4 wpf lbo41197 i
i 6 112 I
)
O i l Figure 6.4-17 Downcomer Level for case 4 8.75 Inch HL Break, 1 CMT, Auto ADS NOTRUMP MAAP4 35 _
^
30 --} t "25-t$ s- --t 20 - in y
$c:n 15 - :g '
-~ --- $-
- i e 10 -:
~c :
5-2 0
- ' ' ' ''''''''''''>ii'ii 0 5$0 10'00 15'00 20'00 25'00 3000 Time (S)
O Results of Primary Cases Rev. 0, Apnl 1997 o \newpro3N603w 4 wp(;1bol!197
" 6-113 s >
i .
+:
4
\
Figure 6.4-18 RCS' Void Fraction .f o r case 4 8.75 1nch HL B r.e a k).- 1 CMT, Auto AD S-WAAP4 Input _of VFSEP ~ MAAP4 Void Froction-1 c- - o - a8- .
'~~~~~~ ------ --- ----------------
/
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pa 'a. 8
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. owwpro).% %03w-4 wpf.lb44l t97.- . + .
W N e' -MMdM WT' 1F- Es- 8-Tur- s- W -'*'r F f MPt* M
6-114 Figure 6.4-19a . NOTRUMP Downcomer Temperature for case 4 8.75 Inch HL Break, 1 CMT. Auto ADS NOTRUMP Downcomer Water Temperature 4- - - - R C S Saturation Temperature m 700 _
- u. :
v 600 -2 e 500 -E
." 400 -E s o : s 300 -:
'~
I -'--'
". [ -_ +___+____p_._
e 200 -: o :
* ~' i ' ' ' ' ' '
100 l ''''''''''l - 0 500 1000 1500 2000 2500 3000 Time (s) Figure 6.4-19b l i MAAP4 Downcomer Temperature for case 4 8.75 Inch HL Break, 1 CMT. Auto ADS MAAP4 Downcomer Water Temperature i I
+--- RCS Saturation Temperature m 700 _
u_ : 600 -E 500 -:D e m 2 : 1
- I O
4 0 0 -E - c. 300 -l
' Q "~+--- w 3 '
_ - - + _ _ -. _ + _ _ _ _ 4 _ _ _ E 200 - : 100 l --
l l 'l t ' ' i 0 500 1000 1500 2000 2500 3000
, - . t \
lime (S) Results of Primary C25cs Rev. O. Apnl 1997 o bewpmjN603* 4 wpt' lb Nt 197
6-115 E 77- (.- l i 1 Figure 6.4-20 De-tail'ed Downc'omer Pressure for case 4 : 8.75 inch HL Break, 1 CMT, Auto ADS j NOTRUMP Downcomer ] d MAAP4 RCS 50 _ i m i o 45 - i m -. Il
- a. 4 0 -2 (N -/ v -
l} t : i V 35 -: g -
\
e- : u- 30 - \, a : #
- 25 -: % . . . .o,'"".=~,....
m : -~
~
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u 20 -: c_ : 15 ' ' ' ' ' ''''''''''''''''''' 0 580 10'00 15'00 20'00 25'00 3000 IIme (S) i O Results of Pnmary Cases Rev. O, Apnl 1997 chspro)M603*-4 wpf:Ib48 t l97 - i:
- 6 116 l
0l Figure 6.4-21 IRWST integrated Injection for case 4 8.75 Inch HL Break, 1 CMT, Auto ADS NOTRUMP MAAP4 150000 120000'-- I ^ : . E ' o : ,' _ 90000 -- ' I w -
/
m 600 00 -: m : , o - 3 - 30000 -[ _ - 3 . 0 'l 'l l ''l , 0 500 1000 1500 2000 2500 3000 l Iime (S) i i O Results of Primary Cases Rev. O. Apnl 1997 oAnew projAV,03w4 wpt'.lb-041197
6 117 - 1 D V
~
l
. -j I
Figure 6.4-22 RCS Mass . inventory for case 4 i
' 8 . 7. 5 Inch H !_ Break, -1 CMT, Auto ADS 3 i
-NOTRUMP. I WAAP4 j 350000 300000 - i n
p 250000 -: O .E :1
- 200000 - 9, v :
.m 150000 -: )
m : o .100000'-:' - 2 __.________________ 50000 -: _ 0 ~'l ''''l ''''l 0- 500 1000 1500 2000 2500 300 0 Time (s) i l 'O i Results of Primary Cases . _. Rev. O. Apnl la91 j owwprojM603w.4 wpf:lb Gill 97
6-118 s O Figure 6.4-23 Vessel Mass inventory for case 4 8.75 Inch HL Break, 1 CMT, Auto ADS NOTRUMP MAAP4 100000
~\ _
-i 80000 - -
E -' ------- - _a v 60000 -
- I
\
~,- h m 40000 --
m - o - 1 - 20000 -- _
~
0 'l 'l 'l 'l 0 500 1000 1500 2000 2500 3000 Time (s) 9 Results of Pnmary Cases Rev. O. Apnl 1997 owwproJN603w4wpf.It441197
6-! !9.: v , I Figure 6.4-24
. C o-r e Mixture LeveI f o r 'c a s e'4' 8 75-lnch HL B r'e a.k , 1 CMT,' Auto ADS '
-NOTRUMP
----MAAP4
-t- - - - T o p o f Core A30
~
26 - _
.__ ==
2 - / . 4 _- 2 2 - _
.t s -
e e _ s -
.._._._ . _ . _ . _ . _4__ . _ . _ . _ . _p_ . _ . _ . _ . _ . ; ._._._.; . _ . _ . _ + . _ . _ . _ . _
e .18 -- e m 14 __ _ 3 x 10 _: _
- s 6
~
0 5$0 10'00 15'00~ 20'00 25'00 3000 Time (S)
,,'(
p: Eesults of Primary Cases kev. 0. Apnl 1997 i oNwwpsoj2\3603w-4.wpf:Ib.041197 9
-. - ,. .,w,- r - ,r-- - . - . -e y , - , - -
6 120 6.5 3.5 Inch Break with Manual ADS ACCIDENT SCENARIO Case 5 is a 3.5" diameter hot leg break with the failure of both CMTs. The PRHR is not credited. Only one accumulator is assumed to function when the RCS pressure decreases below the accumulator pressure of 715 psia. With the failure of the CMTs, ADS occurs as a result of operator action, which is credited 20 minutes after the failed CMT actuation signal. All stage 1,2 and 3 ADS and I stage 4 ADS fail, leaving 3 stage 4 ADS to depressurize the RCS. One DVI line is assumed available for IRWST injection. The containment is conservatively assumed to remain at atmospheric pressure throughout the accident progression.
SUMMARY
OF PLANT RESPONSE Case 5 demonstrates the plant response of an accident type that results in twc periods of core uncovery during the accident progression. During the first 500 seconds of the 3 5" break accident, the steam generators play a role in removing a high percentage of the decay heat. The heat transfer ends when the RCS inventory loss drains the primary side of the SG tubes. This decouples the primary and secondary sides, and the RCS pressure decreases below the SG saferv valve setpoint pressure. At approximately the same time, the level in the hot leg decreases, and the water loss from the break stops. Vapor loss from the break increases, but the overall rate of inventory loss decreases. The RCS coolant inventory continues to decrease, resulting in the uncovery of the top of the core between 10 and 15 minutes after the break occurs. Prior to ADS actuation, the RCS is without any make-up inventory because the CMTs have failed and the RCS pressure is too high for injection from the accumulators. The 3.5" diameter break is near the limiting break size for this type of accident. The break with the deepest and longest uncovery is the largest size that maintains the RCS above the accumulator pressure prior to ADS actuation. For the 3.5" break, the accumulator injects approximately 200 seconds prior to ADS actuation, leadiing to the conclusion that a slightly smaller break would be slightly more limiting. If the break were bigger, the j accumulator would inject, limiting the minimum coolant inventory prior to ADS, as is shown for case 1 6 (Section 6.6). ADS is manually actuated 20 minutes after the failed CMT actuation signal. The decrease in RCS pressure allows inventory injection from the accumulator, which fully recovers the core. The accumulator is empty within a few minutes of ADS actuation. With no more cold accumulator water injection, the downcomer heats up to saturation conditions within 5 minutes. The primary system ! pressure is held-up around 30 psia, slightly above the point at which IRWST gravity injection starts. j Once again, the primary system does not have any water injection, and the top of the core uncovers I again. The uncovery causes the RCS pressure to decrease, which allows IRWST injection to start. The core recovers. The depth of the core uncovery is much less than the core uncovery prior to ADS actuation. However, the duration of the core uncovery is longer because the IRWST injection does i Results of Primary Cases Rev. o, Apnl 1997 o \newproj2\3603w 5 wpf;ib-o41197
t 6-121 l not refill the core as quickly as the accumulator injection.' Peak clad temperature results for this case - are provided in Section 8.0, and are shown to remain below 2200'F.
- A)
DETAILED PLANT RESPONSE MAAP4 an'd NOTRUMP prediction of this transient show similar trends relative to core cooling. The summary of important events are listed in Table 6.5-1 for both MAAP4 and NOTRUMP. Transient plots of key parameters are provided in Figures 6.5-1 to 6.5-20. The following paragraphs provide a more detailed discussion of the plant response as calculated by MAAP4 and NOTRUMP with emphasis on similaritics and differences between the predictions of the two codes. MAAP4 and NOTRUMP predict the same RCS pressure (Figure 6.5-1) trend. The RCS begins an immediate depressurization as a result of the break. Within the first minute, the reactor trips on a low pressurizer pressure signal, and a CMT actuation signal is generated. However, the CMTs are assumed to fail, and the opening of the CMT isolation valves is not modelled. The break flow (Figures 6.5-2 and 6.5-3) is moderately rapid. In the first 500 seconds of the j accident, MAAP4 predicts less water loss and more vapor loss than NOTRUMP due to the simplified ] homogenous fluid modelling in MAAP4 (see Sections 2.1,1 and 2.2.1). When the break location uncovers, both codes predict that the water loss from the break stops, while the vapor loss increases.
- The two codes show the same trend of inventory loss from the break, with MAAP4 slightly
- k underpredicting the total vapor loss.
The steam generators play a minor role for this break size. During the first 500 seconds, both codes predict that more than 50% of the decay heat is being removed via the steam generators (Figure 6.5-4). As a result, the secor dary side inventory in the steam generators (Figure 6.5-5) is reduced, but the steam generators do act come close to emptying. While heat transfer is occurring from the RCS to the steam generators, the RCS pressure stabilizes near the steam generator safety valve setpoint. When the primary and secondary sides decouple due to the substantial inventory loss from the primary side, tne RCS depressurization resumes. Both codes predict the same trend. i An accumulator starts to inject (Figure 6.5-6) at approximately 1000 seconds into the accident, when the RCS pressure decreases below 715 psia. The rate of injection is relatively low because the slow change in the RCS pressure. However, when ADS valves are open, the RCS pressure rapidly decreases, and the accumulator injection rapidly increases. The accumulator empties (Figure 6.5-7) within 250 seconds of stage 4 ADS actuation. Both codes predict the same accumulator behavior. The pressurizer (Figure 6.5-8) empties early in the event, and does not play a role in the remainder of the accident progression. Both codes predict that the pressurizer is empty within the first 150 seconds of the event. 3 (V I Results of Primary Cases Rev. O. Apn) 1997 ! owwproj2\3603w-5.wpf Ib.041197
6-122 After ADS-4 valves are actuated by the operator 20 minutes after the failed CMT actuation signal, both codes predict a brief surge of water relief through the ADS-4 valves (Figure 6.5-9). The water relief occurs a couple hundred seconds after stage 4 ADS valves are opened. The water entering the hot leg (Figure 6.5-11) is due to the injection i.m he accumulator. MAAP4 predicts more water loss from stage 4 ADS than NOTRUMP, but this does not impact the overall accident progression or conclusions of the analysis. The trend of the ADS-4 vapor relief (Figure 6.5-10) is the same for both codes, although MAAP4 underpredicts the integrated loss. i The MAAP4 and NOTRUMP downcomer inventory and level results (Figures 6.5-12 and 6.5-13) are j different in the first 500 seconds of the event while MAAP4 is using the homogeneous two-phase l model. When the MAAP4 RCS void fraction (Figure 6.5-14) reaches the user-input VFSEP value of 0.6, the phases in the RCS separate, and the downcomer inventory suddenly increases at approximately 600 seconds. The MAAP4 prediction of mass distribution in the RCS is more accurate after VFSEP is reached. The MAAP4 downcomer level shows the same trend as the downcomer mass, because the downcomer is a collapsed water pool in MAAP4. In NOTRUMP, the downcomer level is a mixture level, and shows a deviation from the downcomer inventory trend when the downcomer starts to boil (Figures 6.5-15a and 6.5-15b) at approximately 1700 seconds. Both codes predict that the do vncomer reaches a saturated condition after accumulator injection has stopped. IRWST gravity injection is the final phase of the accident progression that is examined for this analysis. IRWST gravity injection occurs when :he downcomer pressure is within approximately I bar (15 psia) of the pressure at the top of the IRWST. The downcomer pressure (Figure 6.516) is quickly reduced below 50 psia with the opening of stage 4 ADS valves, but it takes approximately 1000 seconds until IRWST injection is able to start (Figure 6.5-17). The overall progression of the accident is demonstrated through the RCS mass inventory (Figure 6.5-
- 18) and the vessel mass inventory (Figure 6.5-19) transients. Both MAAP4 and NOTRUMP predict
{ the same trends of decreasing and increasing inventory. The conclusions of the analysis are based on the vessel mixture level (Figure 6.5-20). Both codes predict two periods of uncovery, with the first uncovery being more limiting. Both codes predict that approximately half of the core uncovers prior to ADS actuation, with MAAP4 predicting a slightly longer duration of the uncovery. Section 8.0 shows that the clad temperature response for this case remains below 2200*F. The overall trends for this accident scenario are consistent between MAAP4 and NOTRUMP. The same conclusion of successful core cooling can be drawn from either MAAP4 or NOTRUMP results. O Results of Primary Cases Rev. O. Apnl 1997 o wcwproj20603w.5 wpf Ib-041197 l 1
6-123 Table 6.5-1 Summary of Events for Benclunarking Case 5 - 3.5" Hot Leg Break with y 1 Accumulator (seconds) NOTRUMP MAAP4 Break occurs 0 0 Reactor trips on low pressurizer pressure 27 36 CMT signal on low pressurizer pressure (no actuation) 32 46 Top of core uncovers 863 798 Accumulator starts 1044 1009 l Operator manually opens ADS-4 1232 1246 Top of cote recovers 1260 1314 l Accumulator empties 1450 1446 Top of core uncovers 2325 2010 IRWST injection starts 2460 2244 Top of core recovers 2890 3139 l l O . d l l l l l Results of Primary Cases g,y o,g ,,33 ,997 i ohwproi2\3603* 5 wpf:1M41197 , 1 i
5.cr , 1 Figure 6.5-1 RCS Pressure for case 5 3.5 Inch HL Break, 1 Acc, Manual ADS NOTRUMP
----MAAP4 2500 _
m - o : 2000 - - en - c- ;[ v 1500 '1
- i e %
~ ~ ~4 s 1000 --
a - m : s cn _ e 500 -- - u _ ct - t ii1 I i i i t iI i l ! t i''*r iie i,i 0 , , ,1 , , , , 0 500 1000 1500 2000 2500 3000 3500 4000 Time (s) O; Reschs of Primary Cases ley. O. Apnl 1997 l oNwwprojN603* 5 mpf;tb 041197 l
w 25 1 4
. ,- l O .
l l l Figure 6.5-2 ) J B r-e a k' Integrated Water - for case 5 3.5 Inch HL Break,- 1 Acc, Manuci ADS- . NOTRUMP ]
----MAAP4 I 400000 350000 -2 -
l 4
.m ,
. p- . 3 0 0 0 0 0 -:: -
y 3- ^s 250000 -5: . %J . I _ _ _ _ _ __ 200000 -5' f
- / .
m 150000 - : / I cn /
- s 100000 - /
'- / ,
50000 -: , 2 I O 1 i f f f I I t t t t 1 t iI t i 1 f 1 I I t I t t t I 1 if f i 1 i f f I t 0 5d0 10'00 15'00 20'00 25'00 30'00 3600 4000-
- Time (s) 1 4 l 1
[\ j
- Rewits of Primary Ca<es Rev. 0, Apnl 1997
- oNewpro321'603w.5.wpt:Ibo41197 l
~
w
-- ~ _.- - - - ,.
6-126-O Figure 6.5-3 Break integrated Vapor for case 5 3.5 Inch HL Break, 1 Acc, Manual ADS . NOTRUMP
----MAAP4 120000 -
100000 - E : v o 80000 - c g 60000 -- - - ------ en : ,' cn 40000 -- - e a / s : ' 20000 -- f
- /
~
0"i'l'l'l'l'L' 'l' . 0 500 1000 1500 2000 2500 3000 3500 4000 Time (s) O Results of Prirnary Cases Rev. O. Apnl 1997 o \newproj2\3603w 5 u rf:lb 041197
6-127 l i i 1
'l rs e
i Figure 6.5-4 , SG Heat T r a 'n s f e r for case 5 3.5 Inch HL Break, 1 Acc, Manual ADS - NOTRUMP
----MAAP4 . ,
4- - - - D e c a y H e a t l 1 l
,,100000 -
. l
=- i s -It :
- m. -11 i
.-- 80000 ---ii. . i i
. m m ll ' i
. ,G -
s , o i r -
- 60000 -- \. i '
-\ v o l
a: ?, s-s. - ll i m 40000 -Jj i
^v i 1* . 4
. -t + . ._. 4 - -- , - -+ . - . - . p . - . _ i , _
- I ,
c 20000 -- . t
- I
- I 0- _- i- / ,,,i __
O _ o ~ z -20000 'l'l'l'l'l'l'liiii 0 500 1000 1500 2000 2500 3000 3500 4000
.l .ime (s) !
l 4 i s v Results of Primary Cases Rev. o. Apnl 1997
' owwpro3N603* $.mpf:1b-041197 - ,
i s s e g- d v . -,r -
6-13 _ O Figure 6.5-5 SG Mass Inventory for case 5 3.5 Inch HL Break, 1 Acc, Manual ADS NOTRUMP
----MAAP4 120000 _
100000 - g _ o 80000 -- w ~ 60000 -- m : cn 40000 -- a : =E - 20000 -- _
~
0 'l'l'l'l'l'l'l' 0 500 1000 1500 2000 2500 3000 3500 400 0
.I.ime s
~~
O Results of Primary Cases Rev. O. Apnl 1997 chwproj2\360.1*-$ wpf.Ib441197
6-129 a ~0- ' i i Figure 6.5 i Accumulator Injection for case 5 ! 3:.51 Inch HL 8reok, 1 Acc. -Manua1 ADS. !
..NOTRUMP
- - - -- W A AP 4 n 1000 - ;
m
- s. -
E- - o 800.- - v -
~
e 600 - - t
- - 1 o -
i m x - Ip >
' 4 0 0 -- <
o - u_ 200 - - m - m - l iI f f I I I t I t I f I I t i t l l t g ;g l t l t , , 9 g , , , , Q 0 500 1000 15'00 20'00 25'00 30'00 35'00 400 0 Time (S) w: h Q.-
~
Results of Primary Cases Rev. 0. Apol 1997
- ohnprojN603w 5 apf.lbollt97
6-l.20 0 Figure 6.5-7 A c c u rn u l a t o r Inventory for case 5 3.5 inch HL Break, 1 Acc, Manual ADS NOTRUMP
----MAAP4 120000 _
100000 - - '\ E : o 80000 - - v : 60000 -- _ l I m _ m 40000 -- o : s _ 20000 -- . 0 ''l'l'l'l'l'l'''' 0 500 1000 1500 2000 2500 3000 3500 400 0 Time (s) l l l 9 Results of Primary Cases Rev. O. Apn11997 o VwwprotN603w 5 wpf Ib4 Mil 97 1 M-
6-131-l 3
. (0 '
i
.)
1 Figure 6.5-8 Pr.essurizer I n v e n-t o:r y f-or case 5 3.5 Inch HL Break, 1- Acc, Manual ADS NOTRUMP
----MAAP4 l
1 30000 _
~
. 25000 -
^ _
E - (' o 20000 - - V) v 15000 - en . cn 10000 -:: ; . o : ! 2 . 5000 --
~
0 l'l'l' 'l'l''''''''' 0 500 1000 1500 2000 2500 3000 3500 4000 Time (s) . j i Results of Primary Cases Rev. O. Apnl 1997 ottewproj2\3603w $ wpf:!b-04l197
6-132 O Figure 6.5-9 ADS-4 integrated Water for case 5 3.5 Inch HL Break, 1 Acc, Manual ADS NOTRUMP
----MAAP4 100000
~
m 80000 -- E :
~
v 60000 -- _
~
m 40000 -- m : o 2 20000 -5 I t t t t t iie ,,,,,e i ,,,,,, Q l f f I f f I I f f f I I t 14 i t 0 Sb0 10'00 15'00 20'00 25'00 30'00 35'00 4000 IIme (s) G' Results of Primary Cases Rev. O. Apnl 1997 o \newproj2\3603w.5 wpf.lb@l197 ~
c, 133.
- p' j
i I Figure 6.5-10 ' . 1 LA D S.-.4 lntegrated V a p~o r for case 5~ 3'.5- Inch HL Breok. 1 A c'c , Manual ADS-4 NOTRUMP MAAP4 '
)
/
125000 , 3 m 100000 -2 ~ ' E ,- w 75000 - ,
/
- m. 50000 - -
m : -
- c. -
E 25000 - - <
/
- t /
i t 1 1 t t t t I t t t t t I I I iit t t t t iif f 1 i f 1 ( t I t t 1 0 I i i i i i 1 0 500 1000 1500 2000 2500 3000 3500 400 0 Time (S) L
'. g
\)
Results of Primary Cases Rev. O. Apnl 1997
. ownprop\3603w 5.wpf 1b441197
6-I3I O Figure 6.5-11 Hot Leg Water Level for case 5 3.5 Inch HL Break, 1 Acc, Manual ADS NOTRUMP Unbroken Loop
----MAAP4 Both Loops 4- - - - N O T R U M P Broken Loop 3 0 -- i
~
l t l 28 -- i 7 (i, "26--
~
g e
~ _ l x \ 1 )b N
Y f __p. . a 24 -- g; ; . ; . _ . _+_ . _ . __+_ . _ . _ + . _ . _ + . _ . p,. . a> t 22 --
'''''''L' ''''
20 ! ' ' ' ' ' ' ' ' ' l ' ' ' ' 0 500 1000 1500 2000 2500 30 0 0 35'00 400 0 Time (s) O Results of Pnmary Cases Rev. O. Apnl 1997 o Wrwpro)M603w-5 wpf:10-041197
6-135 [ t
.?
{ .
]
a e -l i i t Figure 6.5-12 ) Downc'omer and Lower P'enum l i nventory for case 5 , 3.5. Inch HL. Break, 1 Acc, Manual ADS NOTRUMP. !
---- MAAP4 !
j
'80000 i
I
-s'60000 - -
E \ gj-v
- _o
_\ _ s s
" 'i ' -
40000 -- \ t ~ s
\ "
m
~
g I s '% s,- W ~
\l %,-
0 - E 2 0 0 0 0 ---
. l l
t I I f f I f f f I f I f f I f f f f f f f f f f f f i f I f f 1 1 I f f I f 0 ' 0 500 1000 15'00 20'00 25'00 30'00 35'00 400 0 Iime (S) O
- Results of Pnmary Cases Rev. O. Apnl 1997 oNwwproj2\3603w-5 wpf:tbe41197 N
6-136 e. Figure 6.5-13 Downcomer Level for case 5 3.5 Inch HL Break, 1 Acc, Manual ADS NOTRUMP
----MAAP4 35 30 -2
.s :s ~ 25 -2s-' r
- 1 i t
w t , 20 - \ , 2 \ l g -+
'-~~~
C 15 - b - it s-s
~
~ ,-
\l s 's, -
cu 10 -: ! I : ! 5-2 I O l'''''''''l'''' 0 $00 1000 1500 2000 2500 3000 3500 400 0 Time (s) I
- l O
Results of Pnmary Cases new. o, Apnt i997 o unpro)2\)603e $ wpf.lbo41197
~6-137I !
,4. ,
n
,4g, ,g.
t '
- ;b" 3c ,
i w ?: ' i t ' J 4
- Figure 6.5 -
RCS Voi~d Fraction for case 5
- 3.5 Inch HL Break,. '1 'A c c , Manual ADS- ,
MAAP4. Input.of. VFSEP
- - - - M A AP 4 Void Fraction 1-
+ c -
.o -
, .8- -
,f s ,
j a- - f.
~
- * /
6 ,
.u_ -
/
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- <n -i l
. o -t Z ' ''''''''''''''''''''<iiiiiiiiiii 3 0 ~ c .0 Sb0 10'00 15'00 20 '0 0 25'00 30'00 35'00 4000 Time (S) i ^ l 1 4-
'i 1
- 1 s
/
- W% . -
4 Results of Pnmary Cases. Rev. 0. Apnl 1997 ; 1 3. _oW*proJ20603w.5 wpf Ib-041197.- L lV r r-I ph d t k -+-f- er s =dw-tw-n#n - .-- p ,:--- .-~.i *-.-.4 .~w= ,,4 . - - .
- 6-138 Figure 6.5-15a g NOTRUMP Downcomer Temperature for case 5 l 3.5 Inch HL Break, 1 Acc, Manual ADS i NOTRUMP Dawncomer Water Temperature
-t- - - - R C S Saturation Temperature m 700 _
u. 600 -- ' r e m 500 -I _ s
\
- 400 -5 I o
; 300 -j
( ,
' - ~ ~
I-o 200 -5 100 -''l'l'l'l'l''''l'4000 0 500 1000 1500 2000 2500 3000 3500 Time (s) Figure 6.5-15b MAAP4 Downcomer Temperature for case 5 3.5 inch HL Break, 1 Acc, Manual ADS
- MAAP4 Downcomer Water Temperature 4- - - - R C S Soturation Temperature
_ 700 _ u_ e 600 -5 -- 500 -E s o : o 400 -E _ 300 -: 200 -
+~~ ~-I ---+
e - 100 =' ''''''''''ii'iiiiiii,ii,iiiii,, 0 5d0 10'00 15'00 20'00 25'00 30'00 35'00 4000 Time (s) O Resuhs of Primary Cases Rev. O. Apnl 1997 o Vwwpro3h3603w 5 wpf.lbollt97
se , t
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Figure 6.5-16 j, De. tail'ed Downcomer. Pressure- for c a.s e 5. . 3.5 1nch H L: Break, 1 Acc, Manual ADS NOTRUMP Downcomer )
----MAAP4 RCS j 50 .
i . l o 45 -: -
.1 I
m : Si a_ 4 0 -- - t i il :35 - ! *b, m : s 1 N 1 c 30 -: 3 : \ , - , _.. , m 25 -: \1 3 ,<,, i J m : % ,,%, m ! t as - u 20 - - Q,. iiiii,,,ie iii,,iiiiiii,,iii,,ii,ii,,,ii .i 15
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h-] l Results of Primary Ca$es . Rev. O. Apnl 1997 oWwproj2\3603w-5.wpf.1b-041197 l i
6- 1J0 O Figure 6.5-17 IRWST integrated Injection for case 5 3.5 inch HL Break, 1 Acc, Manual ADS NOTRUMP
----MAAP4 150000 '
120000 -: ^ : - E - A _a : / W _ 90000 --
~
/
- /
m ' 60000 - ' m ~ s o - , 2 : '
/
30000 - - 0
~
'l'l''''l , 'l'l'
0 500 1000 1500 2000 2500 3000 3500 400 0 Time (S) l l 1 I O I Results of Pnmary Cases Rev. O. Apnl 1997 o WrwproiNW)* 5 wpf IWI197 l 1
. 6 h ik' ' .
.O -
j b
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Figure 6.5-18 l f RCS Mass Inventor .for c a s e'5' : 3 . 51 Inch HL Break, 1- A c c; - Manual ADS :l NOTRUMP: 1
.:s - ._- __ - yAAp4 .
i 350000 ; h !
-)
- 300000 -- _
n
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~.
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- Results of Primary Cases Rev. 0. Apnl 1997 ~
f .c:Wwpsoj20603w 5 wpf.lbeel197 s
*I i \
u , +. - .n.-. ., .- . . . - , , ,
sm O Figure 6.5-19 VesseI Mass inventory for case 5 3.5 inch HL Break, 1 Acc, Manual ADS
-- NOTRUMP
----MAAP4 100000 i
ti g / i (s h g 80000 - - I s
~
\ ' _
E - I i s _a - s I s , W __ 60000 -- s o ' s ' v s s ,,,- j s s ,
- s m 40000 --
m - o - 1 - 20000-- - 0 'l'l'l'l'l'l'l' 0 500 1000 1500 2000 2500 3000 3500 4000 T.ime (s) l l l 9iI
~
Results of Primary Cases Rev. O. Apnl 1997 owwproj2\3603w 5 wpf Ib-04t197
6 143 s 4 . .. ~1 1
. ')
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.1:
q 1 Figure 6.5-20' j l . C'o~r.e' M i x t u r e Level for' case 5. l 3.5 Inch HL B'rsok, 1'Acc, Manual ADS
.NOTRUMP l
- - - -- M A A P 4. .
+-- ; T o p: of Core !
)
.- l
. _- 30 _
, v2 6.. .
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E '''''''''''''''''''''''''''''''''' 6' 0 500 10'00 15'00 20'00 25'00 30'00 35'00 4000 Time (s) l 1
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O l V i I Results of Pnmary Cases . Rev. O. Apn! 1997 ' owepro;2\3603w.5.wpf Ib-041197, . i.,..[ U' .=. .\
6 144 6.6 6.0 Inch Break with Manual ADS ACCIDENT SCENARIO Case 6 is a 6.0" diameter hot leg break with the failure of both CMTs. Only one accumulator is assumed to function when the RCS pressure decreases below the accumulator pressure of 715 psia. With the failure of the CMTs, ADS occurs as a result of operatoc action, which is credited 20 minutes after the failed CMT actuation signal. All stage 1,2 and 3 ADS and 1 stage 4 ADS fail, leaving 3 stage 4 ADS to depressurize the RCS. One DVI line is assumed available for IRWST injection. The containment is conservatively assumed to remain at atmospheric pressure throughout the accident progression.
SUMMARY
OF PLANT RESPONSE Case 6 demonstrates that the plant resp mse to a loss of both CMTs is less limiting as the break size increases. The inventory loss is more rapid fer the 6" break than was shown for the 3.5" break (case 5). The primary and secondary sides decepple within the first 200 seconds, so that the steam generator has a negligible role in the accident progression. The heat iransfer to the steam generators ends when the RCS inventory loss drains the primary side of the SG tubes. At approximately the same time, the level in the hot leg decreases, and the water loss from the break stops. Vapor loss fmm the break increases, but the overall rate of inventory loss decreases. He RCS pressure decreases from the inventory loss, allowing the accumulator to inject at approximately 300 seconds. Accumulator injection starts when the mixture level is near the top of the core, and stops the net l inventory loss. Approximately two-thirds of the accumulator inventory injects prior to ADS actuation. l l l ADS is snanually actuated 20 minutes after the failed CMT actuadon signal. The decrease in RCS pressure causes the remaining accumulator invenury to drain. When the accumulator empties, the vessel mixture level is above the hot leg elevation. There is no make-up injection until IRWST gravity drain starts when the RCS is sufficiently depressurized. IRWST gravity injection is established to maintain successful core cooking for this accidet,t scenario. I DETAILED PLANT RESPONSE i l l MAAP4 and NOTRUMP prediction of this transient show similar trends relative to core cooling. The summary of imponant events are listed in Table 6.6-1 for both MAAP4 and NOTRUMP. Transient l plots of key paameters are provided in Figures 6.6-1 to 6.6-20. The following paragraphs provide a more detailed discussion of the plant response as calculated by MAAP4 and NOTRUMP with emphasis on similarities and differences between the predictions of the two codes. l MAAP4 and NOTRUMP predict the same RCS pressure (Figure 6.6-1) trend. De RCS begins an l immediate depressurization as a result of the break. Within the first 20 seconds, the reactor trips on a Results of Primary Cases Rev o. April 1997 obvproj2\3603w4wpf:lt>041397
6-145 Iow pressurizer pressure signal, and a CMT actuation signal is generated. However, the CMTs are assumed to fail, and the opening of the CMT isolation valves is not modelled. The RCS pressure quickly decreases below the saturation pressure and flashing occurs. MAAP4, using a homogenous model, calculates both stenn and liquid out the break, while NOTRUMP with mt.ltiple nodes and flow paths having drift flux models can allow for slip between the phases. Therefore MAAP4 initially hangs up in pressure, while NOTRUMP continues to depressurize. MAAP4 shifts to a separated model for the two-phase composition within approximately 200 secor.ds. This sudden shift in MAAP4 modelling assumptions results in a more rapid depressurization for MAAP4, and the MAAP4 pressure falls below NOTRUMP's prediction. He break flow (Figures 6.6-2 and 6.6-3) is fairly rapid. When the break location uncovers, both codes predict that the water loss from the break stops, while the vapor loss increases. The two codes show the same trend of inventory loss from the break, with MAAP4 slightly underpredicting the total vapor loss. MAAP4 also predicts a surge of water lost from the break due to accumulator injection when the ADS valves open. The reason for the MAAP4 prediction differing fmm the NOTRUMP prediction is discussed below when the accumulator results are explained. For this break size, primary to steam generator secondary heat transfer is lost quickly (Figure 6.6-4) with a small loss of steam generator secondary side mass (Figure 6.6-5). He steam generator heat transfer does not play a significant role in the accident progression. f% By approximately 300 seconds (MAAP4) and 335 seconds (NOTRUMP) the RCS pressure reaches 715 psia, and accumulator injection starts (Figure 6.6-6 and 6.6-7). MAAP4 and the NOTRUMP accumulator models are different in predicting the instantaneous flow rate but both models get injection over nearly equal time periods. Thus, the integrated average flow rate is nearly equal for both models. The MAAP4 model does not account for fluid inertia effects on flow rate and therefore predicts high flow rates resulting in the RCS pressurizing above the current accumulator pressure. When this occurs, there is a period of no flow followed by a high flow period when RCS pressure again drops below accumulator pressure. Thus, the MAAP4 accumulator flow rate appears as a series of flow spikes while the NOTRUMP flow is relatively smooth. The rate of accumulator injection closely follows the rate of RCS depressurization. Prior to ADS actuation, the injection flow rate is much lower than when ADS actuation causes a sudden decrease in pressure. The rapid accumulator injection immediately following the opening of ADS valves is predicted the same by both codes. However, there is a difference in the amount of accumulator water than spills out the break. MAAP4 uses a different model than NOTRUMP for calculating the core and upper plenum void fractions. As discussed in Section 2.1.2, the MAAP4 core void fraction model calculates an average void fraction for a given steaming rate in the core. NOTRUMP calculates no void fraction within the core if thermal hydraulic conditions permit. Thus as the accumulator water enters the core region, NOTRUMP calculates no void fraction in the bottom nodes of the core. This
~ results in NOTRUMP being able to store more of the accumulator water within the vessel. At the end of the accumulator injection period. MAAP4 calculates less coolant mass in the RCS than NOTRUMP.
Results of Primary Cases Rev. O, April 1997 onne*Troj20603w 6.wpf:lt>441197
6 146 The pressurizer (Figure 6.6-8) empties early in the event, and does not play a role in the remainder of the r.cciJem progression. Both codes predict that the pressurizer is empty within the first 100 seconds of the event. ADS-4 valves are aduated by the operator 20 minutes after the failed CMT actuation signal. Neither code predicts any water relief (Figure 6.6-9) through the valves because the hot legs (Figure 6.6-11) are empty. The trend of the ADS-4 vapor relief (Figure 6.6-10) is the same for both codes, although MAAP4 underpredicts the integrated loss. The MAAP4 and NOTRUMP downcomer inventory and level results (Figures 6.6-12 and 6.6-13) show differences very early in the event while MAAP4 is using the homogeneous two-phase model. When the MAAP4 RCS void fraction (Figure 6.6-14) reaches the user-input VFSEP value of 0.6, the phases in the RCS separate, and the downcomer inventory suddenly increases. However, this is during a period of rapid inventory loss from the break, and the MAAP4 downcomer inventory resumes a rapid decrease. The MAAP4 downcomer level shows the same trend as the downcomer mass, because the downcomer is a collapsed water pool in MAAP4. In NOTRUMP, the downcomer level is a mixture level, and shows an increase when accumulators rapidly inject during the ADS blowdown, and another increase when IRWST injection starts. The accumulator injection during ADS actuation keem the downcomer water subcooled (Figures 6.6-15a and 6.6-15b) until the accumulator empties. NOTRUMP predicts that the downcomer reaches saturated conditions prior to IRWST injection, while MAAP4 predicts that IRWST injection starts prior to downcomer boiling. IRWST gmvity injection is the fm' al phase of the accident progression that is examined for this O analysis. IRWST gravity injection occurs when the dawncomer pressure is within approximately I bar (15 psia) of the pressure at the top of the IRWST. The downcomer pressure (Figure 6.6-16) is quickly , reduced with the opening of stage 4 ADS valves. NOTRUMP predicts that IRWST injection ! (Figure 6.6-17) starts within 250 seconds of ADS actuation, while MAAP4 predicts a delay over 500 seconds. The MAAP4 calculated IRWST injection delay, combined with the accumulator injection ) differences discussed above, cause MAAP4 to predict more limiting RCS mass inventory (Figure 6.6-18) and vessel mass inventory (Figure 6.6-19) transients. l The conclusions of the analysis are based on the vessel mixture level (Figure 6.6-20). Prior to ADS, l there is a difference in the vessel mixture level during the accumulator injection phase. The accumulator injection, which causes an increase in the vessel coolant inventory, is calculated to cause the vessel mixture level to increase to the hot leg elevation in MAAP4. However, NOTRUMP predicts that the accumulator injection maintains the vessel mixture level relatively constant. The j differences between MAAP4 and NOTRUMP are due to the differences in the core void fra: tion l modelling previously discussed. After ADS actuation, the MAAP4 calculated delay until IRWST injection starts causes the vessel mixture level to decrease until the top of the core uncovers. NOTRUMP predicts that the vessel mixture level is maintained above the hot leg elevation. O Results of Primary Cases Rev. O. Apnl 1997 o%ewisuj2\3603w-6.wpf:lb-o41397
6-147
.'the vessel mixture inventory tratesient for this case shows the largest differences between MAAP4 and : . .
NOTRUMP of my of the primary benchmarking cases. Despite the differences, both codes predict that this set of equipment failures, with the initiating break size of 6", does not challenge core cooling. Most of the trends for this accident scenario ~ are consistent between MAAP4 and NOTRUMP, with i MAAP4 showing a more conservative prediction due to the overprediction of accumulator inventory spilled out the break and the delayed IRWST injection. 'Ihe same conclusion of successful core cooling can be drawn from either MAAP4 or NOTRUMP results. O O
. Results of Primary Cases h im 0:W3w4wpf;lb4M1197
6-148 Table 6.6-1 Summary of Events for Benchmarking Case 6 - 6.0" Hot Leg Break with
~
1 Accumulator (seconds) NOTRUMP MAAP4 Break occurs 0 0 Reactor trips on low pressurizer pressure 9 12 CMT signal or. Iow pressurizer pressure (no actuation) 10 16 Accumulator starts 335 298 Top of core uncovers - 298 Top of core recovers - 390 Operator manually opens ADS-4 1210 1216 Accumulator empties 1321 1297 Top of core uncovers - 1719 IRWST injection starts 1460 1742 Top of core recovers - 1800 O l i l i l i i Results of Primary Cases Rev. 0, April 1997 cAnr.wpoj20603w4wpf.lb 041191 l l
=
q 4 -6149' '!
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t t. Figure 6.6-1 . , RCS Pressure for case 6 , 6e0 Inch HL Break, 1 Acc, . Manual ADS : t NOTRUMP
---VAAP4 l 2500- -
- . [
c -
~
2000 -
.m .
~
C1. . . ~ p/ s.
, v 1500 ca s s 1000 -- t m- -
m : \ m . \ e 500 -- N u _ s o_ -
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$ 1.50 9'
Figure G.6-2
. Break Integrated Water for case 6 6.0 Inch HL Break, 1 Acc. Manual ADS NOTRUMP ;
1
----MAAP4 400000 _
- I 350000 -j
- .. 4 E 300000 --
,. l
, _ ,-------- 3,,- _ 250000 -j _ _ _ _ _ _ - - - - 200000 -:- : I m 150000 -; M : 100000 -; =E : ; 50000 -
~
0 l l l 0 500 1000 1500 2000 2500 3000 Time (s) Results of Primary Cases Rev. O. Apnl 1997 owwproj2\3603w 6 wpf:Ibedi197
, . . .. . . ~ ~. - . . - .
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. Break 1 n t e g r a t' e:d -
V a p o r. for case 6l
- 6.0 Inch'HL B r:e a k .. 1 'A c.c . M a n u a l-- ADS- :
~ N0 TRUMP
---MAAP4
]
120000 - o l
- a
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-100000 -- ---------
n - - __ 1
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o.- :. ,' E - f 20000 -- , i i i , i 0 0 500 1'0'00 15'00 20'00 25'00 3000 Iime (s) i V. 4 Results of Pnmary Cases. Rev. O. Apnl 1997 oWwproJ2\3603w4wpf;lb 041197
6-152 O Figure 6.6-4 SG Heat Transfer for case 6 6.0 Inch HL Break, 1 Acc, Manual ADS NOTRUMP
---- MAAP4 4- - - - D e c a y Heat ,100000 -
s -
~
t 3 80000 --U I m t
= 60000 - i h, o
_ 's-- 0: ..
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m Il g e o 20000 --il -
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-20000 l ; l l l 0 500 1000 1500 2000 2500 3000 IIme (S)
O Results of Pnmary Cases Rev. O. Apnl 1997 o \rwwptojN603w-6 wpf:1b481197
g , . .. - .. . . . - - .. . . . . . . - . . - .. . - - .
.u : w .,, ,
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'S G :M a s s-. 1nventor'y for c a's e 6 ;
6.0 - . lnch HL 8reok, .1 Acc, M'a n u a I ' ADS i NOTRUMP
-- - -- - M A A P 4
'120000 _
i t 100000 - - m - E : ,' p
'c 80000 -- +
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- Ib441197
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' 6-154 O
Figure 6.6--6 Accumulator Injection for case 6 6.0 Inch HL Break, 1 Acc, Manual ADS NOTRUMP
----MAAP4 1000
%. - 1 e - il o 800 -- I ll - I 11 e 600 - 1 I o -
,\
c: _ . II ,3 g' -: i i , ll i, [i q 200 i li I II v2 _ l! i ll 5 0
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0 5b0 10'00 15'00 20'00 25'00 3000 Iime (S) e Results of Pnmary Cases Rev. O Apnl 1997 owwprojN603w4 wpf,1 boll 197
6-1551 :
., t A(f^yJ ;
i Figure 6.6-7 ; Accumulator- Inventory for cose6 6.0 I n c h -H L' Break, 1- Acc, Manual ADS. i NOTRUMP
----MAAP4 ,
120000 _ , 100000 - -
's f m -
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s ! O' s :
~
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6 156-O Figure 6.6-8 Pressurizer inventory for case 6 6.0 inch HL Break, 1 Acc. Manual ADS NOTRUMP
---- MAAP4 30000 _ ^
25000 -i _ E : o 20000 -: _ 15000 -[- m : m 10000 -- o -
~ ,2 5000 - -
o
^' l l l l l 0 500 1000 1500 2000 2500 3000 Iime (s) i l
l i 9 Results of Primary Cases Rev. O. Apnl 1997 oNiewpqN60.)w 6 wpf-Ib481197
6-157 -
. [ -- ~ /~k ' . !q . ;
i i Figure 6.6-9
. ADS-4 lntegr.ated W a't e'r for cose6 ,
6'. 0 -l ri c h
- H L- Break, 1 Acc, Manual ADS .
NOTRUMP i
.-----MAAP4 l 100000 -
4
- j m 80000 - -
E : ! s, _a ~ ! Q -- v 60000-- j i cn '40000 -- a E 20000 - f 0 l l l l l 0 500 1000 1500 2000 2500 3000 Time (S) l l p)-- I L$Q l a Results of Primary Cases Rev. O. Apnl 1997 _ 1:: owwprojh3603w.6 wpf:Ibe41197 ;
..1
'l
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s.sse O Figure 6.6-10 ADS-4 Integrated Vapor for case 6 6.0 inch HL Break, 1 Acc, Manual ADS NOTRUMP
----MAAP4 125000 -- _
m 100000 - E : a : ! 75000 -- , I l m 50000 -{ ,- w ,- , a _ 1 OE '
)
25000 -{ ,
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t t .] , 6-159 - ')
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Figure 6.6-11 ;
. Hot Leg Wate-r Le. vel for case 6 ',
- 6.-0<lnch HL Break, 1 Acc, ManuaI ADS- !
NOTRUMP Unbroken. Loop l
-- - M A A P 4 Both' Locos i
~
-t :- ' ' N O T R U M P 8roken Loop .
1 1 30 1
.^28- _, .
' ~
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Iime (s) I
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Results of Pnmay Cases - Rev. D. Apnl 1997
. o \newpro)2\3603w4*pf:Ib441197. - l 1
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6-160 0 Figure 6.6-12 Downcomer and Lower P l e n urn Inventory for case 6 6.0 Inch HL Break. 1 Acc. Manual ADS NOTRUMP
----MAAP4 80000 b '
~ 60000 -r E a
~
\ '
40000 - N ---------
;g
~ .,' - J -
~
CA gl i a - =E 20000 - 0 l ! l l l 0 500 1000 1500 2000 2500 3000 Time (S) O Results of Primary Cases Rev. O. Apnl 1997 o \newprojN(,J3w 6 wpt'.Ib-041197
6-161; -f _. . - x2 1,
e Figure 6.6-13
.. Downcomer Level -f:o r case 6 6.0 Inch HL 8reok, 1 A 'c c. .- 'Manual ADS NOTRUMP
----MAAP4 35 _
3 0. -->
~25- 3
~
s ' 5.1 O'U " 20 -;1I
-. : 1i t _
.cen15 - 5
- , o 's %
~- -
i e 10 -i ^
.I :
5-2
^
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.0 500 1000 1500 2000 2500 3000 Time (S) 4 . A N
Results of Primary Cases . Rev. O. Apnl 1997 - owwprojN60)w-6 mptIb-041197 N
6
.-162 O
Figure 6.6-14 RCS Void Fraction for case 6 6.0 Inch HL Break. 1 Acc, Manual ADS MAAP4 Input of VFSEP
----MAAP4 Void Fraction 1
C - o - _ 8 - ,-~~~_,_-r u,
/
g o
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0 5b0 10'00 15'00 2000 2500 3000 IIme (S) O Results of Primary Cases Rev. O, Apnl 1997 ohwpre}N60.1w 6 wpf:I W I197 I
6-163 h Figure 6.6-15a v
- NOTRUMP D'owncomer Temperature for case 6 lnch.HL Break, Acc. Manual ADS 6.0 1
- NOTRUMP Downcomer Water Temoerature '
- f- - - - R C S Saturat on Temperature m 700 _
i E 600 -r , f i e 500'-: i +
" .4 0 0 -~ 4 .+_ q l
\
' 300 -i 4 ~
'e= 200 -5 100 l l l l l O' 500 1000 1500 2000 2500 3000 Time (s)
A U Figure 6.6-15b MAAP4 Downcomer Temperature for case 6 ! 6.0 Inch HL Break, 1 Acc. Manual ADS
- MAAP4 Downcomer Water Temperature j
-t- - - - R C S Saturation Temperature
_ 700 _
- u. P
- 600 -i m 500 -5
= : 4 '
400 -E o _
~_.t 300 -5 ~__\+
a E 200 -E _____+____ w
* ~ '
100 l l l l l 0 500 1000 1500 2000 2500 3000 Time (s)
-n v
Results of Primary Cases Rev. O. Apnl 1997 owwproj2\3603w-6 =pf.lb-04l197
6.!64 l 1 O 4 Figure 6.6-16 Detoiled Downcomer Pressure for case 6 6.0 inch HL Break. 1 Acc, Manual ADS NOTRUMP Downcomer MAAP4 RCS 50 . o 45 -; - I m : I a 40 -- e I 35 -: ~ b
@ s u 30 -: q a -
s ' m 25 b - m . . ,'* 4 g r *w ...,,,,,,,^^***,,,,, u 20 -- c_ -
~
15 l l l 0 5d0 1000 1500 2000 25'00 3000 Time (s) O Results of Primary Cases Rev. O. Apnl 1997 ohmprojN603w-6 wpf:lb OJll97
(
, > > 1 6-165-1 I
l l i.. 1 t v - A/ !
.l L
~
l 4 e 1 i L Figure L6.6-17: ,
- 1. n t e g r a t e 'd- lnjection 1:R W S T- 'for case 6 :
6.0 -I n c'h' HL Break. 1 Acc, Manual A D S. : NOTRUMP
----MAAP4 3 i
150000 _
.i
-s - 12 0 0 0 0 ~-- !
E : 1 D) _a .
- I C/ _
90000 -: , v -
~
~ ,-
m ' 600001- - o- -
- i s : '
30000'- ,
- - 1
- /
0 T l l ,
'l l 0 500 1000 1500 2000 2500 3000 <
Time (s)
'I l
i
~ ' f% ' l L) .
i Results of Pnmary Cases , Rev. o. Apnl 1997 owwprrj20603w 6 wpf:lb-041197 - t .
- w -4 -
6-166 O Figure 6.6-18 RCS Mass inventory for case 6 6.0 Inch HL Break, 1 Acc, Manual ADS NOTRUMP
---- MAAP4 350000 300000 -
n g 250000 -i
.c 200000 -
- g v :
m 150000 -3 m C 100000 -
':E i 1
s _ M ,_ _}, _________ 50000 -3
~ '
0 l l l l l 0 500 1000 1500 2000 2500 3000 Time (s) i
.I l
l l 1 Results of Pnmary Cases Rev. O. Apnl 1997 o-\newproj20603w4 wpf.lb-OLI 197 j I L
'6 167-l i
' ('~j . I V l 1
s Figure 6.6--19 V e s s e l. .M a s s- Inventory for case 6 ; 6.0 lnch HL Break, 1 Acc, Manual ADS : NOTRUMP
----MAAP4 100000
~
/
80000 -
~
-- I
.. f g
^ -
i
,eds ' ---------
i , s ! _E. v < f. v _ a 60000 - g s, s
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0 l l l 'i ! 0 500 1000 1500 2000 2500 3000 Time (s) i O Results of Primary Cases . Rev. O. Apnl 1997 j c:\nenproj2\3603*4 wpf Ib-(Mil 97, i j
0+103 O Figure 6.6-20 Core Mixture Level for case 6 6.0 inch HL Break, 1 Acc, Manual ADS NOTRUMP MAAP4 4- - - - T o p of Core _ 30 C 26 --
,rrs - s ' ys ,
- 22 U s
\ /
\ ,
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,g_y_._. ,. ._._._. ; ._._ _ .+._._._._ y,s._....... _.+ _._._._. ;._._._
e 14 __ u - 3 : ~x 10 - _
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6 0 5b0 10'00 15'00 20'00 25'00 3000 Time (s) l l O! Results of himary Cases Rev. O. Apnl 1997 o wwprojN603w.6 wpf.)betIi97
i 6-169 6.7 8.75 Inch Break with Manual ADS , 10 l ACCIDENT SCENARIO Case 7 is a 8.75" diameter hot leg break with the failure of both CMTs. Only one accumulator is j assumed to function when the RCS pressure decreases below the accumulator pressure cf 715 psia. With the failure of the CMTs, ADS occurs as a result of operator action, which is credited 20 minutes after the failed CMT actuation signal. All stage 1,2 and 3 ADS and 1 stage 4 ADS fail, leaving 3 stage 4 ADS to depressurize the RCS. One DVI line is assumed available for IRWST injection. ne containment is conservatively assumed to remain at atmospheric pressure throughout the accident progression.
SUMMARY
OF PLANT RESPONSE Case 7 demonstrates the plant response to a loss of both CMTs for the large end of the break ; spectrum. ne inventory loss from the break is at a rapid rate, causing the vessel mixture level to fall l below the hot legs within the first 200 seconds. The RCS depressurization is likewise rapid, allowing the accumulator to inject and increase the mixture level prior to it falling to the top of the core. Accumulator injection lasts for approximately 10 minutes, until the accumulator empties. There is no make-up inventory to the RCS until after stage 4 ADS reduces the pressure to allow IRWST gravity , injection. The core uncovers. ( ) ADS stage 4 is manually actuated 20 minutes after the failed CMT actuation signal. Actuation of stage 4 ADS results in depressurization of the RCS and injection from the IRWST. Both MAAP4 and NOTRUMP respond to ADS stage 4 actuation and IRWST injection by calculating an increase in the RCS and vessel mass and core level. In each code, the core is calculated to be recovered with 10 minutes of stage 4 ADS actuation. DETAILED PLANT RESPONSE MAAP4 and NOTRUMP prediction of this transient show similar trends in RCS pressure and inventory, ne summary of important events are listed in Table 6.7-1 for both MAAP4 and NOTRUMP. Transient plots of key parameters are provided in Figures 6.7-1 to 6.7-20. ne following paragraphs provide a more detailed discussion of the plant response as calculated by MAAP4 and NOTRUMP with emphasis on similarities and differences between the predictions of the two codes. The opening of a 8.75 diameter break in the RCS hot leg results in a rapid loss of RCS inventory with a co Tesponding decrease in RCS pressure (Figure 6.7-1). As long as the RCS inventory remains subcooled with respect to the current pressure, both MAAP4 and NOTRUMP calculate almost exact water inventory losses (Figure 6.7-2). Between 10 and 20 seconds the RCS pressure decreases below the saturation pressure and flashing occurs. MAAP4, using a homogenous model, calculates both () Results of Primary Cases Rev. O. April 1997 c:\newproj20603w 7.wptitW1397
6 170 steam and liquid out the break, while NOTRUMP with multiple nodes and flow paths having drift flux models can allow for slip between the phases (Figure 6.7-3). Therefore MAAP4 initially hangs up in pressure, while NOTRUMP continues to depressurize. MAAP4 shifts to a separated model for the two-phase composition at approximately 80 seconds. This sudden shift in MAAP4 modelling assumptions results in a more rapid depressurization for MAAP4, and by 120 seconds the MAAP4 pressure is less than seen in NOTRUMP. However, MAAP4 does not model slip and therefore the void fraction at the break is lower in MAAP4 than in NOTRUMP. Thus, over the duration of the transient MAAP4 trends to remove more liquid and less steam compared to NOTRUMP. Because of the large size of the break, and the rapid depressurization, primary to steam generator secondary heat transfer is lost quickly (Figure 6.7-4) with a very slight loss of steam generator secondary side mass (Figure 6.7-5). The steam generator heat transfer does not play a role in the accident progression. By approximately 140 seconds (MAAP4) and 165 seconds (NOTRUMP) the RCS pressure reaches 715 psia, and accumulator injection starts (Figure 6.7-6 and 6.7-7). MAAP4 and the NOTRUMP accumulator models are different in predicting the instantaneous flow rate but both models get injection over nearly equal time periods. Thus, the integrated average flow rate is nearly equal for both models. The MAAP4 model does not account for fluid inertia effects on flow rate and therefore predicts high flow rates resulting in the RCS pressurizing above the current accumulator pressure. When this occurs, there is a period of no flow followed by a high flow period when RCS pressure again drops below accumulator pressure. Bus, the MAAP4 accumulator flow rate appears as a series
. of flow spikes while the NOTRUMP flow is relatively smooth.
During the accumulator injection period, there is a net increase in the RCS inventory. However, MAAP4 which uses a different model than NOTRUMP for calculating the core and upper plenum void fractions, spills more of the accumulator water than NOTRUMP. As discussed in Section 2.1.2, j the MAAP4 core void fraction model calculates an average void fraction for a given steaming rate in the core. NOTRUMP calculates no void fraction within the core if thermal hydraulic conditions permit. Thus as the accumulator water enters the core region, NOTRUMP calculates no void fraction in the bottom nodes of the core. This results in NOTRUMP being able to store more of the accumulator water within the vessel. At the end of the accumulator injection period, MAAP4 calculctes less coolant mass in the RCS than NOTRUMP. De pressurizer (Figure 6.7-8) empties early in the event, and does not play a role in the remainder of the accident progression. Both codes predict that the pressurizer empties within the first 100 seconds of the event. l ADS-4 valves are actuated by the operator 20 minutes after the failed CMT actuation signal. Neither code predicts any water relief (Figure 6.7-9) through the valves because the hot legs (Figure 6.7-11) l are empty. The trend of the ADS-4 vapor relief (Figure 6.710) is the same for both codes, although ! MAAP4 underpredicts the integrated loss. i 1 1 Results of Primary Cases Rev. O, Apnl 1997 ohm pro;2\3601w-7.wpf ltro4 t l97
6-171 - De MAAP4 and NOTRUMP downcomer inventory and level results (Figures 6.7-12 and 6.7-13) show differences very early in the event while MAAP4 is using the homogeneous two-phase model. l When the MAAP4 RCS void fraction (Figure 6.7-14) reaches the user-input VFSEP value of 0.6, the j - phases in the RCS separate, and the downcomer inventory suddenly increases. However, this is during a period of rapid inventory loss from the break, and the MAAP4 downcomer inventory resumes a ' J rapid decrease. De MAAP4 downcomer level shows the same trend as the downcomer mass, because the downcomer is a' collapsed water pool in MAAP4. In NOTRUMP, the downcomer level is a
- mixture level, and shows a deviation from the downcomer inventory trend when ADS valves are opened. Flashing occurs in the downcomer when ADS valves are opened, as evidenced by the'-
downcomer water temperature reaching saturated conditions (Figures 6.7-15a and 6.7-15b). IRWST gravity injection is the final phase of the accident progression that is examined for this analysis. IRWST gravity injection occurs when the downcomer pressure is within approximately I bar , , (15 psia) of the pressure at the top of the IRWST. The downcomer pressure (Figure 6.7-16) is quickly reduced with the opening of stage 4 ADS valves. NOTRUMP predicts that IRWST injection (Figure 6.7-17) starts approximately 250 seconds after ADS actuation, while MAAP4 predicts IRWST t injection within 100 seconds of ADS actuation. Both codes predict the similar average rates of , IRWST injection after it begins. he overall progression of the accident is demonstrated through the RCS mass inventory
. (Figure 6.7-18) and the vessel mass inventory (Figure 6.7-19) transients. Both MAAP4 and l NOTRUMP predict similar trends of decreasing inventory. Both codes predict core uncovery to occur
.. when the vessel inventory goes below about 55,000 lbm with MAAP4 showing recovery when j inventory again exceeds 55,000 lbm. However, NO'IRUMP does not predict recovery until the vessel 5 mass exceeds about 67,000 lbm. NOTRUMP requires the higher vessel mass for core recovery due to i the decreasing void fractions in the vessel as a result of IRWST injection cooling and the reduction in decay heat.
)
De conclusions of the analysis are based on the vessel mixture level (Figure 6.7-20). Both codes l predict that the core uncovers. Due to MAAP4 losing more of the accumulator inventory out the .! ! break during the accumulator injection period discussed above, MAAP4 uncovers the core sooner than NOTRUMP. Both codes predict that the IRWST injection recovers the cos:. Section 8.0 shows that j l the temperatures in the core are not challenging during core uncovery, and this case results in j successful core cooling. ) i ne overall trends for this accident scenario are consistent between MAAP4 and NOTRUMP, with MAAP4 showing a more conservative prediction due to the overprediction of accumulator inventory spilled out the break. The same conclusion of successful core cooling can be drawn from either MAAP4 or NOTRUMP results. I s Results of Primary Cases . Rev.O. Apn!1997 0:Wewproj2\3603w-7 wpf;1t>441397 1 < 3
6-171 Table 6.7-1 Summary of Events for Benchmarking Case 7 - 8.75" liot Leg Break with 1 Accumulator (seconds) NOTRUMP MAAP4 Break occurs 0 0 Reactor trips on low pressurizer pressure 5 6 CMT signal on low pressurizer pressure (no actuation) 6 8 Accumulator starts 165 134 Accumulator empties 778 770 Top of core uncovers -- 1077 Operator manually opens ADS-4 1210 1208 IRW5T injection starts 1462 1277 Top of core uncovers 1550 -- Top of core recovers 1720 1554 O I l 2 I O 2 l Results of Primary Cases Rev. O, Apnl 1997 o:WwprojN603w.7.wptib44 tl97
6-173' 4 4 Figure 6;7-1
- RCSL Pressur.e for-case 7 8.75- Inch HL Break., 1 Acc.,- Manual ' ADS.
NOTRUMP-
-----MAAP4
.2500 m :
.o _
2000 - - ro . - y .ct; v 15 0 0 ~- -
.e s 1000 -
- s -
m - t to :) e - 500.-- 1 u : \ Q
+,,,,,,,,=....,,,,,,,,,,,,,
~
0 0 500 10'00 15'00 20'00 25'00 300 0 i Time (S) 4 4,
' Results of Primary Caws . Rev. O. Apnl 1997 ohwproj2\3603w-7.wpf;tt@lt97
,r
-----.J __m______s___- ,,, -
6-171 O Figure 6.7-2 Break Integrated Water for casc7 8.75 Inch HL Break, 1 Acc, Manual ADS NOTRUMP
----MAAP4 400000 _
350000 -E ,-
~
] 300000 - : , .a _, -V & 250000 -~ ,/ ' W 200000 -i m 150000 -: m
" 100000 -5:.
- s 4
50000 -E 0 l ''''''''''''''l 0 500 1000 1500 2000 2500 3000 Time (S) O Results of Primary Cases Rev. O. Apr.i 1997 ohwproj2060)w.7 mpf.lb-041197
6-175-U,s , Figure 6.7-3' Break Integrated-Vapor for case 7
. 8.75 Inch HL Break, 1 Acc, Manual ADS NOTRUMP ~!
- - - - M A AP 4 i
120000 -
~
100000 -- _._____-------- ! n - : E : ' .- ' c 80000 - - Q, ~s - s'
~
w 60000 - _ en : '
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,t 0 'l l l 'l 'l 0 500 1000 1500 2000 2500 3000 Time (s) 1 i NJ Results of Primary Cases. Rev. O. Apnl 1997
- oWwproj2\3603w 7.wpf;Ib-Oli197
6 176 , O Figure 6.7-4 SG Heat Transfer for case 7 8.75 Inch HL Break, 1 Acc, Manual ADS NOTRUMP
- -- M A AP 4
-}- - - - D e c a y Heat a100000 a
N ~ii. C 80000 - S en -l\ v O 60000 -J-11'\ W
=
O 40000 --..,s.N.'+s.-+.. ce : :t m i y : i _ ~ ~'- + - - -. p ._._._ , ._._._. , _, O 20000 -:-\, m _ ]g 0- cn- --. y'7 O _ o ~
-20000 ''l 'l ''''l 0 500 1000 1500 2000 2500 300 0 IIme (s) i
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' i l O! Results of Pnmary Cases Rev. 0. Apnl 1997 c:Vwwprojh3603w 7.wpf.Ibeti197
6-177 ) Av , l l I q l l Figure 6.7-5 i
. ,. . i ca-se7-SG Mass lnvent.ory for 8.75 lnch HL Break,:1 A c c , :M a n u a l ADS .
-NOTRUMP.
- - - -- M A A P 4 ,
e l. 4
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r________________________________ i 1100000 - - 1
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0 500 1000 1500 2000 2500- 300 0
- Time (S) ..
1'
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Results of Primary Cases- Rev. 0, Apnl 1997 q i; o.h.wprgh)60}w.7.wpf;it@l t97 m ~ . . - , . , ~ - 4-.--i
6 178 O Figure 6.7-6 Accumulator injection for case 7 8.75 Inch HL Break, 1 Acc, Manual ADS NOTRUMP
----MAAP4 m 1000 ,
I i o 800 -- tli /, , C ~ li l l i i a, 600 -- Ll i l
'i li Il i
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0 0 500 1000 1500 2000 2500 3000 ' Ilme (s) . l l l l Results of Primary Cases Rev. O. Apnl 1997 o Vewpro;2\3603w 7 wpf Ib-Gill 97 I
' 179 6- 1 -f l
t Figure 6.7-7 : Accumul:ator Inventor-y for case 7-
~8.75 Inch HL Break,. 1 A c c., Manual ADS i
- NOTRUMP MAAP4 i
120000 _
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. owwprojN603w-7.wpf:1b 04I197 !
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6-180 0 Figure 6.7-8 Pressurizer inventory for case 7 8.75 Inch HL Break, 1 Acc, Manual ADS NOTRUMP
----MAAP4 30000 _
25000 -- 7" - c 20000 - g v - 15000 - . m : m 10000 -: o -
~
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4 0 ''''l 'l ''''l 0 500 1000 1500 2000 2500 3000 Iime (S) O Results of Primary Cases Rev. O. Apnl 1997 owwproj2\3603w 7.wpf;tbolll97
6-181 _ i J 1 i Figure 6.7-9 l
-ADS-4 Integrated' Water for. case 7
- 8.75 Inch HL Break, 1 Acc, Manual ADS NOTRUMP MAAP4.
100000 - - -
]
. m 80000 -5 E- :
.o
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v 60000 -I - m 40000 - f m _ 1
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2 20000 - - 0 ''''l ''l 'l 0 5d0 1000 1500 2000 25'00 3000 ] Time (s)
)
d O ,
- Results of Primary Cases Rev. O. Apnl 1997 1
owwproj2\3603*-7.wpf:.'b-Oll t97 ^ I
6 182 l O l l Figure 6.7-10 ADS-4 Integrated Vapor for case 7 8.75 Inch HL Break, 1 Acc, Manual ADS NOTRUMP
----MAAP4 125000 _
m 100000 - E : 75000 -- m 50000-m : - a -
~ '
E 25000- _ 0
~
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0 580 10'00 15'00 20'00 25'00 3000 Time (s) O Results of Primary Cases Rev. O. Apnl 1997 o-%wwpro)M603w.7.wpf.lWI197
6-183
?T -\ g l
1 i Figure 6.7-11 4 Hot Leg Water Level for case 7 H 8'.75 Inch HL Break, 1 Acc, Manual ADS l NOTRUMP Unbreken Loop
----MAAP4 Both Loops
-t-.- - - N O T R U M P 8rokon Loop 30 8
-8
^28-
_, '8I
. f's . - 11
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. _ . _ . , . _ . _ . , . _ . _ . ,, . - . _ . - + - . .
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' Results of Primary Cases Rev. O, Apnl 1997
. oAnesproj2\3603w 7.wpf:lb-04ll97
6 184 I l O Figure 6.7-12 Downcomer and Lower Plenum Inventory for case 7 8.75 inch HL Break. 1 Acc, Manual ADS NOTRUMP MAAP4 80000 ^ 60000 -r C & 40000 - Il , ----- s, - - - - - - - - - - - - - - g J/ 's s { cn -l o \
- s 20000 - -
0 ' ' '' ' ' ' ''''''''''''' 0 500 1000 15'00 20'00 25'00 3000 Time (S) e Results of Primary Cases Rev. O. Apnl 1997 o Ww pojN603w 7.wpf Ib-041197
l s uss qf
- ; 1
' 'J Figure 6.7 ;
Downcomer . Level' for case 7 8 75 - 1nch HL Break, 1 A c c., Manual' ADS : NOTRUMP )
----WAAP4
?35- <
1 A.- [
~-25-t -
'I i
f *
- 3, v :l i 20 -:In
~ :l!t ,
15 - m
~
.c -----
~ ------------ 4 O : 'k ' '%
[l e 10 -- t : ; 5--
~ l i I 1 I l f 8 I I f I f 1 I I f f f f f f f f I t i t I O
0 Sb0 10'00 15'00 20'00 25'00 3000 ,- Iime (S) l l I Results of Primary Cases Rev. 0. Apnl 1997
.' o \aewproj2\3603=-7.wpf.lbo41197
6-186 l l l O Figure 6.7-14 RCS Void Fraction for case 7 8.75 Inch HL Break, 1 Acc, Manual ADS MAAP4 Input of VFSEP
----MAAP4 Void Fraction 1
c - O -
,_ ~~_ ,
, 8- ----
- I e
.6 g
- u. ,
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-t o
> 1 2-3 o I 0 ' 0 500 1000 15'00 20'00 25'00 3000 Time (S) O Results of Primary Cases Rev. O. Apnl 1997 ovewpro;2\3603w 7.wpf.lb-041197
6-187 l I I Figure 6.7-15a (v') NOTRUMP Downcomer Temperature for case 7 8.75 inch HL Break, 1 Acc, Manual ADS i NOTRUMP Downcomer Water Temperature l
+---RCS Saturation Temperature m 700 _
u-v 600 -E e 500 -E
- \
." 400 -E s o : H
~ -4 '
3 300 -j E 200 -5
---+---+---+--
c : 100 ~' ' l '
l '
l 'l 'l .
0 500 1000 1500 2000 2500 3000 l Time (s) i
? .
l \
l Figure 6.7-15b l MAAP4 Downcomer Temperature for case 7 l 8.75 Inch HL Break, 1 Acc, Manual ADS MAAP4 Downcomer Water Temperature
+---RCS Saturation Temperature m 700 _
u_ : 600 -E 500 -5 m - x
- s o 400 -:: '+
~Y'
% 300-5 ,
E 200 -5 M~ ~ - - I ---! ---
* ' ' ' ' ' ' ' ' ' '''''''''iiii'i 100 0 500 10'00 15'00 20'00 25'00 3000 Time (s) q%J Results of Primary Cases Rev. O. Apnl 1997 ohwproj2\)603w-7mpf.lb 041197
1 l 6 138 l 1 l 1 O. l l Figure 6.7-16 Detailed Downcomer Pr' essure for case 7 8.75 Inch HL Break. 1 Acc. Manual ADS NOTRUMP Downcomer l
----MAAP4 RCS '
50 - ^ : I i , a 45 -: i
- i m
a_ 4 0 -:: I v : I l 35 -- i e : i u 30 - : 1 m : I
\ l
- 25 - s. ^> s m : s r e- .'" '+.....,,,. _ i l
w - u 20 _ i f-- l a- - i i ,iiiie i,ie i i,,ii,,,iiiiiiii 15 0 Sb0 10'00 15'00 20'00 25'00 3000 l IIme (S)
^
i l l l 9
- Results of Primary Cases. Rev. O. Apnl 1997
' o Wwproj2\3603w.7.wptibet t 197
6-189 '
-(D,-
1 Figure 6.7-17 IRWST l-n.t e g r a t e d injection f o r- case 7 8.75 1.n c h HL B.r e a k , 1 Acc., Manual ADS
'NOTRUMP
----MAAP4 ,
1 150000 -
~
/
r
./
^
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/
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/
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2
/
0 'l 'l , 'l 'l 0 500 1000 1500 2000 2500 3000
'I i fri t! (S) r Results of Primary Cases . Rev 0 APnl 1997 owwproj20603w 7.wpf.lb-041197
6 190 0 Figure 6.7-18 RCS Mass inventory for case 7 8.75 Inch HL Break, 1 Acc, Manual ADS NOTRUMP
----MAAP4 350000 _
300000 - i m E 250000 - : v 200000 --' m 150000 -2 m :I o 100000 - 'g 2 3 u- ----__ _____________ l 50000 -: 0 l ''''l 'l 'l 0 500 1000 1500 2000 2500 3000 1 Iime (S) l l i l l l Results of Pnmary Cases - Rev. O. Apnl 1997 oinewprcJ2\3603w 7.wpf.Ibell197 I
6-191 l F (~~Y n/.- 5 i 1 i l l J Figure 6.7-19 , Vessel . Mass Inventory for case 7 - 8'.-75 inch HL Break, 1 Acc, Manual ADS NOTRUMP i ! ----MAAP4 l l 100000 ~ I
-s t
)
n 80000 --.i -i E - - - - - ------------- O .a __ 60000 - .1
,I s s
s s -
/
/
v ' _ 's %. -
~
m 40000 -- m - o _ l 1 - l
-20000 -- -
1 I t I I t i1 I I 1 1 1 I I I t f f I I I I I I 1 I f f f f 0 I I 4 6 1 0 500 1000 1500 2000 2500 3000 Time (s) 1 O. s Results of Pnmary Cases- Rev. O. Apnl 1997 owwproj2\3603w.7.wpf:ltHMil97 1
s.m O Figure 6.7-20 Core Mixture LeveI for case 7 8.75 Inch HL Break, 1 Acc, M a n u a'l ADS NOTRUMP
----MAAP4
-t- - - - T o p of Core m 30 _
%=
v26- _
- . , _ _ _ _ . _ === _ :== - 22 - I' Il N /
e -
~
s f
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. . _ . _4. . .k . ._4 . _ . _. . [_ . _._.._._. l .._._._. j._._._..
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6 0 500 10'00 15'00 20'00 25'00 3000 Time (S) e 1 Results of Primary Cases Rev. O. Apnl 1997 o Wu projN603*.7.wpf;tb-Wi l97 l
l 7-1 7 RESULTS OF SENSITIVITY CASES pf c This section presents the results from sensitivity cases analyzed with MAAP4 and NOTRUMP. The sensitivity cases provide further evidence of the validity of the MAAP4 thermal / hydraulic models to accurately predict the impact of variations to multiple-failure successful core cooling accident
)'
scer.arios. As explained in Section 5.3, most of the sensitivity case results are presented as a comparison to a previous case. For sensitivities that are small changes t a previous case, NOTRUMP to NOTRUMP results are shown in an "a" plot, and MAAP4 to MAA" - esults are shown in a "b" j plot. This method is used to illustrate that both codes show the same thermal-hydraulic behavior for a specific change to the accident scenario or analysis assumption. 7.1 Break Location i The first set of sensitivity cases for MAAP4/NOTRUMP benchmarking demonstrates the effect of different break locations. DVI line breaks are analyzed in cases 8 and 8b, and a cold leg break is ~ analyzed in case 9. CASE 8 - DVI LINE BREAK i l DVI line breaks are chosen for benchmarking sensitivity cases because they are important in the PRA.
,( The initiaag event of a DVI line break effectively disables one of the accumulators, one of the A CMTs, and the RNS. An equivalent-sized LOCA on the hot or cold leg with the same functioning equipment is much less likely to occur, since simultaneous equipment failures of one accumulator, one CMT and the RNS lower the frequency of the event by orders of magnitude.
De first DVI line break analyzed as case 8 is a double-ended rupture, with the failure of the CMT isolation valve on the faulted DVI line. Herefore, the break size is limited by the 4" flow restrictor at the reactor vessel inlet'(refer to Figure 3-1). De inventory loss from '.ne other side of the break can come from an accumulator and the IRWST, but not from the RCS. With the accumtilator on the faulted loop spilling out the break, and the accumulator on the intact loop failing, no accumulators are credited. No PRHR nor start-up feedwater is credited. Based on the intact CMT, a low-low CMT level signal actuates 3 stage 4 ADS lines, with all other ADS failing. One DVI line is assumed available for IRWST injection. The containment is conservatively assumed to remain at atmospheric s pressure throughout the accident progression. Case 8 is very similar to the primary benchmarking cases with I CMT and automatic ADS actuation (cases 1,2,3 and 4) except the break location and size.. MAAP4 and NOTRUMP predict similar RCS pressure (Figure 7.1-1) trends. The RCS begins an immediate depressurization as a result of the break. Reactor trip occurs on low pressurizer pressure 4 within 20 seconds after the break occurs. The RCS pressure continues to dn;rease until a quasi-steady
.0 V
Results of Sensitivity Cases Rev. O. Apnl 1997 o%rwproj2\3603w-8.wptit@lt97
7-2 state condition is reached with heat transfer to the steam generators for several hundreds of seconds, and the RCS pressure stabilizes at approximately 1100 psia. When the break location uncovers, there is a sharp decrease in the water loss from the break (Figure 7.1.-2) and most of the inventory loss from the RCS is steam (Figure 7.1-3). The CMT on the intact loop, which was actuated within several seconds after reactor trip on low-low pressurizer pressure, transition from a recirculation phase to an injection phase. The CMT water inver. tori (Figure 7.1-4) and CMT level (Figure 7.1-5) begin to decrease. Heat transfer with the SGs is reduced, and the RCS pressure starts to decrease again. These transitions occir within 600 seconds after the accident starts. MAAP4 predicts the same trends as NOTRUMP, but the timing is delayed in MAAP4 by approximately 150 seconds. For over 1000 seconds, the CMT injection flowrate is higher than the break flowrate, and there is a small net gain in the RCS inventory. He MAAP4 two-phase model is in a separated mode, and MAAP4 predicts that the hot leg is full of water (Figure 7.1-6) and there is a small insurge of water into the pressurizer (Figure 7.1-7). This results in MAAP4 predicting a 100 psia increase in the RCS pressure from 1200 seconds to 1700 seconds, while NOTRUMP's prediction of RCS pressure is relatively constant or decreasing slightly. The difference in this prediction causes minor deviations in the CMT level calculation, but has no significant impact ot! the actuation of ADS-4. ADS-4 valves open as a result of *he CMT on the non-faulted loop draining to the low-low CMT level. NOTRUMP predicts water relief from ADS-4 (Figure 7.1-8) at the time of the valves opening, while MAAP4 does not. Both codes predict similar vapor loss from ADS-4 (Figure 7.1-9). The resulting depressurization (Figure 7.1-10) allows IRWST gravity drain (Figure 7.1-11) to start. The time from ADS-4 actuation to IRWST injection is approximately 850 seconds for NOTRUMP, and 200 seconds longer for MAAP4. The IRWST level (Figure 7.1-12) decreases from the beginning of the event in NOTRUMP, while it does not decrease until IRWST injection starts in MAAP4. This difference is due to the MAAP4 input not modelling the second side of the DVI line break. It is not modelled because the small change in the elevation of the IRWST water level is not important for the duration of this analysis. Conversely, NOTRUMP over-predicts the decrease in the IRWST water leval, because the water loss is assumed to occur at the initiation of the break. However, squib valves would keep the pathway closed until the low-low water level is reached in a CMT. The conclusions from the accident analysis are drawn from the RCS mass inventory (Figure 7.1-13), the vessel mass inventory (Figure 7.1-14) and the core mixture level (Figure 7.1-15). The overall trends for this parameters are consistent between MAAP4 and NOTRUMP, with NOTRUMP predicting a more limiting minimum core mixture level. Section 8.0 provides the basis for the clad tempercre response remaining below 2200*F. The same conclusion of successful core cooling is drawn from either MAAP4 or NOTRUMP results. O Results of Sensitivity Cases Rev, O. Apru 1997 o \newprojNMBw-8 wpf itro41197
7-3 , V i t CASE 8B - DVI LINE BREAK
/ j 1
De second DVI line break analyzed as case 8b is a sensitivity to case 8. Case 8b is the same : scenario as case 8, except the CMT on the faulted loop loses its inventory out the DVI lin'e break. l' This has several impacts on the accident progression. The faulted CMT provides an earlier ADS actuation signal. Earlier ADS actuation is typically a benefit. But modelling the faulted CMT also provides a second pathway for inventory loss from the RCS through the break. Case 8b is analyzed to i demonstrate the net result of these effects. Case 8b is the benchmarking case most similar to a SSAR Chapter 15 DVI line break scenario. He difference in equipment assumptions are no PRHR, no accumulator, and no stage 1,2 or 3 ADS valves in case 8b. MAAP4 cannot directly model the faulted CMT. However, the effects of the faulted CMT can be :i modelled in MAAP4. De NOTRUMP prediction of the faulted CMT level (Figure 7.1-16) shows that the faulted CMT begins to drain within 100 seconds, and is empty within 300 seconds of the accident 1 initiation. His information is used to manually model the timing of the break path through the CMT and the actuation of ADS-4 in the MAAP4 input. MAAP4 models the xcond break path as a generalized opening at the top of the cold leg that opens 50 seconds into the event. De effective area , of the second pathway is based on a 3.7" flow restrictor in the DVI line (refer to Figure 3-1). The RCS pressure (Figures 7.1-17a and 7.1-17b) illustrates the more rapid accident progression that occurs due to the additional RCS inventory loss through the faulted CMT and the earlier ADS actuation. De inflections in the RCS prediction are the same for case 8b as case 8, but they happen ! sooner The intact CMT (Figures 7.1 18a and 7.1-18b) switches fmm recirculation to draining sooner in case 8b than in case 8 due to the additional RCS inventory loss through the faulted CMT. ADS-4 1 actuation (Figures 7.1-19a and 7.1-19b) occurs approximately 1000 seconds sooner due to the actuation signal conning from the faulted CMT. NOTRUMP shows the same rate of ADS-4 vapor loss when comparing case 8b to case 8, while MAAP4 shows a slightly lower vapor loss rate for case 8b compared to case 8. De detailed depressurization (Figures 7.120a and 7.1-20b) and integrated IRWST injection (Figures 7.1-21a and 7.121b) show that the time difference between case 8b and case 8 of approximately 1000 seconds is maintained through the accident progression. Le RCS mass inventory (Figures 7.1-22a and 7.1-22b), the vessel mass inventory (Figures 7.1-23a and 7.1-23b) and the core mixture level (Figures 7.1-24a and 7.1-24b) show that case 8b has lower inventories and mixture levels than case 8 for almost the first 30 minutes of the accident. NOTRUMP and MAAP4 predict the same trend, except MAAP4 does not predict a decrease in the vessel mixture level within the first 200 seconds that NOTRUMP predicts. He difference in the MAAP4 and t NOTRUMP predictions is due to MAiP4's limitation of not modelling se interfacial condensation at the top of the CMT, discussed in Section 2.2.4. O
. Results of Sensitivity Cases Rev.0, Apr01997
- o%ewpmj2\3603w-8.wptits04119,
7-4 Between ADS-4 actuation and the start of IRWST injection. both codes predict core uncovery for case 8, while both codes predict no core uncovery for case 8b. This is due to the availability of make-up coolant from the intact CMT. In case 8, the intact CMT provides the ADS-4 actuation signal, and is almest empty when ADS-4 valves open. In case 8b, the faulted CMT provides a much earlier ADS-4 actuation signal, allowing the intact CMT to provide make-up during the ADS-4 blowdown, maintaining a higher RCS inventory, compared to case 8. The DVI line break scenario analyzed as case 8b is a more probable accident than case 8, since the CMT isolation valve to the faulted DVI line will open most of the time. De comparison of case 8b to case 8 shows that the more probable scenario is less challenging to successful core cooling. The same conclusion can be drawn from either the MAAP4 or the NOTRUMP results. CASE 9 - 5" COLD LEG BREAK A 5" break at the bottom of the cold leg break is analyzed as case 9. He analysis and equipment assumptions are identical to benchmarking case 3, except the location of the break. Results from case 9 are compared to case 3 in Figures 7.1-25 to 7.1-35. Each figure includes an "a" plot showing NOTRUMP to NOTRUMP results, and a "b" plot showing MAAP4 to MAAP4 results. A break in the cold leg results in a higher initial break flowrate (Figures 7.1-25a and 7.1-25b) because the density of the water is higher. However, the elevation of the cold leg is approximately 1.7 feet ! higher than the hot leg, and the break location uncovers earlier. This causes the integrated water lost through the cold leg break to be less than the equivalent hot leg break over the duration of the event. There is more vapor loss from the break (Figures 7.126a and 7.1-26b) for the cold leg break location, although the total water plus vapor loss is less for the cold leg. The CMT behavior (Figures 7.1-27a and 7.1-27b) is relatively unaffected by the break location, although CMT draining occurs seconds earlier for the cold leg break due to the higher inventory loss. When the CMT reaches the low-low level setpoint, the hot leg is filled with water. Both MAAP4 and NOTRUMP predict water relief from ADS-4 (Figures 7.1-28a and 7.1-28b) when the ADS-4 valves open. However, the vapor relief from ADS-4 (Figures 7.1-29 and 7.1-29b)is relatively unaffected by the break location. The overall RCS pressure (Figures 7.1-30a and 7.1-30b) trends are similar for either cold leg or hot leg break location, with MAAP4 and NOTRUMP predicting the same minor deviations. The detailed pressure in the downcomer (Figures 7.1-31a and 7.1-32b) shows that the depressurization down to the range that allows IRWST injection occurs approximately 50 seconds later for the cold leg break than the hot leg break. Both codes predict similar delays in the start of IRWST injection (Figures 7.1-32a and 7.1-32b), but the minimum RCS inventory (Figures 7.1-33a and 7.1-33b) and vessel inventory (Figures 7.1-34a and 7.1-34b) are higher for the cold leg break location. The vessel mixture level (Figures 7.1-35a and 7.1-35b) shows that both codes predict a higher minimum mixture level for the cold leg break compared to the hot leg break. NOTRUMP predicts that the mixture level tums around Results of Sensitivity Cases Rev. 0. Apnl !W7 owwpro;A%0b8 mptit> o41197
s 75' immediately prior to core uncovery. While MAAP4 predicts the tumarou:)d immediately after the top of the core uncovers. The trends of the cold leg break analysis compared to the hot leg break analysis . are the same for both codes.
Ihis sensitivity illustrates why the MAAP4' analyses supporting the PRA focus on hot leg breaks rather than cold le'g bxaks. Although both the hot leg break and cold leg break show similar trends and they both' result in successful core cooling, the hot leg break is slightly more limiting due to its lower elevation.' Event tree modelling in the PRA does not differentiate hot leg and cold leg breaks; sets of success criteria are defined as applicable to either break location. Since most successful core cooling scenarios in the PRA have a large margin to core damage, analyses of either' the hot leg or the cold leg as the break location would not impact the results or conclusions of the PRA.'. Nevertheless, the MAAP4 analyses are generally performed modelling hot leg breaks, to provide greater assurance that all possibilities are considered and bounded, for the multiple equipment failure scenarios modelled in PRA events.
c h O Results of Sensitivity Cases. Rev. O. Apnl 1997 chwprop0603w.8.wpr:lb 041197
t' 7-6 0 Figure 7.1-1 RCS Pressure for case 8 DVI Line Break. 1 CMT injecting NOTRUMP
---- MAAP4 2500 _
n - o , 2000 -- m - C. 1500 - - S _"'
' ~3 1000 -- s a -
s m : N s m - s e 500 -- 's - ~ ~i u : ) C- \ 0 l l l , ; ; ; 0 500 1000 1500 2000 2500 3000 3500 4000 Time (s) 4 O Results of Sensitivity Cases t Rev. O. Apn! 1997 o Wwpro3N603*,8 wpf:Ib 041197 -
A a sa . . . p. s. .,_a-na n ru. . ~3+.--a a. , n e a I 77 , ?
.j 9
9 4 h F Figure 7.1. : 7 B r e.a k- Integrated Water f o r- case 8 DVI Line Break, 1 CMT I n j e c t i n g. - NOTRUMP MAAP4 i 400000 _
~
350000 -2 . y 300000 -f
.q .c ;
__ 250000 - g: ,g i . 200000 -E /
]
; / i m 150000 -;
m : / 100000 -;f ,
=E : !
50000 - 0- l l l l l l l 0 500 1000 1500 2000 2500 3000 3500 4000 Time (s) nu
- Results of Sensiuvity Cases Rev. O. Apnl 1997 j owwpng3603w.s.wpt:Ib44 197.
7-8 O Figure 7.1-3 Break Integrated Vapor for case 8 DVI Line Break, 1 CMT injecting NOTRUMP
- - - - - MAAP4 120000 _
~
100000 -- - n E : ~~____
.c 80000 --
v e, 60000 -- -
/
l O -
/ l cn 40000 -- f i o : /
1 .. / 20000 -- .
/
i
~
/
~
0
'; l 1 l 'l l l 0 500 1000 1500 2000 2500 3000 3500 4000 Iirne (S) l O
Results of Sensitivity Cases Rev. 0. Apnl 1997 owwpojh360) 8.wpf:Ib-041197 r. {
-79 1
7._
/\v/ -
l i
)
Figure 7.1-4 CMT Water i nventory. for , case 8 l DVI Line Break. 1 CMT In.jecting NOTRUMP
----MAAP4 :
140000 ,_ 120000 - - N m \ l g 100000 -- N B (" --
~
\
'V 80000 -- N s
v .
- A cn .60000 - - A s i Ch -
s C 40000 - ' 2 : s s 20000 -- s [ s 1 O i l l 'l l 0 500 1000 1500 2000 2500 3000 3500 4000 IIme (S)
.G/
Results of Sensmvity Cases Rev. O, Apnl 1997 owwprojN603w-8.wpf.lb-041197
7 10
~~
O Figure 7.1-5 CMT Level for case 8 DVI Line Break. 1 CMT injecting NOTRUMP
----MAAP4 25 _
m 20 -fs _ v 15 - -
~ ! s =: .. s m 10 -- s ._ : s e -
s I ' 5 s
\
s
~
N 0 l l l l l 0 500 1000 1500 2000 2500 3000 3500 4000 Time (S) e Results of Sensitivity Cases Rev. O. Apnl 1997 owupro)N603w-8 wpf:lb441197
~
7 11 n
/7 (s. .
~!
Figure 7.1-6 Hot. Leg. Water L.e v e l for case 8 DVI Line- Break, 1 CMT injecting NOTRUMP Unbroken L'oop
----MAAP4Both Loops
. -t- - - - N O T R U M P 8roken Loop '
30 v
,7 c
i ,ygt,;g n ;g
$ / 1 28 --
1 / i' . il ! i j
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a: , en 2 4 -- A. p .=.=.= .2f e ip - _ $ ' _ _- 1 cu I 22 -- 3 20 l l l l l l l 0 500 1000 1500 2000 2500 3000 3500 4000
- Time (s) l-a A
~% __ - (f Results of Sensitivity Cases Rev. O Apnl 1997 s_, o%emproj20'03w4.mpf:1b 041197
7 12 O Figure 7.1-7 Pressurizer Level for case 8 DVI Line Break, 1 CMT Injecting NOTRUMP
----MAAP4 20 m -
~
s a 15 -- c) v O 10 -- l
.C Cn o 5- .
I 0 ;l' l l ' * *- [ * l l l l 0 500 1000 1500 2000 2500 3000 3500 4000 l Iime (s) O Results of Sensitivity Cases Rev. O. Apn! 1997 l o.VwwproiN603w.8 *pf:1b-041197 l
7-13: c: l*
\/
s 9 a 4 Figure 7.1-8
- ADS-4lntegrated Water f'or case 8
.D V I L i.n e Break, 1 CMT Injecting
, NOTRUMP-1 - ---MAAP4
- 100000
~
G
'O 75000 --
.A -
.x ,
~
50000 -- en
~
CD 2 25000 - f
~
~
4 o l l l' ; ; l l 0 500 1000 1500 2000 2500 3000 3500 4000 a Time (s) f i a
)
.d y s'
- ' Results of Sensitivity' Cases Rev. 0, Aptd 1997
. oWwprojN603* 8.wpf:tb-041197
7 14 O Figure 7.1-9 ADS-4 Integrated Vapor for case 8 DVI Line Break, 1 CMT Injeeting NOTRUMP MAAP4 125000 -
~
m 100000 -- , E - .c - 75000 --
~
h
- /
.m 50000 -- ' m : - [ / 2 25000 --
~
I
~
0 ! ! 'l ! l 0 500 1000 1500 2000 2500 3000 3500 4000 Iime (s) O Results of Sensitivity Cases Rev. O. Apnl 1997 ohwpro12\3603w 8 wpf.lb-(Mil 97
I 7 15 1 'h Figure 7.1-10 Detailed Downcomer Pressure for case 8 DVI Line Break, 1 CMT Injecting NOTRUMP Downcomer ,
---- MAAP4 RCS 50 _ !
i
- : i o 45 -: i j i
M i c _ 4 0 ,E-s 35
's s^
ca : u 30 -- s % ,, a : N
- 25 -; "
u 20 -- CL :
~
15 l l l l l l l 0 500 1000 1500 2000 2500 3000 3500 4000 Time (S) s , Results of Sensitivity Cases Rev. o. Apnl 1997 owwpro)20603w-8.wpf.ib4til97
7 O c Figure 7.1-11 IRWST integrated Injection for case 8 DVI Line Break, 1 CMT Injecting NOTRUMP
---- MAAP4 150000 ,
120000 -
^ :
E - w 90000 --
~
- /
f h
/ " 60000 -: l m : /
O - /
. ::E : /
/
30000 - -
- /
~
0 l l l l , l l 0 500 1000 1500 2000 2500 3000 3500 4000 Iime (s) 1 O Results of Sensitivity Cases Rev. 0. Apnl 1997 o wewprojA%03w 8 wpf:1b441197
.- a .a- . . - , a- a a as-- -a., ,,n; sa. 2 L 'j c
~
~ 7-17' ;;
-s ;
[L)? :
-t
'l
'f Figure - 7.1 -12.
r IRWST Level- for - case 8 DVI L i n e. Break, 1 CMT Injecting. ; NOTRUMP
---MAAP4 ,
60 5 0 -- _ s % . U v. :. 30 g-e :.
- 20 4 I-
_J _ 10 -_
- )
~
l I i f I f f 0 ' 5$0 1000 15'00 20'00 25'00 30'00 35'00 4000 , Time (s) l
)
l i ( -. ( - Results of S*nsitivity Cases Rev. O. Apnl 1997
; c:WewprojN603w.8.wpf.lb-041197 .
7 18 - O Figure 7.1-13 RCS Mass inventory for case 8 DVI Line Break, 1 CMT Injecting NOTRUMP MAAP4 350000 __ 300000 - m : E 250000 -- _a : s g4 200000 - \ W v : \ m 150000 - f s m : _\ p __ - C l'10000 - '
~~
1 _ _ ,
- ~~, ~,-
50000 -- '
~ '
0 l l l l l l 0 500 1000 1500 2000 2500 300.0 3500 4000 Time (s) l j O Results of Sensitivity Cases Rev. O. Apnl 1997 owwpro310603w-B wpf:IWI197
i
- 19. l l
. A): -i <
j 2 i
- Figure -7.1-14 .j
. V e s :s e' l Mass. Inventory f'o r e a s e.8 DVI Line Break. 1 CMT InjectEng- :i NOTRUMP' MAAP4 100000 ' .
- . 1 t ___
l N / l 80000 -- - s /. m -- s ,
,^.
E : ' s /
/
p -
\
w( -_ 60000 - - s
/
/
s'
- l m 40000 --
.m -
o :. ;
=E -
20000 - - ,. v - s i,. , i i , i i , 0
.0 5d0 10'00 15'00 20'00 25'00 30'00 35'00 4000 Time (s)
^ i
'\q' - <
- Results of Sensitivity Cases Rev. 0. Apnl 1997 ,
, g;c -iowwyroj20603w s.wpt:Ibest 97 l
7-20 O Figure 7.1-15 Core Mixture LeveI for case 8 DVI Line Break, 1 CMT Injecting . HOTRUMP
----MAAP4
-{- - - - Top of Core
_ 30 _ ~ 26 --
~_ ___________ W ___\ /
e 22 -1 N s
/
g o 18 -
.._._._.+
_._._.__)._._._._ +._._. ; ._. ._._s sl ._ _.4 ,_._._ t_._._. 3 o 14 - - w - m - ~ x 10 -- _
~
2 6 0 5d0 10'00 15'00 20'00 25'00 30'00 35'00 4000 Time (s) l l I O Results of Sensitivity CASCs Rev. 0. Apnl 1991 owwpro)N603w 8 wpf:Ibell197 I
.l 7-21 i
1 j 'Ld) , 1 1 l l I Figure 7.1-16
]
NOTRUMP FauIted CMT LeveI ! DVI .Line Break Sensitiv.ity, Auto ADS 1 Faulted CMT. Drains (Case 8b). ;
.25 n
20 - D-v 15 -
.c : }
en10- - cu _ r - 5--
~
k . O l l l l l l l 0 500 1000 1500 2000 2500 3000 3500 4000 i Iime (S) i i 3 k ); s Results of Sensitivity Cases Rev. D. Apnl 1997 o.wwproj20603w-8 wpf:1bedi197 '
7 22 Figure 7.1-17a g NOTRUMP RCS Pressure DVI Line Break Sensitivity. Auto ADS Faulted CMT Not Modelled (Case 8) FauIted CMT Drains (Case 8b) m 2500 _ o 2000 -i a : 4 " 1500 --- o
- 1000 -; s 3 N l
500 -i 's 0 ,~ 3 s 1000 i 1500 ( i 2000 2500 l 30'00 35'00 4000 0 500 Time (s) Figure 7.1-17b - MAAP4 RCS Pressure DVI Line Break Sensitivity. Auto ADS Faulted CMT Not Modelled (Case 8)
----Faulted CMT Drains (Case 8b)
_ 2500 _ o :
% a 2000 -i 1500 --- , x ; 1000 -
500 -5 \ - a-i '] ---1 ' ' ' 0.- ' 0 500 10'00 15'00 20'00 25'00 3000 35'00 4000 Time (s) i Gil 4 Results of Sensitivity Cases Rev. O. Apnl 1997 ohwpro3N60.1w4 wpf.lb-04I197 i l l
7-23 !
- rigure 7.1-18a NOTRUMP~ Intact CMT Level '
DVI L~i n e Break Sensitivity, Auto ADS
'F o u i t e d CMT Not Modelled (Case 8) ;
----Faulted CMT Drains (Case.8b) I 25 _
m _ ,
- : i
_ 20 -: s v : s
; s
- i s s
i c 10 _:- s s en s > 5-o : 's 1 2 . , e Nm e i e t , 0 , , i, , i ; O 500 1000 1500 2000 2500 30'00 35'00 4000 ' Time (s) :
~
C< rigere 7.,-,8s MAAP4 l n t'a c t CMT LeveI . DVI Line Break Sensitivity. Auto ADS ! FouIted CMT Not Modelied (Cose 8) ,
----Fouitec CMT Drains (Case 8b) l 25 _
^ -
i
. 20 -m s v :
.15 -? s
- : 's
. _c 10 - 's m i
's s-3_
, ,' , , , i 0 , ,i , , , , ,
. O. 500 1000 1500 2000 2500 3000 3500 4000 Time (s)
~ Results of Sensiuvity Cases Rev. 'J. Apnl 1997
= 0:WewproJ20603w-8 wpf:lb-Odll97 1
l 7 24 Figure 7.1-19a NOTRUMP integrated ADS-4 Vapor O DVI Line Break Sensitivity. Auto ADS Foulted CMT Not Modelled (Case 8)
----FouIted CMT Drains (Case 8b) 100000- '
m : ' f 80000 -~ ,- v 60000 -- - 40000 -~ ,- U - / 20000 - j e
~
~
_. t / 1 i t 't i f 0- ' ' ' 0 500 1000 1500 20'00 25'00 3000 35'00 4000 Time (s) Figere 7.1-19b h MAAP4 Integrated ADS-4 Vapor DVI Line Break S e ii s i t i v i t y . Auto ADS FcuIted CMT Not Modelled (Case 8)
----FauIted CMT Drains (Case 8b) 100000 _. -
E ,- n 80000 -f - v 60000 -- ,- 40000 f- - m : ,
* ~
20000 - e 2 ~ 0 ' ' 0 Sd0 10'00 15'00 2000 25'00 3000 35'00 4000 Time (s) O Results of Sensitivity Cases Rev. O, Apnl 1997 o \newproJN603w-8.wpf:1b-04) l97
7-25 Figure 7.1-20a-NOTRUMP DetaiIed D o w n c o rn e r Pressure D.VI- Line B rie a k Sensitivi'ty, Auto ADS Foulted CMT Not Modelled (Case 8)
----Faulted CMT Drains (Case 8b) m 50 ;
e - \ \ 45 -5 1 \
\
m 40 -! s 35 -5 -
\
N
$ 30 -E 's
" ' ~~
m 25 -! ~ __-- y u 20 -i - 15 'l l l l l 'l 0 500 1000 1500 2000 2500 3000 3500- 4000 Time (s) n b Figure' 7.1 -20b MAAP4 Detoiled RCS Pressure DVI Line Break Sensitivity, Auto ADS l Faulted CMT Not Modelled (Case 8)
----Faulted CMT Drains (Case 8b) I
_ 50 , e ~
.- 45 -?' \
m : \ l
- c. 4 0 -E g l
1 35 -i 's ., s ! o E 'N l m 30 -: 's, , e : ~s
= 25 -i m : ".,,s.,'" --.'.._,
~
- 20 -E 6
. CL - '
15 ' 0 5d0 10'00 15'00 20'00 25'00 3000 35'00 400 0 IIme (S) ; n ! O Results of Sensitivity Cases Rev. 0. Apnl 1997 o\newproj2\)603w 8.wpf:Ib<97 i i
7 26 - Figure 7.1-21a NOTRUMP integrated IRWST Injection 9 DVI Line Break Sensitivity. Auto ADS F o u l.t e d CMT Not Modelled (Cose 8)
----Fouited CMT Drains (Case 8b) 100000 _
m -
/
E 80000 -i ,' _o . , C 60000 -~ , m 40000 -} ,' o 20000 - f ,- =E _ - 0 l' l' t' l , 'l 'l 0 500 1000 1500 2000 2500 3000 3500 4000 Time (s) Figure 7.1-21b h MAAP4 integrated IRWST injection DVI Line Break Sensitivity, Auto ADS Fauited CMT Not Madeiled (Case 8)
----Feuited CMT Drains (Case 8b) 100000 _
m - / E 80000 -~ ,
.c _
C 60000 -j ,'
- /
m 40000 -- ,
/
m : / o 20000 -- ,'
=E -
0 l l
'; l l l 0 500 1000 1500 2000 2500 3000 3500 4000 Time (s)
G, i Results of Sensitivity Cases Rev. O. Apnl 1997 o Wwpro)N603* 8 wpf:1b-04I197
7 27" Figure 7.1-22a NOTRUMP RCS Inventory-DVI Li-n'e Break Sensitivity, Auto ADS Toulted CMT Not Modelled (Cose 8) _---Foulted CMT Drains (Case 8b)- 400000 .
) 300000 - ,
\
200000 -I t w ~\ _ \ _ _ _ _ _ _ ~ .
* ~
100000 -- _,
=s : ' ' '
0 'l l l l 0 500 1000 1500 2000 25'00 30'00 35'00 400(I Time (s) Figure 7.1-22b MAAP4 RCS Inventary DVI Line Break Sensitivity. Auto ADS
~
cuIted CMT Not Modelleo (Case 8) Faulted CMT Drains (Case 8b) 400000 _
~
j 300000 -
~\ " 200000 - \
m :s
- \
100000 -- - _ _ _ _7
= : ,
0 l l l ; ; ! l 0 500 1000 1500 2000 2500 3000 3500 400() Time (s) Results of Sensitivity Ctes Rev. O, Apnl 1997 c:\newproj2\3603w-8.wpf. lb-041197
7,20 Figure 7.1-23a g NOTRUMP VesseI inventory DVI Line Break Sensitivity, Auto ADS Fouited CMT Not Modalled (Case 8) Faulted CMT Drains (Case 8b) 160000 E ~ o 120000 - i v - ' 80000 - } 's e\ ~ s - m - 40000 -1 o - CE : 0 l l l l l l ! 0 500 1000 1500 2000 2500 3000 3500 4000 Time (s) L_ Figure 7.1-23b MAAP4 Vessel Inventory DVI Line Break Sensitivity, Auto ADS r euited CMT Not Modelled (Case 8)
----Foulted CMT Drains (Case Sb) 160000 - :1 E
o 120000 --t __ : i
~~----'---------------
80000 -} w - o 40000 -{ 25 : 0 l l l l l l 0 500 1000 1500 2000 2500 3000 3500 4000 Time (s) O Results of Sensitivity Cases Rev. O. Apnl 1997 o \newpro32\3603w-8 wpf.lb4 Mil 97
7-29 o. t v Figure 7.1-24a. NOTRUMP Mixture Level i DVI -Line Break Sensitivity. Auto ADS
*Foulted CMT Not Modelled (Case 8)-
, ----Foulted CMT Drains (Case 8b)
+---Top of Core
_ 30 i 6- ._,_- ___,________ __n,-______ __ l
; 22 -;\/ !
, .._._._. ; ._._._. ;._._._._+._._._. ._._._._.+_. .+ _._._.+ _._ j
- 18 -i - -
.i
- 14 -i 1
~; 10'-
5 6
,i i
i 0 500 1000 1500 2000 2500 3000 3500 4000 Time (s) n i U Figure 7.1-24b MAAP4 Mixture Level DVI L i n'e Break Sensitivity, Auto ADS Pcuited CMT Not Model' led (Case 8)
----Faulted CMT Drains (Cose 8b) 4- - - T o p of Core
_. 3 0 _ C26-5 _________ _. 22 -
,.- .; ._._._. ;._._._._ +._._._. ; ._. ._._.+._._. +_._._.+._._
*s 18 -_ -
*o 14 -i -
~; 1 0 -i
" 6
~ ' ' '
0 5b0 10'00 15'00 20'00 25'00 30'00 35'00 400 0 Time (s)
.ixs -,
i Results of Sensitivity Cases Rev. O. Apnl 1997 ONiem1xoj2\3603w.8 wp(;lb.041197
7-30 Figure 7.1-25a g NOTRUMP Braak Integroted Water 5.0 Inch Break with 1 CMT, Auto ADS Hot Leg IJreak (Case 3)
---- Cold Leg Break (Case 9) 400000 E -
4 300000 -~ ' 200000 -i ,' m i' m 100000 -- o - 2 . . . 9 l ! l 0 500 1000 1500 2000 2500 3000 Time (s) Figure 7.1-25b W l MAAP4 Break Integrated Water 5.0 inch Break with 1 CMT, Auto ADS Hot Leg Breok (Case 3)
---- Cold Leg Break (Case 9) 400000 E :
o 300000 -i _ 200000 -- i~ / g -/ m 100000 -3/ o - 2 ' ' ' ' ' 0 ' 0 5d0 1000 15'00 20'00 25'00 3000 Time (s) O Results of Sensitivity Cases Rev. O. Apnl 1997 chwproJN603w 8 wpf:lMs1197
7-31 I g Figure 7.1-26a NOTRUMP Break Integrated Vapor 5.0 Inch Break with 1 CMT, Auto ADS
'H o t Leg Break (Cose 3)
----Cold Leg Breck (Case 9) 120000 _
~
E 100000 -5 ' o : - 80000 -E ,- 60000 - f ,- m 40000 -j ,' i m - i l a 20000 -E , i E ' 0 l l l ! ! 0 500 1000 1500 2000 2500 3000 Time (s) Figure 7.1-26b ; MAAP4 Break integrated Vapor 5.0 Inch Break with 1 CMT, Auto ADS Hot Leg Break (Cose 3)
----Cold Leg Break (Case 9) 120000 _
~~~~~~~~~~~~
E 100000 -! o - 80000 -E ,- 60000 -5 ,- m 40000 -; / m i ,' a 20000 -E , 0 l l l l l 0 500 1000 1500 2000 2500 300 0 Time (s) Results of Sensitivity Cases Rev. O. Apnl 1907 o Wrmproj20603w-8 wpf:Ib481197
- 32 Figure 7.1-27a g NOTRUMP CMT Level 5~. 0 Inch Break with 1 CMT. Au+a ADS
' Hot Leg Breck (Case 3)
Cold Leg Breck (Case 9) 25 ^ 5 [ 20 -i: v 15 -i
-~ :
c& 10 -i 5-o :
= i i t t t 0
0 5b0 10'00 15'00 20'00 25'00 3000 Time (s) Figure 7.1-27b MAAP4 CMT Leve1 5.0 Inch Break with 1 CMT, Auto ADS Het Leg Break (Ccse 3)
----Cold Leg Break (Case 9) 25
^ w b
. 20 _
v : 15 -i r 10 -: 5-: o :
" ~
0 l l l l 0 500 1000 1500 2000 2500 3000 Time (s) O Results of Setisitivity Cases Rev. 0. Apnl 1997 o WwprojN603w 8 =pf:1b-041197
7 l F F Figure ' 7.1-28a : U ! NOTRUMP ADS-4 Integrated Water 5.0 , Inch Break with 1 CMT, Auto ADS : H o t' Leg Break (Case 3)
- - - - C o'f d Leg Breck (Case 9) ,
I 100000 E - i 4 75000 -1 - r
~
.50000 -- i
- l
- m. -
m- 25000 - ('
'O : i 2 -
0 ' 0 500 10'00 1500 , 20'00 25'00 3000 Iime (sj s D V Figure 7.1-28b MAAP4 ADS-4 integrated Water 5.0 I n c h. Break with 1 CMT, Auto ADS Hot Leg Break (Case 3)
----Cold Leg Break (Case 9) l 1
100000
~
E o 75000 - l' 50000 -} _ m m 25000 - l---------------- a ': I j 0 l : 0 '500 1000 1500 2000 2500 3000 p Time (s) .t V Results of Sensitivity Cases Rev. O. Aprd 1997 j ohwprojN603* 8 wpf;lb-oei197 l
7 34 i Figure 7.1-29a g NOTRUMP ADS-4 Integrated Vapor 5.0 Inch Break with 1 CMT, Auto ADS
. Hot Leg Break (Case 3) ----Cold Leg Break (Case 9) 100000 E :
4 75000 -- 50000 - - m : ' m 2.5000 -- , o 2 : , , 0 0 5d0 10'00 15'00 20'00 25'00 3000 Time (s) Figure 7.1-29b MAAP4 ADS-4 Integrated Vapor 5.0 Inch Break with 1 CMT, Auto ADS Hot Leg Break (Case 3) Cold Leg Break (Case 9) 100000 E i 4 75000 -- 50000 - - m : ' m 25000 -- - o - 0 l l l l l 0 500 1000 1500 2000 2500 3000 Time (s) O Results of Sensitivity Cases Rev. O. Apnl 1997 ohwprogG603w 8 wpf Ib-Gal 197
7-35 qU . Figure 7.1-30a NOTRUMP RCS-Pres _sure ' 5.0 inch Break with 1 CMT, Auto ADS
' Hot Leg Break (Case 3)
Cold Leg Break-(Case 9) l _ 2500 _ o- : n. 2000 -i - 15 0~0 - - o J 1000 -: s 5' : s s 500 -2 2 0 5 .,,,.. , l- A , , 0 580 10'00 15'00' 20'00 25'00 3000 Time (s) nU Figure 7.1-30b i 1 MAAP4 RCS Pressure 5.0 lnch Break with 1 CMT, Auto ADS Hot Leg Break (Case 3)
----Cold Leg Break (Case 9) m 2500 _
o : I 2000 -- a E
~
1500 -L
.a
'o
--1000 - s j
=>
m s j 500 - 2 0 i , ~7 A , , ;) 0 5d0 10'00 15'00 2000 25'00 3000
/,,~
Iime (S) '(g Results of Sensitivity Cases Rev. O. Apnt 1997 onnewprojA3603w-8.wpf:IMM t197
7-36
. Figure 7.1-31a Pressure O
NOTRUMP Detoiled Downcomer 5.0 I n c'h Break with 1 CMT, Auto ADS
-H o t Leg Break (Case 3)
----Cold Leg Break (Case 9)
_ 50 _ o - \
.- 45 -E s m : s a40-? s V
2 \ 35 -E s 5 \ ' s 30- E _' m m 25 -: -
- 20 -: i
' 15 l l l l l 0 500 1000 1500 2000 2500 3000 Time (s)
Figure 7.1-31b h MAAP4 Detoiled RCS Pressure 5.0 Inch Break with 1 CMT, Auto ADS Hot Leg Break (Case 3)
---- Cold Leg Break (Cose 9) 1 m 50 ; i
\ i
.? 4 5 -5 \ \
m 5 a40-? \ l 35 -} b_
"' 3 0 -5 ~s, )
l
= 3 ,
m m 25 -: '
~
s, ;
- 20 -j 2
' 15 l l l ; l-0- 500 1000 1500 2000 2500 300 0 Time (s) ;
Results of Sensnivity Cases . Rev O, Apnl 1997 oMewproj2\3603w 8 wpf:lb-041197
7-37 Figure 7.1-32a O NOTRUMP Integrated IRWST l'n j e c t i o n 5.0 inch Break with 1 CMT, Auto ADS
' Hot Leg Break (Case 3)
---- Cold Leg Break (Case 9) 100000 ,
E 80000 -2 -!
.c :
C 60000 -~ m 40000 -2 - m- : - o 20000 -- ,' 2 : - 0 l l l l 'l 0 500 1000 1500 2000 2500 300(I Time (s) Figure 7.1-32b MAAP4 Integrated IRWST Injeetion 5.0 Inch Break with 1 CMT. Auto ADS Hot Leg Break (Case 3)
----Cold Leg Break (Case 9) 100000 ._
E 80000 -
-o C 60000 -
m 40000 -3 m : 20000 - , a- - 2 : ,' 0 l l l l l 0 500 1000 1500 2000 2500 300(I Time (s) Results of Sensitivity Cases Rev, O. Apnl 1997 o,\newproj2\)603w 8 mpf.lb-041197
7 38 l Figure 7.1-33a ; NOTRUMP RCS Inventory 5.0 inch Break with 1 CMT, Auto ADS !
" Hot Leg Break (Case 3) l
---- Cold Leg Breok (Case 9) 400000
) 300000 -
" 200000 -I- ~
\
\
W m
- s
~- ~~~~____,'~~' '
a 100000 -: __ 2 : 0 l l l l l 0 500 1000 1500 2000 2500 3000 Time (s) Figure 7.1-33b MAAP4 RCS inventory 5.0 inch Break with 1 CMT, Auto ADS Hot Leg Breck (Ccse 3) ,
----Cold Leg Break (Case 9) 400000 m :
) 300000 -
~
200000 -- m - E'~~~~~~~~
~
m a 100000 - -
- \-- _ n ___ -
2 : 0 l l l l l 0 500 1000 1500 2000 2500 3000 Time (s) O Results of Sensitivity Cases Rev. O. Apnl 1997 o%ewpro3N603w 8 wpf;lt904tl97
J 7-39 Figure 7.1-34a
.QO)
'NOTRUMP. Vessel Inventory.
5.0 I n c h- B r.e a k with 1 CMT, Auto ADS Hot Leg Break (Case 3) CoId Leg Break (Case 9) 160000
- m. i E -\ i o 120000 -- - ~~,_\
__. : \ _ l s ~~_ s 80000 - -- -
~~,
m -
* '40000 - l c -
~
OE ~ 0 l ! l l l I 0 500 1000 1500 2000 2500 3000 Time (s) : e,. b Figure 7.1-34b
]
-MAAP4 Vessel Inventory '
5.0 Inch B r e a '< with 1 CMT. Auto ADS
--Hot Leg Break (Case 3)
Cold Leg Break (Case 9) 160000 m : i E - ' ' 120000 -- \ o
\ ~_____-1 i m
80000 -
- ~,
m
.a 40000'- -
- E : ' '
0 l l l l l 0 500. 1000 1500 2000 2500 3000 IIme (s) ,
.%A Results of Sensitivity Cases Rev. 0, Apnl 1997 L .- ohwprojhM03w 8 wpf.It>481197
rao Figure 7.1-35a g NOTRUMP Mixture Leve1 5.0 Inch Break with 1 CMT, A u t.o ADS
' Hot Leg Break (Case 3)
----Cold Leg Break (Case 9)
-t- - - - T o p of Core .
,, 30 _
C26-- ____________s_,, 22 -5 ~ s N
..-.-..'.C.
g m. . . . - . . .....
._.....l . . .-. . . . . . - .
a 14 -i -. ~ 10 -
- , i ,
Ei .i , ,i 6 0 50 10'00 15'00 20'00 25'00 3000
~fime (s)
Figure 7.1-35b MAAP4 Mixture Leve1 5.0 Inch Break with 1 CMT. Auto ADS Hot Leg Break (Case 3)
----Cold Leg Break (Cose 9)
-t- - - - T o o of Core
,. 3 0 _
C26-i ' ' ~ ~ '
.22-_ s -
y
~
e.....-.. . - . . . . . , . . . . , , , , . . . l . . , , . . _ . _ . _ . . , , , . ,_._,_\ g,_',_ a . _
=
14 -[ -
~; 10 -i " 6 0 580 1000 15'00 20'00 25'00 3000 Time (S)
O Results of Sensitivity Cases gev. o. Apni i997 ovewproR3603w.8 wpf.1b.041I97
7-41 i 7.2 Number of CMTs and Accumulators () The second type of sensitivity analysis is to the number of CMTs and accumulators credited. Re primary benchmarking cases credit either one CMT or one accumulator. Accumulators are designed for rapid inventory make-up when the RCS pressure falls below 715 psia. CMTs are able to provide inventory make-up at higher pressures, but cannot inject as rapidly as accumulators. When both CMTs or both accumulators are lost, there is a greater potential for core uncovery because the function of the j lost tanks is unfulfilled. The primary benchmarking cases 1 to 7 assume either a functioning accumulator or a functioning CMT, but never both. i l The first sensitivity to the number of tanks, case 10, shows the impact of crediting an accumulator in ! addition to a CMT in an automatic ADS scenario. No sensitivity is shown of adding a CMT to an ] accumulator-only scenario, since this would fundamentally change the scenario from manual to ] automatic ADS actuation. He second sensitivity to the number of tanks, case 11, shows the impact of crediting both CMTs and both accumulators. His sensitivity illustrates that as long as there is at least 1 CMT and one accumulator, the conclusion of whether the core uncovers is not impacted by whether there are multiple CMTs or multiple accumulators. CASE 10 - 5" BREAK WITH 1 CMT AND 1 ACCUMULATOR The first sensitivity to the number of tanks is case 10, which credits 1 CMT and I accumulator for a 5" hot leg break. This case is identical to case 3, except one accumulator is credited in case 10 compared to no accumulators in case 3. The comparison of these cases demonstrates that the accumulator makes the difference of whether core uncovery occurs. He break size of 5" is chosen because it is a size for which it is not intuitively obvious that the accumulator would prevent core uncovery. 'It is clear to see that small breaks at a high RCS pressure when ADS is actuated would benefit from the rapid inventory injection of an accumulator. Likewise, larger breaks would experience the benefit of an accumulator early in the event. But the effect on an intermediate size is i not as clear-cut, and therefore, the size of 5" is chosen. 4 The decrease in the accumulator inventory (Figures 7.2-la and 7.2-lb) shows that both MAAP4 and NOTRUMP predict gradual accumulator injection starting around 500 seconds when the RCS depressurizes below 715 psia. Over the next 1000 seconds, the accumulator injects approximately one-third of its inventory, as the RCS slowly depressurizes. When ADS-4 valves open, the RCS depressurizes rapidly, emptying the accumulator within a couple hundred seconds. Both MAAP4 and NOTRUMP predict the same accumulator response. The CMT injects more slowly when there is accumulator injection than when there is no accumulator injection. The CMT level (Figures 7.2-2a and 7.2-2b) is similar for case 3 and case 10, but decreases at a slightl3slower rater when 1 accumulator is modelled in case 10. When comparing the CMT injection to the accumulator injection, the CMT provides higher injection flow than the accumulators (j while the RCS pressure is gradually decreasing. However, when ADS-4 is actuated and the RCS Results of Sensitivity Cases Rev. O. April 1997 ohwproja3603w.9.wpf:lt441197
7-42 pressure decreases rapidly, the CMT injection totally stops while the accumulator injects. MAAP4 and NOTRUMP both predict this behaviar, which has also been seen in testing associated with the AP600 plant. De RCS depressurization (Figures 7.2-3a and 7.2-3b) is generally slowed by accumulator injection. However, when the RCS pressure decreases to the low range (Figures 7.2-4a and 7.2-4b) associated with IRWST injection, depressurization is easier because of the subcooling in the downcomer provided by the accumulator. IRWST injection (Figures 7.2-Sa and 7.2-5b) occurs hundreds of seconds earlier when an accumulator is modelled than when no accumulator is modelled. The RCS inventory (Figures 7.2-6a and 7.2-6b) and the vessel inventory (Figures 7.2-7a and 7.2-7b) show that the accumulator is a benefit. The impact on the vessel mixture level (Figures 7.2-8a and 7.2-8b) is that the accumulator prevents core uncovery. His is a successful core cooling scenario with no core uncovery, although there are many assumed equipment failures including PRHR,1 CMT, I accumulator, all stage 1,2 and 3 ADS, and no containment isolation conservatively modelled with an atmospheric containment pressure. CASE 11 - 5" BREAK WITH 2 CMTS AND 2 ACCUMULATORS The second sensitivity to the number of tanks is case 11, which is the same 5" break as case 10 with 2 CMTs and 2 accumulators. His case is selected to demonstrate that the accident progression for 1 CMT and I accumulator is similar to 2 CMTs and 2 accumulators. This similarity is used in the T/H uncertainty resolution process to help group accident scenarios into categories with similar system responses. The total accumulator inventory available for injection (Figures 7.2-9a and 7.2-9b) shows that both codes inject two accumulators faster than one accumulator. However, NOTRUMP predicts that two accumulators empty approximately 100 seconds sooner than one accumulator, while this time difference in MAAP4 is approximately 500 seconds. The difference in the accumulator injection is due to pressure differences, which ara discussed after the CMTs below. The response of a CMT (Figures 7.2-10a and 7.2-10b)is unaffected by the presence of another functioning CMT (Figures 7.2-11a and 7.2-11b). Both CMTs in case 11 drain at the same rate. The differences between case 10 and case 11 are due to the presence of another accumulator. He injection from two accumulators slows the CMT injection, delaying the actuation of ADS-4 on the low-low CMT level signal. The accumulators are empty before ADS-4 valves open, and there is never a period of rapid depressurization where the CMT injection stops due to rapid accumulator injection. The overall RCS pressure response (Figures 7.2-12a and 7.2-12b) is similar between MAAP4 and NOTRUMP. However, MAAP4 shows a greater depressurization from the injection of two accumulators, which in tum causes them to inject even faster. He RCS pressure response at very low pressures (Figures 7.2-13a and 7.2-13b) shows that two accumulators depressurize the RCS below Results of Sensitivity Cases Rev. 0. April 1997 ohw}voj20603w-9.wpf.lbeillG7 1
J l 7-43 1
\ ' j J
100 psia several hundred seconds earlier in MAAP4 than in NOTRUMP. In MAAP4, the downcomer. ) water pool is represented as a single node with one temperature. When the cold water is injected from
. the accumulator, the enthalpy of water flow from the downcomer to the core is reduced, resulting in ~
increased subcooling of the core water and reduced steaming in the core.' Reduced steaming with the break in the primary system causes faster depressurization, resulting in faster accumulator water ] injection. ; I' 3 Prior to ADS-4 actuation, both codes predict an increase in the RCS pressure. In MAAP4, the
- pressure increase occurs as soon as the accumulators empty. The magnitude of the increase is j
. approximately 15 psia over 300 seconds. He NOTRUMP pressure increase occurs a couple hundred seconds after the accumulators empty, and is limited to less than 5 psia by the opening of the ADS-4 I valves. The pressure increase is caused by mostly water break flow and incitased steaming in the l core. -)i Both MAAP4 and NOTRUMP predict that IRWST injection (Figures 7.2-14a and 7.2-14b) is delayed slightly when there are two accumulators and two CMTs compared to only one of each. However, there is no adverse impact on the RCS inventory (Figures 7.2-15a and 7.2-15b) nor on the vessel inventory (Figures 7.2-16a and 7.2-16b). De inventory in case 11 is generally higher than the inventcry in case 10 throughout most of the accident. However, by 3000 seconds, both codes show no i distinguishable differences in the inventories between case 10 and case 11.
De vessel mixture level (Figures 7.2-17a and 7.2-17b) shows that the core remains covered during' the j entire accident progression. The only point of interest is MAAP4's prediction of downward spikes in I the mixture level when accumulator injection starts around 600 seconds. MAAP4 is in a separated two-phase model at this tirne, and the addition of a large mass of very cold water has an immediate impact on the core void fraction. MAAP4 consistently predicts mixture level oscillations such as these , for a range of break sizes, when both accumulators are modelled. De spikes do not threaten to uncover the core, nor do they impact core cooling, nor do they have an impact on the prediction of the . I overall trends. The conclusion from case 11 is that the accident progression of both CMTs and accumulators is
- similar to the accident progression when only one of each tank is credited. Both accident scenarios
!' lead to successful core cooling with no core uncovery. I a -f ( , t
, Results of Sen!,itivity Cases Rev. O. April 1997
,7 ' c:hewpoj20603w-93pf:ltWil97
. . - - . --. ~ , . . - - - --
7-44 Figure 7.2-la O NOTRUMP Accumulator inventory 5.0 Inch Break with 1 CMT, Auto ADS
~1 CMT. No Accumulators (Ccse 3) 1 CMT. 1 Accumulator (Case 10) 120000 ^ :
E 100000 -- 's _a : ' - s
~
80000 -2 __3 60000 - i
- i m 40000 - i m i \
\
a 20000 -: 2 :,.. , i
, , , i i 0 5$0 10'00 15'00 2000 25'00 3000 Time (s)
Figure 7.2-1b h MAAP4 Accumulator inventory 5.0 Inch Break with 1 CMT, Auto ADS 1 CMT. No Accumulators (Case 3)
---- 1 CMT. 1 Accumulator (Case 10) n 120000 -
E o 100000 -$ _'
- ~ ,
80000 -- _ s m_ , 60000 - \
- \
m 40000 - \ m : i a 20000 -i i s : \ 0 l l l l l 0 500 1000 1500 2000 2500 3000 Time (s) O Results of Sensitivity Cases Rev. O. Apnl lW7 ohwproj2\3603w.9.wpf;Ib-04 t l97
\
7-45 i ry Figure 7.2-2a j U ! NOTRUMP CMT Leve1 5.0 Inch Break with 1' CMT, Auto ADS I
'l CMT, No Accumulators (Case 3)
---- 'l CMT', 1 Accumulator (Case 10) ]
~ 25 l
-s : .
-- : i 4
_ 20 -:
- 15 '- '
- 2 s :
c- 10 -3 's s cn -
's .
5-5
's e - s If 0 l l l 'l '
l 0 500 1000 1500 2000 2500 3000 1 Time (s) ! 1 O V
)
- Figure 7.2-2b
\
MAAP4 CMT Leve1 5.0 1.n c h Break with 1 CMT, Auto ADS l 1 CMT, No Accumulators (Case 3)
----1 CMT, 1 Accumulator (Case 10) 25
.s :
a :
. 20 _
15 -3 C en 10 -i s
's, 5~- '
O : -_s N mf a f 1 Q i0 , , t, , , 0 500 1000 1500 2000 2500 300 0 Time (S) i O Results of Sensitivity Cases Rev. 0, April 1997 o:%ewprojA%03w-9.wpf:1b-041197
7-16 Figure 7.2-3a g NOTRUMP RCS Pressure 5.0 Inch Break with 1 CMT, Auto ADS 1 CMT. No Accumulators (Case 3)
----1 CMT. 1 Accumutotor (Case 10) m 700 g .5 600 2 m E
- c. 5 0 0 2 s
400 -@ 's
! 300 '
n m 200 B t a : 1 e 100 -E s a- 0 l F ! 0 500 1000 1500 2000 2500 3000 Time (s) Figure 7.2-3b MAAP4 RCS Pressure 5.0 Inch Break with 1 CMT, Auto ADS 1 CMT. No Accumulators (Case 3)
---- 1 CMT. 1 Accumulotor (Case 10) m 700 _ .5 600 3c m x o- 500 -5 N s
4 0 0 -E N s E 3 00 -f _ 5 m 200 -5 $
\
o 100 _ s O- ' 0 0 5b0 10'00 15'00 20'00 25'00 3000 Time (s) O Results of Sensitivity Cases Rev. o, Apnl 1997 l ohwpmih3603w-9.wpf.Ibetil97
s
' 7-47 u
p
. v Figure 7.2-4a NOTRUMP' De t a i l e d Downcomer Pressure 5.0 - Inch Break with 1 C M T., A-u t o ADS :
'1 CMT. No Accumusators (Case 3 )'
- 1. C M T . 1 Accumulator- (Cose 10)
._75 _
1 i o E i m 65 - : -
\
2 55 - \
\
5 s
. 45 -j \
l
= 35 -j. s 25 -5 ---- - - - --
i E 15 l l l 0 500 1000 1500 20'00 25'00 3000 Time (s) n V Figure 7.2-4b MAAP4 Detoiled RCS Pressure 5.0 inch Break with 1 CMT. Auto ADS 1 CMT. No Accumulators (Cose 3)
---- 1 CNT. 1 Accumulator (Case 10) n 75 _
o : I m 65 -:: i
- I
- a. 5 5 - : i
- l e 45 -5 t m :
= 35 - s 25 -
- - 15 l l l 0- 500 1000 1500 2000 2500 300 0 Time (s)
.%)n Results of Sensitivity Cases Rev. O, Apnl 1997 oAnewproj2\3603w 9 wpf:lbell t97
7-48 Figure 7.2-5a g NOTRUMP integrated IRWST injection 5.0 inch Break with 1 CMT, Auto ADS
'1 CMT. No Accumulators (Case 3) 1 CMT. 1 Accumulator (Case 10) 100000 _
E 80000 - ' .c : , 60000 - v -
~
m 40000 -3 ' m : ' o 20000 -: , 2 ' 0 ' 0 5d0 10'00 15'00 2000 25'00 3000 Time (s) Figure 7.2-5b MAAP4 integrated IRWST Injeetion 5.0 Inch Break with 1 CMT, Auto ADS 1 CMT, No Accumulators (Case 3) 1 CMT. 1 Accumulator (Case 10) 100000 _ E 80000 -3 _o _ ] 60000 - m 40000 -3 ,' ' m : ' o 20000 -- -
- E ,-
0 0 5d0 10'00 15'00 20'00 25'00 3000 Time (s) O Results of Sensitivity Cases Rey, o, Apnl 1997 chwproj20603w-9.wpElWil97 i
7-494 a jn< C, Figure 7.2-6a !
, NOTRUMP RCS . Inventory j l 5.0 Inch Break- with- 1 CMT. Auto ADS :
2 '1 CMT, N 'o Accumulators-(Case 3)
- ---- 1 CMT, 1 Accumulator (Case 10) .
'400000 ~
~
i m E-o 300000 - J 200000 - ~ i
.l
.m -
j
' m - 1 0 0 '0 0 0 -2
.o-. -
c '-
~
I 1 l
- r. -,.,,, , , , , , , , , , ,,, I 0
500 10'00 15'00 20'00 25'00 3000 I d Time (s) fB L' Figure 7.2-6b MAAP4 RCS Inventory . 5.0 Inch Break with 1 CMT, Auto ADS . 1 CMT. No Accumulators (Case 3)
---- 1 CMT, 1 Accumulator (Case 10)
'- 400000 _
- ^ -
E o 300000 -_
" 200000 -{
m.
- 100000 -
,s
_o
=_ -----
=
s : 0 l l 0 500 1000 1500 2000 2500 3000 4= O Iime (S)
. 'Ag' Results of Sensitivity Cases - Rev. 0. Apnl 1997 o:%ewproj2\)603w.9.wpf:Ib-041197 .
7-50 Figure 7.2-7a g NOTRUMP Vesse! Inventory 5.0 Inch Break with 1 CMT, Auto ADS
'1 CMT. No Accumulotors (Cose 3)
---- 1 CMT, 1 Accumulator (Case 10) 160000 m _
p 2 120000 -{ ,s '
~~
----/ __________
30000 -{ w 40000 - o _ 2 : ' 0 l l l ! l 0 500 1000 1500 2000 2500 3000 Time (s) Figure 7.2-7b MAAP4 Vesse! Inventory 5.0 Inch Break with 1 CMT, Auto ADS / 1 CMT, No Accumulators (Cose 3)
---- 1 CMT, 1 Accumulator (Case 10) 160000 , ^ :
E o 120000 -{ 80000 - - -- - -s _ ,______ m -
" 40000 -
o - 2 : 0 l l l l l 0 500 1000 1500 2000 2500 3000 Time (s) Results of Sensitivity Cases Rev. O. Apnl 1997 9l c :\newproj2\3603 w -9.wpf. l b481 197 I
7-51 (~' . Figure 7.2-8a v NOTRUMP Mixture Leve1 5.0 Inch Break with 1 CMT. Auto ADS
'l CMT, No Accumulators (Case 3)
---- 1 CMT, 1 Accumulator (Cose 10) 4- - - - T o p of Core 30 _
C 26 - ____ - - -
,,_,,,__,,,,,n,,, ,_,,,,,
22 -2 a
; ,8.
_3._._._._.+_._._._._._+._._._._._.! 14 -3
= -
~ 10 -i si 6 0 500 10'00 1500 20'00 25'00 3000 Time (s)
,, I i
'd Figure 7.2-8b MAAP4 Mixture Level 5.0 Inch Break with 1 CMT, A u.t o ADS 1 CMT, No Accumulotors (Cose 3)
---- 1 CMT, 1 Accumulotor (Case 10) 4- - - - T o p of Ccre 30 _
C26-2 __s,________ _22-_ 0 1 8 ;- . _ . _ . _ . _ . + _ . _ . _ . _ . _ . _ + . _ . _ . _ . _ . _ . ; a _
- 14 -2
.", 10 - : -
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7 52 Figure 7.2-9a g NOTRUMP Total Accumulator inventory 5.0 Inch Break. Auto ADS 1 CMT. 1 Accumulator (Case 10) 2 CMTs. 2 Accumulotors (Case 11) 250000 ^ : ) 200000 -f--~~' ~, C 150000 -! 's s m 100000 -: _ x s s 50000 - s f
- E , , , , , , . ,s. , ,
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----2 CMTs, 2 Accumulators (Cose 11) 250000 ) 200000 -!--- 's _ s -
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7-53 p Figure 7.2-10a V ' NOTRUMP CMT #1 LeveI 5.0 Inch Break. Auto ADS
'1 CMT. 1 Accumulator (Case 10) 2 CMis. 2 Accumulators (Case 11) 25
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_ 20 - _ v : 15 -i
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7 ._ Figure 7.2-11a O NOTRUMP CMT #2 Leve1 5.0 inch Break. Auto ADS "1 CMT. 1 Accumulator (Case 10) 2 CMTs. 2 Accumulators (Case 11) 25 . 20 -: s v : 's 15 - 's - E 's ' _c 10 -: 's en : 's ' . _ . : ~
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----2 CMTs. 2 Accumulators (Case 11) 25
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7-55 i p Figure 7.2-12a v , NOTRUMP RCS Pressure 5 .'O l'n c h Break. .A u t-o ADS
'1 CMT. 1 Accumulator (Case 10)
- - - - 2 ':C M i s , 2 Accumulators (Case 11) !
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7-56 Figure 7.2-13a g NOTRUMP Detailed Downcomer Pressure 5.0 Inch Break, Auto ADS 1 CMT. 1 Accumulator (Case 10) 2 CMTs. 2 Accumulators (Case 11)
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7-51 T Figure 7.2-14a (v., NOTRUMP Integrated IRWST' lnject' ion 5.0 Inch Break. A u't'o ADS
^1 CMT. 1 Accumulator (Case 10) 2 CMTs. 2 Accumulators (Case 11) 100000 _
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.s -
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,0 Time. (s) Results of Sensitivity Cases . Rev. O, Apn! 1997 c.Wewproj2\3603w-9.wpf-lb441197 l
7 58 Figure 7.2-15a g NOTRUMP RCS Inventory 5.0 Inch Break, Auto ADS
'l CMT, 1 Accumulator (Case 10)
---- 2 CMTs, 2 Accumulators (Case 11) 400000 ~
n _ E o 300000 - _ " 200000 -{ w - m -
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----2 CMTs. 2 Accumulators (Case 11) 400000 ~
m - E - _a 300000 -
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' 7 (~* Figure 7.2-16a l v j NOTRUMP Vessel Inventory' -
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---- 2 CMTs, 2 Accumulators (Case 11)
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---- 2 CMTs, 2 Accumulators (Cose 11) 160000 m :
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7-60
. Figure 7.2-17a g NOTRUMP Mixture Leve1 5.0 Inch Break, Auto ADS 1 CMT, 1 Accumulator (Case 10) 2 CMTs. 2 Accumulators (Case 11)
-f- - - - T o p of Core 30 _
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----2 CMTs. 2 Accumulators (Case 11)
+.- - - Top of Core 30 _
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O Results of Sensitivity Cases Rev. o April 1997 ohwproj2\3603w-9.wpf:lb-041197
7 7.3 Number of ADS O The third type of sensitivity is to the number of ADS valves that are credited. A 2" break was selected for these cases, because this break size produces one of the most limiting core uncoveries. Dere are three sensitivity cases, which are performed for two different reasons. De first two sensitivity cases (12 and 12a) show the impact of crediting more ADS valves. Case 12 adds a'l stage 1,2 and 3 ADS to the assumption of 3 stage 4 ADS, while case 12a credits all ADS valves from
' all stages. The purpose of these erses is to demonstrate no adverse impact on core cooling due to the additional inventory loss that occurs through the open ADS valves. The final sensitivity documented in this section, case 12b. compares the impact of crediting all stage 1,2 and 3 ADS valves in addition to the ADS success criterion of 2 stage 4 ADS in the current PRA.
Before the details of the sensitivity results are discussed, a consistent shortcoming in the MAAP4 ' comparison to NOTRUMP will be explained. The coolant invento:y in the hot leg is an important parameter that impacts the codes' calculations when ADS is opened. In most of the benchmarking cases, only stage 4 ADS is actuated. Differences in hot leg inventory and hot leg level predictions can impact whether water relief through ADS-4 occurs. Water relief through ADS-4, ifit occurs, is typically on the order of 10,000 lbm. However, the water relief through ADS-4 is not substantial enough to be a decisive factor in whether the core uncovers prior to IRWST injection. The ability of the RCS to depressurize is the most important element in determining whether the core uncovers. 5 When stage 1,2 or 3 ADS valves are opened and there is water in the hot leg, water will be pulled into the pressurizer. He pressurizer re-filling with water not only represents a loss of coolant inventory from the core region, but limits the depressurization capability of the RCS. De depressurization of the RCS determines whether IRWST gravity injection starts in time to prevent core uncovery. s here are differences in the MAAP4 and NOTRUMP vessel mixture level prediction of cases 12,12a and 12b due to a difference in whether the hot leg is full of water. The difference is not primarily a j resuh of the details of the hot leg model or stratification, rather the RCS inventory predictions are i significantly different at the time the ADS valves are opened. This can be seen in case 2 where i , MAAP4 predicts a transition from CMT recirculation to draining approximately 600 seconds after ; NOTRUMP, MAAP4% later transition from CMT recirculation to draining causes MAAP4 to predict less coolant inventory in the RCS than NOTRUMP when ADS valves are actuated based on low CMT $ level signals. In case 2, the difference in vessel coolant inventory when ADS is actuated does not have a significant impact on the final results. . His is because both codes predict that the hot leg is empty when stage 4 ADS is actuated. The similarity in the final results predicted by MAAP4 and NOTRUMP for case 2 is unaffected by NOTRUMP's prediction of a brief period of water entrainment , through the ADS-4 valves. ! l f For case 12,12a and 12b, the differences in the event timing, the vessel inventory predictions, and the Js hot leg level have an impact on the final vessel mixture predictions. His is because the hot leg e Results of SensitMty Cases Rev. 0, April 1997 j f c:W:wproj2\3603w.10.wpf:Ib-o41497 ; 4
. . , _ . _ m.. . . . . - ,
W-7-62 l l contains water when NOTRUMP opens stage 1 ADS, but the hot leg is empty when MAAP4 opens ; stage 1 ADS. The conclusioin of the benchmarking case 12,12a and 12b sensitivity studies is that MAAP4 may underp edict the insurge of water into the pressurizer when stage 1,2, and 3 ADS opens. AP600 MAAP4 analysts should be aware that if MAAP4 does not predict an increase in the pressurizer water inventory when ADS stage 1,2,3 valves open, the code may overpredict the resulting RCS depressurization. This can result in a non-conservative prediction of the coolant inventory in the vessel and the vessel mixture level. It is noteworthy, however, that MAAP4 does a very good job of predicting the depressurization due to a single stage 3 ADS valve opening in benchmarking case 1 (Section 6.1) and case 13 (Section 7.4). In both of these cases, MAAP4 predicts water in the pressurizer at the time of, or as a result of, the stage 3 ADS valve opening. Finally, regardless of the MAAP4 limitation, these sensitivity cases show that there is no adverse impact from the actuation of additional ADS valves. "The modelling of the minimum number of ADS valves is a bounding approach to support success criteria definitions in the PRA. CASE 12 - 2" BREAK WITII ALL STAGE 1,2,3 ADS AND 3 STAGE 4 ADS Case 12 is a 2" hot leg break with the same equipment and analysis assumptions as case 2, except ADS stages 1 through 3 are credited. The difference between case 12 and a SSAR Chapter 15 l accident scenario is that case 12 assumes no PRHR, no accumulators and only one CMT. The lack of 3 accumulators is the most important difference in equipment that influences the vessel mixture level. j The results of case 12 are compared to case 2. The RCS depressurizes (Figures 7.3-la and 7.3-lb) approximately 600 seconds earlier than case 2 due to the actuation of stages 1,2 and 3 ADS in j case 12. NOTRUMP models a mixture level in the hot leg (Figure 7.3-2a) that is above the inlet to j the pressurizer surge line. Therdore, when stage 1 ADS opens, the pressurizer level (Figure 7.3-3a) and mass inventory (Figure 7.3-4a) increase. Note, however, that the NOTRUMP mixture level does not indicate the amount of water in the hot leg; the void fraction of the mixture is high when stage 1 ! ADS opens. MAAP4, on the other hand, does not model a mixture level in the hot leg, and the collapsed wster level (Figure 7.3-2b)is below the surge line elevation when stage 1 ADS opens.
]
Althougt MAAP4 pmdicts some water entrainment into the surge line when ADS stage I first opens, the water flow stops as the coolant level falls to the bottom of the hot leg. Therefore, there is no l irrpact on the pressurizer level (Figure 7.3-3b) nor the pressurizer water inventory (Figure 7.3-4b). When stage 2 ADS opens, NOTRUMP predicts water relief through the valves (Figure 7.3-5a), while MAAP4 predicts no water relief (Figure 7.3-5b) because the pressurizer is predicted to have no water in it. Both codes predict similar vapor relief through stage 1,2 and 3 ADS valves (Figures 7.3-6a and . 7.3-6b); the shift in timing between the NOTRUMP and MAAP4 results is due to the differences seen Results of Sensitivity Cases Rev. O. April 1997 c:\newproj2\3603w.10.wpf.lb-041497
, t 7-63 : in case 2 of the transition from CMT recirculation to draining. For case 12, neither code predicts i water relief through the ADS-4 valves (Figures 7.3-7a and 7.3-7b) when they open, although MAAP4 predicts water relief after IRWST injection is established. When compared to case 2, both codes predict less vapor relief through stage 4 ADS (Figures 7.3-8a and 7.3-8b) for case 12, although the ' same number of valves are open. Stage 4 ADS valves open seconds earlier in case 12 than in case 2,
~ due to a slightly faster CMT (Figures 7.3-9a and 7.3-9b) draining rate. :
l Both codes predict that the kCS depressurizes to below 75 psia as a result of stages 1,2 and 3 ADS j (Figures 7.3-10a and 7.3-10b). After stage 4 ADS opens, MAAP4 predicts a faster depressurization l i and stabilizing at a lower pressure than NOTRUMP. Although the MAAP4 predicts less vapor loss from stage 4 ADS, the vapor loss from stages 1,2 and 3 ADS has a larger depressurization impact in MAAP4 than in NOTRUMP because the pressurizer is empty in MAAP4's prediction. When compared to case 2, both codes predict that IRWST injection (Figures 7.3-lla and 7.3-ilb) starts sooner. MAAP4 predicts that stages 1,2 and 3 ADS cause the IRWST to start approximately 400 seconds sooner, while NOTRUMP predicts 250 seconds difference. De RCS inventory (Figures 7.3-12a and 7.3-12b) is lower in case 12 after stages 1,2 and 3 open than in the same time period in case 2. However, because of the earlier IRWST gravity injection, the minimum RCS inventory in case 12 is higher than case 2. His same trend can be seen in the vessel inventory (Figures 7.3-13a and 7.3-13b). There are differences, however, between NOTRUMP's and MAAP4's prediction of vessel inventory. When ADS valves are first opened, NOTRUMP predicts that ( there is approximately 110,000 lbm coolant in the vessel, while MAAP4 predicts approximately 80,000 lbm. His difference is due to MAAP4's delayed transition from CMT recirculation to draining. De difference in coolant inventory predictions when ADS valves open is a factor in the differences in the hot leg level predictions, and the difference in the water insurge into the pressurizer. He vessel mixture level (Figures 7.3-14a and 7.3-14b) is predicted by NOTRUMP to tum around near the top of the core. De top of the core barely uncovers. MAAP4 does not predict any decrease in the vessel mixture level below the hot leg elevation for c:se 12. Despite the differences in the vessel mixture level predictio . NOTRUMP confirms that there is no adverse impact on core cooling when ADS stage 1,2 and : .dves are credited in addition to stage 4 ADS valves. De NOTRUMP minimum vessel mixture level is so close to the top of the core that this scenario is counted as core uncovery in the T/H uncertainty resolution process. This case illustrates that additional depressurization capability (ADS valves) may not be sufficient to prevent core uncovery when neither accumulator is credited. The injection from accumulator (s) would provide make-up inventory during ADS blowdown, and would provide greater downcomer subcooling and lower downcomer pressures. Taking credit for at least one accumulator would change this accident scenario to one in which no core uncovery would be anticipated.
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Results of Sensitivity Cases Rev. O, Apnl 1997 c:Wewproi2\3603w-10.wpf: t b-041497
~7 CASE 12A -- 2" BREAK WITH ALL ADS The potential for an adverse impact on core cooling when more ADS stage 4 valves are opened is explored through case 12a. This case is the same as case 12, except it models 4 stage 4 ADS valves rather than 3 stage 4 ADS valves. Derefore case K'a credits all ADS valves.
The results of case 12a are compared to case 12. Both codes show only minor differences between these two cases. NOTRUMP predicts the same insurge into the pressurizer (Figure 7.3-15a) when stage 1 ADS opens. The pressurizer inventory is lower in case 12a when all stage 4 ADS open. MAAP4 continues to predict no insurge into the pressurimr (Figure 7.3-15b) for the same rearons explained for case 12. De water relief (Figures 7.3-16a and 7.3-16b) and vapor relief (Figures 7.3-17a and 7.3-17b) from stages 1,2 and 3 are the same until an extra stage 4 ADS valve opens in case 12a. This causes a decrease in the vapor flowrate through ADS stages 1,2 and 3. The decrease in ADS stages 1,2 and 3 flow is greater in MAAP4 than in NOTRUMP. For case 124, neither code predicts water relief through the ADS-4 valves (Figures 7.3-18a and 7.3-18b) when they open, although water relief occurs after IRWST injection is established. MAAP4 predicts the water relief through stage 4 ADS within 500 seconds after IRWST injection starts, while NOTRUMP predicts the water relief approximately 1500 seconds after IRWST injection starts. As expected, the vapor flowrate through stage 4 ADS (Figures 7.3-19a and 7.3-19b) is greater in case 12a than in case 12, due to the extra valve being opened. MAAP4 predicts a larger increase than NOTRUMP in the integrated vapor inventory from stage 4 ADS. After stage 4 ADS opens, both codes predict that the RCS depressurizes (Figures 7.3-20a and 7.3-20b) faster and stabilizes at a lower pressure in case 12a compared to case 12. Once again, MAAP4 shows a larger impact than NOTRUMP. Here is a positive impact on IRWST injection (Figures 7.3-21a and 7.3 21b). NOTRUMP shows little impact on the time IRWST injection starts, but the injection rate is higher once it starts. MAAP4 predicts that IRWST injection starts approximately 100 seconds earlier, but there is a negligible impact on the rate. De minor differences between case 12 and case 12a results can be seen in the RCS inventory (Figures 7.3-22a and 7.3-22b), the vessel inventory (Figures 7.3-23a and 7.3-23b), and the vessel mixture level (Figures 7.3-24a and 7.3-24b). The same relative trend between case 12 and ese 12a is predicted by both codes. The difference in the mixture level predictions between MAAP4 and NOTRUMP are the same as seen in case 12. Despite the differences in the vessel mixture level prediction, NOTRUMP confirms that there is no adverse impact on core cooling when an additional ADS stage 4 valve is credited. Although neither code predicts core uncovery, the NOTRUMP minimum vessel mixture level is so clos: to the top of the core that this scenario is counted as core uncovery in the T/H uncertainty resolution process. This case provides further proof of the conclusions from case 12: additional depressurization capability (ADS valves) may not be sufficient to prevent core uncovery when neither Results of Sensitivity Cases Rev. o, Apnl 1997 oAnewproj20603w 10.wpf.lb o41197
~ _ _ . _ _ _ _.. _ . _ _ _ _ _ _ _ . _ _ _ . _
I 7-65 - l accumulator is credited. De injection from accumulator (s) would provide make-up inventory during l ADS blowdown, and would provide greater downcomer subcooling and lower downcomer pressures. Taking credit for at least one accumulator would change this accident. scenario to one without core uncovery. CASE 128 - 2" BREAK WITH'ALL STAGE 1,2,3 ADS AND 2 STAGE 4 ADS Case 12b is a 2" hot leg break with the same equipment and analysis assumptions as case 2, except
- ADS stages 1 through 3 ait credited in " exchange" for 1 stage 4 ADS. The purpose of this case is to demonstrate the plant response when the ADS success criterion defined in the current PRA (2 stage 4 j ADS)is modelled with the addition of all stage 1,2 and 3 ADS. As noted in Section 4.1, the PRA l does ~not usually differentiate the number of stage 1,2 and 3 ADS valves that successfully open.
' Le plant response in case 12b is the same as case 2 until stage 1 ADS opens. Until stage 4 ADS opens, the plant response is the same as presented for case 12 and case 12a. With only two stage 4 l
' ADS valves opening in case 12b, the vapor relief from stage 4 ADS (Figures 7.3-25a and 7.3-25b) is i less than predicted for three stage,4 ADS valves in case 2. De lower vapor loss from stage 4 it also partially due to the vapor loss that occurs from stage 1,2 and 3 (Figure 7.3-26a and 7.3 26b). .- Both codes predict similar ADS stage 1,2 and 3 flowrates until stage 4 opens, and then MAAP4 predicts less vapor loss from stage 4 ADS than NOTRUMP. However, MAAP4 predicts that the RCS depressurizes (Figures 7.3-27a and 7.3-27b) more easily than NOTRUMP. He dfferexe S attributed to the pressurizer water inventory that is predicted by NOTRUMP, which lessens tne depressurization effectiveness of stage 1,2 and 3 ADS.
The difference in depressurization predictions by MAAP4 and NOTRUMP creates a difference in IRWST injection (Figures 7.3-28a and 7.3-28b). NOTRUMP predicts that IRWST injection starts for case 12b approximately 200 seconds later than case 2. MAAP4 predicts that IRWST injection starts for case 12b approximately 200 seconds earlier than case 2. Once IRWST injection begins, there is also a difference in the flowrate predicted by the two codes. NOTRUMP predicts that the IRWST I gravity drain is a slower flowrate than case 2, while MAAP4 predicts a higher flowrate than case 2. He RCS inventory (Figures 7.3-29a and 7.3-29b) and the vessel inventory (Figures 7.3 30a and 7.3-30b) show that the minimum inventory for case 12b is appmximately the same as case 2 based on the NOTRUMP prediction, while MAAP4 predicts that case 12b is less limiting. He NOTRUMP
. prediction of vessel mixture level (Figure 7.3-31a) is that the Aa*h of core uncovery is the same for case 12b as for case 2, but the duration of core uncovery is lo.9,er for case 12b. Successful core l cooling is shown in Section 8.0 with the LOCTA-predicted PCT remaining less than 2200*F. MAAP4
' predicts that the vessel mixture level (Figure 7.3-31b) remains above the top of the core. %e reason 4 for this difference is the same as was discussed for case 12 and case 12a.
Results of Sensitivity Cases Rev. O. April 1997
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----All ADS 1 to 3. 3 ADS-4 (Case 12) m 2500 _
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7-67. Figure 7.3-2a NOTRUMP Hot- Leg Leve1 2.0 Inch Break w i-t h 1 CMT. Auto ADS , No ADS 1 to 3. 3 ADS-4 (Case 2) !
----All ADS 1 to 3. 3 ADS-4 (Case 12) i
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7-68 Figure 7.3-3a g NOTRUMP Pressurizer Level 2.s Inch Break with 1 CMT, Auto ADS No ADS 1 to 3. 3 ADS-4 (Case 2)
----All ADS 1 to 3. 3 ADS-4 (Case 12) 40 m
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---- Al l ADS 1 to 3. 3 ADS-4 (Case 12) 40 ^
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o - 0 l -l ; l ) 0 1000 2000 3000 4000 5000 . Time (s) Oll Results of Sensitivity Cases Rev. O. Apnl 1997 o:\newproj2\3603w-10.wpf:Ib441197
'l 7-69 rigure 7.3-4a fm)
N . NOTRUMP P r e s s u r i z-e r. Inventory
.2.0 1nch Break with 1 CMT. Auto ADS No ADS 1 to 3. 3 ADS-4 (Case 2)
All ADS 1 to.3, 3 ADS-4' (Case' 12) 30000 _ l E 25000 -5. c :
- 2.0 0 0 0 -5 v 4 15000 - :j fg ;
I\ l m 10000 - :J , ss
'm :
->s '
a 5000 -j ,' - 2 " ' 0 l l l l 0 1000 2000 3000 4000 5000 Time (s)
~
O rigure 7.3-48 MAAP4 Pressurizer inventory 2.0 Inch Break with 1 CMT, Auto ADS 1 No. ADS 1 to 3, 3 ADS 4 (Case 2)
----All AOS 1 to 3, 3 ADS-4 (Case 12) 30000 _
o E 25000 -5 - 20000 -E v f 15000 -- : m 10000 -_ m : a _5000 -E 0 l --l l l
-0 1000 2000 3000 4000 5000
, Time (s)
,y Results of Sensitivity Cases Rev.O,Apnl1997 owwproj2\3603w.10.wpf:lb44t l97
l l l 7 70 I I l I Figure 7.3-5a g NOTRUMP Integrated ADS 1 to 3 Water l 2.0 Inch Break with 1 CMT, Auto ADS No ADS 1 to 3. 3 ADS-4 (Cose 2)
---- AlI ADS 1 to 3. 3 ADS-4 (Case 12) 100000 f 80000 -f ..
v 60000 -3 40000 - o 20000 -
^
0 l l l l 0 1000 2000 3000 4000 5000 Time (s) Figure 7.3-5b h MAAP4 Integrated ADS 1 to 3 Water 2.0 inch Break with 1 CMT, Auto ADS No ADS 1 to 3. 3 ADS-4 (Case 2) All ADS 1 to 3, 3 ADS-4 (Case 12) 100000 80000 - v 60000 - 40000 - m : g 20000 - 0 l l l l 3 1000 2000 3000 4000 5000 Time (s) O Results of Sensitivity Cases Rev. O, April 1997 owwproj2\3603w 10.wpf;ltw1197 1
7 71 4 ev Figure 7.3-6a U NOTRUMP Integrated ADS 1 to 3 Vapor . -2 - 0- lnch Break with 1 CMT, Auto ADS No ADS 1 to 3. 3-ADS-4 (Cose 2) Ali ADS 1 to 3, 3 ADS 4 (Case 12)
- -100000 -
I
)
80000 -f e 1 v ~6 0 0 0 0 -- ,
/
4 0000 -: / . m :- f
- 20000 -
~
- 2 -
, / , , ,
0 , .. , , , 0 1000 2000 3000 4000 5000 Time (s) Figure -7.3-6b MAAP4 Integrated ADS 1 to 3 Vapor 2.O Inch Break with 1 CMT,
- Auto ADS 1 No ADS 1 to 3. 3 ADS-4 (Cose 2) J
----All ADS 1 to 3 ., 3 ADS-4 (Cose 12) '
100000
~~~~~~'
f 80000 -f - v 60000 -{ - / f 4 0000 - # rn 20000 - i 2' ' 0 b 10'00 20'00 30'00 40'00 5000 Time -(s) a
-Le Results of Sensitivity Cases Rev. O. April W7 W3w-10.wpr;ggg ,97
7 72 Figure 7 3-7a g NOTRUMP integrated ADS-4 Water 2.0 Inch Break with 1 CMT, Auto ADS No ADS 1 to 3. 3 ADS-4 (Case 2)
----All ADS 1 to 3, 3 ADS-4 (Cose 12) 100000 80000 -
v 60000 -3 40000 - cn : 20000 -3 0 l l ! l 0 1000 2000 3000 4000 5000 Time (s) Figure 7.3-7b h MAAP4 Integrated ADS-4 Water l 2.0 inch Break with 1 CMT, Auto ADS No ADS 1 to 3, 3 ADS-4 (Case 2) Al l ADS 1 to 3. 3 ADS-4 (Cose 12) 100000 f 80000 -
- ,1 v 60000 - c---
/
40000 - s w : ,a 20000 -} ,' 2 ' ' ' 0 ' l 0 10'00 20'00 3000 40'00 50'00 Time (s) e Results of Sensitivity Cases gey,o,Aprij3997 c:\newproj2\3603w 10 wpf.lb-041197 l
~
7-73 p Figure 7.3-8a G : NOTRUMP integrated ADS-4 Vapor
~2.0 Inch Br-eak with 1 CMT. Auto ADS No. ADS 1 to 3. 3 ADS-4 (Case 2) !
All ADS 1 to 3. 3 ADS-4 (Case 12) 100000 80000 - v '6 0 0 0 0 -3 ! 40000 - - m : '
" 20000 - -
i o -
- 1' 2 '
- 2. , , , ,
0 ' 0 10'00 20'00 .3000 40'00 5000 Time (s) O Figure 7.3-8b l MAAP4 Integroted ADS-4 Vapor 2.0 Inch Break with 1 CMT, Auto ADS No ADS.1 to 3. 3 ADS-4 (Case 2)
----All ADS 1 to 3. 3 ADS-4 (Cose 12) i 100000 f 80000 -
v 60000 -3 40000 - f - m . ,- 20000 -3 , 2 - 0 0 ~ 10'00 20'00 30'00 40'00 50'0 0 Time (s) O i Results of Sensitivity Ceses Rev. O, Apnl 1997
. o:W3w 10.wpf:lb-041197 -
7-74 Figure 7.3-9a g NOTRUMP CMT Leve1 2.0 Inch Break with 1 CMT, Auto ADS No ADS 1 to 3, 3 ADS-4 (Case 2)
---- Ali ADS 1 to 3. 3 ADS-4 (Case 12) 25 ^
i
. 20 -:
v : 15 -i c 10 -i 5-; e : l 1 f 1 0 i , i i 0 1000 2000 3000 4000 5000 Time (s) Figure 7.3-9b $ MAAP4 CMT Leve1 2.0 inch Break with 1 CMT. Auto ADS No ADS 1 to 3, 3 ADS-4 (Case 2)
----Al i ADS 1 to 3, 3 ADS-4 (Case 12) 25 ^
i
. 20 _
v : 15 -i
- : l c 10 -; )
O : 5-; e -
~~ '
0 ! l l'- O 1000 2000 3000 4000 5000 Time (s) 9 Results of Sensitivity Cases Rev. D. Apnl 1997 c:\newproj2\3603w 10.wpf:lb 041197 \
i 7-15 l Figure ' 7.3-10a l O.n ; NOTRUMP. Detailed Downcomer Pressure - 2.0 inch Break with 1 CMT, Auto ADS I No ADS 1 to 3. 3 ADS-4 (Case 2) ' AI! ADS 1 to 3, 3 ADS-4 (Case 12) _ 95 _ e \ [ \ E 75 -- ', ' i
,55-- -
\
w \ s : \ 3 5.-- \ e :
~~_ -
' 15 l l l l 0 1000 2000 3000 4000 5000 Time (s)
O ri 9ure 7.3-108 MAAP4 Detoiled RCS Pressure 2.0 Inch Break with 1 CMT, Auto ADS No ADS 1 to 3. 3 ADS-4 (Cose 2)
----All ADS 1 to 3. 3 ADS-4 (Case 12)
_ 95 - a - t
._ s 1 75 - \
i e 55 -{ ', s ; i 35 - _- i s ___ h 0 1000 2000 3000 '4000 5000 - Time (s) nV. Results of Sensitivity Cases Rev.O.Apnl1997 o:\newproj2\3603w.10.wpf:1 bot i 197 e
7-76 Figure 7.3-11a g NOTRUMP Integrated IRWST Injection 2.0 Inch Break with 1 CMT. Auto ADS No ADS 1 to 3. 3 ADS-4 (Case 2) l Ali ADS 1 to 3, 3 ADS-4 (Case 12) 100000 _ , j n - i E 80000 -: / _o : '
/
60000 - f m 40000 - f ,' m ~
/
o / 20000 -3 , i
=E -
~
i 0 l l 'i l 0 1000 2000 3000 4000 5000 Time (s) Figure 7.3-11b $' MAAP4 Integrated IRWST Injecti.on 2.0 inch Break with 1 CMT, Auto ADS No ADS 1 to 3, 3 ADS-4 (Case 2) Ali ADS 1 to 3, 3 ADS-4 (Cose 12) 100000 _ A -
/
E 80000 - / a : / 60000 - ,'
/ 1 m 40000 -} / l m -
/
a 20000 -} 25 -
' i 0 l l l l 0 1000 2000 3000 4000 5000 Time (s)
O' Results of Sensitivity Cases Rev. 0, Apnl 1997 c:bewproj2\)603w 10.wpf:Ib041197
. - . .- . .- . . . ~ . .. . .
7 77-i i i .fN Figure 7.3-12a i N./ j NOTRUMP: R'C S Inventory .
. 2.0 "
1nch-Break with 1 CMT, Auto ADS i No ADS-1 to'3. 3 AD'S-4 (' Case 2)
- . - - - . A l l. A D S' I to 3. 3 ADS-4-(Case '12 )
400000 E' o 300000 - <
" 200000 -{ ;
, m -
* \ -
100000 -{ s___ __
=s : ' '
u o l l l l i 0 1000 2000 3000 4000 5000 Time (s.) 1 () Figure 7.3-12b
]
]
1 MAAP4 RCS Inventory 2.0 Inch Break with 1 CMT, Auto ADS No ADS 1 to 3. 3 AOS-4 (Case 2) All ADS 1 to 3, 3 ADS-4 (Case 12) l I 400000 E o 300000 - -
.__ : i Y 200000 -I _
m -
"l _10 0 0 0 0 -{ ,
_ _ _ _ _ _7
- s . : -
l- l l l 0 -0 1000 2000 3000 4000 5000 Time (s) a
- \_/
Results of Sensitivity Cases Rev. 0, Apnl 1997 ofmewproj20603w 10.wpf;1b041197
7-78 Figure 7.3-13a g NOTRUMP Vessei Inventory 2.0 Inch Break with 1 CMT, Auto ADS No ADS 1 to 3, 3 ADS-4 (Case 2)
----Ait ADS 1 to 3. 3 ADS-4 (Case 12) 160000 ~
n
) 120000 - ' - : 1 -
80000 - -
\ \ -
w -
~
- 40000 --
o - s : 0 l l l l 0 1000 2000 3000 4000 5000 Time (s) Figure 7.3-13b h MAAP4 Vessel Inventory 2.0 inch Break with 1 CMT, Auto ADS No ADS 1 to 3. 3 A05-4 (Case 2) All ADS 1 to 3, 3 ADS-4 (Case 12) 160000 _ 120000 - v ~~------- 80000 - _ c' 40000 - OE : 0 l l l l 0 1000 2000 3000 4000 5000 Time (s) O l Results of Sensitivity Cases Rev. O. April 1997 1 I o:\newproj2\3603 w.10.wpf:l b4 1197
7-79 Figure- 7.3 14a NOTRUMP Mixture Leve1 2l. O ' -lnch Break with 1 CMT, Auto ADS No ADS-1 to 3. 3 ADS-4 (Case.2) All ADS 1- to 3. 3 ADS-4 (Case 12)
-t- - - - T o p of Core 2
30 _
~26-% ~ is
_. 22 - s- s - l; 3._._. ;._._._. ;._._._. ._._.__p_. ..c.Q._._.+ ._.
;._.__+.._._.y
_, 1 8 _ a 14 -i .
~ 10 -i~
3 6 l l l l 0 1000 2000 3000 4000 5000 Time (s) n LJ Figure 7.3-14b MAAP4 Mixture Leve1 2.0 Inch Break with 1 CMT, Auto ADS Nc ADS 1 to 3. 3 ADS-4 (Case 2) Al ACS 1 to 3. 3 ADS-4 (Case 12)
-+- - - - T o o of Core 30 .
~
26 - ____________ . _22-_ k l; _, 1 8 _ . _ . . _ . ;._._._. ._._._. l ._._._ +._._._.4._ _._p_._. l._._ ._._.y 14 -E
- m. -
; .10 -i
= '6 i i i i
.0 1000 2000 3000 4000 5000 Time (S)
'O
.(/
Results of Sensitivity Cases Rev.O.Apnl1997 o:%ewproj2V603w.10.wpf:Ib 041197
c. 7-80 Figure 7.3-15a g NOTRUMP Pressurizer inventory 2.0 Ineh Break with 1 CMT, Auto ADS All ADS 1 to 3, 3 ADS-4 (Cose 12)
---- All ADS 1 to 3, 4 ADS-4 (Case 12o) 30000 _
E 25000 -5 c : 20000 - ; v 15000 -~ m 10000 -i
$ 5000 -f _ - ,,_,
OE ' ' 0 l l l 0 10'00 2000 3000 4000 5000 Time (s) Figure 7.3-15b MAAP4 Pressurizer inventory 2.0 Inch Break with 1 CMT, Auto ADS All ADS 1 to 3. 3 ADS-4 (Cose 12) Al l ADS 1 to 3, 4 ADS-4 (Cose 12o) 30000 _ E 25000 -5
.c - 20000 -
v 15000 - m 10000 -_ ; m : l a 5000 -j IE : . , _i i i l l 0 10'00 20'00 30'00 40'00 5000 : Time (s) : O l kesults of Sensitivity Cases Rev. O. April 1997 ohwproj2\3603w-10.wpf:1 bel 1197
l \ 7-81 Figure 7.3-16a (vN NOTRUMP integrated ADS 1 to 3 Water 2.0 Inch Break with 1 CMT, Auto ADS All ADS 1 to 3. 3 ADS-4 (Case 12) All ADS 1 to 3. 4 ADS-4 (Cose 120) 100000 f 80000 - v '60000 -~ 40000 - m : 20000 -3 2 ' ' 0 l l 0 1000 2000 30'00 40'LO 5000 Time (s) p () Figure 7.3-16b MAAP4 Integrated ADS 1 to 3 Water 2.0 inch Break with 1 CMT, Auto ADS All ADS 1 to 3. 3 ADS-4 (Case 12) All ADS 1 to 3. 4 ADS-4 (Case 12a) 100000
)
80000 -f - v 60000 -~ 40000 - m : 20000~3 0 l l l l l 0 1000 2000 3000 4000 5000 Time (s)
,r\
i
\a) .
l l Results of Sensitivity Cases Rev. 0, April 1997 ) o:\newprus2\3603w IO.wpf:lbal197
)
l l l
7-82 NOTRUMP Figure 7.3-17a Integrated ADS 1 to 3 Vapor e 2.0 Inch Break with 1 CMT, Auto ADS All ADS 1 to 3, 3 ADS-4 (Case 12) All ADS 1 to 3, 4 ADS-4 (Case 12a) 100000 f_ 80000 - g ------
- -~~
v 60000 - 40000 - m : 20000 - !
}
2 ~ 0 0 10'00 20'00 30'00 40'0'0 5000 Time (s) Figure 7.3-17b $ MAAP4 Integrated ADS 1 to 3 Vapor 2.0 Inch Break with 1 CMT, Auto ADS All ADS 1 to 3. 3 ADS-4 (Case 12) All ADS 1 to 3, 4 ADS-4 (Case 12a) 100000 --- E 80000 - h o _ _ _ - - - - - - - v 60000 -
- i 40000 -1 l m :
20000 - 2 ~ 0 - O 10'00 20'00 30'00 40'00 5000 Time (s) l 0 Results of Sensitivity Cases Rev. 0, Apnl 1997 o:\newproj2\3603w- 10. wpf: l b-041 197
l 7 83 7 - Figure 7.3-18a (. ! NOTRUMP integrated ADS-4 Water 2.0 Inch Break with 1 CMT, Auto ADS Al1 ADS 1 to 3. 3 ADS-4 (Case 12) All ADS 1 to 3. 4 ADS-4 (Cose 12a) 1 100000
)
80000 -f v '60000 -- - 40000 - / m : ,- 20000 -} f 0 l l l 'i 0 1000 2000 3000 4000 5000 Time (s)
\
(#) Figure 7.3-18b MAAP4 Integrated ADS-4 Water 2.0 Inch Break with 1 CMT, Auto ADS All ADS 1 to 3, 3 ADS-4 (Case 12) Ali ADS 1 to 3, 4 ADS-4 (Case 120) n 100000 - t , f 80000 -f _,- C 60000 -f ,I' 40000 -- ,> m : _, 20000 -3 / 0 l l l l l 0 1000 2000 3000 4000 5000 Time (s) O Results of Sensitivity Cases Rev. 0, Apnl 1997 oAnewproj2\3603w 10.wpf:lb44tI97
i 7-84 Figure 7.3-19a g NOTRUMP Integrated ADS-4 Vapor I 2.0 inch Break with 1 CMT, Auto ADS All ADS 1 to 3, 3 ADS-4 (Case 12) l All ADS 1 to 3, 4 ADS-4 (Case 12a) I 100000 f 80000 - : l v '60000 -- ,- 40000 - m : i 20000 - 2 -
, , i i '
0 1 0 10'00 20'00 30'00 40'00 5000 Time (s) Figure 7.3-19b h 1 MAAP4 Integrated ADS-4 Vapor ! 2.0 inch Break with 1 CMT, Auto ADS ' All ADS 1 to 3, 3 ADS-4 (Case 12) All ADS 1 to 3, 4 ADS-4 (Cose 12o) 100000 f 80000 - v 60000 -3 - 40000 -1 - m : ,- 20000 -3 ,- 0 l 3 l 0 1000 2000 3000 4000 5000 Time (s) O Results of Sensitivity Cases Rev. 0 Apnl 1997 o Anewproj2\3603 w- 10.wpf:l b481197
~
f 7-85 i L ; y Figure 7.3-20a
.NOTRUMP-Detailed Downcomer Pressure !
2.0 Inch Break with 1 CMT. Auto ADS ' All ADS 1 to 3, 3 ADS-4 (Case 12) ! AlI ADS 1 to.3. 4 ADS-4 (Cose 12o) { _ 95 _ ; o _ l E 75 -- ! 55 -- i
- s
- i
! l 35 -- l i e m
- 15 ' ' ' '
0 10'00 20'00 30'00 40'00 5000 : Time (s) O Figure 7.3-20b l MAAP4 Detailed RCS Pressure ! 2.0 Inch Break with 1 -CMT, Auto ADS All ADS 1 to 3, 3 ADS-4 (Cose 12) !
----All ADS 1 to 3, 4 ADS-4 (Cose 12o) m 95 o : !
1 75 -- i l
. 55 -- ~
~
lU 35 -- ( g _ N
~~-- -________
0 1000 2000 3000 4000 5000
- Time (s) 10i !
- l Results of Sensitivity Cases Rev. O, April 1997 o:\rewprojn3603w.10.wpf:lb-041197 l
7-86 Figure 7.3-21a g NOTRUMP integrated IRWST Injection 20 Inch Break with 1 CMT, Auto ADS All ADS 1 to 3, 3 ADS-4 (Cose 12)
---- AlI ADS 1 to 3, 4 ADS-4 (Case 120) 100000 -
/
E 80000 -i ,' 1 n - , C 60000 --
/
m 40000 -j /
- /
o 20000 -3 ,' s -
~
e 0 l l l l 0 1000 2000 3000 4000 5000 Time (s) j Figure 7.3-21b h MAAP4 Integroted IRWST Injeetion 2.0 Inch Break with 1 CMT, Auto ADS All ADS 1 to 3, 3 ADS-4 (2 se 12) All ADS 1 to 3, 4 ADS-4 (s se 12c) 100000 i E 80000 - ,' l D - i 60000 -- 1 --
/
cn 40000 - h ,' Cn / o 20000 - / 1 : /
~
0 l l l l 0 1000 2000 3000 4000 5000 Time (s) O Results of Sensitivity Cases Rev. O, Apnl 1997 ohwpmj2\3603w.10 wpf:lb-041197
l 7-87 1 ( Figure 7.3-22a NOTRUMP RCS Inventory 2.0 Inch Break with 1 CMT, Auto ADS All ADS 1 to 3, 3 ADS-4 (Case 12)
---- All ADS 1 to 3, 4 ADS-4 (Case 12a) 400000 - ~
n f 300000 --
~
200000 -- _ cn -
~
] 100000 -- _ f ~~~~~~
- s :
0 l l l l 0 1000 2000 3000 4000 5000 Time (s) A V Figure 7.3-22b MAAP4 RCS Inventory 2.0 Inch Break with 1 CMT, Auto ADS All ADS 1 to 3. 3 ADS-4 (Case 12) All ADS 1 to 3, 4 ADS-4 (Case 12a) 400000 ~ m f 300000 --
" 200000 -{
o :
" 100000 -- ,,
2 _- l 0 1000 2000 3000 4000 500 0 l i Time (s) Results of Sensitivity Cases Rev. 0, Apnl 1997 o \newproj2\3603w-10 wpf:lb-041197
7-88 i Figure 7.3-23a l NOTRUMP VesseI inventory h! . 2.0 inch Break with 1 CMT, Auto ADS All ADS 1 to 3. 3 ADS-4 (Case 12)
---- All ADS 1 to 3. 4 ADS-4 (Case 12o) l L
160000 l m :
) 120000 -}
_ _ ,p-.-- -- 80000 -} ,- w -
~
c 40000 -- - 2 _~ 0 - l l l !. 0 1000 2000 3000 4000 5000 Time (s) . Figure 7.3-23b h MAAP4 Vessei Invenfory 2.0 Inch Break with 1 CMT. Auto ADS All ADS 1 to 3. 3 ADS-4 (Case 12) All ADS 1 to 3, 4 ADS-4 (Case 120) 160000 ~ m 120000 -} 80000 -} ,- - w -
~
- 40000 --
o - 2 0- l l l l 0 1000 2000 3000 4000 5000 Time (s) l O Results of Sensitivity Cases Rev, O. Apnl 1997 c:\rewproj 2\3603 w- 10.wpf: 1 b-041 197 l
. . - - _ _ _ _ _ . _ _ _ _ _ . _ . _ ~ _. _ _ _ _ _ . _ . . _ . _ . _ - . . _
l i h 7-89 Figure 7.3-24a O NOTRUMP Mixture LeveI 1 2.0
- inch Break with 1 CMT, Auto ADS l
All ADS 1 to 3. 3 ADS-4 (Case 12) : All ADS 1 to 3. 4 ADS-4 (Case 120) l
+---Top of Core ;
30 _
.~. 2 6 -A -
; 22 -: -
_, 1 8 __ f_ . ; , _ . _ .+. _ . + . _ , ; . _ . ._ 14 -2
= -
; 10 -;
E g f f I . I i i 4 0 1000 2000 3000 40'00 5000 Time (s) 1 lO Figure 7.3.24s l MAAP4 Mixture Leve1 2.0 Inch Break with 1 CMT, Auto ADS A!I ADS 1 to 3. 3 ADS-4 (Case 12) All ADS 1 to 3. 4 ADS-4 (Case 120) ! +--- Top of Core ; i ( _. 3 0 _ l- _ C 26 -i r=- l .22-_: 1B_;._._. ._._.+._._.p._. l _,
;._._._. ; ._._._. ; ._._. l ._. ; ._. ; ; . _ . ._
" 14 -2
=
; 10 -;:
- E i 6 ,t ,I ,I ,
0 1000 2000 3000 4000 500 0 . Time (s)
;O 4
l l Results of Sensinvity Cases Rev. 0. Apsil 1997 c:Wewproj2\3603w.10.wpf:Ib-041197 l
7-90 1 Figure 7.3-250 g NOTRUMP integrated ADS-4 Vapor l 2.0 Inch Break with 1 CMT, Auto ADS No ADS 1 to 3. 3 ADS-4 (Case 2) Ali ADS 1 to 3. 2 ADS-4 (Case 12b) ! 100000 f 80000 - v 60000 - w 40000 -3 - m ' 20000 - b e - 2 ' ' 0 O 10'00 20'00 30'00 40'00 5000 Time (s) Figure 7.3-25b h MAAP4 Integroted ADS-4 Vapor , 2.0 inch Break with 1 CMT, Auto ADS l No ADS 1 to 3. 3 ADS-4 (Case 2) Ali ADS 1 to 3. 2 ADS-4 (Case 12b) 100000 - l
)
80000 - 4 v 60000 -3 40000 - b m : ' 20000 ,-
~
0 l l l' 0 1000 2000 3000 4000 5000 l Time (s) O Results of Sensitivity Cases Rev. O. Apnl h7 o:inewproJ2\3603w-10mpf:lb-041197
7 91 Figure 7.3-26a NOTRUMP integroted ADS 1 to 3 Vapor 2.0 inch Break with 1 CMT, Auto ADS No ADS 1 to 3, 3 ADS-4 (Case 2)
----All ADS 1 to 3, 2 ADS-4 (Case 12b) 100000 - -
'~
f 80000 -f - v 60000 -3 ,'
- /
40000 -- / m : / 20000 -3 , s : ./ i , 0 i 0 1000 20'00 30'00 40'00 5000 Time (s) O rigure 7.3-268 MAAP4 Integroted ADS 1 to 3 Vapor 2.0 Inch Break with 1 CMT, Auto ADS No ADS 1 to 3, 3 ADS-4 (Case 2) Ali ADS 1 to 3, 2 ADS ~4 (Case 12b) 100000 = f 80000 -3 ,- v 60000 -- ~ -
/
40000 - ' t.n - f g 20000 - 1
~
0 l l l l 0 1000 2000 3000 4000 5000 Time (s) bo Results of Sensitivity Cases Rev. O, Apnl 1997 o:\newproj2\3603w.10.wpf: I b-041 197 l
i l 7-92 Figure 7.3-27a g NOTRUMP Detoiled Downcomer Pressure 2.0 Inch Break with 1 CMT, Auto ADS No ADS 1 to 3. 3 ADS-4 (Case 2)
---- AlI ADS 1 to 3, 2 ADS-4 (Case 126) m 95 _
O
- s 1 75 -- ]
g a 55 -- \ m
\
m : \ l l 35 -- s a - _~________
' 15 l l l l 0 1000 2000 3000 4000 5000 Time (s)
Figure 7.3-27b h MAAP4 Detoiled RCS Pressure l 2.0 i nch Break with 1 CMT, Auto ADS No ADS 1 to 3. 3 ADS-4 (Case 2)
----Al 1 ADS 1 to 3, 2 ADS-4 (Case 12b)
_ 95 _ , O i l i
- s 1 75 -- \
i e 55 -5 \
~
1 l 35 -- \' l ' E f _ . _ ._ _ _ _h,
' 15 l l l l 0 1000 2000 3000 4000 5000 Time (s)
O Results of Sensitivity Cases Rev. O. April 1997 ohwproj2\3603w-10 wpf:lboti197
L 7-93 Figure 7.3-28a ' O NOTRUMP integrated IRWST Injection 2.0 Inch Break with 1 CMT, Auto ADS No ADS 1 to 3, 3 ADS-4 (Case 2) L ----AlI ADS 1 to 3. 2 ADS-4 (Case 12b) O 3 100000 E 80000 -: n , C 60000 -- ,' e m 40000 -j ' w .. o 20000 -j ,- 2 - 0 ./ , 3 0 1000 2000 30'00 40'00 5000 3 Time (s) O rigure 7.3-288 MAAP4 integroted IRWST Injection 2.0 Inch Breok with 1 CMT, Auto ADS No ADS 1 to 3. 3 ADS-4 (Case 2)
----All ADS 1 to 3. 2 ADS-4 (Case 12b) 100000 m 2 /
E 80000 -j , n - 60000 -- ,
/
m 40000 -} / w - / o 20000 -j , 2 - i 0.- l 0 1000 2000 _30'00 40'00 5000 Time (s) O Results of Sensitivity Cr.ses c:\newpro)2\3603w-10 wpf:lb481197
7-94 l Figure 7.3-29a e; NOTRUMP RCS inventory 2.0 Inch Break with 1 CMT, Auto ADS No ADS 1 to 3, 3 ADS-4 (Case 2)
----All ADS 1 to 3, 2 ADS-4 (Case 12b) 400000 m : ) 300000 -- " 200000 -}
m :
" 100000 -- N___
E _ 0 l l l !. 0 1000 2000 3000 4000 5000 Time (s) Figure 7.3-29b $ MAAP4 RCS Inventory 2.0 Inch Break with 1 CMT, Auto ADS No ADS 1 to 3, 3 ADS-4 (Cose 2) Al I ADS 1 to 3, 2 ADS-4 (Case 12b) 400000 ~ m 300000 - 200000 -} m -
- 100000 -2 ' ----
a ___ OE _ 0 l l l l 0 1000 2000 3000 4000 5000 Time (s) l 0 Results of Sensitivity Cases Rev. O. Apnl 1997 o:\newproj2\3603*- 10.wpf: l b-041 197
7 .17 i. l Figure 7.3-30a NOTRUMP Vessel inventory
-2 . 0 Inch Break with 1 CMT, Auto ADS '
No ADS 1 to 3. 3 ADS-4 (Case 2) ,
----Ali ADS 1 to 3, 2 ADS-4 (Case 12b) ;
160000 -
'm : i E '
A 120000 -_ l i
/
80000 -I _
\ ._ ~ - -
m _ s, ,___- ,
~
o 40000 -- - i
.s :
i i l 0 '.l l l l l 0 1000 2000 3000 4000 5000 > l Time (s) i !O Figure 7.3-30b l. MAAP4 Vessel inventory 2.0 Inch Break with 1 CMT, A u.t o ADS No ADS 1 to 3. 3 ADS-4 (Case 2) Al! ADS 1 to 3. 2 ADS-4 (Case 12b) 160000 m : E ~ o 120000 - v 80000 -- - w
- 40000 -1
' ~~
_l o - i
~
2 _ 0 l .l l l l
. 0 1000 2000 3000 4000 5000 L Time (s)
!O 4 1 1 Results of Sensitivity Cases Rev. O, April 1997 l o:Wwproj2\3603w-10.wpf:Ib&l197
7-96
)
j Figure 7.3-31a g NOTRUMP Mixture Level 2.0 Inch Break with 1 CMT, Auto ADS No ADS 1 to 3. 3 ADS-4 (Case 2)
----All ADS 1 to 3. 2 ADS-4 (Case 12b)
+--- Top of Core 30 _
0 26 -%
! '-'s g 3g _- ._._. ;._._._. l._._._. ;._._._ +._.3_.+_._.+ ._. j;_ , p_._.q
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" 6
~
l l l 0 1000 2000 3000 4000 5000 Time (s) Figure 7.3-31b h MAAP4 Mixture LeveI 2.0 inch Break with 1 CMT, Auto ADS No ADS 1 to 3. 3 ADS-4 (Case 2) All ADS 1 to 3. 2 ADS-4 (Case 120)
+---Top of Core 30 _
C 26 -E
E a 18 -
- 14 -~
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= -
~ 10 -E " 6 i i i i 0 1000 2000 3000 4000 5000 Time (s) O Results of Sensitivity Cases Rev.0, April 1997 o:\newproj2\3603 w - 10.wpf: ! b-041 197 , l
7-97 i l- , 7.4 Partial Depressurization for RNS Injection i !4 i All the other benchmarking cases conclude with stage 4 ADS actuation to achieve IRWST gravity injection. The focus on IRWST gravity injection is due to this being the more limiting passive-only scenario that is considered more challenging to correctly predict the analytical plant response. l I However, there are success paths on the AP600 PRA event trees that credit pumped RNS injection l rather than IRWST gravity injection. The RNS also draws the water inventory from the IRWST, but ! ! the pumped RNS system is similar to low pressure ECCS injection in current operating plants. l An AP600-specific element of the success paths that credit RNS is that ADS actuation must occur to I depressurize the RCS below the RNS shutoff head. The success :riterion for these " partial j depressurization" paths is I valve from either stage 2,3 or 4 ADS. Stage 2 and 3 ADS valves are the , same size, with stage 3 opening later than stage 2. S: age 4 valves are larger, and generally provide i better depressurization because they vent directly from the hot leg to the containment, rather than through the pressurizer to the IRWST. The opening of one stage 3 ADS valve provides the most l limiting response to bound the possibility of other ADS valves. 1 l Case 13 demonstrates that MAAP4 correctly predicts the plant response to the opening of a single stage 3 ADS valve. He break size of 2" was selected. The break location of the cold leg was selected, because as shown in Section 7.1, the higher elevation of the cold leg may cause the hot leg I l to contain water for a longer time period. As shown in Section 7.3, there will be an insurge of water x into the pressurizer when ADS opens, if the hot leg contains water. Water held up in the pressurizer is both a source of inventory loss from the vessel, and has the effect of causing it to be harder to depressurize the RCS. Other assumptions for case 13 are no accumulators,1 CMT, no PRHR nor start-up feedwater, and RNS injection via one DVI line. He containment is assumed to remain at atmospheric pressure throughout the accident progression. The overall RCS pressure (Figure 7.4-1) response is similar to other 2" break benchmarking cases until l ADS is actuated. The integrated water loss from the break (Figure 7.4-2) shows that MAAP4 predicts l a lower water flowrate than NOTRUMP, but both codes predict the same integrated loss once the L break location uncovers. MAAP4 predicts vapor loss from the break (Figure 7.4-3) sooner than j NOTRUMP due to the simplified homogenous fluid modelling in MAAP4 The integrated vapor loss l from the break is predicted to be higher in MAAP4 than in NOTRUMP. l The CMT water inventory (Figure 7.4-4) and the CMT water level (Figure 7.4-5) once again show the same trends as other 2" break benchmarking cases. MAAP4 transitions from Chff recirculation to CMT draining approximately 600 seconds later than NOTRUMP. The difference of the timing affected 2" hot leg breaks that credit stage 1,2 and 3 ADS (Section 7.3). However, for the cold leg break, both codes predict the insurge of water into the pressurizer (Figure 7.4-6). Both codes predict that the hot leg level (Figure 7.4-7) falls below the surge line elevation, and the water flow into the pressurizer rtops until after RNS injection starts. d V Results of Sensitivity Cases Rev. O. April 1997 oAnewproj2\3603w-!!.wpf:lb-041197 i i
7-98 When one stage 3 ADS valve is opened, NOTRUMP predicts a brief period of water relief. Both codes predict water relief through stage 3 ADS (Figure 7.4-8) after RNS injection starts. The vapor loss from stage 3 ADS (Figure 7.4-9) i; :imilar for both codes, with MAAP4 a higher integrated loss than NOTRUMP. Once water relief through stage 3 ADS starts, both codes predict the same rate of water and vapor loss. The detailed pressure (Figure 7.4-10) shows similar trends from both MAAP4 and NOTRUMP. Both codes easily depressurize the RCS below the RNS shut-off head, and further depressurize until the pressure is approximately 100 psia. The differences in timing of achieving injection from the pumped RNS is consistent with the difference in the transition time from CMT recirculation to draining. The same trends for the RCS coolant inventory (Figure 7.4-11) and the vessel inventory (Figure 7.412) are predicted by both codes after CMT draining starts. Except for the shift in the accident progression timing, the prediction by MAAP4 matches the NOTRUMP prediction very well. The conclusion of successful core cooling is demonstrated by no core uncovery (Figure 7.4-13). O i l Results of Sensitivity Cases Rev. o, April 1997 c:\newproj2\3603w-11.wpf;1b411197
7-99 I L i, O ( l : i l . ; Figure 7.4-1 ; R'C S Pressure for Case 13 J l 2.0 Inch CL Break, RNS i njection l NOTRUMP ] MAAP4 2500 _ n _ l c - l 2000 - 7m. .v. _ i - ,V 1500 - - S hl -------- .... I
' 1000 --
3 I w ~. \ w - \ e 500 - - s
- u
- N s
L l u C' 0
,i
, k ','
4 L 0 1000 2000 3000 4000 500 0 Time (S) I I
- i
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\
Results of Sensitivity Cases Rev. 0, April 1997 c:Wwprtq2\3603w.ll.wpf:Ib 041197 I i
7-100 0 Figure 7.4-2 Break Integrated Water for Case 13 2.0 Inch CL Break, RNS Injeetion NOTRUMP MAAP4 400000 _ 350000 - E 300000 -j _a - 250000 -E ' v : - - 200000 -j ,- m m 150000 -i ' O s 100000 - :
'/
50000 - ! 0- l l l l 0 1000 2000 3000 4000 5000 IIme (S) 9 Results of Sensitivity Cases Rev. O, Apnl 1997 otewproj2\3603w.ll.wpf:ib441197
7-101 , 1 l
'O Figure 7.4-3 Break Integrated Vapor for Case 13 2.0 Inch CL Break, RNS Injection NOTRUMP
---- MAAP4 120000 _
~
, 100000 - - E : O o 80000 -- C - 60000 - m : m 40000 - - o 7 : ,,__ 20000 - _- - 0 __s- i , 0 10'00 2000 30'00 40'00 5000 Time (s) n v Results of Sensitivity Cases Rev. 0. Apnl 1997 o.Wewproj2\3603w- I I .wpf: l b-041197
7-102 O Figure 7.4-4 CMT Water Inventory for Case 13 2.0 Inch CL Break. RNS Injection NOTRUMP
---- MAAP4 140000 -
120000 -- ~- m _ \ s E 100000 -:
-Q 80000 --
s s h m 60000 -- s
" : s C 40000 - -
s , 2 : s 20000 - s s s 0 l l l l 0 1000 2000 3000 4000 5000 Time (s) l l l O Results of Sensitivity Cases Rev. 0, April 1997 c:Vewproj20603w-I t.wpf;1t> 041197
7 103-O Figure 7.4-5 CMT LeveI for Case 13 2.0 inch- CL Break. RNS l'n j e c t i o n NOTRUMP l MAAP4 i L 25 1 m 20 ----- s ____ -
- \
A 2 \ lQ l
" 15 - -
s s i - s l r : ' l cn 10 -- s l .__ : s O [ s L I 5- N { s s s
, , , s ,
0- , , i, , 0- 1000 2000 3000 4000 5000 Time (S) \ l l tV 1 (- Results of Sensitivity Cases Rev. O, Apnl 1997 l ohwproj2\3603w II.wpf lb-04t l97
7 104 O Figure 7.4-6 Pressurizer Inventory for Case 13 2.0 Inch CL Break. RNS Injection NOTRUMP
---- MAAP4 100000 _
m 80000 -- ~ _,.-t E / _O ~ '% \ v 60000 -- / _ f
/
m 40000 -- ~ f m _ \ /
/
o ' IE 20000 - , I* I
,'~"/
'l 0 l -l l 0 1000 2000 3000 4000 5000 Iime (s)
O Results of Sensitivity Cases Rev. O, Apn! 1997 chwproj2\3603w-ll.wpf:lbolll97
7-105 O Figure 7.4 -7 Hot Leg Water LeveI for 2.0 inch CL Break. RNS injection Case 13 NOTRUMP Pressurizer Loop
----MAAP4 Both Loops 36
_ i 34 -- I l _, 32 -- ' C C 3o -i C 28 -- l(1 = \ l i I f
,tIWje,4# die U ~
f "* " *'r {
*26--
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- 24 --
7 / 22 -- 20 ' 0 10'00 20'00 30'00 4000 5000 T ,i m e (s) [ Results of Sensitivity Cases ohwproj2\3603w.llapf:lb Gil197 Rev. O April 1997
7-106 O l Figure 7.4-8 ADS 3 i n.t e g r a t e d Water for Case 13 2.0 Inch CL Break, RNS Injection NOTRUMP l
---- MAAP4 l
150000 _ m 120000 -j E - _a : ,'
/
U 90000 -~ /
/
co - 60000 - f f cn / _~ o -
/
CE 30000 -j ,'
- /
/
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f
' ' (
0 0 10'00 20'00 30'00 40'00 5000 Time (s) O Results of Sensitivity Cases Rev. O, April 1997 o:Wj2\3603w-ll.wpf:1b-041197
7-107 n l U 1 Figure 7.4-9 ADS 3 Integrated Vapor for Case 13 2.0 Inch CL Break, RNS Injection NOTRUMP MAAP4 150000 _ m 120000 -? E : es .c - b v 90000 -2 m 60000 -3 ,' Cn -
/
a : / CE 30000 -~ ' f
/
/
0 - ' ' l ! ! ! 0 1000 2000 3000 4000 5000 IIme (s) Figure 7.4-9 Results of Sensitivity Cases Rev. O. Apnl 1997 c:\newproj2\3603 w- i l .wpf: I b-041197 I
7-108 O Figure 7.4-10 De. tailed Downcomer Pressure for Case 13 2.0 Inch CL Break, -RNS Injection NOTRUMP Downcomer
----MAAP4 RCS
-{- - - - R N S Shut-off Head 400 m -
)
C - 1
~
\
1
" i l
C. 300 - 1 l _ v _ \ _ s _ \ 200 -- g _._._.; ._._.__4._._._. ; ._._. j ._ ; .\,.p _. j ._. ; ._.4 _. l ._ c -
's, $ 100 -f o _
u - 0- - 0 l l l l 0 1000 2000 3000 4000 5000 Ilme (s) l l 9 Results of Sensitivity Cases Rev. 0. April 1997 c:\newproj2\3603w. l l .wpf; 1 b-041197
7-109 0
, Figure 7.4-11 RCS Mass i n v e n t c, r y for Case 13 2.0 Inch CL Break, RNS Injection NOTRUMP
... - - - M A A P 4 350000 300000 -3
- s E 250000 -_: s O N "v 200000 -i -
's s ,-
\ /
m 150000 -i s m : ~___ - L oE .100000 -i _ l l 50000 -: l : ?
- l. 0 -
l l l l , , 0 1000 2000 3000 4000 500 0 . ! Iime (s) ! 1 l l I l l lO Results of Sensitivity Cases Rev. 0, Apnl 1997 l
- o
- %ewproj2\3603w-i l.wpf:I b-041197 l
7 110 0 Figure 7.4-12 VesseI Mass i nventory for Case 13 2.0 Inch CL Break, RNS Injection NOTRUMP MAAP4 160000 s
\
_ \
\
^ 12 0 0 00 -- \ /- E ,_____/ o N 4 k ' ~ ]s -, g 80000 --
~
m
~
M o - s 40000 -- o l l l l 0 1000 2000 3000 4000 5000 Time (s) I O Results of Sensitivity Cases Rev. O Apnl 1997 c:\rewproj?3603w Il.wpf:1b-04!197
7-111 r t s Figure 7.4-13 Core Mixture Level for Case 13 2.0 Inch CL Break. RNS Injection NOTRUMP
----MAAP4
-t- - - - T o p of Core
_ 30 _
~ -
- 26 %
_ M __________ _ _L _ _ em U - 22 -- . m 18-- ._._. l . _ . _ . _ . 4_ _ . _ . _ . _ + . _ . _ . _ ._4.. _ . _ + . _ . ; . _ . ; ._.+._._+._.;._ S u 14-- -
~
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":E i e i i 6 i i i 0 1000 2000 3000 4000 5000 Time (S) i' l
l l 1 i } Results of Sensitivity Cases Rev. O. AprC 1997
. ohwproj2\3603w-ll.wptit441197 :
7-112 7.5 IRWST Injection The final benchmarking sensitivities examine the impact of IRWST injection boundary conditions. O Case 14 shows the benefit of a higher containment pressure. The higher containment pressure could be due to the containment being isolated, or a more realistic modelling of a containment isolation failure. Case 15 shows the impact of a higher IRWST temperature. The higher temperature could be due to the operation of the PRHR heat exchangers, or the outlet of hot vapor and water from stages 1, 2, and 3 ADS. A conservative IRWST water temperature of 200 F is selected for the sensitivity. Case 16 is a sensitivity to crediting both DVI lines as injection paths for the IRWST gravity injection; all other benchmarking cases demonstrate injection through only 1 DVI line. CASE 14 - 2" HL BREAK WITH 30 PSIA CONTAINMENT PRESSURE Case 14 is a 2" hot leg break with all the same assumptions as case 2, except a higher containment pressure is modelled. A higher containment pressure is a benefit, allowing earlier 1RWST injection and higher IRWST injection flowrates. The RCS does not have to depressurize as far to achieve the needed AP from the top of the IRWST to the RCS to allow 1RWST gravity injection to begin. More energy can be released by the steam at higher pressures, and thus depressurizing the RCS is easier. The value of 30 psia for the containment pressure is selected to illustrate the effect of the containment pressure. In the long-term, the containment pressure is e:.pected to be lower than 30 psia when containment isolation is successful. However, the steam released from stage 4 ADS to the containment cacses the containment to pressurize at a time that is beneficial to acMeving IRWST gravity injection. Case 14 is more accurately described as a sensitivity to the con ainment pressure being 30 psia at the start of IRWST gravity injection. This is because a constant :ontainment pressure is not easily modelled in MAAP4. A containment pressure of 30 psia when IRWST gravity injection 2 starts is achieved in MAAP4 by modelling a containment isolation failure of 93 in . In NOTRUMP, the containment pressure is a boundary condition input that was changed in a restart of case 2 prior to IRWST injection. The containment pressure assumed in NOTRUMP is shown in Figure 7.5-la, and the containment pressure calculated by MAAP4 is shown in Figure 7.5-lb. Both MAAP4 and NOTRUMP predict a minor impact on the ADS-4 vapor (Figures 7.5-2a and 7.5-2b) when there is a higher containment pressure. Both codes show the same minor deflections in the integrated ADS-4 vapor release, with less release in the long-term. The RCS pressure (Figures 7.5-3a and 7.5-3b) stabilizes at a higher value when there is a higher containment pressure, because the system is dependent on the AP from pressure to containment, not an absolute value of pressure. The NOTRUMP RCS pressure stabilizes at a relatively constant value, while MAAP4 shows a downward trend. This is due to the difference in the containment pressure assurnptions, necessary because of the different modelling capabilities of the code.
'Ihe higher containment pressure causes the IRWST injection (Figures 7.5-4a and 7.5-4b) to stan approximately 200 seconds earlier, and to inject at a faster flowrate. Both codes predict this trend.
Results of Sensitivity Cases Rev. O. April 1997 o:\newproj2i3603w.12.wpf:1t>-041197
l 7-113 l The same trends of RCS inventory (Figures 7.5-5a and 7.5-5b), vessel inventory (Figures 7.5-6a and 7.5-6b), and vessel mixture level (Figures 7.5-7a and 7.5-7b) are predicted by MAAP4 and l NOTRUMP. Relative to case 2, case 14 has higher minimum coolant inventories and the depth and { j duration of core uncovery are not as liraiting. i 4 Although core uncovery is not prevented in case 14 by a containment pressure of 30 psia when IRWST injection starts, case 14 illustrates the beneficial impact of containment pressure. Furthermore, i case 14 is another example of MAAP4 predicting the same trends as NOTRUMP for a specific change , in analysis assumptions / scenario. CASE 15 - 2" HL BREAK WITH 200*F IRWST TEMPERATURE j1 Case 15 is a 2" het leg break with all the same assumptions as case 2, except a higher IRWST water ' temperature is modelled. A higher IRWST temperature is a penalty because the water injected into the RCS is not as subcooled. The higher IRWST water temperature could be due to the operation of the PRHR heat exchangers, or the outlet of hot vapor and water from stages 1,2, ar.d 3 ADS. PRHR and stages 1,2 and 3 ADS use the IRWST water as a heat sink. He value of 200*F is selected for the IRWST water temperature to illustrate the effect of this input boundary condition on MAAP4 and NOTRUMP calculations. The 200*F temperature is unrealistically high for several reasons. De systems that could cause the IRWST heat up are not being credited. he heat removal benefit of the PRHR and the depressurization benefit of stage 1,2 and 3 ADS are j conservatively ignored. Furthermore, when the IRWST could heat up to 200*F, the decay heat in the l core would be at a much lower level than modelled in case 15. He value of 200*F is selected to be a l bounding value to illustrate that successful core cooling is still predicted. Case 15, with an IRWST temperature of 200*F is compared to case 2, with an IRWST temperature of 120*F. He value of 120*F is the Tech Spec maximum for normal plant operation, and is assumed for all the other benchmarking cases. De accident progression is the same as case 2 until IRWST ! injection (Figures 7.5-8a and 7.5-8b) starts. Both MAAP4 and NOTRUMP predict that the IRWST injection flowrate is reduced when the IRWST temperature is higher. His is due to a higher RCS pressure (Figures 7.5-9a and 7.5-9b) caused by the higher water temperature. Due to less coolant inventory from IRWST injection, the RCS inventory (Figures 7.5-10a and 7.5-10b) and vessel inventory (Figures 7.5-11a and 7.5-11b) are slower to secover. However, the minitnum vessel inventory is not impacted. His is also true for the vessel mixture level (Figures 7.5-12a and 7.5-12b). He maximum depth of core uncovery is the same regardless of the IRWST temperature,
' but the duration of core uncovery is longer for the higher IRWST temperature. Both codes predict similar trends, with NOTRUMP predicting a larger impact from the higher IRWST temperature.
NOTRUMP's prediction of core uncovery (depth, duration and time since reactor trip) is very similar ,- to NOTRUMP's prediction of case 12b. Based on the PCT remaining less than 2200*F for case 12b
- . (Section 8.0), successful core cooling is also predicted for case 15.
Results of Sensitivity Cases Rev. O. Apnl 1997 c:\newproj20603w-12.wpf.It> 041197
. _ - ~ - --. . _ , - - -. .. - . . .. - - . . , --- , .
I 7-114 l l CASE I6 - 2" HL BREAK WITH 2 DVI LINES FOR IRWST INJECTION Case 16 is a 2" hot leg break with all the same assumptions as case 2, except both DVI lines are credited for IRWST gravity injection. Havmg two parallel injection paths is a benefit, allowing higher { IRWST injection flowrates. The purpose of this case is to show the magnitude of the benefit, and to j compare the MAAP4 prediction to results from NOTRUMP. l The case 16 accident progression is the same as case 2 until IRWST injection (Figures 7.5-13a and 7.5-13b) starts. Both MAAP4 and NOTRUMP predict that the IRWST injection flowrate is increased ! with two DVI paths. However, MAAP4 does not predict a significant impact until after the top of the core recovers, while NOTRUMP predicts an increase in the integrated IRWST injection as soon as it starts. The RCS pressure (Figures 7.5-14a and 7.5-14b) is slightly higher for case 16, until the core recovers. After core recovery, NOTRUMP predicts that case 16 has a higher pressure than case 2, while MAAP4 predicts a lower pressure than case 2. l l Due to more coolant inventory from IRWST injection, the RCS inventory (Figures 7.5-15a and 7.5-15b) and vessel inventory (Figures 7.5-16a and 7.5-16b) recover faster. However, the minimum vessel inventory is not impacted. This is also true for the vessel mixture level (Figures 7.5-17a and 7.5-17b). 'Ihe maximum depth of core uncovery is the same regardless of the IRWST temperature, but the core recovers faster for 2 DVI lines. Both codes predict similar trends, with NOTRUMP predicting a larger benefit from both DVI lines. Case 16 illustrates, however, that crediting more DVI lines does not alter whether or not an accident scenario results in core uncovery. The same conclusions are drawn from either MAAP4 or NOTRUMP. l l l l l l l O, i Results of Sensitivity Cases Rev. 0. April 1997 o$newproj2\3603w.12.wpf. I b-04 I I 97 l
7-115'- o Figure 7.5-1a U _ NOTRUMP Containment Pressure 2.0 Inch Break with 1 CMT, Auto ADS
----30 14 7 psio Containment Pressure (Cose 2)
! psia Contoinment Pressure (Case 14) _ 35 _
.E 3 0 -E m : - - - - - - - - - - - - - - - - - - - -
3 25 -j i i 20 -5
- 3 I
E w 15 -j - m 10 -5 m : o m 5-5 _ 0 ' I 0 1000 2000 30'00 40'00 5000 Time (s) O rigure 7.5-18 MAAP4 Containment Pressure 2.0 inch Break with 1 CMT, Auto ADS i 14 7 psic Conto.inment Dressure (Case 2)
----30 psic Contoinment Pressure (Case 14) l l~ _ 35 i 30-5 t
m : [s 's a 25 -E ' ' I
~~
20 - _:: - --- _________ ,- j' l .E 15-a - ; m 10-5 m : , m 5-_i 0 ' I ! ! i 0 1000 2000 3000 4000 5000 IIme (s) D Results of Sensitivity cases Rn. 0, Aga N o:\newproj2\3603w- 12.wpf;1 b.041197
7 116 Figure 7.5-2a g NOTRUMP Integrated ADS-4 Vapor CMT, Auto ADS 2.0 Inch Break with 1 14 7 psio Containmen* Pressure (Case 2)
----30 osia Contoinment Pressure (Case 14) 125000 _
f 100000 -f v 75000 -5 - 50000 -5 , m : )
" 25000 - : I a
2 l l 0 l l 0 1000 2000 3000 4000 5000 1 Time (s) Figure 7.5-2b MAAP4 Integrated ADS-4 Vapor 2.0 Inch Break with 1 CMT, Auto ADS 14 7 psia Contoinment Pressure (Case 2) j
---- 30 psia Containment Pressure (Case 14) 125000 i ^ :
f 100000 -f _ v 75000 -i l : l 50000 -2 m : 25000 -- 0 l l l- l 0 1000 2000 3000 4000 5000 Time (s) O Results of Sensitivity Cases Rev. O. Apnl 1997 ohwproj20603w-12 wpf Ibe41197 l
.- __ _ _ _ _ _ _ _ _ _ . . . _ _ _ . . _- . ~ _ . _ _ . _ _ . _ _ _ _ _ . _ _ _ .
7-117 1 l p] u Figure 7.5-3a j
\
NOTRUMP Deta'iled Downcomer Pressure ! 2.0 inch Break with 1 C M T ., Auto ADS 14 7 psio Contoinment Pressure (Case 2) L 30 psio Containment Pressure (Case 14) l m 95 ; i .5 85 -E
~
1 75 -! L 65 -E _ l
. 55 }
; 45 -g '
s
' ' '~~~~~--
l 35 -5 '- E 25 -! ' i
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l l l 0 1000 2000 3000 4000 5000 ; Time (s)' j i i Figure 7.5-3b ; MAAP4 Detailed RCS Pressure ! 2.0 Inch Break with 1 CMT, Auto ADS
'4 7 psio Contoinment Pressure (Case 2) >
30 psic Containment Press'ure (Case 14) ' m 95 _ 1
.5 85 -j ;
1 75 -j 65 -E , o 55 -
; 45 -E f \ s i l35-! s~,~~
E 25 -j % i
' 15 l l l !
I l 0 1000 2000 3000 4000 5000 ; Time (s) l LO l Results of Sensitivity Cases Rev. O. Apnl 1997 o:\newproj2\3603 w.12.wpf: l b-N i l 97
7-118 l Figure 7.5-4a g NOTRUMP integrated IRWST Injeetion 1 l 2.0 Inch Break with 1 CMT. Auto ADS
'4 7 psic Containment Pressure (Case 2) {
30 psic Containment Pressure (Cose 14) 100000 -
/
n - E 80000 - ~
/
Q _ /
] 6'0000 - f e 40000 -3 ,
w - i a 20000 -- / 2 i ' ' s' ' 0 ' 0 10'00 20'00 3000 40'00 5006 Time (s) Figure 7.5-4b MAAP4 integrated IRWST Injection 2.0 i nch Break with 1 CMT, Auto ADS
'A 7 psio Contoinment Pressure (Case 2) 30 psio Containment Pressure (Case 14) 100000 _
m _
/
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m 40000 -3 ,' m -
/
a 20000 -l ~
/
! s ; j 0 l l l 0 1000 2000 3000 4000 5000 Time (s) O Results of Sensiuvity Cases Rev. 0, Apnl 1997 oMewpro;20603w 12.wpf:1b-(Mi197
7-119 l Figure 7.5-5a O NOTRUMP RCS Inventory i l 2.0 Inch Break with 1 CMT, Auto ADS
'14.7 psia Containment Pressure (Case 2)
----30 psio Contoinment Pressure (Case 14) l 400000 m ~_
E ~ o 300000 -- i
~
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'\
l
" 100000 --
- N- , _ _ _ _ . _ _
E _ 0 l l l l 0 1000 2000 3000 4000 5000 l Time (s) l n'V Figure 7.5-5b MAAP4 RCS Inventory 2.0 Inch Break- with 1 CMT, Auto ADS l 14 7 psic Containment Pressure (Cose 2)
---- 30 psia Contoinment Pressure (Case 14) l 400000 ~
l ^ _ E l o 300000 -- l
~
! M 200000 -- - l
" 100000 -- ,
=8 0 l l l l 0 1000 2000 3000 4000 5000 Time (s)
Resetts of Sensitivity Cases Rev. O. Apnl 1997 o:\new proj2\3603w.12.wpf.1b-041197 j l
1 7-120 I Figure 7.5-6a g l NOTRUMP VesseI inventory 2.0 Inch Break with 1 CMT, Auto ADS i 14 7 psic Contcinment Pressure (Case 2) l ---- 30 psio Containment Pressure (Case 14) 160000 _ E
~
o 120000 -- , _______ 80000 - ^ ,- w _
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" 40000 --
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0 ! ! l 0 10'00 20'00 3000 4000 5000 l Time (s) Figere 7.5-6b MAAP4 Vessel Inventory 2.0 Inch Break with 1 CMT, Auto ADS 14 7 psic Contoinment Pressure (Case 2) 30 psio Containment Pressure (Cose 14) 160000 _ E ~ o 120000 --
'~~~~~
80000 -} m W o 40000 - V'
- E _
0 l l l ! 0 1000 2000 3000 4000 5000 Time (s) O l Results of Sensitivity Cases Rew 0,ApnlIW7 ! o:\newproj2\3603w- 12.wpf: l b-o41 197 {
l 7-121 3 Figure 7.5-7a l (J NOTRUMP Mixture Level i 2.0 Inch Break with 1 CMT, Auto ADS ! 14 7 psia Contcinment Pressure (Case 2)
----30 psia Contoinment Pressure (Case 14)
-f- - - - T o p of Core l 30 _
~
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- V Figure 7.5-7b MAAP4 Mixture Leve1 2.0 1nch Break with 1 CMT, Auto ADS 14 7 psio Contoinment Pressure (Case 2) 30 psio contoinment Pressure (Case 14)
-t- - - - T o p of Core
_ 30 g 5 26 -5
; 22 -5 '
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Results of Sensitivity Cases Rev. O, Apnl 1997 o:\newproj2\3603 w- 12.wpf: l b-041 197 l l
7-122 Figure 7.5-8a g NOTRUMP Integrated IRWST injeetion 2.0 inch Break with 1 CMT, Auto ADS 3 120 deg-F IRWST Temperature (Case 2)
----200 ceg-F IRWST Temperature (Case 15) 100000 _
E 80000 -- - _o : , C 60000 - ,- m 40000 -3 ,- m : - o 20000 -- -
=E -
0 l l l l 0 1000 2000 3000 4000 5000 Time (s) Figure 7.5-8b MAAP4 Integrated IRWST Injection 2.0 inch Break with 1 CMT, Auto ADS 120 deg-F IRWST Temperature (Case 2)
---- 200 deg-F IRWST Temperature (Case 15) 100000 _
E 80000 -: _a : C 60000 -- m 40000 - ,- m . a 20000 - '
=E :
0 l l l l 0 1000 2000 3000 4000 5000 Time (s) O Results of Sensitivity Cases Rev. O. Apnl 1997 c:vwwproj20603w.12mpf:lb-041197
7-123 Figure 7.5-9a sO NOTRUMP Detailed Downcomer Pressure 2.0 Inch Break with 1 CMT, Auto ADS 120 deg-F IRWST Temperature (Case 2 -) 200 deg-F IRWST Temperature (Case 15') _ _,,, 5 0 = _ E 45 -! v E 40 d . 35 -E _ E 30 -5 25 -5 - ' -
- E -
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i l 7-124 l l Figure 7.5-10a g' NOTRUMP RCS Inventory 2.0 Inch Break with 1 CMT, Auto ADS 120 deg-F IRWST Temperature (Case 2)
----200 deg-F IRWST Temperoture (Case 15) 400000 -
m 3 300000 -
" 200000 -}
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---- 200 deg-F IRWST Temperature (Case 15) 400000 -
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I 7-125 l l ' I O Figure 7.5-11a U ] NOTRUMP Vessel Inventory 2.0 lnch Break with 1 CMT, Auto ADS >
'120 deg-F tRWST Temperature (Case 2) 200 deg-F IRWST Temperature (Case 15) l .
. 160000 l ^ : ! E ~ l o 120000 -- 80000 - , l
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7-126 l l l NOTRUMP Figure 7.5-12a Mixture LeveI e ; 2.0 Inch Break with 1 CMT, Auto ADS l
'120 deg-F IRWST Temperature (Case 2) 1 200 deg-F IRWST Temperoture (Case 15)
+---Top of Core I
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7-127 i l Figure 7.5-13a ! NOTRUMP integrated IRWST Injection i l 2.0 Inch Break with 1 CMT, Auto ADS .
'1 IRWST Line (Case 2) ;
---- 2 IRWST Lines (Case 16) 1 i
l 100000 l m : / E 80003 -3 _a _
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- 1. IRWST Line (Case 2) 2 IRWST Lines (Case 16) 100000 _ j l E 80000 -: /
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7-128 l l Figure 7.5-14a g NOTRUMP Detoiled Downcomer Pressure 2.0 Inch Break with 1 CMT, Auto ADS 1 IRWST Line (Case 2) 2 IRWST Lines (Cose 16) _ 50
.5 45 -5 m :
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.5 45 -~
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7-129 I p Figure 7.5-15a O , NOTRUMP RCS lnventory l , -2.0 Inch Break with _ 1 CMT, Auto ADS l
'1 1RWST Line (Case 2) 2 iRWST Lines (Case 16) 400000
^ :
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----2 IRWST Lines (Case 16) 400000 _
1 n o 300000 --
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i 7-130 l Figure 7.5-16a g NOTRUMP Vessel inventory l 2.0 Inch Break with 1 CMT, Auto ADS '
'1 IRWST Line (Cese 2)
----2 !RWST Lines (Case 16) 160000 m :
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r j 7-131 n v Figure 7.5-17a NOTRUMP Mixture Level 2.0 Inch Break with 1 .CMT, Auto ADS
'1 IRWST Line-(Case 2) 1
----2 IRWST Lines (Cose 16)
+--- Top of Core 30 _
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----2 IRWST Lines (Case 16) 1
+---Top of Core l
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L I l j 8 ' l< 8 LOCTA PCT RESULTS L O Core uncovery was seen in many of the benchmarking cases. To determine if adequate core cooling l was maintained with core uncovery, the Westinghouse small break clad heatup code (LOCTA) of ; Reference 15 as modified by Reference 16, was used to determine the Peak Cladding Temperature on i the lead rod. he cladding heatup code of References 15 and 16 applies to the AP600 design since: l
- 1. De AP600 uses the 17x17V5H fuel design already in use in conventional Westinghouse l l_ designed PWRs. His fuel' type lies within the assumptions and models employed in the code.
l L - i I !. 2. He low pressures seen in the AP600 small break transients subsequent to ADS actuation are j still within the limits of the small break heatup code, since this code is a version of the l Westinghouse large break heatup code which must operate at low pressures. !
- 3. The AP600 uses a 12 foot core design and has peaking factors similar to current Westinghouse designed operating reactors. Thus, the power shape used in the AP600 cladding heatup l
calculation was taken from data for current core designs.' The power shape based on current l core designs, which are low leakage pattem designs with integral absorbers, while not i t l representative of AP600 core designs bounds the AP600 core which' will be a low power ! l- density design with less axial peaking. l ! A ! jty . Nominal assumptions for decay heat and power were applied to the analysis. The decay heat input to , j the small break cladding heatup code was modified to remove the 20% uncertainty from the 10CFR50 i l -- Appendix K specified decay heat. Therefore the decay heat was the ANS 1971 infinite decay heat l without uncertainties. Furthermore, the 102% calorimetric power error.was not applied. Note, l however, that this decay heat assumption is more limiting than ANS 1979 decay heat input for the l
. NOTRUMP analyses. Additiorially, the cladding heat up analysis assumed a total core peaking factor (FQ) of 2.60 and an enthalpy rise peaking factor (FAH) of 1.65.
l ! [ he MAAP4/NOTRUMP benchmarking cases with core uncovery cover a range of AP600 passive ECCS equipment available, a range of break sizes and location, including a break in the Direct Vessel Injection (DVI) piping. Case 1, case 2, case 5, case 12b and case 15 have the highest core vapor temperatures as a result of the calculated core uncovery. De NOTRUMP core exit vapor temperature l is a good indicator of expected peak cladding temperature since the core exit vapor temperature is both a function of depth of cor'e uncovery and duration of the uncovery.' Furthermore, the NOTRUMP transient for core mixture level, core average vapor flow, core pressure and normalized power are direct boundary conditions for the LOCTA code. NOTRUMP results from all of the core uncovery cases are summarized in Table 8-1. Thus, cases 1,2,5,12b and 15 are expected to have the highest cladding temperatures based on the core exit vapor temperature. Cases 1,2,' 5 and 12b were analyzed using the small break cladding N LOCTA PCT Results Rev. O. April 1997 cMewproj2\3603w-13.wpf;1t>041197
8-2 heatup code. Case 15 was not analyzed since the core uncovery is similar to case 12b. Furthennore, the analyzed cases cover both automatic and manual actuation of the ADS, effects due to CMT or accumulator operation, and different levels of decay heat when core uncovery occurs. Thus, these cases address a range of AP600 passive ECCS features. Casel, a 0.5' inch diameter hot leg break with 1 CMT, I stage 3 ADS, and 3 stage 4 ADS actuated on low CMT level signals, resulted in a Peak Cladding Temperature of 1489'F at 10.75 feet and 13,753 seconds. The maximum local zirconium oxidation is 0.4%. A plot of the clad temperature versus time is given in Figure 8-1. Rese results for cladding temperature end oxidation are well below established embrittlement limits for Zircaloy and demonstrate that adequate core cooling was maintained during the period of core uncovery. Case 2, a 2.0 inch hot leg break with I CMT and 3 stage 4 ADS, actuated on a low-low CMT level signal, resulted in a Peak Cladding Temperature of 1475'F at 11.25 ft and 3361 seconds. The maximum local zirconium oxidation is 0.4%. A plot of the clad temperature versus time is in Figure 8-2. These results are well below the established embrittlement limits for Zircaloy and demonstmte that adequate core cooling was maintained during the period of core uncovery. Case 5, a 3.5 inch hot leg break with I accumulator and 3 stage 4 ADS actuated manually at 20 minutes, resulted in a Peak Cladding Temperature of 1461*F at 10.75 ft and 1240 seconds. The maximum local zirconium oxidation is 0.2%. A plot of the clad temperature versus time is in Figure 8-3. These results are well below the established embrittlement limits for Zircaloy and demonst ate that adequate core cooling was maintained during the period of core uncovery. Case 12b, a 2.0 inch hot leg break with 1 CMT, all stage 1,2 and 3 ADS, and 2 stage 4 ADS, actuated on low CMT level signals, resulted in a Peak Cladding Temperature of 1546 F at 11.75 ft and 3647 seconds. The maximum local zirconium oxidation is 0.8%. A plot of the clad temperature versus time is in Figure 8-4. Rese results are well below the established embritticment limits for Zircaloy and demonstrate that adequate core cooling was maintained during the period of core uncovery. The peak clad temperature results are summarized in the final column of Table 8-1. O LOCTA PCT Results Rev. O. April 1997 o Anewproj2G603 w- 13.wpf: 1b-041197
\,J '%.)
N o t* Table 81 Core Cooling Information for Benchmarking Cases With Core Uncovery U NOTRUMP Calculation LOCTA
$d E g Minimum Core Duration of Time Since Reactor Maximum Core Maximum p3 Mixture Level Core Uncovery Trip When Core Uncovery Vapor Temp During Core Cladding Temp Case Case Summary (ft) * (sec) Starts (sec) Uncovery (*F) (*F) 1 0.5* IIL break with I CMT -8.3 675 11504 959 1488
{ 2 2.0* 11L lxeak with I CMT -4.8 875 2715 989 1475 3 5.0" HL break with I CMT - 1.8 41 2188 420 - 4 8.75* HL break with I CMT -1.4 195 320 500 - 5 3.5* IIL lxeak with I accum -6.1 865
- 865 II55 1461 7 8.75* IIL break with I accum -2.0 200 1545 335 -
8 DVI line tweak with I CMT injecting -3.7 600 2246 686 - 12 2* HL break with all stages 1. 2 and 3 and 3 - stage 4 ADS -0.5 65 2800 244 12b 2* IIL break with all stages I,2 and 3 and 2 stage 4 ADS -4.4 1600 2805 1014 1545 14 2* IIL break,3 stage 4 ADS and containment -2.7 370 2675 488 - isolated 15 2* IIL break with 3 stage 4 ADS and IRWST - water temperature of 200*F -4.5 1520 2715 984 16 2* IIL break with 3 stage 4 ADS and 2 out 2 - IRWST injection lines -4.5 505 2770 714 Notes: (1) The minimum mixture level is given relative to the top of the con:. p (2) Two distinct core uncovery periods of 360 and 505 seconds duration.
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8-4 O Figure 8-1 LOCTA Peak Clad Temperature for Case 1 0.5 inch Break with 1 CMT TCABY 29 0 0 ELEV 10 75 2200 m - LL_ - 1700 --
" ~
j 1200 -- O 0 e _ Q- 700 -- E - o _ l-- 200 ' ' ' ' ' '''''''''''''''''' 0 2500 5000 7500 10000 12500 1500 0 Time (S) O LOCTA PCT Results Rev. O, Apnl 1997 o:\newproj2\3603w.13.wpf:Ib-041197
8-5 i O 1 1
' Figure 8-2 i LOCTA-Peak Clad Temperature.For Case 2 i 2.0' inch Break with~1 CMT
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8-6 0 Figure 8-3 LOCTA Peak Clad Temperature For Case 5 3.5 Inch Break with 1 Accumulator TCABY 29 0 0 ELEV 10.75 2200 L
- u. -
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' ' ' ' ' ' ' - - ' 1 0 1000 20'00 30'00 4000 !
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i Figure 8-4 LOCTA Peak Clad Temperature for Case 12b ; 20 inch Break with 2 Stage 4 ADS l TCA8Y 33 0 0 ELEV 11 75 2200 m - l w _ 1 v _ : 1700 -- j 1200 -- - o ~ L m C- 700 -- E- - m - i-- -
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_ _ .- ..__ _ _ -. _ . . _._ ~.__-._._ _. _ _ _ _ _ ._ ._.._ . _. _ _. _ _ _ _ 9-1 9 EVALUATION OF RESULTS
)
Sections 6.0 and 7.0 show detailed transient compansons of output parameters from MAAP4 and NOTRUMP on a case by case basis. De purpose of Section 9.0 is to provide an overview of how the codes compare across the spectrum of benchmarking cases. The evaluation is divided into an f assessment of the high importance phenomena (Sn tion 9.1) and the high interest phenomena (Section ( 9.2). High importance phenomena are identified as ones that have a controlling influence on minimum l vessel inventory. High interest phenomena are identified as ones that are unique to AP600 and/or ! PRA scenarios that should be examined, but moderate differences in the predictions are not expected i to have a controlling influence on the minimum vessel inventory. 9.1 Assessment of High Importance Models/Phenomenu i i The PRA PIRTs were developed at the beginning of the MAAP4 / NOTRUMP benchmarking effort, ; as described in Section 3.2. Accident progressions were discussed and the phenomena that could have a controlling influence on the fmal result (minimum vessel inventory) were identified as high importance phenomena. The purpose of identifying high importance phenomena is to provide a framework to assess the adequacy of the code. It was stated during the development of the PRA PIRTs that high accuracy is needed in the calculation of high importance phenomena. Yet the term "high accuracy" was not dermed. If MAAP4 were
, being compared to NOTRUMP to justify that it could replace NOTRUMP, then a high level of precision would be needed. However, since MAAP4 is being used primarily as a screening tool to support the PRA, a lower level of precision is acceptable when comparing MAAP4 results to {
I NOTRUMP results. I i l Bere is no numerical criterion that is established for how close MAAP4's calculations must be to NOTRUMPt. The results of the benchmarking cases in Sections 6.0 and 7.0 consistently show that the trends predicted by the two codes are similar for a large number of benchmarking cases. The i focus is on the vessel mixture leul and whether successful core cooling is expected for the multiple-
- l. failure accident scenarios. M,.AP4 is a simplified code, and the results are not always as accurate as j those from a more detailed code. An analyst uses MAAP4 as a tool to understand the general l response of the plant and whether the core remains cooled during the accident. Core uncoveries are generally shallow and of short duration. Differences such as core uncovery for 500 seconds versus 300 seconds, or a depth of uncovery of I ft versus 2 ft below the top of the core, do not impact successful core cooling conclusions for the types of accident scenarios analyzed with MAAP4.
Although these differences given as examples, would appear to be very large if viewed as percentage differences, it is the proper prediction of trends that is important. Thus, no numerical criterion is established for how close is close enough. Instead, the differences are considered within the context of the judgements being made. f Evaluation of Results Rev. O, April 1997 oAnewproj20603w.14.wpf;1b 041297 l' . - , _ --
9-2 There are eight models identified as high importance phenomena in the PRA PIRTs. For each of the high importance phenomenon, code comparison plots are developed to assess the MAAP4 results for the key variables. Code comparison plots summarize how well the two codes predict a single item for multiple cases. MAAP4 results are presented on the x-axis, and NOTRUMP results are on the y-axis. A perfect match between the codes' results yields data points in a straight,45* line. The choice of the variable is important, and must be something that can be represented as a single value. Whenever possible, the selection of the variables for the code comparison plots was made based on how MAAP4 is used in supporting the AP600 PRA. For example, successful core cooling will be judged from MAAP4 analyses based on the vessel mixture level. Ifit remains above the top of the core, successful core cooling is predicted. If the vessel mixture level falls below the top of the core, then the depth and duration of uncovery and the level of decay heat will be examined. If these parameters fall within the range of the results for which the PCT has been shown to remain below 2200*F in Section 8.0, successful core cooling is predicted. Therefore, the code comparison plots that examine core cooling (Section 9.1.3) are developed around this needed information. Because the MAAP4 analyst focuses on the prediction of the vessel mixture level, the results presented in Section 9.1.3 are the most important to demonstrating the adequacy, and limitations, of MAAP4. Code comparison plots for other high importance phenomena and models play a supporting role in providing an overall confidence level in the MAAP4 results. It should once again be emphasized that the precision that is needed from the MAAP4 calculations is not the same as needed from more detailed codes. Table 9-1 identifies the high importance items from the PRA PIRTs, the parameter (s) that have been O defined to summarize the model, and the applicable cases. The cases that are defined as applicable are usually self-explanatory. However, it should be noted that if a sensitivity case is identical to a previous case for that particular issue, it is not listed. For example, cases 14,15 and 16 are sensitivities examining variations of assumptions related to IRWST injection for case 2. Until the time of IRWST injection, all of these cases are the same. Therefore, for a parameter such as integrated break inventory at time of ADS, cases 14,15 and 16 are not considered applicable since they are the same as case 2 for this parameter. The results of the code comparison plots are discussed in the following sections. I Evaluation of Results Rev. O. Apnl 1997 ' o Anewproj 2\3603w- 14. wpf: I b-041397
9-3 Table 91
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i Code Comparison Plots for High Impertance Phenomena from PRA PIRTs ! Parameter (s) Item from PRA PIRT Figure Examined with Scatter Plot Applicable Cases Break 9-la Inventory loss through the break I,2,3,4,5,6,7,8,8b,9,10, I at time of ADS opening 11,12,13 ' 1 9-lb RCS pressure immediately prior to ADS actuation Interfacial condensation 9-2a Time CMT drains (overview) 1,2,3,4,8,9,10,i1,13 on CMT water surface 9-2b Time CMT drains (detailed) i Core cooling / vessel 9-3a Minimum vessel mixture level All ! mixture level ' 9-3b Duration of core uncovery after 1,2,3,4,5,6,7,8,12.12b.14, ADS 15,16 9-3c Time from reactor trip to start of 1,2,3,5,7,8 core uncovery l Downcomer 9-4 Duration of saturated conditions All except 15 in the downcomer after ADS ADS-4 9-Sa Integrated ADS-4 flow for 1000 All except 13 seconds O V 9-5b Time from ADS-4 opening to All except 13 i 1RWST injection 9-Sc Hot leg level when ADS 1,2,3,4,5,6,7,8,8b,9,10, actuates 11,12,13 ADS 1 to 3 9-6 Integrated ADS 1 to 3 flow for 1,12,12a,12b,13 1000 seconds IRWST 9-7 Integrated IRWST flow for 1000 All except 13 seconds Accumulator 9-8 Duration of accumulator 5,6,7,10,11 injection C1 D Evaluation of Results Rev. O. April 1997 otewproj20603w.14 wpf:lt@l297
9-4 9.1.1 Break Model The break flow rate determines the rate of inventory loss, the system depressurization, and the timing of the accident progression. For larger breaks, the prediction of break flow and depressurization is most important during the blowdown phase because it can impact coolant inventory in the core region. For smaller breaks, inaccuracies in break flow predictions may have a cumulative effect, impacting the timing of the accident progression. Benchmarking cases were defined to cover the spectrum of break sizes that are analyzed with MAAP4. The first variable to examine with a scatter plot is the integrated inventory loss through the break. The selection of this variable is obvious, but the time period over which to integrate the flow is more subjective. The time when ADS valves open was chosen because the break flow is the only method of inventory less, in most cases, until the ADS valves open. In addition, the break location is usually uncovered at the time of ADS actuation, and therefore the rate of inventory loss from the break has decreased substantially. After ADS actuation, the inventory loss from the break is not usually an I important factor in the accident progression. l I The results of the integrated break inventony loss at the time of ADS actuation are shown in { Figure 9-la. Both water and vapor loss are integrated for the applicable cases (1,2,3,4,5,6,7,8, 8b,9.10,11,12, and 13). The inventory loss from the majority of the cases is between 200,000 and 400,000 lbm. Rese cases typically credit only 1 CMT or 1 accumulator. The least inventory loss from the break is less than 150,000 lbm and is predicted for case 1. This is a 0.5" break that loses more inventory from the pressurizer safety valves than through the break. The most inventory loss from the break is over 600,000 lbm from case 11, which credits both CMTs and both accumulators. Therefore, much of the inventory from the CMTs and accumulators is spilled out the break before ADS actuation occurs. As shown in Figure 9-la, MAAP4's prediction of the integrated brea'c inventory loss at the time of ADS actuation is within 10% of NOTRUMP's prediction for all the cases. The cases that are close to a 10% difference are cases 1 and 12. The underprediction of the integrated break loss in case 1 is not significant because the break is so small that the majority of the primary coolant loss is through the pressurizer safety valves. The overprediction of the integrated break loss in case 12 plays a role in the accident progression. MAAP4's prediction of a lower primary-side coolant inventory when ADS is actuated is responsible for the hot legs being empty. This impacts the surge of water into the pressurizer, and the depressurization of the RCS. However, the differences are not due to a deficiency in the break model in MAAP4, rather it is due to the differences in the timing of CMT draining and ADS actuation, as discussed in Section 7.3. The second variable that is examined with a scatter plot is the RCS depressurization that occurs as a result of the break. MAAP4 analyses are used to predict the depressurization of the RCS due to the break, which is the basis for the size definitions of the PRA LOCA categories. If MAAP4 were not adequate for this purpose, it could have an impact on the quantification of the PRA initiating event Evaluation of Results Rev. O. Apn! 1997 oAnewproj2\3603w.14 wpf ?b-041297 l
9-5 frequencies. To assess the depressurization as a result of the break only, the RCS pressure is taken immediately before an ADS valve is opened. L Re results of the RCS pressure at the time of ADS actuation are shown in Figure 9-lb for the applicable cases (1,2,3,4,5,6,7,8,8b,9,10,11,12, and 13). Due to the break, the RCS pressure is decreased 'to values less than 100 psia for the largest breaks. The highest RCS pressure is seen in case 1, which is a 0.5" break. In case 1, the break depressurizes the RCS initially, but since the break is not large enough to remove the decay heat, the system repressurizes after the secondary side of the steam generators empty. As shown in Figure 9-lb, MAAP4's prediction of the RCS pressure at the time of ADS actuation is within 10% of NOTRUMP's prediction for all the cases except the DVI line breaks. MAAP4 l overpredicts the RCS pressure when only the inta-t CMT is modelled (case 8) and underpredicts the RCS pressure when the faulted CMT is credited for an earlier ADS actuation (case 8b). As shown in Section 7.1, these pressure differences do not have a controlling impact on the accident progression nor the conclusions of the analysis. Furthermore, the DVI line break is modelled in a sepnate PRA event tree, so there is no need to categorize it based on the depressurization that occurs due to the break. He agreement between MAAP4 and NOTRUMP on the integrated break inventory loss and the RCS pressure at time of ADS actuation is excellent. MAAP4's break model is shown to be adequate for the range of break sizes from 0.5" to 8.75". The break modelis also valid for a range of break locations, including the hot leg, the cold hg, and the DVI line. There are no new break model limitations or cautions for the MAAP4 user, other than these identified in Section 2.2.1, O Rev. O. Apnl 1997 Evaluation of Results o%ewproj2V603w.14.wpf.lb-041297
9-6 O Figure 9-1a Integrated Break at T ,i m e Inventory Loss of ADS Actuation 700000
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i 1 9-7 !O Figure 9-1 b . I i RCS Pressure l at Time .o f ADS Actuation l 2700
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9-8 9.1.2 Interfacial Condensation on CMT Water Surface One of the high importance phenomena identified in the PRA PIRT for scenarios with CMTs is O interfacial condensation on the CMT water surface. For small breaks, the CMT liquid heats during the recirculation of the CMT such that the interfacial condensation is very small. As the break size increases, the recirculation time for the CMT decreases such that the CMT liquid stays cold and the interfacial condensation will occur. The impact of the condensation is to reduce the pressure at the top of the CMT such that the CMT drain flow is reduced. The overall draining rate of the CMT is important since it determines the time of ADS actuation. As identified in Section 2.2.4, MAAP4's CMT model does not include the ability to model the interfacial condensation on the CMT water surface. The impact of this model deficiency is seen in breaks with diameters of approximately 5" and larger. The variable that is examined with a scatter plot for this phenomenon is the time that CMT draining starts. An overview of the time CMT draining starts is shown in Figure 9-2a for all the applicable cases (1, 2, 3, 4, 8, 9,10,11,13). Lecause case 1 is a slow-progressing accident, this figure does not clearly show the data from most of the cases. What is shown in Figure 9-2a, is that MAAP4 overpredicts the time for smaller break sizes (0.5" and 2.0") to transition from CMT recirculation to draining. 'Ihis effect is not due to interfacial condensation, and is discussed in Section 9.2. Figure 9-2b is also a plot of the time that CMT draining starts, with the axes adjusted to show the results for breaks greater than 2". As expected, MAAP4 underpredicts the time to transition to CMT draining for break sizes starting at approximately 5" Cases 3,9,10 and 11 are all 5" breaks, for which MAAP4 predicts the transition time under 300 seconds, while NOTRUMP predicts the transition time later than 300 seconds. There is no significant impact on the accident progression or the conclusions of the analyses due to the difference in the 5" cases. Case 4, however, is an 8.75" break for which MAAP4 predicts a transition to CMT draining approximately 150 seconds earlier than NOTRUMP. The rate of coolant loss for this break size is large enough that this timing difference impacts the coolant inventory in the RCS. In MAAP4's calculation, the earlier draining of the CMT causes the CMT to be a make-up water source sooner than realistic. Due to the make-up water from the CMT, MAAP4 calculates the core remains covered during the early part of the event when the I core is predicted to uncover using more detailed models. The uncovery is relatively shallow with a short duration (see Section 6.4). The interfacial condensation on the CMT water surface is shown to impact only the larger break sizes analyzed with MAAP4. This limitation is identified in Section 2.2.4. There are no new limitations or cautions for the MAAP4 user related to the inte: facial condensation on the CMT water surface. Evaluation of Results Rev. O. Apnl 1997 c:\newproj2\3603w.14.wpf;lb-041497 I 1
i 9-9
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9-10 l 9 Figure 9-2b Time CMT Draining Starts DetoiIed ' 500 400 -- _ MAAP4 Underpredicts
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l 1 9-11 . l l 9.1.3 Core Cooling / Vessel Mixture Level 1
/ I I bl Core cooling and the vessel mixture level are identified as high importance phenomena on the PRA PIRTs. However, these items are more than individual phenomena they determine the end results of the analysis. The impact on the minimum vessel mixture level was the only criterion for selecting the high importance phenoment ! i the PRA PIRTs. The vessel mixture level is the key element to determining whether a clad temperature heat up occurs. The vessel mixture level is the parameter used m the T/H uncertainty resolution process to identify the most thermal-hydraulically limiting j accident scenarios. The vessel mixture level is the key parameter to be examined for the PRA success I criteria to determine if the core remains cooled. MAAP4's ability to predict the vessel mixture level is very important.
His section contains three code comparison plots that are related to core cooling. The first and most important is the minimum vessel mixture level. He second and third code comparison plots are based on parameters that will be examined for the PRA success criteria analyses to determine if successful core cooling occurs when the mixture level falls below the top of the core. If core uncovery occurs, then the depth and duration of uncovery and the level of decay heat will be examined. If these parameters fall within the range of the results for which the PCT has been shown to remain below 2200 F in Section 8.0, successful core cooling is predicted. Herefore, the second and third code comparison plots for core cooling are duration of core uncovery and length of time that the reactor has n been shut-own when core uncovery starts.
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VESSEL MIXTURE LEVEL The minimum vessel mixture level predicted by MAAP4 for all benchmarking cases is compared to the NOTRUMP calculation in Figure 9-3a. The figure is divided into four quadrants, and the results in each quadrant will be discussed. Most of the benchmarking cases fall within the bottom left quadrant, which means that both MAAP4 and NOTRUMP predicted core uncovery. The depth of core uncovery predicted by MAAP4 follows the same general trends as NOTRUMP, i.e., general categorizations about shallow or moderate uncovery could be made based on MAAP4 results. The only notable deviation in this quadrant where MAAP4 underpredicts the core uncovery depth is in case 1. This is a slow-progressing accident scenario. The core uncovery in case 1 occurs at a time of very low decay heat. The difference in MAAP4's prediction does not impact the overall accident progression or the conclusions of the analysis. The bottom right quadrant contains results from cases for which NOTRUMP predicted core uncovery, but MAAP4 did not. There am three benchmarking cases that fall within this quadrant. Case 4, an 8.75* hot leg break with I CMT, uncovers the core early in the accident progression as a result of the g high inventory loss through the break and no r.nmulators to provide rapid inventory make-up. As (3) discussed in Section 9.1.2, the reason that MAAP4 does not predict core uncovery is that it cannot Evaluation of Resuhs Rev. 0. Apnl 1997 o$newproj2\3603w.14.wpf:lb-o41497 i l_ _ _ _ _ _ _ _ _ _ - _ _ _ _ _ _ _ - _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ . _ _ _ _ _ _ _ _ _ -
9-12 l model the interfacial condensation on the CMT water surface. However, MAAP4 does predict that the mixture level comes within approximately 1 ft of the top of the core, while NOTRUMP predicts the , core uncovery is relatively shallow (less than 2 ft below the top of the core). This difference is only expected for the largest breaks analyzed with MAAP4. The other two cases for which NOTRUMP predicts core uncovery, while MAAP4 does not, are 2" hot leg breaks that credit stage 1,2 and 3 ADS. Case 12 credits three stage 4 ADS, and NOTRUMP predicts that the cole barely uncovers. Case 12b credits only two stage 4 ADS in addition to the other stages, and NOTRUMP predicts a moderately deep uncovery. MAAP4 does not predict core uncovery for these cases because of a later timing prediction of the accident progression. When ADS actuates, MAAP4 predicts that the hot leg is empty, while a mixture level in the hot leg is still predicted by NOTRUMP. This results in a difference in the water surge into the pressurizer, and the depressurization of the RCS. Details of these cases are discussed in Section 7.3. The conclusions from these differences are that MAAP4 should not be used to justify the effect of stage 1,2 and 3 ADS if MAAP4 does not predict an increase in the pressurizer water inventory, unless further benchmarking work is performed to assess what break range for which the MAAP4 limitation is applicable. This is not expected to impact the success criteria analyses for the PRA, since ADS success criteria are based on the number of stage 4 ADS valves. The upper left quadrant on Figure 9-3a shows cases for which MAAP4 predicts core uncovery, but NOTRUMP does not. Only two cases fall within this quadrant. For case 6 and case 9, NOTRUMP predicts that the mixture level turns around just in time to prevent core uncovery. MAAP4, however, predicts very shallow uncovery for these cases. There is no significance to the minor differences. However, it is noteworthy that the existence of case results within this quadrant illustrates that MAAP4 can neither be categorized as always conservative nor always non-conservative relative to whether core uncovery is predicted. The final quadrant on Figure 9-3a is the upper right quadrant, for which both codes predict that the core remains covered. Results from five of the benchmarking cases fall within this quadrant. Two l cases, which are near the border to other quadrants, are case 11 and case 12a. Case 11 is a 5" hot leg break that models both CMTs and both accumulators. MAAP4 predicts minor oscillations in the vessel mixture level when both accumulators inject, causing MAAP4 to underpredict the minimum vessel mixture level. However, the oscillations are insignificant, and do not impact the accident progression nor the conclusions from the analysis. Case 12a is a 2" hot leg break that credits all ADS. NOTRUMP predicts that the core almost uncovers, for the same reasons discussed above for cases 12 and 12b. DURATION OF CORE UNCOVERY The duration of core uncovery is shown on Figure 9-3b for all of the benchmarking cases that ! experience core uncovery. The applicable cases are 1, 2, 3, 4, 5, 6, 7, 8,12,12b,14,15,16. Data l Evaluation of Results Rev. 0, Apnl 1997 oAnewproj2\3603w.14.wpf;1bo41497
9-13 from cases with two separate periods of core uncovery are given separately for each period of core uncovery. 1
' De majority of the data points fall in the lower left-hand region, where the duration of core uncovery 1 l is short. Even for cases where MAAP4 does/does not predict core uncovery when NOTRUMP does not/does, this figure shows that the duration of those core uncoveries is usually very low. He region '
where both codes predict a duration of core uncovery less than 1000 seconds is also highlighted on ; j Figure 9-3b. His is because it has been the intent, but not a criterion, to limit core uncovery to l approximately 1000 seconds for scenarios that are credited as successful core cooling within the PRA. s ! If the region is extended to include cases for which NOTRUMP predicts the duration to be less than l' l 1000 seconds, while MAAP4 slightly overpredicts the uncovery duration, fourteen of the sixteen data points fall within this area. ' ) . Success criteria analyses for the PRA will use duration of core uncovery predicted by MAAP4 as one l of the pieces of information to assess successful core cooling for cases with core uncovery. It must l } fall within the range of the cases within this benchmarking report to conclude that the PCT is less than ; 2200*F. Information in Figure 9-3b shows that there is no need to bias MAAP4's prediction of the ! core uncovery duration when comparing it to the NOTRUMP-calculated core uncovery duration in Section 8.0. De only exception to this is illustrated in case 12b, for which there are no plans to use i MAAP4 for similar cases.
- l. DECAY HEAT LEVEL AT CORE UNCOVERY ;
He level of decay heat when the co e uncovers is based on the length of time since the reactor has been tripped. Figure 9-3c shows the length of time that the reactor has been shutdown when the core < starts to uncover. The agreement betsveen MAAP4 and NOTRUMP is very good for this variable. Here are no cases for which there is a notable discrepancy. l l l l I I I 1 Evaluation of Results Rev. O. Apnl 1997 c:hewproj2\3603w.14.wpf:I b 041497 s
9-14 1 1
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9-15 l l O
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I 9-16 i O Figure 9-3c ' 1 Shutdown Time When Core Starts to Uncover 14000 12000 --
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m . _ - 9-17 9.1.4 Downcomer O The downcomer is identified as a high importance modelin the PRA PIRTs. ne stored energy in the { vessel wall can irnpact'the pressure of the RCS during the IRWST gravity injection phase. The stored l energy is a potential source of additional steam generation, which may provide additional challenges to l the ADS venting capacity. 1 i lt is difficult to define individual parameters to demonstrate the downcomer model.' The adequacy of l MAAP4's downcomer model is ultimately shown based on whether IRWST injection is established to provide successful core cooling. One variable that is defined to help deterinine the role of the , downcomer in this prediction is the duration of downcomer saturated conditions after ADS actuation. The 'saturated conditions may be due to either flashing as the system depressurizes, or boiling as energy in the vessel wall is transferred to the coolant. i Figure 9-4 shows the MAAP4-calculated duration of saturated conditions in the downcomer (after i ADS actuation) compared to the NOTRUMP-calculated value. All cases are considered, except case 15. Case 15 models an IRWST water temperature close to saturation, and the time period of saturated conditions in the downcomer is off the scale for this figure. Based on Figure 9-4, MAAP4 adequately predicts the general trend of downcomer saturation. MAAP4 predicts the duration of downcomer saturation within an error band of 5 minutes for the majority of the cases. MAAP4 underpredicts the duration of downcomer saturated conditions by more than 5 minutes for only three cases: 5,8b and 12b. MAAP4 overpredicts the duration by more than 5 minutes for only two cases: 9 and 13. The MAAP4 underprediction/overprediction may be partially responsible for the differences seen in cases 8b,12b, and 9. However, the differences in MAAP4's downcomer saturation prediction for case 5 and case 13 do not appear to impact the vessel mixture level. Thus, although Figure 9-4 provides additional interesting information, the adequacy of MAAP4's downcomer model is ultimately based on the ability of MAAP4 to predict IRWST injection to establish successful core cooling. i l l' i iO I Evaluation of Results Rev. O. Apnl 1997 o:\newproj2\3603w.14.wpf:Ib-o41397 I-1
9-18 i O Figure 9-4 Duration of Saturated Conditions in the Downcomer After ADS Actuation 1500 - _ MAAP4 Underpredicts 12b E e Up to 5 Minutes ' f
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9-19 9.1.5 ADS-4 l-N[ \ l
- Stage 4 ADS is identified as a high importance model in the PRA PIRTs. It is given increased l
! importance, compared to DBA, because there is a reduced venting capacity in PRA multiple-failure L ' scenarios. The stage 4 ADS lines are the primary venting paths to reduce the system pressure to
- achieve and maintain IRWST gravity injection. ,
l' l- This section contains three code comparison plots that are related to stage 4 ADS. The first is the l integrated inventory that is lost from stage 4 ADS within the first 1000 seconds of the valves opening. { { Dis time period was chosen because it is the time frame in which most cases have depressurized low
-l l enough to achieve IRWST gravity injection. The second scatter plot is a measure of how well stage 4 >
ADS depressurizes, by examining the length of time until IRWST injection starts.- (Note that Figure . 9-lb already showed that the RCS pressure when ADS actuates is well-predicted by MAAP4.) ne
- l. final scatter plot shows the hot leg level at the time of ADS actuation. De flow regime in the hot leg j determines the mixture that is entrained into the stage 4 ADS lines. !
he results of the integrated ADS-4 inventory loss 1000 seconds after ADS actuation are shown in
- Figure 9-Sa. Both water and vapor loss are integrated for the applicable cases (all except case 13). !
The inventory loss is generally higher from smaller breaks and lower for larger breaks that also get i l substantial venting through the break. ! l l , MAAP4's prediction of the integrated ADS-4 inventory loss at the time of ADS actuation is within ; 10% of NOTRUMP's prediction for most of the cases. MAAP4 overpredicts the ADS-4 venting by j more than 10% in three cases: 10,12 and 12a. Case 10 is a 5" hot leg break that credits an
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l accumulator in addition to the CMT. MAAP4 predicts greater water relief than NO'IRUMP when the ; ) ADS-4 valves open. This is due to the insurge of water from the accumulator. Cases 12 and 12a are l- 2" hot leg breaks. The overprediction by more than 10% is a result of water relief from stage 4 ADS , i after IRWST injection has started and the hot leg is flooded. Herefore, these differences are largely
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due to the selection of the 1000 second time frame. MAAP4 underpredicts the ADS-4 venting by more than 10% in a number of cases, but for similar l reasons. Cases 2,14,15 and 16 are all 2" hot leg breaks for which MAAP4 does not predict any l water relief when the valve opens, while NOTRUMP does. Case 8 is a 4" DVI line break with the same difference. Case 12b is the only other case for which MAAP4 underpredicts the ADS-4 i
. inventory loss by more than 10%. ;
i The results of how well ADS-4 depressurizes the RCS are shown in Figure 9-5b. For the applicable benchmarking cases (all except for case 13), the provided information is the time delay from ADS-4 I [ actuation until IRWST injection starts. The time delay is generally less than 1000 seconds. MAAP4 ! predicts the start of IRWST injection within 5 minutes of NOTRUMP for all cases, with the notable ! exception of case 12b. l l 7 Evaluation of Results Rev. O, April 1997 '! oAnewproj2\3603w.14.wpf;l b-o41397 t
9-20 The hot leg level at the time of ADS actuation is shown in Figure 9-5c. Although identified in the PRA PIRTs as related to stage 4 ADS, the hot leg level was shown in the benchmarking cases to also be relevant for the other stages of ADS. Therefore, this figure is the hot leg level when any stage of ADS opens, extending the case applicability to include case 12 and 13. It does not include cases that were included in the previous two figures if the case is the same as another case until ADS valves open. The hot leg level that is compared in Figure 9-5c is the water level that extends into the steam generator. The hot leg in MAAP4 is within the same water pool as the hot side of the steam generators. The level output from MAAP4 is a collapsed value, which is compared to a mixture level from NOTRUMP. The discrepancy of collapsed versus mixture level is partially responsible for differences seen in Figure 9-5c. Hcwever, there is not a straightforward method of comparing more-similar variables between the two codes. As shown in Figure 9-5c, the coolant level is at or below the bottom of the hot leg in approximately half of the benchmarking cases, when ADS is actuated. This is the condition predicted by both MAAP4 and NOTRUMP in all of the primary benchmarking cases, except case 1. Case 10 and case 11, which are sensitivities to the number of CMTs and accumulators, also have levels within or at the bottom of the hot leg. Both codes predict this. All other cases are predicted by both codes to have levels well above the top of the hot leg when ADS is actuated, with the exception of case 12 and case 8b. In case 12, the hot leg level difference is the reason for significant differences in the vessel mixture level prediciton by MAAP4, as discussed in Section 7.3. In case 8b, MAAP4 predicts the collapsed level is within the hot leg, while NOTRUMP predicts the mixture level is well above the top of the hot leg. This accident scenario does not credit stage 1,2 and 3 ADS, and both codes predict similar rates of water relief through ADS-4 when the valves open. Therefoie, the difference in the code prediction of hot leg level for case 8b does not impact the final results. O Evaluation of Results Rev. 0, April 1997 o Anewproj2\3603w.14 m pf. l b-041397 i
9-21
- Figure 9-Sa l
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9-22 O Figure 9-5b Time Delay from ADS 4 Actuation Until IRWST Injection Starts 1500 , MAAP4 Underpredicts / Up to 5 Minutes / _ /
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i 9-24 9.1.6 ADS 1 to 3 In PRA full depressurization scenarios (to IRWST gravity injection), ADS stage 1 to 3 are only used O in high pressure scenarios to reduce the pressure below the 4th stage interlock. ADS stages 1 to 3 do not have a controlling influence on the event progression. However, stage 2 or 3 ADS valves are the only ADS valve. credited in PRA partial depressurization scenarios (to RNS gravity injection). Therefore, the ADS stne a to 3 model is identified as "high importance" in the PRA PIRTs. The ability of a single stage 2 or 3 ADS valve to depressurize the RCS to below the RNS shut-off head was demonstrated with case 13, which is a 2" cold leg break. The depressurization rate is shown to be similar between MAAP4 and NOTRUMP. This demonstrates the validity of the MAAP4 stage 2 or 3 'model for use in partial depressurization cases. To provide a broader picture of MAAP4's capability to model stage 1,2 and 3 ADS, data from the limited number of benchmarking cases (1,12,12a,12b, and 13) that credit the valves was compiled. Figure 9-6 is the integrated ADS stage 1 to 3 inventory loss for 1000 seconds. The time frame of 1000 seconds was chosen to limit the overlap when stage 4 ADS is also open in most of the cases. The results show that MAAP4 underpredicts the inventory lost in all cases by mole than 10%. The results in Sections 6.1,7.3 and 7.4 show that the difference in the integrated flow rate predictions is not the reason for the major differences seen between MAAP4 and NOTRUMP in any of the cases. An assessment of the stage 1,2 and 3 ADS model in MAAP4 would not be complete without making note of the limitations identified in cases 12,12a and 12b and discussed in Section 7.3. When stage 1, 2,- 1 ADS valves are opened and there is water in or near the hot leg, water will be drawn into the pressurizer. The pressurizer re-filling with water not only represents a loss of coolant inventory from the core region, but affects the RCS depressurization effectiveness of stage 1,2 and 3 ADS. In some cases, MAAP4 code simplifications cause the vessel coolant inventory prediction to be lower than more detailed NOTRUMP predictions when ADS is actuated. Although at first this would appear to be a conservative prediction, it was found that the underprediction can also have an adverse impact on MAAP's ability to accurately predict the plant conditions. The difference in the vessel inventory prediction was found to have an impact only if the hot leg inventory prediction differs when ADS stage 1,2 or 3 valves are opened. The surge of water into the pressurizer is impacted, which causes not only a loss of water inventory from the cere region, but more imponantly it impacts the depressurization effect of the stage 1,2 and 3 ADS valves. The MAAP4 results of benchmarking cases P 12a and !2b do not match NOTRUMP well because of l the limitation discussed above. However, there ce also benchmarking cases (1 and 13) in which MAAP4 does a very good job in predicting the depressurization due to stage 3 ADS valves opening. In these cases, MAAP4 predicts water in the pressurizer at the time of, or as a result of, the stage 3 ADS valve opening. The caution to the AP600 MAAP4 user is that if MAAP4 does not predict water drawn into the pressurizer when ADS stage 1,2 or 3 valves open, the code may overpredict the resulting RCS depressurization; the conclusions of the MAAP4 analysis should not be used unless Evaluation of Results Rev. O. April 1997 o:\newproj2\3603w.14.wpf:Ib-041397
[ 9-25 furtherjustification can be provided of why there would be no insurge of water into the pressurizer for I the accident scenario. This limitation does not seriously restrict MAAP4's applicability to PRA success criteria analyses, since stage 1,2 and 3 ADS play a minimal role in success criteria - definitions. l l l !- .I s L i l i 1 l l- -
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! l l i l l l l i { j l l. 1 l l 1 s-l ! i i Evaluation of Results nev. o. Aprii 1997 o:%ewproj2\3603w 14.wpf lb-041397 l l
9-26 l I h; Figure 9-6 Integrated ADS 1 to 3 Inventory Loss for 1000 seconds 200000 ,
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9-27 9.1.7 IRWST l
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IRWST gravity injection is identified as a high importance model because it provides a relativelv long-f
- term water source for core cooling. Gravity draining is dependent on the pool level of the tank, the i primary system pressure, the pressure drops in the vent paths, and the line resistances in the injection lines. De impact of these considerations is summarized with a code comparison plot of the intepated .
IRWST injection for 1000 seconds. This supplements the data shown in Section' 9.1.5 on the time IRWST injection begins after ADS-4 actuation. i i De results of the integrated IRWST injection for 1000 seconds -- shown in Figure 9-7. He time frame of 1000 seconds was chosen because this is generally the d:.e in which the core recovers in ! coru'uncovery cases. Data from all cases are shown in Figum 9-7, except case 13, which credits pumped RNS injection from the IRWST. MAAP4 predicts the integrau d IRWST injection within 10% of NOTRUMP's calculation for seven of the benchmarking cases. For two of the most limiting benchmark cases (2 and 5), MAAP4 underpredicts the IRWST injected flow by more than 10%. For ! all the other benchmarking cases, MAAP4 overpredicts the IRWST injected flow by more than 10%. ! Note, however, than an overprediction of the flow in this time period does not necessarily indicate that l the MAAP4-calculated core uncovery is non-conservative. For example, MAAP4 predicts longer
- durations of core uncovery than NOTRUMP for cases 6,9 and 16 although the integrated IRWST j injection is overpredicted by MAAP4 for the first 1000 seconds of injection. !
I ne most important aspect of IRWST injection for PRA success criteria analyses is that it starts. The tum-around of the vessel mixture level is closely linked to the start of IRWST injection. De turn-around of the cladding heat-up is also associated with the start of IRWST injection. The IRWST l injection flowrate must be greater enough to recover the core if it is uncovered, and to match the break j flow in the long term. But the MAAP4 prediction of the IRWST flowrate can deviate somewhat from
~
l the NOTRUMP prediction without impacting the conclusion of successful core cooling. y ) i l i l < i l A U
. Evaluation of Results Rev. O. Apnl 1997 o%ewproj2\3603w.14.wptib 041397 a .- ., .- -- .
9-28 O Figure 9-7 Integrated IRWST Injection for 1000 seconds 120000 ,
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9-29 ! l i 9.1.8 Accumulator O,, Prior to ADS actuation, the accumulators provide the only source of reactor coolant make-up in PRA scenarios without CMTs. The rate of delivery can play a key role in the primary inventory mass. Here are five benchmarking cases that model one or more accumulators. Results in Section 9.1.1 have already shown that MAAP4 predicts the RCS depressurization rate very well. Since accumulator injection begins when the pressure decreases below 715 psia, the stan of accumulator injection occurs at similar times in MAAP4 and NOTRUMP analyses. It is also a given that the accumulators will empty as the RCS depressurizes, so that the integrated accumulator injection is the same for both codes. Herefore, the only remaining element is the period of time over which the injection occurs. The duration of accumulator injection is shown in Figure 9-8. There is excellent agreement in all the cases that model one accumulator. For the case with two accumulators, case 11, MAAP4 predicts that l the injection occurs faster than in NOTRUMP. The reasons for this are explained in Section 7.1. l Although the prediction of the faster accumulator injection causes minor oscillations in the vessel' i mixture level, the overall trends of the accident progression are not affected. The accumulator model l in MAAP4 is shown to be adequate. l l fi l 1 I l l f i l ! i i
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Eva6ation of Results Rev. O. Apnl 1997 o:bproj20603w-14.wpf:1b-041397 \
9-30 0 Figure 9-8 Duration of Accumulator Injection 1500 1200 -- E11 E10 ^ o - MAAP4 Ur.derprediets a) 6 ro 900 -- v Q_ 2 - -D Ct: 600 -- 7 O _ Z 5 300 -- _ MAAP4 Overpredicts 0 l l l l 0 300 600 900 1200 1500 MAAP4 (sec) O Evaluation of Results Rev. O, Apnl 1997 o:\newproj2\3603w- 14.wpfd '.,-041397
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9-31 L 9.2 Assessment of High Interest Models/ Phenomena - O ' High interest phenomena identified in the PRA PIRTs are ones that are unique to AP600 and/or PRA scenarios that should be examined, but moderate differences in the predictions are not expected to c have a controlling influence on the minimum vessel inventory. Here are three models discussed in ! this section: the CMT, the pressurizer, and the steam generators. CMT
- The CMT is a water injection source that is unique to the AP600 plant. It performs a function to
. provide make-up inventory for LOCAs that is similar to high pressure ECCS injection pumps in current operating plants. In addition, CMTs also are able to operate in a recirculation mode to provide cool, borated water to the core when there is not a need for significant coolant inventory make-up.
When enough'RCS coolant inventory has been lost through a break or pressurizer safety valves that longer term inventory from the IRWST will be needed, the RCS pressure may need to be reduced to allow injection from either RNS pumps or IRWST gravity injection. He reduction of pressure is accomplished with ADS valves, which are actuated on low and low-low CMT level signals. Three aspects of the CMT model were identified as high interen in the PRA PIRT: the period of recirculation, the transition from recirculation to draining, and thewsl stratification of the water in the CMT. During CMT recirculation, relatively cold water flows from the CMT, through CMT injection lines, to
% DVI line which attaches to the downcomer of the vessel. Relatively warm water flows from the cold leg, through the balance line, to the CMT. He flowrates of the water to and from the CMT are similar, so there is little net impact on the CMT water inventory. During a long period of recirculation, which can occur in a small LOCA such as benchmarking case 1 (0.5" break), the CMT water inventory does decrease during recirculation, but at a very slow rate. He CMT level, however, does not change. Both MAAP4 and NOTRUMP predict similar recirculation flowrates in and out of the CMT, the same net effect on the CMT water inventory during recirculation, and the same CMT level during recirculation.
l During recirculation of the CMT, the water in the tank will develop a thermal stratification. The Tech i Spec maximum initial water temperature is 120*F. The top layer of the CMT quickly increases in tem.perature, as water from the cold leg enters the top of the CMT. NOTRUMP has four nodes in the CMT to model the thermal stratification that occurs. MAAP4, on the other hand, only has one node in the CMT, and cannot model any thermal stratification. His is a model simplification, but the question
'is whether it adversely impacts the ability of MAAP4 to predict the overall plar.t response to the 1 accident. -
g Transient plots of the CMT water temperature are provided for benchmarking cases 1,2,3 and 4 in lV Sections 6.1 to 6.4. In the smallest break, case 1, the MAAP4 prediction of the CMT water l-Evaluation of Results Rev. O, April 1997 c:\newproj2\3603w.14.wpf:lt441497
.~ ~__ _ __ --, - _ _ _
1 1 9-32 , 1 l l temperature is approximately the average of the top and bottom CMT node temperatures m ' NOTRUMP. As the break size increases, the recitrulation period is shorter, and the single node in MAAP4 experiences less of a temperature increase. His temperature behavior is also true for the bottom node in NOTRUMP; however NOTRUMP predicts a temperature increase for the top node of several hundreds of degrees regardless of the break size. The differences in the CMT tempemture predictions, and the lack of thermal stratification in MAAP4, does not impact the flowrates calculated. However, it does have two effects. At the top of the tank, interfacial condensation can occur on the water surface, impacting the drain rate of the CMT. This is identified as a high importance item, and is addressed in Section 9.1.2 The second impact of the lack of a thermal stratification model in MAAP4 is the difference in the temperature of the coolant that is injected into the downcomer. His can impact the level of subcooling in the downcomer, which in turn could be important to conectly predicting the start of IRWST injection. Although there are some differences between MAAP4 and NOTRUMP in the prediction of the downcomer temperature that are attributed to the CMT model simplifications in MAAP4, the differences do not impact the overall plant response. This is demonstrated in primary benchmarking cases 1,2,3 and 4. Section 9.1.4 also provides relevant information on the downcomer saturation predictions of the two codes. Finally, the CMT transition from recirculation to draining is identified as a high interest item. Code comparison plots in Section 9.1.2 show information on how well MAAP4 predicts the transition time, compared to NOTRUMP. In larger breaks, MAAP4 predicts too early of a transition, which is the subject of Section 9.1.2. For smaller breaks, however, MAAP4 errs on the side of a later transition than MAAP4. This is due to the simplified two-phase modelling in MAAP4, which is discussed in Section 2.2.1. He timing differences are usually small, and do not generally impact the accident progression. Pressurizer 1 1 The pressurizer is identified as a high importance item because it can impact the distribution of mass in the RCS. In most of the benchmarking cases, the pressurizer empties early in the event (within the first 100 seconds), and does not play any further role in the accident progression. However, in cases that credit stage 1,2 and 3 ADS, the pressurizer does play a role because these ADS lines are connected to the top of the pressurizer. Case 1 is a primary benchmarking case that models stage 3 ADS because it is a part of the success l criterion requirement to achieve successful core coou j for that break size. In this case, the MAAP4 pressurizer predictions closely match NOTRUMP, as shown in Section 6.1. Case 13 is also a benchmarking cases that models stage 3 ADS because it is the success criterion (minimum equipment needed) to achieve pumped injection from the RNS. In this case, MAAP4 also predicts a pressurizer trend similar to the NOTRUMP prediction. 9 ( Evaluation of Results Rev. O. Apnl 1997 o$newproi2\3603w 14 wpf.!b-o41397 i'
! l i 9-33 2 l j he differences in the prediction of the pressurizer response in cases 12,12a, and 12b are not due t
~
l differences in the pressurizer model, but are due to differences in the vessel inventory predictions, as I explained in Section 7.3. i l t Stemni Generators De steam generators are identified as high interest because'they are the only source of heat removal l except the break flow. The role of the steam generators in the accident progression is dependent on ; { break size. Dere is limited heat transfer with the steam generators after reactor trip for the larger breaks. De break is able to remove all the decay heat, and the primary and secondary systems quickly decouple from one another. l l l i i For smaller breaks, the steam ger.e:ators do play a role in the accident progression. In case 1, the 0.5" i break is too small to remove all of the decay heat. De steam generators remove the decay heat by boiling off the secondary side inventory through the steam generator safety valves. When the steam j generators empty, the RCS pressurizes to the pressurizer safety valve setpoint. Section 6.1 shows that MAAP4 predicts the same heat transfer rate to the steam generators as NOTRUMP, and the boilmff of the secondary side water occurs over the same time period. Section 6.2 shows that the steam generators play a rainor role in a 2" break, and that once again the two codes predict the same trend. i ! l l 1 i i l 1 l l 4 [\ Evaluation of Results Rev. O. April 1997 chwproj2\3603w.14.wpf:1b-041397 '
10-1 f iA 10 CONCLUSIONS j U Westinghouse undenook an extensive effon to analyze the thermal / hydraulic response of AP600 to suppon claims of successful core cooling for multiple failure accidents in the AP600 Probabalistic i Risk Assessment (PRA). MAAP4 was chosen as the code for this task because ofits flexibility and ease of use. He code is fast-mnning, making it feasible to analyze a large number of scenarios, variations of the scenarios, and sensitivities. However, concerns have been raised on the suitability of l MAAP4 models for assessing successful core cooling, particularly for plants with passive safety l systems. Derefore, as documented within this repon, MAAP4 was benchmarked against the more detailed . models in NOTRUMP, the Westinghouse-validated code for AP600 small-break LOCAs. A total of nineteen benchmarking cases were analyzed with both MAAP4 and NOTRUMP. De first seven cases were chosen at limiting break sizes across the spectrum of the break sizes analyzed with MAAP4, as discussed in Section 4.2 of the repon. They demonstrate the basic phenomena that are identified in the PRA Phenomena Identification Ranking Tables (PIRTs) in Section 3.2. He remaining cases are sensitivities that demonstrate the capability of MAAP4 to predict trends for different break locations, l different number of core make-up tanks (CMTs) or accumulators, different number of automatic l depressurization system (ADS) lines, and different parameters affecting in-containment refueling water j storage tank (IRWST) gravity injection. I There is excellent agreement in the trends predicted by the two codes for most of the benchmarking l cases. Sections 6.0 and 7.0 of the benchmarking repon show detailed output from each case, comparing'the prediction of specific parameters for different components and systems within the plant. Section 9.0 provides code comparison plots for issues identified as highly imponant through the PIRT process. Core uncovery of limited depth and duration occurs in approximately half of the ! benchmarking cases with similar trends predicted by both MAAP4 and NOTRUMP. For each case, the reason that the core uncovers is understood, and both codes predict similar system actuations and timing leading to the core uncovery. Both codes also predict similar accident progressions for scenarios that do not include core uncovery. . However, the MAAP4/NOTRUMP benchmarking effon identified one accident scenario where MAAP4 did not adequately predict the vessel mixture level, which is used to determine whether the core uncovers. The difference is due to a limitation of the MAAP4 code when applied to the AP600 j plant.' MAAP4 code simplifications cause the vessel coolant inventory prediction to be lower than more detailed NOTRUMP predictions when ADS is actuated. Although at first this would appear to be a conservative prediction, it was found that the underprediction can also have an adverse impact on MAAP's ability to accurately predict the plant conditions. The difference in the vessel inventory prediction was found to have an impact only if the hot leg inventory prediction differs when ADS L stage 1,2 or 3 valves are opened. He surge of water into the pressurizer is impacted, which causes
- O I
Conclusions Rev. D. April 1997 c:%ewproj2\3603w-15.wpf:!b-041497 l
i l 10-2 l not only a loss of water inventory from the core region, but more importantly it impacts the depressurization effect of the stage 1,2 and 3 ADS valves. He MAAP4 results of a few of the benchmarking cases (Section 7.3) do not match NOTRUMP well because of the limitation discussed above. However, there are also benchmarking cases (Sections 6.1 l and 7.4)in which MAAP4 does a very good job in predicting the depressurization due to stage 3 ADS i valves opening. In these cases, MAAP4 predicts water in the pressurizer at the time of, or as a result of, the stage 3 ADS valve opening. The caution to the AP600 MAAP4 user is that if MAAP4 does not predict water drawn into the pressurizer when ADS stage 1,2 or 3 valves open, the code may overpredict the resulting RCS depressurization; the conclusions of the MAAP4 analysis should not be used unless furtherjustification can be provided of why there would be no insurge of water into the pressurizer for the accident scenario. This limitation does not seriously restrict MAAP4's applicability to PRA success criteria analyses, since stage 1,2 and 3 ADS play a minimal role in success criteria definitions. l he benchmarking of MAAP4 against NOTRUMP illustrates not only the capabilities of the MAAP4
)
code, but the adequacy of the input modelling used for AP600. The benchmarking effon shows that i the MAAP4 parameter file and input decks previously developed for AP600 are accurate, with one I exception. The input model for MAAP4 did not adequately account for resistances in the ADS stage 4 piping. The line resistances have a minor impact on the flowrate through the ADS-4 valves when the flow is choked, but they have a large impact at low pressures when the flow through the valve is unchoked. When a better input model of the stage 4 piping resistances was developed for MAAP4, the prediction of RCS depressurization was impacted. The result was that it takes 3 stage 4 ADS valves to achieve approximately the same plant response as was previously attributed to 2 stage 4 ADS l valves. Herefore, although the ADS success criteria in the current PRA is based on 2 stage 4 ADS valves for full depressurization, most of the benchmarking cases are analyzed with 3 stage 4 ADS I valves. He update of Appendix A of the PRA, which documents the MAAP4 success criteria analyses, will address any PRA impact of the ADS-4 line resistance finding. The conclusions of the MAAP4/NOTRUMP benchmarking effort are as follows.
- 1. The thermal-hydraulic models in the MAAP4 code can model the key thermal-hydraulic phenomena with sufficient accuracy that it can be used as a screening tool to determine whether core uncoverv occurs. De use of MAAP4 is subject to the limitation identified above, and the potential impact of the code simplifications discussed within Sections 2.1 and 2.2 of this report.
- 2. If core uncovery occurs, MAAP4 predicts the depth and duration of uncovery well enough for j an assessment of successful core cooling to be justified,if the depth and duration of uncovery are similar to that demonstrated within this report. The assessment of core cooling for core uncovery cases can be based on the NOTRUMP/LOCTA PCT results remaining well below 2200 F for the benchmarking cases, as shown in Section 8.0 of the report.
l Conclusions Rev. O. Apnl 1997 o-inewproj2\3603w-15.wptlis041497
__ - _ . _ _ _ .._.__._._.__.______m..__ . . . _. _ . _ . . _ . _ . __ _ _ . _ _ _ . . _ 10-3 1 1
- 3. -
MAAP4 (.an be used to estimate operator action times for the PRA. The accident progression _ predicted by MAAP4 generally has similar timing compared to the NOTRUMP calculation. Any differences in the accident progression timing will be considered in the PRA Appendix A - l update, if they have the potential to impact PRA operator action times. l l The benchmarking of MAAP4 against the more detailed models in NOTRUMP has demonstrated that I MAAP4 is an adequate, useful tool to support the AP600 PRA claims of successful core coohng m ; multiple-failure accident scenarios. Isecause the running time of MAAP4 is tens of minutes while :
~
more detailed codes such as NOTRUMP run for multiple days, it is feasible to consider many { combinations of equipment failures with MAAP4 analyses. The case of using MAAP4 leads to a j thorough understanding of the integral AP600 plant response to multiple failure accident scenarios. > l I 1 l l l l 1 J I l l. l j i 1 I l Conclusions Rev. O, April 1997
- c
- Wj20603w.liwpf:1b-041497
11 1 t 11 REFERENCES i O, i 1. AP600 Probabilistic Risk Assessment, Appendix A. Revision 2, January 31,1995. l 2. WCAP-14807, Rev. O, "NOTRUMP Final Validation Report for AP600," December 1996. l
- 3. NSD-NRC-%-4796/ CDP /NRC0576, Docket Number STN-52-003, Letter from Brian McIntyre (Westinghouse) to T. R. Quay (NRC) on "AP600 Passive System Reliability Roadmap," 8/9/96. 1
- 4. MAAP4, Modular Accident Analysis Program, User's Manual," Rev. 0.0, May 1994, i
l S. EPRI TR-100743, "MAAP PWR Application Guidelines for Westinghouse and Combustion ! Engineering Plants," June 1992. l
- 6. " Advanced Light Water Reactor Utility Requirements Document," Volume III, Chapter 1, Appendix A, Revisions 5 & 6, December 1993.
- 7. WCAP-14807, Rev. O, "NOTRUMP Final Validation Report for AP600," Section 1.3, December 1996.
- 8. " Decay Heat Power in Light Water Reactors," Revised American National Standards, ANSI /ANS-5.1-1979,1979.
- 9. Shames, Irving H., Mechanics of Fluids, Second Edition, McGraw-Hill Book Company,1982.
- 10. EPRI TR-100167, " Recommended Sensitivity Analyses for an Individual Plant Examination .
Using MAAP 3.0B. I
- 11. Westinghouse letter NSD-NRC-96-4920, B. A. McIntyre (W) to T.R. Quay (NRC),
"NOTRUMP Final Validation Report for AP600 - WCAP 14807," December 18,1996.
- 12. NRC Letter from Architzel, Ralph E (NRC) to McIntyre, B. A. (W), " Summary of Meeting with Westinghouse to discuss the AP600 MAAP4 Benchmarking Process," May 14,1996 (Table 2 of the attached slides). ;
- 13. Meyer, P. E., "NOTRUMP, A Nodal Transient Small Break and General Network Code,"
WCAP-10079-P-A (Proprietary) and WCAP-10080-A (Non-Proprietary), August 1985. . I
- 14. Lee, N., et al., " Westinghouse Small Break ECCS Evaluation Model Using the NOTRUMP l i Code," WCAP-10054-P-A (Proprietary) and WCAP-10081-A (Non-Proprietary), August 1985.
References Rev. O. Agil 1997 o:\newpmj2\3603w-16.wpf;1b-041497
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- 15. WCAP-8301, LOCTA-IV Program, Loss-Of-Coolant Transient Analysis," F. M. Bordelon, D. L. Burman, G. Collier, M. Ohkubo, A. C. Spencer, & J. W. Yang, June 1974
- 16. WCAP-10054 P-A, Westinghouse Small Break ECCS Evaluation Model Using the NOTRUMP Code," N. Lee, et al. August 1985.
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