ML13074A796

Small Break LOCA Sensitivity Study Summary Report, ANP-3205NP, Rev 0

ML13074A796
Person / Time
Site:	Millstone
Issue date:	02/28/2013
From:	AREVA NP
To:	Office of Nuclear Reactor Regulation, Dominion Nuclear Connecticut
References
12-578A ANP-3205NP, Rev 0
Download: ML13074A796 (27)

Text

Serial No. 12-578A Docket No. 50-336 ATTACHMENT 2 MILLSTONE UNIT 2 SMALL BREAK LOCA SENSITIVITY STUDY

SUMMARY

REPORT (NON-PROPRIETARY)

DOMINION NUCLEAR CONNECTICUT, INC.

MILLSTONE POWER STATION UNIT 2

A AREVA ANP-3205NP Millstone Unit 2 Small Break LOCA Revision 0 Sensitivity Study Summary Report February 2013 AREVA NP Inc.

(c) 2013 AREVA NP Inc.

Copyright © 2013 AREVA NP Inc.

All Rights Reserved

AREVA NP Inc. ANP-3205NP Revision 0 Millstone Unit 2 Small Break LOCA Sensitivity Study Summary Report Page i Nature of Changes Section(s)

Item or Page(s) Description and Justification

1. All Initial Release

AREVA NP Inc. ANP-3205NP Revision 0 Millstone Unit 2 Small Break LOCA Sensitivity Study Summary Report Paqe ii Contents PaQe

1.0 INTRODUCTION

............................................................................................... 1 1.1 Question 8 - Break Spectrum Resolution .............................................. 2 1.2 Question 12 - Modeling of Upper Downcomer Leakage Paths ..................................................................................................... 4 1.3 Loop Seal Clearing ............................................................................... 5

2.0 CONCLUSION

S .............................................................................................. 14

3.0 REFERENCES

............................................................................................... 15

AREVA NP Inc. ANP-3205NP Revision 0 Millstone Unit 2 Small Break LOCA Sensitivity Study Summary Report Page iii List of Tables Table 1: Millstone Unit 2 Current Licensing SBLOCA Results with Added Cases and I] ............................................................... . . 4 Table 2: PCTs for Millstone Unit 2 Current Licensing Basis SBLOCA and Supplement 1 S ensitivity C ases ............................................................................... 7

AREVA NP Inc. ANP-3205NP Revision 0 Millstone Unit 2 Small Break LOCA Sensitivity Study Summary Report Page iv List of Figures Figure 1: Downcomer Level for the 0.083 ft2 Case .................................................. 10 Figure 2: Downcomer to Broken Leg Flow Rate for the 0.083 ft2 Case ................... 11 Figure 3: Integrated Break Flow for the 0.083 ft2 Case .......................................... 12 Figure 4: Inner Core Mass Inventory for the 0.083 ft2 Case .................................... 13

AREVA NP Inc. ANP-3205NP Revision 0 Millstone Unit 2 Small Break LOCA Sensitivity Study Summary Report Page v Nomenclature Acronym Definition AOR Analysis of Record CE Combustion Engineering CFR Code of Federal Regulations ECCS Emergency Core Cooling System EM Evaluation Model NRC Nuclear Regulatory Commission PCT Peak Cladding Temperature RAI Request for Additional Information SBLOCA Small Break Loss of Coolant Accident

AREVA NP Inc. ANP-3205NP Revision 0 Millstone Unit 2 Small Break LOCA Sensitivity Study Summary Report Page 1

1.0 INTRODUCTION

On August 28, 2012, Dominion received a request for additional information (RAI) from the NRC [1] regarding the 30-day report submitted on January 25, 2012, for Emergency Core Cooling System (ECCS) evaluation model changes pursuant to the requirements of 10 CFR 50.46 [2]. Dominion submitted a RAI response in a letter dated November 1, 2012 [3]. In a subsequent teleconference on November 20, 2012, the NRC, Dominion, and AREVA discussed the NRC's follow-up questions regarding the modeling of three items in the Small Break LOCA (SBLOCA) Evaluation Model (EM), that are not related to the error in the 30-day Report of Reference 2. These items are as follows:

1) Question 8 - break spectrum resolution, 2) Question 12 - modeling of leakage paths, and, 3) assumption for loop seal clearing. Additional information is provided herein on the estimated effect on peak cladding temperature (PCT) of each of these modeling assumptions for the Millstone Unit 2 SBLOCA EM, that conforms to the NRC-approved methodology in EMF-2328(P)(A), Revision 0 [4]. At the end of the November 20, 2012 teleconference, it was proposed that the sensitivity studies combine the effects of the three changes together, rather than report the separate effects against the SBLOCA analysis of record (AOR). There was an expectation that each model change would produce an increase in PCT and that bundling the three changes together would provide a large positive PCT result. However, as described below, the SBLOCA EM for Millstone Unit 2 is relatively insensitive to the first two modeling items and changing the loop seal clearing assumption in accordance with experimental data and analytical predictions [ ] produces a large PCT decrease for Millstone Unit 2. Thus, it was decided that reporting of the separate effect results for each of the modeling items provides a more accurate evaluation of PCT impact for each NRC question.

AREVA NP Inc. ANP-3205NP Revision 0 Millstone Unit 2 Small Break LOCA Sensitivity Study Summary Report Page 2 The sensitivity study results reported below have been obtained using the Millstone Unit 2 FSAR SBLOCA AOR model, updated to incorporate the EM changes and errors identified as 10 CFR 50.46 PCT assessments in Attachment 2 of Dominion's letter dated January 25, 2012 [2]. This updated SBLOCA model, that incorporates the EM changes and errors, establishes the licensing basis PCT of 1801 OF that was reported in Reference 2, provides the appropriate baseline for the sensitivity studies, and is referred to as the "current licensing basis PCT" herein.

1.1 Question 8 - Break Spectrum Resolution Portions of the NRC question from Reference [1] are copied below.

"Since the initial analysis using this break spectrum was performed, staff review activities have indicated that a more refined break spectrum is necessary to provide assurance that the limiting break sizes, locations, and other properties have been analyzed, and that the most severe postulated LOCA has been calculated. Changes in the break area by as little as 0.005 ft2 can produce increases in PCT from 100 -200 F. Typically, the limiting small break is that maximum break size that just precludes SIT actuation and suggests a break between 0.06 and 0.08 ft2 could be more limiting since SIT actuation occurs at the time of the PCT for the 0.08ft2 break. Also, there is the potential for the worst break to be between 0.08 and 0.1 ft2. The possibility for more limiting break sizes to be identified when a coarse spectrum is used is documented; for example, see Section 5.3 of ADAMS Accession ML110390263. The treatment of this issue as an error in the application of an ECCS evaluation model, and its associated safety significance for plants who's PCTs exceed 1700 degrees Fahrenheit is also documented in ML062000027. As such, the staff requests that additional breaks be analyzed to produce an estimate of the effect of a potential error in the break spectrum analysis, or to show that the limiting break has been identified in the spectrum analysis."

AREVA NP Inc. ANP-3205NP Revision 0 Millstone Unit 2 Small Break LOCA Sensitivity Study Summary Report P~qn~P In short, the NRC questioned the break size increment used in the AOR in terms of whether the used break size increment captured the maximum PCT. [

] Refer to Table 1 for the refined break spectrum results.

For Millstone Unit 2, the observed PCT changes around the AOR limiting break size of 0.08 ft2 are small and well within the resolution expected of SBLOCA evaluation models.

As such, the study affirms the fidelity of the original spectrum analysis results.

AREVA NP Inc. ANP-3205NP Revision 0 Millstone Unit 2 Small Break LOCA Sensitivity Study Summary Report Paae 4 1.2 Question 12 - Modeling of Upper Downcomer Leakage Paths NRC Question 12 asked whether the hot leg nozzle gaps or core barrel leakage paths were modeled in the S-RELAP5 nodalization of the Millstone Unit 2. [

1 To respond, a limited number of break sizes from the expanded break spectrum were analyzed [

]to be 28°F for the 0.08 ft2 break and 31 °F when combined with the refined break spectrum. For Millstone Unit 2, the observed PCT changes, including both, break spectrum refinement and [ ], are small and within the resolution expected of SBLOCA evaluation models. Thus, the fidelity and the modeling choices made in the Millstone Unit 2 SBLOCA AOR are affirmed as reasonable for the satisfaction of the criteria of 10 CFR 50.46.

Table 1: Millstone Unit 2 Current Licensing SBLOCA Results with Added Cases and [ I

AREVA NP Inc. ANP-3205NP Revision 0 Millstone Unit 2 Small Break LOCA Sensitivity Study Summary Report P~ae 5 1.3 Loop Seal Clearing In the Millstone Unit 2 SBLOCA AOR,[ _ _J for the PCT limiting case of 0.08 ft 2. The AOR PCT was 1941 'F, before addressing all EM changes and errors. The ECCS evaluation model changes made subsequent to the AOR analysis yielded a current licensing basis PCT of 1801°F. The loop seal biasing approach used in the AOR is described and justified in EMF-2328(P)(A), Revision 0, Section 3.3.1.1 [4]:

CJ In 2010, after a detailed review of the SBLOCA analysis methods, the NRC approved a SBLOCA analysis for a CE plant. The review prompted numerous changes to the SBLOCA analysis methods, including a change in the treatment of loop seal biasing.

The limiting case, a 0.09 ft2 break size, included modifications to allow [

Later in 2010, a SBLOCA for a different CE plant was submitted to the NRC for review.

Again, modifications were introduced such that, in the limiting case, [

AREVA NP Inc. ANP-3205NP Revision 0 Millstone Unit 2 Small Break LOCA Sensitivity Study Summary Report Page 6 A revised SBLOCA analysis was submitted for review whereby [

I The NRC stated that this approach is reflective of available experimental data and tempers the erratic behavior observed in break spectrum results when the original biasing method is applied. In the revised analysis, the PCT decreased by approximately 250°F relative to the original analysis.

In March 2012, AREVA submitted EMF-2328(P), Revision 0, Supplement 1 [5], which adopts the more mechanistic loop seal clearing procedure described above; I 1 Supplement 1 is currently under NRC review.

In response to the NRC inquiry, a sensitivity study was performed, using the Millstone Unit 2 SBLOCA model and applying the revised loop seal clearing process of EMF-2328(P), Revision 0, Supplement 1 [5], [

] Table 2 presents the results for two sets of sensitivity cases: 1) "Set 1",

which implements a revised loop seal biasing scheme as per Supplement 1, compared to the current licensing basis with a refined break spectrum and 2) "Set 2" with the revised biasing scheme per Supplement 1 and [ 1, compared to the current licensing basis loop seal biasing case set and assumed

[ I When the [ ", the PCT decreased by magnitudes from 180OF to a 2

maximum of 268°F; a decrease of 194 F is calculated for the break size of 0.083 ft .

0 These results are shown in the 4 th column in Table 2.

AREVA NP Inc. ANP-3205NP Revision 0 Millstone Unit 2 Small Break LOCA Sensitivity Study Summary Report Page 7 Table 2: PCTs for Millstone Unit 2 Current Licensing Basis SBLOCA and Supplement I Sensitivity Cases

AREVA NP Inc. ANP-3205NP Revision 0 Millstone Unit 2 Small Break LOCA Sensitivity Study Summary Report Paae 8 This trend is attributed to several observed phenomena:

" When the [

• By contrast, [

I

AREVA NP Inc. ANP-3205NP Revision 0 Millstone Unit 2 Small Break LOCA Sensitivity Study Summary Report Page 9 When the [ Jinconjunction with the loop seal biasing scheme per EMF-2328(P), Revision 0, Supplement 1 [5], a larger decrease in PCT is observed, ranging from 294°F to 384°F (refer to Table 2, Set 2 and last column).

[ ] consistently resulted in the larger break sizes in the Supplement 1sensitivity cases to [

AREVA NP Inc. ANP-3205NP Revision 0 Millstone Unit 2 Small Break LOCA Sensitivity Study Summary Report Page 10 Figure 1: Downcomer Level for the 0.083 ft 2 Case I

AREVA NP Inc. ANP-3205NP Revision 0 Millstone Unit 2 Small Break LOCA Sensitivity Study Summary Report Page 11 Figure 2: Downcomer to Broken Leg Flow Rate for the 0.083 ft 2 Case

AREVA NP Inc. ANP-3205NP Revision 0 Millstone Unit 2 Small Break LOCA Sensitivity Study Summary Report Page 12 Figure 3: Integrated Break Flow for the 0.083 ft 2 Case

AREVA NP Inc. ANP-3205NP Revision 0 Millstone Unit 2 Small Break LOCA Sensitivity Study Summary Report Pagqe 13 Figure 4: Inner Core Mass Inventory for the 0.083 ft 2 Case

AREVA NP Inc. ANP-3205NP Revision 0 Millstone Unit 2 Small Break LOCA Sensitivity Study Summary Report Page 14

2.0 CONCLUSION

S The following conclusions are derived from the sensitivity study using the updated Millstone Unit 2 SBLOCA Evaluation Model that explicitly incorporates all EM changes and errors reported as 10 CFR 50.46 PCT assessments:

Small changes in PCT were observed over small increments in break size around the AOR limiting case of 0.08 ft2. The small changes in PCT are within the resolution of the SBLOCA Evaluation Model. The study affirms the fidelity of the original SBLOCA analysis results.

[ ] for the current licensing basis SBLOCA has a small PCT effect that is within the resolution of the SBLOCA Evaluation Model. [

The Millstone Unit 2 AOR treatment for loop seal clearing [

] is conservative compared to the most probable case of a[ ], which is supported by the experimental data, supported by analytical expectations of loop seal clearing at CE 2x4 plants, and is the licensing basis for another CE plant using S-RELAP5 for the SBLOCA analysis.

It is concluded that the Millstone Unit 2 current licensing basis SBLOCA analysis provides a conservative PCT prediction due to the treatment of loop seal clearing employed in the AOR. The Millstone Unit 2 current licensing basis SBLOCA analysis is conservative with respect to the combined effects of the three changes discussed above.

AREVA NP Inc. ANP-3205NP Revision 0 Millstone Unit 2 Small Break LOCA Sensitivity Study Summary Report Page 15

3.0 REFERENCES

1. Letter from James Kim (USNRC) to David. A Heacock (Dominion), "Millstone Power Station, Unit 2 - Request for Additional Information Regarding 30-Day Report for Emergency Core Cooling System Model Changes Pursuant to the Requirements of 10 CFR 50.46 (TAC No. ME7881)," August 28, 2012.

2. Letter from J. Alan Price (Dominion) to USNRC, "Dominion Nuclear Connecticut, Inc., Millstone Power Station Unit 2, 30-Day Report for Emergency Core Cooling System Model Changes Pursuant to the Requirements of 10 CFR 50.46," Serial No.11-708, January 25, 2012.

3. Letter from J. Alan Price (Dominion) to USNRC, "Dominion Nuclear Connecticut, Inc., Millstone Power Station Unit 2, Response to Request for Additional Information Regarding the 30-Day Report for Emergency Core Cooling System Model Changes (TAC No. ME7881)," Serial No.12-578, November 1,2012.

4. AREVA Report EMF-2328(P)(A), Revision 0, "PWR Small Break LOCA Evaluation Model, S-RELAP5 Based," March 2001.

5. AREVA Report EMF-2328(P), Revision 0, Supplement 1, Revision 0, "PWR Small Break LOCA Evaluation Model, S-RELAP5 Based," March 2012.

Serial No. 12-578A Docket No. 50-336 ATTACHMENT 3 AREVA APPLICATION FOR WITHHOLDING AND AFFIDAVIT DOMINION NUCLEAR CONNECTICUT, INC.

MILLSTONE POWER STATION UNIT 2

AFFIDAVIT COMMONWEALTH OF VIRGINIA )

) ss.

COUNTY OF CAMPBELL )

1. My name is Gayle F. Elliott. I am Manager, Product Licensing, for AREVA NP Inc. (AREVA NP) and as such I am authorized to execute this Affidavit.

2. I am familiar with the criteria applied by AREVA NP to determine whether certain AREVA NP information is proprietary. I am familiar with the policies established by AREVA NP to ensure the proper application of these criteria.

3. I am familiar with the AREVA NP information contained in the document "ANP-3205P Revision 0, 'Millstone Unit 2 Small Break LOCA Sensitivity Study Summary Report'," and referred to herein as "Document." Information contained in this Document has been classified by AREVA NP as proprietary in accordance with the policies established by AREVA NP for the control and protection of proprietary and confidential information.

4. This Document contains information of a proprietary and confidential nature and is of the type customarily held in confidence by AREVA NP and not made available to the public. Based on my experience, I am aware that other companies regard information of the kind contained in this Document as proprietary and confidential.

5. This Document has been made available to the U.S. Nuclear Regulatory Commission in confidence with the request that the information contained in this Document be withheld from public disclosure. The request for withholding of proprietary information is made in accordance with 10 CFR 2.390. The information for which withholding from disclosure is

requested qualifies under 10 CFR 2.390(a)(4) "Trade secrets and commercial or financial information":

6. The following criteria are customarily applied by AREVA NP to determine whether information should be classified as proprietary:

(a) The information reveals details of AREVA NP's research and development plans and programs or their results.

(b) Use of the information by a competitor would permit the competitor to significantly reduce its expenditures, in time or resources, to design, produce, or market a similar product or service.

(c) The information includes test data or analytical techniques concerning a process, methodology, or component, the application of which results in a competitive advantage for AREVA NP.

(d) The information reveals certain distinguishing aspects of a process, methodology, or component, the exclusive use of which provides a competitive advantage for AREVA NP in product optimization or marketability.

(e) The information is vital to a competitive advantage held by AREVA NP, would be helpful to competitors to AREVA NP, and would likely cause substantial harm to the competitive position of AREVA NP.

The information in the Document is considered proprietary for the reasons set forth in paragraphs 6(b) and 6(c) above.

7. In accordance with AREVA NP's policies governing the protection and control of information, proprietary information contained in this Document has been made available, on a limited basis, to others outside AREVA NP only as required and under suitable agreement providing for nondisclosure and limited use of the information.

8. AREVA NP policy requires that proprietary information be kept in a secured file or area and distributed on a need-to-know basis.

9. The foregoing statements are true and correct to the best of my knowledge, information, and belief.

SUBSCRIBED before me this ___

day of 2013.

Sherry L. McFaden NOTARY PUBLIC, COMMONWEALTH OF VIRGINIA MY COMMISSION EXPIRES: 10/31/2014 Reg. #7079129 SHERRY L.MCFAD:EN Notarg Public Commonwealth of Virginia My Commission7079129 0 Expires Oct 31, 2014