ML041950218

Day Report of Emergency Core Cooling System (ECCS) Evaluation Model Changes Pursuant to the Requirements of 10 CFR 50.46

ML041950218
Person / Time
Site:	North Anna
Issue date:	07/01/2004
From:	Matthews W Virginia Electric & Power Co (VEPCO)
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
04-393
Download: ML041950218 (7)

Text

VIRGINIA ELECTRIC AND POWIER COMPIANY RIci[MOND, VIRGINIA 23261 July 1, 2004 United States Nuclear Regulatory Commission Serial No.04-393 Attention: Document Control Desk NLOS/ETS Washington, D.C. 20555 Docket No. 50-339 License No. NPF-7 VIRGINIA ELECTRIC AND POWER COMPANY (DOMINION)

NORTH ANNA POWER STATION UNIT 2 30-DAY REPORT OF EMERGENCY CORE COOLING SYSTEM (ECCS) EVALUATION MODEL CHANGES PURSUANT TO THE REQUIREMENTS OF 10 CFR 50.46 Pursuant to 10 CFR 50.46(a)(3)(ii), Dominion is providing information concerning changes to the AREVA ECCS Evaluation Model for Large Break LOCA at North Anna Unit 2 and its application in existing licensing analyses. Information is also provided that quantifies the effect of these changes upon reported results for North Anna Power Station Unit 2, and demonstrates continued compliance with the acceptance criteria of 10 CFR 50.46. provides information from AREVA describing plant-specific evaluation model changes associated with the application of the AREVA Large Break LOCA ECCS Evaluation Model for North Anna Unit 2.

Information regarding the effect of the ECCS Evaluation Model changes upon the reported large break LOCA analysis of record (AOR) results is provided for North Anna Unit 2 in . To summarize the information in Attachment 2, the calculated peak cladding temperature (PCT) for the large break LOCA analyses for North Anna Unit 2 is 1861 OF. This result represents a significant change, based on the criterion established in 10 CFR 50.46(a)(3)(i).

The AREVA large break LOCA result for North Anna Unit 2 is confirmed to have sufficient margin to the 22000F limit of 10 CFR 50.46. Based upon our evaluation of this information and the associated changes inthe applicable licensing basis PCT results, no further action is required to demonstrate compliance with the 10 CFR 50.46 requirements.

10 CFR 50.46(a)(3)(ii) requires that the 30-day report include a "proposed schedule for providing a reanalysis or taking other action as may be needed to show compliance with Section 50.46 requirements." The assessments reported herein are due to a reanalysis to address the specific model changes discussed in Attachment 1. As such, no other

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Serial No.04-393 Docket Nos. 50-339 reanalysis is currently planned by Dominion. No further action is required at this time to maintain compliance with 10 CFR 50.46.

If you have further questions or require additional information, please contact Mr. Thomas Shaub at (804) 273-3763.

Very truly yours, W. R. Matthews Senior Vice President - Nuclear Operations Commitments made in this letter:

1. None.

Attachments:

1) Report of Changes in Application of the AREVA ECCS Evaluation Model to the Large Break LOCA for North Anna Unit 2

2) Reporting of 10 CFR 50.46 Margin Utilization - AREVA Large Break LOCA ECCS Evaluation Model - North Anna Unit 2 cc: U.S. Nuclear Regulatory Commission Region II Sam Nunn Atlanta Federal Center 61 Forsyth Street, SW Suite 23T85 Atlanta, GA 30303-8931 Mr. S. R. Monarque U. S. Nuclear Regulatory Commission One White Flint North 11555 Rockville Pike Mail Stop 8-H12 Rockville, MD 20852 Mr. M. T. Widmann NRC Senior Resident Inspector North Anna Power Station

ATTACHMENT 1 REPORT OF CHANGES IN APPLICATION OF THE AREVA ECCS EVALUATION MODEL TO THE LARGE BREAK LOCA FOR NORTH ANNA UNIT 2 VIRGINIA ELECTRIC AND POWER COMPANY NORTH ANNA POWER STATION (DOMINION)

Change in Application of the AREVA Large Break Loss of Coolant Accident (LOCA)

Evaluation Model at North Anna Unit 2 AREVA has informed Dominion of errors discovered in the Large Break LOCA Analysis for North Anna Unit 2. The results of AREVA's revised North Anna Unit 2 realistic large break LOCA (RLBLOCA) analysis are summarized below. The analysis was revised to correct three errors discovered in the prior RLBLOCA analysis.

• The initial steady-state core power in the original analysis was incorrectly apportioned between the top and bottom halves of the core. The axial power distribution input was developed assuming a uniform size for each axial fuel rod heat structure. In fact, the heat structures above the mid-plane where the Mid-Span Mixing Grids (MSMGs) are located, are smaller. This input error caused the North Anna plant model to contain too much power in the top half of the core and too little inthe bottom half. Total core power was correctly modeled. Such modeling led to over prediction of PCTs. This item is characterized as an error in application of the evaluation model per 10 CFR 50.46(a)(3)(i).

• The North Anna units have Westinghouse 93A reactor coolant pumps. The original RLBLOCA analysis used the built-in S-RELAP5 Westinghouse pump parameters, which apply to the Type 93 pump. For the original analysis case set, the effect of this difference was evaluated and concluded to be negligible. For the reanalysis, however, it was determined that the North Anna plant model would be changed to include the appropriate Westinghouse 93A pump homologous parameters. The 93A pump parameters were input to the S-RELAP5 North Anna plant model and applied in all analysis cases. This item is characterized as an error in application of the evaluation model per 10 CFR 50.46(a)(3)(i).

• The revised case set experienced execution failures and instabilities in several cases.

This behavior, which had not been observed in previous case sets, was traced to an incorrect prediction of choked flow applied during the period at the end of accumulator injection when the nitrogen cover gas enters the system. The logic in the S-RELAP5 code was revised to correct this problem, and the updated S-RELAP5 code version was certified and used in the Unit 2 reanalysis. This item is characterized as an error in the evaluation model per 10 CFR 50.46(a)(3)(i).

The limiting PCT for the Unit 2 case set decreased significantly (a change of -2430 F). The limiting PCT was 1,7890F for the reanalysis versus 2,0320 F for the previous analysis of record (AOR). The maximum oxidation is 1.8% and the total oxidation is 0.04%. The Unit 2 reanalysis showed that the 10 CFR 50.46(b) criteria were met with ample margins.

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ATTACHMENT 2 REPORTING OF 10 CFR 50.46 MARGIN UTILIZATION AREVA LARGE BREAK LOCA ECCS EVALUATION MODEL NORTH ANNA UNIT 2 VIRGINIA ELECTRIC AND POWER COMPANY NORTH ANNA POWER STATION (DOMINION)

Reporting of 10 CFR 50.46 Margin Utilization AREVA Large Break LOCA ECCS Evaluation Model - North Anna Unit 2 The information provided herein is applicable to the AREVA large break LOCA ECCS Evaluation Model for North Anna Power Station, Unit 2. It is based upon reports from AREVA for issues involving the ECCS evaluation models and plant-specific application of the models in the existing analyses. Peak cladding temperature (PCT) values and margin allocations represent issues for which permanent resolutions have been implemented. The assessments for large break LOCA are presented below.

10 CFR 50.46 Margin Utilization - AREVA Larae Break LOCA ECCS Evaluation Model -

North Anna Unit 2 A. PCT for Analysis of Record (AOR) {1} 17890 F B. Prior PCT Assessments Allocated to AOR {2}

1. Forslund-Rohsenow Correlation Modeling +640 F (1,2)

2. RWST Temperature Assumption +80 F (1,2)

3. LBLOCA/Seismic SG Tube Collapse 0F (2)

C. PCT Assessments for 10 CFR 50.46(a)(3)(i) Accumulation 0F D. LBLOCA Licensing Basis PCT (AOR PCT + PCT Assessments) {3} 1861°F Notes( { and References ( ) on the following page Page 1 of 2

Notes:

{1} The current report is the initial quantification of AREVA's revised North Anna Unit 2 realistic large break LOCA (RLBLOCA) analysis. Refer to the Report of Changes in Application of ECCS Evaluation Model Changes provided in Attachment 1.

{2} The accumulation of changes which have been reported to the NRC in Reference 2 have been rolled up from PCT Assessments for 10 CFR 50.46(a)(3)(i) Accumulation to Prior PCT Assessments Allocated to AOR.

{3) For North Anna Unit 2, the change in the licensing basis PCT from Reference 2 for the AREVA large break LOCA is greater than 500F. This is a significant change, as defined in 10 CFR 50.46(a)(3)(i).

References:

(1) Letter from USNRC to D. A. Christian, "North Anna Power Station, Unit 2 -

Issuance of Amendment Re: Use of Framatome ANP Advanced Mark-BW Fuel (TAC NO. MB4715)," dated April 1, 2004.

(2) Letter from L. N. Hartz (Va. Electric & Power Co.) to USNRC, "Virginia Electric and Power Company, Surry and North Anna Power Stations Units 1 and 2, Annual Report and 30-Day Report of Emergency Core Cooling System (ECCS) Evaluation Model Changes Pursuant to the Requirements of 10 CFR 50.46," Serial No.04-334, dated June 18,2004.

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