ML063260569

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

ML063260569
Person / Time
Site:	Millstone
Issue date:	11/20/2006
From:	Gerald Bichof Dominion Nuclear Connecticut
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
06-981
Download: ML063260569 (6)

Text

Dominion Nuclear Connecticut, Inc.

5000 Dominion Boulevard, Glen Allen, Virginla 2.3060 Wet, Address: www.dom.com November 20, 2006 U.S. Nuclear Regulatory Commission Serial No.06-981 Attention: Document Control Desk MPS LicANDB RO Washington, DC 20555 Docket No. 50-423 License No. NPF-49 DOMINION NUCLEAR CONNECTICUT. INC.

MILLSTONE POWER STATION UNIT 3 30-DAY REPORT OF EMERGENCY CORE COOLING SYSTEM (ECCS) MODEL CHANGES PURSUANT TO THE REQUIREMENTS OF 10 CFR 50.46 In accordance with 10 CFR 50.46(a)(3)(ii), Dominion Nuclear Connecticut, Inc. (DNC) hereby submits information regarding changes to the Westinghouse Emergency Core Cooling System (ECCS) Evaluation Model for the BASH Large Break Loss of Coolant Accident (LBLOCA) analysis for Millstone Power Station Unit 3 (MPS3) and its application in existing analyses. provides a report describing changes associated with the Westing house BASH LBLOCA ECCS Evaluation Model for MPS3.

Information regarding the effect of the ECCS evaluation model changes upon the reported LBLOCA analysis of record (AOR) result for MPS3 is provided in Attachment 2.

To summarize the information in Attachment 2, the calculated peak cladding temperature (PCT) for the LBLOCA analysis is increased by 74°F to a new value of 2048°F. This result represents a significant change in PCT, as defined in 10 CFR 50.46(a)(3)(i).

10 CFR 50.46(a)(3)(ii) requires the licensee to provide a report within 30 days, which includes a proposed schedule for providing a reanalysis or taking other action as may be needed to show compliance with 10 CFR 50.46. Dominion has reviewed the information provided by Westinghouse and determined that the adjusted LBLOCA PCT value and the manner in which it was derived continue to conform to the requirements of 10 CFR 50.46. As such, Dominion considers the schedular requirements of 10 CFR 50.46(a)(3)(ii) to be satisfied with the submission of this notification. Dominion routinely tracks adjustments to the Small Break Loss of Coolant Accident (SBLOCA) and LBLOCA calculated PCT values to ensure that reasonable margins to the acceptance value set by 10 CFR 50.46 are maintained.

This information satisfies the 30 day reporting requirements of 10 CFR 50.46(a)(3)(ii).

Serial Number 06-981 Docket No. 50-423 bc Page 2 of 2 If you have any further questions regarding this submittal, please contact Mr. David W.

Dodson at (860) 447-1791 , Extension 2346.

Very truly yours,

~ e r a l T.

d Bischof w Vice President - Nuclear Engineering Commitments made in this letter: None Attachments: (2)

1) Report of Changes in Westinghouse BASH Large Break LOCA ECCS Evaluation Model - Millstone Power Station Unit 3.

2) Reporting of 10 CFR 50.46 Margin Utilization - Westinghouse BASH Large Break LOCA ECCS Evaluation Model - Millstone Power Station Unit 3.

Serial Number 06-981 Docket No. 50-423 ATTACHMENT 1 REPORT OF CHANGES IN WESTINGHOUSE BASH LARGE BREAK LOCA ECCS EVALUATION MODEL DOMINION NUCLEAR CONNECTICUT, INC.

MILLSTONE POWER STATION UNIT 3

Serial Number 06-981 Docket No. 50-423 Attachment 1, Page 1 of 1 REPORT OF CHANGES IN WESTINGHOUSE BASH LARGE BREAK LOCA ECCS EVALUATION MODEL MILLSTONE POWER STATION UNIT 3 Identification of ECCS Evaluation Model Chancres The current large break loss of coolant accident (LBLOCA) analysis for Millstone Power Station Unit 3 (MPS3) was performed using the Westinghouse BASH LBLOCA Evaluation Model. Westinghouse identified the change described below and provided the results of an assessment to determine the impact on peak cladding temperature (PCT).

Change: BASH Minimum and Maximum Time Step Sizes Westinghouse reviewed recent BASH LBLOCA Evaluation Model sensitivity calculations. This review led to a recommendation to reduce the minimum and maximum time step sizes in the BASH LBLOCA Evaluation Model during the reflood phase of the accident. Westinghouse performed sensitivity calculations using the BASH LBLOCA Evaluation Model with reduced minimum and maximum time step sizes. The results showed a decrease in the integral flooding rate late in the reflood phase of the accident that resulted in a 44°F increase in PCT (APCT = 44°F).

Conclusion Dominion has performed an evaluation of PCT for comparison to 10 CFR 50.46 requirements. The Analysis of Record (AOR) PCT is 1974°F. Considering the current PCT change as well as all previously reported changes, the corrected LBLOCA PCT is 2048°F. The MPS3 LBLOCA results have sufficient margin to the 2200°F limit specified in 10 CFR 50.46(b)(1). The PCT assessments for 10 CFR 50.46(a)(3)(i) accumulation include the current assessment (APCT = 44°F) and a previous assessment resulting from a rebaseline of the AOR (APCT = 30°F). The 10 CFR 50.46(a)(3)(i) accumulation of APCT = 74°F is greater than the 50°F limit for reporting; hence, the changes are significant and submittal of this 30 day report to the NRC is required.

Serial Number 06-981 Docket No. 50-423 ATTACHMENT 2 REPORTING OF 10 CFR 50.46 MARGIN UTILIZATION WESTINGHOUSE BASH LARGE BREAK LOCA ECCS EVALUATION MODEL DOMINION NUCLEAR CONNECTICUT, INC.

MILLSTONE POWER STATION UNIT 3

Serial Number 06-981 Docket No. 50-423 Attachment 2, Page 1 of 1 10 CFR 50.46 Margin Utilization Large Break LOCA Plant Name: Millstone Power Station Unit 3 Utilitv Name:

I Dominion Nuclear Connecticut, Inc.

Analvsis Information EM: BASH Limiting Break Size: Cd=0.6 Analysis Date: 08/90 Vendor: Westinghouse FQ: 2.6 FAH: 1.7 Fuel: RFNR FA-2 SGTP (%): 10 Notes: All V5H assemblies have been removed from the core; the current fuel type is RFNRFA-2.

Clad T e m (~O F )

LICENSING BASIS Analysis of Record PCT 1974 PCT ASSESSMENTS (Delta PCT)

A. Prior ECCS Model Assessments

1. None B. Planned Plant Modification Evaluations

1. CHG/SI Alternate MiniFlow C. 2006 ECCS Model Assessments

1. BASH Minimum and Maximum Time Step Sizes 44 D. Other

1. Rebaseline of AOR LICENSING BASIS PCT + PCT ASSESSMENTS PCT = 2048