ML18153C799
| ML18153C799 | |
| Person / Time | |
|---|---|
| Site: | Surry  |
| Issue date: | 10/29/1991 |
| From: | Stewart W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 91-134C, NUDOCS 9111060257 | |
| Download: ML18153C799 (3) | |
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e VIRGINIA ELECTRIC AND POWER COMPANY RICHMOND, VIRGINIA 23261 October 29r 1991 United States Nuclear Regulatory Commission Attention: Document Control Desk Washington, D. C. 20555 Gentlemen:
VIRGINIA ELECTRIC AND POWER COMPANY Serial No.
NL&P/CGL Docket Nos.
License Nos.
SURRY POWER STATION UNITS 1 AND 2 SUPPLEMENTAL INFORMATION ON SURRY INDIVIDUAL PLANT EXAMINATION / INTERNAL FLOODING ANALYSIS 91-134C RO 50-280 50-281 DPR-32 DPR-37 The purpose of this letter is document the October 29, 1991 conference call between the NRC and Virginia Electric and Power Company.
The conference call was conducted to discuss the core damage frequency (CDF) for internal flooding considering the current plant configuration at Surry Power Station. Specifically, the following* items have been factored into calculation of a reduced CDF for internal flooding:
Expansion joints on the circulating water and service water systems and associated MOVs, which are significant contributors to any flood damage state frequency, have recently been replaced.
Inspections on MOV bolting have recently been completed. (MOV bolt failure was considered a significant initiating event in the original IPE analysis.)
A minimum of seven of nine turbine building sump pumps are being maintained operable.
Considering the above and using the same methodology as was used in the original IPE analysis (August 30, 1991 submittal - Serial No.91-134), the CDF for internal flooding is now reduced to 1.7E-4 per reactor year.
Also discussed during the conference call were additional physical plant modifications that will be completed by November 22, 1991. These physical modifications include:
Charging pump cubicle drain lines will be modified to prevent backflow. Planned installation of backflow devices or temporary installation of blank flanges to close the drains lines will be completed. This modification eliminates core damage sequences that initiate from RWST supply floods in either safeguards building.
Flow shields on the six expansion joints in the service water supply lines for bearing cooling and component cooling will be installed.
This modification reduces the maximum flow rate which could occur upon failure of the expansion joints to less than the dewatering capacity of the sump pumps.
Considering the above physical modifications and using the same methodology as was used in the original IPE analysis (August 30, 1991 submittal), the CDF for internal flooding will be further reducedto 9.9E-5 per reactor year. summarizes the total reductions in CDF discussed in this letter. It should be noted that no credit is being taken for interim administrative controls or the accelerated schedule for plant modifications discussed in our October 28, 1991 submittal (Serial No. 91-134B).
If you have questions regarding this transmittal, please contact us.
Very truly yours, lJL~
W. L."'~e~0 \\
Senior Vice President - Nuclear Attachment - Reduction of CDF for Internal Flooding for Current Configuration and Planned Short Term Modifications cc:
U. S. Nuclear Regulatory Commission Region II 101 Marietta Street, N. W.
Suite 2900 Atlanta, Georgia 30323 Mr. M. W. Branch NRC Senior Resident Inspector Surry Power Station
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I ATTACHMENT 1 REDUCTION OF CDF FOR INTERNAL FLOODING FOR CURRENT CONFIGURATION AND PLANNED SHORT TERM MODIFICATIONS IPE Report (8/30/91)
October 9, 1991 Meeting with NRG (10/9/91)
Credit taken for Procedural Revisions and 7 of 9 Sump Pumps Operable Current (1029/91)
Credit taken for Expansion Joint Replacement and MOV Replacement/Bolt Inspection 7 of 9 Sump Pumps Operable Planned Short Term Modifications (by 11/22/91)
Charging Pump Cubicle Isolation Expansion Joint Shields 1.1 E-3
<8.0E-4
- 1. 7E-4 9.9E-5