ML20126A722
| ML20126A722 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 12/14/1992 |
| From: | Stewart W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML20126A725 | List: |
| References | |
| REF-GTECI-023, REF-GTECI-A-45, REF-GTECI-DC, REF-GTECI-NI, TASK-023, TASK-23, TASK-A-45, TASK-OR 92-774, GL-88-20, NUDOCS 9212210199 | |
| Download: ML20126A722 (5) | |
Text
. _,
s l
o,-
4' VIHCINIA ELEcTrslC AND POWER COMi%NY Ricnwoxo. Vr.unm A caeon Deer er 14, 1992 United States Nuclear Regulatory Commission Gerial No.92-774 Attention: Document Control Desk NA&F/RST NL&P/RMN Washington, D.C. 20555 Docket Nos.
50-338 50-339 License Nos.
NPR-4 NPR-7 Gentleman:
VIRGINIA ELECTRIC AND POWER CC:MPANY NORTH ANNA POWER ST ATION UNITG 1 AND 2 RESPONSE TO CENEBJ9 LETTER 38-20 AND SUPPLEMENT 1 INDIVIDUAL PLANT EXAMINATION (IPE)
FOR SEVERE ACCIDENT VULNERABILITIES g
Generic Letter 88-20, " Individual Plant Examination for Severe Accident Vulnerabilities," and Supplement 1 requested holders of operating licenses to perform an Individual Plant Examination (IPE) of their plants for severe accident vulnerabilities.
The following paragraphs summarize the enclosed final report for the North Anna Power Station IPE, a Level 1/ Level 2 PRA.
No significant vulnerabilities were identified by the IPE.
The intemal events portion (excluding internal flooding) of the study resulted in a point estirnate core damage frequency (CDF) of 6.8E-5 per reactor year. The Internal flooding portion of the study resulted in a point estimate CDF of 3.6E 6 per reactor year. Attachment 1 presents the contribution to CDF by initiating event type. The results of the IPE assume that certain hardware modifications and procedural enhancements have been initiated to reduce the frequency of the dominant accident sequences. Attachment 2 identifies the hardware and procedural changes and their implementation dates. As indicated in Attachment 2, the hardware modifications designed to further enhance the flood protection system have already been completed, in addition, the majority of the procedural changes identified to reduce the risk from internal events, including internal flooding, have also been implemented.
Per the requirements of Generic Letter 88 20 and as indicated in Section 2.2.4 of the enclosed fina n: port, Unresolved Safety Issue (USI) A-45, Shutdown Decay Heat Removal Re -
ements," has been resolved by the North Anna IPE. In addition, USI A-17, "Systeins Interactions in Nuclear Power Plants," and Generic Issue GI-23,
" Reactor Coolant Pump Seal Failure," have also been resolved by the IPE. The resolution of these two items is discussed in Section 3.4.4 of the enclosed final report.
n n n.m
- BA22;gggogsgga hj P
I Please note that it is our intention to use the enclosed North Anna IPE in future evaluations relative to plant modifications, Technical Specification changes, procedural revisions, etc. If you have questions regarding this submittal, please contact us.
Very truly yours, n
<~ r.
s
\\.
01 7
W. L. Stewart Senior Vice President - Nuclear Enc.losure cc:
U.S. Nuclear Regulatory Commission Region ll 101 Marietta Street, N.W.
Suite 2900 Atlanta, Georgia 30323 Mr. M. S. Lesser NRC Senior Resident Inspector North Anna Power Station C
~ - -.. -. -
Core Damaae Freauency by Initiatina Event Tvoe Point Estimate Frequency Percentage initiatina Event Tvos ner Reactor Year of Total LOCA 2.1 E 5 31 Loss of Offsite Power 2.0E-5 29 Transients 1.8E-5 27 Steam Generator Tube Rupture 7.0E-6 10 Interfacing LOCA 1.6E-6 2
-ATWS
.4Jh2 1-Total (Intemal Events) 6.8E-5 100 Core Damaae Freauency From Internal Floodina Point Estimate Frequency Percentage Flood Area ner Reactor Year of Total Auxiliary Building Floods 2.6E-6 73 MCR/ESGR Chiller Room Floods 9.7E-7
,2Z Total (Intemal Flooding) 3.6 E-6 100 4
.m... -,
i l
l l
Individual Plant Examination i
Recommendations Summarv i
4 Implementation Activity Schedule internal Events Procedure Enhancements:
Revise periodic test procedures to include Complete j
i verification that the auxiliary feedwater full flow recirculation valves are closed.
Revise periodic test procedures to include Complete i
independent verification that the quench spray and recirculation spray piping is restored after testing.
Revise emergency operating procedures to 08 20-93
- add the alternate Si header to the i
response not obtained (RNO) column if the normal SI header falls.
Stagger LHSI pump tests to test one train Complete every 45 days and each pump every 90 days.
Administrative!y eliminate preplanned dual Complete l
maintenance outages for the MCR/ESGR
- chillers, i~
Improve maintenance practices to minimize Complete the total time MCR/ESGR chillers are out j
of service.
L Provide procedure guidance for trouble-Complete shooting and repairing MCR/ESGR chiller i
protective circuitry.
l Procedure enhancements have been initiated '
4 i
..--m..
....-r.
.m,c.-.-., - _..,.
--e,--.
. (Continued)
Individual Plant Examinatlor, flecommendations Summary implementation Activity Schedule Internal Floodina Hardware Modifications:
Install back flow prevention devices in Complete Charging Pump Cubicle floor drains.
Improve the piping penetration fire Complete barrier between the Quench Spray Pump House and Auxiliary Building to limit the flooding flow rate.
Add a dike to protect the Chiller Complete Room / Fan Room doors (both units) and modify of the Chiller Room /
Turbine Building doors (both units).
Internal Floodino Procedure Enhancements:
Periodic inspection / replacement of the Complete Charging Pump Cubicle drain back flow prevention devices.
Establish administrative control to ensure Complete periodic inspection of all flood dikes and barriers.
Revise Periodic Test procedures to test 06-18-93*
alarms and all automatic equipment actuations for the flooding level swi+ches.
Revise the abnormal procedure for 08-20-93*
t Auxiliary Building flooding to include steps which identify and isolate remotely isolatable floods and RWST floods.
Procedure enhancements have been initiated