ML20072P888
| ML20072P888 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 08/30/1994 |
| From: | Ohanlon J VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 94-459, NUDOCS 9409080290 | |
| Download: ML20072P888 (3) | |
Text
_-
k i
VINGINIA ELi:cTurc AND POWElt COMPANY H icirMoNn, VIHOINIA 200 61 August 30, 1994 i
U.S. Nuclear Regulatory Commission Serial No.94-459 Attention: Document Control Desk NL&P/JBL R0 Washington, D.C. 20555 Docket Nos.
50-339 License Nos. NPF-7 Gentlemen:
VIRGINIA ELECTRIC AND POWER COMPANY NORTH ANNA POWER STATION UNIT 2 LICENSEE PEER REVIEW COMMENTS PRELIMINARY ACCIDENT SEQUENCE PRECURSOR (ASP)
As requested by your letter dated July 21,1994, Virginia Electric and Power Company has reviewed the NRC's Preliminary Accident Sequence Precursor (ASP) analysis for North Anna Unit 2.
Our review indicates that the results are comparable with the Individual Plant Examination (IPE) model for North Anna Power Station.
This conclusion was reached by checking the ASP analysis and by performing a sensitivity analysis on the IPE model. We have no significant additions or corrections to the NRC's ASP evaluation. The attachment to this letter provides the results of our review.
If you have any further questions, please contact us.
Very truly yours, Y%v p r?c h James P. O'Hanlon Senior Vice President - Nuclear Attachment cc:
U.S. Nuclear Regulatory Commission Region 11 101 Marietta Street, N.W.
Suite 2900 Atlanta, Georgia 30323 Mr. R. D. McWhorter NRC Senior Resident inspector North Anna Power Station
($\\
(,,
94o90 eor 90 940eso PDR ADOCK 05000339 P
4 Attachment Peer Review Comments for the North Anna Unit 2 Preliminary Accident Sequence Precursor (ASP)
4 Peer Review Comments for the North Anna, Unit 2 ASP Evaluation A review of the ASP evaluation performed for the North Anna, Unit 2 reactor trip of April 93 has been completed. The review concentrated on Enclosure I to the NRC cover letter dated July 21,1994. Enclosure 1 is a PSA analysis of the reactor trip along with the immediately following system response and operator actions. He analysis was performed by NRC contractors as part of an on-going program to review operating events that could be considered as precursors to severe accidents.
De PSA modeling approach used is appropriate. De " Transient with MFW Available" is the proper event tree fbr the analysis. De analysts have modeled the scenario assuming that the AFW system is failed but recoverable. He non-recovery probability used is the smallest allowed by the ASP program guidelines. It is appropriate to use a small non-recovery probability since the AFW pumps could be recovered from the control room simply by moving the pump selector switch from the pull-to-lock position to the auto position.
He ASP results are given on pages 5 and 6 of Enclosure 1. Since the sequence probabilities are obtained by multiplying along the path that Ibrms each sequence it was possible to check the results.
He total non-recovery probability fbr each sequence could be duplicated using the stated AFW value of.04. However, the AFW non-recovery probability, when calculated from the sequence probability, is not the same for each sequence. He stated value of.04 was found for all sequences except #17 and #22. contains podions of the ASP document including Appendix A. In Section A.l.5 sample calculations are given. Using the approach given therein (i.e., multiplying successes and failures along each path) the sequence probabilities were calculated and are compared below:
Sequence ASP Va Power Number Review 12 1.6E-8 1.7E-8 22 4.6E-8 4.1E-9 15 4.5E-7 4.5E-7 16 4.9E-8 5.0E-8 17 4 91_2 ME-2 Sum (ed) 1.1 E-6 9.4E-7 Of course, these answers are nearly identical and the differences are certainly not significant given the approximate nature of the calculations.
De results were also checked by performing a sensitivity analysis on the IPE model. The sensitivity results were slightly higher than those above. However, no effort was made to include a non-rtcovery probability for this scenario in the sensitivity analysis. If a non-recovery probability had been calculated using the Virginia Power IPE methodology, it would likely have been an order of magnitude lower than the 0.04 value contained in the ASP guidelines. Eus, the IPE sensitivity results are slightly lower than those from the ASP analysis. His would be expected given the purpose of the ASP program.