NSD-NRC-97-4928, Forwards Draft Rept, Resolution of T/H Uncertainty Issues for AP600 Passive Sys Reliability
| ML20133B860 | |
| Person / Time | |
|---|---|
| Site: | 05200003 |
| Issue date: | 01/02/1997 |
| From: | Mcintyre B WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP. |
| To: | Quay T NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML20133B864 | List: |
| References | |
| NSD-NRC-97-4928, NUDOCS 9701060238 | |
| Download: ML20133B860 (3) | |
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b Westinghouse Energy Systems se Electric Corporation Pittsburgh Pennsylvania 15230-0355 NSD-NRC-97-4928 DCP/NRC0695 Docket No.: STN-52-003 January 2,1997
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Document Control Desk U.S. Nuclear Regulatory Commission Washington, D. C. 20555 ATTENTION:
T.R. QUAY
SUBJECT:
DRAFT REPORT - RESOLUTION OF T/H UNCERTAINTY ISSUES FOR AP600 PASSIVE SYSTEM RELIABILITY
Dear Mr. Quay:
Enclosed please find the Westinghouse draft report " Resolution of T/H Uncertainty Issues for AP600 Passive System Reliability."
The central question of the thermal / hydraulic uncertainty issue is whether the consideration of T/H uncertainty in PRA success criteria analyses would significantly affect the conclusions of the AP600 PRA. The T/H uncertainty resolution process (as defined by the enclosure to Westinghouse letter NSD-NRC-96-4781, dated July 29,1996, and by discussions with the NRC staff at an August 27, 1996 meeting) identifies a set of low-margin, risk significant accident scenarios, and shows acceptable T/H performance when the uncertainties are bounded.
The first step of the T-H uncertainty resolution process is to expand the PRA event trees and to quantify the frequency of the success paths. The next step is to categorize the success paths based on similarities in the accident progressions, and to further identify which categories fit into the low-margin, risk-significant definition. From the risk-significant categories, a set of cases is defined for T/H analyses with uncertainties to complete the T/H uncertainty resolution process.
As discussed with the NRC staff during a telecon on December 4,1996, Westinghouse had performed the expansion of the PRA event trees and would provide the staff with a document that summarizes the results of the event tree expansion. The enclosure to this letter provides this information. Since the MAAP4 benchmarking work is not yet cenpleted, there is a possibility that information in Sections 5 through 8 of the report could change, thus the report is labeled as " draft"
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The NRC technical staff should review the enclosed material. Feedback from the staff is essential to maintain momentum on the path to resolving this issue.
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NSD-NRC-97-4928 January 2,1997
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Please contact Cynthia L. Haag on (412) 374-4277 if you have any questions concerning this tiansmittal, ff f
Brian A. McIntyre, Manager Advanced Plant Safety and Licensing 2
Enclosure cc:
W. Iluffman, NRC (enclosure)
A. Levin, NRC (enclosure)
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l T. Collins, NRC (w/o enclosure) i.
N. J. Liparulo, Westinghouse (w/o enclosure) i i
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l Enclosure to Westinghouse Letter NSD-NRC-97-4928 January 2,1997 I
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