ML20034E522
| ML20034E522 | |
| Person / Time | |
|---|---|
| Site: | 05200003 |
| Issue date: | 02/23/1993 |
| From: | Borchardt R Office of Nuclear Reactor Regulation |
| To: | Liparulo N WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP. |
| References | |
| NUDOCS 9302260276 | |
| Download: ML20034E522 (3) | |
Text
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UNITED STATES.
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February 23, 1993 m
Docket No.52-003 Y
Mr. Nicholas J. Liparulo 4
Nuclear Safety and Regulatory Activities Westinghouse Electric Corporation P.O. Box 355 Pittsburgh, Pennsylvania 15230
Dear Mr. Liparulo:
SUBJECT:
TREATMENT OF SEVERE ACCIDENT ISSUES IN CONTAINMEn; EVENT TREES OF THE PROBABILISTIC RISK ASSESSMENT (PRA) FOR THE AP600 j
During the review of the AP600 probabilistic risk assessment (PRA), the staff noted that the level 2 containment event trees (CETs) omitted potentially significant-phenomenological and containment loading issues.
These issues-include:
hydrogen deflagration and detonation, direct' containment heating /high pressure melt ejection, rapi neam generation 'and steam explo-sions, temperature-induced steam generato. tube rupture, and 'ex-vessel' core debris coolability. Also, the containment fragility' curve and.the probability.
of containment failure at pressures less than the ultimate containment failure pressure were not evaluated in the CETs. Accordingly,-the staff' requested.
Westinghouse to include these issues in their CETs (see letter dated Septem-ber 23, 1992, Q720.51).
Westinghouse subsequently submitted WCAP-13388 that concluded that these phenomena do not pose a credible threat to containment integrity,.and there-fore, do not need to be treated within the CETs. The staff concludes that the analyses and information provided in the WCAP and during the December 15, 1992, meeting Nith Westinghouse does not provide an adequate basis for concluding that these phenomena could not fail the APf 00 containment.
As noted by the staff during the December meeting, the Westinghouse evaluations:
(1) are generally conservative but not bounding, (2).did not consider the possibility of containment failure-at pressures lower than the estimated i
ultimate pressure capacity, and (3) did not probabilistically treat the key-contributors to uncertainty in estimating each containment load.
For example, decomposition trees or some other systematic. approach such as used in NUREG/CR-5423 for the Mark I containment shell melt-through issue could be used. Accordingly, the. staff requests that Westinghouse use' tools such as sensitivity analyses complemented by probabilistic techniques to'systemati-cally treat the uncertainties in each of these key phenomena, and factor the results into the.CETs. Reflecting these phenomena within the event trees is necessary so that their treatment isLtraceable and scrutable as a part of the.
complete design certification package.
Inclusion of the phenomena in the CETs.
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y Mr. Nicholas J. Liparulo February 23,~1993 would also provide insights into the significance of each containment chal-lenge for the AP600 design and tolerance of the AP600 design to severe.
accidents.
The staff is prepared to. meet with Westinghouse to further discuss potential-approaches for addressing severe accident issues in the CETs.
If you have any questions regarding this matter, you can contact the project manager, Thomas J. Kenyon, at (301) 504-1120.
Sincerely, OriginalSigned Ry:
Richard W. Borchardt, Acting Director Standardization Project Directorate Associate Director for Advanced Reactors and License Renewal Office of Nuclear Reactor Regulation cc:
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DOCUMENT NAME:
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,i Mr. Nicholas J. Liparulo Westinghouse Electric Corporation Docket'No.52-003 AP600 cc:
Mr. B. A.'McIntyre Advanced Plant Safety & Licensing Westinghouse Electric Corporation Energy Sys+ ems Business Unit P.O. Box 3bs Pittsburgh, Pennsylvania 15230 Mr. John C. Butler Advanced Plant Safety & Licensing Westinghouse Electric Corporation Energy Systems Business Unit Box 355 Pittsburgh, Pennsylvania 15230 Mr. M. D. Beaumont Nuclear and Advanced Technology Division Westinghouse Electric Corporation One Montrose Metro 11921 Rockville Pike Suite 350 Rockville, Maryland 20852 Mr. Sterling Franks U. S. Department of Energy NE-42 Washington, D.C.
20585 Mr. S. M. Modro EG&G Idaho Inc.
Post Office Box 1625 Idaho Falls, Idaho 83415
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