ML20212A461
| ML20212A461 | |
| Person / Time | |
|---|---|
| Issue date: | 12/17/1986 |
| From: | Ward D Advisory Committee on Reactor Safeguards |
| To: | Zech L NRC COMMISSION (OCM) |
| References | |
| ACRS-R-1234, NUDOCS 8612240153 | |
| Download: ML20212A461 (2) | |
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o UNITED STATES j
}s NUCLEAR REGULATORY COMMISSION r
ADVISORY COMMITTEE ON REACTOR SAFEGUARDS WASHINGTON, D. C. 20555 O,
g December 17, 1986 The Honorable Lando W. Zech, Jr.
Chairman U. S. Nuclear Regulatory Commission Washington, DC 20555
Dear Chainnan Zech:
SUBJECT:
ACRS COMMENTS ON PROPOSED BWR MARK I CONTAINMENT REQU MEMENTS FOR SEVERE ACCIDENTS During our 320th meeting, December 11-13, 1986, the members of the Advisory Comittee on Reactor Safeguards discussed proposed new require-ments for Boiling Water Reactor (BWR) Mark I containments with regard to their capability to withstand severe accidents.
During our review, we had the benefit of discussions with representatives of the NRC Staff and SWR Owners' Group (BWROG), as well as the benefit of the documents referenced.
Discussions were also held with the Staff during our 315th meeting, July 10-12, 1986, and information was developed during the Containment Requirements Subcommittee meetings on September 23 and December 9, 1986.
The Staff's proposed requirements for BWR Mark I containments were presented in a draft generic letter with an attachment evaluating containment performance during severe accidents.
This evaluation is admittedly open to question ir regard to conditional containment failure probabilities, and it lacks detailed technical justification for the se-lection of certain procedures or parameters, e.g., a reduction of 90*. in
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th2 arywell spray flow rates.
We recommend that the Staff strengthen, to the extent feasible, the detailed technical analysis to support the proposed requirements.
We 21so believe that additional information is needed in several areas, including the following:
e an estimate of the contribution to core melt frequency and to containment failure from significant external events, including seismic events greater than the Safe Shutdown Earthquake i
e a tabulation of information concerning significant differences l
among the family of Mark I containments sufficient to ascertain that the proposed generic requirements would not necessitate l
special exceptions and/or additions fh J
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The Honorable Lando W. Zech, Jr. December 17, 1986 e
an examination of possible adverse effects of pool bypass as a result of transient thermal stresses and their possible effect on drywell connections to downcomers an analysis of the proposed Emergency Procedure Guidelines (for e
example, circumstances under which emergency sprays may be initi-ated or reinitiated) which considers the effects of venting and spraying operations on the continuing availability of the vapor suppression processes and other engineered safety features which may continue to be needed or highly desirable Until sufficient information has been developed on matters such as these, we are unwilling to agree with the proposed position in the draft generic letter:
"Given the implementation of the generic improvements of Mark I containments, there is no need for an Individual Plant Eval-uation (IPE) for containment performance."
Nevertheless, the Staff should issue the proposed generic letter for public comment.
The BWROG containment studies and the Staff's evalua-tion of the Emergency Procedure Guidelines are expected to be issued during the proposed public comment period. The results of these studies should be considered along with public comments as part of the final resolution of this issue.
We would like to consider this matter at a future meeting when the actions noted above are completed.
Sincerely,
.I David A. Ward Chairman
References:
1.
Memorandum from R.
Bernero for R.
Fraley,
Subject:
Proposed Generic Letter on Improvements for BWR Mark I Containments, dated December 3, 1986.
2.
BWR Owners' Group, " Emergency Procedure Guidelines," OEI Document 8390-4, Draft Revision 4AF, dated August 14, 1986.
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