ML16328A369

ACRS Comments on Proposed BWR Mark I Containment Requirements for Severe Accidents

ML16328A369
Person / Time
Issue date:	12/17/1986
From:	Ward D Advisory Committee on Reactor Safeguards
To:	Zech L NRC/Chairman
References
Download: ML16328A369 (2)

Text

D861217 The Honorable Lando W. Zech, Jr.

Chairman U. S. Nuclear Regulatory Commission Washington, DC 20555

SUBJECT:

ACRS COMMENTS ON PROPOSED BWR MARK I CONTAINMENT REQUIREMENTS FOR SEVERE ACCIDENTS During our 320th meeting, December 11-13, 1986, the members of the Advisory Committee 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 BWR 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 in 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 the drywell spray flow rates. We recommend that the Staff strengthen, to the extent feasible, the detailed technical analysis to support the proposed requirements.

We also believe that additional information is needed in several areas, including the following:

o 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 o a tabulation of information concerning significant differences among the family of Mark I containments sufficient to ascertain that the proposed generic requirements would not necessitate special exceptions and/or additions o 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 o an analysis of the proposed Emergency Procedure Guidelines (for 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, 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.