ML16281A255

Further ACRS Comment on Proposed Resolution of Generic Issue 99, Improved Reliability of RHR Capability in PWRs

ML16281A255
Person / Time
Issue date:	02/16/1989
From:	Remick F Advisory Committee on Reactor Safeguards
To:	Zech L NRC/Chairman
References
D890216
Download: ML16281A255 (2)

Text

D890216 The Honorable Lando W. Zech, Jr.

Chairman U.S. Nuclear Regulatory Commission Washington, D.C. 20555

SUBJECT:

FURTHER ACRS COMMENT ON PROPOSED RESOLUTION OF GENERIC ISSUE 99, "IMPROVED RELIABILITY OF RHR CAPABILITY IN PWRs" During the 346th meeting of the Advisory Committee on Reactor Safe-guards, February 9-11, 1989, we further considered the proposed resolu-tion of Generic Issue (GI) 99, "Improved Reliability of RHR in PWRs,"

together with the staff's response to our comments in our report of September 14, 1988. During this meeting, we also had the benefit of presentations by the NRC staff and of the documents referenced.

This generic issue addresses concerns about the possible failure of core cooling during shutdown operations in PWR plants. Analyses have shown there is a significant risk of core damage from overheating due to the loss of RHR circulation from a number of possible causes. The leading cause of this risk, as indicated by both analysis and experience, is loss of core cooling as a result of errors made during so-called "mid-loop" operation. The staff issued a generic letter that identifies a number of actions licensees are advised to take to reduce the likelihood of such incidents. The generic letter also recommends that licensees develop certain appropriate procedures and equipment that will permit rapid closing of any containment openings in such emergencies so that, if core damage does occur, release of fission products from the containment will be minimized.

In our September 14 report, we expressed agreement with most of the recommendations of the staff's generic letter, but questioned whether the plan for emergency closure of containment openings had been suffi-ciently analyzed, given the many varieties of containment openings that exist in actual plants. In our recent discussions with staff members, we learned that they intend to conduct inspections in all plants for compliance with recommendations of the generic letter. These in-spections will be carried out by the resident inspector staff at each plant and will be supplemented by more in-depth inspection conducted by specialists from the headquarters staff for selected plants.

We are particularly interested in the conclusions about the effec-tiveness of the proposed containment closure procedures that will be drawn as a result of these inspections. We want the staff to brief us within a few months, and we will be especially interested in information about the nature of the containment closures involved. For example, some closures are designed so that pressure within the containment will tend to compress closure seals. Other closures are designed so that pressure will tend to decompress and perhaps open gaps in containment seals. It is apparent that the proposed procedures for rapid installa-tion of closures will be more effective in achieving containment for

those with the former type of seal than with the latter.

A more general policy issue, which should be considered by the Com-mission rather than the staff, is apparent in the GI 99 resolution. The staff has presented estimates to us which show that the risk caused by loss of RHR cooling under shutdown conditions is a significant fraction of the total risk from reactor operation. Despite this, resolution of GI 99 is being carried out by informal means, through recommendations in a generic letter, rather than by more formal means, e.g., through rulemaking. We believe the staff's approach probably will be effective, and we have no quarrel with it. However, we question why more formal methods, ultimately more burdensome to licensees and staff, are used in resolution of other issues less important from the risk standpoint.

There does not appear to be any well-defined policy direction from the Commission concerning which regulatory approach should be taken for a given circumstance.

We hope you will find these comments useful.

Sincerely, Forrest J. Remick Chairman

References:

1. U.S. Nuclear Regulatory Commission Generic Letter dated October 17, 1988,

Subject:

"Loss of Decay Heat Removal (Generic Letter No.

88-17) 10 CFR 50.54(f)"

2. U.S. Nuclear Regulatory Commission, NUREG/CR-5015, "Improved Reliability of Residual Heat Removal Capability in PWRs as Related to Resolution of Generic Issue 99," dated May 1988

3. Memorandum dated December 21, 1988 from V. Stello, Jr., Executive Director for Operations, NRC, to Raymond F. Fraley, ACRS,

Subject:

341st ACRS Meeting (September 8-10, 1988) Follow-Up Items - Supple-ment"