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UNITED STATES y
7, NUCLEAR REGULATORY COMMISSION M
WASHWGTON. D. C. 20555 o...+ /
November 1, 1991
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Mr. Byron Lee, Jr.
President and Chief Executive Officer l
Nuclear Management and Resources Council 1776-Eye Street, N.W., Suite 300
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Washington, DC 20006-2496
Dear Mr. Lee:
l This memorandum is in response to your May 21, 1991 letter to Commissioner Curtiss, which stated that a reduction in current EDG accelerated testing l
requirements should be pursued independent of closure of the B-56 issue.
l Please be advised that the staff is revising the station blackout rule (10 CFR 50.63) and Regulatory Guide 1.9, Revision 3 (proposed) in response to the Commission's direction as outlined in the Staff Requirements Memorandum dated June 26, 1991. This approach incorporates NUMARC's " double" trigger l
concept and the " problem" emergency diesel generator which would reduce accelerated testing requirements. We plan to issue the revised rule and regulatory guide early next year for public comment. This schedule is about l
the same as NUMARC's effort related to performance-based regulations and l
their application to emergency diesel generator reliability described in Mr. J. F. Colvin's letter to Mr. J. H. Sniezek dated August 5,1991.
Emergency diesel generators play a very important role in the safe operation of nuclear power plants. Therefore, it is critical that high EDG reliability f
be maintained. After years of debate, the staff plans to issue a proposed rule that provides criteria for maintaining high EDG reliability and also minimize the need for accelerated testing.
In this context, the staff plans to utilize NUMARC'S double trigger concept (e.g. 5/50 and 8/100 for a station blackout EDG reliability target of 0.95) as a clear indication that diesel reliability has fallen below the previously selected target level.
If these criteria are satisfied by licensees, the need for accelerated testing would not arise unless there is significant deterioration of an EDG (i.e., 4 l
failures in 25 demands). Therefore, implementation of the double trigger values would be necessary as a technical basis to reduce the need for accelerated testing, i.e., support a 4/25 criterion. Consequently, I have instructed the staff to develop generic guidance for revising technical specifications consistent with the NUMARC concept and the proposed rule which could be voluntarily adopted by licensees, as an interim measure, until the rulemaking is completed.
l We hope that the above approach can be used by you in developing NUMARC guidance for use by the utilities.
Sincerely,
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QOMI UWG
/ ' arris M. Taylor
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l xecutive Director for Operations L)G\\s 9306160287 930422 n
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