ML19351E482
| ML19351E482 | |
| Person / Time | |
|---|---|
| Issue date: | 11/21/1980 |
| From: | Dircks W NRC OFFICE OF THE EXECUTIVE DIRECTOR FOR OPERATIONS (EDO) |
| To: | Plesset M Advisory Committee on Reactor Safeguards |
| References | |
| ACRS-R-0899, ACRS-R-899, NUDOCS 8012100193 | |
| Download: ML19351E482 (1) | |
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NOV 211980 MEMORANDUM FOR: Milton S. Plesset, Chairman, Advisory Committee on Reactor Safeguards FROM:
William J. Dircks, Executive Director for Operations
SUBJECT:
SEISMIC QUALIFICATION OF PWR AUXILIARY FEEDWATER SYSTEMS This is to acknowledge your letter of October 15, 1980, in which you pro-vided observations and recommcndations concerning the staff's review of seismic qualification of auxiliary feedwater systems.
The recommendations have been incorporated into the scope of the review program, which was dis-cussed with the Committee on November 6,1980. A letter has been sent to all PWR licensees identifying our concerns and requesting that they begin reviewing their plant systems with respect to decay heat removal capability following earthquakes. As progress is made through the program, we will keep you informed.
A copy of the letter sent to licensees dated October 21, 1980, is enclosed for your information.
(Signe:D William L Dircks William J. Dircks Executive Director for Operations
Enclosure:
10/21/80 NRC Letter.
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October 15, 1980 Mr. William J. Dircks Executive Director for Operations U. S. Nuclear Regulatory Commission Washington, D. C. 20555
SUBJECT:
SEISMIC QUALIFICATION OF AUXILIARY FEE 0 WATER SYSTEMS
Dear Mr. Dircks:
'I In a letter to you dated June 10, 1980, the Advisory Committee on Reactor Safeguards expressed its concern that the NRC Staff's level of effort in reviewing the seismic qualification of auxiliary feedwater systems mignt not be consistent with timely resolution of the matter. We recommended that the necessary manpower be committed to assure completion of ne Staff's short-tera review in two or three months.
We recommended also that the affected licensees perform independent reviews of this matter on the same time scale.
In a memorandum to Chairman Ahearne dated August 27, 1980 Harold R. Denton transmitted a memorandum dated August 8, 1980 from Roger J.
Mattso n to Carrell 3.
Eisenhut which described an i nterim risk study.
Mr. Denton stated that the study indicates that the risk to the public health and safety for the next three years is acceptable and that tne plants could be pemitted to i:antinue to operate during this period.
Mr. Denton also stated that a bounding analysis, using conservative assumptions regarding seismic camage to auxiliary feedwater equipment, shows nat operation for the next several months would not result in an unacceptable increase in risk to the public.
We continued to review this matter during our 246th meeting, October 9-11, 1980.
In our review we had the benefit of a Subcommittee meeting on Octo-ber 8, 1980.
We offer the following observations and recommendations:
1.
The interim risk analysis performed by the Staff is useful.
The Com-mittee notes that this study does not appear to have been subjected to independent peer review or given the necessary degree of quality assur-ance that a risk analysis, which may enter im;:ortantly irito safety decision making, should receive.
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o Mr. William J. Dircks October 15, 1980 2.
The August 8,1960 memorandum from Roger Mattson does not provide the expected (or mean) value of ' risk.
Since detailed knowledge of all the components, equipment, and systems important to the auxiliary feedwater function is not available to the Staff, it is not clear that a sound basis exists for the terms "conservatise" or "very conservative".whicn.
are used 'in this memorandum.
Under these circumstances, it is possible that for one or more of the plants, the risk will be found to be larger than that estimated.
3.
The Staff's estimated risks of a seismic event causing a serious accident due to loss of shutdown heat removal capability range from six to fifteen times. the estimated risk of core melt due to all causes for the PWR examined in WASH-1400.
The Staff has preposed a course of action in terms of these estimated risks which implies a quantitative safety goa.1 and a threshold risk level for certain kinds of action.
Such safety goals and action levels 'may prove to be acceptable to the NRC after review and evaluation.
However, we believe that these should not become de facto criteria without the benefit of proper consideration.
Further-mo re, in the absence of an evaluation of tne uncertainties in and the expected value of the risk, the risk estimates presented may not be representative of the_ actual risk.
4.
The risk estimates presented in the memorandum from Roger Mattson of August 3,1980 are large enough, if accurate, to warrant considerable priority by the NRC and the affected utilities.
In particular, efforts should de.nade to better quantify the risk on a plant specific basis in the next few months.
Furthermore, we recommend that each affected licensee be ast:ad to review his specific plant design and to take early remedial measures, as practical, if there is reason to suspect that any important aspect of the auxili ary feedwater system is likely not to perfona its function during an earthquake similar to a safe shutdown earthquake for tne plant.
5.
We agree with the Staff. that 'high priority should be given to resolu-tion of this matter.
We expect to continue to follow this subject closely.
Si ncerely,
Milton S. Plesset Chainnan i
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