ML19345H595
| ML19345H595 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 05/12/1981 |
| From: | Mark J Advisory Committee on Reactor Safeguards |
| To: | Hendrie J NRC COMMISSION (OCM) |
| References | |
| ACRS-R-0929, ACRS-R-929, NUDOCS 8105210345 | |
| Download: ML19345H595 (2) | |
Text
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UNITED STATES
~g NUCLEAR REGULATORY COMMISSION o
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ADVISORY COMMITTEE ON REACTOR SAFEGUARDS o
e WASHINGTON, D. C. 20555 g
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[/r0 N 1 May 12,1981 4
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Honorable Joseph M. Hendrie gf 7
Chaiman C
2 4,,g,dQ,7 ISS U. S. Nuclear Regulatory Commission 9
Washington, D. C.
20555
SUBJECT:
PROPOSED MODIFICATIONS TO THE NORTH ANNA STATION UNIT 240L N[Q PRESSURE INJECTION AND RESIDUAL HEAT REMOVAL SYSTEMS
Dear Dr. Hendrie:
Commissioner Gilinsky, in a separate statement dated August 20,1980 on the full power authorization for the North Anna Nuclear Plant Unit 2, noted that it appeared that the low pressure injection (LPI) and residual heat removal (RHR) systems could be improved substantially in terms of their ability to deal with accidents. The specific changes suggested were the environmental qualification of the RHR system and the addition of a heat exchanger to the LPI system. Commissioner Gilinsky requested that the desirability of these modifications be examined by the Advisory Committee on Reactor Safeguards (ACRS) and the NRC Staff.
At a meeting of an Ad Hoc ACRS Subcommittee on Decay Heat Removal Systems held on May 5,1981 and again at a meeting of the ACRS on May 7,1981, the NRC Staff and the North Anna licensee discussed the North Anna decay heat removal systems and the modifications proposed by Comissioner Gilinsky.
The Staff has concluded that the existing North Anna design confoms with all regulatory requirements and that, within the framework of current NRC review criteria, the proposed modifications would not improve these systems significantly. The licensee described the design bases for the LPI and RHR systems and the ability of the plant to cope with a spectrum of abnomal situations involving accidental degradation of the nomal systems' capacity.
Further, results were presented of a study conducted for the NRC Staff by Brookhaven National Laboratory which indicated there would be little or no safety improvement with addition of a heat exchanger in the LPI system.
The study pointed out that the North Anna LPI system already includes in its design a significant improvement over that of the Surry system analyzed in the Reactor Safety Study, WASH-1400. This improvement reduces potential for one accident sequence (S,3C) which was a major cuntributor to the core melt probability calculated f8r Surry.
l Also presented to the Subcommittee by the Staff was an updated description of preliminary Task Action Plan A-45, on the Unresolved Saf;ty Issue of decay heat removal requirements, which had been presented to the ACRS on April 10, 1981.
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8105210 % {-
Honorable Joseph M. Hendrie May 12, 1981 We concur with Cosnissioner Gilinsky's desire to improve the reliability of decay heat removal systems. Probabilistic and deterministic assessments have concluded that potential failures in decay heat removal systems are major contributors to risk in operation of light water reactors. We con-clude that aggressive development of Task A-45 and rapid implementation of any new decay heat removal requirements deriving from the Task Action Plan will best serve to improve the reliability of such systems for all LWRs, including North Anna. We have listed below several suggestions which we believe will improve the Task Action Plan, and we urge the Commission to take these into account while assigning a high priority to Task A-45.
The plan should give careful consideration to alternative decay heat removal systems, such as those used in some foreign LWRs and reviewed in the current Sandia study being conducted for RES.
Probabilistic studies such as RSSMAP, RSS, and IREP should furnish valuabic insights in assessing system improvements, but engineering evaluation should not rely solely on these studies.
The estimated completion date,1984, is not likely to be realized for the ambitious program outlined unless the Commission assigns high priority to the work and allo-cates Staff resources to assure its timely completion.
We understand that a draft Task Action Plan for Task A-45 will be available in the very near future. We request the opportunity to comment on the plan 4
in more detail.
Sincerely, J. Carson Mark Chainnan l
l l
1
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