ML25196A324

01-14-76 Interim Report on Anticipated Transients Without Scram (ATWS)

ML25196A324
Person / Time
Issue date:	01/14/1976
From:	Moeller D Advisory Committee on Reactor Safeguards
To:	Anders W NRC/Chairman
References
Download: ML25196A324 (1)

Text

ADVISORY COMMITTEE ON REACTOR SAFEGUARDS NUCLEAR REGULATORY COMMISSION Honorable William A. lmders Chairman WASHINGTON, D. C. 20555 January 14, 1976

u. s. Nuclear P..egulatory Commission Washington, OC 20555

SUBJECT:

INTERIM P-EFORI' ON l\..NTICIPATED TRANSIENTS WITHOUI' SCRAM (A'IWS)

D2ar Mr..l'..nders:

At its 189th meeting, January 8-10, 1976, the Advisory Committee on P-eactor Safeguards reviewed the Nuclear Regulatory Commission Staff's status reports on A'IlvS in water reactors and the analyses and proposals of four reactor vendors, The Elabcock and Wilcox Company, Combustion Engineering, Inc.,

Westinghouse Electric Corporation, and General Electric Company, on this matter. Subcommittee meetings -~-rere held with representatives of the vendors, and with NRC Staff in Washington, OC, on. ~cember 11-12, 1975, and on January 7, 1976. 'Ihe Committee had the benefit of the documents listed.

'Ihe Committee commented on the NRC Staff's proposal to revise the criteria for "Class A" pla..1ts, as categorized in WASH-1270 "Anticipated Transients Without Scram for Water Cooled Fower Reactors," in a letter to ff.tr. Lee v.

Go.ssick dated <£tober 17, 1975. 'Ihe Committee had previously cormnented on the regulatory position eventually published in v?ASH-1270, in letters to Mr. L. ~.arming Muntzing dated April 16, 1973, and May 10, 1972.

'Ihe ACRS endorses the general approach and safety objectives adopted by the NRC Staff i.~cluding the use of a goal of 10-7 per reactor year as the rr.~xi-mum probability, from all causes, of A'IWS with unacceptable consequences.

Implicit in the use of a probabilistic goal is the application of proba-bilistic methods in the analysis of the reactor systems. Although WASB-1400 provides assistance in this area, data for some systems are still suffi-ciently sparse that engineering judgJrent must be used, both in synthesizing the analytical :models and in choosing appropriate input data.

Under the 1903

Honorable William January 14, 1976 circumstances there is a need for some conservatism in the choice of models and the selection of data. Even so, there are a number of approaches to the mcdelling that may prove to have equal validity and the ACRS suggests that both the NRC Staff and the vendors give further consideration to various alternatives. For example it may be feasible to treat t.he time-varying moderator temperature coefficient probabilistically.

'Ihe Corrnnittee also recommends that vendors be encouraged to continue to make design changes that decrease the probability of transients that are likely to cause difficulty and to wake improvements that ameliorate the consequences. As appropriate these should be taken into account in the A'IWS analysis. Continuing attention should be given to improving the reliability of the reactor shutdown systems.

During the course of these meetings comrrents -were made which indicated that in some cases the NRC Staff needed further information from vendors in order to conclude its review of A'IWS.

'Ille Committee urges that appro-priate action be taken to obtain this information as soon as feasible.

'Ihe ACRS expects to complete its review of A'Il'lS after further information has been developed and the Staff has completed its evaluation. 'Ille Committee urges that the NRC Staff and the vendors expedite efforts in this regard.

1904 Sincerely yours, Dade w. Moeller Olairman

Honorable William January 14, 1976

REFERENCES:

1. letter dated January 5, 1976, from Tobias w. T. Burnett, to T. G. lt:Creless concerning request for oral presentation to ACRS i'brking Group on A'IWS on January 7, 1976 and to ACRS on January 8, 1976.

2. Draft Copy of Presentation to the ACRS entitled, "'Ihe A'IWI' Issues: 'lhe Industry Consensus As To '!heir Resolution," by T. w. T. Burnett, Chaianan, ANS-51 A'IWI' ~rking Group.

3.

NRC Staff's Status Report on Anticipated Transients Without Scram for Babcock and Wilcox Reactors, dated December 9, 1975.

4.

NRC Staff's Status Report on Anticipated Transients Without Scram for Combustion Engineering, dated December 9, 1975.

5.

NRC Staff's Status Report on Anticipated Transients Without Scram for General Electric, data December 9, 1975.

6. NRC Staff's Status Report on Anticipated Transients Without Scram for Westinghouse, dated December 9, 1975..

7. Proposed American National Standard Evaluation of Anticipated Transients Without Trip on Pressurized Water Reactor Plants, N661, March 1975.

8. U.S. Atomic Energy Commission Regulatory Staff's Technical Report on Anticipated Transients Without Scram For Water-Cooled Po,;,,,er Reactors, WASH-1270, dated September, 1973.

1905