ML20236J267

Safety Evaluation Supporting Amend 89 to License DPR-54

ML20236J267
Person / Time
Site:	Rancho Seco
Issue date:	11/03/1987
From:	Office of Nuclear Reactor Regulation
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ML20236J249	List: ML20236J246 ML20236J257 ML20236J267
References
NUDOCS 8711050236
Download: ML20236J267 (3)

Text

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E g NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 j

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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION l SUPPORTING AMENDMENT N0. 89 TO FACILITY OPERATING LICENSE NO. OPR-54 SACRAMENTO MUNICIPAL UTILITY DISTRICT RANCHO SEC0 NUCLEAR GENERATING STATION DOCKET NO. 50-312

1.0 INTRODUCTION

By letter dated June 18, 1986, as supplemented January 7,1987, Sacramento Municipal Utility District (the licensee) requested approval of a proposed ]

change to Technical Specification (TS) 4.5.2, " Reactor Building Cooling Systems." This change consists of deleting the requirement for surveil-lance of the Reactor Building Upper Dome Air Circulators (RB-UDAC). In its justification for the proposed change, the licensee referred to sub-stantial additional information obtained by the nuclear industry through research efforts conducted since the Rancho Seco plant was licensed. l These data indicate that hydrogen generated from postulated post-LOCA core !

damage would mix with the containment air much better than was originally 4 anticipated when the plant was designed. Therefore, assuming good mixing is obtained from the containment cooling fans and sprays, no pockets con-taining high concentrations of hydrogen will exist in the upper contain-ment dome area.

2.0 EVALUATION In 1974, when the Rancho Seco plant was licensed, the staff was concerned that the turbulence generated in the containment by the air coolers and sprays following a postulated design basis LOCA would not be sufficient to mix the hydrogen produced during post-LOCA conditions with the containment air. Consequently, it was assumed that hydrogen may accumulate in the upper containment dome area forming potentially explosive mixtures. To prevent this from occurring, Rancho Seco was fitted with the RB-UDAC sys-tem. Since that time, substantial experimental work in this area has been performed at a number of research establishments. Much of the work on hydrogen / air mixing was carried out in Los Alamos, Sandia, and Pacific Northwest Laboratories in this country and in several laboratories abroad.

Also, an NRC/EPRI sponsored test performed at the Neveda Test Site provid-ed some very significant additional data. The information obtained from these research efforts indicated that hydrogen can mix with air relatively easily and once mixed, forms a stable mixture. It was further determined P %mg L 3

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that the turbulence provided by the containment cooling fans, containment {

sprays and to some extent natural convection provided enough capability to {'

thoroughly mix the hydrogen with air before it reached the upper contain-ment dome location. As long as these mixing mechanisms remain operable during the hydrogen release, no measurable accumulation of hydrogen will occur in the upper containment dome and therefore, there is no need for  ;

special gas mixing devices in this location. To provide further assurance

.of this hydrogen mixing capability in the containment, the containment j 1

cooling fans and/or over a 30-day periodcontainment sprays should after the beginning be periodically) of an accident (LOCA oractuated as long as active sources of hydrogen are detected in the containment. The licensee has committed to include this requirement in Rancho Seco's emer-

] I gency operating procedures. The presently existing RB-UDAC system is not required to perform a safety function following a postulated LOCA, there-fore, its surveillance requirements can be removed without diminishing the LOCA mitigation capability.  !

Based on the above considerations, the staff concludes that the deletion '

of the requirement for surveillance of the operability of the Reactor Building Upper Dorte Air Circulators, as specified in TS 4.5.2, is accept-able since periodic operation of the containment cooling fans and/or sprays will provide adequate mixing of any hydrogen released to the con-tainment following a LOCA before it reaches the upper dome area. In addi-tion, the requirements of 10 CFR 50.44 concerning combustible gas control continue to be satisfied. i j

3.0 CONTACT WITH STATE OFFICIAL The NRC staff has advised the Chief of the Radiological Health Branch, State Department of Health Services, State of California, of the proposed determination of no significant hazards consideration. No comments were received.

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4.0 ENVIRONMENTAL CONSIDERATION

This amendment involves changes in the installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20. I The staff has determined that the amendment involves no significant in- l crease in the amounts, and no significant change in the types, of any l effluents that may be released offsite, and that there is no significant  !

increase in individual or cumulative occupational radiation exposure. The Commission has previously issued a proposed finding that this amendment involves no significant hazards consideration and there has been no public comment on such finding. Accordingly, this amendment meets the eli ity criteria for categorical exclusion set forth in 10 CFR (9). 51.22(c)gibil-Pursuant to 10 CFR 51.??(b), no environmental impact statement or environ-mental assessment need be prepared in connection with the issuance of this l amendment.

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5.0 CONCLUSION

}4f have concluded, based'on the considerations discussed above.-that (1)-

there is reasonable assurance that the healthLard-safety of the public will not endangered by operation ~ in the proposed manner, and (2) such .

! ', activities will be conducted in compliance with the Commission's regula- i E tions,and(3)Ltheissuanceoftheamendrentwillnotbeinimicaltocom-  !

mon' defense and security.or;to the. health and safety of the public, j

! F Principal Contributor:- K. Parzcewski j Dated:.. November 3, 1987-  !

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