ML19309A929

Discusses Limited Boron Dilution Incident Caused by Inadvertent Sodium Hydroxide Injection Into RCS During Cold Shutdown.Requests Facility Analyze Boron Dilution Accident Potential & Consequences & Submit Results within 90 Days

ML19309A929
Person / Time
Site:	Rancho Seco
Issue date:	09/14/1977
From:	Reid R Office of Nuclear Reactor Regulation
To:	Mattimoe J SACRAMENTO MUNICIPAL UTILITY DISTRICT
References
NUDOCS 8004010683
Download: ML19309A929 (3)

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DISTRIBUTION: y September 14,1977 Docket File V NRC PDR L PDR Dochet No.:

50-312 ORB #4 Rdg RReid RIngram L01shan TCarter Sacranento ilunicipal Util.ty District CNelson ATTU: Mr. J. J. Hattinoc Attorney, OELD Assistant General Manager M I&E (3)

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and Chief Enoineer DEisenhut 6201 S Street TBAbernathy P. O. dox 15a30 JRBuchanan Sacranento, California 95013 ACRS (16)

Gray File 6enti ce.cn:

RE: RZCHO SECO fiUCLEAR GELERATING STATIDH P.ccently at an operating PP, facility, a limited baron dilution incicent occurred oue to the inadvertent injection of a portion of the conter.ts of the t;a0n tant into the reactor coolant systen while the reactor was in the cold shutdcun condition. While perfoming surveillance testing (valve cycling) of the NaOH tank isolation valve, with the Decay lieat Removal (GhR) systen lined up for reactor coolant recirculation, a portion of the tank's contents drained into the DMR system.

Lipon resunption of coolant recirculation this fla0ti uns injected into the reactor coolant systen.

In the above-nentioned case, only a i:

ced amount of haCS (approxiuately G30 gallons) was injected and the reactor retsained subcritical by a large margin. However this event highlighted the fact that a postulated single n

failure at this facility (i.e., aisposition of the isolation valve for the haOH tank wnen the DHP. system is lined up for recirculation or operating in the recirculation code) could result in a ooderator dilution incident which had not been previcusly considered.

Subsequent analysis by the licen::ce and his vendor revealed that, for certain conservative assumptions (e.c., reactor in the cold shutdown condition, vessel temerature less than 6

100 i, beginning of core life characteristics, vessel drained to a level coprcat.mately equal to the height of the outlet no::zic,1 west inital coron concentration allowed ny Technical Specifications, the naximum worth control rod stuck in tha fully out position, ad no credit assuned for operator action), the injection of the haOH tank contents into the reactor coolant systen due to the nisposition of a single isolation valve could result in reactor criticality with the control reds inscrted.

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Sacramento Municipal Utility

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Di strict t Based upon our review of this particular incident, we concluded that the assumption that operator action would not be taken in suf-

,:.g ficient time to teminate the event prior to reactor criticality would be overly conservative. This detemination was influenced by the length of the dilution tine necessary before return to criticality and by the number of indications and alams available to the operator at this facility.

Due to plant-specific system design and instru:aen-

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tation of fferences, we are not able at this time to reach a similar con-clusion for all PWR's. Furthemore nost PWR boron dilution analyses have been limited to addressing a malfunction in the makeup and purification systen (chemical and volume control system). The incident discussea above is an exanple of a boron dilution accident not covered by these analyses. Therefore we are requesting that each licensee of a PWR

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facility provide an analysis of the potential for and consequences of r

bc-on dilution accidents at his f acility.

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You are requested to perfem and subnit the results of such an analysis witnin 90 days of receipt of this letter.

Your analysis should be based upon conservative assunptions consistent with the cesign of your facility and your Technical Specifications and shculd include the assumption of the is nost limiting single failure. The analysis should also, include an assess-ncnt of the factors which affect the capability of the operator to take corrective action veich would teminate the postulated events prior to achieving reactor criticality.

If, based on the results of this ana;ysis, you detemine that corrective actions (design or procedural) are rcquired to preclude the occurrence or nitigate the consequences of postulated boron dilution accidents, your response should include proposals for scch actions.

Sincerely, Robert W. Reid, Chief f

Operating P.cactors Branch #4 Divisinn of Operating Reacters Cc:

3ee MSXI page C-0@{ @ v fgB#4:00R ORB #4:00p L01shan:rm CNe$ ion RReilf 9/y/77 9/lA/77 9/t(/77

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.....;.s Sacramento Municipal. Utility Di.,trict

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-J cc: David S. Kaplan, Secretary and

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General Counsel Tf...

6201 S Street Post Office Box 15830

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Sacramento, California 95813

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Business and Municipal Department s

Sacramento City-County Library 828 I Street Sacramento, California 95814

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