ML19259B882

LER 79-008/03L-0 on 790314:while Steam Generator Eddy Current Testing in Progress,Loss of Structural Design Criteria Experienced.Caused by RCS Draining Down to Low Levels in Hot Leg.Procedures Changed to Ensure Suction

ML19259B882
Person / Time
Site:	Millstone
Issue date:	04/12/1979
From:	Crockett J NORTHEAST UTILITIES
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
Shared Package
ML19259B881	List: ML19259B880 ML19259B882
References
LER-79-008-03L-01, LER-79-8-3L-1, NUDOCS 7904200224
Download: ML19259B882 (2)

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EVENT oESCRI, Tion ANo PRoBA8LE CONSEQUENCES b10 o 2 i Steam generator (SG) eddy current testing in progress, plant in Mode 5, SG primary ,

a a Lside manways open, RCS on shutdown cooling (SDC) with RCS level at hot leg centr.r lineg e., i . I A loss of SDC was experienced due to LPSI suction air binding. Recovery was g 5Tsl I accomplished by floodup of the RCS from the RWST. Prior to restoring full SDC flow, ,

a s 1 RCS temperature reached 208 degrees F, resulting in entry to Mode 4. RCS temperature i

57 I was subsequently lowered to 120 degrees F.  ;

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i o I Lost LPSI suction loop seal prime during initial RCS draindown. Partial flow g E I restored on RCS floodup from RWST and full flow restored by vacuun priming suction i l seal.

p i oop Compliance with all Mode 4 LCO's was verified and containment purge i E I valv'es were shut. Procedures were changed to provide adequate priming and g g l operator responses. -

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-' D ATTACHt!ENT LER 79-08/3L-0  :

Millstone Unit 2 Docket No. 50-336

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Event Description .

Prior to commencing refueling operations, the RCS was drained down to the het leg center line, the steam generator (SG) primary manways were removed for SG tube eddy current testing and the plant was in !!ade 5. RCS cooling was via the Shutdown Cooling (SDC) System with one LPSI pump maintaining RCS temperature at 150*F. Difficulty was being experienced in achieving nomal SDC flow rates, which was p' rtially attributable to problems detemining an RCS hot leg level of sufficier.: accuracy to prevent overflow to the SG plenums. The LPSI pump experienced a loss of suction pressure and subsequent cavitation, necessitating securing the pump. Attempts at pump venting and transfer to the alternate pump were unsuccessful. RCS temperature was increasing and at approximatdy 190'F.

the LPSI suction from the RWST was opened to prime the punp suction. This action restored flow, but resulted in RCS floodup and spillover of approximately 15,000 gallons of water through the open SG manway to the containment.

Prior to this action, containment integrity had been established and no personnel were in the containment. SDC flow was stabilized and the RCS-temperature, which recched 208'F during the transient, was restored to nomai.

This occurrence, thus, resulted in entering Mode 4 inadvertently. The containment purge valves were closed, containment integrity was verified and compliance with all necessary flode 4 LCO action statements was verified.

i Cause Description The loss of SDC flow was due to a loss of prime of the SDC System suction loop seal off the RCS hot leg. This condition was aggravated during the RCS drain-down to relatively low levels in the hot leg to ensure no water in the SG plenums. Following SDC restoration by RCS floodup, the suction loop seal was vacuum primed and full LPSI pump flow restored.

The pemanent corrective action for this occurrence includes procedure changes to specify additional operator actions to ensure SDC suction priming with a variety of nethods at specified action points. In addition, the use of SDC suction vacuum priming has been incorporated in procedures and will be routinely used during subsequent RCS draindowns. Finally, action was already in progress to provide pemanently installed remote refueling level instrumentation to provide better indication of draindown levels.

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