05000336/LER-1979-008-03, /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

/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: 05000336/LER-1979-008, Forwards LER 79-008/03L-0 05000336/LER-1979-008-03, /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
References
LER-79-008-03L-01, LER-79-8-3L-1, NUDOCS 7904200224
Download: ML19259B882 (2)

LER-1979-008, /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

Event date:
Report date:
3361979008R03 - NRC Website

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5 to St DOCK ET NUMSER 68 69 EVENT DAT0 74 75 MEPoRTDATE 80 EVENT oESCRI, Tion ANo PRoBA8LE CONSEQUENCES b10 i Steam generator (SG) eddy current testing in progress, plant in Mode 5, SG primary o

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Prior to restoring full SDC flow, 1 RCS temperature reached 208 degrees F, resulting in entry to Mode 4.

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.4 47 CAUSE oESCRI, Tion AND CORRECTIVE ACTIONS 27 I Lost LPSI suction loop seal prime during initial RCS draindown.

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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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