ML19350B514

LER 81-004/01T-0:on 810225,review Indicated That If Backup Scram Solenoids Failed,Actuation of ATWS Sys Would Prevent Closure of Scram Discharge Vol Vent & Drain Valves,Violating Primary Containment.Cause Due to Oversight in Design

ML19350B514
Person / Time
Site:	Pilgrim
Issue date:	03/10/1981
From:	Mcloughlin M BOSTON EDISON CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
Shared Package
ML19350B513	List: ML19350B512 ML19350B514
References
LER-81-004-01T, LER-81-4-1T, NUDOCS 8103200704
Download: ML19350B514 (2)

Text

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4 68 63 EVENT DATE 74 75 7 O ATE 1 St EVENT CESCRIPTICN ANO PRCS ASLE CCNSEQUENCES h t o 121 I In the event that the AWS System aLtuates in Lts intended c:anner analysis indi-  !

Io 6 3i i cates that a violatioa of primary containment would exist. The flow path j i j o .4 ; l would be from the scram Discharge Volume through the vent and drain valves to i 4

1o is1 l the reactor building atmosphere. Refer to attachment for additional information. I 104511 l l047l l l 10 i s t i I F S 9 8I SYSTEV CAUSE CAUSE CCM P. VALV E COCE CCOE SUSCCCE COMPCNENT " COE JU8COOE SLSCOCE FfT1 7 3

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4i 42 43 lu ZI 91 91 9l@ 47 CAUSE CESCRIPTION AND CCRRECTIVE ACTIONS h I i t o t I The direct cause of this situation was an oversizht in the desien. Ac tua tion of the !

Ii6il l AWS ARI solenoids, which were installed as ourlied in Pncu 79-2 5. would t,revent t i,,2! l bleed-of f of the instrument air header which must be decleted to oermit the vent andl 4

, i3; Idrain valves to close. On March 3,1981 a oicine modification was implemented to end I i

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BOSTON EDISON CodPANY ,

PILGRIM NUCLEAR POWER STATION '

DOCKEI NO. 50-293 Attach =ent to Ln 81-004/01T-0_

Descrip tion On February 25, 1981, the ORC reviawed thc operation of the ATWS system i which was installed on May 12, 1980 during.PNPS Refuel IV Outage. The i

review indicated that, in the event that the Backup Scram Solenoids failed

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and the ATWS System initiated to scram the reactor, closure of the Scram

. Discharge' Volume (SDV) vent and' drain valves would be inhibited because the vent path ~ for their' air solenoids would be blocked. This blockage occurs because actuation of the ATWS/ARE Solenoid Valves isolates the SDV air colenoids air supply header from the vent. Inability of SDV vent and drain valves 'to close' following a scram would result in a breach of primary con-tainment in that a scram discharge water flow path would exist through the SDV Isolation Valves to the reactor building. f Cause and Corrective Action ' ,

' The root cause of ~ this problem was inappr'opriate review of the design modi-fication.'. On March 3,1981 a SDV. air s apply line design chenge was imple-mented via. Field Revision Notice Number 79-25-44. TSis -modification revised

,tne original ~ desian to correct its deitaiencies. The modification consisted -

/ - - of relocating the half-inch copper air supply line for the SDV Isolation Valves. from the upstream to the downstream side of the ATWS/ARI Solenoid  !

' JValves so' that isolation of the SDV occurs on actuation of either RP5 or l ATWS/ARI. 9 l

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~PNPS _is 'in the process of revising our methods of reviewing and approving

'modificatio'ns with more emphasis being placed on ' the conceptual phase and l increased operational input from the station' which .should minimize the possi- (-

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-ibility of a recurrence'cf similar' events.

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