05000338/LER-1979-141-01, During Sys Operation Review,Sys Returning to Nonsafety Mode Following Engineered Safety Feature Reset Found to Operate Less Conservatively than Assumed in Fsar.Cause Unknown.Design Suspected

During Sys Operation Review,Sys Returning to Nonsafety Mode Following Engineered Safety Feature Reset Found to Operate Less Conservatively than Assumed in Fsar.Cause Unknown.Design Suspected

ML19331B682
Person / Time
Site:	North Anna
Issue date:	08/07/1980
From:	Cartwright W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML19331B524	List:
References
LER-79-141-01X-01, LER-79-141-1X-1, NUDOCS 8008120584
Download: ML19331B682 (3)

LER-1979-141, During Sys Operation Review,Sys Returning to Nonsafety Mode Following Engineered Safety Feature Reset Found to Operate Less Conservatively than Assumed in Fsar.Cause Unknown.Design Suspected

Event date:
Report date:
3381979141R01 - NRC Website

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UPDATE REPORT - PREVIOUS REPORT DATE 11-20-79 f)

U.S. NUCLEAR REGULATORY COMMISSION v

LICENSEE EVENT REPORT CONTROL BLOCK / / / / / / / (1)

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E DOCKET NUMBER EVENT DATE REPORT DATE EVENT DESCRIPTION AND PROBABLE CONSEQUENCES (10)

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During a review of system operation, it was discovered that design deficiencies /

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could result in ESF equipment operating less conservatively than assumed in the/

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FSAR.

Specifically:

systems returning to non-safety mode following reset of /

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ESF: and time delay start systems not going to completion following reset of

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ESF.

HV, RS, MS and SW systems are affected. The safety of the public was not/

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affected. Reportable pursuant to T.S. 6.9.1.8.i.

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SYSTEM

CAUSE

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ACTION FUTURE EFFECT SHUTDOWN ATTACHMENT NPRD-4 PRIME COMP. COMPONENT TAKEN ACTION ON PLANT METHOD HOURS SUBMITTED FORM SUB. SUPPLIER MANUFACTURER

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CAUSE DEFCRIPTION AND CORRECTIVE ACTIONS (27)

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The exact cause for the nonconservative operation of these ESF Systems is

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unknown at this time, however, a design deficiency by the architect engineer is/

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suspected. The problem was evaluated and the necessary corrective actions were/

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implemented.

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NAME OF PREPARER W. R. CARTWRIGHT PHONE (703) 894-5151

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UPDATE REPORT - PREVIOUS REPORT DATE 11-20-79 Virginia Electric and Power Company North Anna Power Station, Unit #1 Attachment: Page 1 of 2 Docket No. 50-338 Attachment to LER 79-141/01X-1

Description of Event

On November 6, 1979, during a review of system operation following a review of system performance during a recent unit trip and subsequent safety injection, it was discovered that the control room air-operated dampers which isolate the control room from outside air on an SI signal return to their non-safety mode when the SI signal is reset. This is contrary to FSAR comment 7.4 which states that two actions are required to return ESF equipment to a non-safety feature mode. Specifically, it is accomplished by resetting the appropriate actuation signal and sub-sequently operating the control switch for the device.

A review was immediately initiated to determine if any other de-ficiencies existed.

The following is a list of potential design deficiencies that were discovered.

The following systems return to their non-safety mode following reset of an ESF signal:

Control Room Habitability System (HV)

Supply Air Damper A0D-HV-160-1 Exhaust Air Damper A0D-HV-161-1 Dampers reopen after SI signal is reset.

Safeguards Area Ventilation System (HV)

Exhaust Air Dampers A0D-HV-128-1,-2,-3,-4 Filter Bank Dampers A0D-HV-107A-1,A-2,A-3,A-4,B-1,B-2,B-3,B-4 Dampers re position to bypass filters after Containment Depressur-ization Actuation (CDA) signal is reset.

Containment Ventilation System (HV)

Containment Recirculation Cooler Fan, 1-HV-F-1A,-B Control Rod Drive Cooling Fan, 1-HV-F-37A,B,C,D,E,F Fans restart after CDA signal is reset Service Water System (SW)

Supply to Air Cooling Coils, MOV-SW-110A,B & 114A,B Supply to Air Cooling Coils, TV-SW-101A,B Valves reopen to provide service water to the ccatainment air coolers af ter CDA signal is reset. This occurs only when the control switch for cooling had previously been placed in the service water position. Normal cooling of the recirculation air cooler is with chiller water.

Main Steam System (MS)

Steam supply valves to Steam Driven Auxiliary Feedwater Pump, TV-MS-111A,B Valves reclose after SI signal is reset if not " sealed in" by the tripping of the main feedwater pumps on safety injection.

s UPDATE REPORT - PREVIOUS REPORT DATE 11-20-79 Attachment: Page 2 of 2 The following systems do not go to completion if the CDA signal is reset prior to expiration of the starting time delay relay:

Recirculation Spray System (RS)

Outside Recirculation Spray Pump, 1-RS-P-2A, B Inside Recirculation Spray Pump, 1-RS-P-1A, B Service Water System (SW)

RS Heat Exchanger Radiation Monitoring Sample Pumps, 1-SW-P-5,6,7,8 Probable Consequences of Event The reset capability of ESF signals is required to permit action in the post accident period. With the present design, the protective actions of the affected systems could be prevented or cancelled once the associated actuation signal is reset which is in noncompliance with IEEE Standards. The health and safety of the general public were not endsn-gered by this event. Unit 2 systems have the same reset design and are similarly affected.

Cause of Event

The cause of these discrepancies is not known at this time. However, it appears that they may have resulted from a possible design deficiency by Stone and Webster.

Immediate Corrective Action

The problem was evaluated by Engineering Services to detenmine the i

corrective actions required. The reset circuitry for each affected ESF l

equipment, with the exception of MOV-SW-110A,B, 114A,B and TV-SW-101A,B, was then appropriately modified to be consistent with station design.

The reset design for the service water supply valves to the air cooling coils were not modified because the mode of cooling has never been ~used and is under administrative control and because the containment isolation valves, which are in series with the SW valves, remain closed following reset of the ESF signal.

Scheduled Corrective Action No scheduled corrective action is required.

Actions Taken to Prevent Recurrence No further actions are required.