05000338/LER-1981-002-03, /03L-0:on 801231,pressurizer Power Operated Relief Valve Declared Inoperable Because of Low Nitrogen Gas Supply Tank Pressure in 1-GN-TK-1A.Caused by Excessive Usage of Nitrogen to Cycle Relief Valves to Reduce RCS Pressure

/03L-0:on 801231,pressurizer Power Operated Relief Valve Declared Inoperable Because of Low Nitrogen Gas Supply Tank Pressure in 1-GN-TK-1A.Caused by Excessive Usage of Nitrogen to Cycle Relief Valves to Reduce RCS Pressure

ML19341A251
Person / Time
Site:	North Anna
Issue date:	01/15/1981
From:	Cartwright W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML19341A250	List: 05000338/LER-1981-002, Forwards LER 81-002/03L-0 05000338/LER-1981-002-03, /03L-0:on 801231,pressurizer Power Operated Relief Valve Declared Inoperable Because of Low Nitrogen Gas Supply Tank Pressure in 1-GN-TK-1A.Caused by Excessive Usage of Nitrogen to Cycle Relief Valves to Reduce RCS Pressure
References
LER-81-002-03L, LER-81-2-3L, NUDOCS 8101220456
Download: ML19341A251 (2)

LER-1981-002, /03L-0:on 801231,pressurizer Power Operated Relief Valve Declared Inoperable Because of Low Nitrogen Gas Supply Tank Pressure in 1-GN-TK-1A.Caused by Excessive Usage of Nitrogen to Cycle Relief Valves to Reduce RCS Pressure

Event date:
Report date:
3381981002R03 - NRC Website

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U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT CONTROL BLOCK / / / / / / / (1)

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/1/2/3/1/8/0/ (8) /WVVVWV W OUR DOCKET NUMBER EVENT DATE REPORT DATE EVENT DESCRIPTION AND PROBABLE CONSEQUENCES (10)

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During Mode 5 operation, a pressurizer power operated relief valve was

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declared inoperable because of low nitrogen gas supply tank pressure in

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1-GN-TK-1A.

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was established in accordance with T.S. 3.4.9.3.

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The PORV was declared inoperable due to low nitrogen pressure caused by

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frequent cycling of the valve to reduce the RCS pressure to atmospheric when

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the unit was being prepared for refueling. A vent path of greater than 2.07

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square inches was established as per T.S. 3.4.9.3.

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NAME OF PREPARER W. R. CARTWRIGHT PHONE (703) 894-5151 810122Oy g

Virginia Electric and Power Company North Anna Power Station, Unit #1

Attachment:

Page 1 of 1 Docket No. 50-338 Report No. LER 81-002/03L-0

Description of Event

On December 31, 1980, during Mode 5 operation, the pressurizer power operated relief valves (PORV's) were required to be operable for overpressure protection in accordance with T.S. 3.4.9.3.

In this condition, nitrogen is used as the cycling medium for the PORV's. The nitrogen supply pressure dropped to below the pressure necessary to maintain the PORV's in an operable status.

Probable Consequences of Occurrence Overpressure protection for cold shutdown condition is required to prevent pressurization in the non-ductile range of the materials used in the reactor coolant system. Since a greater than 2.07 square inch vent path was established there was no affect on the health and safety of the public.

Cause of Event

The cause of the PORV becoming inoperable was the nitrogen supply tank pressure dropping below the pressure necessary to provide this protection function. The low nitrogen supply in this system was created by excessive usage of nitrogen to cycle the PORV's to reduce the RCS pressure to atmospheric during the shutdown of the unit.

Immediate Corrective Action

A greater than 2.07 square inch vent path was established by blocking open PCV-1455C and MOV-1456.

Scheduled Corrective Action The nitrogen supply system has been investigated and corrective actions initiated.

Actions Taken to Prevent Recurrence No further actions are required.

l Generic Implications Inadequate nitrogen supply has been a recurring problem with North Anna Units 1 and 2.

Design modifications have been undertaken to correct this deficiency.

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