PNO-I-99-016, on 990406,operators Initiated Plant Cooldown from Normal Operating Pressure & Temp in Mode 3,hot Standby. Cooldown Was Necessary to Minimize Further Degradation of Bonnet Pressure Seal for Valve 2-SI-652 & to Repair Valve

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PNO-I-99-016:on 990406,operators Initiated Plant Cooldown from Normal Operating Pressure & Temp in Mode 3,hot Standby. Cooldown Was Necessary to Minimize Further Degradation of Bonnet Pressure Seal for Valve 2-SI-652 & to Repair Valve
ML20205H899
Person / Time
Site: Millstone Dominion icon.png
Issue date: 04/07/1999
From: Linville J
NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
To:
References
PNO-I-99-016, PNO-I-99-16, NUDOCS 9904090104
Download: ML20205H899 (1)


c 1 April 7, 1999 PRELIMINARY NOTIFICATION OF EVENT OR UNUSUAL OCCURRENCE PNO-I-99-016 This preliminary notificatior: constitutes EARLY notice of events of POSSIBLE safety or public interest significance. The information is as initially received without verification or evaluation, and is basically all that is

'known by Region I staff in King of Prussia, Pennsylvania on this date.

Facility Licensee Emeraency Classification Northeast Utilities Notification of Unusual Event Millstone 2 Alert Waterford, Connecticut Site Area Emergency Dockets: 50-336 General Emergency X Not Applicable

Subject:

PLANT COOLDOWN TO REPAIR SHUTDOWN COOLING SYSTEM ISOLATION VALVE At about 4:30 a.m. on April 6, 1999, operators initiated a plant cooldown from normal operating pressure and temperature in Mode 3, Hot Standby.

The cooldown was necessary to minimize further degradation of the bonnet pressure seal for valve 2-SI-552 (the shutdown cooling system suction isolation valve) and to place the plant in a condition to repair the vaive. The valve is not isolable from the reactor coolant system (RCS),

because it is located in the 12-inch diameter. shutdown cooling suction line just downstream from its intersection with the RCS hot leg piping.

The licensee first identified leakage from this valve when the plant was in Operational Mode 4, Hot Shutdown, when the shutdown cooling system was secured. At the time of discovery, the leak rate by the pressure seal of the valve was less than 0.01 gallons-per-minute (gpm). Because'the design of the valve causes increased compression of the seal at higher pressure and because previous experience indicated that seal leakage of this type of valve stops at higher pressure, the licensee proceeded with a plant heatup to normal operating pressure and temperature. However, once the plant was at normal operating temperature and pressure, the seal leakage increased from 0.03 gpm to 0.15 gpm, which indicated that the pressure seal was degrading.

The licensee is currently evaluating options for repair of this valve.

The resident inspectors are following the licensee's resolution of this issue. The resident inspectors have been discussing this issue with NRC personnel in Region 1 and at Headquarters.

The State of Connecticut has been notified.

Contact:

J. Linville-(610)337-5129

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