PNO-I-89-028, on 890411,shutdown Initiated from Full Power When RCS Unidentified Leak Rate Reached 1.5 Gpm.Charging Flow Control Valves Closed to Limit Amount of Boron Injected.Caused by Crack on Leakage Monitoring Valve

PNO-I-89-028:on 890411,shutdown Initiated from Full Power When RCS Unidentified Leak Rate Reached 1.5 Gpm.Charging Flow Control Valves Closed to Limit Amount of Boron Injected.Caused by Crack on Leakage Monitoring Valve

ML20244B424
Person / Time
Site:	Millstone
Issue date:	04/13/1989
From:	Durr J, Mccabe E, Raymond W NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
To:
References
PNO-I-89-028, PNO-I-89-28, NUDOCS 8904190192
Download: ML20244B424 (3)

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• DCS No: 50432890411 Date: April 13, 1989 i PRELIMINARY NOTIFICATION OF EVENT OR UNUSUAL OCCURRENCE--PNO-I-89-028

.This preliminary notification constitutes EARLY nctice 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 the Region I staff on this date.

Facility: Licensee Emergency Classification:

Northeast Nuclear Energy Co. X Notification of Unusual Event Millstone Nuclear Station Unit 3 Alert Docket No. 50-423 Site Area Emergency Waterford, CT General Emergency Not Applicable

Subject:

REACTOR COOLANT SYSTEM (RCS) UNIDENTIFIED LEAKAGE At 11:45 p.m., April 11, a shutdown from full power was begun when the RCS unidentified leak rate reached 1.5 gpm (Technic.:1 Specification limit is 1.0 gpm). Increased leakage started during Engineered Safety Features (ESF) slave relay surveillance tasting earlier in the day (4:00 p.m. to 6:00 p.m.). The RWST suction valves to the charging pumps were being opened for the test. Operators closed down on the charging flow control valve to limit the amount of 2300 ppm boron that was injected to the RCS (to limit post-surveillance dilution to return boron concentration to its normal end of cycle concentration). Charging flow was reduced rapidly, causing a decrease in heat transfer across the regenerative heat exchanger. That caused flashing downstream of the letdown orifices. A subsequent manual increase in charging flow apparently collapsed this bubble, causing a water hammer and letdown relief valve actuation. The unidentified leakage probably began at this point.

B2 tween 8:00 p.m. and 10:00 p m., increases were noted in containment radiation levels and . sump punn-out rates. The Shift Supervisor ordered the sumr sampled. Sample activity was reported at 11:30 p.m. as RCS liquid, confirming the leak indications.

An Unusual Event was declared at 11:45 p.m., April 11 and the NRC was notified via the ENS at 12:07 a.m., April'12. A power reduction was begun to reduce inside containment radiation levels in preparation for containment entry. The entry team located the leak on a cracked weld on a shut leakage monitoring valve (3CHS*V995) between the containment wall and the containment inboard isolation valve on the letdown line at 3:20 a.m. The weld connected the valve body to a 3/4 inch vent line. Spray was observed coming from the weld in a 270 degree arc. The leak is isolable by shutting the inboard containment isolation valve and the orifice isolation valves, but isolation also involves securing seal (charging) water to the reactor coolant pumps. Leak repair therefore required cold shutdown. Reactor shutdown was completed at 9:11 a.m.,

April 12 and the licensee began a cool down to effect repairs. J The State of Connecticut has been notified.

8904190192 890413 PDR ILE .-

PNO-I-89-028 PDC

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CONTACT: E. McCcbe J. Durr' W. Raymond 215-337-5231 215-337-S233 '203-442-5357 DISTRIBUTION:

OWFN 'MNBB H-St. NL Mail: .ADM:DMB Chairman Zech AE00- XGil RGS DOT:Trans only Comm.. Roberts ARM PDR Com. Carr OGC' NRC OpsC tr

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SECY NMSS NSAC----

CA . .NRR-OGC' OIA Regional Offices GPA 01 RI Resident Office PA SLITP EDO OE Licensee:

{ReactorLicensees)

Region I-Form 83-(Rev. April-1988)

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