PNO-I-87-052, on 870605,reactor Trip Occurred Due to Closure of All Four Msivs.Caused by Loss of One of Two Safeguards Electrical Buses.On 870606,MSIV a Failed Part Stroke Testing.Reactor in Cold Shutdown for MSIV Repair

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PNO-I-87-052:on 870605,reactor Trip Occurred Due to Closure of All Four Msivs.Caused by Loss of One of Two Safeguards Electrical Buses.On 870606,MSIV a Failed Part Stroke Testing.Reactor in Cold Shutdown for MSIV Repair
ML20214V125
Person / Time
Site: Millstone Dominion icon.png
Issue date: 06/08/1987
From: Mccabe E, Shedlosky J
NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
To:
References
PNO-I-87-052, PNO-I-87-52, NUDOCS 8706110459
Download: ML20214V125 (1)


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DCS No: 50623870605 Date: June 8, 1987 PRELIMINARY NOTIFICATION OF EVENT OR UNUSUAL OCCURRENCE--PNO-I-87-52 This preliminary notification 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 the Region I staff on this date.

Facility: Northeast Nuclear Energy Company Licensee Emergency Classification:

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

Subject:

REACTOR TRIP AND SHUTDOWN FOR GREATER THAN 48 HOURS A Reactor Trip occurred at 1:28 p.m., 6/5, due to the closure of all four Main Steam Isolation Valves (MSIVs). This was caused by the loss of one of the two safeguards electrical buses. During circuit breaker troubleshooting, an operator dropped a breaker elevator motor (removed for troubleshooting) which struck the wall of an adjacent cubicle of the metal clad 4160v switchgear. The mechanical shock apparently actuated the contacts of a relay located in the adjacent cubicle. This protective relay deenergized the safeguards electrical bus. The closure of the MSIVs on loss of a safeguards bus is in accordance with plant design. All systems appear to have func-tioned properly after the Reactor Trip, which was from high negative rate power range neutron flux. There was no post-trip sequence of events report from the process computer because of the loss of its power supply at the time of the trip. No equipment damage was found to have resulted from this trip. The resident inspector observed post-trip activities, including the licensee's post-trip review.

The reactor was made critical at 5:56 a.m., 6/6. At 11:16 a.m., 6/6, the "A" MSIV failed part stroke testing, and the reactor was taken to cold shutdown for MSIV repair.

Startup is expected late on June 9.

There has been media coverage; the licensee issued a press release. The State of Connecticut has been informed.

CONTACT: J. Shediosky E. McCabe 203-442-5357 215-337-5231 8-488-1231 DISTRIBUTION:

H. St. MNBB Philli:s E/W Willste Mail: ADM:DMB Chairman Zech EDO NRR IE NMSS DOT:Trans only Comm. Bernthal PA OIA RES Comm. Roberts ELD AE00 NRC Ops Crt Comm. Asselstine Comm. Carr ACRS Air Rights INPD----

SECY SP NSAC----

CA POR Regional Offices TMI Resident Section RI Resident Office  ? ~7 o Licensee:

) )l 8706110459 870608 (Reactor Licensees)

PDR I&E PNO-I-87-052 PDR I

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