PNO-III-86-138, on 861120,both Component Cooling Water Pumps Tripped,Rendering Sys Inoperable for 12 Minutes.Caused by Pressure Surge Resulting in Lifting of Relief Valve on Excess Letdown HX Line.Line Will Be Removed & Examined

PNO-III-86-138:on 861120,both Component Cooling Water Pumps Tripped,Rendering Sys Inoperable for 12 Minutes.Caused by Pressure Surge Resulting in Lifting of Relief Valve on Excess Letdown HX Line.Line Will Be Removed & Examined

ML20214G020
Person / Time
Site:	Byron
Issue date:	11/20/1986
From:	Forney W, Warnick R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
To:
References
PNO-III-86-138, NUDOCS 8611250526
Download: ML20214G020 (2)

D/k/3 PRELIMINARY NOTIFICATION OF EVENT OR UNUSUAL OCCURRENCE--PNO-III-86-138 Date November 20, 1986 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 III staff on this date.

Facility: Commonwealth Edison Company Licensee Emergency Classification:

Byron Unit 2 Notification of an Unusual Event Byron, IL 61010 X Alert Site Area Emergency Docket No. 50-455 General Emergency b Not Applicable

Subject:

COMP 0NENT COOLING WATER SYSTEM FAILURE On November 20, 1986, during a containment isolation test involving the component cooling water system, both of the Unit 2 component cooling water pumps tripped in succession, rendering the system inoperable for a 12 minute period.

Unit 2 was in cold shutdown at the time of the event. Fueling loading has been completed, and the plant is undergoing precriticality testing.

During the test, the licensee shut down the 2A component cooling water pump, which had been in operation, and started the 28 pump. During the pump changeover, a pressure surge apparently caused a relief valve on the excess letdown heat exchanger line (part of the component cooling water system) to lift. The licensee believes that the relief valve did not reseat, allowing water to flow out of the system to the containment floor drain system.

The decreasing water level in the system (and its associated surge tank) caused the operating 2B pump to trip on low level. The 2A pump started automatically and operated until it drained the 2A portion of the surge tank and then it, too, tripped on low level.

At 10:38 a.m. (CST), 12 minutes after the event began, the licensee had shut the system's containment isolation valve, thus isolating the relief valve, refilled the surge tank, and restored pump operability.

Following preliminary evaluation of the event, the licensee declared it to be an Alert under its emergency plan at 11 a.m. (CST). The alert was simultaneously terminated, however, because the component cooling water system had been restored to operability.

DISTRIBUTION:

H. St. ED0 NRR E/W Willste Mail: ADM:DMB Chairman Zech PA IE NMSS D0T:Trans only Comm. Roberts ELD OIA RES Comm. Asselstine AE0D NRC Ops Ctr M[f Comm. Bernthal

Comm. Carr ACRS SP

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N-IIN86-138PDR Uho ber 1986 \

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PRELIMINARY NOTIFICATION OF EVENT OR UNUSUAL OCCURRENCE--PNO-III-86-138 Date November 20, 1986

_2_

The licensee plans to remove and test the two relief valves on the system to determine the cause of the apparent reseating failure. The resident inspectors are monitoring the licensee's evaluation of the event.

The State of Illinois will be informed of this event.

Region III (Chicago) was notified of this event at 11 a.m. (CST), November 20, 1986, by the Resident Inspector. This information is current as of 3 p.m. (CST), November 20, 1986.

k.Abff/ZWfec W. L. Forney

$Okk CONTACT: R. F. Warnick FTS 388-5590 FTS 388-5575