PNO-IV-89-033, on 890512,unusual Event Declared When Two of Four Pressurizer Water Level Indication Channels Inoperable. Reactor Shutdown.Possibly Caused by Valve Disc Stuck on Valve Seat.Insulation Installed on Piping

PNO-IV-89-033:on 890512,unusual Event Declared When Two of Four Pressurizer Water Level Indication Channels Inoperable. Reactor Shutdown.Possibly Caused by Valve Disc Stuck on Valve Seat.Insulation Installed on Piping

ML20246N732
Person / Time
Site:	South Texas
Issue date:	05/15/1989
From:	Holler E NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
To:
References
PNO-IV-89-033, PNO-IV-89-33, NUDOCS 8905190521
Download: ML20246N732 (2)

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u May 15, 1989

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PRELIMINARY NOTIFICATION OF EVENT OR UNUSUAL OCCURRENCE -- PN0-IV-89-33 i

This preliminary notification constitutes EARLY notice of events of POSSIBLE l safety or public interest significance. The information is as initially received 5 without verification or evaluation, and is basically all that is known by the Region IV staff on this date.

FACILITY: Houston Lighting & Power Company Licensee Emergency Classification:

South Texas Project, Unit 2 X Notification of Unusual Event .

Docket No. 50-499 ~

Alert Site Area Emergency General Emergency Not Applicable

SUBJECT:

REACTOR SHUTDOWN BECAUSE OF INOPERABLE PRESSURIZER LEVEL INDICATION On Friday, May 12, 1989, at 2:25 p.m. (CDT) with the reactor at 30 percent power, Houston Lighting & Power Company (HL&P) declared an unusual event at South Texas project, Unit 2 (STP-2), because of inoperable pressurizer level indication channels. HL&P declared two of the four pressurizer water level indication channels inoperable and began a reactor shutdown as required by Technical Specifications (TS). At 8:10 p.m. (CDT) on May 12, 1989, with STP-2 in Mode 3 (hot shutdown), HL&P terminated the notification of unusual event.

STP-2 was at 30 percent reactor power conducting power coefficient determination testing with three of four pressurizer level indication channels operable, as allowed by TS. The fourth channel was inoperable because of maintenance. After completion of the power coefficient testing, one of the operable channels began oscillating and was declared inoperable.

Initial investigation by HL&P indicated that an isolation valve associated with the steam line to the condensing pot of the oscillating level indication channel may have the valve disc stuck on the valve seat. Investigation of the root cause continues. HL&P does not intend to shut down and cool down STP-2 to effect repairs to the isolation valve at this point in the startup test program.

As part of its investigation of the oscillating level indication, HL&P determined through temperature profiles that a difference in the temperature of the level indication piping between the pressurizer and the level indication condensing pot existed among the four level piping systems. With the advice of Westinghouse, HL&P made a temporary modification to install insulation on this section of piping for the four level indication piping systems. The modification is an enhancement and was not part of the original design. Installation of the insulation did not correct the oscillating level indication.

HL&P returned to service the level indication channel that had been out of service for maintenance. On Sunday, May 14, 1989, at approximately 8 p.m. (CDT) with three of four pressurizer level indication channels operable, HL&P restarted STP-2. STP-2 is currently at 16 percent reactor power. HL&P intends to continue to investigate the cause of the oscillating level indication channel and to perform special testing of the pressurizer level indication channels at 30 percent reactor power before continuing with the STP-2 startup program.

The licensee has issued a press release.

The state of Texas has been informed. '

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Region IV received' notification of this occurrence by telephone from the resident inspector at 3:30 p.m.'(CDT) on May,12, 1989. Region IV has. informed

NRR.

This information has'been confirmed with a licensee representative.

. CONTACT: E. J. Holler, 728-8287

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