PNO-IV-88-039, on 880506,review of Eddy Current Test Data Revealed Wear on 19 Thimble Tubes.Caused by Flow Induced Vibrations.Util Expecting Recommendation for Corrective Action from Westinghouse

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PNO-IV-88-039:on 880506,review of Eddy Current Test Data Revealed Wear on 19 Thimble Tubes.Caused by Flow Induced Vibrations.Util Expecting Recommendation for Corrective Action from Westinghouse
ML20154D418
Person / Time
Site: South Texas STP Nuclear Operating Company icon.png
Issue date: 05/09/1988
From: Constable G
NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
To:
References
PNO-IV-88-039, PNO-IV-88-39, NUDOCS 8805190184
Download: ML20154D418 (2)


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5 May 9, 1988 PRELIMINARY NOTIFICATION OF EVENT OR UNUSUAL OCCURRENCE -- PNO-IV-88-39 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 IV staff on this date.

FACILITY: Houston Lighting & Power Co. Licensee Emergency Classification:

South Texas Project Unit 1 Notification of Unusual Event DN: 50-498 Alert Site Area Emergency General Emergency X Not Applicable

SUBJECT:

SOUTH TEXAS PROJECT UNIT 1 THIMBLE TUBE WEAR South Texas Project Unit I reported late Friday, May 5, 1988, that a review of eddy current test data on the 58 bottom mounted instrument thimble tubes revealed wear on 19 thimble tubes. Significant wear (greater than 25% of the wall thickness) was found on five thimble tubes. The significant wear was in the area of the flow limiters and ranged from 28% to 59%. An additional 14 thimble tubes exhibited wear as follows: 5-12%, 2-15%, 1-16%, 5-20% and 1-25%. Ten percent wear is the minimum detectable.

HL&P had made a commitment to the NRC to conduct eddy current tests on the instrument thimble tubes after 12 weeks of operation. This was based on thimble tube wear problems at the Tihange 3 reactor in Belgium. Eddy current tests were conducted on the Doel reactor (also in Belgium) after thimble tube leaks were found in March 1988. These leaks appeared after approximately ten months of operation. Significant wear was found on 33 thimble tubes in the Doel reactor. The flow limiters at STP, which were designed to limit thimble tube wear, are nearly identical to those installed in the Doel and Tihange reactors.

These thimble tubes allow neutron detectors to be inserted into the reactor core to provide a detailed map of core power. Flow induced vibrations are believed to cause thimble tube wear which could lead to leakage of reactor coolant into the containment sump.

HL&P is expecting a recomendation for corrective action from Westinghouse today.

The licensee has issued a press release.

The state of Texas will be informed.

Region IV received notification of this occurrence by telephone call from the Senior Resident Inspector at 4:30 p.m. , May 6,1988. Region IV has informed NRR and PA0.

This information has been confirmed with a licensee representative.

CONTACT: G. L. Constable (FTS 728-8151 k

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