ML20086D049

Special Rept:On 911011,discovered That Surveillance Procedure for Four Element Seismic Monitoring Sys Performed Incorrectly & Instrumentation Declared Inoperable.Recalibr of Instruments Planned During Present Reactor Shutdown

ML20086D049
Person / Time
Site:	Millstone
Issue date:	11/18/1991
From:	Scace S NORTHEAST NUCLEAR ENERGY CO., NORTHEAST UTILITIES
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
MP-91-973, NUDOCS 9111250224
Download: ML20086D049 (2)

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• e coaw 7 P.O. Box 270 M. L ET2 No***' c co" pany HARTFORD. CONNECTICUT 06141-0270 Nomeast v'"'t ** S*'"gy' Nucter Ev Compav (203)365-5000 Docket No. 50-336 Re: 10CFR50.36 Novmter 13, 1991 m-91-473 U.S. Nuclear Regulatory Commission Document Control Desk Washington, D.C. 20555

References:

(1) Regulatory Guide 1.12, Instrumentation Fc Earthquakes.

(2) ANSI /ANS-2.2-1987, Earthquake Instrumentation Criteria for Nuclear Power Plants (3) ANSI /ANS-2.10-1978, Guidelines for Retrieval, Review, Processing, and Evaluation of Records Obtained from Seismic Instrumentation.

Subject:

Millstone Nuclear Power Station. Unit Ne. 2 Inoperable Seismic Monitoring Instrumentation Gentlemen:

This Special Report is being submitted pursuant to the requirements of plant Technical Specifications 3.3.3.3.b: SEISMIC INSTRUMENTATION, and 6.9.2: SPECIAL REPORTS. The Technical Specification requires that the Special Report outline the cause of the malfunction and the plans for restoring the instruments to OPERABLE status.

Millstone Unit 2 has a four element seismic monitorinc system whic:1 is in full compliance with ANSI Standard N18.5, Earthquake Instruminta' tion Criteria for Nuclear Power Plants, and Regelatory Guide 1.12, Instrumentation for Earthquakes. The system consists of 5 channels of Time. History Accelerographs, 4 channels of Peak Shock Accelerographs,1 Seismic Trigger and 1 Response Spectrum Recorder.

In response to questions raised concerning Millstone Unit 3 seismic equipment, a recent review of data taken during the October 11, 1990 calibration of Unit 2 Peak Shock Accelerographs revealed that the surveillance procedure had been performed incorrectly. On October 9,1991 with the plant in mode 1, at 100G power, the Peak Shock Accelerographs were declared inoperable.

Recalibration of the instruments is planned during the present reactor cold shutdown.

Upon successful completion of the calibration the instruments will be returned to operable status.

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i The remaining 3 elements of the seismic monitoring system are not affected. The 7 active / passive seismic instruments listed on Technical 5pecification Table 4.3-4 are operable and in compliance with Regulatory Guide 1.12. These instruments will provide sufficient data for evaluation of the response of the plants structures and equipment to any seismic motion. A Special Report update will be for'varded to the Staff on the issue of the inoperable Peak Shock Accelerographs upon completion of the corrective action.

The licensee contact for this Special Report is Terry Arnett, who may be contacted at (203)444-5447 l

l Very iruly yours, NORTHEAST NUCLEAR ENERGY COMP \NY

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Steph n E. Scace Director hiilMone Station i SESTA:ame cc: T. T. h1artin, Region 1 Administrator W. J. Raymond. Senior Resident Inspector hlillstone Unit Nos.1. 2 an13 G. S. Vissing. NRC Project hianager, hiilluone Unit No. 2 u _-