ML20085C961

AO 50-254/74-32:on 741010,switch 1 in Level Instrument of Low Low Water Level ECCS Initiation Instrument LIS-1-263-72C Would Not Trip at Test Pressure.Caused by Excessive Gap Between Mercury Switch & Actuating Magnet

ML20085C961
Person / Time
Site:	Quad Cities
Issue date:	10/18/1974
From:	Kalivianakis N COMMONWEALTH EDISON CO.
To:	Oleary J US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20085C963	List: ML20085C961 ML20085C964
References
AO-50-254-74-32, NJK-74-334, NUDOCS 8307130274
Download: ML20085C961 (3)

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%., k October 18, 1974 Mr. John F. O' Leary, Director Directorate of Licensing Regulation U.S. Atomic Energy Commission Washington, D. C. 20545

REFERENCE:

Quad-Cities Nuclear Power Station Docket No. 50-254, DPR-29 Appendix A, Sections 1.0.A.2, 3.2.B, Table 3 2.2, and 6.6.B.1.a.

Dear Mr. O Leary:

Enclosed please find Abnormal Occurrence Report No. AO 50-254/

74-32 for Quad-Cities Nuclear Power Station. This occurrence was previously reported to Region III, Directorate of Regulatory Operations by telephone on October 11, 1974 and to you and Region III, Directorate of Regulatory Operations by telecopy on October 11, 1974.

This report is submitted to you in accordance with the require-ments of Technical Specification 6.6.B.l.a. -

Very truly yours, COMMONWEALTH EDISON COMPANY QUAD-CITIES NUCLEAR POWER STATION A

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N. J. Kalivianakis

- Station Superintendent NJK/RAR/lk cc: Region III, Directorate of Regulatory Operations J. S. Abel A!D 0 10SG3 s g .g 7 g,A A

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o o REPORT NUMBER: A.O. 50-254/74-32 REPORT DATE: October 18, 1974 OCCURRENCE DATE: October 10, 1974 FACILITY: Quad-Cities Nuclear Power Station Cordova, Illinois 61242 IDENTIFICATION OF OCCURRENCE:

Low-Lou drift. Water Level ECCS Initiation instrument LIS-1-263-72C CONDITIONS PRIOR TO THE OCCURRENCE:

Unit I reactor in the Run mode at approximately 200 MWe and decreasing.

DESCRIPTION OF OCCURRENCE:

At 1500 hours0.0174 days <br />0.417 hours <br />0.00248 weeks <br />5.7075e-4 months <br /> on October 10, 1974 the instrument department was doing routine cuarterly calibration surveillance of LIS-1-263-72C when it~was discovered that the number one switch in the level instrument would not trip at any test pressure.

No actions other than re-alignment of the switch were needed to bring the situation under control. This failure of the level switch was in violation of Technical Specification 3 2.B and Table 3.2.2.

DESIONATION OF APPARENT CAUSE OF OCCURRENCE:

Component Failure: .

The apparent cause of this occurrence is designated as component failure. The cause of the failure was apparently due to an ex-cessive gap between the mercury switch and the actuating magnet

-within the instrument. The position of the magnet varies with changes in the level sensed by the instrument. When the position of the magnet reaches the set point, the mercury switch is actuated.

If the gap between the magnet and the mercury switch is too large, the mercury switch will not trip. The exact cause of the excessive gap could not be determined; however, it was caused either by a shift of the mercury switch mounting bracket or by a gradual weck-ening of the strength of the field of the magnet.

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. O O AO 50-254/74-32 october 18, 1974 ANALYSIS OF OCCURRENCE:

The safety implications related to this occurrence are minimal.

All of the number one switches of the four low-low level instru-ments used for ECCS initiation are used in the Core Spray System logic. The logic scheme is a one out of two twice arrangement.

The three other switches were found to operate satisfactorily at the time of this occurrence. Thus, the low-low level portion of the core spray system logic would have functioned as needed.

As a result of this occurrence there were no adverse effects on the safe operation of the unit nor on the health and safety of the public.

CORRECTIVE ACTION:

The immediate corrective action taken to correct this occurrence was to reposition the mercury switch bracket and recalibrate the instrument according to the Instrument Surveillance Test Proce-dure. The switch calibration was checked on October 11, 1974 and found to be satisfactory. The normal monthly functional test to be performed in November will verify the adequacy of the above action.

FAILURE DATA:

There have been no previous failures of this particular instrument, so there is no failure data to report for it. However, an identical instrument for Unit 2, LIS-2-263-72D, has failed four times since January 17, 1974 and is presently undergoing increased surveillance testing as an interim measure until a new instrument can be pro-cured and installed. The instruments involved are Yarway Model 4418C level indicating switches calibrated for a range of 120 inches of. water level.

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