ML20084S814

AO 50-254/75-8:on 750414,three of Four Electro Hydraulic Control Fluid Low Pressure Sensors Tripped at Values Less than Tech Specs Limit.Caused by Instrument Drift.Pressure Switches in Question Were Recalibr

ML20084S814
Person / Time
Site:	Quad Cities
Issue date:	04/21/1975
From:	Kalivianakis N COMMONWEALTH EDISON CO.
To:	Oleary J Office of Nuclear Reactor Regulation
Shared Package
ML20084S817	List: ML20084S814 ML20084S818
References
AO-50-254-75-08, AO-50-254-75-8, NJK-75-219, NUDOCS 8306170439
Download: ML20084S814 (3)

Text

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.2 06 Post 640 1ss Generating Station Box 216 i .Q Cordova, Illinois 61242 W Telephone 309/654-2241 ,

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p ;./< ' ' . ;Z April 21, 1975 -

, (l, Mr. John F. O' Leary, Director , , , ,f\),'

Directorate of Licensing Regulation '-C,t_-

U.S. Nuclear Regulatory Commission Washington, D. C. 20545

REFERENCE:

Quad-Cities Nuclear Power Station, Unit 1, Docket No. 50-254, DPR-29 Appendix A, Sections 1.0.A.2, 3.1 and 6.6.B.I.a

Dear Mr. O' Leary:

Enclosed please find Abnormal Occurrence Report No. 50-254/75-8 for Quad-Cities Nuclear Power Station. This occurrence was previously reported to Region Ill, Directorate of Regulatory Operations by telephone on April 15, 1975 and to you and Region ill, Directorate of Regulatory Operations by telecopy on April 16, 1975 This report is submitted to you in accordance with the requirements of Technical Specification 6.6.B.I.a.

Very truly yours, COMiiOINEALTH EDISON COMPANY QUAD-CITIES' NUCLEAR POWER STATION

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N. J. Kallvianakis Station Superintendent NJK/RAR/vmm Enclosure cc: Region ill, Directorate of Regulatory Operations J. S. Abel

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REPORT NUMBER: A0-50-254/75-8 REPORT DATE: April 24, 1975 OCCURRENCE DATE: April 14, 1975 FACILITY:

Quad-Cities Nuclear Power Station Cordova, Illinois 61242 IDENTIFICATION OF OCCURRENCE:

Instrument setpoint drift of EHC Fluid Low Pressure sensors.

CONDITIONS PRIOR TO OCCURRENCE:

The unit was operating at 2400 MWt and 800 MWc.

DESCRIPTION OF OCCURRENCE:

On April 14, 1975, while doing routine surveillance calibration, three of the four EHC Fluid Low Pressure sensors tripped at values less than the Technical Specifica-tion limit of > 900 psig. The fourth switch tripped within limits. The "as found" values for the four switches are as follows:

1-5600-PS-1 850 PSIG l-5600-PS-2 865 PSIG l-5600-PS-3 900 PSIG l-5600-PS-4 895 PSIG No operator actions were required to bring the situation under control.

DESIGNATION OF APPARENT CAUSE OF OCCURRENCE:

The designated cause of the occurrence is instrument drif t. One switch, 1-5600-PS-2, had drifted the previous month and at that time its piston assembly was replaced.

This climinated any possibility of the occurrence being due to some physical defect or failure.

AtlALYSIS OF GCCURRENCE:

The EHC fluid pressure sensors are part of the Reactor Protection System. Their function is to scram the reactor before the EHC fluid pres ure decreases to a value where proper operation of the stop, control and bypass valves could not be depended upon. The reactor protection. system is arranged in a one out of two twice logic. PS-1 and PS-3 are in the "A" channel and PS-2 and PS-4 are in the .

"G" channel. Since PS-3 tripped at 900 psig and PS-4 tripped at 895 psig, the unit would have scrammed when the EHC fluid pressure reaches 895 psig. This is well within the operating range of the EHC system. Therefore the safety impli-cations of this occurrence are minimal.

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CORRECTIVE ACTION:

l The pressure switches in question were recalibrated and their frequency of l calibration will be increased to once per week until their reliability can '

be demonstrated. An Action item Record has been initiated to the Station Nuclear Engineering Department to investigate the possibilities of replacing these switches, and other similar instruments, with a more reliable type of sensor or trip system.

FAILURE DATA:

Equipment identification:

Equipment Piece Number 1-5600-PS-1, 2, and 4 Manufacturer Barksdale Model C9612-2 Range 135-1500 psi Previous Failures:

Date Unit Switch Number 9-14-74 1 1-5600-PS-4 3-20-75 1 1-5600-PS-7 These are the failures occurring since the January 12, 1973, instrument set-point change for these switches. Due to the instrument drift experience, investigation of a more acceptable substitute has been requested as noted above.

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