ML20084N728

AO 50-249/75-40:on 750827,during Routine Instrument Surveillance,Pressure Switches PS3-263-51A & 51B Had Setpoints Above Tech Spec Limit.Caused by Drifting Due to Long Periods at Zero Pressure.Switches Reset

ML20084N728
Person / Time
Site:	Dresden
Issue date:	09/04/1975
From:	Stephenson B COMMONWEALTH EDISON CO.
To:	James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML20084N732	List: ML20084N728 ML20084N741
References
579-75, NUDOCS 8306090050
Download: ML20084N728 (2)

Text

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Commo Ith Edison Oro First N msnal Plaza, Chicago, llinnois O

3 1 / Address Reply to: Post Office Box 767

,, (j Chicago, Illinois 60690 BBS Ltr. #579-75 Dresden Nuclear Power Station R. R. #1 '

Morris, Illinois 60450 September 4, 1975 .f f>'M L M' N;h Mr. James G. Keppler, Regional Director eq ,' 9.//F . ,fmO, Directorate of Regulatory Operation-Region III U. S. Nuclear Regulatory Co::Inission #M

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799 Roosevelt Road /N ';O' Glen Ellyn, Illinois 60137 'd , M

SUBJECT:

REPORT OF AE?'ORMAL OCCURRE;CE PER S!ITICN 6.6.A 0F THE TECMTICAL SPEIPICATIC:!3 REACTOR PRESSURE 600 PSI SWITCH SEPPOI!;T DRIPP

References:

1) Regulatory Guide 1.16 Rev. 1 Appendix A

2) Notification of Region III of U. S. Nuclear Regulatory Comission Telephone P. Johnson, 0920 hours0.0106 days <br />0.256 hours <br />0.00152 weeks <br />3.5006e-4 months <br /> on August 28, 1975 Telegram: J. Keppler, 1045 hours0.0121 days <br />0.29 hours <br />0.00173 weeks <br />3.976225e-4 months <br /> on August 28, 1975 -

3) Drawing Number 12E2465 Report Number: 50-249/75 40 Report Date: September 4, 1975 Occurrence Date August 27, 1975 Facility: Dresden Nuclear Power Station, Morris, Illinois IDD7TIFICATION OP OCCURRD;CE On August 27, 1975, during routine instrument surveillance, pressure switches PS3-263-51A and -51B were found with setpoints above the Technical Specification limit of 6600 pai.

CONDITIONS PRICR TO OCCURREICE Unit-3 was in the shutdown mode for a refueling outage.

8306090050 750904 PDR ADOCK 05000249 .

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.Jame]G.Kjppler September 4, 1975 DESCRIPTION OF OCCURRENCE

- Pressure switches 263-51A and -51B were found with setpoints of 605 pai and * ~

615 psi respectively. The switches perinit the Iow Condenser Vacuum and Main Stcam Line Valve Closure scram signals to be bypassed when reactor pressure is less than 600 pai.

DESIGNATION OF APPARENT CAUSE OP OCCURRENCE (Unktsual Service. Conditions)u: -

Iong periods at zero pressure apparently allow instrument setpoints to drift signif--

icantly out of calibration. The deihiitive cause of setpoint drift has not been established.

ANALYSIS OP OCCURRENCE The setpoints of switches 263-51A and -51B had last been checked on March 8,1975 Both switches were within the station limits at that ti=o, five weeks before the unit shutdown for refiloling. Because the switches have been demonstrably reliable between routine surveillances, it is considered unlikely that etny significant setpoint drift occurred during operation. In any event, the setpoint values "as found" would have provided a scram permissive at 605 pai. Consequently, the public was not endangered by this occurrence.

C_0RRECTIVE ACTION The switches were immediately reset to within the station limit of 580 5 pai.

Additional action will be taken as definitive drift causes are identified.

FAILURE DATA Pressure switches 263-51A and -51B are Meletron Model 372 pressure sensors with a range of 28-1400 psi. These switches have had a history of setpoint drifting at Dresden. Station evaluation of replacement instrumentation is continuing.

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B. B. Stephenson Superintendent BBS:WER:smp File /NRC

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