ML20084N841

AO 50-249/75-37:on 750826,pressure Switches PS3-263-53A,53B & 53C Had Setpoints Above Tech Spec Limit.Apparently Caused by Setpoint Drift Due to Long Periods at Zero Pressure. Setpoints Reset

ML20084N841
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
ML20084N845	List: ML20084N841 ML20084N853 ML20084N859 ML20084N861
References
578-75, NUDOCS 8306090092
Download: ML20084N841 (2)

Text

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,' Commo :lth Edison p/

4 w } Ont Fast I al Plaza. Chicago, Illinois 7- *

((,e) Addecss to: Post Othee Box 767 Chicago,RIlknois 60690 BBS Ltr. #578-75 Dresden Nuclear Power Station R. R. #1 Morris, Illinois 60450, M1 September 4, 1975 YA b g ,/],

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Mr. James G. Keppler, Regional Director -

Directorate of Regulatory Operation-Region III # .Q!

U. S. Nuclear Regulatory Cc=nission 4~.,D $ /

799 Roosevelt Road Th/

ke Glen Ellyn, Illinois 60137 SUBJiX:T: REPORT OF AE:OR"AL OCURRENCE PER SE TION 6.6. A OF THE TECH'IICAL SPECIFICATIONS REACTOR HIG3 FRESSL*RE I':ST2CG.T S..7. POI';T DRIPP

References:

1) Regulatory Guide 1.16 Rev. 1 Appendix A

2) Notification of Region III of U. S. Nuclear Regulatory Co::rnission Telephone: R. Knop, 1710 hours0.0198 days <br />0.475 hours <br />0.00283 weeks <br />6.50655e-4 months <br /> on August 26, 1975 Telegram J. Koppler, 1347 hours0.0156 days <br />0.374 hours <br />0.00223 weeks <br />5.125335e-4 months <br /> on August 27, 1975

3) Drawing Ku=ber 12E2506  ;

Report Nu=ber: 50-249/75-37 .

Report Date: Septe=ber 4, 1975 Occurrence Dates August 26, 1975 Facility: Dresden Nuclear Power Station, Morris, Illinois IDDTTIFICATION OF OCCURRENCE On August 26, 1975, during routine instrument surveillance, pressure switches -

PS3-263-53A, -533, and -53C vere found with setpoints above the Technical y Specification limit (c1070 psig). '

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CONDITIONS PRIOR TO OCCURREICE  !

l l i Unit-3 was in the shutdo m mode during a refueling outage. 4 l

l l l DESCRIPTION OF OCCURRDiCE Pressure switches 263-53A, -53B, and -53C were discovered with setpoints of 1080  ;

psi, 1077 pai, and 1112 psi respectively. Pressure switches 263-53A-D initiate ,

i operation of the isolation condenser in response to sustained high reactor vessel  ;

pressure.  ;

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, Mr.JameJG.K;pplcrk) kJ Septet,9 r 4, 1975

' DESIGNATION OF APPARENT CAUSE OP OCCURRDICE (Unusual Service Conditions)

The recent trend of similar instrument setpoint drifting sugger.ts that extended periods at zero pressure allow minor setpoint deviatious(which are routinely corrected during plant operation) to significantly accu =ulate. The length of the current refueling outage undoubtedly contributed to excescive setpoint variations on many types of pressure-sensitive instrumentation. The cause of discrete, incremental setpoint drifts is unknown.

ANALYSIS OF OCCUPRE!CE The last surveillance of these switches had been perfomed on April 7,1975, nine days before the beginning of the refueling outage. All four switches (263-53A-D) had been found within limits. The switches have proven to be reliable when checked routinely, and it in considered improbable that any. significant setpoint drift occurred during reactor operation.

Had setpoint drifting of this magnitude occurred during reactor operation, the two-channel logic of this system would have ensured system availability at a reactor pressure no greater than 1080 psi. This occurrence did not jeopardize the safety of plant personnel or the public.

CORRECTIVE ACTION The switches' setpoints were 12:rediately reset to within the Dresden " band" of 1o5515 psi. Further corrective action will be taken when specific drift causea are identified.

FAILURE DATA Pressure switches 263-53A-D are Meletron Model 372 Bourdon tube pressure sensors with a range of 28-140C psi. Meletron Model 372 pressure sensors have had a history of setpoint drifting at Dresden. The station is currently evaluating suitable replacement instru=entation.

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