ML20084L780

AO 50-237/1974-28:during Routine Instrument Surveillance, Reactor Pressure 600 Psi Bypass Switch Observed to Operate at 604 Psi.Caused by Instrument Drift Due to Lack of Factory Precycling.Switch Reset & Will Be Recycled

ML20084L780
Person / Time
Site:	Dresden
Issue date:	07/26/1974
From:	Stephenson B COMMONWEALTH EDISON CO.
To:	Oleary J US ATOMIC ENERGY COMMISSION (AEC)
References
541-74, NUDOCS 8305230718
Download: ML20084L780 (2)

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j /w On2 First Int.onst Pfara. Chicago tilinois Address Heply to: Post Office Box 767 Chicago, litmeis 60690 BBS Ltr.f541-74 Dresden Nuclear Power Station R. R. #1 _ . _ .

Morris, Illinois 60450'

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July 26, 1974 /

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50-237 [' i i t

g q p g\h g Mr. J. F. O' Leary, Director - h, Kh "

Directorate of Licencing V.

U. S. Atoctic Energy Co::xnission Washington, D. C.

• 20545 jbc SUMECT: REPORT OF AENCRIML OCCURRENCE PER SECTION 6.6.B.1.a OF THE

_ TECHNICAL SPECIFICATTONS.

REACTOR PRESSURE 600 PSI BYPASS SWITCH SETFOINT D_ RIFT.

References:

1) Regulatory Guide 1.16 Rev.1 Appendix A

2) Notification of Region III of AEC Regulatory Operations Telephone: Mr. F. Maura, 1145 hours0.0133 days <br />0.318 hours <br />0.00189 weeks <br />4.356725e-4 months <br /> on 7/22/74 Telegram: Mr. J. Keppler, 1330 hours0.0154 days <br />0.369 hours <br />0.0022 weeks <br />5.06065e-4 months <br /> on 7/22/74 Report Number: 50-237/1974-28 Daps.re nata. h ol y 7 /., 1Q74 Occurrence Dato: July.20, 1974 pacility: Dresden Nuclear Power Station, Morrie, Illinois IDEh'FIFICATION OF OCCURRENCE Reactor pressure 600 psi hypass switch PS 263-51A observed to operate at 604 psi, which is above the 600 psi limit.

CONDITIONS PRIOR TO OCCURRENCE Dresden Unit 2 was in the run mode at 721 PMe. Routine instrument surveillance was in progress.

DESCRIPTION OF OCCURRENCE During routine conthly calibration surveillance of PS-253-51A, it was observed that switch operatien occurred at 604 psi, which is above  ;

the Technical Specification limit of 600 psi.

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J:1y 26, 1974 Mr.J.F.!O'Le:r DESIGNATION OF APPARE!C CAUSE OF OCCURRENCE Instrument drift due to lack of factory pre-cycling of switch prior to installation.

. ANALYSIS OF_ OCCURRENCE The function of switches PS-263-51A and 51B is to bypass The the low vacuum scram contacts until reactor pressure has reached 600 psi.

system is designed so that either SLA or 51B will activate the low co vacuum scram function.

51B operated at 599 psi. The system therefore was operable at all times.

CORRECTIVE ACTION The immediate corrective action was to reset the switch to 580 psi.

In addition, the switch will be sent to the factory for pre-cycling as soon as practicable.

FAILURE DATA Similar setpoint violations on switch 263-51A have occurred during l Hy cf 1071 (297 p-9, ano sune of '970 (000 p:1) .

The switch is a Heletron Model 372 with a range of 28-1400 psi.

Sincerely,

~ (xilaRLs  ;

(7%I. B. Stephenson ,

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' Superintendent l

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