ML20235F119

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Ro:On 720620,stack Gas Monitor Sample Pump Tripped,Low Flow Annunciator Failed to Sound & Monitoring Sys Out of Svc for 4.5 H.Cause Under Investigation.Annunciator Bad Connection Fixed & Tested
ML20235F119
Person / Time
Site: Monticello, 05000000
Issue date: 06/30/1972
From: Mayer L
NORTHERN STATES POWER CO.
To: Giambusso A
US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20235B311 List: ... further results
References
FOIA-87-111 NUDOCS 8709280422
Download: ML20235F119 (2)
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REC OSXEC REG 5 0 - 2 6 s'*7 (3 NSP 672 NORTHERN STATES POWER COMPANY Minneapolis, Minnesota 55401 June 30, 1972 4 N \

85 Mr. A. Giambasso .~ M 6 jg]?, P -2 Deputy Director for Reactor Pro-jects.

United States Atomic Energy Commission E Washington, D. C. 20545 Dea- Mr. Giambusso:

NONTICELLO NUCLEAR GENERATIN3 PLANT Doekei No. 50263 License No. DPR-22 Lapse of Off Gas Monitoring A condition occurred at the Monticello Nuclear Generating Plant which we are reporting to your office in accordance with provisions of Section 6.6.8.3 of Appendix A, Tech,ical Specifications of the provisional Operating License DPR-22. On June 20, 1972, the Stack Gas Monitoring System was out of service for a period of about 41/2 hours. Continuous operation of this system is required by Technical Specification 3.8. A.

The Region ill Compliance Office has been notified of the occurrence.

At approximately 0430 on June 20, 1972, while operating at rated power, the stack gas monitor was observed to show a gradual decrease in the stack gas release rate. The remotely operated source was actuated and the monitors responded correctly. The monitoring chambers were purged by remte operation from the control room and the monitor readings did not drop as they should have, indicating that there was no sample flow through the chambers, however, the significance of this response was not realized. Approxi mately two and one half hours later, it was discovered that the stack gas monitor sample pump had tripped. The standby pump was started and the monitoring system restored to normal operation by 0730. Daring the investigation of the event, all other plant monitoring instrumentation including the air ejector monitors, were observed and indicated no change in activity levels or release rates. (The stack gas monitors provide only ala ms functions; the air ejector monitors provide the automatic actions if high off gas activities occur.)

A review of the recorder trace showed that the sample pump had tripped about 0315 without initiating the sample system low flow alarm.

The reason for the pump trip has not been determined, but it is suspected that the problem may be associated with the automatic flow operation.

Operation in the manual flow control mode of operation has continued with-out difficulty with either pump and a search for the cause of the initial pump trip is continuing. The failure of the low flow a,nunciator was caused 8709280422 870921 h28- 1 PDR {'/(Wgg g g p

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by a bad connection within the annunciator circuit. A weekly surveillance test has~ been initiated to verify the continued operability of the annancia .

tor..

The failure of the low flow annunciator- resulted in the failure to recognize the problem ~immediately; however, considering the failure of .the annunciator, the outage time-of the monitoring system should have been less than two- ,

hours. The specifics of this event will be discussed with all operating personnel to stress the importance of proper response to similar problems, i fJ they should occur, in the future.

An Abnormal Occurrence Report will' be available at the plant for review by the Region 111 Compliance inspector.

Yours very truly, he L. O. Mayer Di rector-tbelear Support Services FLF/kik l.

l ll L_____________.____  :$

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