ML20056B723
| ML20056B723 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 12/20/1971 |
| From: | Mayer L NORTHERN STATES POWER CO. |
| To: | Morris P US ATOMIC ENERGY COMMISSION (AEC) |
| References | |
| NUDOCS 9102080434 | |
| Download: ML20056B723 (2) | |
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Regulatory File 0.7 NORTHERN STATES POWER COMPANY Minneapolis, Minnesoia
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December 20, 1971 DOCMUEB IMER l
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Dr. Peter A. Morris, Director g
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United States Atomic Energy Commission CLEE
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Dear Dr. Morr is:
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i IONTICELLO NUCLEAR GENERATING PLANT D /
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Docket No. 50263 License No. DPR-22 Failure of ECCS Pump Start Permissive Switch and Relay A condition has occurred recently at the Monticello Nuclear Generating Plant which we interpret to be reportable in accordance with Section 6.6.C.1 of the 1
Technical Specifications. The Region t il Compliance office has been notified of this event.
Summarv of Occurr ence On Novmber 20, 1971, while performing a regularly scheduled surveillance test, the trip setting of ECCS pump start permissive switch PS 2-3-53A, switch #2, was found to be 433 psig,12 psi below the required trip setting of _> 450 psig.
During this surveillance test it was also discovered that a relay in the ECCS pump start permissive logic failed to energize with the pump start permissive switch PS 2-3-53A, switch #1, closed.
An investigation of this occurrence revealed that the two switches contained in PS 2-3-53A were not designed for the 125V DC application for which they were i
being used. This investigation also revealed that the air gap on the failed l
relay was too large requiring a high pull-in voltage to energize the relay.
New switches designed for 125V DC use will be purchased and installed for all instruments of this type. The pump permissive switches have been calibrated to trip at 460 psig, to allow for setpoint drift. The relay air gap was reduced and the pull-in voltage was adjusted to less than 80% of rated voltage. The relay was tested and found to operate satisfactorily.
Surveillance testing of this instrument will be performed more frequently until the drift problems have been corrected. The correct relay pick up voltage setting will be verified with the manufacturer and the settings adjusted as necessary on this and all similar relays.
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9102080434 711120 M
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. A Significant Operating Event reperi has been written for this occurrence and will be available to the Region Ill Compliance Inspector for review during his next visit.
Yours very truly, t
0 L. O. f/ayer Director of Nuclear Support Services LOM/GHJ/mm