ML20056B657
| ML20056B657 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 01/12/1971 |
| From: | Duncanson R NORTHERN STATES POWER CO. |
| To: | Morris P US ATOMIC ENERGY COMMISSION (AEC) |
| References | |
| NUDOCS 9102070681 | |
| Download: ML20056B657 (1) | |
Text
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NORTHERN STATES POWER COMPANY Minneapolis, Minnesota 55401 h
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Dr. Peter A. Morris, Director j$U l
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Division of Reactor Licensing gsu
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Dear Dr. Morris:
MONTICELLO WCLEAR GENERATl fG PLANT E-5979 Docket No. 50-263 License No. DPR-22 Unsafe Failure of Protection System Sensor An unsafe failure of a protection system sensor has occurred at the L'onticello Nuclear Generating Plant.
We interpret this occurrence to be re-ortable to your office in accordance with Section 6.6.C.1 of A endix A echnical Specifications, of the Provisional Operation License hR-22. khe Region ill Compliance office has been previously notified of the occurrence.
Summarv Descrintion of Occurrence On December 23, 1970, a failed low reactor water level scram switch was discovered while perform' q a regularly scheduled surveillance test of the reactor low water lev;l scram and isolation instruments. The level switch failed to open at the scram setpoint of 6" (downscale). The switch was replaced and the instrument successfully tested on December 23rd.
As a result of the occurrence one of the four reactor level scram input signals to the Plant Protection Sy(stem was inoperable for an unknown period of time not exceeding one month.
The last functional test of the in-strument was successfully completed on November 25, 1970). The single failure did not defeat the reactor low water scram and isolation protection since the functional test performed on the remaining three instruments verified that they were operable.
An on-site Unusual Occurrence investigation of the occurrence has been completed and a report has been written.
This information w;11 be available to the Region 111 Compliance Inspector for review during his next site inspection.
Yours very ru l y, sw $kW i
R.O. Duncan, son, Jr., P.E.
Gen. Supt. of Power Plants-Mechanical Chairman-Monticello Safety Audit Committee 253(
ROD /caf 9102070601 710112 CF ADOCK 05000263 CF
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