ML20127G457
| ML20127G457 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 05/16/1973 |
| From: | Mayer L NORTHERN STATES POWER CO. |
| To: | Oleary J US ATOMIC ENERGY COMMISSION (AEC) |
| References | |
| NUDOCS 9211160605 | |
| Download: ML20127G457 (1) | |
Text
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NORTHERN STATES POWER COMPANY
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M f N N E A P O L.i t M I N N E G OT A 95408 May 16, 1973
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k4fg/ pyy Mr. J F O'icary, Director
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h Directorate of Licensing United States Atomic Energy Commission c9 of'...
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Dear Mr. O' Leary:
MONTICELLO NUCLEAR GENERATING PIANT Docket No. 50-263 License No. DPR-22 Reactor Building to Torus Vacuum Breaker Differential Control Switch Set Point Change A condition occurred at the Monticello Nucicar Generating Plant recently which we are reporting to your office in accordance with Section 6.7.B.2.b of Appendix A, Technical Specifications, of Provisional Operating License DPR-22.
On May 2, 1973, while performing a surveillance test, the set point of one of two differential pressure switches which control the reactor building-to-torus vacuum breakers was found to exceed the Technical Specification limit of 0.5 psi.
Both switches are normally calibrated to trip at approximately 0.4 psi.
One switch was found to trip at approximately 0.6 pai, 0.1 psi above the limit stated in the Technical Specifications. The second unit was tested immediately and was found l
to trip at the desired trip setting.
Although the cause of the change in set point has not been identified, satisfac-tory repeatable operation of the switch was demonstrated in subsequent testing of the unit.
Both differential pressure switches which serve to control the reactor l
building-to-torus vacuum breakers have been placed on an accelerated surveillance test schedule.
On November 16, 1972, an unrelated failure of a similar instrument was reported to your office. The cause of that failure has since been identified by the manufac-turer as a failure in the overrange protection components of the DP unit. To pre-vent similar overrange failurco, it has been recommended by the manufacturer that DP units with kick-off springs be used in all low range ( <50" WC) applications which operate in an overrange condition during normal operation. As a result of this recommendation, both of the reactor building-to-torus vacuum breaker differ-ential pressure control switches will be replaced with units containing the over-range kick-off spring.
p Yours very truly, p
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u L 0 Mayer, P.E.
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Director of Nuclear Support Services C
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Minnesota Pollution Control Agency Attn:
Ken Dzugan 9211160605 730516 PDR ADOCK 05000263 S
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