ML20235F193

Ro:On 721107,differential Pressure Switch That Initiates Reactor bldg-to-torus Vacuum Breakers Found Failed.Cause of Failure Not Identified.Bellows Assembly of Switch Replaced

ML20235F193
Person / Time
Site:	Monticello, 05000000
Issue date:	11/16/1972
From:	Mayer L NORTHERN STATES POWER CO.
To:	Giambusso A US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20235B311	List: IA-87-111, Submits Rept on Plant,As Discussed in ACRS 150th Meeting on 721012-14.Listed Items Can Be Resolved During Const & Facility Can Be Constructed W/Reasonable Assurance for Operation W/O Undue Risk to Public Safety IR 05000254/1972009 IR 05000358/1972003 IR 05000358/1973001 IR 05000358/1973002 IR 05000358/1973003 IR 05000358/1973005 IR 05000358/1973006 IR 05000358/1973007 IR 05000358/1974001 IR 05000358/1974002 IR 05000358/1974003 IR 05000358/1975004 ML20235B308 ML20235B364 ML20235B401 ML20235B405 ML20235B424 ML20235B456 ML20235B461 ML20235B465 ML20235B477 ML20235B488 ML20235B507 ML20235B552 ML20235B582 ML20235B585 ML20235B588 ML20235B605 ML20235B618 ML20235B623 ML20235B649 ML20235B656 ML20235B662 ML20235B670 ML20235B679 ML20235B683 ML20235B687 ML20235B702 ML20235B708 ML20235B713 ML20235B714 ML20235B718 ML20235B720 ML20235B730 ML20235B734 ML20235B748 ML20235B754 ML20235B762 ML20235B764 ... further results
References
FOIA-87-111 NUDOCS 8709280447
Download: ML20235F193 (1)

Text

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/ DT5ti DEBEn &cear-sn n- 4o NORTHERN STATES POWER C0MPANY Minneapolis, Min esota 55401 November 16, 1972

,,6 0 Mr. A. Giambusso <f Deputy Director for Reactor Proja:ts /f Directorate of Licensing United States Atomic Energy Conrn:ssion ._

(S Wa shington, D. C. 20545 .

M-Dear Mr. Giambuseo 6 .s- .

LONTICELLO NUCLEAR GENERATING PLANT '? '-

Docket No. 50-263 License No. DPR-22  ;

Failure of Reactor Building to Torus Vacuun Breaker Differential Pressure Control Switch A condition occurred at the Monticello Nuclear Generating Plant recently which we are reporting to your office in accordance with Section 6.6.C.1 of Appendix A, Teche,ical Specifications, of Provisional Operating License DPR-22.

On November 7,1972, while performing a surveillance test, one of two differential pressure switches which initiate the reactor building-to-torus vacuum breakers was found failed in the untripped condition. The failure resulted in an inoperability of one of the two 2005 vacuun relief breakers. The redundant unit was tested inrned-lately and determined to be operable.

The cause of the failure has not been identified; however, it is known that the failure occurred in the bellows assernbly of the DP switch. The bellows assernbly of the switch was replaced, the DP switch was calibrated, and the systern was functionally tested. The failed bellows assembly has been returned to the manu-facturer for further analysis of the failure. Both differential pressure switches which serve to control the reactor building to suppression chamber vacutrn breakers have been placed on an accelerated eight week surveillance test schedule.

Yours very truly, 0- ,

L. O. Mayer P. .

Director Nuc, lear Support Services LOWmmm ec: BH Grier E

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