ML17252A986

Letter Reporting a 04/09/1973 Occurrence in Which Main Steam Line Pressure Switch PSL-3-261-30A's Setting Was Found to Have Drifted -Dresden Unit 3

ML17252A986
Person / Time
Site:	Dresden
Issue date:	04/17/1973
From:	Worden W Commonwealth Edison Co
To:	Giambusso A US Atomic Energy Commission (AEC)
References
WPW Ltr. #308-73
Download: ML17252A986 (2)

Text

50-249 Commonwealth_ Edison Company ONE FIRST NATIONAL PLAZA* CHICAGO. ILLINOIS Address Reply to' POST OFFICE BOX 767 *CHICAGO, ILLINOIS 60690 Dresden Nuclear Power station R. R. #1 Morris, Illinois 60450 WPW Ltr. #308-73 April 17, 197.3 Mr. A. Giambusso Deputy Director for Reactor Projects Directorate of Licensiiig*

U. S. Atomic Ehergy Commission Washington, D.c. 20545 _

SUBJEX::T: UCENSE DPR . 25, DRESDEN NUCLEAR POWER STATION, UNIT #3, SFCTION 6.6.B.3 OF.THE TEX::HNICAL SPECIFICATIONS.

Dear Mr. Giambusso:

This is to report a condition:-relating to the operation or the Unit in which on April 9, 1973, a main steam line pressure switch setting was found to have drifted. Pressure switch PSL-3-261-.30A was found tripping at 816 PSI which

.is below the Technical Specification limit of' 850 PSI as described in Section

.3.2.a.

PROBLEM AND INVESTIGATION During a slirveillance inspection of* t_he -main steam line low pressure switches the set poi.iit for Barksdale switch 3-261-.30A was found to have drifted

• to 816 PSI~ The switch had been previously set at 871 PSI. The purpose of the pressure switch is to sense a drop in pressure due to a break in a ins.in steam line, and initiate a group I isolation. The electrical arrangement for a group I isolation initiation from a main steam line break is a one-out-of-two-twice logic. Therefore, it would have required two switch failures to prevent an isolation at 850 PSI.

../

Had a maiD steam line break occurred While the pressure setting of the PSL-3-261-JOA switch was 816 PSI all the main steam isolation valves would have closed at 850 PSI. Thus, the failure of switch .3-261-.30A did not present a hazard to.the public safety since an isolation would have occurred at 850 PSI as designed.

2602

CORRECTIVE ACTION The immediate corrective action was to reset the pressure switch setting to 872 PSI. The PSL-3-261-JOA swit~h will be replaced prior to the*

unit-startup due to its failure history {Reference our letter dated December 29, 1972).

• In addition, this switch type is presently under investigation by the manufacturer and the Station Instrument Department to determine the cause of set point drift. Fd;nciings of the investigation will dictate future corrective actions.

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Sincerely,

~~- JJ(,(~ ,. -

/) ""' W. .P. Worden

.fW '< Superintendent

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