ML20084S131

Ro:On 730524,reactor Low Pressure Switch Ps 3-263-52A-1 Setting Found to Have Drifted Above Tech Spec Limits.Caused by Shifting of Micro Switch Since Last Insp.Pressure Switch Recalibr & Support Bolts Tightened

ML20084S131
Person / Time
Site:	Dresden
Issue date:	05/31/1973
From:	Worden W COMMONWEALTH EDISON CO.
To:	Giambusso A US ATOMIC ENERGY COMMISSION (AEC)
References
415-73, NUDOCS 8306160170
Download: ML20084S131 (2)

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typ"e .' Address Reply : P at othee nox 767 N Chicago, lit.ncis 00690 50-249 WPW Ltr.#415- 73 Dresden Nuclear power Station R. R. #1 Morris, Illinois 60450 c. ._

May 31, 1973 *

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• Cl q.'3C .M Q Hr. A. Giambusso ;ly Q1 kg Deputy Director for Reactor Projects  :. a s. g.4' D s jk /s/

Directorate of Licensing

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SUBJECT:

LICENSE _ DPR-25, DRESDP.N NUCLEAR POWER STATION, UNIT #3, SECTION 6.6.H.3 OF THE TECHNICAL SPECIFICATIONS.

Dear Mr. Giambusso:

This is to report a condition relating to the operation of the

[" (' unit in which on May 24, 1973, at 1500 hours0.0174 days <br />0.417 hours <br />0.00248 weeks <br />5.7075e-4 months <br />, a reactor low pressure switch

. . setting was found to ha've drifted. ' Pressure switch PS 3-263-52A-1 was '

' , , - found tripping ,at 357 psi which is above the Technical Specification limit -

(, f of 350 psi as described in Section 3.2.2. The reactor was in the shutdown 4

mode at the tir: of the incident. This condition was related to Mr. Hugh

( Dance of Region III Compliance at 1345 hours0.0156 days <br />0.374 hours <br />0.00222 weeks <br />5.117725e-4 months <br /> on May 25, 1973.

v PROBLEM AND INVESTIGATION During monthly surveillance inspection of the reactor low pressure r '} switches, the setpoint of Meletron pressure switch PS-3-263-52A-1 was found to have drifted to 357 psi. The switch was previously checked on April 9, (lf 1973 and was found to be within Technical Specification limits at that time.

The purpose of the switch is to sense that reactor pressure has decreased to less than 350 psi during a loss of coolant accident. Upon reaching a decreasing pressure of 350 psi, a low pressure coolant injection (LPCI) and core spray permissive signal is initiated by closure of the switch

contacts. The electrical arrangement for the permissive logic for LPCI and core spray systems is a one out of two logic. It would have required two i switch failures to disabic the permissive logic.

' Had a loss of coolant accident occurred during the period when the reactor low pressure switch was tripped at 357 psi instead of 350 psi, both "A" and "B" loops of core spray and LPCI would have operated.

i_ Reference P & ID numbers M-357, 358, and 360. However, since the setpoint l of the PS3-263-52A-1 switch was 7 pounds high it would have initiated a i permissive signal for the "A" loops at 357 psi instead of at 350 psi.

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8306160170 730531

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'14r'. A. Giambusso o o hky 31, 1973 l

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The safety of the plant and public was not jeopardized since the system would have operated as required and since LPCI and core spray would have injected water into the reactor vessel earlier than required.

An investigation of the problem revealed that a micro switch,  ;

internal to the pressure switch, had shif ted positions, since its last  ;

' inspection. The micro swite.h is designed to be held securely to a support '

bracket by two bolts. In this incident, the two bolts were found to be loose which allowed the micro switch to shif t positions.

This is the first known malfunction of this type. While drift problems have been experienced in these switches, reference our letters dated September 29, 1972 and October 13, 1972, this particular failure is 1

considered to be an isolated case.

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The station is continuing to investigate the instrument drift problems experienced with Meletron and other switches, reference our letters dated April 19, 1973 and January 29, 1973 on both Units 2 and 3, in a n effort

] to determine the cause of the instrument drifts.

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• _ CORRECTIVE ACTION The immediate corrective action was to recalibrate the pressure switch and tighten the support bracket bolts for the micro switch. To prevent this type of failure in the future, the micro switch support bracket bolts will be examined during future surveillance inspections on Units 2 & 3.

Sincerely,

. YW W. P. Worden Superintendent WFW:do J '8 e

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