ML20027A318

LER#78-056/01T-0 on 781012:diff Press Switch Isolation Valve for DPIS 2-1622A Was Found Closed Because of Unknown Cause. Subj Valve Will Be Opened Slowly After Dis 1600 Survey

ML20027A318
Person / Time
Site:	Dresden
Issue date:	11/01/1978
From:	Lindberg C COMMONWEALTH EDISON CO.
To:
Shared Package
ML17173A356	List: ML17173A355 ML20027A318
References
LER-78-056-01T, LER-78-56-1T, NUDOCS 7811140199
Download: ML20027A318 (2)

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6 60 Cd REPORT DATE EVENT CESCalPTION AND PROBABLE CONSECUENCES h o I:I l While performing quarterly Surv. DIS 1600-3, Diff. Press. Sw. Isol. Valve for DPIS l o ;3; j 2-1622A was found closed. DPIS 2-1622 A monitors press. between Torus and Rx. Bld. anj O l4 l l is calibrated to trip open at -12.5 +/- 1 in. H2O increasing. Isolation valvemay havel Ols11 been left closed during previous surv. on 7/13/78. Safety significance minimal while l 016 l l remaining vacuum sv. 2-1622B was operable to actuate redundant vacuum breaker. On l T '. l 10/1/78, redundant vacuum breaker was inoperable for approx. 8 hrs. to replace -

e i s 1 i fuse F-16 on panel 902-3. No previous similar events. I d a 80 SYSTEM CAUSE CAUS E CovP. VALVE CODE CODE SUSCODE COMPONENT CODE SL8 CODE SUSCODE

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,;O, l Cause unknown. Surv. DIS 1600-3 requires isolation valve to be opened slowly upon l j [ completion of surv. DIS 1600-3 has been revised to require Inst. Mech. to sign I

,7, j data sheet upon valving isol. valve back into service. For 90 days, IM supervisors l

,;3i l will visually examine "AS LEFT" position of all critical non-indicating safety l

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. * .'i ATTACHMENT TO LICENSEE EVENT REPORT 78-056/01T-0 COMMONWEALTH EDISON COMPANY (CWE) -

DRESDEN UNIT -2 (TT.DRR-2)

DOCKET # 050-237 While performing quarterly surveillance DIS 1600-3, the differential pressure switch isolation valve for DPIS 2-1622A was found closed. The Differential Pressure Switch is designed to monitor the AP between the Torus i

and Reactor Building and is calibrated to trip open at -12.5 +/- 1 inch H2 O vacuum increasing. Technical Specification 3.7.3.a limits the maximum

( negative A P referenced to Torus at -13.7 inches H2 0 At -12.5 +/- 1" H2O increasing vacuum, either A0 2-1601-20A is opened by switch DPIS 2-1622A or A0 2-1601-20B opens in response to DPIS 2-1622B (both vacuum breaker valves arranged in parallel). This relieves the torus negative pressure from the reactor building.

All trip setpoints in the surveillance were found within the Dresden Tech Spec Limits. However, prior to the surveillance the isolation valve upstream of Differential Pressure Switch 2-1622-A, was found closed which caused the switch to be inoperable. It is assumed that the isolation valve was lef t closed af ter completion of the previous quarterly surveillance on 7/13/78. The safety consequence was minimal while the remaining Pressure Suppression to Rx Building Vacuum Switch 2-1622B and vacuum breaker A02-1601-20B were operable. On 10/1/78, the A0-2-1601-20B valve was also rendered inoperable for approximately 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />, however, to replace Fuse F-16 on panel 902-3.

During that period, vacuum protection was not available for the torus.

DIS 1600-3 had already correctly contained a step requiring the insu.. ment isolation valve to be opened slowly upon completion of the surveillance. However, to provide better assurance that the step is completed, DIS 1600-3 has been additionally modified to require the Instrument Maintenance Mechanic assigned to the surveillance to sign the data sheet upon valving the switches back into service.

l In addition for the next 90 days an Instrument Maintenance Supervisor will visually examine the "As Left" position of all critical-non-indicating Safety-Related valves which are repositioned during instrument surveillances and similarly co-sign each associated surveillance upon its completion. The 'ressure Suppression to Rx Building Vacuum Switches will continue to be tested quarterly to ascertain compliance with the Technical Specification s.

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