ML19347C956

LER 81-004/01T-0:on 810220,four Low Condenser Vacuum Switches Tripped in Excess of Tech Specs During Test.Caused by Setpoint Drift.Switches Recalibr

ML19347C956
Person / Time
Site:	Quad Cities
Issue date:	03/02/1981
From:	Kopacz J COMMONWEALTH EDISON CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML19347C953	List: ML19347C952 ML19347C956
References
LER-81-004-01T, LER-81-4-1T, NUDOCS 8103100384
Download: ML19347C956 (2)

Text

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?S Rt*C81T 3 ATE EV ENT DESCHi* TION A*.3 PACS APLE CONS EO. E*.CES h Wy l While performing Ql5 19-1, Quarterly Low Condenser Vacuun Calibration and Functional I

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,{4; l-Inches Hg vacuum, as required by Technical Specifications. The low condenser vacuum 1 l r 1 g scram is a backup scram to the Turbine Stop Valve Closure scram of 22 inches Hg. t 1.

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CAuSE DESCAl* TION AND CCARECTIVE ACTIONS h lijog] The cause of this occurrence is instrument setpoint drift. All switches were 1 i

, g l immediately recalibrated and functionally tested satisfactorily. I I

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1. LER NUMEER: LER/R0 81-4/01T-0

11. LICENSEE NAME: Connonwealth Edison Company Quad-Cities Nuclear Power Station 111. FACILITY NAME: Unit Two IV. DOCKET NUMBER: 050-265 V. EVENT DESCRIPTION:

On February 20, 1981, Unit Two was operating at 2467 MWt, 781 MWe.

Quarterly surveillance test Ql5 19-1 (Low Condenser Vacuum Calibration and Functional Test) was performed to verify proper instrument trip set-points. All four switches were found to trip in excess of Technical Specification Table 3.1-3 requirements, greater than or equal to 23 inches Hg vacuum. A low condenser vacuum scram would have resulted at 22.8 inches Hg based upon the "as found" pressure switch setpoints.

These setpoints were as follows: 2-503A, 22.4; 2-503B, 22.8; 2-503C, 22.8; and 2-503D, 22.4. All switches were recalibrated to within

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allowable limits, and functionally testeJ.

'/ l . PROBABLE CONSEQUENCES OF THE OCCURRENCE:

The low condenser vacuum switches anticipate a condenser loss of vacuun and scram the reactor prior to the stop and bypass valve closure. The transient created from the low vacuum scran is less severe than that caused by stop valve clofare scram. In both cases, these are analyzed transients; therefore, the consequen".es are minimal.

Vll. CAUSE:

The cause of this occurrence was instrument setpoint drift. The largest drift occurred on switch 2-503D of 1.05 inches Hg. All other switches drifted less than 1 inch Hg.

Vill. CORRECTIVE ACT':.H:

The switches were recalibrated to within their proper setpoints. The as-left setpoints were 2-503A, 23.3; 2-5038, 23.4; 2-503C, 23.35; and 2-503D, 23.45 no other corrective action is deemed necessary, as tnese switches have had few drift problems in the past.

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