05000254/LER-1981-005-01, /01T-0:on 810220,during Testing,Three of Four Condenser Low Vacuum Scram Switches Found Outside Setting Per Tech Spec 3.1-3.Caused by Instrument Setpoint Drift.All Switches Recalibr

/01T-0:on 810220,during Testing,Three of Four Condenser Low Vacuum Scram Switches Found Outside Setting Per Tech Spec 3.1-3.Caused by Instrument Setpoint Drift.All Switches Recalibr

ML20008E920
Person / Time
Site:	Quad Cities
Issue date:	03/02/1981
From:	Dunesia Clark COMMONWEALTH EDISON CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML20008E912	List: 05000254/LER-1981-005, Forwards LER 81-005/01T-0 05000254/LER-1981-005-01, /01T-0:on 810220,during Testing,Three of Four Condenser Low Vacuum Scram Switches Found Outside Setting Per Tech Spec 3.1-3.Caused by Instrument Setpoint Drift.All Switches Recalibr
References
LER-81-005-01T, LER-81-5-1T, NUDOCS 8103100506
Download: ML20008E920 (2)

LER-1981-005, /01T-0:on 810220,during Testing,Three of Four Condenser Low Vacuum Scram Switches Found Outside Setting Per Tech Spec 3.1-3.Caused by Instrument Setpoint Drift.All Switches Recalibr

Event date:
Report date:
2541981005R01 - NRC Website

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6 60 61 DOC A ET NUY8 E R sid b9 EV ENT DATE 74 15 RE80RT DATE 80 EVENT DESCRIPTION AND PROB ABLE CONSEQUENCES h l o l 21 l While performing QlS 19-1, Quarterly Low Condenser Vacuum Calibration and Functional l

o ;3 j l Test, three of the four switches were found to trip in excess of greater than or I

go;4; l equal to 23 inches Hg vacuum as required by Technical Specifications. The low l

1, g l condenser vacuum scram is a backup scram to the Turbine Stop Valve Closure scram of 1

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LER NUMBER: LER/R0 81-5/0lT-0 ll.

LICENSEE NAME: Commonwealth Edison Company Quad-Cities Nuclear Power Station lil. FACILITY NAME: Unit One IV.

DOCKET NUMBER: 050-254 V.

EVENT DESCRIPTION

On February 20, 1981, the condenser low vacuum scram switches were calibrated and functionally tested in accordance with procedure Qls 19-1.

Three out of the four vacuum swi tches were found to be outside the setting as required in the Limiting Conditions of Operation in Technical Specification Table 3.1-3 The Technical Specification trip level setting for the switches is greater than or equal to 23 inches Hg vacuum.

The as-found settings were as follows:

1-503A, 22.7; l-503B, 22.5; l-503C, 22.9; and 1-503D, 23.0.

Recallbration of the vacuum switches was begun immediately.

VI.

PROBABLE CONSEQUENCES OF THE OCCURRENCE:

The probable consequences of this occurrence were minimal. The condenser low vacuum scram is an anticipatory scram of the reactor to minimize pressure and neutron flux transients. The scram occurs prior to the main turbine stop valve closure on low condenser vacuum, which is used to protect the. turbine. WI S the one-out-of-two-twice logic of the reactor protection system, the i tor would have scrammed at 22.9 inches Hg vacuum. This is only C.

iches Hg greater than the Technical Specifica-tion -limitation, and 2.! 1.ches Hg prior to closure of the main turbine-stop valves. The 2.9 t.ich Hg differential should be sufficient to safely shutdown the reactor before a turbine trip occurs. Safe operation of the reactor was not affected as a result of this occurrence.

Vll. CAUSE:

The cause of this occurrence has been designated as instrument setpoint drift. The procedural setpoint range for these switches are 23.3 to 23.6 inches Hg.

The largest drif t occurred on switch 1-503B, which drif ted 0.9 Inches Hg'to a setpoint of 22 5 inches Hg vacuum.

The vacuum switches are diaphragm type switches, manufactured by Barksdale Company, Model DIT-H1855 Vill. CORRECTIVE ACTION:

The immediate corrective action was to recalibrate the vacuum switches to within_ Technical Specification and procedural limitations. The as-left setpoints of the switches are as follows:

1-503A, 23.4; l-5038, 23.45; 1-503C, 23.35; and 1-503D, 23.45 The switches were successfully functional tested following recalibration. The last setpoint drift problem with these switches occurred in 1973; thus, this corrective action is deemed adequate to prevent recurrence.