ML20010A206

LER 81-013/03L-0:on 810715,pressure Switch 2-203-3B Tripped at 1.142 Psig During Testing.Caused by Instrument Drift. Switch Recalibr

ML20010A206
Person / Time
Site:	Quad Cities
Issue date:	07/23/1981
From:	Schnack J COMMONWEALTH EDISON CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML20010A203	List: ML20010A202 ML20010A206
References
LER-81-013-03L-03, LER-81-13-3L-3, NUDOCS 8108110175
Download: ML20010A206 (2)

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LICENSEE EVENT REPORT CQNTROL BLOCK: l 1

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EVENT DESCRIPT!ON AND PROBABLE CONSEQUENCES h O 2 l While performing Reactor High Pressure Automatic Blowdown Calibration and l Functional Test, QlS-40, presst.re swi tch 2-203-3B tripped at 1142 psig. This is 3 g

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,,,,)g psig greater than the Technical Specification 4.6.E limit. The consequences are g minimal because the other relief v-Ive pressure switch calibrations were found to be j j ITIS 1 I acceptable. l f l 0 [s ] l l

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CAUSE DESCRIPTION AND CORRECTIVE ACTIONS h i O I The cause of this event was instrument drift. The switch was immediately recalibratedl i i l No other corrective action is necessary as the history of these switches has shown' l

, , l no adverse trends. J l

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l. LER NUMBER: LER/R0 81-13/03L-0

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

On July 15, 1981, Unit Two was operating at a power of 1950 MWt and at a load of 600 MWe. While performing the Reactor High Pressure Automatic Blowdown Calibration and Functional Test, QlS-40, pressure switch 2-203-3B was found to trip at 1142 psig. This is in excess of the limiting condi tion for operation of 1139 psig per Technical Specification 4.6.E.

(These values include 9 psig head correction.) The last failure of this type occurred on April 18, 1978, and is documented by R0 78-21/03L.

VI. PROBABLE CONSEQUENCES OF THE OCCURRENCE:

Pressure switch 2-203-3B actuates the electromagnetic relief valve 2-203-38. These relief valves are designed to prevent over pressurization of the Reactor vessel in the event of Main Steam Line Stop Valve closure.

The safety implications of this event were minimal because the pressure switches which activate the other four (4) relief valves were found to be calibrated within Technical Specification limits; furthermore, relief valve 3B would have opened at a pressure just 3 psig above the Technical Specification limit.

Vll. CAUSE:

The cause of this event was instrument drift. These switches are of the Bourdon Tube type and are manufactured by Dresser, Model number 1539Vv.

l Vill. CORRECTIVE ACTION:

The immediate corrective action was to recalibrate the switch to a trip setpoint of 1129 psig. These switches are set conservatively at approximately 10 psig below Technical Specification limits. These

- itches are showing no adverse trends, therefore no further corrective l action 's necessary.

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