ML20086S332

AO-S1-74-14:on 741119,magnetic Amplifiers for Low Level Alarm LS-CW-1018 & Turbine Trip LS-CW-101C Found Out of Calibr.Caused by Changes in Temp & Humidity & Aging of Components.Test Initiated to Verify Calibr

ML20086S332
Person / Time
Site:	Surry
Issue date:	01/03/1975
From:	Stallings C VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	Moseley M NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
References
360, AO-S1-74-14, NUDOCS 8403010510
Download: ML20086S332 (6)

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• ' %QTjf Mr. Norman C. Moseley, Director Serial No. 360 Directorate of Reculatory Operations P0&M/JTB:c1w United States Atomic Energy Commission Docket No. 50-280 Region II - Suite 818 50-281 230 Peachtree Street, Northwest 30303 License No. DPR-32 Atlanta, Georgia DPR-37

Dear Mr. Moseley:

d Pursuant to Surry Power Station Technical Specification 6.6.B.1, the Virginia Electric and Power Company hereb'r submits forty (40) copies of Abnormal Occurrence Report No. A0-SI-74-14.

The substance of this report has been reviewed by the Station Nuclear Safety and Operating Committee and will be placed on the agenda for the next meeting of the System Nuclear Safety and Operating Committee.

Very truly yours,

$$ ' f C. M. Stallings Vice President-Power Supply and Production Operations 1

Enclosures 40 copies of A0-SI-74-14 cc: Mr. K. R. Goller, Assistant Director for Operating Reactors e

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COPY SENT REGION

.. O O ABNORMAL OCCURRENCE REPORT REPORT NO. A0-SI-74-M INTAKE CANAL LEVEL MAGNETIC AMPLIFIERS NOVEMBER 29, 1974 DOCKET NOS. 50-280 50-281 LICENSE NOS. UPR-32 DPR-37 SURRY POWER STATION VIRGINIA ELECTRIC AND POWER COMPANY L ___;

O_ Os I. INTRODUCTION In accordance with Technical Specification 6.6.B.1 for Surry Power Station, Operating License Nos. DPR-32 and DPR-37, this report describes an abnormal occurrence which was identified on November 19, 1974. The Directorate of Regulatory Operations, Region II, was notified on Nov-ember 19, 1974.

The occurrence reported herein is classified as an abnormal occurrence pursuant to Technical Specification 1.0.I.6 which states that: "An abnormal occurrence is defined as: Engineered Safeguard System malfunction or other component or system malfunction which rendered or could render the engineered safeguard system incapable of performing its intended safety function." The occurrence described herein could have permitted the intake canal level to fall below the +18 foot elevation during reactor operation without energizing the turbine trip solenoid or closing the circulating water condenser valves.

II.

SUMMARY

OF OCCURRENCE On November 19, 1974, both reactors were in a cold shutdown condition.

The instrument technicians were checking the calibration of the intake canal level magnetic amplifiers. It was determined that the Unit No. I magnetic amplifiers for the low level alarm (LS-CW-1018) and turbine trip (LS-CW-101C) wer'e out of calibration. The low level alarm would have activated at 15'-4" instead of 20'-0". The turbine trip solenoid would not have been activated regardless of the canal water level. The Unit No. 2 magnetic amplifier for the low level alarm (LS-CW-2018) was within the tolerance and would have been activated at approximately 20 feet. The turbine trip magnetic amplifier (LS-CW-201C) was out of calibration and

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would not have been activated rebardless of the canal water level.

Remotely operated butterfly valves are installed at the four inlets and outlets of each main condenser and in the supply lines to the re-circulating spray heat exchangers. The circulating water condenser valves are designed to close autormically with a low level alarm for an intake canal level of +18 foot elevation. Due to the instrumentation not being in calibration, the condenser valves of both units would not have closed automatically regardless of the canal water level.

III. ANALYSIS OF THE OCCURRENCE The intake canal level transmitters measure the water level of the canal over a range of 0 to 144 inches. The zero point of the level transmitter corresponds to a canal water level of +15 feet elevation and the 144 inch point corresponds to a canal water level of +27 feet elevation.

The output of the level transmitters to the magnetic amplifiers is a current which varies f rom 4 to 20 mil 11 amperes. Zero inches on the trans-mitter range (15 feet elevation) produces 4 milliamperes and 144 inches (27 f eet elevation) produces 20 mil 11 amperes.

This output current is fed into the magnetic amplifier through a 250 ohm resistor which produces a voltage of 1 to 5 volts depending on the current. Because the minimum current output of the level transmitters is 4 mil 11 amperes, the minimum voltage developed across the magnetic amplifier input resistors will be one volt. A potentiometer in the circuit with other components is utilized to adjust the setpoint at-which the output relay will trip. A change in value of-these components due to temperature, humidity or aging will change the level of input voltage l

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to the magnetic amplifiers which is required to trip the output relays.

this particular instance, the magnetic amplifier output relays should trip l

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,on a decreasing voltage of 2.666 volts for the low level alarm, 2.000 volts for the turbine trip solenoid and for the circulating water condenser valves. It was found that the Unit No. I relays tripped at 1.113 volts and 0.822 volts and Unit No. 2 relays tripped at 3.645 volts and 0.890 volts, respectively. Because the minimum current of 4 milli-amperes output from the level transmitters produces a minimum of one volt across the input resistor of the magnetic amplifier, the turbine trip relays would never trip due to intake canal low level, nor would the con-denser valves of both units close automatically, due to intake canal low level.

The Unit No. 1 magnetic amplifiers were last calibrated on July 29, 1971 and the Unit No. 2 magnetic amplifiers on January 20, 1972. The ef fect of the changes in temperature and humidity and the aging of the components caused the various component values to change which changed the relay trip setpoint.

IV. CORRECTIVE ACTION TO PREVENT RECURRENCE The immediate corrective action to prevent a recurrence was to initiate a periodic test to verify the calibration of the level transmitters and the setpoints of the magnetic amplifiers. Electronic components usually change values due to aging at a very slow rate. Therefore, an annual periodic test of the system has been instituted.

V. ANALYSIS AND EVALUATION OF SAFETY IMPLICATION OF THE OCCURRENCE Both reactors were in a cold shutdown condition at the time of this incident. However, it is possible the magnetic amplifiers were out of calibration for some indeterminate period of time during which the reactors

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\'v1 vere operational. This fact notwithstanding, the possibility of the canal' falling below the +18 foot level during reactor operations was remote.

In addition to the two low level alarms, one of which would have functioned to alert the operators of a low canal level, each operator has a visual canal water level display which is closely monitored during reactor operations. Each of the displays is prominently marked to attract the operator's attention to a falling water level situation. If the situation cannot be corrected, the operator can manually trip the turbines and/or reactor when the canal water level falls to +18 feet.

If the intake canal fell below the +18 foot level during reactor operations, the Technical Specification 3.14A requirement for 25,000,000 gal. of water in the intake canal for critical services would be violated.

Gravity flow between the high level intake canal and discharge canal seal pit supplies service water to parallel flow loops through four (4) re-circulation spray heat exchangers per un t. i The recirculation spray system of one unit requires 24,400 gpm.

Since the water in the intake canal is required only under accident conditions, there were no safety Laplications associated with the occurrence.

VI. CONCLUSIONS The licensee concludes that :

1. The magnetic amplifiers were out of calibration due to the normal aging of electronic components.

2. The occurrence described herein did not affect the safe operation of the station.

3. The occurrence described herein did not affect the health and saf ety of the general public.

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