ML20085L537

Ro:On 710810,during Required Surveillance Testing,Core Spray Injection Valve 3-1402-25C Failed to Open Rendering Core Spray Subsys B Incapable of Performing.Possibly Caused by Breaker Thermal Overload Set Too Low for Ambient Temp

ML20085L537
Person / Time
Site:	Dresden
Issue date:	08/20/1971
From:	Hoyt H COMMONWEALTH EDISON CO.
To:	Morris P US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20085L542	List: ML20085L537 ML20085L572
References
NUDOCS 8311010492
Download: ML20085L537 (2)

Text

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S'E ~b,- LICUSE DPR-25, DRESDEN NUCLEAR POWER STATION. UNIT #3, SECTTON f.6. .

' OF 'TFE "ECUSC4L SPECIFTCATIONS j d cence: 1) Letter to Dr. Peter A. Morris from H. E. Hoyt, dated August 20, 1971, regarding Unit 2/3 Diesel Generator Failure to start.

Desr Dr. Morris: .

"%is is to report a cc:tdition relating to the operation of the statice when, durfrt; a required surveillance test, core spray injection vah e 3-14'2-25C failcd to opr.n, thuc rendering the "B" core spray sub-syste incapable of performing its intended function as requirec by section 3.5.F.1 of the Dresden Unit #3 Technical Specifications.

JR0ELEM AND INVESTIGATION The reactor was in the "run" mode and operating at 366 MWe on

^ugast 10, 1971. Following a routinc surveillance test of the Unit 2/3 J diesel generater, it was found to be inoperable, as described in reference (1) above. As required, by rection 3.5.F.1 of the technical specification, testing of all low pressure core cooling subsyctems vac initiated. At 5:30 A.M. core spray injection valve 3-1402-250 failed to open by manual cperstion from the remote control switch in the control room. An operator, was dispatched to the valve motor operator breaker and he found it in the normcl. "on" position. He turned the breaker from "on" to "recet" to "off" and then back to "or." and depressed the therm 1 overload reset button.

Thc valve operated satisfactorily thereafter and the malfunction could not be d=glicated. -

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August 20, 1971 i Dr. Peter Morris ft is postulcted that the breaker thermal overload was-set too Icw for the ambient temperature condition and had tripped. When the operator reset the thermal overload, the valve operated properly.

CORRECTTVE ACTION 4

The breaker thermal overload was replaced with one of proper rcting to prevent recurrence.

Sincercly.

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Dear Dr. Morris:

This is to report a condition relating to the operation of the station when, following the completion of a successful surveillance test, the Unit 2/3 diesel generator, was found incapable of being restarted.

The diesel generator was then declared inoperable.

PROBLEM AND INVESTICATIO_N At approximately 2:15 A.M. on August 10, 1971, a Unit 2/3 diesel generator surveillance test was successfully conducted in preparation for a Unit 2 diesel generator routine maintenance outage. Following shutdown of the Unit 2/3 diesel generator, and prior to taking Unit 2 diesel generator out of service, an operator, making routine c, hecks, noted tha t the air com-pressors for the diesel start system were running. Further investigation showed that the starting air accumulators were depressurized and that the '

starting air motor solenoid valve was open. The accumulators were then isolated and repressurized, and a restart of the diesel generator was attempted. The engine failed to start but air was observed to be blowing from the s'ir motor exhaust ports. The Unit 2/3 diesel generator was then declared " inoperable". The Unit 2 diesel generator was lef t in service and the required surveillance of the low pressure coolant injection subsystems ~

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investigation revealed that, when the diesel gen-l N rator was started, the starting air motors had not disengaged when the speed of the diesel reached 200 rpm as designed. The starting motor l < remained engaged with the " bull ring gear", following the start sequence, l

thus causing the f ailure of the starting motor.

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It was concluded that the starting air solenoid had not closed, i l

thus maintaining air pressure on the startins motors which kept them"enga ged.

Inspection of the relay which activates the starting air solenoid valve found the relay in good condition. Ilowever, upon disassembly and inspection of the solenoid valve, a vgry small peice of " grit" was found on the valve seat.

The valve seat also had a small " scratch". The foreign material in the sole-noid valve is believed to be the cause of the malfunction.

While the diesel generator was down its e,ix month inspection was successfully completed.

CORRECTIVE ACTION To preclude recurrence, (1) The starting air solenoid valve was replaced, (2) One of the starting air motors was replaced and the other starting air motor overhauled, (3) The starting air supply system was inspected and cleaned.

Following the above' repairs the diesel generator was started satisfactorily and declared " operable."

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