ML20086F711
| ML20086F711 | |
| Person / Time | |
|---|---|
| Site: | Robinson  |
| Issue date: | 02/06/1975 |
| From: | Utley E CAROLINA POWER & LIGHT CO. |
| To: | Moseley N NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| Shared Package | |
| ML20086F712 | List: |
| References | |
| AO-50-261-75-3, NG-75-169, NUDOCS 8401040608 | |
| Download: ML20086F711 (4) | |
Text
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Carolina Power & Light Company February 6, 1975 File: NG-3513 (R)
Serial: NG-75 1 W
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Mr. Norman C. Moseley, Director Directorate of Regulatory Operations
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U. S. Nuclear Regulatory Commission
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Region II, Suite 818 n, i
.y h[2 230 Peachtree Street, N.W.
i' Atlanta, Georgia 30303
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Dear Mr. Moseley:
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H. B. ROBINSON UNIT No. 2 LICENSE NO. DPR-23 COMPONENT COOLING PUMP "C" OUT OF SERVICE In accordance with 6.6.2.a of the Technical Specifications for H. B. Robinson Unit No. 2, the attached Abnormal Occurrence Report is submitted for your information. This report fulfills the requirement for a written report within ten days of an Abnormal Occurrence and is in accordance with the format set forth in Regulatory Guideline 1.16, Revision 1.
Yours very truly, t
E. E. Utley Vice-President Bulk Power Supply TAW:KPY:mvp Attachment cc: Messrs. N. B. Bessac W. E. Graham P. W. Hr,we D. Knuth J. B. McGirt D. B. Waters 8401040608 750206 PDR ADOCK 05000261 S
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Abnormal Occurrence Report 1.
Report No.
50-261/75-3 2a.
Date February 3, 1975 2b.
Occurrence Date January 26, 1975 3.
Facility H. B. Robinson Unit No. 2 Hartsville, South Carolina 4.
Identification of occurrence Overcurrent trip of "C" component cooling water pump.
This constitutes an abnormal occurrence as defined in Technical Specification Section 1.8.d.
5.
Conditions Prior to Occurrence The plant was at 100% nuclear power with all parameters normal.
Operations personnel were conducting the weekly routine of swapping auxiliary component loads.
6.
Description of Occurrence At approximately 0200 on January 26, 1975, operations personnel were in the process of swapping auxiliary loads. At 0243 "B" Component Cooling Water Pump (CCWP) was running.
It was intended that "C" CCUP be started and "B" CCWP stopped. The control operator initiatad a start signal for "C" CCWP from the control board.
However, the red light which indicates the pump is running did not illuminate. Thinking he did not hold the control switch in the " START" position a sufficient length of time for the breaker to fully close, the operator attempted to restart "C" CCWP with the same result. Approximately 30 seconds after the initial start attempt an alarm was received indicating "C" CCWP had tripped due to an overload. Auxiliary operators inspected "C" CCWP and rotated the pump shaft to insure its free movement. The shift foreman examined the breaker which feeds "C" CCWP. No problems were identified and another attempt to restart the pump was initiated.
The pump started at that time but the outboard mechanical seal developed a leak which stopped after a short period of time.
In an attempt to verify the pump and its control circuit were operating properly, "C" CCWP was stopped and again started. This time the leak from the seal became excessive.
Repairs were effected on the leaking seal.
Instrumentation and Control Technicians were called out to inspect the breaker which feeds "C" CCWP.
No electrical problems were identified, and following seal replacement the pump was restarted satisfactorily and declared operable at 1441 on January 26, 1975.
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Description of Apparent Cause of Occurrence The red indicating light (pump ruaning) on the RTGB was defective.
When the operator initially attempted to start the pump he had no true indication of the pump starting status.
The adjacent lights on the RTGB " flickered" when the start was initiated giving an indication that the breaker did close and power was supplied to the pump.
The pumps outboard mechanical seal was examined and found to be cracked.
Excessive damage could c't be detected and the pump turned freely.
Due to this limited damage, binding of the pump shaf t was ruled out as a possible cause of the. overload. The pump discharge check valve was disassembled and inspected. There was no evidence of malfunction or defect. A thorough examination was also made of the breaker. No mechanical or electrical deficiency was found.
The most probable cause of the trip is backleakage through the pumps discharge side check valve due to debris impeding its full closure.
This conjectured backleakage would have caused the pump to rotate backwards. The motor which drives "C" CCWP is an induction type motor which is characterized by a low starting torque. Under the postulated conditions when the pump was started, the motor could not develop enough torque to quickly overcome the backward rotation.
Therefore, the motor drew an abnormally high amount of current. The higher starting current eventually enabled the motor to start rotating in the proper direction. The resulting water pressure lifted the check valve enough to release the debris caught on the valve seat. The motor current at this time was still abnormally high due to low pump speed.
The high current caused the 30 second time delay overcurrent devices to trip the breaker. With the debris cleared from the check valve, the valve seated properly.
8.
Analysis of Occurrence Technical Specification Section 3.3.3.2 requires two component cooling water pumps which are fed from the emergency busses to be operable during normal plant operation.
If one pump is out of service for more than 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, the reactor must be shut down.
For this occurrence, while "C" CCWP was inoperable, "B" CCWP was running. Also "C" CCWP was returned to service within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. Therefore, no limiting condition for operation was violated.
In addition, "A" CCWP (which is fed from 4160 volt Bus No. 3 via a 4160/480 volt station service transformer) was'available for use in the event of an emergency.
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Corrective Action The leaking mechanical seal and the status light module on the control board for "C" CCWP were replaced. The breaker which feeds "C" CCWP was thoroughly examined and determined to be in proper working condition.
"C" CCWP has been stopped and started a number of times since the occurrence without trouble, verifying the check valve operability. No i
further corrective action is deemed necessary.
10.
Failure Data i
No previous failures of this type have occurred.
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