05000220/LER-2002-002
| Event date: | |
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| Report date: | |
| 2202002002R00 - NRC Website | |
I. pescription of Event On October 17, 2002, at approximately 1100 hours0.0127 days <br />0.306 hours <br />0.00182 weeks <br />4.1855e-4 months <br />, with Mme Mile Point Unit 1 (NMP1) at approximately 100 percent power, the #12 control rod drive (CRD) pump failed to start during performance of the quarterly surveillance. The pump was visually observed to begin rotation and then coast to a stop. No abnormal conditions (sight, sound, odor etc.) were noticed at the pump. In-rush current on control room metering was observed at approximately 200 amperes, decaying to zero amperes. The green "OFF' indicator light did not go out and the red "ON" indicator never illuminated. Visual inspection found the circuit breaker in the "OPEN" position. The surveillance was placed on hold. The control room was notified and a 7-day limiting condition for operation (LCO) action statement, as required by Technical Specification (TS) 3.1.6b, was entered. The redundant #11 CRD pump was verified operable as required by TS 4.1.6c. Additionally, an Action Request was generated to perform troubleshooting of this event.
Troubleshooting confirmed that the circuit breaker (General Electric 600 Volt Model AK-2A-25) had attempted to shut and immediately tripped open. Review of the breaker's maintenance history revealed that its routine preventive maintenance bad been completed on September 24, 2002. During that preventive maintenance, the breaker's original phase "A" instantaneous over current (type EC-2A) trip device had failed its "as-found" test and was replaced. The "as-left" EC trip device test was satisfactory. It is significant to note that post maintenance testing was conducted with the breaker racked out to the "Test" position rather than being in the "Racked In" position. Testing the breaker in this manner verifies functionality of the breaker's control circuit but does not pass load current through the instantaneous over current trip device, and therefore does not test the breaker's ability to perform its design function to start the pump. This is also contrary to the higher level procedure requiring that the applicable surveillance, including starting the pump in this particular case, be performed after any breaker maintenance.
During troubleshooting for this event, the "as-found" and "as-left" tests were successfully performed on the breaker's EC trip devices with no failures noted. However, during additional EC trip device testing, the phase "A" EC trip device trip set point was found to have drifted slightly below the lower tolerance limit. However, the low trip occurred only once out of five times during the troubleshooting. The breaker was quarantined for analysis. A spare breaker was then identified and installed after successful completion of the preventive maintenance procedure. The CRD pump was successfully started three times. The redundant #12 CRD train was declared operable and the LCO action exited on October 19, 2002 at approximately 1315 hours0.0152 days <br />0.365 hours <br />0.00217 weeks <br />5.003575e-4 months <br />.
On November 4, 2002, it was determined that this event is reportable. This determination was based on an assessment that the #12 CRD pump had been inoperable from the time it was taken out of service for maintenance on September 24, 2002, until it was successfully tested and declared operable on October 19, 2002 (total of 25 days). This period of inoperability exceeded the 7-day LCO action statement in TS 3.1.6b.
II. Cause of Event
The cause of this event was determined to be inadequate post maintenance testing. Contributing causes included a defective circuit breaker over current trip device (EC trip device) where the set point drifted slightly below the lower tolerance limit, and lack of compliance with applicable higher level administrative procedures.
III. Analysis of Event
This event is reportable in accordance with 10CFR50.73(aX2X0 (B), "Any operation or condition which was prohibited by the plant's Technical Specifications....
Ill. Analysis of Event (Cont'd.1 The # 11 and #12 CRD pumps are part of the control rod drive hydraulic system. This system is designed to change the control rod positions within the reactor core in response to manual control signals, charge the scram accumulators, and provide high pressure makeup to the reactor vessel for a "Twenty-five gallons per minute total leakage ...," as specified in TS 3.2.5, "Reactor Coolant System Leakage." The system can also provide core cooling in the event of a small line break (up to 0.003 square feet). Normal system operation is with one pump running and the other pump on standby. Electrical power for this system is normally available from the reserve transformer. Automatic initiation is provided to start each pump from its respective diesel generator in case offsite power is lost.
Each CRD pump can supply 50 gpm within 60 seconds of receipt of an automatic initiation signal. The 60-second delay in pump starting assures that automatic pressure blowdown is not actuated for the TS specified leakage rate of 25 gpm.
TS 3.1.6, "Control Rod Drive Pump Coolant Injection," requires the coolant injection system to be operable whenever irradiated fuel is in the reactor vessel and the reactor coolant temperature is greater than 212°F with one exception: if a redundant component (such as #11 or #12 CRD pump) becomes inoperable, the control rod drive pump coolant injection system shall be considered operable provided the inoperable component is returned to an operable condition within 7 days and the operability of the redundant component is verified "immediately and daily thereafter.
Currently, no credit is taken for the CRD high pressure coolant injection function to mitigate the consequences of a Loss of Coolant Accident (LOCA), as evaluated in the 10CFR50 Appendix K LOCA analysis. A probabilistic risk assessment evaluation concluded that the increase in core damage frequency due to this event is small (2.57E-7/year) and as such this event has low safety significance.
Based on the above, the event did not pose a threat to the health and safety of plant personnel or the public.
IV. Corrective Actions
1. Maintenance replaced the defective circuit breaker with a suitable spare breaker.
2. Maintenance conducted a thorough review of all safety-related and non-safety related 600 Volts AC GE Model AK circuit breakers installed at NMP1. Three circuit breakers were identified as needing further testing and the testing was successfully completed. No other GE Model AK circuit breakers at NMP1 are impacted by this event 3. The Maintenance and Operations Managers issued written guidance to Operations, Work Control, Planning, and Maintenance organizations clarifying management expectations regarding conduct and control of post maintenance testing on circuit breakers to ensure compliance with the higher level procedure.
WIC FARM 366A U.S. NUCLEAR REGULATORY COMMISSION (1-206) FACILITY NAME (1) DOCKET (2) LER NUMBER (6)
V. Additional Information
A. Failed components:
Circuit breaker � General Electric � 600 Volt Model AK-2A-25
B. Previous similar events:
During an event in 1999 (refueling outage number 15), shutdown cooling pump #13 tripped immediately on a start attempt. The other two shutdown cooling pumps were available and one was already running. The breaker (GE Model AK) EC trip devices were found to be tripping slightly low. Upon review, the set point specifications were found to be lower than design guidance. The calculation was revised and the set point specifications were changed to conform to design guidance. The trip devices were then reset accordingly.
C. Identification of components referred to in this Licensee Event Report:
Components PF.FF. 805 System 1:1) IEEE 803A Function Control Rod Drive System AA N/A Reactor Core System AC N/A Low Voltage Power System EC N/A Emergency Diesel System EK N/A Reactor Recirculation System AD N/A Pump AA P Circuit Breaker EC, AA 52 Fuel Rod AC ROD Control Rod AA ROD Trip Device EC N/A Indicator (Light) EC IL Accumulator AA ACC