05000280/LER-2003-001
| Document Number | |
| Event date: | 01-14-2003 |
|---|---|
| Report date: | 03-14-2003 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 2802003001R00 - NRC Website | |
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05000 - 280 FACILITY NAME (1) SURRY POWER STATION YEAR I SEQUENTIAL 1 REVISION NUMBER � NUMBER LER NUMBER 6) 1.0 DESCRIPTION OF THE EVENT On January 14, 2003, at 0126 hours0.00146 days <br />0.035 hours <br />2.083333e-4 weeks <br />4.7943e-5 months <br /> with Surry Unit 1 operating at 100 percent power, a Reactor Coolant Pump (RCP) 1C Shaft Alert annunciator [EIIS-AB-MO-ANN], a RCP Shaft Danger annunciator, and high motor lower radial bearing temperature alarms [EllS- AB-MO-TA] were received in the Main Control Room [EIIS-NA]. The operating crew entered the appropriate abnormal procedure and began monitoring related RCP parameters to validate the alarms. The motor lower radial bearing temperature on RCP 'C' increased to approximately 403 degrees Fahrenheit (F) and the 'C' motor cubical rate of rise temperature alarm was received on the plant computer. The operating crew confirmed the validity of the condition and initiated a manual reactor trip at 0137 hours0.00159 days <br />0.0381 hours <br />2.265212e-4 weeks <br />5.21285e-5 months <br />.
Following the reactor trip, the affected RCP was secured at 0138 hours0.0016 days <br />0.0383 hours <br />2.281746e-4 weeks <br />5.2509e-5 months <br />. Automatic actuations occurred as expected, including Turbine Trip by Reactor Trip, Auxiliary Feedwater [EIIS-BA] initiation on low low steam generator [EIIS-SG] level, Main Generator Trip, and AMSAC initiation. Individual Rod Position Indicator (IRPI) [EllS-AA- Z1] E-11 initially indicated 25 steps and normal boration was initiated to meet the required shutdown margin. At 0400 hours0.00463 days <br />0.111 hours <br />6.613757e-4 weeks <br />1.522e-4 months <br />, IRPI E-11 indication was observed to drift to approximately 12 steps.
A four-hour and an eight-hour non-emergency report were made to the NRC as required by 10 CFR 50.72(b)(2)(iv)(B) and 10 CFR 50.72(b)(3)(iv)(A). This report is being submitted pursuant to 10 CFR 50.73(a)(2)(iv)(A) for a manual actuation of the reactor protection system and the initiation of the Auxiliary Feedwater system.
2.0 SIGNIFICANT SAFETY CONSEQUENCES AND IMPLICATIONS This event resulted in no significant safety consequences or implications. The reactor was manually tripped prior to securing the affected RCP in accordance with station abnormal procedures. Auxiliary Feedwater automatically initiated on low low steam generator level following the trip. As a result of the loss of turbine load, the secondary power operated relief valves [EIIS-SB-RV] actuated during the transient. The Reactor Coolant System (RCS) jEllS-AB] cooled to a minimum Tave temperature of approximately 543 degrees F and then stabilized to the no load Tave value of 547 degrees F. Therefore, the health and safety of the public were not affected.
The operating crew noted the one IRPI indication and in accordance with emergency operating procedures, initiated normal boration and calculated the required shutdown margin. At 0517 hours0.00598 days <br />0.144 hours <br />8.54828e-4 weeks <br />1.967185e-4 months <br />, the boron concentration was verified to be greater than the amount required, ensuring adequate shutdown margin.
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05000 - 280 FACILITY NAME (1) SURRY POWER STATION 1 YEAR I SEQUENTIAL � REVISIONNUMBER � NUMBER LER NUMBER 6) 3.0 CAUSE I The direct cause for the Main Control Room indications and alarms resulting in the manual trip of the unit was the degrading conditions of RCP 'C'. A slow loss of oil in the RCP motor lower oil reservoir resulted in the failure of the motor lower radial bearing causing elevated temperatures and high shaft vibrations.
During the initial inspection of the RCP 'C', no oil level was observed in the motor's lower reservoir sight glass. The motor was uncoupled and moved to the operating deck of containment where the lower bearing was disassembled and inspected. The drainpipe flange, the aluminum oil pan joint, and the level column drain cap were identified as potential sources of oil leakage. A % inch misalignment was found on the reservoir's drainpipe flange. None of the sources could be positively identified as the point source.
The lower radial bearing assembly was removed and all six bearing shoes were found damaged.
A Root Cause Evaluation (RCE) team was assembled to determine the root cause and to address actions to preclude recurrence. Preliminary findings also indicate that the RCP motor radial bearing failure can be attributable to the loss of lubrication in the lower RCP motor radial bearing. In addition, the RCE team found that the lower oil reservoir level switch failed to actuate and alert the operating crew on low reservoir level due to a broken internal spacer plate bracket. No adverse trend or alarm in the lower radial bearing resistance temperature detector (RTD) temperature was noted preceding the event because the RTD was not in direct contact with the bearing shoe as required by the manufacturer's drawing.
4.0 IMMEDIATE CORRECTIVE ACTION(S) The damaged radial bearing was disassembled, inspected, and replaced. Internal components, parts and gaskets were installed in accordance with the assembly procedure and vendor recommendations. The lower radial bearing RTD was replaced and installed in accordance with the manufacturer's drawings. The lower oil reservoir gaskets and seals were replaced, and the drainpipe flange misalignment was corrected. During corrective maintenance, strong backs were installed for the RCP 'C' aluminum oil pan fasteners to eliminate further leakage. Oil levels were adjusted as necessary.
Post maintenance testing was completed, and the lower reservoir was inspected for leaks prior to returning the pump motor to service.
5.0 ADDITIONAL CORRECTIVE ACTIONS Due to the findings in the RCP 'C' motor, oil level alarms for the other Unit 1 RCPs were FACILITY NAME (1)
SURRY POWER STATION
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05000 - 280 LER NUMBER 1 6) PAGE (3) functionally tested. The RCP 'B' upper oil reservoir level switch failed its functional test.
Upon inspection, the same failure mechanism as the RCP 'C' lower switch was identified.
All unit 1 level switches were inspected and the two defective switches were replaced.
6.0 ACTIONS TO PREVENT RECURRENCE Unit 2 RCP level switches will be functionally tested and the RCPs will be inspected for evidence of oil leakage during the next refueling outage and corrective actions will be implemented as appropriate.
Additional actions to prevent recurrence that are identified by the RCE will be tracked through the corrective action system.
7.0 SIMILAR EVENTS None 8.0 MANUFACTURER/MODEL NUMBER Westinghouse/CS VSS Reactor Coolant Pump Motor 9.0 ADDITIONAL INFORMATION Unit 2 was not affected by this event and remained stable at 100% reactor power.