05000336/LER-2006-003

LER-2006-003,

Docket Number
Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown
3362006003R00 - NRC Website

1. Event Description On March 31, 2006 at 2200 hours0.0255 days <br />0.611 hours <br />0.00364 weeks <br />8.371e-4 months <br /> with the unit at 100% power, Millstone Power Station Unit 2 commenced a shutdown of the reactor in accordance with Technical Specification (TS) 3.7.1.2.a due to the inability to restore the Turbine Driven Auxiliary Feedwater [BA] (TDAFW) pump to an operable status following a planned maintenance activity. The shutdown was completed at 1406 on April 1, 2006.

On March 29, 2006, Technical Specification (TS) 3.7.1.2 was entered when the TDAFW pump was taken out of service for maintenance and subsequent post-maintenance operability testing. During the operability test, white smoke was observed coming from the TDAFW pump outboard bearing housing vent. The test was terminated and subsequent inspection determined that the pump outboard thrust bearing had failed. The time of failure was the time of discovery. The TDAFW pump could not be restored to an operable status within the specified TS allowed outage time so a shutdown was commenced on March 31, 2006, at 2220 hours0.0257 days <br />0.617 hours <br />0.00367 weeks <br />8.4471e-4 months <br />. The unit reached hot shutdown at 1406 hours0.0163 days <br />0.391 hours <br />0.00232 weeks <br />5.34983e-4 months <br /> on April 1, 2006.

The damaged components were replaced; the pump was successfully tested and restored to an operable status.

This condition is being reported under the provision of 10 CFR 50.73(a)(2)(i)(A) as the completion of any nuclear plant shutdown required by the plant's Technical Specifications.

2. Cause A Root Cause Evaluation of the event has been completed. The root cause of the bearing failure was overloading as a consequence of balance drum/sleeve wear caused by balance drum/sleeve misalignment.

3. Assessment of Safety Consequences During the shutdown, both motor-driven AFW pumps were available and all safety systems performed as designed.

4. Corrective Action After thorough inspection of the pump internals, the only damaged components were the bearing, balance drum and sleeve. These components were replaced and the pump was reassembled, tested and returned to service.

Actions to prevent reoccurrence include reviewing procedures that affect shaft alignment on HTMA model pumps (such as the TDAFW pump) to ensure correct pump assembly.

Additional corrective actions are being taken in accordance with the station's corrective action program.

5. Previous Occurrences No similar bearing failures of the TDAFW pump have occurred at the Unit within the previous three years.

Energy Industry Identification System (EIIS) codes are identified in the text as [XX].