05000281/LER-2006-001
| Surry Power Station | |
| Event date: | 07-27-2006 |
|---|---|
| Report date: | 09-25-2006 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability |
| 2812006001R00 - NRC Website | |
1.0 DESCRIPTION OF THE EVENT The charging pump cooling water subsystem provides component cooling (CC) water for the charging pump seal coolers. CC water circulating in the charging pump mechanical seal cooling loops is cooled by intermediate seal coolers which reject heat to the charging pump service water system. The charging pump cooling water subsystem consists of two full-capacity charging pump cooling water pumps and two full-capacity intermediate seal coolers providing 100% redundancy. To ensure that CC water is continually available to the charging pump seal coolers, one charging pump cooling water pump is placed in operation while the other pump is maintained in standby. The standby charging pump cooling water pump is automatically actuated on low pump discharge pressure to supply CC water in the event of failure of the operating pump.
On July 27, 2006, with Unit 2 operating at 100% power, repair of a leak on the Unit 2 'A' charging pump intermediate seal cooler's CC water discharge line was completed.
After the repair, the CC water side of the intermediate seal cooler was vented in accordance with procedures by opening the intermediate seal cooler vent valve (high side) and valving in system pressure. At 1947 hours0.0225 days <br />0.541 hours <br />0.00322 weeks <br />7.408335e-4 months <br />, while restoring the intermediate seal cooler to a normal line-up, a main control room annunciator alarm was received indicating that the CC water pressure had decreased. The standby charging pump cooling water pump started automatically, as expected, but no CC water flow was observed. The operating Unit 2 charging pump continued to run throughout this event however, since the charging pump cooling water subsystem is a subsystem of the charging pumps, the Unit 2 charging pumps were declared inoperable and a 6-hour clock to hot shutdown (1-ISD) was entered in accordance with Technical Specifications (TSs) 3.0.1.
The charging pump cooling water subsystem was successfully vented and at 2043 hours0.0236 days <br />0.568 hours <br />0.00338 weeks <br />7.773615e-4 months <br />, CC flow was restored at 25 gallons per minute (GPM). The flow rate of the subsystem continued to increase and, at 2125 hours0.0246 days <br />0.59 hours <br />0.00351 weeks <br />8.085625e-4 months <br />, the 6-hour TS 3.0.1 clock was exited prior to initiating actions to shutdown the unit.
This report is being issued pursuant to 10 CFR 50.73(a)(2)(i)(B), any operation or condition prohibited by TSs. Since the event caused two independent trains to become inoperable, this report is also being issued pursuant to 10 CFR 50.73(a)(2)(vii).
2.0 SIGNIFICANT SAFETY CONSEQUENCES AND IMPLICATIONS During normal operation, the charging pumps are used as part of the chemical and volume control system and take suction from the volume control tank. Normal operating temperature of the source water is within the operating range of the mechanical seals.
During accident conditions, the charging pumps are used as high head safety injection to provide charging to Unit 2. Therefore, with the low risk and availability of the crosstie, the health and safety of the public was not affected by this event.
3.0 CAUSE The procedure used to return the charging pump intermediate seal cooler to service was determined to be inadequate to ensure proper venting of the entire intermediate seal cooler. Procedure guidance did not account for the intermediate seal cooler piping configuration that required the cooler to be slowly filled during return to service to ensure sufficient venting of the cooler. As a result, air remaining in the cooler was introduced into the charging pump cooling water subsystem and caused air binding of both charging pump cooling water pumps.
4.0 IMMEDIATE CORRECTIVE ACTION(S) Both charging pump cooling water pumps were stopped and the outlet of the 'A' intermediate seal cooler was isolated. The standby charging pump cooling water pump discharge valve was also isolated. The standby charging pump cooling water pump was then started and its discharge valve slowly opened while monitoring discharge pressure. The cooling water subsystem was vented and the standby charging pump cooling water pump was restored to partial flow at 2043 hours0.0236 days <br />0.568 hours <br />0.00338 weeks <br />7.773615e-4 months <br />. The standby charging pump cooling water pump discharge valve was fully opened and CC water flow was restored to normal flow on the standby pump at 2125 hours0.0246 days <br />0.59 hours <br />0.00351 weeks <br />8.085625e-4 months <br />.
5.0 ADDITIONAL CORRECTIVE ACTIONS The Unit 2 'A' charging pump intermediate seal cooler was placed in service following completion of all Post Maintenance Testing (PMT).