05000364/LER-2009-001
| Docket Numbersequential Revmonth Day Year Year Month Day Yearnumber No. 05000 | |
| Event date: | 10-06-2009 |
|---|---|
| Report date: | 03-01-2010 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(vii)(D), Common Cause Inoperability 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition |
| 3642009001R01 - NRC Website | |
Westinghouse -- Pressurized Water Reactor Energy Industry Identification Codes are identified in the text as [XX]
Description of Event
On August 02, 2009, while swapping Service Water (SW) pumps [BI] (start of 2E/secure of 2C) in preparation for the train swap (B-Train to A-Train ), plant personnel heard sounds that resulted in a decision to secure the 2E SW Pump shortly after being started. As soon as the 2E SW pump was secured, the sound stopped. Investigation discovered that the seismic support assembly for the 2E SW pump was no longer capturing the pump column. Inspection of the underwater seismic support assembly indicated the lower two of the four wall plate bolts were degraded and missing the nuts.
SNC determined that the two remaining wall plate bolts would support the required torque and the seismic support assembly would perform its design function. A Prompt Determination of Operability was completed to document that the 2E SW pump seismic support assembly was operable but degraded.
SNC established a plan to inspect the remaining Unit 2 SW pump seismic supports to determine the extent of condition that was found on 2E SW pump. Additional vendor support was required to perform the inspections (contract divers). SNC Engineering developed a plan for replacing any degraded seismic supports. Material was procured, supports fabricated and underwater support was arranged. The plan was ready to implement the first week of October 2009.
Inspection of the 2E SW pump support discovered that the retaining bolts were loose. SNC decided to replace the seismic support and the mounting bolting for 2E SW pump. The 2D SW pump was found to be in an operable condition with the four mounting bolts being intact. The top two mounting bolts were found to have adequate torque value while the two lower bolts were in place but not fully torqued. An engineering evaluation showed that this was an acceptable configuration to justify operability of 2D SW pump.
With 2D and 2E SW pumps operable, the B-Train SW System was considered operable and inspection activities moved on to the A-Train pumps 2A, 2B and 2C (the swing SW Pump 2C was aligned to A-Train). On October 6, 2009 at 17:45, the Unit 2 SW system A-Train was removed from service for inspection. The 2A, 2B and 2C SW pump seismic supports base plate bolting was determined to require replacement due to the inability to establish required torque on the nuts of the mounting bolts. At this point SNC had one operable train of SW pumps (2D and 2E) and entered a 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> Limiting Condition for Operation (LCO) for the A-Train SW pumps being inoperable. On October 8, 2009, SNC submitted a request for a one time Emergency Technical Specifications (TS) amendment to allow an additional 96 hours0.00111 days <br />0.0267 hours <br />1.587302e-4 weeks <br />3.6528e-5 months <br /> to complete repairs to the A-Train SW Pumps. This amendment was approved on October 9, 2009 as Unit 2 TS Amendment 177. On October 9, 2009 at 22:42, A-Train SW was returned to service with 2B and 2C SW pumps being declared operable.
Efforts to replace seismic supports for the five Unit 2 SW Pumps were completed on October 10, 2009 at 15:15. New seismic supports and mounting bolts were installed for each pump.
� Reporting Requirements Review The SW system provides a heat sink for the removal of process and operating heat from safety related components during a Design Basis Accident (DBA) and/or transient. During normal operation, and a normal shutdown, the SW system also provides this function for various safety related and non-safety related components. The principal safety related function of the SW system is the removal of decay heat from the reactor via the Component Cooling Water System. The SW system consists of two separate, 100% capacity, safety related, cooling water trains. Each train consists of two 50% capacity pumps, one shared 50% capacity spare pump, piping, valves, and instrumentation. Train A contains SW Pumps A and B. and Train B contains SW Pumps D and E.
SW Pump C is a swing pump. Four pumps are normally in operation on each unit, with one (swing pump not in service. In the event of failure of a pump, plant operators must manually align the swing pump to the train containing the failed pump, maintaining two pumps per train.
At the point of discovery that the Unit 2 A-Train pumps seismic supports would not withstand a seismic event, the Unit 2 B-Train pumps seismic supports had been repaired. Therefore. SNC determined that no reporting requirements under 10 CFR 50.72 had been met. SNC has determined that prior to the repair of Unit 2 B-Train SW pump seismic supports; a condition existed in which four of the five SW pumps in Unit 2 did not meet the design requirements to withstand a seismic event. SNC has determined that this condition is reportable under the following sections of 10 CFR 50.73:
10 CFR 50.73(a)(2)(ii)(B), "Any event or condition that resulted in the nuclear power plant being in an unanalyzed condition that significantly degraded plant safety.
10 CFR 50.73(a)(2)(v)(D), "Any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident.
10 CFR 50.73(a)(2)(vii)(D), "Any event where a single cause or condition caused ... two independent trains ... to become inoperable in a single system designed to mitigate the consequences of an accident.
Cause of Event
During the initial installation of the carbon steel seismic supports in a raw water system. SNC failed to establish appropriate monitoring of these supports to identify degradation.
Safety Assessment Further analysis of the service water pumps and the need for seismic rings to withstand a design basis earthquake were performed. SNC determined the vendor had utilized more conservative values for the seismic activity. These values were refined and additional analysis related to stresses of the Sulzer SW pumps was performed. This analysis determined that the pump would not have been adversely affected by seismic activity and thus the pumps would have remained operable. Therefore, the safety and health of the public was not adversely affected by the degraded condition of the SW Pumps seismic supports.
Corrective Action The seismic support for each SW Pump (2A, 2B, 2C, 2D and 2E) has been removed and new bolting and supports installed. A corrective action from the Root Cause Evaluation to inspect the seismic supports for Unit 1 and Unit 2 SW Pumps, on an established frequency, has been entered into the sites Corrective Action Program, As an extent of condition review, Unit 1 SW Pump seismic supports were also inspected. Results demonstrated that the Unit 1 supports were adequate and operability of the Unit 1 SW Pumps was confirmed. A corrective action from the Root Cause Evaluation to replace the Unit 1 seismic supports has been entered into the sites Corrective Action Program.
Additional Information
Previous Similar Events
None were identified.
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