05000352/LER-2008-004
| Limerick Generating Station, Unit 1 | |
| Event date: | 11-11-2008 |
|---|---|
| Report date: | 12-31-2008 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition |
| 3522008004R00 - NRC Website | |
Unit Conditions Prior to the Event Unit 1 was in Operational Condition (OPCON) 1 (Power Operation) at approximately 100% power. Unit 2 was in Operational Condition (OPCON) 1 (Power Operation) at approximately 100% power. There were no other structures, systems or components out of service that contributed to this event.
Description of the Event
On Tuesday, November 11, 2008, an engineer was participating in senior reactor operator certification training in the main control room (MCR) simulator. The engineer observed that the remote shutdown procedure (SE-1) did not agree with the supporting design calculations for the fire safe shutdown (FSSD) method being implemented by the procedure.
The calculations assume that the reactor core isolation cooling (RCIC) (EIIS:BN) system suction will be aligned to the suppression pool during the remote shutdown event. The RCIC system suction is aligned to the condensate storage tank (CST) (EIIS:TK) during normal operation.
The remote shutdown procedure was promptly revised to include a step to align the RCIC system suction to the suppression pool while operating the system at the remote shutdown panel.
This event resulted in the nuclear power plant being in an unanalyzed condition that could have significantly degraded plant safety. This LER is being submitted pursuant to the requirements of 10CFR50.73(a)(2)(ii)(B).
Analysis of the Event
There were no actual safety consequences associated with this event. The safety consequences of this event could have been significant under certain circumstances since this condition had the potential to cause a loss of the only credited high pressure coolant injection source during a remote shutdown event. This would have resulted in operator reliance on TRIP procedure direction for depressurization and use of the unaffected low pressure injection system to stabilize reactor level. The RCIC system was capable of being operated at the remote shutdown panel for the majority of affected credible fire scenarios that could occur in the MCR or cable spreading room. However, it was possible that an analyzed fire for these areas could cause one or both motor-operated-valves (MOVs) (EIIS:V) on the CST suction line to fail closed due to a hot-short.
The RCIC and high-pressure coolant injection (HPCI) systems are normally aligned to the CST during plant operation. The CST suction line is equipped with two in-series 20" MOVs located inside the CST dike that are remotely controlled from hand switches located in the MCR. During a design basis fire in the MCR or cable spreading room it is postulated that these MOVs could close due to a hot-short.
The FSSD analysis assumes that RCIC is used as the source of high-pressure injection during a remote shutdown event. It is assumed that the RCIC system suction will be manually aligned to the suppression pool early in the event while being operated at the remote shutdown panel. The step to perform this alignment was not included in the remote shutdown procedure when it was initially developed.
Cause of the Event
The cause of the event was a failure to include a required step in the remote shutdown procedure when the procedure was developed. The required step aligns the RCIC system suction to the suppression pool during a remote shutdown event as assumed in the FSSD analysis.
Corrective Action Completed The remote shutdown procedure was revised to include a step to align the RCIC system suction to the suppression pool while operating the system at the remote shutdown panel.
Previous Similar Occurrences There were no previous similar events during the last three years that adversely affected the capability to perform a remote shutdown.
Component data:
System: BN Reactor Core Isolation Cooling System Component: TRB Turbine Component Number: 10-S212 Manufacturer: T147 Terry Steam Turbine Co Model Number: GS-2 TYP Serial Number: T-36691-A