05000352/LER-2013-001
| Limerick Generating Station, Unit 1 | |
| Event date: | 03-20-2013 |
|---|---|
| Report date: | 05-20-2013 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident |
| Initial Reporting | |
| ENS 48837 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident |
| 3522013001R00 - NRC Website | |
Unit Conditions Prior to the Event Unit 1 was in Operational Condition (OPCON) 1 (Power Operation) at 100% power. There were no structures, systems or components out of service that contributed to this event.
Description of the Event
On Wednesday, March 20, 2013, Unit 1 was operating at 100% power with the HPCI (EIIS:BJ) system pump, valve, and flow surveillance test (ST- 6-055-230-1) in progress. The HPCI turbine was secured at 1445 hours0.0167 days <br />0.401 hours <br />0.00239 weeks <br />5.498225e-4 months <br /> and the auxiliary oil pump cycled on during turbine coast down as expected maintaining the turbine oil system pressurized. At approximately 1447 hours0.0167 days <br />0.402 hours <br />0.00239 weeks <br />5.505835e-4 months <br />, equipment operators identified an oil leak at an electrical junction box near the turbine stop valve and at the electrical housing of a pressure switch (EITS:PS). The HPCI system was declared inoperable at 1447 hours0.0167 days <br />0.402 hours <br />0.00239 weeks <br />5.505835e-4 months <br /> and Technical Specification (TS) 3.5.1 Emergency Core Cooling Systems (ECCS) - Operating, action "c.1", was entered which required restoration within 14 days.
An investigation identified that an oil pressure switch located in the turbine governor journal bearing oil supply line (PSL-056-160) had failed allowing oil to enter the switch electrical housing and connected flexible conduit. The failed pressure switch was replaced and the HPCI system was tested successfully. The Unit 1 HPCI system was restored to operable status on Thursday, March 21, 2013 at 1300 hours0.015 days <br />0.361 hours <br />0.00215 weeks <br />4.9465e-4 months <br />.
This event resulted in a condition that at the time of discovery could have prevented the fulfillment of the HPCI system safety function.
The 8-hour NRC ENS notification (#48837) required by 10CFR50.72(b)(3)(v)(D) was completed on Wednesday, March 20, 2013, at 2052 hours0.0238 days <br />0.57 hours <br />0.00339 weeks <br />7.80786e-4 months <br />. This LER is being submitted pursuant to the requirements of 10CFR50.73(a)(2)(v)(D).
Analysis of the Event
There was no actual safety consequence associated with this event.
The potential safety consequence of this event is significant since the oil leak was of sufficient magnitude to have caused a loss of HPCI system injection capability during a design basis accident. The reactor core isolation cooling (RCIC) system and low pressure emergency core cooling systems (ECCS) remained operable during the period when the HPCI system was rendered inoperable by the oil leak.
The affected pressure switch is calibrated on a 6-year frequency.
There is no preventive maintenance task that performs periodic replacement of the switch. The failed switch had been in service since initial plant operation.
Failure analysis concluded that the observed oil leak resulted from a crack in the pressure sensing bellows of the pressure switch. The failure mechanism of the brass bellows was determined to be consistent with corrosion fatigue, which results from the combined action of corrosion and cyclic stresses.
Cause of the Event
The cause of the HPCI inoperability was a failure of a bellows actuated pressure switch which resulted in a significant turbine oil system leak. The apparent cause of the pressure switch bellows failure was corrosion fatigue.
Corrective Action Completed The failed pressure switch was replaced and the HPCI system tested successfully.
Corrective Action Planned A similar service pressure switch, Unit 1 HPCI oil filter differential pressure switch, will be replaced as an extent of condition action.
A review of HPCI and RCIC (EIIS:BN) turbine lube oil system components will be performed to determine if any additional components are potentially susceptible to failure as a result of historical exposure to oil with high moisture content.
Previous Similar Occurrences There were no previous similar occurrences of unplanned HPCI system inoperability due to oil leakage in the past 5 years.
Component data:
System: High Pressure Coolant Injection System Component: HPCI Turbine Bearing Low Oil Pressure Alarm Switch (PSL-056-160) Manufacturer: 5345 Square D Company Model Number: 9012-ACW-3 Serial Number: None