05000325/LER-2015-001
| Brunswick Steam Electric Plant (Bsep), Unit 1 | |
| Event date: | 02-12-2015 |
|---|---|
| Report date: | 12-21-2015 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident |
| 3252015001R01 - NRC Website | |
comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by internet e-mail to used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
Brunswick Steam Electric Plant (BSEP) 05000- 325
3. LER NUMBER
001 2015 - 01 Energy Industry Identification System (EIIS) codes are identified in the text as [XX].
Background
Initial Conditions At the time of this event, Unit 1 was in Mode 1, at approximately 100 percent of rated thermal power (RTP).
The Reactor Core Isolation Cooling (RCIC) system [BN], Automatic Depressurization System (ADS), Low Pressure Coolant Injection (LPCI) system [BO], and Core Spray (CS) system [BM] were operable at the time of the event.
Reportability Criteria This condition is being reported in accordance with 10 CFR 50.73(a)(2)(v)(D), as an event or condition that could have prevented the fulfillment of the safety function of a system that is needed to mitigate the consequences of an accident. The NRC was initially notified of this event on February 12, 2015 (i.e., Event Number 50816).
Event Description
At 1336 Eastern Standard Time (EST) on February 12, 2015, the Unit 1 High Pressure Coolant Injection (HPCI) System [BJ] was declared inoperable due to a failure of the HPCI auxiliary oil pump. The pump tripped after running for approximately 18 minutes and then restarted approximately 18 minutes later. The HPCI system auxiliary oil pump provides hydraulic pressure required to open the HPCI turbine stop valve and the HPCI turbine control valve during initial HPCI startup. Failure of the HPCI auxiliary oil pump prevents the HPCI system from performing its design safety function.
The HPCI system was returned to operable status on February 20, 2015.
Event Cause The direct cause of the pump's intermittent failure was a poor electrical connection within the magnetic motor contactor coil (i.e., M-coil, General Electric Model 22D154G3A), which is part of the HPCI turbine auxiliary oil pump motor contactor 1-1XDA-B11-M.
Subsequent laboratory testing confirmed that the old M-coil intermittently failed after approximately 18 minutes of operation at an ambient temperature of 71 degrees F. Initial static electrical testing of the failed M-coil found no fault, but the coil did periodically present an open circuit (i.e., 180 MOhms) when exposed to temperature stresses, due to an apparent weak electrical connection at the terminal.
The most probable cause was determined to be long term thermal cycling. Laboratory analysis of the M-coil revealed signs of thermal cycling and material creep which led to a break in an electrical connection. When ' comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by internet e-mail to used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
Brunswick Steam Electric Plant (BSEP) 001 05000- 325 2015 - 01 the relay body was cold, the connection was able to pass current and energize the coil. But as the coil warmed, thermal expansion broke the weak connection, interrupting the circuit and de-energizing the auxiliary oil pump motor.
Safety Assessment The safety significance of this event was minimal. The HPCI system is an emergency core cooling system (ECCS) designed to inject water into the reactor vessel. Backup systems to the HPCI system include the RCIC system, ADS, LPCI system, and CS system. These backup systems were all operable at the time of the event. The HPCI system was restored to operable status within the 14 day Technical Specification Completion Time.
Corrective Actions
Any changes to the corrective actions and schedules noted below will be made in accordance with the site's corrective action program.
The following corrective actions have been completed:
- The coil was replaced and the HPCI system was returned to operable status on February 20, 2015.
Based on the age of the M-coil (i.e., about 38 years), a one-time replacement is expected to prevent recurrence of this failure through the end of licensed operation for BSEP. Therefore, no periodic replacement was recommended.
Previous Similar Events
A review of LERs for the past five years identified the following previous similar occurrence.
governor operation caused by a failed ramp generator signal converter (RGSC) operational amplifier. The root cause of the RGSC failure is the lack of a replacement preventive maintenance (PM) task for the RGSC. The corrective action to prevent recurrence for this event is to establish the appropriate PM for periodic replacement of the RGSC on both units' HPCI systems Since the causes of the events were different, the actions from LER 1-2012-004 could not have reasonably been expected to prevent the condition reported in LER 1-2015-001.
Commitments No regulatory commitments are contained in this report.