05000397/LER-2004-002
| Docket Number | |
| Event date: | |
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| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident |
| 3972004002R00 - NRC Website | |
Description Of Event On February 21, 2004, Columbia Generating Station (Columbia) was in Mode 1 with the reactor operating at approximately 100 percent of rated thermal power. At approximately 08:41, the control room received alarms for Reactor Core Isolation Cooling System (RCIC) Division 1 Out Of Service and Motor Operated Valve Network Power Loss. Investigation found that motor operated valve RCIC- V-13 (RCIC reactor pressure vessel injection valve) position indication lights were deenergized, indicating a loss of control power. The RCIC system was declared inoperable and the High Pressure Core Spray system (HPCS) and the HPCS dedicated diesel generator (DG-3) were verified operable and placed in protected status.
An operator was dispatched to investigate the problem and reported that the disconnects to the RCIC-V- 13 motor operator were shut and the overloads were reset. RCIC-V-13 still indicated deenergized in the control room. Maintenance was contacted and a work request was initiated to investigate.
Maintenance determined that an under-voltage relay (27 relay) in the RCIC-V-13 motor starter (RCIC- 42-S2IA5B) cubicle had failed.
The function of this under-voltage relay is to sense a loss of voltage (250 Volts DC) to the valve motor operator and to interrupt the 125 V DC control power to the valve motor operator and provide .annunciation in the control room. In this case, the relay failure had the same effect as a loss of voltage to the valve motor operator. It was later determined that RCIC-V-13 motor operator power was available. However, the failed relay interrupted control power to the valve motor operator.
A new relay was bench tested and installed. Operators verified the indication to RCIC-V-13 was working properly and declared the RCIC system operable on February 21, 2004, at approximately 21:29.
Cause of Event
_ - The relay that failed was an ITE Model J13P20 relay rated at 250 V DC. This particular relay is normally energized. A failure analysis determined the relay coil had failed due to a shorted coil and that the coil was subjected to long term heating. No evidence has been found to indicate this relay had been replaced prior to this event.
A root cause analysis was performed and identified this relay was not included in the preventative maintenance program. During the 1990s, industry experience and plant operating experience identified that normally energized relay failures were occurring due to thermal aging (reference NRC Information Notice 92-27 and 92-27 Revision 2). Energy Northwest took action during this time period to review relay failure trends and determine what preventative actions were required. The reviews showed that Columbia had experienced failures of normally energized relays involving different manufacturers. As a result, critical relay types were identified and periodic replacement schedules were developed. The developed. The relay population reviewed were those that had unique identification numbers and were included in the plant Master Equipment List (MEL). The MEL includes plant components that have Equipment Part Numbers (EPNs). Not all plant sub-components have EPNs. The relay that failed during this event does not have a specific EPN. Therefore this relay was not in the MEL and was not captured during the reviews in the mid-1990s.
Safety Significance
The RCIC system is designed to operate either manually or automatically following reactor pressure vessel isolation accompanied by a loss of coolant flow from the feedwater system to provide adequate core cooling and control of reactor pressure vessel water level. Under these conditions, the HPCS and RCIC systems perform similar functions.
After the loss of RCIC, control room operators entered Technical Specification (TS) Action Statement 3.5.3.A, which requires that with the RCIC inoperable, the High Pressure Core Spray must be verified operable immediately and the RCIC system restored to operable status within 14 days. Since the HPCS was operable and protected and the total duration of this event was approximately 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> 48 minutes, the TS requirements were satisfied. In addition, the relay failure did not affect the ability of the RCIC- V-13 to be controlled from the remote shutdown panel. Therefore, it is concluded that this event posed no threat to the health and safety of the public or plant personnel.
This event is reported in accordance with 10 CFR 50.73(a)(2)(v)(D), "Any event or condition that alone could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident.
Immediate Corrctive Actions Control room operators_ entered and complied with TS Action Statement 3.5.3.A,.by verifying that HPCS was operable. Operators then proceeded to protect HPCS and its dedicated diesel generator (DG-3). A work request was initiated, and the investigation determined that the reason for the loss of control power and indication to RCIC-V-13 was a failed undervoltage relay. The failed relay was replaced and the valve indication was verified to be working properly. RCIC-V-13 was inoperable for a period of approximately 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> and 48 minutes.
Further Corrective Actions 1. Thermography was performed on 43 installed normally energized relays in the DC distribution system. One relay was found to be approximately 18 degrees Farenheight warmer than the others of the same voltage rating. A work request was written to replace this relay.
26158 R2 2. Work requests will be generated to replace the currently known normally energized relays in the DC distribution system that do not have EPNs.
3. DC switchgear drawings will be reviewed to identify other normally energized relays and work requests will be created to replace any new relays that are found. Preventative Manitenance procedures (PMs) will be developed or enhanced to replace any additional normally energized relays identified in DC switchgear.
4. A selected population of 480 V AC switchgear drawings will be reviewed to search for normally --energized relays that do not have EPNs. Any relays identified will be replaced as necessary and PMs- developed as necessary.
5. Other selected DC system equipment, such as battery chargers and inverters, will be reviewed to identify normally energized relays that should be periodically replaced and PMs developed as necessary.
Previous Similar Events
This is the second known event involving this relay manufacturer/model or similar model at Columbia Generating Station. Maintenance Work Request (MWR) AS0640 replaced a defective undervoltage relay in the DC switchgear for RCIC-V-19 in June 1989. However, the exact relay failure mechanism was not described in the MWR.
There has been one previous reportable event due to a relay failure at Columbia Generating Station.
performance of a surveillance test of the of the high reactor water level turbine trip channel B logic.
This scram occurred because a normally energized Agastat relay in the redundant channel A logic had previously failed in an intermediate position.
Text Reference System Component Reactor Core Isolation Cooling System
BN
High Pressure Core Spray System BG RCIC-V-13 BN INV Diesel Generator-3 BN DG RCIC-42-S21A5B BN MSTR Under-voltage relay BN 27 26158 R2