05000397/LER-2015-002
| Docket Number | |
| Event date: | 04-29-2015 |
|---|---|
| Report date: | 06-26-2015 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3972015002R00 - NRC Website | |
(01-2014) Estimated burden per response to comply with this mandatory collection request: 80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br />.
Reported lessons learned are incorporated into the licensing process and ted back to industry.
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Columbia Generating Station YEAR SEQUENTIAL REV
Event Description
On April 29, 2015, it was determined that the Division 1 120/240 volts alternating current (VAC) vital instrumentation bus [ED] had been inoperable since July 1993. This was the result of a plant modification that added a vendor control panel for the reactor building effluent monitor [ILQ containing a Non-Class 1 E cooling fan with only a single fuse [FU] isolation protection. A coordination study was conducted to provide a detailed review for the electrical coordination of the Division 1 120/240 VAC bus. This detailed review revealed that there was an electrical coordination issue with this bus and a Non-Class 1 E electrical cabinet cooling fan [FAN] load that may occur under very limited conditions. In the event that a short circuit occurs in the cooling fan coincident with a loss of off-site power, there was not an adequate isolation device between the Class 1 E source and the Non-1 E load such that the fault on the cooling fan could potentially impact the Division 1 120/240 VAC bus and cause an under voltage condition due to the limitations in the short circuit design capacity of the associated inverters [INVT].
Cause
The root cause evaluation is still in progress; however, a preliminary root cause is provided. If the final root cause for the completed evaluation is significantly different, a supplement will be submitted.
The direct cause was a vendor provided electrical panel for the reactor building effluent radiological monitor was not wired adequately to meet circuit isolation requirements as required by the procurement specification.
The root cause was that the modification to install the reactor building effluent radiological monitor in 1993 was implemented without verifying the vendor information.
Extent of Condition Based on the coordination study, there are no additional concerns with the Division 1 120/240 VAC bus. All Non-Class 1 E loads were removed from the Division 2 120/240 VAC bus during the 2015 refueling outage so there is no concern with this bus.
Immediate Corrective Action The cooling fan was disconnected to remove the possibility of a fault impacting the Division 1 120/240 VAC bus.
Further Corrective Actions A fuse was added to the configuration to provide adequate electrical isolation between reactor building effluent radiation monitor cabinet cooling fan and the Division 1 120/240 VAC bus.
26158A R3 NRC FORM 366A (01-2014) Operating Experience & Previous Occurrences Columbia has not experienced similar occurrences in the past, based on a review of Licensee Event Report historical records.
Assessment of Safety Consequences
The safety consequences for this issue are very low. This event can only happen when a fault occurs in the cooling fan coincident with a loss of off-site power. The loss of power condition for the Division 1 120/240 VAC bus will result in most of the components failing to their safety position. This loss of power condition for the bus will only exist until the bus is repowered from the emergency diesel generator (within 15 seconds). The emergency diesel generator has sufficient capacity to clear the fault and repower the bus. Additionally, the Division 2 120/240 VAC bus would still be available.
Energy Industry Identification System Information Energy Industry Identification System Information codes from IEEE Standards 805-1984 and 803-1983 are represented in brackets as [X] and [XX] throughout the body of the narrative.
26158A R3 NRC FORM 366A (01 -2014)