At 4:40 p.m. Central Time Tuesday, officials at the South Texas Project nuclear power plant near Bay City, Texas, notified the NRC’s Operations Center that a fire had broken out in the main transformer of Unit 2, causing an automatic shutdown. Unit 1 was unaffected and continued to operate at full power.
As designed, the plant’s emergency diesel generators energized to power safety-related equipment. All four auxiliary feedwater pumps started as required to supply power to the plant’s steam generators for cooling. However, power to non-safety related electrical buses was lost, cutting off power to the plant’s reactor coolant pumps. As part of the plant’s design, natural draft circulation continued to cool the plant’s shutdown reactor to remove decay heat.
The plant declared an Unusual Event – the lowest of four categories of nuclear emergency — due to the transformer fire at 4:55 p.m. The plant’s on-site fire brigade responded and quickly extinguished the blaze, so no off-site assistance was required.
The NRC’s resident inspector, who was on-site at the time, responded to the event by going to the plant’s control room to observe the licensee’s response to the event. The NRC’s Region IV Office in Arlington, Texas, activated its Incident Response Center to monitor the event.
There were no personnel injuries and no radiological releases were reported. The Unusual event was terminated at 7:47 p.m., although the NRC’s resident inspector remained onsite until about midnight.
As part of its ongoing oversight, the NRC will monitor the licensee’s follow-up actions. These include identification of the cause of the transformer fire; a review of the behavior of the plant’s electrical protection systems; and various repair activities.
“Overall, from what we now know, plant operators responded well to the event,” said Acting Deputy Regional Administrator Steve Reynolds. “The NRC will conduct an independent and comprehensive assessment of this incident as part of its oversight process.”