Entergy (NYSE:ETR) said June 30 that its internal investigation found that a May 9 transformer fire at the Indian Point 3 nuclear plant in Buchanan, N.Y., was caused by a failure of insulation.
The fire happened May 9 and Entergy returned the nuclear unit to service around May 26.
The Nuclear Regulatory Commission (NRC) is also examining the cause of the fire and subsequent leakage of fluid into the Hudson River. NRC said May 19 that it a three-member NRC team was immediately starting a special inspection at the facility. Results of the NRC investigation should be available soon.
The accident triggered much media attention around New York City and provided more ammunition for critics who oppose 20-year license extensions for Indian Point Units 2 and 3. The long-running proceedings on the future of the nuclear units are continuing before the NRC.
Entergy said the failure of insulation caused a main transformer to short-circuit and catch fire. The company also said its internal investigation confirmed that water and foam used to extinguish the fire, together with fluid from the transformer on the plant’s non-nuclear side, exceeded a containment system’s capacity.
Since the fire and the plant’s safe shutdown, the transformer has been replaced, Unit 3 has returned to service, and no remediation was warranted at most locations of reported sheens from fluids that reached the Hudson River, Entergy said in its June 30 news release.
“We have been working closely with independent engineers, and with federal and state agencies, to address issues surrounding the May 9 transformer failure, and corrective actions are well under way,” said Entergy Wholesale Commodities President Bill Mohl. EWC is the Entergy affiliate that owns Indian Point.
Entergy’s engineers and an independent engineering firm traced the transformer problem to the failure of internal insulation that caused a short circuit in a high-voltage winding coil. Indian Point’s transformers are tested routinely for signs of degradation but no immediate problems were identified prior to May 9 in the unit that failed. While additional forensic work on the transformer is still under way, Entergy is reviewing the initial findings to identify potential corrective actions.
Entergy’s investigation into the release of the transformer’s dielectric fluid — a clear mineral oil that acts as an electrical insulator and coolant — to the ground and ultimately the Hudson River confirmed that automatic sprinkler systems dispensed more water than the capacity of the moat containment system. Some of this fluid mixed with firefighting water and foam, and then flowed from the moat into a storm drain leading to the plant’s discharge canal and ultimately the Hudson River. Contractors placed sorbent and hard environmental protective booms in and outside the discharge canal and removed fluid that had spilled in the transformer yard, storm drains and adjacent areas.
As previously reported, the U.S. Coast Guard, using data from the National Oceanographic and Atmospheric Administration (NOAA), estimated about 3,000 gallons of dielectric fluid reached the river. During operation, this transformer contained 24,300 gallons of dielectric fluid.
About 8,300 gallons of fluid have been recovered from the moat beneath the transformer, inside the transformer, drains and areas around the transformer yard, or were combusted.
Contractors are investigating the transformer yard and other areas onsite to see if more transformer fluid can be recovered and prevent any potential migration.
Indian Point Units 2 and 3 are both pressurized water reactors (PWRs) and each is listed with an operating capacity of roughly 1,000 MW.