A reactor unit at the Palo Verde Nuclear Generating Station in Arizona was nearly back to full production Friday after what its operator described as a minor explosion in a cabinet that held electrical switching gear.
Arizona Public Service Co. reported the Tuesday night incident as an "unusual event," the lowest of four emergency levels classified by the federal Nuclear Regulatory Commission. The company and an inspector with the regulatory commission said no radioactive material was released.
Palo Verde's Unit 1 automatically reduced its power production to 60 percent but started ramping back up Thursday, reaching 95 percent by early Friday afternoon.
APS spokesman Betty Dayyo said the explosion consisted of arcing inside a cabinet, called a "load center," that routes electricity to equipment in a turbine building. "This is really a minor incident," said Dayyo, adding the cause was under investigation.
Palo Verde's own fire department responded but found no fire, APS said.
Arizona, California, New Mexico and Texas utilities own the three-reactor plant, 50 miles west of downtown Phoenix.
John Reynoso, the Nuclear Regulatory Commission's senior on-site inspector for Palo Verde, said he went to the plant right after the evening incident and inspected the load center.
He said it was blackened by an apparent flash-over but said he saw no immediate indication of shortcomings that would indicate a broader problem.
NRC inspectors will monitor the operator's investigation, Reynoso said. "We're real interested in how they learn from this."
APS and another Arizona utility, the Salt River Project, own the plant along with Public Service Co. of New Mexico, El Paso (Texas) Electric Co, Southern California Public Power Authority, Southern California Edison Co. and the Los Angeles Department of Water and Power.