A special investigation is underway at Progress Energy’s Brunswick nuclear plant near Wilmington, NC, after a highly unusual mishap caused boiling water to flow out of a reactor chamber not sealed properly, Nuclear Regulatory Commission (NRC) officials said.
Inspectors will spend much of next week at the twin reactor Brunswick plant to determine what went wrong, NRC officials said.
The incident at the Unit 2 reactor posed no risk to Progress employees or to the public, and Brunswick’s Unit 1 reactor has continued to generate electricity without interruption. Raleigh-based Progress also is investigating.
The NRC will issue a report within 45 days of the special inspection, which could include fines and other enforcement actions. A special inspection involves NRC specialists pulled from agency headquarters near Washington, regional offices around the country or other nuclear plants to work with NRC’s on-site inspectors at the affected plant to determine how the malfunction happened.
Brunswick’s Unit 2 reactor shut off since operators discovered the overflow early morning Wednesday. At one point, moderately radioactive water, coming directly from the reactor core, poured out of the reactor vessel at 10.1 gallons per minute, about 100 times more volume than would flow out under normal circumstances.
The water that escaped came from the reactor core where it had been in contact with nuclear fuel. The water collected in a drain for normal processing of low-level nuclear waste. The cause of the leakage was an improperly fastened reactor lid. The reactor vessel functions as a giant teapot that boils water with an infused element — in this case, nuclear fuel rods — to generate steam at high pressure which then runs an electric generator.
The NRC inspection will look to determine why the vessel lid was ajar.
Because it was not fastened properly, as pressure built up in the reactor, the cover became unsealed, said Randy Musser, NRC branch chief based in Atlanta whose unit oversees all Progress Energy nuclear plants in the Carolinas.
The water pressurizes at 1,000 pounds per square inch and boils at more than 600 degrees Fahrenheit.
Brunswick operators had just completed a planned outage for repairs and replacement of components Wednesday, and began engaging Unit 2 to ramp up to full power.
The unit reached 7 percent of power capacity before it shut off. The water likely overflowed for about four hours when plant monitors detected it.
“It’s more embarrassing than it is a safety near-miss,” said David Lochbaum, a former NRC engineer now with the Union of Concerned Scientists safety watchdog organization.