RICHLAND, Wash. -- A small amount of hydrogen gas trapped in a pipe at a Washington nuclear power plant ignited in a brief, six-inch flame Thursday when workers cut into the pipe, a utility spokesman said.
No one was injured and no equipment was damaged in the "puff," which Energy Northwest spokesman Mike Paoli said lasted less than a second. Still, the Columbia Generating Station declared an "unusual event" and temporarily evacuated the immediate area.
Officials notified the Nuclear Regulatory Commission.
The pipe is located in the plant's main turbine building, which is a non-nuclear area, Paoli said.
"There's no association whatsoever with the reactor building or radiation," he said.
An "unusual event" describes a condition at a commercial nuclear power plant or its surroundings that could potentially compromise normal safety levels. It's the least serious of four NRC emergency classifications.
The plant is located on the Hanford nuclear reservation in southcentral Washington.
The Columbia Generating Station began a scheduled refueling outage on Wednesday that will keep the plant off line until mid-June.
The gas ignited during work that is part of the refueling outage.
During normal operations, the pipe is filled with water and some hydrogen, which is used to cool the generator, the spokesman said.
Paoli said the pipe had been closed and purged of gas -- "or so they thought" -- when a small amount of residual trapped gas escaped when workers cut the pipe.
He said he wasn't sure how many people were evacuated.
After a safety inspection by Columbia officials, "work resumed in the general area after an hour and a half or so," he said.
Energy Northwest is a joint operating agency including 28 public power member utilities. It operates a mix of hydroelectric, solar and wind energy projects as well as the nuclear plant.