A small amount of hydrogen gas ignited in a six-inch flame at a Washington nuclear power plant Thursday when workers cut into a pipe, a spokesman said.
Columbia Generating Station declared an "unusual event," evacuated plant areas near the pipe for about 90 minutes, and notified the Nuclear Regulatory Commission.
No one was injured in the one second-long "puff" of gas that had been trapped in the pipe in the plant's non-nuclear turbine building, Energy Northwest spokesman Mike Paoli said.
Paoli said there was "no association whatsoever with the reactor building or radiation."
Workers had shut the reactor down on Saturday to begin the process of changing out the fuel rods, KIRO-TV reported. The bi-annual process takes about 30 to 45 days to complete, the station said.
The pipe that released the gas is typically filled with water and hydrogen, which are used to cool the generator, The Olympian reported. Paoli told the newspaper the pipe had been closed and cleaned out — "or so they thought" — at the time of the incident.
An "unusual event" describes a condition that could potentially compromise normal safety levels, the least serious of four NRC emergency classifications.