It’s unclear just when the Columbia Generating Station will be back in operation.

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The Columbia Generating Station, near Richland, has been shut down since Sunday morning because of an equipment malfunction at a Bonneville Power Administration (BPA) substation that connects the state’s only nuclear-power plant to the grid.

Because of the malfunction, the Columbia Generating Station lost a 500-kilovolt transmission line, and that forced an automatic safety shutdown of the reactor at 11:24 a.m. Sunday.

It’s unclear just when the plant will be back in operation; transformers and other equipment must be inspected.

“It’s not weeks, but days,” said Mike Paoli, spokesman for Energy Northwest, which runs the plant as part of the region’s public power-supply system.

The 1,190-megawatt plant can generate enough electricity to power Seattle. On a typical day, that power, which is supplied to the BPA, is worth about $1 million, according to Paoli.

Later Sunday, a leak was detected in a high-pressure flow line that is part of the plant’s safety system.

The leak was not classified as an emergency, but its location compromised the integrity of the plant’s “primary containment,” according to a report filed with the Nuclear Regulatory Commission.

It is unclear whether the leak was related to the plant’s shutdown. Paoli said the leak in the flow line has been fixed.

Kevin Wingert, a BPA spokesman, said the malfunction is under investigation. It appeared to be related to a breaker that did not operate properly when a line went down, possibly from subzero temperatures.

The problem must be resolved so it doesn’t force the power plant to shut down again, he said.