The nuclear power plant near Richland has been returned to normal oversight, after the Nuclear Regulatory Commission reversed a March decision.
It decided that the Columbia Generating Station should have been included in the list of plants in the nation that are top performers and receive normal oversight based on performance in 2017.
"We're pleased with such a thorough re-assessment from the independent Nuclear Regulatory Commission, which places us in the top performance level for public safety," said Grover Hettel, Energy Northwest's chief nuclear officer.
The NRC notified Energy Northwest, which operates the Pacific Northwest's only commercial nuclear power plant, on Thursday that it had retroactively rated Columbia Generating Station in the top performance category.
"That's good news for the economic health of our community, as well as our state and region," Hettel said. "That's because Columbia carries the load in the cold and dry seasons, and provides grid flexibility during periods of oversupply."
In March, the NRC had told Energy Northwest that its annual assessment had found an issue with two unexpected scrams, or shutdowns, with complications during a four-quarter period.
As a result, Columbia Generating Station would remain on the 2018 list of plants requiring increased oversight by the NRC. However, just one additional inspection was needed to remove it from the list.
The NRC said then that 83 of the nation's reactors met all safety and security performance objectives and would have standard oversight. But the plant near Richland was among 13 plants needing additional inspection and follow-up corrections.
One of the scrams at issue was in August 2017, when plant operators shut the plant down after an air removal valve in the plant's turbine building closed. It caused a loss of vacuum pressure in the system that turns steam back into water for reuse on the plant.
Initially, the scram was reported by Energy Northwest has having complications.
But the NRC now has determined that the shutdown did not meet one of the criteria on its list of what is considered a complication in a scram.
Energy Northwest did have a scram with complications in December 2016, but that was not enough by itself to pull down the plant's NRC ranking.
Unusually cold weather caused the loss of the 500 kilovolt line connecting the nuclear plant's main output transformers to the Bonneville Power Administration's nearby Ashe Substation.
The NRC uses a color-coded performance matrix for commercial nuclear reactor performance. The NRC says all of Columbia Generating Station's are now in the expected "green" band, after the one "white" finding was reversed.
This month the Columbia Generating Station had another unplanned scram. It's too soon to know how that will affect the plant's evaluation by the NRC.
The plant's main power transformers automatically disconnected from the transmission system following a grid disturbance May 18. The transformer's protection system detected an issue and tripped, which caused the main generator also to trip and the plant to stop operating.
There was no threat to public health or safety.
A part of the transformer that tripped has been sent off-site for analysis, with no information available yet on the exact cause of the scram.
The plant reconnected to the grid May 24.