The Northwest’s only commercial nuclear power plant reconnected to the electric grid Sunday morning after a short shutdown, just in time to power air conditioners during a heat wave forecast for parts of Washington, Oregon and Idaho.

The Columbia Generating Station came back from its biennial refueling outage on June 16 after the nuclear reactor was shut down for 65 days.

The planned outage was to switch out a third of its 764 nuclear fuel assemblies in the reactor core with new fuel and for both major and minor maintenance projects that could not be done while the reactor is operating.

The work, which required an additional 2,000 workers to be hired, was timed to match the spring snow melt and runoff in the Northwest, when hydroelectric generation is high and the impact of a temporary halt to nuclear power production is minimized.

The Columbia Generating Station, about 10 miles north of Richland in Eastern Washington, is the third largest electricity generator in Washington state, producing enough electricity to power the equivalent of about 1 million homes.

But after the nuclear plant reconnected to the grid and reached 80% power following the refueling outage, turbine vibration readings increased to higher than expected, preventing full-power operation of the plant.

The plant was taken off the grid on Monday, June 23, for a turbine rebalancing procedure.

A similar turbine rebalance needed in December 2021 also required temporary disconnection from the grid.

Over the past week, Energy Northwest workers installed two 24-ounce balance weights on the main turbine. The weights are designed to minimize vibration and allow optimal performance of the turbine.

Energy Northwest will continue to monitor vibration levels to determine whether any additional balancing is needed to support safe and reliable operation throughout the station’s next two-year operating cycle.

Columbia’s turbine system includes three low-pressure turbines and one high-pressure turbine, with a combined rotating mass of about 1.2 million pounds.

Precise alignment and balance are essential for reliable operation, as the turbines drive the main generator to produce electricity for the region, according to Energy Northwest.

The plant is back on the grid and powering up as the National Weather Service forecasts a heat wave Monday and Tuesday across Central and Eastern Washington and extending into Idaho and Oregon. A heat advisory had been issued.

During this spring’s refueling outage, a major project was accomplished — installing a new adjustable speed drive system. The system needed to be replaced after there were a few issues that required powering down to fix components.

The speed drive controls the pumps that control the water inside the core, which in turn controls the amount of power the reactor produces, according to Energy Northwest.

The heat produced by a chain reaction boils the water within the core, creating steam that turns turbines attached to an electric generator.

Other work included repairing the circulating water basin, electrical generator inspection and replacing a reactor recirculation pump and motor.

Electricity produced by the nuclear power plant is sold at cost to the Bonneville Power Administration for distribution.

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