Energy Northwest said the plant ran continuously, except for 10 days of maintenance in May, and generated 9.34 million megawatts for the regional grid.
The nuclear plant accounts for nearly 10 percent of the electricity generated in Washington, enough to power Seattle.
Energy Northwest said the Columbia Generating Station has remained online for more than three years without any unplanned outage.
Energy Northwest is an association of 27 public utilities.
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