​​​Every two years, Energy Northwest takes Columbia Generating Station offline for a refueling outage. ​​​​​​​​Columbia’s 26th refueling outage (R-26) will begin May 5, 2023 and is scheduled for 35 days. 

About 1,250 skilled workers, hired locally and from across the country, will join Energy Northwest’s workforce of about 1,000 e​mployees, to support refueling and maintenance projects. 

Workers will replace 248 of 764 nuclear fuel assemblies in Columbia’s core with new fuel. Fuel assemblies that have been in the reactor core for six years will be placed in Columbia's used fuel pool, which removes residual heat from the assemblies. 

After a minimum of five years in the pool, the used assemblies are moved to Columbia’s on-site dry cask storage, where they are stored securely in above-ground, 185-ton, concrete and steel, dry-storage casks. There are currently 54 casks on site, containing most of Columbia’s 38 years of used fuel​.​