Work has begun on a protective enclosure for a former reactor on the US Department of Energy's Hanford site in Washington State. The K East Reactor is the seventh at the site to be placed in interim safe storage.

Caption: Contractor Central Plateau Cleanup Company places the structure's steel columns - each weighing up to 28 tons - around the reactor (Image: DOE EM)

The K East Reactor was built to produce plutonium for US defence purposes and operated from the mid-1950s until 1971. The steel cocoon is designed to protect the reactor building while the radioactivity in the deactivated reactor core decays over the next several decades, making it safer and easier to complete disposition of the reactor in the future.

Construction of the structure's steel frame, which is one of the DOE Office of Environmental Management's key construction priorities for 2022, could begin after workers finished backfilling and compacting the area around the former reactor before pouring a 6-foot (1.8-metre)-thick concrete foundation to support construction of the cocoon. The first steel columns for the enclosure were placed in mid-May.

The structural steel skeleton, with metal siding on the walls and roof to fully enclose the building, is expected to be finished by the autumn. The completed structure will be more than 150 feet wide and 120 feet tall, and has been designed to allow for routine inspections of the reactor, which will take place every five years.

According to the DOE Office of Environmental Management, about 80% of the buildings and auxiliary structures needed to support reactor operations are demolished and removed before cocooning takes place. The remaining 20% of the reactor complex, including the reactor core itself, is enclosed in a cement and steel, airtight and watertight structure which prevents any remaining radiation or contamination from escaping to the environment.

The Hanford site was established in 1943 as part of the Manhattan Project. Cleanup of the site is now managed by DOE's Richland Operations Office and the Office of River Protection. K East's "sister" reactor, the K West Reactor, will be the last of Hanford's nine plutonium production reactors to be cocooned. One reactor - the B Reactor - has been preserved as part of the US National Park Service's Manhattan Project National Historical Park.

DOE has shared a time-lapse video of the construction of the steel structure.

Researched and written by World Nuclear News