Shares of Perma-Fix Environmental Services rose to a one-year high Wednesday after the company said it was awarded part of a $4.37 billion U.S. government contract to treat and dispose of nuclear waste.

The stock was up 18% at $20.96 in early trading.

The Atlanta-based nuclear-waste treatment company said the subcontract, awarded by Hanford Tank Waste Operations & Closure, covers the treatment and disposal of pretreated liquid mixed low-level waste from the U.S. Energy Department's Hanford site in southeastern Washington.

The multiple-award contract has a maximum cumulative value of $4.37 billion and covers as much as 50 million gallons of waste. That maximum value is to be shared among all companies awarded subcontracts, however, and is not solely destined for Perma-Fix.

The company will perform the work at its Perma-Fix Northwest facility in Richland, Wash., near the Hanford site.

The Hanford site, a former nuclear-production complex, contains some of the country's largest inventories of radioactive and hazardous waste. The DOE has been working for decades to clean up millions of gallons of waste stored in underground tanks at the site.

Perma-Fix said it had invested in its Richland operations in anticipation of the program, including upgrading facilities, purchasing large-scale treatment equipment, hiring and training workers and acquiring land connecting its facility to a short-line railroad serving the Port of Benton.

Perma-Fix said the U.S. government would retain legal title to and responsibility for the waste under the agreement.