Workers at the Hanford Nuclear Reservation are shown on the job near a tank farm where highly radioactive waste is stored underground near Richland, Washington, in 2010.

Workers at the Hanford Nuclear Reservation are shown on the job near a tank farm where highly radioactive waste is stored underground near Richland, Washington, in 2010.

Shannon Dininny/AP

The U.S. Department of Energy is proposing a seven-year plan to clean up a radioactive waste spill under a building on the Hanford Nuclear Reservation.

The structure is known as the 324 Building and is located on the former nuclear weapons production site near Richland.

Contractor Washington Closure Hanford wanted to have the building down in the fall of 2013. But the company discovered a highly radioactive spill under the building from a hot cell leak.

The Tri-City Herald reports the building is 1,000 feet from the Columbia River. There is no evidence that the spill has migrated toward the river.

After the leak was discovered, a new plan was developed to install remotely operated equipment to clean up the spill.

Hanford for decades made plutonium for nuclear weapons.