SPOKANE, Wash. (AP) - Some workers on the Hanford Nuclear Reservation have decided to stop working in some of the radioactive waste tank farms because of safety concerns over chemical vapors.

Hanford for decades made plutonium for nuclear weapons, and now contains millions of gallons of radioactive waste stored in 177 underground tanks in southeastern Washington. The government is spending $2 billion a year to clean up the site.

The Hanford Atomic Metal Trades Council on Monday issued a "stop work" order at the double-walled tanks that contain dangerous wastes from the past production of plutonium for nuclear weapons.

Council President Dave Molnaa said workers are demanding they be supplied with bottled air when they work at any of the tank farms. Currently, bottled air is required only when working among the older, single-walled underground tanks.

Officials for Washington River Protection Solutions, the private contractor that operates the tank farms for the U.S. Department of Energy, confirmed the work stoppage at the double-walled tank farms.