For the last half-century, the US government has taken care to maintain a strict separation between civilian and military nuclear reactors and related technologies. Then last month, the Department of Energy (DOE) started manufacturing tritium for nuclear weapons at the Watts Bar civilian nuclear plant, owned by the Tennessee Valley Authority.

During a scheduled refueling at Watts Bar last month, four lithium-filled rods were loaded into the reactor to produce tritium. The Nuclear Regulatory Commission approved the plan on 16 September, despite protests that civilian nuclear programmes should be separate from military ones and that the move would have a negative effect on efforts to prevent the spread of nuclear weapons.

The DOE started using civilian reactors for tritium production because its own reactors have broken down and its current supplies are decaying. An order signed by the US president, Bill Clinton, specifies that the country has to be able to make more tritium by the year 2005.