Washington

Nuclear watchdogs and former weapons scientists are taking issue with a proposal to use weapons-grade uranium and plutonium at the US National Ignition Facility. The facility is supposed to help scientists assess the nation's ageing nuclear stockpile without testing the weapons themselves, but there are fears that it could now be used to design new warheads.

Opponents of new weapons were preparing to denounce the plan at public hearings this week in Washington and at the Lawrence Livermore National Laboratory in California, where the facility is located. They say that the proposal will speed the development of ‘mini-nukes’, which have been promoted by the Bush administration (see Nature 415, 945; 200210.1038/415945a). “Such experiments link directly to new, low-yield weapons,” warns Ray Kidder, a retired weapons physicist who was based at the Livermore laboratory.

Livermore officials deny that the research will be used to design new weapons. Instead, says laboratory spokeswoman Lynda Seaver, it will investigate how existing bombs detonate, so that the stockpile can be maintained without testing the weapons it contains.

The National Ignition Facility uses 192 high-power lasers to fuse hydrogen isotopes together, releasing energy. But part of its environmental-impact statement, released in February, announced plans to line the hydrogen fuel pellets with fissile materials, which would split apart under the laser light. The statement says that this is necessary “to accurately evaluate the properties of nuclear material in the laboratory and to validate weapons test data”.

Kidder and other critics question this claim. The move would allow researchers to optimize designs for low-yield nuclear weapons, he says. A 1995 Livermore panel on which he sat warned that such work might be seen as provocative by other nations, Kidder adds.

The environmental-impact statement also proposes doubling the amount of plutonium held at the laboratory and restarting a plutonium enrichment programme. “This work is going in the wrong direction,” warns Loulena Miles, a lawyer at Tri-Valley CAREs , an anti-nuclear weapons group based next to Livermore. “It is moving the laboratory towards weapons manufacturing.” But Seaver says that the statement is “only a proposal” for future activities at the lab.