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Bill Richardson, the US energy secretary, signed a statement of intent last week that will allow the United States to continue work on the International Thermonuclear Experimental Reactor (ITER) design until next July.

The move has relieved fears among other nations participating in ITER that a complete US withdrawal would paralyse the global fusion energy research project (see Nature 394, 511; 1998).

Richardson signed the statement at the International Atomic Energy Agency conference in Vienna, after coming under heavy pressure from Japanese, European and Russian officials. Russia is said by one source to have threatened to block important agreements on the disposal of nuclear weapons materials unless the United States stayed on board.

The statement says that the United States will participate in the three-year extension to the ITER engineering design activity — which Europe, Japan and Russia agreed to in July — for a period of one year. “Participation in this process will be subject to the availability of appropriated funds and is not a commitment to construct a device,” it says, reiterating the US desire for “a new international agreement on fusion science”.

Richardson called Joseph McDade (Republican, Pennsylvania), chairman of the House appropriations subcommittee which funds his department, from Vienna to obtain his agreement to the statement. But both the agreement and the call to McDade infuriated another congressman, James Sensenbrenner, the chairman of the House Science Committee, who was not consulted.

Sensenbrenner immediately issued an angry statement condemning the deal, and describing the decision as “irresponsible”. He added: “The project has failed and it's time to move forward. It defies common sense that the United States should agree to continue to participate in a dead-end project that continues to waste the American taxpayer's dollars”.

Energy department officials were surprised at the vehemence of this, pointing out that Sensenbrenner had previously said that he was neutral on ITER, and merely wished McDade's concerns to be addressed. Ernie Moniz, the energy undersecretary, wrote to Sensenbrenner on his return from Vienna saying that the twelve month agreement will “allow for an orderly closing out of US participation under the existing agreement, and a reasonable transition to a new one.”

Even at that, the statement was greeted with relief in the US fusion community. “I'm very, very pleased,” says Anne Davies, head of fusion energy sciences at the Department of Energy. “This gives us a way forward.”

Susumu Nakamura, director of fusion energy at Japan's Science and Technology Agency, says: “It is encouraging that the United States is at least showing some willingness to continue with the ITER collaboration”. But he also says that the STA “believes that the one year extension is renewable,” a view which Moniz's letter appears to contradict.