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The National Security Council intervened to block a study by the Arms Control and Disarmament Agency (ACDA) into the maintenance of the US nuclear weapons stockpile, according to the scientist who had been about to undertake the study.

Ray Kidder, a veteran nuclear weapons designer, was informed last month by ACDA that his help was no longer needed because the Department of Energy (DOE) would not give him access to a 1990 classified study of weapon remanufacture. Kidder believes that access was refused because of his public criticism of the DOE's stockpile stewardship programme — most notably an article in Nature last spring (see Nature 386, 645; 1997).

In the article, Kidder questioned the need for the stockpile stewardship programme, which uses supercomputers and major new experimental facilities to simulate nuclear weapons. He proposed a smaller alternative which would maintain the weapons by remanufacturing components as they age.

Carmen MacDougall, deputy assistant secretary for communications, says that the DOE “fully supports the need for ACDA to review the study” and that it gave the agency a technical briefing on its contents. “We offered ACDA the briefing and they accepted it,” she says. “The allegations of retribution and revenge are baseless and bizarre.”

The issue is sensitive for the US government. President Bill Clinton is trying to win Senate ratification for the Comprehensive Test Ban Treaty this year, on the basis of as broad a coalition of support as possible for the $4.5 billion-a-year stockpile stewardship programme.

In November, Pierce Cordon of ACDA wrote to Kidder asking him to work for the agency as a consultant, to help determine “whether the US can be confident of weapons using remanufactured components”. Cordon's letter asked Kidder to review the previous, classified study, which DOE conducted for Congress in 1990.

Kidder has the security clearance to access the study, provided he has a “need to know”. A request for permission was referred to the office of Vic Reis, assistant secretary at DOE. According to Kidder, Reis could not dispute his need to know, and therefore asked Robert Bell, special assistant to the president at the National Security Council, to press ACDA to stop the study.

“My information is that Bell called ACDA and told them not to allow this to go forward,” says Kidder.

But MacDougall denies that Reis asked Bell to block the study.