NEWS France and US in late conversion to 'zero-yield' nuclear test ban

Paris. Prospects for the introduction of a Australia - which has pressed for a zero­ the Clinton administration will seek to Comprehensive Test Ban Treaty ( CTBT) yield test-ban treaty - said France had reverse. were revived last week after France con­ taken "an important step forward", adding The JASON panel found that "a persua­ firmed that it will support a ban on all that if the decision is confirmed in the treaty sive case has not been made for the utility of nuclear tests, no matter how small, from it would be a "major breakthrough, exactly hydronuclear tests" in monitoring the relia­ next year (see Nature 376, 283; 1995). the commitment that we have asked from bility of the weapons stockpile. The tests The French decision - which has been France". could help to confirm the safety of the interpreted as an attempt to turn the tables The announcement by Clinton that the weapons in the event of accidental detona­ on critics of its planned series of tests in the tion of one of their explosive charges, the South Pacific - was immediately followed panel said, but "the US arsenal has neither a by a similar endorsement of a total test ban present nor anticipated need for such re­ by the US President Bill Clinton. "I applaud confirmation". the French statement," he said. "It will make Hydronuclear experiments are used to it much easier for us to get a comprehensive obtain information on the fission phase of a test ban." nuclear explosion. What distinguishes an Indeed, the French and US statements HNE from a nuclear test is that the chain will break the deadlock in negotiations on reaction is stopped before a full yield explo­ the CTBT at the Conference on Disarma­ sion occurs. HNEs were developed in the ment in Geneva, where the permanent five US so that they could continue research nuclear weapons-state members of the Unit­ during the 1958-1961 test ban, when at least ed Nation's Security Council -France, the one new weapon was developed using United States, China, Russia and the United HNEs. Kingdom - have been considering intro­ The panel also assessed the usefulness of ducing a loophole in the ban that would other types of nuclear tests and experiments allow low yield nuclear explosions of up to 1 that have been proposed as alternatives to kiloton (see Nature 376,283; 1995). full-scale weapons testing. It Although such tests would not allow full found that 'reduced yield' tests testing of conventional nuclear weapons, of up to 500 tonnes TNT equiva­ observers argue that they would provide lent yield from fission could help nuclear states with data that would give to ensure stockpile reliability. them added confidence in a new design. But such tests would be useful Non-nuclear weapons nations oppose a only if they were continued treaty containing such a loophole, as they indefinitely, it said, so the US consider it would drop disarmament from should not propose them unless the goals of the CTBT. United States will also push for it intends to downgrade the By ruling out large tests, the US and what he described as a "true- Comprehensive Test Ban Treaty France will make the treaty easier to accept zero" test ban, ends months of to a threshold test-ban treaty. for non-nuclear nations that are either argument within the administra- Chirac: turns tables on Clinton subsequently announced unable or unwilling to carry out such tests. lion about the need for critics of Pacific tests. that the US will push for a ban These nations agreed to an indefinite exten­ hydronuclear and other low- on such low-yield tests, which sion of the Nuclear Non-Proliferation Treaty yield nuclear tests, and comes after a panel some in the Pentagon had wanted to (NPT) earlier this year on the understanding of leading physicists and weapons designers conduct. that a test ban would be sufficiently compre­ ruled that the US does not need such tests to But the panel said that so-called hydrody­ hensive to encourage disarmament as well assure the safety and reliability of its nuclear namic experiments - which use chemical as non-proliferation. weapons stockpile. explosives to compress uranium and pluto­ In particular, the clarity of last week's The case for hydronuclear tests, yielding nium, and provide data on the sequence of statement by Gerard Errera, the French del­ less than four pounds of TNT equivalent events between the detonation of a warhead egate to the Conference on Disarmament - through nuclear fission, was studied and up until the start of the nuclear chain - are which said that France would press for a ban rejected by a panel convened this summer useful, and should continue. These are not on "all tests of nuclear arms and all nuclear under the JASON programme, which pro­ expected to be covered by any test-ban explosions" - if confirmed in a formal vides top-level technical advice to the US treaty, because they do not involve a nuclear treaty, would dispel suspicions that France government. The panel was chaired by Sid chain reaction. intends to develop a new generation of Drell, the Stanford physicist, and included Clinton said, however, that the US would weapons. the most senior weapons designers at each reserve the right to withdraw from any test "We are very happy with the statement, of the three US weapons laboratories. ban on the grounds of "supreme national it's as good as we hoped but better than we An unclassified executive summary of the interest", for example if it ever lacked confi­ expected," says Patricia Lewis, head of the full, classified report was released by the dence in a needed weapon. This condition London-based Verification Technology Department of Energy last week, after parts was said to be needed to win support from Information Centre (VERTIC), who adds, of it were referred to in a Senate debate on the joint chiefs of staff, and William Perry, however, that "we're still trying to read funding for hydronuclear tests. The Senate the Defense Secretary for his call for a total between the lines". voted to appropriate $50 million for such test-ban. Gareth Evans, the foreign minister of tests during 1996 - a budget proposal that Declan Butler & Colin Macilwaln 540 NATURE · VOL 376 · 17 AUGUST 1995