French scientist Harry Bernas gives reasons for opposing the Mururoa nuclear tests

The main reason French president Jacques Chirac gave for resuming nuclear tests in the Pacific during the coming months is that they are needed to provide the fitting parameters for a forthcoming nuclear test simulations programme.

The latter will combine computer modelling with laser-fusion experiments and very low-power, even subcritical, nuclear tests in order to design new arms while still complying with the expected requirements of the Comprehensive Test Ban Treaty (CTBT) to be signed next year. When announcing his decision, Chirac said nuclear tests were resumed "at the request of military experts and scientists".

Scientists - at least most of them - have a very sore point: Hiroshima. "We have known sin", said J. R. Oppenheimer after the massive destruction wreaked by a weapon on which some 10,000 scientists had worked for years. After 50 years, the word "science" has not lost that resonance in the public mind, despite all that research has done to help us understand the world and solve some of humanity's more serious problems.

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So when the responsibility of a decision to set off several atomic bombs was laid at their doorstep, 400 French scientists reacted by signing an appeal: "Don't lift the nuclear test ban", which had been drawn up overnight. This appeal now has some 1,000 French signatories, and it has been signed by about 1,000 colleagues from 20 countries. Other protests are strong in the science community: a Japanese chain letter on the World Wide Web has more than 25,000 signatures. As the French appeal puts it, we react as scientists and citizens in discussing Chirac's reasons.

The world has changed since 1989. The two super powers' arsenals no longer freeze lesser ambitions; the social, economic and military situation in Russia cannot be ignored; when wars occur - and God knows they do - they have nothing to do with the massive, high-tech, centralised and anti-city strategies of the Cold War.

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Today, the main dangers are nuclear proliferation and nuclear dissemination. Atomic bomb technology has been around for 50 years and, despite, obvious secrecy measures, the basic features of bomb structure are fairly well-known. Schematic designs have even been published in popular science magazines and any country with a reasonably equipped industry and a competent science force can put together a bomb which may not have the ultimate power, but will still be terribly effective. Israel, Pakistan, India, China, South Africa at least are known to have trodden this path. The main limitation, so far, has been the availability of plutonium and of highly enriched uranium, which require elaborate technologies and specialised production facilities, such as nuclear reactors and large isotope separation factories which barely go unnoticed (remember, however, the surprise of United Nations inspectors in 1992 on discovering how far Iraq had progressed along this line). Today, that limitation is disappearing: dissemination is at hand.

The fall of the Soviet state has left the Russian arms system in a large state of disruption no better than the economy; salaries are ridiculous and the Mafia stalks. Plutonium is priced on the black market at a million dollars per kilo. Significant quantities of both plutonium and highly enriched uranium filtering through Russia, Czech Republic, Slovakia and Germany have been captured by police. A frightening figure has been cross-checked many times by independent study groups: 25 tonnes of plutonium have simply disappeared from the ex-Soviet arms complex weapon.

John Le Carre wrote fairy tales compared to the factual description of the arms and fissile materials storage conditions in Russia. The foreseeable consequences are dizzying. Dissemination of plutonium and military-grade uranium means proliferation, even unto less developed countries. Worse still: pack a few hundred grammes of either material into a chemical explosive and any terrorist bombing will turn into a major radioactive and chemical catastrophe.

Heads of state must have strong minds to sleep in this situation. Efforts by scientists and politicians - particularly in the United States and in the former Soviet Union - have led to an arms dismantlement and control programme which, combined with the SALT and Non Proliferation Treaty (NPT) agreements, is attempting to improve the situation. The process is slow and difficult, but rather effective (half of the US and former Soviet Union missiles are being dismantled). There is a dire need for it to be speeded up and extended. The latter can only occur if pressure is maintained worldwide to prevent dissemination. This ranges from helping Russian storage site scientists and employees fight fuel leakage to negotiating the CTBT at government level.

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Let us consider President Chirac's decision from the perspective of the Geneva Disarmament Conference. Military advisors to governments are hard at work on the latter's main issue: What is that level of nuclear weapons testing that can be kept as "activities not treaty prohibited"? Translated into simple terms, this means that several governments - which happen to be the permanent five nuclear weapon states of the UN's Security Council - are actively discussing at what level new nuclear weapons can be developed by circumventing the CTBT. This is where the "simulation" programme comes in. The latter involves weapons tests with chemically-induced explosions of "subcritical" quantities of fissile material, which release little or no nuclear fission energy while still allowing detailed studies of the bomb core's behaviour by using elaborate detecting and computer systems. Combined with laser fusion experiments which simulate plasma behaviour in the thermonuclear part of a weapon, this provides a country whose research capabilities are appropriate with the means to develop new weapons. The CTBT, meanwhile, prevents other countries from doing the same because their knowledge is insufficient to extrapolate from subcritical test experiments to real-size weapons. This is Pandora's box. For military buffs in all the nuclear powers, Chirac's decision clearly means that nuclear weapons development will continue in spite of the CTBT. This is an incentive for other powers to request a rise in the treaty's threshold of "nuclear yield" (ie, the maximum allowed explosive power) so as to avoid deepening the divide between the highly developed nuclear powers and the others.

This is a straightforward extrapolation of old-fashioned power politics that ignores the turning point of 1989 and the consequences of dissemination. The purpose of the CTBT should be twofold. First, enforce rules that avoid any new nuclear weapons development and at the same time progressively dismantle existing missile arms. Only this can convince governments and their constituents around the world that disarmament is truly possible. Second, firmly control - and progressively get rid of - the existing plutonium and its deadly proliferation. The latter will not happen if the CTBT is bypassed by new arms techniques developments. New techniques mean new arms, and the latter require fissile materials - the stockpiles and their dangers will remain with us.

As stated in our appeal, mankind deserves a better future. Remember Pandora: she finally shut the lid just before Hope could disappear. Perhaps today Hope is in the nuclear test ban.

Harry Bernas is a physicist with the French Centre National de la Recherche Scientifique. He is among the initiators of the Appeal "Don't lift the Nuclear Test Ban" signed by nearly 1,000 French scientists, as well as by an equal number of their foreign colleagues.

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