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Issue 43, November 1999

Japan's nuclear disaster

THE NUCLEAR disaster at Tokaimura near Tokyo has been rated by the International Atomic Energy Agency as the worst since Chernobyl and the worst ever in Japan. Sixty-nine people were contaminated when a nuclear reaction began accidentally at the reprocessing plant of a company called JCO, a subsidiary of the Sumitomo corporation.

Three workers were employed on a process to make uranium dioxide used for fuel rods in nuclear reactors which involved pouring a solution containing the radioactive isotope Uranium 235 into a tank. Approximately three kilogrammes of the 235 isotope is needed to form a critical mass and start a nuclear reaction and so the tanks contents should never have been allowed to come near this amount. It now appears however, that the employees could have been confused because 18% of the liquid they were handling was the enriched 235 isotope rather than a more common concentration of 2%. They kept on pouring bucket after bucket of the solution into the tank until there was 16 kilogrammes, including a critical mass of 3kg of Uranium 235.

Even then it was not certain that a reaction would take place but the water also in the tank played a key role. It acted to 'moderate' or control the reaction by slowing down the release of neutron atomic particles and thus making it more likely that they would collide with other atoms and continue the chain reaction. This is what happened as the reaction began with a blinding blue flash as the surrounding air was ionised.


The workers involved, who will almost certainly die of their injuries, have been heavily criticised for their recklessness, but it is possible that they did not know the danger of what they were doing due to lack of training and a very low level of safety culture in the private reprocessing company. Certainly, the response of the nuclear authorities and government to the accident was complacent and slow. The critical mass came together at 10.30am on September 30 and the uncontrolled nuclear reaction began shortly afterwards. It wasn't until 2.30am the following day, however, that any action was taken to stop the release of radiation.

The authorities both in Japan and internationally may find it convenient to blame the individuals concerned and point to the inherent safety of the technology in the nuclear industry, whose spokespersons are keen to point out the alleged miniscule risks of a technical failure. Indeed, the whole nuclear industry is built on statistical calculations that chances of equipment failure are often one in millions and the appalling consequences of an accident are justified on this basis.

This approach completely misses the point however. All the main nuclear disasters of the past 50 years have been caused mainly, or in large part, by human error, not technical failure. Three Mile Island in the USA, Chernobyl, and now this disaster, clearly fall into this category.

It appears that the accident at JCO in Tokaimura was only the latest of a string of similar mishaps in the same area of Japan in the last four years. In March 1997, two fires broke out in barrels containing radioactive waste in a nearby plant to JCO and thirty workers were exposed to radiation. In August 1997 rainwater seeped into a storage pit for highly toxic radioactive waste threatening pollution of water supplies, and in July this year 20 tonnes of radioactive coolant water escaped from a power station north west of Tokyo. In these, as in other similar, regularly occurring incidents throughout the world, it just takes poorly trained or stressed workers to take the wrong decision at a crucial moment for a disaster with global implications to ensue. This is the reason that despite soothing claims from Labour ministers, the nuclear industry will remain inherently unsafe. Privatisation of the nuclear industry as planned by New Labour will only make matters worse. One of the candidates in the sell-off, British Nuclear Fuels, were recently exposed as having falsified documents about safety checks on reprocessed nuclear waste bound for Japan.

Pete Dickenson

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