Friday, October 1, 1999 Published at 16:37 GMT 17:37 UK
Experts play down fallout danger
A number of workers at the plant are seriously ill
The Tokaimura nuclear accident has been confirmed as the world's most serious since the explosion at the Chernobyl nuclear reactor in 1986.
But, according to David Kydd of the IEAE, this classification could be increased after more detailed inspection of the site.
A much smaller radiation was released into the environment than at Chernobyl.
He says there would have been a complex mixture in the vessel before the explosion.
It is not yet clear at what stage in the process the accident happened, so, according to Dr Clarke, the radioactive material could be a mixture of particles including uranium, fluoride, nitrate and oxide, which will fall to ground fairly quickly.
However, some of the uranium could be gaseous, which would mean it would disperse into the atmosphere.
According to Lothar Wedekind of the IEAE, this latest incident bears no resemblance in magnitude to the Chernobyl incident.
It has been described as a site-related event and, according to the agency, radiation levels dropped quickly.
Three workers from the plant are seriously ill after being exposed to potentially fatal doses of radiation.
According to Dr Clarke, contaminated land clean-up will most likely be confined to areas around the plant and long-term effects will be confined to a local scale.
The Chernobyl accident was classified as a level seven. Fission products were released in large quantities and there was massive radioactive fallout.
Massive pieces of matter including radioactive particles can fall back to earth within minutes, forming localised fallout. Smaller, still visible particles fall within several hours.
Microscopic particles stay aloft for longer periods of time, and can be swept around the world and brought to earth with rain and other forms of precipitation.
After the meltdown of the Chernobyl reactor, smoke churned out radioactive iodine and radioactive caesium. Much of this material came down close to the plant itself. The rest of it was blown by the wind across Belarus, the Ukraine and Europe.
These dust particles were breathed in by humans and hundreds of thousands suffered ill-effects.
Radioactive iodine, in particular, is absorbed by the thyroid gland, where it causes thyroid cancer. After Chernobyl there were high incidents of this type of cancer, especially in children. This is the most easily detectable fallout product in humans.
Radioactive caesium can end up in animal foods, including milk, after cattle ingest particles with grass.
After fire destroyed the core of a reactor at the Windscale nuclear complex in Britain in 1957, cows milk had to be destroyed after fears it had become contaminated.
At times of nuclear emergencies, the threat from airborne radioactive particles can be reduced by keeping people indoors. The authorities insisted on this in Tokaimura.