Magpie Country Nukes Headliner

nuclear issues news brief from Japan

Criticality accident at Tokai uranium processing plant



15 October 1999

It has now become clear, according to the analysis by the accident investigation unit of the Nuclear Safety Commission, that the Tokai criticality accident started with what the nuclear physicists call "prompt criticality", rather than the reactor-type delayed criticality. This means the accident could have been much worse and totally out of control.

JCO admitted that a limited amount (20Bq/m^e, i.e. twice the allowed limit!) of radioactive iodine-133 had been kept going out into atmosphere after the accident via exhaust system of the building in which the criticality occurred. The exhaust system switch was on until October 11. More than 10 days after the accident, JCO hastily sealed up the windows of the building in question in order to avoid further release. (More workers exposed during the operation!)

Apparently, Prefecture and STA knew about the iodine release thruough the exhaust system, but they took no measure considering that the escaping quantity was negligible. Concentration of 0.04Bq/m^3 of I-131 was detected 50m southwest of the building (the monitoring point is still within the JCO premises).

Almost all the mass media stopped reporting about the conditions of the hospitalized workers suffering acute radiation injuries. US marrow transplant ex pert, Dr Robert Gale, who also treated Chernobyl liquidators, arrived at Tokyo to attend the victims. We have very little information about the kind of treatment that is being tried on.

Executives of the JCO Sumitomo now confessed that their employers had been taught almost nothing about nuclear criticality, why and how they should avoid it.

IAEA experts team arrived at Japan in order to investigate into the accident . The three members of the team are interviewing administrators of STA, Ibaraki Prefecture and Tokai Village (Tokai-mura). They will also visit the site of the accident.

On the 3rd of October, after the accident, STA sent a site inspection team to the JCO plant. This is the very first time in 10 years that a site inspection, which is legally prescribed, on this plant is carried out. Unlike powerplants with nuclear reactors, periodic inspection is not obligatory in fuel processing facilities in Japan.

It was also revealed that STA had conducted no site inspection either at Tokai Reprocessing Plant (operated by JNC) or at Rokkasho-mura Enrichment Plant (operated by JNFL) over six years. STA claims they were too busy.

... Too busy with safety PR activities?

Toshiba, Hitach and US General Electric are jointly preparing for a new nuclear fuel plant in Japan, and JCO had been expected to supply 50% of UO2 material for this new facility. Now that JCO is definitly out of business, Toshiba/Hitach/GE has decided to import all the material uranium from overseas. [Nikkei, 14 Oct 99]

UK journal Nature No.401 carried an editorial opinion harshly criticising the sloppy, rubber-stamping practices of the Japanese nuclear safety regulation, and casting a serious doubt whether the situation improve significantly after the accident.

Greenpeace Japan requested in writing that STA should conduct follow-up surveys on the health of the near-by residents. Evacuation of 350m radius of the ground zero was no doubt insufficient. And the evacuation started only after 4 or 5 hours after the criticality sparked. This means that all the people who were in the area, perhaps as far as 500 to 600m radius zone, were subject to a quite dangerous level of neutron shower. Latent radiation injury is likely to occur.

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