The accident which occurred on 30 September at a nuclear fuel fabrication plant in Tokai-mura, Japan, is not a public health concern outside Japanese territory and is unlikely to have any public health impact beyond the local population, the World Health Organization (WHO) said today.

Known technically as a criticality event, the accident involved the unscheduled fissioning of uranium 235. This led to the generation of a strong external radiation field comprising neutrons and gamma-rays and the release of radioactive materials in the form of fission products which have been detected off site.

However, Dr Mike Repacholi stressed, "Such criticality events are self-limiting and, although the fission reaction was sustained for several hours, the likely magnitude of fission product release does not constitute a public health concern outside Japanese territory and is unlikely to have any public health impact beyond the local population."

In the case of the Tokai-mura accident doses to two persons reported by the  International Atomic Energy Agency (IAEA) as in the region of 8 Gy, raise concern for their lives. Dose estimates for the other exposed people are not so far available.

As far as the local population is concerned, restrictions were placed on activities out of doors and on drinking rainwater. Locally produced farm produce is being monitored. Such actions to protect local public health are part of the normal procedures for operating such facilities.

According to the IAEA, three staff members on site were severely irradiated and 36 less severely. Ten non-staff personnel, three of them firemen, were also less severely irradiated. A number of precautions, for example, evacuation of residents of some areas and the advice to stay indoors, were taken by the Japanese authorities to protect the local population. Japanese authorities have indicated that the criticality has been terminated. Apparently no further danger exists to the local population.

There have been a number of criticality events in the past, the most notable in the Y12 uranium separation plant at Oak Ridge in the USA some 40 years ago. Uranium containing solution was inadvertently collected in a drum while the part of the plant was undergoing maintenance. Several workers in the vicinity were irradiated but no deaths resulted.