The nuclear accident in Japan 1999 – KAMEDO-report 78

The Kamedo-reports are published by the Swedish Disaster Medicine Study Organisation (Kamedo), at the National Board of Health and Welfare. Observers study the medical, psychological, organisational and social aspects of disasters. The results, with a focus on experiences gained, are presented in the reports.

This report is entirely in Swedish. Only summary in English.


On 30th September 1999 an accident involving nuclear technology occurred at a nuclear fuel plant at JCO Company LTD in Tokaimura, 120 km north-east of Tokyo. The accident, which took place during the production of enriched uranium, drew great attention internationally and was closely followed by the mass media. Apart from the problems involving rescue and illness purely caused by nuclear technology, a problem also arose with information. This is, among other things, illustrated in an early press release from the National Institute of Radiation Protection.
The accident was caused by two workers pouring a highly-enriched uranyl nitrate solution from a vat directly into a precipitation vessel with highly-enriched solution in contravention of the safety provisions in force. A critical situation arose in the precipitation vessel with a resulting nuclear fission reaction. Gamma and neutron radiation evolved and the two workers were exposed to high doses of radiation . A third worker in a room close by were also exposed. The three workers were first taken care of at the local hospital where they received first aid. At the hospital it was difficult to determine what kind of accident that had occured and to what doses of radiation the injured had been exposed.
The injured workers were soon transferred to the National Institute of Radiological Sciences (NIRS) Hospital in Chiba. After complicated physical and biological measurements of radiation doses it was possible to estimate the radiation doses absorbed. The measurement for patient A was 24.5 Gy, for patient B 8.3 Gy and for patient C 3.9 Gy.
The injured received advanced, multidisciplinary intensive medical care which included the latest international treatment principles within the respective specialist area.
The two workers, A and B, who were exposed to the higher radiation doses rapidly felt sick with vomiting. They soon showed signs of effects on their blood and blood-forming organs which could be remedied with bone-marrow transplants. However, it wasn´t possible to successfully treat the later complications on the skin and mucous membranes of the stomach-intestinal tract and the airways. After long-term intensive care they both died of heart and lung failure.
Besides the three workers directly involved, 229 people within the factory area, emergency and nursing personnel as well as technical personnel were exposed to measurable radiation doses (0.07-48 mSv). The population of 207 people that lived within a radius of 350 m of the factory was also exposed to lower radiation doses (0.01-21 mSv). The accident led to immediate consequences for the population in the community of Tokaimura. The local authorities evacuated the area within a radius of 350 m of the factory. The regional authorities at county level recommended that the population within a radius of 10 km stayed indoors. Schools and shops were also closed within this area. Approx. 310 000 people were thus directly affected by the accident. The technical handling of the accident with regard to nuclear protection took time. Not until the day after was it possible to stop the so-called criticality reaction so that radiation was halted.
The accident in Tokaimura also received much attention internationally. In the flow of information there were some misunderstandings, for example, that there had been a major radioactive leak from a nuclear reactor of the Chernobyl type. This underlines the importance of accurate and adequate information.

The observers' conclusions:

• Dosimeters should be located in risk areas in case of accidents involving radiation.
• It is absolutely vital to have well-devised and rehearsed emergency plans for accidents involving radiation.
• Personnel from companies handling radioactive material should have protective clothing in order to be able to provide first aid and to accompany any people damaged by radiation to hospital. Thus, the personnel may also provide essential information about the accident and about possible doses of radiation absorbed.
• The emergency services that are expected to operate in the front line require special training and protective clothing.
• It is important for treatment and prognosis that the radiation dose absorbed can be estimated at an early stage. This requires complex laboratory technology which should be available at selected hospitals where continued treatment also can be provided.
• Early signs that one has been exposed to a high dose of radiation can be loss of consciousness, feeling sick, vomiting and diarrhoea.
• A high dose of radiation affects most organ systems. Some of these, such as changes in the blood count, can be treated. But despite advanced treatment methods, changes in the cells of the skin and mucous membranes which occur later cannot be effectively treated yet.
• The slightest suspicion that someone has been exposed to radiation should result in calculation of the possible radiation dose absorbed and continued observation at the hospital.
• The psychological effect on people damaged by radiation and on the population living in the vicinity of a radioactive leak is certainly greater than in the case of other accidents. It is therefore important that psychosocial care is provided at an early stage.
• In the case of accidents involving radioactive material, it is extremely important that the public receives as accurate information as possible via mass media. Those who provide the information should have specialist knowledge within the field of radiation and good language skills.

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Susannah Sigurdsson
+46 (0)75 247 30 00