1999 Tōkaimura nuclear accident

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Coordinates: 36 ° 28 ′ 47 ″  N , 140 ° 33 ′ 13 ″  E

Tokaimura scene of the accident

The 1999 Tōkaimura nuclear accident occurred on September 30, 1999 at the fuel assembly plant of the Japan Nuclear Fuel Conversion Company (JCO) in the Japanese coastal city of Tōkaimura . The criticality incident in Tokaimura was the worst nuclear accident in Japan until the Fukushima nuclear disaster in 2011.

The accident was assigned to category 4 (accident with local consequences) on the seven-point international rating scale for nuclear incidents .

The Tokaimura criticality incident is due to human error . Two workers died as a result of the increased radiation.

course

The disaster occurred during a chemical cleaning process for U 3 O 8 (uranium oxide) enriched to 18.8% . This cleaning process should be carried out in three steps approved by the Japanese government : In the first step, the uranium oxide is mixed with nitric acid in a container that is critical because of its shape. In the second step, the uranyl nitrate solution created by the mixture is pumped into a criticality-safe intermediate container in which the uranium concentration and the uranium mass are determined. In the third step, the uranyl nitrate solution is pumped into a precipitation tank. Step three serves a control function, since the precipitation container is not criticality-safe due to its geometry. This should only be filled with a uranium mass of 2.4 kg.

In order to speed up the process and thus save money, the workers at the plant filled the precipitation container with 16.6 kg of uranium instead of the permitted 2.4 kg on that day - a six-fold increase. The critical mass , which in this case was 5 kg, was clearly exceeded, which resulted in an explosive accumulation of fission neutrons . This inevitably led to an uncontrollable chain reaction , which the workers perceived as a “blue flash” ( Cherenkov light), accompanied by a loud bang. The workers who were involved in the work processes at this point were not or only partially informed about the dangers of criticality .

The nuclear chain reaction released gamma and neutron radiation over a period of 20 hours . The end of the criticality and thus the danger situation could finally be achieved by employees alternately draining the cooling water, which was around the tank affected by the accident and which maintained the criticality as a neutron reflector , and led neutron-absorbing boric acid trimethyl ester into the tank.

Government response

On September 30, 1999 at around 10.35 a.m. local time, the alarm was triggered for the first time in the fuel element factory. Only after two hours did they begin to evacuate the neighboring residents. Another 310,000 people in the area were asked by loudspeakers not to leave their homes. Students were immediately released home. In addition, the radius around the fuel element factory was cordoned off by 350 meters.

Keizō Obuchi , Prime Minister of Japan from July 30, 1998 to April 5, 2000

It took several hours for the then Prime Minister Keizō Obuchi to learn of the serious incident. The International Atomic Energy Agency (IAEA) assumed at the time that a highly technological country like Japan was armed against such a nuclear disaster. However, at that time , those responsible were not able to inform the population and the government in good time.

After a team specially equipped to ward off chemical attacks had reached the scene of the accident, it quickly became apparent that they were helpless against nuclear contamination. Even in a nuclear city like Tokaimura, the authorities had not prepared an evacuation and disaster plan for an emergency. There was also no practice for crisis situations, as the public did not want to worry unnecessarily. The government spokesman told Kyodo News Agency that the government had been slow to respond to the incident and had underestimated the situation. After the 1997 nuclear accident in the same city, doubts arose among the population as to whether the country's nuclear facilities were sufficiently safe. As a result, the Japanese nuclear lobby was heavily criticized.

Effects

Employee

The nuclear response to the neglected security measures resulted in two deaths. Two of the three workers involved in the mixing process, who stood directly at the reaction vessel and filled the liquid, died of radiation sickness as they were exposed to extremely high radiation doses, estimated at between 6 and 20 sieverts . The 55-year-old Yutaka Yokokawa supervised the process and stood a little apart; he received an estimated dose of 1 to 4.5 sieverts of radiation.

After the high X-ray and neutron radiation had escaped, the seriously injured workers were looked after only improvised: colleagues wrapped them in plastic wrap and took them straight to the nearest hospital. However, the helpers of the three victims were also exposed to radiation of 0.5–4.1 mGy during the transport, as they were only protected with cloth gloves and plastic face masks. Shortly after admission to the hospital, the typical effects of high radiation on the human body became apparent in the three participants: nausea, vomiting, diarrhea, shock and changes in blood count are the consequences of increased radiation.

12 weeks after the nuclear accident, the 35-year-old worker Hisashi Ouchi died as a result of the massive radiation in the University Hospital in Tokyo. In April 2000, seven months after the criticality accident, the 40-year-old Masato Shinohara died, also of internal bleeding, immune weakness and multiple organ failure. Due to the high radiation exposure, the genetic material was irreparably damaged in both. Although a bone marrow transplant stabilized the hematopoietic system of both accident victims, the deterioration of the other organs including the mucous membranes continued, since cell division and regeneration were no longer possible due to the defective set of chromosomes.

Another 56 workers who were on the site at the time of the accident received doses between 0.1 and 23 mGy. 27 employees of JCO (Japan Nuclear Fuels Conversion Company), who were involved until the end of the criticality accident, were deliberately and inevitably exposed to the radiation. 21 of these employees were busy draining the cooling water from the affected tank. The other six workers who dumped the trimethyl borate into the tank received radiation doses between 0.03 and 0.61 mSv.

Another 161 employees were exposed to a collective dose of around 0.48 Sievert.

environment

Within a radius of ten kilometers, no radioactivity could be detected in rain, sea or sea water or in the drinking water supply . However, the government ordered that farmers destroy their vegetables and milk, and fishermen were not allowed to venture out.

Samples obtained from the prefecture of Ibaraki , in which the coastal city of Tokaimura is located, showed that marine and land animals did not show any increased radiation values. Agricultural products also showed no increased radiation values ​​in soil samples. Radioactive iodine could only be detected in 15 of 115 vegetable samples. It was below the Japanese limit.

Political, legal and economic consequences

Despite the serious accident, which caused strong criticism against nuclear energy, the government stuck to it, because the resource-poor country does not want to be so dependent on foreign oil supplies. In 1999 the country owned 52 nuclear power plants, from which 35% of the total electricity was obtained.

It took about three and a half years for a Japanese court to convict five executives and the then head of JCO's fuel assembly plant. The five senior executives have been sentenced to between two and three years in prison. The manager of the fuel element factory was sentenced to three years imprisonment, which was suspended for five years, and an additional fine of the equivalent of 3,900 euros.

The Parliament adopted a law on special measures for nuclear disasters. This law defines a clear distribution of roles for the departments involved.

In addition, a private network for nuclear energy safety was established to improve and monitor the safe operation of the nuclear facilities. Not only the Japanese nuclear industry was criticized. In Germany, the Society for Radiation Protection called for an accelerated phase-out of atomic energy, since uncontrolled chain reactions are also possible in the most technically developed countries.

The "Nuclear Safety Network" (NSN) wanted to improve safety awareness in the nuclear industry with the help of mutual inspections and information exchange between the individual members. In 2014, the Nihon Genshiryoku Kenkyū Kaihatsu Kikō (Japanese Atomic Energy Research and Development Organization) announced that the reprocessing plant in Tokaimura would be shut down because it would be too expensive to adapt the safety measures after the nuclear disaster in Fukushima . The cost would have been the equivalent of $ 915 million.

attack

About three months after the accident, in 2000, an attack on the fuel element factory by police officers was prevented. The Mainichi Shimbum newspaper reported that the unemployed repeat offender Tatsufumi Oshiba was upset about the JCO company, so that he first wanted to blow up the factory with a remote-controlled explosive device in a bag and then wanted to kill himself. However, the assassination attempt on the fuel element factory failed.

literature

  • Naoto Kan: As prime minister during the Fukushima crisis. IUDICIUM Verlag GmbH Munich,  ISBN 978-3-86205-426-8
  • NHK: 83 days: The slow death of nuclear worker Hisashi Ouchi by radiation. Redline Verlag, 2011,  ISBN 978-3-86881-315-9
  • Susan Boos: Fukushima sends its regards: The consequences of a worst-case scenario. Rotpunktverlag, 2012, ISBN 978-3-85869-474-4

Web links

Individual evidence

  1. ↑ Tokaimura, Japan 1999. Fandom, accessed January 29, 2017 .
  2. ↑ a b Naoto Kan: As Prime Minister during the Fukushima crisis . IUDICIUM Verlag GmbH Munich, ISBN 978-3-86205-426-8 .
  3. ↑ a b c Tokaimura Criticality Accident 1999. World Nuclear News, October 2013, accessed on February 4, 2017 (English).
  4. ^ A b Criticality accident in Tokai-mura. September 29, 1999, accessed January 26, 2017 .
  5. ↑ a b c NHK: 83 days: The slow death of atomic worker Hisashi Ouchi by radiation . Redline Verlag, 2011, ISBN 978-3-86881-315-9 , pp. 190 .
  6. ↑ a b Too Hot to Handle. TIME Magazine, October 11, 1999, accessed January 27, 2017 .
  7. ↑ a b c Blue lightning in the Far East. SPIEGEL Online, October 4, 1999, accessed January 25, 2017 .
  8. ↑ Susan Boos: Fukushima sends its regards: The consequences of a worst-case scenario . Rotpunktverlag, 2012, ISBN 978-3-85869-474-4 , p. 272 .
  9. ↑ Mr. Ouchi dies from radiation. n-tv, September 11, 2011, accessed on January 28, 2017 .
  10. ↑ Hirama et al: Initial medical management of patients severely irradiated in the Tokai-mura criticality accident , British Journal of Radiology, Vol. 76, May 2003, p. 246-253
  11. ^ Criticality accident in Tokai-mura. Nuclear Forum, September 29, 1999, accessed January 29, 2017 .
  12. ^ Tokaimura: suspended sentences. Greenpeace.de, March 3, 2003, accessed January 26, 2017 .
  13. ↑ Chain reaction stopped. SPIEGEL Online, September 30, 1999, accessed January 27, 2017 .
  14. ↑ Tokai reprocessing plant to shut. World Nuclear News, September 29, 2014, accessed January 29, 2017 .
  15. ^ Out of anger about a nuclear accident. SPIEGEL ONLINE, January 13, 2000, accessed January 26, 2017 .