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An accident not to be forgotten
10 Years have passed since the JCO Criticality Accident

It is painful to remember this dreadful accident, but to commemorate the tenth anniversary I decided to jot down a few thoughts.

The initial shock
At noon on September 30, 1999 NHK news reported that a criticality accident had occurred at Tokai-mura and that two workers where in a semi-conscious state. The accident, which occurred at the JCO Uranium Conversion Plant, was the first criticality accident in Japan. It was not hard to predict from the NHK report that the accident would end in tragedy for these two workers. Immediately after hearing the news, I had a conversation with professor Takasugi who I happened to meet in Yokkaichi University. He had not yet heard about the accident.

Furukawa: This afternoon's top news item is decided then.
Takasugi: Did something happen?
F: There was a criticality accident at Tokai-mura. I think two people are going to die.
Mr. Takasugi had worked in NHK for 35 years and his background was in humanities. Like a true journalist he immediately checked it out on the internet.
T: It says they were seriously injured. It sounds bad.

Recalling the background to the accident
JCO was a subsidiary of Sumitomo Metal Mining Co. Its main work was "reconverting" low enriched uranium (U-235 isotope ratio 3-5%) from uranium hexafluoride form to uranium oxide.

On this occasion, however, JCO was using medium enriched uranium (U-235 isotopeÅ@ratio 18.8%). It is much easier for uranium of this enrichment to reach criticality. JCO had received an order from the former Power Reactor and Nuclear Fuel Cycle Development Corporation (PNC) and was refining medium enriched uranium scrap to produce a concentrated solution. The solution had to be homogeneous and, because of the risk of a criticality accident, the process was very time consuming.

For whatever reason, JCO decided to bypass these long-winded procedures. It tried to create a homogeneous solution by mixing a large quantity of concentrated uranium solution in a "precipitation vessel", even though the dimensions of the precipitation vessel were such that the solution could easily go critical. Using the natural uranium solution this procedure was not difficult, but because of the high concentration and enrichment, on this occasion it was very dangerous. Many of the plant's staff must have been aware of the danger, but no one ordered the workers to stop. Clearly communication within the company was very poor. Another issue is that the work should have been carried out by staff who were experienced in handling nuclear fuel.

The solution went critical and stayed critical. Early the following morning (October 1) the coolant around the precipitator was removed and borate solution (a good neutron absorber) was poured in. Criticality was finally stopped, but by that time neutrons and volatile radioactive substances had been continuously emitted from the solution for 20 hours.

The two workers involved were Hisashi Ohuchi and Masato Shinohara. When the accident happened they were both right next to the precipitation vessel, so they received very high radiation doses. Ohuchi died late December the same year and Shinohara died in April the next year. I pray for the souls of these two innocent young men.

They are the only workers in the history of Japan's nuclear industry to have died of acute radiation disease. This was also possibly the only nuclear accident in the world to have exposed people living in the surrounding area to direct neutron radiation, so in that sense too it is natural that the accident should have attracted so much international attention.

Article in Nature
The 7 October 1999 issue of Nature (Vol. 401 Issue 6,763) contained a scathing article about the accident. Below is an extract about Japan's nuclear bureaucracy.

"The Japanese government seems unable to set up competent regulatory bodies with sufficient staff and expertise. The Science and Technology Agency's Nuclear Safety Commission is a group of part-time academic experts who rubber-stamp documents produced by a small team of officials, who are far too few in number, and lack the expertise needed to regulate the safety of such a huge and potentially dangerous industry. Similarly, the country has not equivalent of the US Food and Drug Administration, even though it pharmaceutical market is of comparable size to that of the United States."

These are harsh words, but the article makes very important points about the problems of Japan's nuclear bureaucracy. Re-reading them I was impressed by how insightful they were.

I am reminded of Parkinson's Law, the adage articulated by English social scientist C.N. Parkinson in the best selling book Parkinson's Law: The Pursuit of Progress. The law goes, "Work expands so as to fill the time available for its completion." The book, laden with irony, is an insightful analysis of all sorts of social phenomena. It seems to me to make similar points to the above article in Nature.

After the accident the nuclear safety administration was changed, but although the staff of the Nuclear Safety Commission increased, I do not believe that problems with the nuclear safety assurance system were resolved. Just looking at the response to the impact of the July 2007 Chuetsu-oki Earthquake on the Kashiwazaki-Kariwa nuclear power station, it is even possible to see areas where the system has deteriorated.

Problem of the plant's location
It might not have been so when the plant was first constructed, but at the time of the accident the plant was surrounded by houses. Nuclear fuel should not be handled in such places.

The American movie Silkwood (starring Meryl Streep), which is based on a true story, presents a very real picture of nuclear fuel production. The scene where the main characters enter the plant site gives the impression that there are no other buildings in the vicinity. If you are going to produce nuclear fuel, that is the type of place to do it.

Even if it is hard to find such a place in Japan, it is essential to avoid situations in which residents could become exposed to neutron radiation. The conversion test building where the accident occurred was near the edge of the site, nearer to residents' houses than to the central office building. Permission should not be given to fabricate nuclear fuel using medium enriched uranium in such a place. It was claimed that it is difficult to rescind approval once it has been granted, but there were opportunities to rescind the approval. The license was reviewed when JCO became independent. At that time the license to handle medium enriched uranium should have been rescinded. The Science and Technology Agency (STA), the regulatory authority at the time, bears a heavy responsibility.

Responsibility for the accident
However, all the responsibility should not be pinned on JCO and STA. PNC was also responsible. It should have carried out the work itself. Nevertheless, it must also be recognized that PNC was given too many tasks to carry out with the limited staff and skills available to it. The fast breeder reactor, reprocessing and disposal of nuclear waste are each very complicated tasks in their own right. On this basis we must conclude that the heaviest responsibility lies with the government and its promotion of the nuclear energy program.

Final remarks
Perhaps the average member of the Japanese population has forgotten this accident by now, but there are some who have not forgotten. I would like to be numbered among the latter group. I intend to remain interested in the problems of nuclear power and to remember the lessons and warnings from this accident.

Michiaki Furukawa (Emeritus Professor of Nagoya University, nuclear chemist, member of CNIC Board of Directors. His major is nuclear chemistry.)

In October 1999 CNIC and Gensuikin jointly established the Committee for Comprehensive Social Impact Assessment of the JCO Criticality Accident to carry out an independent investigation of the background and causes of the accident. The committee's findings were compiled in two Japanese pamphlets published in September 2000 and October 2005 respectively. CNIC also published the following English pamphlet in May 2000:
Criticality Accident at Tokai-mura - 1 mg of uranium that shattered Japan's nuclear myth.

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