As reported in the Engligh version of Japan’s Mainichi newspaper, six former officials of the nuclear fuel processing company JCO are likely to evade imprisonment even though they were convicted of negligence over a nuclear criticality accident in 1999 that claimed the lives of two workers. “The accident had a huge impact on society, and damaged the public’s trust in the safety of nuclear fuel,” Presiding Judge Hideyuki Suzuki said as he handed down the ruling. The half dozen JCO company managers were charged with failing to provide thorough safety instructions to employees. On Sept. 30, 1999, workers used stainless steel buckets to pour massive amounts of uranium — in excess of the upper limit set by the company — into a tank, triggering nuclear criticality. There was so much uranium in the tank that it started a nuclear chain reaction right there in the water, an unshielded nuclear reactor whose neutron output made the water glow blue. In the accident, two of the three workers who were heavily exposed to radiation have since died and more than 600 people including local residents were exposed to radiation and forced around 320,000 people to shelter indoors for more than a day. Plant head Koshijima was fined Y500,000 ($7000) and given a three-year suspended jail sentence; he will be made to serve his jail term should he break the law within the next five years. JCO, accused of supervisory lapses that permitted dangerous practices to be conducted routinely, was fined Y1 million ($14,019) in the incident.
The only comparable incidents in the United States occurred back in 1958 during separate accidents at Los Alamos and at the Y-12 nuclear weapons manufacturing facility in Oak Ridge, Tennessee. However, there has been some concern that other U.S. nuclear criticality incidents may have occurred unnoticed in various nuclear waste pits in Oak Ridge and elsewhere.