The worst nuclear accident in Japan's history was the result of human error and serious breaches of safety principles, according to a report on a preliminary fact-finding mission by the International Atomic Energy Agency (IAEA).
The agency's report, issued Nov. 15, concludes that the incident at the Tokaimura nuclear fuel processing facility essentially was an "irradiation" accident and not a "contamination" accident because it did not result in a significant release of radioactive materials. Several workers were overexposed, with two suffering very severe acute radiation syndrome and another having a moderate degree of the ailment.
IAEA indicated the event did not have significant off-site risk. Sixty-nine people were exposed to radiation, the Japanese government said Oct. 15. All but 10 of the 69 are workers at the plant.
The accident happened because of a technique, not used in the United States and illegal in Japan, where uranium powder is dissolved in nitric acid during final stages of fuel element production. Company officials believe too much uranium was put into the acid, causing an uncontrolled atomic reaction and sending radiation spewing into the air.
Workers were exposed to radiation levels 50 to 100 times higher than what is considered safe to receive over the course of a year, according to a report submitted by Japan's Nuclear Safety Commission. Workers at the facility routinely violated safety procedures, were under pressure to get the job done quickly and had not received proper training.
The IAEA report, compiled after three experts visited the site for five days in October, is not meant to be an extensive investigation of all circumstances of the accident. However, it recommends that an investigation should include procedures, emergency responses and safety features at the plant.