Читать книгу Industrial and Medical Nuclear Accidents - Jean-Claude Amiard - Страница 33

The most serious accident in a civilian manufacturing plant is the Tokai-Mura accident. This site is a major nuclear complex, with a spent fuel reprocessing plant, a uranium reprocessing plant and experimental reactors. The site is located in Japan 160 km from Tokyo. The plant where the accident occurred is owned by the Japan Nuclear Fuels Conversion Company (JCO), a subsidiary of the Sumitomo Trust. It converts uranium hexafluoride (UF₆) enriched in uranium 235 into uranium oxide (UO₂) for the manufacture of nuclear fuel. The conversion is carried out by a “wet process”: uranium, initially in the form of gaseous UF₆, is transformed in the presence of water and then ammonia before being calcined in a furnace to obtain uranium oxide powder.

On Thursday, September 30, 1999, at about 3:30 p.m., following a human error in the quantity of fissile material introduced into the furnace, a so-called criticality accident occurred. The quantity of uranium introduced into a settling tank was indeed abnormally high (16.6 kg) and far exceeded the safety level (2.3 kg). This accident resulted in contamination outside the plant, and three workers were seriously injured. It was classified at level 4 on the INES.

In France, the first stages of the fuel cycle are not immune to accidents, and radioactive releases into the environment are not always negligible. This was the case at the Pierrelatte (Comurhex) plant in 1977 (January 1 and November 25) where several tons of uranium hexafluoride leaked into the atmosphere without apparently contaminating the soil away from the plant site. A 30 m³ leak of a solution containing 74 kg of uranium occurred on July 9, 2008 in a plant at the Tricastin nuclear site in Bollène (Vaucluse), part of which spilled into surrounding rivers [AMI 13a].