Limits on the use of rainwater and garden produce have been relaxed somewhat at Fleurus, Belgium, as more information about the radioactive emission emerges.
It is now known that the release of 45 GBq in iodine-131 came as a result of a transfer of liquid radioactive wastes in the basement of Institute of Radioelements factory near Fleurus. Iodine-131 is one of the medical products the plant extracts from high-enriched uranium targets exposed to radiation in European research reactors. IRE produces about 75% of the world's supply of I-131, which goes on to be used for diagnosis and therapy worldwide.
According to France's Institute for Radiological Protection and Nuclear Safety (Institut de Radioprotection et de Sûreté Nucléaire, IRSN), wastes from the recovery of useful isotopes are stored in 50 litre tanks in the basement of the factory. When these are full, the wastes are transferred to 3000 litre versions to await treatment. IRSN said it was after one such transfer that the release occurred.
Gases from the tanks travel through ducts fitted with filters and traps meant to limit iodine emissions, but measurements from the chimney stack of the plant indicated that an extraordinary 45 GBq of radiation was released over the weekend 23-24 August. Belgium's Federal Agency for Nuclear Control (Fanc) ordered it to be shut down on 25 August.
The theoretical radiation dose to someone living at the plant perimeter has been upwardly revised to 0.16 mSv from an earlier estimate of 0.10 mSv. The typical regulatory dose limit for a member of the public is 1 mSv, but residents in an area extending about five kilometers to the north west of the plant were warned not to eat fruit or leafy vegetables from their gardens and not to use rainwater anyway. This zone was reduced to a three km stretch yesterday morning and will apply until 7 September. Iodine-131 has a half-life of eight days.
Tablets of stable iodine can be taken to prevent the absorption of unstable radioactive iodine isotopes, but this was not recommended by Fanc. Fleurus is just 30 kilometers from the border with France, where authorities said that the Cattenom and Chooz nuclear power plants have not noticed any unusual activity after heightened environmental monitoring.