Iodine 131 leaked during the transfer of a liquid effluent between 2 tanks in a medical laboratory of a institute specialising in the production of therapeutic radioactive elements. The plant is the world’s second largest producer of radioactive elements marketed in liquid form to be used in medical imaging and cancer treatment. On Monday, the staff of the institute observed an abnormally high isotope content in an evacuation stack following a failure of the plant’s filtration system. The AFCN (Belgian federal agency for nuclear safety) that was alerted to the accident also informed the ASN (corresponding French body for nuclear control)

The accident was initially said to be consequence free, and then further to the analysis of plant samples in the vicinity, the authorities warned the people a few days later of possible contamination. To this effect, the police communicated messages in the roads using loudspeakers asking the 20,000 inhabitants of the district to refrain from consuming fruit and vegetables from the gardens, rain water and milk from neighbouring farms. These measures concern several villages within a radius 5 km from the point of release. The radius was reduced to 3 km in the end of August when the air and water samples were free of radioactive substances. To reassure the masses, several hundred children underwent a salivary gland test the following week.

The conducted enquiry assessed 45 GBq of emissions released in 4 days, i.e. the dosage absorbed at one go by 12 patients suffering from thyroid cancer. Once in the body, 30% of the iodine 131 settles on the thyroid gland (given the short life time of iodine 131). The health impact is therefore considered to be extremely low. The accident was however rated 3 out of the 7 level International Nuclear Event Scale.

The accident is believed to have resulted from a handling error. Failure of the computed managing the alarms was also mentioned. The technician on duty thought it to be a “filter problem” and tool no special measures, allowing the production cycle to run for over 24 hours.

According to the press, both the French and Belgian nuclear safety agencies had identified defects in the laboratory’s safety system during a joint audit carried out in November 2007.