Some differences may exist between french and english regulations. Lessons learned are only a translation of those of french incident and are not adapt to english regulation.
Description of the incident
The incident occurred during the transportation of 60 packages containing radioactive waste from hospitals and research sites. After unloading the waste, measurements revealed contamination on the floor of the truck.
A transport company was responsible for collecting waste packages over a wide region. The majority were transported to a storage centre; the others (approximately 10 per cent of the waste), comprising packages of frozen putrescible waste in polyethylene drums, was sent to another company.
The sequence of events was as follows:
- A driver delivered 10 packages of frozen waste. After unloading, the driver noticed that the frozen waste drums had left traces of moisture on the floor of the vehicle, from the condensation on the packages.
- Two hours later, the vehicle went to the main storage centre to deliver the 50 remaining packages. Upon opening the back door of the vehicle, the driver found that a cylinder was lying loose in the vehicle. This was due to the movement of the restraints used for stowing packages, during the first unloading.
- The driver picked up the cylinder without realizing that a few drops of liquid had been released and had contaminated the floor of the vehicle. The weight of the cylinder upon arrival was identical to its weight upon departure. When unloading, the few drops of contamination were mixed with the residual condensation left by the first delivery.
- At the end of the unloading, the radiation protection supervisor at the storage site, discovered contamination of the floor of the vehicle.
The cylinder in question contained liquid waste of activity of 4.3 GBq, mainly due to carbon-14 and tritium. It was a cylinder type which is no longer produced, but is sometimes still used by smaller waste producers.
The radiological checks (using smears) after unloading revealed a removable surface beta contamination level on the cylinder of 60 Bq/cm 2; and 10 Bq/cm 2 (average) and 60 Bq/cm 2 (maximum) over the vehicle floor.
The contamination was confined to the vehicle and the cylinder, and the radiological surveys carried out on the handler who carried out the unloading revealed no surface contamination. No analysis of urine was performed.
Lessons to be learned from the incident
The following recommendations were made:
- To carry the "old model" cylinders in an overpack (a metal drum, for example) which would provide additional containment.
- Positioning the cylinders in full walled crate pallets to ensure secure stowage.
- Ensuring the cylinders were not over-filled, especially the older models.
- After unloading a portion of the packages, the carrier must verify what remains in the vehicle before restarting; he must also ensure the proper stowage of the remaining packages.
Although, in this incident, the origin of the contamination was established, the carrier should have investigated the traces of humidity left by the frozen packages during the first unloading, and verified that no contamination was present before proceeding.