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
In a hospital authorized to undertake therapeutic treatment using iodine-131, rooms had been specially upgraded on one of the hospital floors. The washrooms in these rooms were equipped with a double evacuation system designed to collect and store I-131 in patients’ urine by means of a dedicated collection network. This network included a PVC pipeline that transferred effluent to the building’s basement where the storage and decay tanks are located.
The fall of an object inside the pipeline caused a leak in a joint located on the ground floor. This resulted in the release of several litres of contaminated effluent on the ground floor, which then spread to the lower floors.
The leak was detected by department personnel located on the ground-floor. After intervention by the hospital plumber and the person competent in radiation protection, the origin of the effluent was quickly identified, the contamination was confirmed, and steps to protect hospital personnel and patients were taken. The residual contaminated effluents were first removed, then the decontamination and repair of the premises and of the line were undertaken.
The radiological consequences were very low. There was no contamination of the wider environment, due to the quantity of effluent dispersed and the sealing of the ground at the lowest level of the building.
A measurement at 1 metre from the spill on the ground-floor revealed a dose rate of 15 µSv/h. The plumber and the radiation protection person remained close to the effluent puddles for a few minutes. Tests on these two persons, undertaken one month after the incident, did not reveal any significant internal contamination by I-131.
Lessons to be learned from the incident
The investigation of the causes of the pipeline leak revealed a dislocation of the joint between two floors of the building. This did not, by itself, result in any leakage of effluent. However, subsequent work was undertaken to reinforce fire protection, which required the creation of concrete slabs between floors. During this work, liquid concrete was able to enter the pipeline: when it solidified, it broke loose and fell off. Given the great height of the pipeline, the concrete lump landed with sufficient force to break the PVC joint on the pipeline. Although this sequence of events is hard to foresee, the following lessons may be learned.
- The design of an effluent collection circuit must take into account the risk of strains on this circuit and define the optimum materials and geometry. In this case, the great vertical height of the conduit and the nature of the pipe material were not favourable elements.
- A preventive maintenance programme for the effluent collection system should also be implemented, in order to prevent its degradation, either by destruction as in this incident, or by the accumulation of deposits (stagnating/dried urine in certain parts of the conduit, presence of paper residues, etc.) that can obstruct the flow. A regular cleaning of the circuit should be performed.
- A regular visual inspection of the whole effluent collection circuit would have revealed the original joint dislocation.
- To the extent possible, retention devices to contain any leaks in the pipes should be provided. In this incident, there was no special means of spill containment under the vertical part of the conduit.
- In terms of the internal exposure risk from short-lived radionuclides, such as Iodine 131, it is important to perform internal dosimetry tests as quickly as possible after the incident, in order to determine the level of exposure with as much precision as possible. In this case, it is clear that the time between the exposure and tests (actually urine sampling) was much too long.
It is necessary to be aware of the juxtaposition of different hazards and the various means for reducing risks. In this case, improvements in fire protection were partly responsible for the degradation of protection against radiological risk. The integrated approach to risk management is made even more important where nuclear medicine facilities have to be incorporated into existing facilities, and where the maximum level of radiological protection cannot always be achieved.