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 portal radiation detection alarm (set at 2.5 times background) at an incineration centre was triggered by the passage of a dump truck carrying hospital waste. The container in which the radioactive waste was located was isolated and placed away from the incineration centre buildings.
The next day, the regulatory authorities, contacted by the person responsible for the incinerator, intervened to carry out a radiological check of the container. The dose rate in contact with the container was up to 160 µSv/h.
Some fifty bags of waste were then taken out of the metal container and checked individually using a radiation meter. This resulted in the isolation of two bags, which gave the following readings:
- First bag: 1010 µSv/h in contact, and 18 µSv/hr at 1 metre.
- Second bag: 70 µSv/h in contact, and 1 µSv/hr at 1 metre.
Qualitative analysis identified the radioactivity as iodine-131.
The hospital that produced the waste (urine) was identified, but it did not have a nuclear medicine department. The investigation revealed that the waste did come from a patient at this hospital, but who had received I-131 for his thyroid disease in the nuclear medicine department of another hospital. The patient returned to the original hospital a few hours after his treatment.
The nuclear medicine department had recommended (in writing) that the hospital collect waste from the patient for the first three days after treatment, and to decay and store it for 7 days. However, waste was handled in the usual manner and transferred to the incinerator two days before the scheduled date.
The two contaminated bags identified were returned to the nuclear medicine department and kept in their decay store for the required time.
Although the dose rate measured in contact with the bags of waste was significant, it is estimated that doses to the waste handlers were likely to be very low (at most a few 10’s of µSv). However, had the waste been stored close to routinely occupied areas, the doses could have been much higher (several mSv), and above the public dose limit of 1 mSv/y.
Lessons to be learned from the incident
Any establishment receiving a patient that has undergone a nuclear medicine procedure must be informed of the necessary radiation protection precautions to be taken, and the correct procedures for the storage and disposal of any radioactive waste arising. This information should be prepared by the nuclear medicine department and attached to the patient's file. Equally important is that these instructions are observed, and it should be ensured that all relevant persons have appropriate instructions and training.
Where there are requirements associated with the disposal of radioactive waste, appropriate equipment and procedures for monitoring the waste should be available. This is becoming more important as the number of portal detectors at incinerators and other waste receiving sites increases. These portals are often set at very low alarm thresholds, and waste suppliers and receivers should, where possible, co-operate so that the number of incidents is reduced.