Overexposure to Radiation Worker

This is an isotope manufacturing facility. The licensee technician needed to transfer a Co-60 source drawer into a shielded container called a therapy head. A special handling tool had been bolted to the end of the source drawer and this tool was needed to safely transfer the source back inside the therapy head. The technician attempted to move the source drawer in order to gain access to the handling tool but the source drawer was stuck, so the technician pulled on the drawer. In doing so, the drawer slid out of the cask about 22.8 cm (9 inches), bringing the source to within an estimated 5.1 cm (2 inches) of the cask external surface and exposing the technician. The technician quickly pushed the source drawer back inside the cask and noted that the electronic personnel dosimeter (whole body) being worn by the individual was reading 56.2 mSv (5.62 rem). The technician was not wearing extremity dosimetry. The technician immediately left the area. The licensee’s preliminary calculations are a whole body dose of 169 mSv (16.9 rem). Depending on various assumptions, the extremity dose is estimated to be between 2,370 mSv and 9,500 mSv (237 to 950 rem). The technician’s badge has been sent for emergency processing and the individual is being restricted from radiation work for the time being. NRC EN51331

UPDATE: The NRC conducted a comprehensive follow up inspection for this event. The NRC and company officials found, through a review of the video surveillance, that the technician actually removed the source drawer from the cask and replaced it within 4-5 seconds. The source drawer contained approximately 135.6 TBq (3,664 curies) of Cobalt-60 and the design of the source drawer was such that the radiation beam was highly collimated. On October 1, 2015, the company informed the NRC that it was assigning a whole body deep dose equivalent of 56.2 mSv (5.62 rem) for the August 20, 2015 event, and a maximum extremity dose of 384 mSv (38.4 rem) to the technician’s left hand. The licensee determined that the root cause of the event was poor coordination and control and the technician’s removal of the source drawer. Corrective actions included personnel training and procedure modifications. NRC EN51331

Location: Idaho Falls, ID/ International Isotopes, Inc.
Event date: Thu, 20-08-2015
Nuclear event report
Legenda & explanation