CBRN event in United States of America on Wed 17th April 2024

An employee received a dose of 0.95 Sv (95 rem) to the extremities (hands) due to improper handling and response to an incident involving a damaged 85.1 MBq (2.3 mCi) Co-60 source. This dose was estimated by the Illinois Emergency Management Agency and confirmed by the licensee. The source was initially damaged when molten steel flowed over the source housing, severing the source into at least two pieces. The smaller portion, estimated to contain approximately 2.0 MBq (53 uCi), was inadvertently withdrawn from its shielded housing, fused with solidified steel and later partially recovered by the employee.

The remainder of the Co-60 source was found to have been covered in solidified steel that prevented its return to the shield. The employee used a 4-inch angle grinder in an effort to remove the solidified steel so it would fit back into the shield. Inspection findings indicate the employee used gloved hands to effect recovery and handle both source fragments. Inspection findings also identified routine handling of intact sources during installation/removal. The combined activities, duration of the movements and frequency of handling were used to estimate the above extremity dose. During the grinding operation, the internal Co-60 wire was impacted and gave rise to site contamination.

An examination of the source and estimates from the manufacturer indicate the amount of activity involved in the grinding operation (much less the portion available for respiration amongst sparks/abrasive material) was insufficient to result in an inhalation dose in excess of regulatory limits. The causes of the incident were inadequate training and failure to follow operating procedures. In addition, the improper handling of sources was due, in part, to an unauthorized modification of the sealed source, dated shielding assemblies and repeated physical damage and fouling of the threads atop the sealed source. The employee has ceased work with radioactive materials for the year. Corrective actions taken by the licensee in response to this event include writing a new procedure, making an engineering change to the system, and implementing improved procedures. The dose to the employee exceeded the U.S. regulatory limit for the annual dose to the skin of the extremities of 0.5 Sv (50 rem).