Radiation Protection and Dose Measurements During the Operation of Reloading of 3.41 PBq 60Co Sources

Full text: The panoramic 60Co irradiation facility at the Rudjer Boskovic Institute is suitable for a variety of applications: from medium doses used in radiobiology to high doses pertaining to radiation processing and radiation chemistry research. It was designed and constructed to provide maximum flexibility with respect to dose rate. The irradiation source itself is formed by 24 source assemblies arranged in a cylinder, 26 cm in diameter. In February 1983 1.85 PBq of 60Co, produced in the USSR, in the form of 48 pencils were loaded in 12 source holders, 4 pencils in each holder. In June 1991 additional 3.5 PBq of 60Co in the form of 42 pencils were loaded in 12 source holders, 6 holders containing 4 pencils and 6 holders containing 3 pencils. Due to the decrease of 60Co activity 12 source holders installed in 1983 had to be exchanged and new sources installed. In June 2000 new 3.41 PBq of 60Co, in the form of 48 pencils were received by the Rudjer Boskovic Institute. We had first to unload 12 source holders (186.5 TBq) installed in 1983 and after that to load the new 48 sources (3.41 PBq) into the irradiator. So the irradiator reached its maximum rated activity (4.42 PBq). The radiation protection measures during unloading of old sources and loading of the new ones are described in detail. All operations were planned in advance. Lessons learned during the two previous loading operations were analysed and taken into account. Necessary technical and organisational improvements were made. All personnel were trained in accordance with the previously prepared scenario, in which each operation was described and the person designated to carry out that operation was defined, as well as the person supervising that particular operation. The highest whole body dose during the exchange of sources was 0.42 mSv. (author)