A mobile whole-body counter for measuring internal contamination at nuclear power plants

A mobile whole-body counter was constructed at the Institute of Radiation Protection for the measurement of internal contamination in persons working at Finnish nuclear power plants. Another important use for this mobile system is contamination measurements in people involved in radiation accidents. The whole-body counting system was installed in a truck. The background shielding of the counter consisted of lead and weighed about 2500 kg. The measurements were performed in a modified chair geometry with a NaI(Tl) detector. Since 1976 measurements have been carried out on persons working at the nuclear power plants. Detectable amounts of 51Cr, 54Mn, 58Co, 60Co, sup(110m)Ag and 124Sb were found during or after the annual maintenance and partial refuelling period. The highest amounts of radioactivity were found in persons participating in mechanical work. Work with insulation, cleaning, waste and decontamination was also found to involve risks of internal contamination. (author)