Present situation of occupational radiation exposure in nuclear power plants

The present situation of the radiation exposure of workers, including both employes and subcontractors, in the nuclear power plants in Japan, is presented. Twenty seven nuclear power reactors in operation and under construction are tabulated with the name, the owner, the electric output and the commissioning year of each plant. The results of exposure of the workers in these plants are shown, classifying the dose rate into less than 0.5 rem, 0.5 - 1.5 rem, 1.5 - 2.5 rem, 2.5 - 5 rem and more than 5 rem, and the workers into employes and subcontractors. It is noted that the exposure dose of the subcontractors occupies about 88% of all exposure dose, and the exposure is concentrated during regular inspection period. The exposure dose of about 80% of the workers is less than 0.5 rem, and no one was irradiated more than 5 rem in a year. The total exposure dose, which has especially the tendency of increasing with extended maintenance period and decreasing during plant operation period, shows also the trend of increasing with the lapse of operation years. As for the point of view of whole exposure dose, the value is 0.06 -- 0.43 man-rem/106 kWh in 1976 FY. It is considered to be necessary to grasp the total exposure dose of each worker wandering from one plant to another, and the central registration center for the workers in radioactive environment was established in 1978. The whole exposure dose data of each worker are stored in the central computer in this center. This system is highly appreciated in radiation exposure management. The total exposure dose is related to the rate of utilization of nuclear plants, and it is expected to decrease with the decrease of plant outage. (Nakai, Y.)