TREND OF OCCUPATIONAL RADIATION EXPOSURE AT NUCLEAR POWER PLANTS

Now in Japan, 24 nuclear power reactors are in commercial operation, and about 20% of the total electric power supply is provided by nuclear power. Corresponding to the development of nuclear power plants, the number of workers engaged in jobs with radiation exposure has also been increased markedly. The annual statistical summaries of occupational radiation exposure at each nuclear power plant were compiled by reactor types, and the trend of occupational exposure at the nuclear power plants was investigated for the years 1970-80. The summary of results and comments are as follows. 1. The individual exposure level has been well controlled below the occupational dose limit (5 rem/yr). 2. The collective dose (man-rem) has been increasing with plant age, and the diffrence of collective dose among reactor types is noticeable. 3. The proportion of external personnel to the total workers in both the number of radiation workers and the collective dose has been gradually increasing. In 1980, 89% of the total number of workers and 93% of the total collective dose were occupied by external personnel. 4. Most occupational exposure at nuclear power plants has been incurred during maintenance and repair rather than the routine operation, so the annual collective dose is in inverse proportion to the plant annual availability. 5. Occupational exposure at the nuclear power plants must be controlled as low as reasonably achievable (ALARA), not only for the individual dose but for the colletive dose to total workers. To achieve ALARA, reactor and plant design reducing exposure, automation and remote control in radiation work and radiation protection training for the radiation workers must be developed.