Estimating the population's exposure
Estimating the population’s exposure
Exposure to radiation among residents of the area around nuclear power plants is assessed annually based on power plants’ discharge data and environmental samples as well as meteorological measurements.
Discharges from nuclear power plants are effectively absorbed into the massive amounts of air and water around them; that is, into the atmosphere and the sea. For this reason, only very tiny amounts of radioactive substances accumulate in the environment around plants. These can only be detected with highly sensitive measurement methods (see the results of environmental radiation monitoring). The amount of substances discharged from the plant during normal use is so small that it is impossible to measure the radiation dose to which the population is exposed. For this reason, radiation doses are determined through analytical estimation.
The radiation exposure of the population is calculated by defining an individual from the “critical group” (a person representing the group of people most exposed), for whom the largest possible radiation doses can be determined based on the individual’s place of residence and lifestyle. It is not a real person. The calculations are made using an imaginary person who lives in the vicinity of the nuclear power plant. This person’s diet consists mainly of natural produce from the area around the power plant, including berries, mushrooms and fish, as well as milk from a nearby farm and local grain and meat products. In addition, the person spends a lot of time on the shores near the nuclear power plant and swims in the sea. The results of the calculations are very conservative—in practice, it is the largest possible radiation dose that a person can be exposed to when living in the vicinity of the nuclear power plant. In reality, people living near nuclear power plants are exposed to much smaller radiation doses.
If plants discharged so much radioactive material that it increased the radiation levels in the vicinity, the situation would be detected immediately by the monitoring networks surrounding the plants. The networks are made up of measuring stations located 1–5 kilometres away, from which information is sent directly to the computers at the plants and can be checked at any time by the Radiation and Nuclear Safety Authority. If the dose rate at a plant increases above the alarm limit of 0.4 microsieverts per hour, the system sends an alert to STUK’s emergency team. In Finland, background radiation varies from 0.05 to 0.30 microsieverts per hour (µSv/h).