Calculation of radiation exposure

Modelling of the transfer of radionuclides starting from the discharge of radioactive substances from the exhaust air stack through the biosphere to humans.

By means of the assessed discharges provided by the operator the radiation exposure in the vicinity of every nuclear installation is calculated for a reference person. This reference person is a hypothetical individual, whose behaviour in regard to location and consumption habits results in the highest possible exposure to radiation (conservative assumptions).

Calculating radiation exposure using computer simulation

Dispersion models are used for the calculation. Using computer simulations, they calculate the transport processes of radionuclides from a nuclear installation into the various areas of the environment (see figure "Modelling of the transfer of radionuclides").

Dose fractions of the radioactive substances discharged in exhaust air during the operation of nuclear power plants

The radiation exposure of the population can be determined from these concentrations of radioactive substances in the various environmental media (e.g. by means of the calculation model DARTM). In accordance with the Radiation Protection Ordinance, the exposure must not exceed

• 0.3 millisievert for the effective dose,
• 0.9 millisievert for the thyroid and
• 1.8 millisieverts for the bone surface

in one calendar year.

The greatest proportion of radiation exposure during normal operation is due to the radionuclide carbon-14 (see figure "Dose fractions of the radioactive substances discharged in exhaust air during the operation of nuclear power plants"). In this context, especially the intake of carbon-14 in the form of carbon dioxide through food (ingestion) is relevant to the dose.

Activity discharges in exhaust air

Calculated effective dose of the reference person “adult” due to discharges in exhaust air (time period 1990 to 2016)

Under conservative assumptions, the radioactivity discharges in exhaust air add up to a radiation exposure of

• less than 10 microsieverts in one calendar year for toddlers
• less than 5 microsieverts in one calendar year for adults.

These values are at significantly less than one per cent of the natural radiation exposure of the population (see figure "Calculated effective dose of the reference person "adult" due to discharges in exhaust air").

Activity discharges in waste water

The discharge of radioactive substances in waste water has been clearly reduced by high-performance systems for the treatment of waste water from nuclear installations.

Calculated effective dose of reference persons “adults” and "toddlers" due to discharges in waste water in 2016

Now, the calculated radiation exposure due to waste water is

• less than 2 microsieverts in one calendar year for toddlers
• less than 1 microsievert in one calendar year for adults (see figure "Calculated effective dose of the reference person “adult” due to discharges in waste water").

Reporting is a statutory mandate

The radiation exposure of the population determined from the activity discharges in exhaust air and waste water is documented in the parliamentary report and in the BMU annual report "Environmental Radioactivity and Radiation Exposure".