Regulatory oversight of radiation safety

Employee radiation exposure

STUK monitors the radiation safety of nuclear power plant employees by inspecting the plant’s exposure monitoring, radiation measurements, radiation protection procedures, the radiation circumstances in the facility and radiation protection arrangements of work tasks.

Olkiluoto and Loviisa employ a permanent staff of about 1,000 people, who are covered by individual radiation dose monitoring. During annual maintenance and repair works, there are several hundreds or even thousands of outside workers at the plants, whose radiation doses are also monitored. Radiation dose monitoring at Finnish nuclear power plants covers approximately 3,000–5,000 people annually. Occupational doses are mainly caused during annual maintenance of nuclear power plants, when employees work with active components and near opened systems. The length of the annual maintenance and significant tasks from a radiation protection viewpoint affect the combined dose size.

Discharge of radioactive substances

During operation, radioactive substances are formed in the nuclear reactor. The radiation emitted from these substances may affect people’s health. Radioactive substances are mainly attached to the nuclear fuel in the reactor. However, a small part of the substances are also in the reactor cooling system and attached cleaning and waste systems. The facility’s water and air discharges are cleaned by filtering and delayed so that their radiation impact on the environment is very small compared to the effect of radioactive materials which occur normally in nature. Gaseous discharges are led to the power plant’s ventilation chimneys and water discharges are led into the sea along with the cooling water. Discharges are measured carefully and ensured to be clearly below the limits set.

Nuclear power plant companies report discharge data to the Radiation and Nuclear Safety Authority on a quarterly basis. Methods of measurement of nuclear power plant discharges have been approved by the Radiation and Nuclear Safety Authority. The Radiation and Nuclear Safety Authority regularly inspects the power plants’ discharge systems.

Monitoring of environmental radiation

Environmental studies of Finnish nuclear power plants started before the plants were commissioned, and now a diverse and comprehensive radiation monitoring programme approved by STUK is carried out in the surroundings of nuclear power plants. Every year approximately 600 samples from Loviisa and Olkiluoto are collected an analysed. Samples are taken from, for example, household water, foodstuffs, air, rain water, the ground, sea water and the seabed. External background radiation and radioactivity in people living in surrounding areas is also measured regularly.

Residents’ exposure to radiation

Residents’ exposure to radiation is assessed annually based on power plants’ discharge data and environmental samples as well as meteorological measurements. In Finland, the Government has set a radiation dose constraint of 0.1 millisieverts per year for individual residents in areas surrounding nuclear power plants, when the radiation is caused by normal operation in the plants. This is about one fortieth of the average radiation dose received by Finns from different sources during the year. In recent years, the radiation dose caused by nuclear power plants in Finland to nearby residents has been less than one percent of the constraint set by the Government (see also).