Finnish nuclear power plants must be so safe that an accident requiring people to shield themselves against radiation cannot happen. The nuclear power companies are responsible for the safety and the Radiation and Nuclear Safety Authority (STUK) supervises that the companies operate in accordance with regulations.

Although the probability of discharges in a Finnish nuclear power plant leading to protective measures  is known to be extremely low, accidents causing discharges must be prepared for. For preparedness, the best possible calculations of the spread of radioactive substances are needed.

According to Senior Inspector Mikko Voutilainen from STUK, now was the right time to update the dispersion calculations made in the 1990s. Calculation methods and tools have evolved, so the dispersion of radioactive substances can be assessed more accurately than before. The new calculations have been published in STUK's report “Potential consequences of a hypothetical nuclear power accident in Finland”.

“The new calculations are based on the Finnish Meteorological Institute's more accurate weather forecast data for four years, which are as realistic as possible, while the older calculations were based on estimates of the worst possible weather conditions at the time,” says Mikko Voutilainen.

The calculations provide additional information on how far from the accident site preparedness arrangements for different protective measures could be considered.

The report's calculations are based on the assumption that radioactive substances would somehow be discharged from the nuclear power plant into the air. It has not been assessed what accidents should take place in nuclear power plants or what safety systems should fail in order for the radioactive discharges on which the calculations are based to occur.

In addition, the probabilities of the releases examined have not been considered in the work. They must be taken into account when making emergency plans.