The design of the Hanhikivi 1 nuclear power plant takes into consideration the various natural phenomena that affect plant safety, and, for example, the escalation of weather phenomena caused by climate change.
Nuclear safety design must be carried out systematically to ensure that the total risk for society is small. To ensure safety, different external hazards and phenomena that can be assumed to occur less frequently than once in a hundred thousand years are taken into account in the design values for a nuclear power plant. The probability of the phenomena occurring is thus less than 10-5 per year.
In the Finnish conditions and especially in the Hanhikivi headland area, phenomena to consider include variation in the sea water level, whirlwinds and downbursts, and weather phenomena potentially becoming more extreme as a result of climate change – in practice, the impact of storms and extreme conditions on plant safety.
When determining the design values for the plant, we have primarily used the observation history of the Finnish Meteorological Institute. However, observations have been recorded only for the last hundred years or so, depending on the phenomenon. Determining the probability of the phenomena recurring and the extreme values corresponding to them for a recurrence interval of up to 10 million years has required a lot of quantitative analysis and the utilization of expert knowledge. We have also taken the impact of climate change into account in the calculations in accordance with the different climate change scenarios of the Intergovernmental Panel on Climate Change (IPCC). This way, we have determined design values for the plant that cover the entire life cycle of the plant.
For example, according to our calculations, the sea water level of the plant area that corresponds to the probability of 10-7 per year is 308 cm. The power plant area has been raised to a level of 4.6 meters and the Hanhikivi 1 nuclear power plant will be watertight up to a level of 4.9 meters to ensure that among other things, the impact of climate change and waves are taken into account sufficiently in the plant design. In addition, the Hanhikivi 1 nuclear power plant will be able to withstand whirlwinds of the worst tornado category F5, and the sea water temperature rising to a tropical level of 32 °C will neither jeopardize the plant’s safety.