Exceptional weather and nuclear power plant safety in Finland&#160;
Authors: Jylhä Kirsti , Olsson Taru , Rantanen Mika , Rauhala Jenni , Laurila Terhi , Leijala Ulpu , Luomaranta Anna , Särkkä Jani , Virman Meri 
Published: June 2022

&lt;p&gt;More than 80 % of total electricity consumption in Finland is covered by domestic production. While 52 % of the Finnish electricity production in 2020 was based on renewable energy sources, 34 % of electricity was generated with nuclear power. Currently there are five nuclear power plant (NPP) units in the country, two in Loviisa in the south and three in Olkiluoto in the west, all along the seashore. Because of the importance of the NPPs to national electricity production, no external or internal events should hamper their normal operation.&lt;/p&gt;&lt;p&gt;As defined by the Finnish Radiation and Nuclear Safety Authority (STUK), overall safety management over the life cycle of an NPP unit requires, among others, probability estimates for external events triggered by exceptional weather events, such as very high and low atmospheric temperatures, high winds including tornadoes and downbursts, rain, snow, hail, freezing rain, lightning, and drought. The probability estimates are used in the safety assessments of existing and new NPP units and in the design of new safety features.&lt;/p&gt;&lt;p&gt;This presentation shows some results from our weather-related studies conducted within the Finnish Research Programme on Nuclear Power Plant Safety (SAFIR2022). A closely related presentation in this session, given by Leijala et al., focuses on sea level research relevant for nuclear safety.&lt;/p&gt;&lt;p&gt;Our current topics include the climatology of convective sea-effect snowfall, heavy precipitation jointly with high sea level, large-scale windstorms and derechoes, i.e., clusters of downbursts. &amp;#160;Changes in the seasonal cycle of sea-effect snowfall have been studied based on reanalysis data (ERA5) and trends in the frequency of the compound precipitation and sea level events using observational data. In addition, we have examined tracks and clustering of large-scale windstorms based on ERA5 and occurrence of derechoes based on the FMI network of meteorological stations and weather radar data.&lt;/p&gt;&lt;p&gt;Even very low annual probabilities of occurrence are of relevance for the NPPs. Therefore, meteorological and climatological research conducted for other applications, including building regulations, land use planning and infrastructure protection, is supportive but typically not sufficient. The topics discussed here have been selected based on feedback from STUK and the Finnish NPP companies. For example, although intense snowfall does not pose a direct threat to the safety systems of the NPPs, it might hamper the normal operation of the support systems and their interface with the environment, e.g., by blocking ventilation air intakes.&lt;/p&gt;&lt;p&gt;References:&lt;/p&gt;&lt;p&gt;Leijala et al.: Examining extreme sea levels for the support of nuclear power plant safety in Finland.&lt;/p&gt;&lt;p&gt;Official Statistics of Finland (OSF): Production of electricity and heat [e-publication].&lt;/p&gt;