Estimate unfavorable meteorological conditions based on ERA5 data for the transport of radionuclides from the nuclear power plant site

The main goal of this study is to estimate the most unfavorable stability conditions for the purpose of transport and dispersion simulations of radioactive nuclides from hypothetical accidental releases at a planned nuclear power plant location. Based on these weather sequences, it is possible to determine, with a high degree of confidence, the maximum extent of Emergency Planning Zones (EPZs) around nuclear power plants, thereby enabling effective preparedness planning and optimized emergency response strategies. The analysis is based on the ERA5 reanalysis data set for the 24- year period between 2000 and 2023. The Pasquill-Gifford stability conditions were computed with the use of ERA5-derived near-surface winds and net surface radiative fluxes. The different methods for estimating net surface radiative flux allow the selection of the most unfavorable stability conditions from the point of the adverse effects on the environment and humans. A continuous multi-day sequence, based on different combinations of stability classes, depicts possible realistic scenarios. The statistical analysis led to the selection of the reference year for the purpose of accompanying site evaluation studies with a numerical dispersion modelling suite. The short-range simulations of instantaneous atmospheric dispersion with JRODOS/RIMPUFF models are performed to compare the expected doses for the selected meteorological conditions.