SOurce CHAracterizatiOn accounting for meTeorologIcal unCertainties (SOCHAOTIC) – final report: Final report of the NKS-B SOCHAOTIC activity

In recent years, events have occurred in which radionuclides were detected by filter stations in Europe without knowledge on the origin of those radionuclides. In such cases, there is a need to locate potential release sites. However, if the release site is actually known, or if a potential release site has been localized by inverse methods, then there is an additional need to estimate the release rates from this location as a function of time for the various radionuclides detected. While in the SLIM NKS project, methodologies were developed to localize an unknown source of radionuclides dispersed in the atmosphere, the SOCHAOTIC project has developed methodologies, suited for operational use, by which characterization of the source, whose location is known, can be derived, i.e. to estimate the temporal release profiles of the radionuclides detected. For operational use, nuclear decision-support systems should be extended with modules handling and analysing such monitoring data automatically, and conveying the data together with the geographical coordinates of the release point to the national meteorological centre accompanied by a request to estimate the temporal evolution of the release rates. A number of case studies have been selected, viz. the ETEX-1 and the October 2017 case of Ru-106 in Europe as well as an artificial case. Methods for estimation of the temporal release profiles have been developed, and they have been applied to the selected cases by using the DERMA, MATCH, SILAM and SNAP atmospheric dispersion models. The methods have been applied both by using deterministic numerical weather prediction (NWP) model data and ensemble-statistical NWP model data derived by setting up and running the non-hydrostatic high-resolution Harmonie model for the selected cases. Finally, an interface to a nuclear decision-support system, ARGOS, is described.