Mapping the deposition of 137Cs and 131I in North America following the 2011 Fukushima Daiichi Reactor accident

Abstract

The 2011 Fukushima Daiichi Reactor accident generated a large data set of global radionuclide observations. Frequent observations of xenon, caesium and iodine radioisotopes provided an opportunity to examine the performance of inter-continental scale meteorological models, in particular, the important mechanisms of in-cloud scavenging, precipitation, and deposition. Previous studies investigated these phenomena over short range, but this is the first time a global, coordinated surveillance system and in particular, a non-scavenged noble gas data set was available for use in such a study. Since particle size distributions are very different at long range, the parametrization of the deposition is important for accurate atmospheric modelling. The accuracy of these models are crucial in the Comprehensive Nuclear-Test-Ban Treaty (CTBT) context where discrimination of local and distant civilian sources from a potential nuclear test is a challenging problem. Beyond the CTBT context, accurate prediction of deposition is important for emergency and consequence management of nuclear emergencies, allowing a small set of data, combined with an appropriate model to represent a much larger domain, even up to continental scales. The modelling results for ground deposition and airborne activity of radiocaesium and radioiodine are presented and validated against the actual measurements.