How are radioactive deposits redistributed among watersheds in post-accidental situations? Lessons learned from the Chernobyl and Fukushima accidents

As radioactive releases in the atmosphere resulted in heterogeneous deposits on large continental surfaces including forests, farming lands and residential areas, water runoff in contaminated areas governs the downstream redistribution of caesium 134 and 137. Based on several published studies, this report proposes a synthetic overview of the knowledge of radionuclide flows associated to these processes. The quantity of radio-caesium concerned by watershed washouts has been studied, and appeared to be the result of complex hydrologic and erosive processes. Some studies noticed that, in this respect, the comparison between exported flows in Chernobyl and in Fukushima is difficult because the washout of radio-caesium was essentially solid in Fukushima while liquid in Chernobyl. Thus, the strategy applied for the management of aquatic environments is different