Conséquences des crues du Rhône sur les flux de 137Cs, 238Pu, 239+240Pu vers la mer Méditerranée

Titre du congrès :11th International Symposium on the Interactions between Sediments and Water
Ville du congrès :Esperance
Date du congrès :17/02/2008

The continental shelf of the Gulf of Lion (NW Mediterranean Sea) is one of the largest in the Mediterranean Sea and is characterised by large amounts of terrestrial material inputs and high rates of biological productivity. Sediment inputs to this environment are dominated by those from the Rhône River. The major role played by floods in annual sediment budgets is generally known and has been demonstrated in various case studies. For the North Western part of Mediterranean Sea, floods of the Rhône River are considered to be key moments for sedimentary fluxes. Important industrial and agricultural activities in the river basin result in strong nutrient and pollutant fluxes to the Rhône, an anthropogenic impact that also affects the marine system, since the Rhône inputs play a leading role in the functioning of the whole Gulf of Lion. Almost twenty nuclear reactors are located along the Rhône valley, representing Europe's biggest concentration of nuclear power plants. Until its closure in 1997, the Marcoule reprocessing plant of spent nuclear fuel released most of the liquid radioactive wastes to the river. Radioactive isotopes observed in the Rhône also originate from the weathering of the catchment basin contaminated by the global atmospheric fallout from the past nuclear tests carried out between 1945 and 1980 and the atmospheric fallout from the Chernobyl accident in 1986. These primary radioactive inputs are today several orders of magnitude lower than those observed at the beginning of the 90s. Nevertheless, floods strongly act on the reuptake of contaminated sediment accumulated over the past 40 years of nuclear production/reprocessing. This particularly concerns long-lived particle reactive artificial radionuclides such as 137Cs, 238Pu and 239+240Pu. Our studies conducted from 2002 to 2004 show that more than 50% of caesium and plutonium annual fluxes are driven to the marine environment during floods that occurs only 10 to 20 days per year. 30% to 90% of these fluxes originate from the remobilisation of sedimentary storages.