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Sedimentary Beds as a Delayed Source of 137Cs, 238Pu and 239+240Pu for the Rhône River Freshwaters.


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F. EYROLLE and C. DUFFA 9th International symposium on the interaction between sediments and water, 5-10 May 2002, Banff Springs Canada. International Association for Sediment Water Science (IASWS)

Résumé

137Cs, 238Pu and 239+240Pu in the Rhône River originates both from the weathering of the catchment basin submitted to the global atmospheric fallout and from the Marcoule reprocessing plant liquid releases. Industrial discharges have decreased first from 1991 due to a new treatment process applied to the liquid effluents and second from 1997 for 137Cs only due to the Marcoule installation stoppage and dismantling. Today, while 238Pu industrial inputs are still about ten fold higher than terrestrial inputs, 239+240Pu inputs from industrial and terrestrial source terms are of similar importance, i.e. 1 GBq y-1 each, and 137Cs industrial inputs are lower than terrestrial ones. Water samples were collected at the lower course of the Rhône River over the 1987-1999 period and analysed for 137Cs, 238Pu and 239+240Pu content. The results obtained evince that the river sediment compartment act either as a sink or a delayed-source term of caesium and plutonium isotopes for the freshwaters depending on the hydraulic regime and flood events. Sediments stocks are time scale dependant. 137Cs and plutonium isotopes sedimentary storages are estimated for the 1998-1999 and 1987-1998 periods, respectively.