Inputs of plutonium isotopes from the Rhône River to the Gulf of Lion (North Western Mediterranean Sea) over the 1945-1998 period: Mass balances, fluxes and predictive trend.

EYROLLE F., DUFFA C. and CHARMASSON S. International Conference in the Radioactivity in the Environment - 2/5 sept 2002 - Monaco.

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. Due to a new treatment process applied to the liquid effluents, a decrease of two order of magnitude of industrial plutonium discharge in the Rhône River has been registered from 1991. Today, 238Pu industrial inputs in the Rhone River are still about ten fold higher than terrestrial ones while 239+240Pu inputs from industrial and terrestrial source terms are of similar importance, i.e. 1 GBq y-1. As the Marcoule reprocessing installation is being dismantled, a new consistent decrease of industrial releases is expected in the near. The plutonium industrial primary source for the Rhône freshwaters may then have a slight contribution compared to the terrestrial one. Nevertheless, our results evince that the River sedimentary compartment act either as a sink or a delayed-source term of plutonium for the freshwaters depending on the hydraulic regime and flood events. This compartment may then represent an important industrial delayed-source term for the Rhône River freshwaters. These results have been obtained from samplings collected at the lower course of the Rhône River over the 1987-1998 period and analysed for 238Pu and 239+240Pu contents. Both River sedimentary stocks of plutonium isotopes and effective outputs from the Rhône River towards the Golf of have been yearly estimated over the 1945-1998 period. Regarding 239+240Pu, the continental sedimentary stock accumulated since 1945 is estimated to 120 +/- 30 GBq which is a non negligeable source term at the Rhône watershed scale.