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Plutonium isotopes in the lower reaches of the River Rhône over the period 1945-2000: fluxes towards the Mediterranean Sea and sedimentary inventories.


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Frédérique Eyrolle , Sabine Charmasson, Didier Louvat

Journal of Environmental Radioactivity 74 (2004) 127-138

Type de document > *Article de revue

Mots clés > plutonium, Rhône/Vallée du Rhône, sédiment

Unité de recherche > IRSN/DEI/SESURE/LERCM

Auteurs > CHARMASSON Sabine, EYROLLE Frédérique

Date de publication > 20/05/2004

Résumé

Plutonium isotopes in the Rhône River originate from both the weathering of the catch­ment basin contaminated by global atmospheric fallout, and the liquid effluents released from the Marcoule reprocessing plant since 1961. Due to a new treatment process applied to the liquid effluents, a decrease of two orders of magnitude in the industrial plutonium dis­charged into the River Rhône has been registered from 1991. Today, 238Pu industrial inputs to the River Rhône are still about 10 times higher than those derived from global fallout, while 239+240Pu inputs from industrial and global fallout sources are of similar importance, i.e. 1 GBq y-1. Our results indicate 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 River Rhône freshwaters in the coming years as the Marcoule reprocessing plant is being dismantled. These results were obtained from samples collected from the lower course of the River Rhône over the 1987-1998 period and analysed for 238Pu and 239+240Pu activities. Both river sedimentary inventories of plutonium isotopes and effec­tive outputs from the River Rhône towards the Gulf of Lions have been estimated for each year over the 1945-2000 period. Regarding 239+240Pu, the sedimentary inventory accumu­lated since 1945 is estimated to be 172 ± 35 GBq. If mobile, this amount represents a signifi­cant delayed-source term of plutonium on the scale of the Rhône watershed