Plutonium fluxes from the Rhône River to the Mediterranean Sea.

F. Eyrolle, M. Arnaud, C. Duffa and P. Renaud Actes du congrès ECORAD, 3-7 sept 2001, Aix en Provence, France Radioprotection - Colloques, volume 37, C1-87 / C1-92.

Plutonium isotopes carried by the Rhône River mainly come from the catchment basin weathering affected by atmospheric fall-out and from the liquid effluent discharges from the fuel reprocessing plant located at Marcoule. Nowadays, while 238Pu industrial inputs are still at least ten times higher than terrestrial inputs, 239+240Pu inputs from industrial and terrestrial source terms are of similar importance, i.e. 1 GBq y-1 each. An empirical relation between the 239+240Pu activities in the river water downstream Marcoule an the Rhône flow rate is obtained from data collected over the 1987-1998 period. This relation underlines that the river bed sediments act as a delayed source of plutonium depending on the hydrological conditions of the river. During flood events this delayed source may contribute up to 40% of the plutonium activity at the lower course of the Rhône River. Furthermore over the 1987-1998 period the accumulated 239+240Pu and 238Pu activities within the whole sedimentary compartment of the river or deposited on the terrestrial surroundings during flood events are 15 and 4 GBq respectively, thus representing about 10% of inputs. At present, this stock that can potentially be re-suspended, is an important 239+240Pu source term at the scale of the Rhône River catchment basin.