Plutonium fluxes from the Rhône River to the Mediterranean Sea

Abstract

Plutonium isotopes carried by the Rhone 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 238 Pu industrial inputs are still at least ten times higher than terrestrial inputs, 239+240 Pu inputs from industrial and terrestrial source terms are of similar importance, i.e. 1 GBq y-1 each. An empirical relation between the 239+240 Pu activities in the river water downstream Marcoule and the Rhone 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 Rhone River. Furthermore over the 1987-1998 period the accumulated 239+240 Pu and 238 Pu activities within the whole sedimentary compartment of the river or deposited on the terrestrial surroundings during flood events arc 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+240 Pu source term at the scale of the Rhone River catchment basin.