Plutonium fluxes from the Rhône River to the Mediterranean Sea

¹ Institut de Protection et de Sûreté Nucléaire, Département de Protection de l'Environnement/SERNAT, CEN-Cadarache, BP. 1, 13108 Saint-Paul-lez-Durance cedex, France
² Institut de Protection et de Sûreté Nucléaire, Département de Protection de l'Environnement/SERNAT, Base IFREMER, BP. 330, 83507 La Seyne-sur-Mer cedex, France

Abstract

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 and 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 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+240Pu source term at the scale of the Rhône River catchment basin.