Plutonium and Americium repartition in the terrestrial environment of the lower Rhone Valley.
Céline DUFFA, doctorate thesis of the University of Aix Marseille III, speciality: Geosciences of Environment, defended on the 27th March 2001.
The radionuclides 238Pu, 239+240Pu and 241Am are omnipresent in the surface environment due to the fallout from atmospheric nuclear tests (1945?1980) and the disintegration of a US nuclear reactor satellite in 1964. Actinide activities resulting from this global fallout are estimated to be 770 GBq over an 11000 km2 area in the lower Rhone valley. Deposits, which are characterized by a low 238Pu/239+240 Pu activity ratio, are homogeneously distributed.
Some particular areas of the lower Rhone valley show higher surface activities and activity ratio, related to Marcoule nuclear plant releases.
Additional actinide activities are estimated to be 2.8 GBq within a 30 km2 area around Marcoule facility. It has been shown that they are mainly due to old atmospheric releases.
The Rhone River, which is used to dilute liquid releases, is a water supply for many cultivated areas. Some 0.6 GBq were transferred to soils since 1960 via the BRL ditch, and a total amount of 3.5 GBq were deposited onto rice fields in the Camargue for 40 years.
The 1993/1994 Camargue floods also represented a way for Marcoule liquid releases to be deposited onto soils. The 238Pu/239+240Pu activity ratio is used as a tool to trace the Rhone River inputs. Measurement results suggest a very heterogeneous deposit.
Activities transferred to vegetation represent less than 0.1% of the soil total stock. Even though this region is an agricultural one, annual crops lead to very low activity exports.