Plutonium Isotope Remobilization from Natural Sediments (Gulf of Lions, Northwestern Mediterranean Sea): Estimation Based on Flume Experiments.

For the last forty years, military and industrial spent-nuclear fuels were reprocessed at the Marcoule plant located along the Rhone valley (France). Low-level plutonium isotopes contained in liquid wastes were released into the Rhone River, which represents the main fresh water input to the western Mediterranean Sea. Over these years, a reservoir of artificial radionuclides was built up both in sediments of the river and in sediments of the Rhone mouth in the Mediterranean Sea. Because of the high affinity of plutonium for suspended particles, coastal sediment could be considered as one of the major sinks for plutonium but not the ultimate one. In fact, this reservoir can act as a delayed source of plutonium for the water column by redissolution, thermal and photochemical reactions, and punctually during resuspension events. Later process occurs largely during most of the year because winds are highly frequent in this region. In 1997, the Marcoule reprocessing plant ceased its activities, leading to a significant decrease in the discharges. Therefore, in the Gulf of Lions, the contribution of the sedimentary source term could become significant. This has provided a unique opportunity to investigate the behaviour of plutonium at the sediment-water interface in a dynamic coastal environment, in order to predict with confidence the ultimate sink. [ABSTRACT FROM AUTHOR]