Post-depositional reactivity of the plutonium in different sediment facies from the English Channel - an experimental approach

Titre du congrès :Colloque quadriennal du CIRMAT Ville du congrès :Rouen Date du congrès :06/12/2005

The post-depositional reactivity of the plutonium was investigated in bottom sediments collected in the central English Channel using an experimental approach. Medium to coarse grained surficial sediments and fine-grained undisturbed sediment cores were spiked with 238Pu. After a one-month incubation, pore waters were extracted under strictly anoxic conditions and dissolved plutonium was analysed by liquid scintillation techniques. Kd values ranged from 102 to 105 in surficial sediments undergoing oxic diagenesis, and were shown to be grain-size dependant. In fine-grained sediments undergoing anoxic diagenesis, Kd values ranged between 103 and 105. Kd profile suggests an active recycling of the plutonium in the topmost sediment layers, and subsequent efficient uptake process at depth, tentatively acido-volatile sulphide (AVS) precipitation. This hypothesis was further confirmed by a correlation between the AVS content and the loosely bound plutonium extracted using an oxidising/complexing solution from sediment subsamples. In surficial sediments, by contrast, loosely bound plutonium was likely to be associated with the carbonate phase as surface complexes