Americium retention and migration behaviour in Boom Clay. Topical report, first full draft

This report presents the most up-to-date understanding and data of americium (Am) transport in the Boom Clay formation. Americium prevails under Boom Clay conditions as a redox stable trivalent actinide ion. Am is chemically analogous to Europium, which has been equally intensively studied for its speciation and migration behaviour in Boom Clay, and to other, less-studied, trivalent actinides and lanthanides such as Cm3+, Sm3+, Ac3+ and Pu3+. The phenomenological model for these elements is based on a dual transport pathway: americium is either transported as a dissolved species with high retention by sorption or as a colloidal species associated with dissolved organic matter. Exchange between the two species follows a kinetic rate law. In this report the main experimental data underbuilding this model are summarised and appropriate transport equations and parameter value ranges are derived.