Geochemical boundary conditions relevant for assessing corrosion processes for the supercontainer design. Status on February 2006.

Recently, ONDRAF/NIRAS has selected the Supercontainer (SC) with an OPC buffer as the preferred design option for the geological disposal of high-level radioactive waste in Boom Clay. In order to evaluate the corrosion aspects, this report describes the current knowledge on the geochemical boundary conditions that should be taken into account. Mainly two elements sulfur and chlorine , present in Boom Clay pore water, need to be considered as they strongly affect corrosion. As sulphur species are very reactive and also play an important role in biogeochemical reactions, all main species of sulphur are discussed. In addition, information is given on the possible microbiology, as microbes are the most plausible source of reducing oxidised sulphur species into more agressive sulphur species. This report gives an overview of the available data to be considered for each time step in the evolution of a repository. Chlorine is considered a conservative element and no major changes are expected during the evolution of a repository. Therefore, all available information on this element is described in one section. Finally, a general overview of the boundary conditions to be considered with respect to corrosion is given.