Provision of diffusion coefficients for argillaceous media in support of preliminary safety assessment within the French HLW disposal programme

A review of experimental diffusion measurements was carried out to provide estimates of apparent diffusion coefficients for a range of elements of importance in the French HLW disposal management programme. For the purpose of preliminary safety assessment, and in the absence of site-specific data, experimental data from a number of sources have been used as a basis for recommending diffusion coefficients for 13 elements under oxidising and reducing conditions; recommended values range from 5•10−11 m2 s−1 for I and Tc (under oxidising conditions), to 10−14 m2 s−1 for actinides U, Np and Pu under reducing conditions. This paper also outlines the type of information which would enhance an understanding and interpretation of diffusion measurements on site-specific media.