Tritiated water retention and migration behaviour in Boom Clay. SFC1 level 5 report: First full Draft – status 2009

This report presents an overview of tritiated water (HTO) transport in the Boom Clay formation (status 2009). HTO is a small, neutral and non-sorbing radioactive tracer. Therefore, HTO is ideally suited for studying the transport characteristics inherent to the clay formation itself, and serves as a reference molecule for migration parameters of a whole range of solutes. The major parameters which influence the diffusive behaviour of HTO are: 1) temperature, with higher temperatures leading to higher pore diffusion coefficients; 2) anisotropy, with the preferential orientation of clay platelets leading to different path lengthening depending on the direction of diffusion; 3) the degree of compaction, or the confinement pressure, with a higher pressure leading to a general decrease of both the pore diffusion coefficient and the diffusion accessible porosity. The pore water chemistry, including ionic strength and near-field effects, clearly has a smaller impact on the migration parameters, indicating that diffusion of HTO is predominantly subjected to physically-determined processes. This report contains Source and Expert Ranges for HTO migration parameters in Boom Clay (status 2009). The report is also available as NIROND Technical Report NIROND-TR 2009-16E.