Radionuclide migration and retention in Boom Clay

The Belgian radioactive waste management organisation, ONDRAF/NIRAS, is responsible for the long-term management of radioactive waste in Belgium. At present, the long-term solution proposed by ONDRAF/NIRAS is a deep disposal facility for low-level and intermediate-level long-lived radioactive waste (LILW-LL) (Category B waste), vitrified high-level radioactive waste (HLW) and spent nuclear fuel (SNF, or SF-spent fuel), together comprising Category C waste. The primary aim of the ONDRAF/NIRAS programme for Category B and C wastes is to establish the feasibility of a deep disposal facility, without any presumption about precise repository location. This report is part of the ONDRAF/NIRAS RD&D plan in support of the establishment of a Safety and Feasibility Case (ONDRAF/NIRAS, 2013) This report summarises the detailed phenomenological studies within the ONDRAF/NIRAS Safety and Feasibility Case 1 (SFC-1) that are relevant to contaminant migration and retention processes through an undisturbed host rock and discusses the phenomenology that governs these processes. The report will provide both qualitative (understanding of the underlying mechanisms) and quantitative (migration parameters) justifications for the safety-relevant arguments that are made, and document the associated uncertainties. This report concentrates on the undisturbed host rock, which is seen as the principle barrier against contaminant transport to the biosphere in the Post-thermal phase (>1000 years) where breaching of the engineered barriers may occur.