Recent safety assessments nuclear waste repositories have shown that the formation and stability of colloids may have a direct impact on the overall performance of the repository.The main aim of the BELBaR project is increase the knowledge of the processes that controls clay colloid stability, generation and ability to transport radionuclides. The overall purpose of the project will be to suggest a treatment of the issues in long-term safety assessment.The key areas of research will be:• erosion of bentonite buffers, the main objective of these studies will be to understand the main mechanisms of erosion from the bentonite surface and to quantify the extent of the possible erosion under different conditions• clay colloid stability studies under different geochemical conditions. The colloids formed at the near/far field interface would be stable only if favourable conditions exist and therefore their relevance for radionuclide transport will be strongly dependent on the local geochemical conditions• interaction between colloids and radionuclides and the host rock, how colloid mobility may be affected be the composition of the host rock and the mechanism of sorption and de-sorption of radionuclides on the colloidsIn these areas substantial laboratory studies will be undertaken.The modelling studies will support the laboratory studies through development of conceptual and mathematical descriptions of the observed phenomena.The final outcome is to consider how colloids and related phenomena can be considered in the long term safety case and to make recommendations on how the safety case could pursue to address this potentially very significant issue.The project will have strong focus on cooperation and integration. This will be achieved by exchange of staff between partners and arrangement of frequent seminars.The BELBaR consortium consists of research institutes, implementers and universities from within and outside the European Union.