[en] The paper presents insights from studies aiming at clarifying the release mechanisms and their role in the overall safety of the final disposal of spent fuel in hard precambrian bedrock. The expected chemical conditions are defined with respect to the materials introduced into the repository, taking into account their possible long-term changes. The main parameters affecting the barrier performance are identified. The parameters affecting the leaching and the solubility of the actinides in the repository are discussed basing on preliminary experimental and theoretical studies. The role of release mechanisms for the safety of the overall disposal system under different conditions is discussed. The importance of the source term is increased when the conditions are assumed to be normal, e.g., the engineering barriers of the repository are damaged. The source term modelling requirements and the data needs are evaluated