To build confidence in future applications of nuclear energy systems, and the continuing use of existing ones, there has to be confidence that spent nuclear fuel and radioactive wastes can be securely stored and safely disposed. Numerical models play a key role in nuclear waste isolation projects. This publication presents the outcome of an IAEA coordinated research project in which numerical modelling is used to address the pertinent issue of site characterization and its impact on the safety, using data and information from a potential repository site.