Leaching tests formally recognized by the International Atomic Energy Agency (IAEA) or by the American Nuclear Society (ANS) are used to evaluate the release of radioactivity from a waste form under idealized conditions. These conditions do not represent the reality of disposal environments, where engineered barriers are in place to limit access of water and to retard the migration of radionuclides into the biosphere. A test program underway at Chalk River, Ontario is attempting to provide an understanding of the release and transport of radionuclides under more realistic conditions. Preliminary results indicate that releases are suppressed by at least an order of magnitude when the effects of barriers in a repository failure are considered. However, migration mechanisms cannot be fully explained by classical concepts involving saturated flow. Research effort is now focused on measurements in an unsaturated, reducing environment, the condition which will be expected to be found in a well-designed repository.