Abstract：The Radioactive Waste Management Funding and Research Center(RWMC) in Japan has been conducting (research and development) for the disposal of radioactive waste since its establishment in 1976. More recently，RWMC has focused on important sociological and technical issues for geological disposal，such as monitoring，remote-handling and site investigation technology. Among these issues，the evaluation of gas migration from a repository is important for the development of more reliable safety assessments. This issue has been studied in a large scale in-situ experiment，the“gas migration test(GMT) in engineered barriers”at Nagra¢s Grimsel test site(GTS) in Switzerland. GMT has focused on issues related to waste-generated gas migration through the engineered barriers in a silo-type disposal. A reduced scale EBS(engineered barrier system) consisting of a concrete silo with a permeable gas vent and bentonite/sand buffer has been emplaced and instrumented in a specially constructed silo cavern at the GTS. The concrete silo was 2.5 m in height and 2.5 m in diameter and was located in an approximately 4 m diameter shaft excavated from the upper cavern. After saturation of the EBS and water permeability tests，gas was injected into the silo during two main injection periods. After the first gas injection，repeat water permeability tests were performed to identify changes in EBS performance. The second gas injection used a cocktail of gas tracers which were sampled from multiple points in the EBS and geosphere. Following the end of gas injection，the EBS was carefully excavated and characterized using a range of techniques.
