Study on gas migration behavior through bentonite buffer material

Gasses generated due to the corrosion of metals contained in the waste packages and engineered barrier materials will accumulate in the Engineered Barrier System (EBS) of a radioactive waste repository, and may affect long-term stabilities of the EBS. To evaluate gas migration behavior through the bentonite buffer materials in conjunction with a reasonable design model is one of the challenges to be solved for the performance assessment of a radioactive waste repository. A series of studies have been conducted for more than 10 years under the leadership of the Radioactive Waste Management Funding and Research Center (RWMC) in Japan to better understand gas migration behavior through bentonite. In this report, the outline of the framework of the gas migration study by RWMC as well as some of the results from laboratory gas injection tests are presented. The laboratory test results focusing on the interfaces in bentonite materials (bentonite/bentonite interfaces) showed that water flow through the interface was blocked (self-healed) due to the swelling of the bentonite. In addition, the gas injection test after full saturation, indicated no significant differences in breakthrough pressure compared to the intact (e.g. no interface) specimen. These findings suggest that the interface is unlikely to become a dominant gas migration pathway in a saturated buffer. It is expected that all findings acquired through this decade of study are summarized and integrated within this fiscal year (2017) taking into consideration the parallel studies on gas scenario development and integration of coupled modelling, and contribute to a reliable advanced repository design and performance assessment. (author)