Is Gas a Problem for Long-term Safety of a Repository in Boom Clay?

Performance assessment studies of the geological disposal of radioactive wastes in clay formations have repeatedly shown the paramount role of the clay barrier in providing long-term radiological safety. Therefore, due attention has to be given to the effects of disturbances of this barrier. Gas generation, predominantly caused by the anaerobic corrosion of metals from the waste forms and other repository components, is such a process that could perturb the clay host rock and the engineered barriers. The degree to which this may affect the long-term performance of a repository system will be explored in this paper, primarily on a methodological level. Assessing the importance of the gas problem for a repository in Boom Clay is a challenging task, because of its complexity and the significant uncertainties associated with both the source term and the gas transport processes. Assessments of the gas impact on long-term safety can be done based on a combination of mass-balance type calculations, the assessment of the water volume displaced by gas and complementary qualitative arguments. However, to underbuild statements on the safety of geological disposal, improvements are still desirable in understanding the phenomenology of the system and assessing the predictive capability of our models.