Gas breakthrough pressure in compacted Fo–Ca clay and interfacial gas overpressure in waste disposal context

It is well established that high-level nuclear waste underground disposal will be associated with gas generation. In a multibarrier system including a waste package with steel overpack surrounded by an engineered clay barrier, gas could accumulate and thus jeopardize the safety of such a system. In order to characterize the behavior of the engineered barrier, the French Atomic Energy Commission (CEA) has previously carried out an experimental program on H2 gas migration within Fo–Ca clay. Gas permeability, gas entry and breakthrough pressures were measured during extended gas migration tests. This paper deals with a complementary work concerning the modeling of gas pressure at the overpack–engineered barrier interface and its comparison with the clay gas breakthrough pressure. This was made possible by integrating the results of past and recent studies in this area that suggest that breakthrough pressure roughly corresponds to the sum of the clay swelling pressure and external water pressure. The conclusion is that gas breakthrough pressure and estimated gas interfacial overpressure are of the same order of magnitude and that gas is a key issue for clay-engineered barrier performances and thus for disposal safety.