Host laboratory: Unit for Expertise and Modelling of Storage Facilities (UEMIS)
Beginning of the thesis: October 2018
Student name: Abdellah AMRI
Significant production of hydrogen (and other gases) is expected within a geological repository for high and intermediate level radioactive waste. The exact quantities vary depending on the storage concept and assumptions about the physico-chemical production mechanisms (mainly anaerobic corrosion of steel components). A gaseous phase could appear and change the flows, mechanical conditions and potentially the transport of radionuclides in the repository components including the host rock. Thus, the containment capacity of the storage system could be altered due to gas generation and migration.
This thesis aims to improve the capabilities for assessing gas migration within such a facility. In particular, it will be necessary to determine the uncertainty on i) the calculation of the piston effect and its extent on the transport of radionuclides in the engineered barriers; ii) the calculation of storage resaturation times, and iii) the calculation of the hydrogen limit pressures reached in the cells and which may cause fracturing of the host rock, thus favouring the preferential transport of radionuclides in COx.
The objective is to evaluate the importance of certain physical phenomena that are well described but yet absent from the simulations at the scale of the structures. The models already implemented in the calculation codes used in the host laboratory (Code_Bright, TOUGH2-MP) will be used as support. Modelling of the experimental results will be carried out to adjust parameters and verify the existence of a significant impact on the behaviour at the scale of the structures. The models of phenomena evaluated as relevant will then have to be implemented in a single simulator to be used for the simulations in support of the expertise. In particular, the effect of taking into account : i) the non-zero gas inlet pressure in the capillary pressure model of a porous component (argillite, EDZ, bentonite, concrete); ii) the hysteresis phenomenon generated by the imbibition and drainage cycles ; iii) the effect of capillary pressure on Henry's law; iv) the initial presence of air; v) hydromechanical modelling of interfaces (simplified geo-mechanical model of linear elasticity); vi) the dependence of the source term on water saturation.