Pore pressure response to disposal of heat generating radioactive waste in a low permeability host rock

Abstract

Low permeability rocks provide an attractive option for disposal of radioactive waste because transport of radionuclides will be diffusion dominated and hence slow. However, heat generated by the waste will cause an increase in the pore pressure which may become high enough to damage the rock creating higher permeability areas and faster radionuclide transport paths. It is therefore important to understand the magnitude of pore pressure changes caused by the heating effect of the waste, to develop confidence that the rock will maintain its low permeability.This paper considers coupled Thermal-Hydraulic-Mechanical (THM) modelling of two experiments at the Meuse/Haute-Marne URL: the TED experiment at 1/5th scale and the ALC experiment at full repository scale. Modelling these experiments has enabled testing of understanding of key processes and parameterisation through a blind prediction of the results of the ALC experiment based on modelling of the TED experiment. Calibration of models to both experimental data sets has improved understanding of the importance of processes and parameters in determining pore pressures.The modelling captures the key features of the experiment, demonstrating that the physical processes are well represented in the model whilst spatial variability of physical properties can lead to significant uncertainties in pore pressure estimates. The work demonstrates the benefits of conducting experiments at full-scale, ideally located close to the repository site, and of building a good understanding of the spatial variability of the host rock properties.