Modelling of Coupled Hydraulic-Mechanical Behaviour of MX-80 Bentonite under Hydration with Groundwater

As stated in the EU directive 2011/70/EURATOM [1] every member state (country) is responsible for the implementation of a safe and sustainable solution for spent nuclear fuel (SNF) and radioactive waste management and disposal. Radioactive waste disposal is among the basic radioactive waste management steps following the nuclear reactor operation and decommissioning. Geological disposal concept is based on multi-barrier system made of engineered and natural barriers. The radioactive waste management development program has been approved by Lithuanian Government in 2015. It foresees the geological disposal of RBMK-1500 spent nuclear fuel from Ignalina nuclear power plant (Lithuania) starting in 2066. Particular clay (bentonite) is among the materials considered for engineered barriers due to its properties such as low hydraulic conductivity, high sorption capacity, swelling potential, etc. This paper presents the results of the analysis on coupled hydraulic-mechanic MX-80 bentonite behaviour under its hydration with groundwater. Numerical model was based on Richard's equation and linear swelling model including non-linear couplings. Numerical modelling was performed with computer code COMSOL Multiphysics (USA) and the results were compared to experimental results of hydration of MX-80 bentonite sample at laboratory. The overall modelling results were in line with experimental data. Data on measured void ratio, moisture content at different parts of specimen were slightly underestimated with more significant differences for the upper part of specimen. Modelled axial pressure was estimated being higher than radial pressure while measured radial pressure was higher than the axial pressure in the experiment.