Gas migration phenomena in potential components of near-field barrier system

Gas production resulting from mechanisms which includes metal corrosion and microbial degradation in a geological repository are able to lead an overpressurisation and enhanced release of radionuclides. An improved method of gas injection test of clay materials regarding test conditions and methods of gas flow rate measurement were examined and some key issues are recommended. Gas injection experiments of saturated mortar and cement paste and quantitative evaluation of gas and water flow properties in these materials were carried out. Water permeability of saturated mortar and cement paste are 10-20 m2 and 10-17 m2 respectively, although their gas permeability of dried sample were 10-18 m2 and 10-16 m2 respectively. Under the condition of constant injection pressure and axial flow, gas breakthrough phenomenon at which sharp increase of gas outflow rate after rapid rise in outflow rate of water was observed. Then the injection pressure rose a peak value range from 0.5 MPa to 8.2 MPa higher than backpressure. Afterward, outflow rate of gas increased to a steady state value in the permeability range 10-20 - 10-19 m2. Outflow of water continued after gas breakthrough phenomenon. A conventional continuum two-phase flow model was applied for simulation of the gas injection experiments. The simulation results of gas injection test were compared with measured test's data. The results of the simulation were in reasonably agreement with obtained experimental data. (author)