Survey on the State of the Art of Development of Gas Migration Models in Barrier System

Tanai, Kenji ; Yamamoto, Mikihiko*

Suitable modelling of gas production and migration behaviour is strongly required for performance assessment of radioactive waste disposal in a geological repository. Especially for gas migration in buffer materials, it is very important to examine their ability to reproduce in herent gas migration behaviour which is caused by creation of discrete pathways in clay materials. JNC has examined the limitation of reproducibility of conventional two-phase flow model and anhanced TOUGH2 which has newly developed module implemented expanded Kozeny-Carman relationship and pathway dilation/resealing model. JNC also surveyed the state of the art of model development of gas migration in multi-barriers. In FY 2003, the surverillance of gas migration modelling was continued and handled migration mechanisms, basic mathematical models, strength and weakness of each developed gas migration models were extracted and tabulated. Based on these outcomes, thebasic correspondence of models to barrier materials, which should apply to performance assessment for a near-field system, was examined. In consequence, conventional two-phase flow models of gas migration are generally applicable for cementitious materials and rocks without mudrocks. But if it is required to understand more precisely the distribution of gas release at the surface, then more detailed uderstanding of flow in fractures would be required. For clay and mudrocks, it is necessary that comparison of applicability with three types of models, which include GAMBIT-GWS model, conventional two-phase flow models coupled with effect of stress field and expanded Kozeny-Carman relationship with pathway dilation/resealing model.