Development of a gas modelling code for the postclosure safety assessment of OPG's proposed L&ILW deep geologic repository, Canada.

Earlier this year, as part of the postclosure safety assessment of Ontario Power Generation's (OPG's) proposed Deep Geologic Repository (DGR) for Low and Intermediate Level waste, Quintessa and Intera Engineering completed the first iteration of the associated gas modelling.

This work was undertaken on behalf of the Nuclear Waste Management Organisation (NWMO) and involved the development of a T2GGM, a TOUGH2 based gas and water transport code with a coupled Gas Generation Model (GGM). T2GGM has been used to calculate the generation and build up of gas in repository due to the corrosion and microbial degradation of the metallic and the organic wastes present and the two-phase exchange of gas and groundwater between the repository and the surrounding rock and between the rock and the surface environments. The results of this detailed modelling were used to inform assessment-level models of gas flow and transport and to determine biosphere impacts.

The work and its finding were recently presented as an oral paper at the ICEM '09/DECOM '09 International Conference on Environmental Remediation and Radioactive Waste Management, Liverpool.

A second iteration of the safety assessment and associated gas modelling is now under way. This will contribute to the Preliminary Safety Report required for the application for a facility construction licence.