Numerical Modelling of Coupled Heat Transfer and Groundwater Flow: Applications to Tailings Management Facility in Permafrost Environments in Northern Canada

E.E. Dagher, T.S. Nguyen, J.G. Su

Dans les comptes rendus d’articles de la conférence: GeoManitoba 2012: 65th Canadian Geotechnical Conference

Session: M1C - Cold Regions Engineering I

ABSTRACT: Tailings generated from the milling of the uranium ore would be disposed in an open-pit tailings management facility (TMF). The warm tailings disposed of in the pit could create a thaw bulb in the existing permafrost and potentially influence future long-term contaminant migration. In order to assess the extent of the thaw bulb and the modification in the groundwater regime in the surrounding geological formations, parametric numerical studies were performed for a proposed TMF. The coupled processes of heat transfer (conduction and convection) with phase change and groundwater flow were modelled to identify the potential permafrost degradation and talik development underneath a TMF. The results showed that at an initial baseline tailings temperature of 10°C the tailings in the TMF would completely freeze-over after a 400 year simulation time. The contribution of convection to the overall heat transfer mechanism was also shown to be negligible, due to the relatively low permeability of the geological formations. Future studies should include the additional effects of global warming.

RÉSUMÉ: Les résidus miniers résultant de la concepourraient être stockés dans une installation de gestion des résidus (IGR) en fosse. Le stockage de résidus miniers à température plus élevée dans la fosse pourrait créer un bulbe de dégel dans le pergélisol actuel et pourrait éventuellement avoir une incidence à long terme sur la souterraines dans les formations géologiques adjacentes, des études numériques paramétriques ont été réalisées pour une IGR proposée. Les processus couplés de transfert de chaleur (conduction et convection) avec changement de du référence de 10 °C, les résidus miniers stockés dans une IGR mettraient environ 400 ans, selon les simulations, pour être complètement gelénégligeable, en raison de la perméabilité relativement faible des formations géologiques. Les études futures devraient tenir compte des effets additionnels du réchauffement de la planète. 1. INTRODUCTION 1.1 Mining in Northern Canada Since 2004, Canada has received the largest share in exploration spending, holding 19% of the global investment to date (The Mining Association of Canada 2011). In recent years, this has led to hundreds of millions of dollars invested in prospecting and exploration operations in efforts to increase the production of urces (Natural Resources Canada mineral and metal potential are located in the far northern regions such as Nunavut and the Northwest Territories in areas engulfed in frozen ground known as permafrost. resources and is the second largest uranium producer and exporter in the world (World Nuclear Association 2011). With the global renewed interest in nuclear energy, the construction and operation of uranium mines in Canada is gaining much of this exploration interest, particularly in the northern continuous permafrost zone of Canada. Vast amounts of waste are produced in uranium mining, including mine waste rock and mill tailings. Proper management of these tailings relies heavily on the proper design of the TMFs. However, little is known on the environmental impacts to groundwater and nearby surface water that could result from uranium mining and milling activities in continuous permafrost regions. 1.2 Permafrost and Continuous Permafrost Regions of Canada In Canada, frozen ground underlies more than 50% of the surface (Natural Resources Canada 2003). This frozen ground, known as permafrost, is defined as ground that has remained at temperatures at or below 0°C for at least two consecutive years (Davis 2001; Holubec Consulting

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