Predicted groundwater circulation in fractured and unfractured anisotropic porous media driven by nuclear fuel waste heatgeneration

Abstract

The concept of nuclear fuel waste disposal underground is drawing increasing attention due to its many advantages against the current storage methods at surface. In this paper, we employ the Galerkin finite-element technique to solve the coupled time-dependent heat transfer and fluid flow differential equations and to predict the evolving behaviour of groundwater flow and subsurface temperature distribution associated witha proposed disposal system at the Whiteshell Research Area in southeastern Manitoba. A two-dimensional (2-D) numerical model is conceptualized from geologicalconstraints in this particular area. To investigate the free convection of groundwater flow driven by nuclear fuel waste heat generation, we assume the 2-D model has a flat upper boundary so as to eliminate the effect of topography head. Buoyancy force due to fluid density variationsis, therefore, the sole driving mechanism for fluid migration. Case studies for both unfractured and fractured porous media confirm that thermal decay of the buried fuel waste can initiate fluid circulation. In the presence of discrete fractures, the deep and hot fluid nearby the disposed contaminant can discharge to the biosphere, thus potentially threatening human health and the natural environment.