Time-Dependent Reliability Analysis of the Contaminant Migration of Radioactive Waste in Groundwater

Abstract

Nuclear power is an efficient source of power generation with low carbon emissions. But one of the serious problems encountered in the nuclear industry is the development of proper disposal facilities for radioactive waste. The safety of a waste disposal facility depends on the efficiency of its design against contaminant migration. The transport mechanisms of the contaminant are complex processes which involves advection, diffusion and dispersion considering radioactive decay. The heterogeneity of the aquifers and the existence of uncertainty (data and model uncertainty) affect greatly the predictive ability of groundwater flow and contaminant transport models. As a result, in a complex structural system like a near surface disposal facility (NSDF) where low and intermediate level wastes are disposed, the amount of radionuclide released into groundwater post closure is a major concern for the design. It is essential to know the probability of the concentration of radionuclide in the drinking water pathway exceeding the permissible value (probability of failure). Further, the long timescales considered in NSDF are a key feature making treatment of uncertainties more challenging and since the parameters influencing the contaminant process evolve in time, there is a need for a time dependent reliability analysis in this regard. In the present study, the contaminant migration is modelled as a convolution of the repository failure and the transport of the contaminant to groundwater through advection and dispersion. The uncertainties are modelled by considering variability in parameters and the time dependent probability of failure is estimated using Monte Carlo simulations.