Numerical analysis of radionuclide migration through engineered barriers

A finite-element simulation has been performed to study the effects on the radionuclide flux, of the failure characteristics of a nuclear fuel disposal waste container, the buffer configuration, and the backfill properties, assuming an intact borehole rock wall. The results show that the total integrated flux from a failed container, through the buffer to a backfill with a diffusion coefficient and hydraulic conductivity higher than that of the buffer, increases as the radial buffer thickness increases, and the vertical buffer thickness decreases. The total flux can be estimated by a one-dimensional diffusion equation. If the backfill has the same diffusion coefficient and hydrualic conductivity as the buffer, the total flux will be reduced by approximatley 30% compared with the situation when crushed rock or sand is used as backfill. For localized failure of the waste container, the total flux is mainly dependent on the failure location regardless of the area of the failed surface. 6 references, 6 figures