Radionuclide Transport through Perforations in Nuclear Waste Containers

Abstract

Previous analytical models for the steady-state radionuclide release rate through perforations in nuclear waste containers into the surrounding medium, are based on a zero wall thickness assumption. In this paper we investigate the effect of the wall thickness on the mass transfer rate through isolated circular holes. We solve the steady-state diffusion equation for the concentration field and derive a model based on the analytical solution. By direct comparison, we show that the zero wall thickness model overpredicts the mass transfer rate by about 1300 percent for a circular hole with 1 cm radius and a wall thickness of 10 cm. As expected, the zero-thickness model becomes even less accurate as the hole radius decreases; it predicts a greater release rate from a large number of small holes than the mass transfer rate from an uncontained waste form cylinder. In contrast, the results predicted by our model remain bounded for isolated holes and never exceed the mass transfer from an uncontained waste form.

sup 14 C release from failed spent fuel containers

“…can be obtained from the literature. 5 The steadystate, diffusive release of a solute per unit area from a cylindrical hole into an infinite medium can be represented as follows: This assumption is justified a posteriori noting that the diffusion coefficient is large enough to assure rapid establishment of a steady-state profile.…”