ABSTRACTA defense-in-depth engineered barrier system (EBS) is employed in the
current design concept for the potential high-level nuclear waste repository
at Yucca Mountain, Nevada, USA. Simplifying the geometry of the cylindrical
waste container into the equivalent spherical configuration, and
incorporating detailed analysis of the mechanics of water flow around the
waste container surface, a mathematical model is developed for advective
release from a “failed” (or perforated) waste container under dripping
water. It is shown that the advective release rates are controlled by
diffusion through the perforations in the waste container, and affected
insignificantly by the dripping flow rate for the flow
rate range considered. The release rates depend strongly on the number of
perforations (or pit penetrations) in the waste container. The insensitivity
of the release rate to the dripping flow rate is explained by the fact that
radionuclide is released from the container surface to the boundary layer of
the water film which contacts the container surface and is relatively
stagnant. Also, since a laminar flow around the waste container surface is
assumed in the model development, radionuclides transport across the water
layers in the film by diffusion only. Additionally, the insignificant effect
of the flow rate is contributed by the “short” penetration depth of
radionuclide into the water film assumed in the model development. The
analyses show that the number of perforations, the size of perforation, the
container wall thickness, and the geometry (i.e., radius) of the waste
container are important parameters that control the advective release rate.
It is emphasized that the “failed” (or perforated) waste package container
can still perform as a potentially important barrier to radionuclide
release.
