Stationary Transport of Dissolved Species in the Backfill Surrounding a Waste Canister in Fissured Rock: Some Simple Analytical Solutions

In a final repository for spent nuclear fuel, the waste canister may be surrounded by some backfill. For low-permeability backfills, the transport of dissolved species such as corrosive agents for radionuclides leached after canister penetration is faster by diffusion than by flow. In fissured rock the migrating species will have a large cross-section area for transport while in the bulk of the backfill, but a very small area for transport at the mouth of the fissure. A somewhat idealized physical model has been used as a basis for a mathematical model that has been solved analytically. It shows the influence of fissure widths, backfill thickness, and distance between fissures. Some calculations are performed using some geometrical configurations of interest. They show that the influence of fissure width on the transport rate is small.