Migration of radionuclides from a granite repository

Abstract

Migration of radionuclides in the fracture of a host rock matrix surrounding a high‐level waste repository is discussed in terms of two coupled one‐dimensional equations, one for the fracture and the other for the porous rock matrix. The processes considered are advection, dispersion, radioactive decay and adsorption on the surface of the fracture, and diffusion, radioactive decay and adsorption in the microfissures of the host rock. The temporal and spatial distribution of concentration and flux at the outlet of the fracture for some typical radionuclides encountered in high‐level radioactive waste has been computed using two‐component leaching from the waste matrix and budgeting the total inventory. It is observed that the concentration of 90Sr and 239Pu markedly decreases with distance along the fracture due to sorption and decay. However, either travel time or sorption do not present enough delay for significant decay of 129I in fracture water. While the peak flux of 129I shows insignificant variation at different fracture lengths for varied fracture apertures, that of 239Pu has functional dependence on both parameters.