Radionuclide Migration: A Numerical Study

• Autor(a) principal: SILVEIRA, Claudia S. da
• Data de Publicação: 2007
• Outros Autores: LIMA, Zelmo Rodrigues de, ALVIM, Antonio Carlos Marques, [e-mail], [e-mail], [e-mail]
• Tipo de documento: Artigo de conferência
• Idioma: eng
• Título da fonte: Repositório Institucional do IEN
• Texto Completo: http://carpedien.ien.gov.br:8080/handle/ien/1724
• topic: Radionuclide Migration; Crystalline rock

Crystalline rock has been considered as a potentially suitable matrix for high-level radioactive waste (HLW) repository because it is found in very stable geological formations and may have very low permeability. A common problem encountered in this context is the modeling of migration of radio nuclides in a fractured medium. Generally, this consists of a large main fracture, which is surrounded by a rock matrix. Transport in the main fracture is usually assumed to obey an advection-dispersion relation, while molecular diffusion is the assumed dominant mechanism of transport in the porous rock. In this work, a numerical study of the governing partial differential equations is done, to describe radionuclide movement in the fracture and within the rock matrix. The adopted physical system consists of the rock matrix containing a single planar fracture situated in water saturated porous rock. The initial radionuclide concentrations are assumed to be zero in both fractured and rock matrices. As inlet boundary condition, a kinetic solubility-limited dissolution model is used, in order to calculate the radionuclide concentration in the fracture. The solution of the governing partial differential equations was obtained by finite difference methods, namely: fully explicit, fully implicit and Crank-Nicolson discretization schemes. Note that the influence of the advective term was considered in the partial differential equation in the fracture, in such discretization schemes. It was shown that all numerical schemes are consistent and that the explicit method, in all configurations of the advective term, and the implicit methods and Crank-Nicolson, for the forward discretization in the advective term, presented stability conditions to be considered.