Radionuclide Transport in Fractured Rock: Numerical Assessment for High Level Waste Repository

Abstract

Deep and stable geological formations with low permeability have been considered for high level waste definitive repository. A common problem is the modeling of radionuclide migration in a fractured medium. Initially, we considered a system consisting of a rock matrix with a single planar fracture in water saturated porous rock. Transport in the fracture is assumed to obey an advection-diffusion equation, while molecular diffusion is considered the dominant mechanism of transport in porous matrix. The partial differential equations describing the movement of radionuclides were discretized by finite difference methods, namely, fully explicit, fully implicit, and Crank-Nicolson schemes. The convective term was discretized by the following numerical schemes: backward differences, centered differences, and forward differences. The model was validated using an analytical solution found in the literature. Finally, we carried out a simulation with relevant spent fuel nuclide data with a system consisting of a horizontal fracture and a vertical fracture for assessing the performance of a hypothetical repository inserted into the host rock. We have analysed the bentonite expanded performance at the beginning of fracture, the quantified radionuclide released from a borehole, and an estimated effective dose to an adult, obtained from ingestion of well water during one year.

Effect of nonlinear sorption on multispecies radionuclide transport in a coupled fracture-matrix system with variable fracture aperture: a numerical study

“…Thereby, for a two species decay chain radionuclide transport, there will be two coupled transport equations within the fracture and two coupled transport equations within the rock matrix. The partial differential equations governing the transport in fracture and rock matrix have been adopted from Silveira et al (2013), with minor modifications to account for variation of fracture aperture. Equations (1) and (2) represent the transport of parent and daughter radionuclide species in fracture, respectively.…”

“…The key reason being the low permeable fractured rocks is considered as the natural nuclear waste repository for storing radioactive nuclear wastes. Of the numerous studies conducted on flow and transport in fractured media, only few of them are dedicated to the transport of nuclear waste (Natarajan and Suresh Kumar 2010;Silveira et al 2013;Steefel and Lichtner 1994;Suresh Kumar 2014a). The radioactive wastes are extremely hazardous due to its radioactive nature and its associated half-life period.…”

“…Earlier studies conducted on flow and transport in a coupled fracture-matrix system either includes single or multi-species radionuclide transport using the conventional parallel plate model with a constant fracture aperture thickness (Lever et al 1983;Nair et al 2010;Silveira et al 2013;Yamashita and Kimura 1990). However, very few studies have incorporated the complex variation of fracture aperture in analyzing the transport through fractured porous media (Chrysikopoulos and Abdel-Salam 1997;James and Chrysikopoulos 2000;James et al 2005).…”

A Geomechanical Model Test on the Construction Stability and Overload Failure Process of an X-Type Cross Cavern Group

“…We then prove the validity of the designed plan and ofer technical support for the design and construction of the URL for the deep buried geological disposal of HLW. [23,24]. Underground projects for the burial of HLW are known as geological repositories.…”