Abstract: With the vertical fractures filled with sands of grain diameters 0.5-0.63 mm, a fractured rock model is fabricated by using granite rock blocks taken from the Beishan area in Gansu province, which is being investigated as potential site for the high-level radioactive nuclear waste repository in China. Fluid flow and heat transfer experiments and numerical simulations are conducted for the model; and the influences of heat source temperature, the water velocity and aperture of the vertical fractures on the steady-state temperature of the model are also parametrically analyzed. The experiment results reveal that for a 120 ℃ heat source temperature, there is no phase change in the fracture water, and the steady-state temperature field is similar in pattern to that for 95 ℃ heat source temperature; the range of influence of the heat source and the time for asymptotic steady-state temperature field increased with the heat source temperature; sands filled in the fractures enhanced the heat conduction of neighboring rock matrix, making the range of influence of the heat source and the time for asymptotic steady-state both larger than the unfilled fracture model. The temperature field from the experiment is similar in pattern to that from the numerical simulation; however, since some degree of boundary heat loss in the experiment is unavoidable, the measured temperatures are smaller than the numerical simulation results for adiabatic boundary conditions; and the differences increased with the heat source temperature. Numerical parametric sensitivity analyses reveal that the fracture water flow adjacent to the heat source controlled the temperature field of the model, while the vertical fracture water flow further away from the heat source mainly affected the time for the model temperature approaching steady-state and the far side boundary temperature, the retardation of the horizontal heat transfer due to vertical fracture flow is more significant for higher water velocities and larger vertical fracture apertures.

Key words: high level radioactive nuclear waste, rock with sand-filled fractures, flow and heat transfer, model test, numerical simulation