Effects of depth on transport of 129I in crystalline rock

In the present paper, a model for the transport of iodine through fractures in granitic rock has been developed by taking into account the variation of parameters with depth in order to investigate the effects of depth on repository performance. First, the evolution of groundwater chemistry with depth has been modeled by considering the physical and chemical conditions that vary with depth. Second, iodine-water interactions and iodine-rock interactions under groundwater-chemistry evolution with depth in crystalline rocks have been modeled using PHREEQC, with which the distribution coefficients of iodine have been numerically evaluated as a function of depth. These values and other depth-dependent parameters such as fracture aperture, groundwater velocity, and diffusion coefficients have been used in the iodine transport simulation to observe differences in the iodine concentration in the water from repositories located at 500 and 1000 m depths. The results show that iodine stays within the vicinity of the repository if it is disposed of at a greater depth. The main reason is that the retention effect of matrix diffusion increases and relative contribution of advection along fractures decreases at depth due to the cubic law for the water flow velocity in fractures. (C) 2014 Elsevier Ltd. All rights reserved.