Radionuclide migration through an unsaturated clay buffer under thermal and hydraulic gradients for a nuclear waste repository

Abstract

This study presents a numerical model simulating the radionuclide migration behavior in an engineered barrier system of a nuclear waste repository. The migration of iodide and cesium through a compacted bentonite buffer with variable saturation and temperature gradient was analyzed. The modeling was performed using a computer program, TOUGH2, which analyzes the multi-dimensional fluid and heat flows of a multiphase, multicomponent fluid mixture in an unsaturated medium. The radionuclide transport in both aqueous and gas phases and the radioactive decay were considered. The diffusional transport of radionuclide was assumed, and the adsorption of radionuclides on the bentonite was modeled as reversible instantaneous linear sorption. An engineering scale experiment simulating the thermal, hydrological and chemical processes occurring in the engineered barrier system of a nuclear waste repository was carried out. The presented model can reasonably simulate the experimental results.