Centrifuge Modeling of Radioactive Waste Migration Through Backfill in a Near Surface Disposal Facility

Investigations on the performance of backfill barrier in Near Surface Disposal Facility (NSDF) for radioactive wastes are important to ensure the long term safety of such disposal option. Favorable condition to delay migration of radionuclides from disposed waste to far fields is diffusion process. However, advective dispersion/diffusion mechanism plays an important role due to changes in backfill over a period of time. In order to understand these mechanisms, detailed laboratory experiments are usually conducted for developing mathematical models to assess the behaviour of backfill. However, these experiments are time consuming and suffer with the limitations due to material complexity. Also, there are constraints associated with validation of theoretical predictions due to intricacy of boundary conditions as well as the time scale is quite different as compared to the time required for completion of the processes in the field. Keeping in view these aspects, centrifuge modeling technique has been adopted by various researchers to model and understand various geoenvironment problems in order to provide a link between the real life situation termed as the ‘Prototype’ and its model, which is exposed to a higher gravitational field. An attempt has been made in this paper to investigate the feasibility of this technique to model advective dispersion/diffusion mechanism of radionuclides through saturated Bentonite-Sand (B:S) backfill. Various stages of centrifuge modeling are highlighted. Column tests were conducted in the centrifuge to evaluate the hydraulic conductivity of B:S mixture under prototype NSDF stress conditions. Results showed that steady state hydraulic conductivity under saturated conditions was 2.86 × 10⁻¹¹m/sec. Studies indicate the feasibility of centrifuge modeling technique and usefulness to model advective diffusion of radionuclides through B:S backfill.