Heat transfer aspects of nuclear waste disposal

Thermal aspects of the disposal of high-level nuclear waste (spent fuel) are reviewed as fundamental heat transfer problems on several time and space scales. At the canister level, free convection and combined free convection and thermal radiation in rod bundles will determine fuel rod and waste package surface temperatures. Engineering heat transfer correlations available for local and average Nusselt numbers in the bundle are reviewed. Heat transfer across the waste/rock interface presents a problem in free convection in a porous annulus of small to moderate gap width. If this annulus is water-saturated, there appears to be a sufficient base of experimental data and theoretical analysis to allow accurate prediction of average and local heat fluxes. On the geologic scale, the presence of the repository can be viewed as a source of heat and radioactive species that must be contained. Several methods of heat transfer analysis, as well as experimental data obtained with laboratory simulations, are summarized. Depending on the accuracy needed in the prediction of repository temperature and/or heat fluxes to the earth's surface, one of several alternative results can be utilized. This provides designers and evaluators with multiple tools for repository performance assessment and licensing