Tritium Percolation, Convection, and Permeation in Fusion Solid-Breeder Blankets

Models are developed to describe the steady-state percolation of tritium through the solid-breeder interconnected porosity to the purge stream, convection of tritium by the helium purge stream, and permeation of tritium through the structural material to the primary coolant system. Important parameters in the models are tritium generation rate, breeder microstructure, tritium species in the gas phase, temperatures, tritium diffusivities and permeabilities, and effectiveness of oxide barriers. The models are used to perform calculations for fusion-blanket conceptual designs. The results indicate that for isotopic swamping of the purge stream with protium and relatively high oxide impedance factors (∼100 for nonbreeder-side surfaces) the leakage rate from the blanket can be limited to less than 100 Ci/day for reasonable purge flow rates and pressure drops. However, for lower impedance factors and/or for decreased protium partial pressure in the purge, problems do arise with limiting the tritium leakage.