Robust Cellular Solid Breeder Material for Enhanced Tritium Production and Release, Phase II

In current fusion reactor solid breeder blanket designs, small pebbles of ceramic breeder are packed into a blanket container in order to breed and release tritium. The current sphere-packed technology imposes severe design and operational limitations as a result of poor thermal conductivity between pebbles, limited operating temperature due to pebble sintering, cracking/fragmentation due to high Hertzian stresses at pebble contacts, creep deformation leading to bed reconfiguration, and limits on the packing fraction that increases the need for neutron multipliers. Purge gas blockage due to fragmentation may reduce temperature control and safety. Ultramet, UCLA, and Digital Materials Solutions (DMS) propose the development and testing of a cellular solid breeder structure at & gt;85 vol% overall breeder density with an engineered and stable internal network of interconnected microchannels for efficient release of tritium. The advantages of this approach are a robust free- standing breeder material structure with a high tritium release rate, higher tritium breeding ratio, high thermal conductivity, elimination of large breeder/structure interface temperature drop, elimination of pore closure due to sintering, minimal bed reconfiguration, and very low production cost. In Phase I cellular, solid breeder structures of multiple breeder materials were fabricated with an engineered network of interconnected microchannels. The nominally 85 vol% dense structures produced represent a 20% increase in breeder density over pebble beds. Analysis showed a twofold increase in thermal conductivity and nearly twofold increase in tritium release rate at much lower temperatures compared with an equivalent pebble bed breeder. Analysis also showed a more than twofold increase in span between coolant walls for a typical U.S. ITER solid breeder test blanket module design. These promising results indicate the potential for substantial performance improvements in solid breeder blankets. In Phase II, microengineered cellular breeders will be optimized and demonstrated that offer substantial performance and lifetime improvements relative to current pebble bed breeders. This will be accomplished through breeder materials and structures development and fundamental properties testing at Ultramet, design and analysis at DMS to establish the optimal combination of breeder material, density, and thermomechanical properties, and materials characterization and testing under prototypical operating conditions at UCLA, which is a leader in development and design of the U.S. ITER solid breeder test blanket module. Commercial applications and other benefits: Nuclear fusion offers a replacement for increasingly scarce fossil fuel energy sources. Alternatives to fossil fuels (e.g. wind, solar, geothermal) cannot generate sufficient energy to meet current needs. Fusion, with its low generation of radioactive waste, is ideal for large-scale energy generation. Development of advanced solid breeder materials is necessary to enable the U.S. industrial base to participate in near-term commercial applications of fusion energy (e.g. ITER test blankets, DEMO, and beyond).