High-Performance Cellular Lithium Titanate Solid Breeder Material with Enhanced Tritium Release

Solid breeder materials that have been considered in the past are all lithium-based ceramics, including lithium oxide, silicate, titanate, and zirconate, in pebble-bed configurations to enhance tritium release and recovery. However, the current pebble-bed configuration imposes severe design and operational limitations as a result of poor thermal conductivity and high Hertzian stress between pebbles at the contact points, which leads to pebble deformation, cracking, fragmentation, and sintering. These failures, along with low pebble packing fraction <65% dense), limit the operating temperature range and increase the need for neutron multipliers. Purge gas blockage due to these failure modes reduces temperature control and safety. In recent work for DOE, Ultramet and Digital Materials Solutions DMS) developed an advanced lithium zirconate Li2ZrO3) solid breeder material in the form of a cellular ceramic. Lithium zirconate is melt infiltrated into highly porous open-cell carbon foam, after which the carbon foam is removed by oxidation. The process leaves a nominally 90% dense breeder material with an internal network of interconnected microchannels for enhanced tritium release. Thermal conductivity is increased relative to pebble beds, high temperature sintering is eliminated, and durability is increased. In this project, Ultramet proposes to modify the established cellular lithium zirconate processing temperature, pressure, time, precursor purification) toward fabrication of cellular lithium titanate Li2TiO3) breeder material to take advantage of the increased lithium content and reduced radioactivity for easier waste disposal benefits offered by lithium titanate. 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).