Characterization of tritium breeding ratio and energy multiplication factor of lithium-based ternary alloys in IFE blankets

Lawrence Livermore National Laboratory (LLNL) developed an inertial fusion energy (IFE) chamber concept that uses liquid lithium as the tritium breeder and primary coolant. Lithium metal has multiple benefits including high tritium breeding capability and excellent heat transfer properties. Nevertheless, lithium highly reacts with air and water to create an alkali metal fire. As a result, LLNL is now conducting research and development to identify lithium-based ternary alloys that will keep the favorable attributes of lithium while reducing the chemical reactivity and fire hazards. 3-D Monte Carlo calculations of a simplified model of the laser IFE reactor were performed for the assessment of two characteristics: tritium breeding ratio (TBR) that is the ratio of tritium produced in the system to tritium consumed, and the fusion energy multiplication factor (EMF) that is the ratio of the total power deposited in the blanket and other regions outside the IFE chamber by neutrons, gammas, and alpha particles to the fusion power. The TBR and EMF were calculated for each ternary combination as a function of the alloy composition varying the atomic percent of each element in the mixture from 0 to 100% by increments of 5%. Mixtures that guarantee a TBR of at least 1.02 and an EMF of at least 1.10 were considered viable. It was found that (1) alloys containing bismuth or lead offer the wider range of acceptable compositions; (2) ternary alloys made of lithium, with either lead or bismuth, and a third element of zinc, strontium, barium, or copper can reduce the lithium concentration below 20%. In evaluating the overall performance of the blanket coolant, it is important to maintain the lithium concentration at a minimum to reduce chemical reactivity in lithium.