Two-phase MHD energy conversion from buoyancy-driven flows of liquid metal coolant in a fusion reactor

The present consensus for generating electrical power from a tokamak is to use a well-established energy conversion method: the conversion of heat to electricity through gas or steam turbines. The objective of our research has been to compare alternative methods of conversion. This has culminated in a proposal that utilises two-phase liquid metal magnetohydrodynamic (TPLMMHD) energy conversion in a topping cycle. The resulting power cycle configuration, with the current design specifications for a dual-cooled lithium-lead (DCLL) blanket, involves a high-pressure Brayton cycle that takes helium directly from the blanket, utilises TPLMMHD topping, and includes three low-pressure low-temperature Rankine bottoming cycles. Several studies have been undertaken, including limited small-scale experimental work, and a computer model developed to predict a power output of 22 MW_e via TPLMMHD with the circulation of Pb-17Li through a DCLL blanket by buoyancy. This removes the need to pump Pb-17Li and saves an additional 6.3 MW_e However, far greater gains than this 28 MW_e can come from an increase in the helium pressure in the gas turbines from 8 MPa to 34.5 MPa. The net electric power output for a PPCS model-C plant including our proposal for higher helium pressures is increased from 1480 MW_e to 1909 MW_e, which yields an increase in overall plant efficiency from 43.4% to 56%. This sensitivity to helium pressures is an important subsidiary outcome of the study.