Design study of helium-solid suspension cooled blanket and divertor plate for a tokamak power reactor

High temperature helium gas will provide a thermal efficiency greater than 40%, even using a conventional steam turbine. In addition, helium gas will not react chemically with blanket materials, and surrounding air and water. Tritium will be easily extracted from the coolant too, making it an attractive coolant from all points of view. However, a large volumetric flow rate is required. This requires a larger reactor size, larger circulating power and more penetrations, which may increase radiation streaming. We suggest in this study, a helium-solid suspension flow as coolant, to increase the heat capacity and heat transfer coefficient. A gas pressure of 5MPa, and inlet and outlet temperatures of 400 C and 700 C were chosen. There are few candidates for the structural material which can be used at temperatures higher than 900 C. We have proposed an intermetallic compound of titanium aluminide (TiAl) as candidate structural material of the blanket. Although the database for TiAl is incomplete, it has high strength and ductility. Using TiAl, radioactive waste management will be mitigated, since its activity will decrease rapidly. In this study, spherical pebbles of lithium oxide and small blocks of beryllium were chosen as the breeder and neutron multiplier. Manganese blocks were installed to enhance energy multiplication. A tritium breeding ratio of 1.38 and energy multiplication ratio of 1.35 were obtained with the blanket. The net plant efficiency exceeds 40%, including the circulating power. The peak surface heat flux on the divertor plate was decreased with gas puffing. In spite of this, the expected peak heat flux was still several MWm-2 from the result of numerical calculation of the edge plasma. To remove so high a heat load, an impinging helium-solid suspension jet was applied to the high heat flux region of the divertor plate. Molybdenum alloy was used as the structural material in this region to keep the surface temperature and thermal stress. TiAl was used as the structural material of other regions in the divertor chamber. To prevent excessive sputtering erosion, the electron temperature in the divertor plasma must be kept lower than 20eV. ((orig.))