The Use of Zirconium-Palladium Windows for the Separation of Tritium from the Liquid Metal Breeder-Blanket of a Fusion Reactor

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Abstract
Any first generation fusion power reactor must be surrounded by a heat tranfer medium and a tritium breeder-blanket containing lithium in some form. Liquid lithium and liquid lithium alloys are considered to be particularly attractive choices for both purposes; the main disadvantage of these materials is the difficulty of tritium separation. The use of zirconium-palladium windows for tritium separation is shown to have many advantages over the best alternative devices. This is based on the materials properties and costs as they stand in 1983. The design of a typical permeation window resembles that of a shell and tube heat exchanger; liquid lithium or lithium alloy loaded with tritium from the reactor, flows through on the zirconium side of the window, while a purge stream of argon and oxygen flows through on the side with the palladium coating. Oxygen is present so that sufficiently low tritium pressures may be maintained on the downstream side of the window. Tritium is recovered as T2O. Data are presented regarding the thermodynamics and the transport properties of tritium in lithium, in lithium-lead alloy, and in zirconium. Data are also presented for the reaction rate on a palladium surface. A permeation window is described; its cost is estimated to be $9,300,000 for use on a liquid lithium breeder-blanket or $1,100,000 for use on a lithium-lead alloy breeder-blanket. Some remaining problems are outlined.