Problems of tritium extraction from solid blankets

Tritium extraction from fusion reactor blankets must regenerate tritium at an average rate equal to that of burning plus losses. This rate depends of parameters that will be discussed: A) Equilibrium values of vapor pressures lead to minimum sweeping rates requirements. They depend, through Sievert's constants, on tritium concentration in the blanket. The optimum value of this concentration is discussed using the formula n=f. j.p (n=ppm of T m blanket f = fraction of blanket treated j = days between extraction sup(1/)p = fraction of T extracted). B) The literature provides extraction rates of tritium from various materials. This enables an estimation of the inventory in the blanket through the relation I = tauP (I=inventory tau defined residence time of tritium P production rate of tritium). C) The blanket must be designed in such a way that tau is acceptable. Parameters of influence are concentration, discussed in A, but also temperature, structure of the blanket i.e. elementary radius of particles, specific surface, density, etc... in the case of solids. Relations between tau and those characteristics have yet to be subjected to experimental verifications. Minimum rates of sweeping, by extraction gases, have also to be investigated. Other important parameters of the design have an indirect influence on extraction rates, that should be kept in mind. Such as: total blanket volume, Li concentration and enrichment in ₆Li. In addition the design of the extraction system must also be such that diffusion in the gas phase does not limit the rate of extraction. Finally if helium is used as coolant it's tritium content from leakage from the blanket and ²₃He capture of neutrons may require part of the coolant to be regularly processed with the extraction gas. (author).