Multistage permeation cascades have been designed for the removal of radioactive krypton and xenon from nuclear reactor atmospheres. These cascades could serve for the decontamination of the atmosphere within a reactor containment dome following a nuclear accident and for other applications of interest to the nuclear industry. The stages of the cascades are assumed to consist of permeator modules using silicone rubber capillaries as separation membranes. All stages are to be operated in a countercurrent mode with shell-side feed.

It is shown that it is possible to design an ideal cascade for the separation of multicomponent mixtures by matching the concentrations of a suitable key component in interstage streams that are mixed. This procedure minimizes the cascade volume and power requirement. It is also possible to design a cascade with constant stage cuts in its enriching and stripping sections that approximates the performance of an ideal cascade. The krypton and xenon content of a feed mixture containing about 1 × 10−3 mol% Kr and 1 × 10−2 mol% Xe in air can be lowered by factors of 103 and 108 respectively in a 27-stage permeation cascade. Methods of reducing the number of stages and the effects of irradiation on the membrane performance are also discussed.