Processing Design for a Pyrochemical-Distillative Recovery Alternative in Nuclear Waste Management

A conceptual design of a chloride distillation-based processing plant for spent nuclear fuel, also known as used nuclear fuel (UNF), processing, including recycling of the zirconium cladding material, was developed and fully simulated. First, the fuel is separated from zirconium cladding material. Cladding material and fuel are chlorinated and the components, mainly as chlorides, are separated by fractional distillation, respectively: for the fuel at ambient pressure and the cladding material at pressures above 23 bar. Simulation results have shown that neptunium tetrachloride and uranium tetrachloride as light boilers and plutonium trichloride with lanthanum, cerium and praseodymium trichloride impurities can be separated excellently within a distillation column with a minimum height of 1.22 m, applying the fractional distillation. The separation of these impurities can be carried out by a fractional distillation. If higher separation effort of maximum separable chlorides is required, the minimum column height increases to 4.25 m. Pre-fractionation of the chlorinated fuel material by, among others, single-stage distillation processes with crystallization at 625 K - 1135 K serves to separate volatile components and solids from the remaining chlorides. Fundamental goal of the present study was to propose entirely new options in nuclear waste management leading to reduction and closing fuel cycles to avoid final disposal. Furthermore, combination of the distillation process with reactors utilizing fast neutrons and operating at high temperatures of order 1200 K, proposed within the Dual Fluid principle, makes it even possible to burn out UNF material, and the remaining waste would only need to be stored for a few hundred years. Consequently, only 6 distillation-based separation units of 1000 t/a capacity each, working together with liquid fuel reactors for about 60 years, could completely consume the nuclear waste collected by the reactors of the second generation. (author)