Development of advanced reprocessing system based on precipitation method using pyrrolidone derivatives as precipitants. Overall evaluation of system

An advanced reprocessing system for spent FBR fuels based on two precipitation processes using pyrrolidone derivatives as precipitants has been proposed. In order to develop this system, we have examined precipitation behavior of U(VI), Pu(IV), Pu(VI), and other metal cations with various pyrrolidone derivatives, the heat- and radiation-resistance of precipitants, the thermal decomposition properties of precipitates. As a result, it was found that N-n-butyl-2-pyrrolidone (NBP) and N-neopentyl-2-pyrrolidone (NNpP) are the appropriate precipitants for the first and second precipitation processes, respectively, that the decontamination factors for most of simulated fission products are more than 102, that the precipitant components are recovered by vaporization with heating the precipitates, and that the recovered precipitants are used repeatedly. Furthermore, we have performed the engineering investigation, and confirmed that the precipitation and the filtration can be done efficiently using the continuous precipitation apparatus and centrifugal separation machine, and that the pellets with density of 85- 90% TD and residual carbon less than 100 ppm are prepared by the calcination of the precipitates under wet-H2 at 1750degC. On the basis of results of basic and engineering investigations, we evaluated our proposed reprocessing system from the viewpoints of technical feasibility, safety, economical matter, effective use of U and Pu, reduction of radioactive wastes, nonproliferation, and so on. As a result, it was evaluated that our proposed system is expected to be one of candidates of the future reprocessing systems for spent FBR fuels. (author)