Development of zeolite column systems for treatment of molten chloride salt generated in pyro-reprocessing of nuclear fuel

To avoid accumulation of fission products (FPs) in electrorefiner molten chloride salt bath during pyroprocessing of spent nuclear fuel, a spent salt treatment process making use of zeolite-A has been proposed. To realize both a high decontamination factor and a high throughput at a spent salt treatment process using the zeolite, a zeolite column system is under development. For this purpose, an engineering-scale zeolite column apparatus was installed. Measurements of superficial velocities of molten salt passing through columns filled with granular form zeolite-A showed that conventional relationship on velocity and pressure loss in components of the apparatus, which were derived mainly from results of water flow tests, are applicable to the molten salt system. Then, a demonstration test to simulate the decontamination of an FP, represented by non-radioactive cesium, was conducted. Since concentration of cesium in the effluent salt exhibited a breakthrough curve, some of the cesium in the salt was absorbed in the zeolite. Hence, feasibility of the zeolite column system was exhibited. Meanwhile, it is necessary to estimate FP absorption rate because both FP absorption in zeolite granules and molten salt flow in columns must be considered simultaneously for evaluating the column system's performance. Therefore, a kinetic model, which was originally developed for estimating the contaminated water treatment generated at Fukushima-Daiichi nuclear power plant, was applied to the molten chloride salt system. After estimating unknown kinetic parameters using literature results of zeolite immersion experiments in LiCl-KCl-CsCl melt, the model and the estimated parameters were verified by the above mentioned column experiment result. According to these results, the column performance in a reference process flowsheet was preliminarily evaluated. (author)