Development of spent salt treatment technology by zeolite column system

In the pyrometallurgical reprocessing of metal fuel, the spent electrorefiner salt containing fission product (FP) elements is purified and reused. For this purpose, a salt treatment process by using selective absorption of FPs on zeolite 4A is under development. For obtaining the basic data of salt treatment process by using 'column type method' in which molten salt flows through columns filled with zeolite, an experimental apparatus equipped with a fraction collector was developed. The relationship between velocity of molten salt passing through the columns filled with zeolite 4A powder and argon gas pressure to push the molten salt through the columns was measured by using columns of 1 cm in inner diameter and 10 cm or 30 cm in length. The average flow velocity increased in proportional to the gas pressure and decreased inversely proportional to the column length. The relationship between velocity and gas pressure was close to that of obtained by using water, whose kinematic viscosity is similar to that of molten LiCl-KCl salt. Additionally, the absorption behaviour of cesium, which was used as a representative of univalent FP elements, on zeolite 4A in the columns was measured by taking the effluent molten salt samples by using the fraction collector. It was revealed that the decontamination factor of cesium was highest at the beginning of the salt flow and the value decreased with the increase of amount of the passed molten salt. From these results, feasibility of the zeolite column system for purification and recycle of the spent salt was confirmed. (author)