One of released radioactive gases from a spent fuel is cesium (137Cs) as semi-volatile fission products and reticulated ceramic foam could be used for capturing the gaseous cesium. It has threedimensional open-pore structures and consumes cesium above 600°C to form cesium species including Cs-nepheline (CsAlSiO4) and pollucite (CsAlSi2O6) phases. Kaolinite-based foam filter is a favorable ceramic filter because they exhibit superior capture characteristics compared to other aluminosilicate minerals and other shape filters. However, for usage in special conditions, structural limitations such broken struts must be improved. Here, recoating by using centrifugation, followed by a pre-sintering cycle was conducted for covering the cracks and voids, resulting from the burnout of the polyurethane sponge as a sacricial template. The slurry including additives was chosen by considering viscous behavior of slurries for the centrifugation. The microstructure and strength was improved by the recoating.

Reticulated foams have a continuous skeleton network consisting of aluminosilicates and are used for capturing gaseous cesium released from spent nuclear fuel at high temperature. It has high stability to high temperature and good capturing performance. Homogeneous cell distribution and modified surface structures are indispensable conditions for stable operation and handling. In particular, triangularly shaped holes inside the struts were generated during the pyrolysis of polyurethane sponge as a sacricial template, which lead to limite the strength of the reticulated foam as well as cracks. However, several attempts have been focused on the increasing the strut thickness. Here, we have prepared ceramic foams by the polyurethane sponge replication method with roller squeezing. Ceramic slurry including additives was determined with consideration of its viscous behavior. After pre-sintering, infiltration under vacuum was conducted. Metakaolin slurry was filled partially into the triangular void. As a result, the compression strength was improved by structure modification without composition change.

The stabilization technology for the damaged spent fuel is being developed to process the damaged fuel into sound pellet suitable for dry re-fabrication. It requires several treatments including oxidative decladding followed by reduction treatment for oxidized powder closely related to the quality of oxidized powders for pellet fabrication. For the development of operating condition for the reduction treatment, in this study, we evaluated the effect of air-cylinder based vertical shaking previously applied to oxidative decladding on powder reduction. For U3O8 of 50-100 g, the reduction test were applied with and without vertical shaking at 700°C under reduction atmosphere (Ar + 4%H2) and the concentration of hydrogen in effluent was measured to evaluate the reduction reaction. It was found that the vertical shaking system has allowed the reaction time of 50 g and 100 g U3O8 reduced by 33% compared to the test in static mode. Based on XRD analysis, the better crystallinity of the products was also achieved.

The damaged spent fuel rods must be stabilized by encapsulation or dry re-fabrication technologies before geological disposal. For applying the dry re-fabrication technology, we manufactured a vertical type furnace to perform the fuel material recovery from damaged fuel rods by oxidative decladding technology. As driving forces to accelerate oxidative decladding rate, magnetic vibration and pulse hammering generated by a pneumatic cylinder were used in this study. The oxidative decladding efficiency and recovery rate of fuel oxide powder with rod-cut length, oxidation temperature and time, oxygen concentration, and gas mixtures were investigated using simfuel rod-cuts in a vertical furnace for fuel material recovery and powder quality improvement. The oxidative decladding was performed for 2.5-10 h as following operation parameters: simfuel rod-cut length of 50-200 mm, oxidative temperature from 450 to 580°C, oxygen concentration of 49.5 or 75.6%, and gas mixtures in O2/Ar or O2/N2. In magnetic vibration, oxidative decladding was progressed only at bottom portion of fuel rodcut. Whereas, oxidative decladding in pulse hammering was occurred at both top and bottom portions of fuel-rod. In pulse hammering method, the oxidative decladding conditions to declad rod-cuts of 50- 200 mm in length were established to achieve both decladding efficiency of ~100% and fuel material recovery rate of > 99%. These conditions were as follows: oxidation temperature and time at 500°C and 2.5-10 h, oxygen concentration at 75.6% under O2/N2 gas mixtures. As operation conditions for a pneumatic cylinder, stroking, actuating, and waiting times were 0.5, 3, and 12 s.