Title : Synthesis of Cs pollucite ceramic waste form and long-term leaching behavior
Radioactive cesium (Cs) is representative fission products of spent nuclear fuel with high heat generating. Since radioactive Cs has high solubility and mobility in groundwater, it should be immobilized in a chemically durable waste form. Ceramic waste form has higher thermal stability and lower solubility than glass and cement waste form. Various ceramic waste forms for Cs immobilization have been researched. The Cs pollucite consists of an aluminosilicate framework and Cs ion incorporated in a matrix lattices. Previous studies have shown that pollucite has high chemical durability due to their structure. In this study, Cs pollucite powders were synthesized using Cs2CO3 and aluminosilicate denoted Absorbent Product (AP). Batches in which the precursors were mixed were placed in a 1000°C oven for 2 hours and then transferred to a 1200°C oven for 2 hours. The targeted compositions of Cs pollucite powders were 0.1, 0.2, 0.4, 0.5, 0.6 and 0.8 in the weight ratio of Cs2O to AP. These pollucite powders were pelletized by cold pressing with polyvinyl alcohol (PVA) as binder material. The fabricated Cs pollucite pellets were sintered at 1400 or 1500°C for 5 to 36 hours at ambient atmosphere. The characterization of the pollucite powder and pellets were analysed by XRD, TGA, and SEM-EDS. The chemical durability of pollucite powder was evaluated by PCT-A method and the concentration of elements was determined by ICP-MS/OES. The minimum normalized release of Cs in pollucite waste form was 1.22×10-4 g/m2/day. The optimal condition with well-made ceramic waste form is confirmed low Cs2O/AP ratio and pelletizing pressure, high sintering temperature and time. The long-term leaching test was performed using the modified MCC-1 method. Allard groundwater and deionized water were used for leachate in the leaching test, and replaced 7 contact periods which is 0.125, 3, 7, 14, 28, 60, and 120 days and analysed by ICP-MS. The Cs pollucite waste form developed in the present study had chemical durability than spent nuclear fuel.
Audience TAke Away:
- The audience can learn about the research status of waste form for radioactive Cs using the products of the Cs capturing process developed at Korea Atomic Energy Research Institute.
- The contents of this study can be referred to develop advanced Cs solidification or waste form technologies.
- Engineering design studies can be conducted on the equipment of immobilization process.
- Long-term leaching test results can be used in research to find leaching mechanisms of Cs pollucite waste form.