Abstract
Low level radioactive waste containing sodium nitrate is generated in reprocessing steps of nuclear fuel cycle. The technology which converts sodium nitrate into sodium carbonate is developed for environmental loading reduction. Therefore solidification of low level radioactive waste containing Na2CO3 solution is requested. In this research, we discussed the solidification of Na2CO3 solution by BFS-OPC system and the reaction mechanism of blast furnace slag（BFS）-ordinary Portland cement（OPC）-Na2CO3 system at 50℃.
When the replacement ratio of OPC increased, the setting time of BFS-OPC-Na2CO3 system became shorter. However the compressive strength of hardened paste at 7days was decreased by using of OPC. From these results, it is concluded that the adequate replacement ratio of OPC for BFS is 10～15％. The ignition loss of hardened BFS-OPC-Na2CO3 system did not depend on the replacement ratio of OPC. And calcium-silicate hydration product（C-S-H（Ⅰ））, calcite（CaCO3）and mono carbonate（AFm（CO3））were observed in this system. Gaylussite was not observed at 50℃. However, the porosity of hardened BFS-OPC-Na2CO3 paste was increased when the replacement of OPC increased. As the replacement ratio of OPC increased, the amount of mono carbonate was increased. So we can consider the compressive strength of hardened paste depends on the generation of Mono carbonate.
