Recently the demand for the development an immobilization technology for long half-life radiocarbon (C-14) has arisen in the nuclear industry. A significant challenge today is the mineralization of carbon dioxide into its natural host minerals. There are, however, some specific requirements to be met to ensure the thermal stability of immobilized waste forms considering heat generated and thus the potential for fire accidents during transportation, storage, and disposal. One of important tasks with regard to the radiocarbon immobilization is to minimize the potential for the release of radiocarbon from immobilized waste forms due to the thermal decomposition. The first part of this study conducted experiments of immobilization of CO2 into various calcined host minerals, such as calcite, dolomite and certain shell materials in a high pressure reactor under supercritical CO2 conditions. A non-isothermal TG analysis of CO2-immobilized minerals were then conducted to the temperatures as high as 1000 °C to establish kinetic parameters of thermal decomposition of CO2 from host minerals. Kinetic predictions using established kinetic parameters were then conducted to know the thermal stability of mineralized CO2 at 800 °C for half an hour, which is the thermal stability criterion established by IAEA [1]. As results of kinetic prediction, among the tested minerals, calcined conch shell was selected as the most promising minerals.