Natural sintering of carbonate powder for use as a carbon-14 immobilization matrix

Carbon-14 generated during fuel irradiation in the reactor is later partially released as 14CO2 during reprocessing. It must not be released directly into the environment because of its long half-life and rapid assimilation by living organisms. The waste volume generated by conditioning depends not only on the type of fuel but especially on the selected conditioning matrix. We propose that a sintered carbonate be used directly as an alternative to cement with the main objective of providing a significant waste volume reduction while ensuring durability equal to or better than that of cement. Many carbonates are difficult to sinter naturally because of their relatively low thermal decomposition temperature. They also exhibit low hardness and are generally friable. We show that a binary carbonate BaCa(CO3)2 yields a sintered carbonate with satisfactory mechanical properties and acceptable water solubility. The carbonate fabrication, pelletizing and sintering conditions are examined and discussed.