Interaction between BaCO3 and OPC/BFS composite cements at 20 °C and 60 °C

A BaCO3 slurry, containing radioactive 14C, is produced during the reprocessing of spent nuclear fuel. This slurry is encapsulated in a Portland-blastfurnace slag composite cement. The effect of BaCO3 on the hydration of OPC and Portland-blastfurnace slag cements has been studied in this work. Samples containing a simulant BaCO3 slurry were cured for up to 720 days at 20 and 60 °C and analysed by XRD, SEM(EDX) and ICC. BaCO3 reacted with OPC to precipitate BaSO4 from a reaction between soluble sulfate and BaCO3. Calcium monocarboaluminate subsequently formed from the carbonate released. The monocarboaluminate precipitated as crystals in voids formed during hydration. At 60 °C in OPC, it was not identified by XRD, suggesting the phase is unstable in this system around this temperature. In the Portland-blastfurnace slag cements containing BaCO3, less monocarboaluminate and BaSO4 were formed, but the hydration of BFS was promoted and monocarboaluminate was stable up to 60 °C.