Synthesis and sintering of a monazite–brabantite solid solution ceramic for nuclear waste storage

Various geological arguments suggest that monazite can be an interesting waste-form for actinides such as Np, Pu, Cm and Am. We set up a simple procedure for making dense pellets of monazite–brabantite solid–solution ceramics with composition Ca0.092Th0.092Ce0.089La0.727PO4. It consists of co-milling CaCO3, ThO2, CeO2, La2O3, and NH4H2PO4, 1250 °C calcination, milling, cold-pressing, and sintering at 1450 °C for 4 h. X-ray investigations showed that the reaction scheme from oxides to monazite is complex and involves various P+La-based intermediate compounds. The final density of the the product is around 95% of the theoretical density. The texture is homogeneous with a typical grain of size 5–20 μm. This process is designed to be adapted to hot cells and telemanipulators.