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 Ca_0.092Th_0.092Ce_0.089La_0.727PO₄. 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.