CaTh(PO4)2 cheralite as a candidate ceramic nuclear waste form: Spark plasma sintering and physicochemical characterisation

In order to fulfil the requirements as an actinide waste form, cheralite (CaTh(PO4)2) needs to be stabilised into a dense material. Thermal stability studies indicated that heat treatment causes gradual decomposition of CaTh(PO4)2 into the corresponding oxides above 1550 K. Thus, conventional sintering of this material cannot be applied. However, we demonstrate that rapid densification without decomposition can be achieved by using spark plasma sintering. High density pellets of pure cheralite were produced and the thermal diffusivity and mechanical properties (hardness and elastic modulus) were measured. Within this study, 31P MAS NMR was used to complete the structural characterisation of the synthetic cheralite.