Phase evolution in reaction sintered Th-Monazite ceramic waste forms by SPS and PLS.

Monazite ceramic is one of the potential waste forms to incorporate actinides in planned nuclear waste repositories. Inspired by recent progress on the low-temperature sintering and enriching radionuclides by wet-chemistry, the sintering processes of monazite ceramic with/without pre-sintering are investigated by spark plasma sintering and pressureless sintering using La 0.8 Sr 0.1 Th 0.1 PO 4 ·nH 2 O rhabdophane as raw materials. Some specific issues such as the behavior of dissociation, structural evolution, and physicochemical properties affected by SPS and PLS are discussed in detail. The results reveal that a low-temperature appears to be a prevailing factor for SPS under 40 MPa with a suggested 1050 °C for 15 min process to prepare La 0.8 Sr 0.1 Th 0.1 PO 4 monazite ceramic without forming Th(PO 3) 4 phase, and the relative density and Vickers hardness of ceramic are more than 98 % and 600 (HV10). The dissolution experiment based on the ASTM-1220 method indicates that La 0.8 Sr 0.1 Th 0.1 PO 4 monazite ceramics is a typical example of an incongruent reaction, associated with Sr2+ is more likely to be dissolved out form monazite lattice compared with Th4+ and La3+. [ABSTRACT FROM AUTHOR]