Rhabdophane (REPO4.H2O; LREE = La to Dy) and churchite (REPO4.2H2O; RE = Gd to Lu and Y) are secondary minerals formed via aqueous alteration of primary rare-earth minerals such as monazite (REPO4; RE = La to Gd) and xenotime (RE′PO4; RE′ = Tb to Lu and Y). The monazite and xenotime are promising host matrices for actinides resulting from the reprocessing of spent nuclear fuel and historical legacy wastes. However, the aqueous alteration of these materials in a geological repository could result in the precipitation of rhabdophane and churchite. In this scenario, the actinides could partition into the secondary phases, and the subsequent alpha-decay of actinides could compromise their structural stability. The effect of radiation on their structure is unknown and this study bridges this critical knowledge gap by exploring the radiation stability of rhabdophane (REPO4.H2O; REE = Sm, Gd, Dy) and churchite (REPO4.2H2O; REE = Gd, Dy, Y) materials.1 The rhabdophane and churchite nanocrystals were synthesized via a precipitation route. The structure of these materials was determined using a 3D electron diffraction tomography and powder X-ray diffraction. The alpha recoil damage was mimicked using a 650 keV Xe2+ ion beam and the structural response to ion irradiation was monitored in situ using a TEM and electron diffraction. The rhabdophane materials were observed to undergo amorphization at a higher ion fluence than churchite. The rhabdophane materials exhibit a critical amorphization temperature (Tc) in the range of 623 K to 698 K. The churchite materials have a comparatively low thermal stability (T ~ 200°C) and became amorphous at all temperatures within their thermal stability limit, preventing Tc determination using Xe ions. The radiation performance of these secondary phases was compared against their anhydrous counterparts, and it was found that the monazite and xenotime materials are more radiation tolerant than their secondary phases. This study has demonstrated that the rhabdophane and churchite are more susceptible to radiation damage and future work is needed to better understand how it may impact their actinide retention capacity under disposal conditions.
1 Mohamed Ruwaid Rafiuddin, Anamul Haq Mir, Yingjie Zhang; In Situ Observation of Radiation Damage in Rhabdophane- and Churchite-Type Rare-Earth Phosphate Nanocrystals. Inorg. Chem. 8 June 2026; 65 (22): 12509–12523.