Monazite-Type SmPO4 as Potential Nuclear Waste Form: Insights into Radiation Effects from Ion-Beam Irradiation and Atomistic Simulations

Abstract

Single-phase monazite-type ceramics are considered as potential host matrices for the conditioning of separated plutonium and minor actinides. Sm-orthophosphates were synthesised and their behaviour under irradiation was investigated with respect to their long-term performance in the repository environment. Sintered SmPO4 pellets and thin lamellae were irradiated with 1, 3.5, and 7 MeV Au ions, up to fluences of 5.1 × 1014 ions cm−2 to simulate ballistic effects of recoiling nuclei resulting from α-decay of incorporated actinides. Threshold displacement energies for monazite-type SmPO4 subsequently used in SRIM/TRIM simulations were derived from atomistic simulations. Raman spectra obtained from irradiated lamellae revealed vast amorphisation at the highest fluence used, although local annealing effects were observed. The broadened, but still discernible, band of the symmetrical stretching vibration in SmPO4 and the negligible increase in P–O bond lengths suggest that amorphisation of monazite is mainly due to a breaking of Ln–O bonds. PO4 groups show structural disorder in the local environment but seem to behave as tight units. Annealing effects observed during the irradiation experiment and the distinctively lower dose rates incurred in actinide bearing waste forms and potential α-radiation-induced annealing effects indicate that SmPO4-based waste forms have a high potential for withstanding amorphisation.

Grazing-incidence synchrotron radiation diffraction studies on irradiated Ce-doped and pristine Y-stabilized ZrO2 at the Rossendorf beamline

“…By bombarding materials with energetic (kiloelectronvolts to megaelectronvolts range) ions of He (to simulate alpha particles) or ions of heavy elements (typically to simulate the recoil of daughter products), such as gold or noble gases, defects and microstructural damage can be created in corresponding crystal structures. The possibility to change the fluence of generated ion beams allows for controlled and accelerated experiments that can reveal mechanisms and kinetics of radiation damage in different materials (Sickafus et al, 1999;Shu et al, 2020;Yan et al, 2015;Lenz et al, 2019;Leys et al, 2022).…”

Synthesis under hydrothermal conditions and structural transformations of nanocrystals in the LaPO4-YPO4-(H2O) system

“…For the synthesis of nanocrystalline materials based on rare-earth orthophosphates, soft chemistry methods are commonly used, such as precipitation [28,[32][33][34], sol-gel [3,[35][36][37][38], hydrothermal and hydrothermal-microwave synthesis [1,4,[38][39][40][41]. At times, precipitates obtained by soft chemistry methods are annealed at temperatures ≥ 500 • C to obtain samples with monazite and xenotime structures [18,20,43].…”