Higher stability of nanophase Gd2O3–CeO2 upon 400 keV Kr+ ion irradiation over bulk: role of defect annealing across grain boundaries

Abstract

The concept of inert matrix fuel (IMF) has been proposed to utilize the energetic value of Pu and transmute minor actinides in nuclear reactors. In order to offset the initial reactivity of nuclear fuel, gadolinium (Gd³⁺) is employed as a burnable poison, owing to its high neutron absorption cross-section. To gain insights into the radiation stability and influence of grain boundaries on irradiation behaviour, 5 mol% Gd-doped ceria samples, sintered at varying temperatures, were subjected to irradiation using 400 Kr⁺ ions. In order to examine the correlation between the radiation response and variations in particle size, a variety of characterization techniques were employed, including X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) studies. The study employed systematic methodologies to investigate the structural, chemical, and spectroscopic features of irradiated pellets. Gd₂O₃–CeO₂ nano powders underwent sintering and palletization at 800 °C (S800), 1000 °C (S1000), and 1300 °C (S1300). Microstructural analysis via field emission scanning electron microscopy (SEM) revealed significant distinctions among the specimens. Glancing angle X-ray diffraction (GIXRD) and field emission scanning electron microscopy (FESEM) were performed on pristine samples to study the initial phase studies, crystal structure, variations in crystallite size and microstructures. Samples irradiated with 400 keV Kr⁺ were studied by GIXRD, Rietveld refinement analysis and Raman spectroscopy. None of the samples completely amorphized at the highest fluence of 1 × 10¹⁷ ions per cm². Under low-energy ion beam irradiation, the nanosized ceria samples accumulate a larger number of defects (oxygen vacancies and Ce³⁺ resulting from Ce⁴⁺ reduction to maintain charge neutrality) compared to the μ-sized sample. To emulate the bombardment of ions into the material, SRIM and TRIM (computer simulations) were also performed to follow the paths of ions and their trajectories. Critical analysis elucidates that there is an exceptional radiation tolerance in nano-grained-sized samples in comparison to bulk grain-sized samples. The role of grain boundaries and the grain size effect in the nuclear energy loss regime (S_n) has been critically discussed in this study.