Work

Thermal expansion and degradation of uranium mononitride under high-temperature oxidative conditions

Year: 2025

Type: article

Abstract: The chemical and physical properties of advanced nuclear fuels, particularly in the moderately high temperature regime relevant for fuel storage, remain largely understudied. In this work, we combine in situ high-temperature (high-T) experiments with ab initio molecular dynamics (AIMD) simulations to investigate the behavior of UN under thermally oxidizing conditions. The phase composition and the coefficient of thermal expansion (CTE) were determined by in situ high-T X-ray diffraction (XRD) and Raman spectroscopy. UO 2 was identified as the only major intermediate phase, while minor α-U 2 (N,O) 3+x phases detected in the bulk and β-U 2 N 3 on UN surface. A significantly higher CTE was observed under oxidizing conditions (12.3 × 10 -6 at 500 K). AIMD simulations, supported by in situ XRD and Raman spectroscopy, attribute this increase to UN lattice distortion, rather than to oxygen diffusion.

Source: npj Materials Degradation

DOI: 10.1038/s41529-025-00708-1