Study of the Decomposition and Phase Transition of Uranium Nitride under UHV Conditions via TDS, XRD, SEM, and XPS.

Abstract

Uranium nitrides are among the most promising fuels for Generation IV nuclear reactors, but until now, very little has been known about their thermal stability properties under nonequilibrium conditions. In this work, thermal decomposition of nitrogen-rich uranium nitride (denoted as UN2-x) under ultrahigh-vacuum (UHV) conditions was investigated by thermal desorption spectroscopy (TDS). It has been shown that the nitrogen TDS spectrum consists of two peaks at about 723 and 1038 K. The X-ray diffraction, scanning electron microscopy, and X-ray photoelectron microscopy results indicate that UN2-x (UN2 phase) decomposed into the α-U2N3 phase in the first step and the α-U2N3 phase decomposed into the UN phase in the second step.