Raman studies of advanced gas-cooled reactor simulated spent nuclear fuels

Analysis of advanced gas-cooled reactor (AGR) simulated used nuclear fuels (SIMFuels) has been carried out using micro-Raman spectroscopy in order to understand the effect lanthanide species (e.g. Nd, Y, Ce), representative of fission products generated during fuel burnup, have on the structure of the UO2 matrix in spent AGR fuel. Results show a decrease in perfect fluorite character with increasing burnup as well as the development of a broad lattice distortion peak between 500 and 650 cm-1. Peak analysis of this broad band reveals in it comprised of three overlapping peaks at 534 cm-1, 574 cm-1 and 624 cm-1. The peak at 534 cm-1 has been examined and is suggested to be due to a local phonon mode associated with oxygen-vacancy-induced lattice distortion as a result of lanthanide 3+ ion incorporation into the UO2 bulk matrix.