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. (author)