Phase separation characteristics of [O.sub.2] solid solutions by high temperature oxidation

The phase separation characteristics of the Nd element from SIMFUEL (simulated spent fuel) by high temperature oxidation was investigated in terms of the temperature range between 1,150 and 1,300 °C and the initial concentration of Nd (x) in the pellets of ([U.sub.1-x][Nd.sub.x])[O.sub.2 with] x = 0.03, 0.037 and 0.09. The XRD and SEM results indicate that an increase of the heat treatment temperature increases the amount of the Nd-rich ([U.sub.1-y][Nd.sub.y])[O.sub.2+v] phase, while decreasing that of the Nd-poor [([U.sub.1-z][Nd.sub.z]).sub.3][O.sub.8-w] phase after heat treatment. Since the solubility of Nd in the [([U.sub.1-z][Nd.sub.z]).sub.3][O.sub.8-w] phase was almost constant regardless of the heat treatment temperature, the decrease of the Nd concentration in the Nd-rich ([U.sub.1-y][Nd.sub.y])[O.sub.2+v] phase with increasing heat treatment temperature seems to be due to a diffusion of the U ions from the Nd-poor (U1-zNdz)3[O.sub.8-w] phase to the Nd-rich ([U.sub.1-y][Nd.sub.y])[O.sub.2+v] phase. The phase separation ratio of Nd was not nearly affected by the heat treatment temperature, but was increased with an increase in the initial concentration of Nd (x) in the pellets of ([U.sub.1-x][Nd.sub.x])[O.sub.2.00]. However, the phase separation ratio of U was slightly decreased with an increase in the heat treatment temperature and was strongly decreased with an increase in the initial concentration of Nd (x) in the pellets of ([U.sub.1-x][Nd.sub.x])[O.sub.2.00]. Keywords SIMFUEL * Dry recycling * High temperature oxidation * Phase separation