High-temperature reaction of (U,Gd)O-2 with zirconium

The reaction between (U, Gd)O-2 and Zr was examined to elucidate the effect of Gd on the reaction kinetics and morphology. The (U, Gd)O-2 pellets with Gd2O3 contents from 1-8 wt% (8 mm empty set X 2.5 mm) and Zr disks (8 mm empty set x 5 mm) were used as specimens. The reaction between (U, Gd)O-2 and Zr was carried out in the temperature range of 1100-1400 degrees C for 2-50 h in a vacuum below 10(-5) Pa. The heating and cooling rates were kept 5 degrees C/s. The UO2/Zr reaction produced typically three layers: alpha Zr(O)+(U, Zr), (U, Zr) and alpha Zr(O). For the (U, Gd)O-2/Zr reaction, the morphology of the reaction layers was slightly different from that of the UO2/Zr reaction. The reaction was found to follow the parabolic rate law. The layer growth rate constants and the activation energy for the reaction were estimated from the experimental data. Below a temperature of 1200 degrees C, the growth rate constants wen smaller for (U, Gd)O-2/Zr than for UO2/Zr. The activation energy for the layer growth was larger for (U, Gd)O-2/Zr than for UO2/2r. (C) 1997 Elsevier Science B.V.