Thermal expansion of corium prepared from UO_2 and Zircaloy-2

摘要

In this study, sintered pellets were prepared from Zircaloy-2 oxide and UO_2 as a parameter of content ratio (Zr contents were 0, 24.3, 49.0, 73.4, and 97.9 at% in metal). The sintered pellets were heated in 5%Hj/Ar gas. UO_2 pellets underwent simple thermal expansion caused by thermal vibration while Zircaloy-2 oxide pellets underwent thermal expansion and volume change with phase transformation. Finally, the 24.3, 49.0, and 73.5 at%Zr-UO_2 pellet specimens showed both phenomena. However, phase transformation temperatures were lower than that of Zircaloy-2 oxide, and volume changes were much smaller. X-ray diffraction patterns obtained after thermal expansion measurements showed that the 24.3 at%Zr-UO_2 specimen contained tetragonal and cubic (Zr, U)O_2 while the 73.5 at%Zr-UO_2 specimen contained mainly monoclinic ZrO_2.