Thermal expansion of ZrO2-20 mol%Gd2O3 measured by XRD

K. Kang1, S. Na1 and G. Park1

1Korea Atomic Energy Research Institute, Korea

Keywords: XRD
property: thermal expansion, density, lattice parameter
material: ZrO2-20 mol%Gd2O3

To increase maximum fuel discharge burn-up and the period in reactor, higher contents of fissionable materials such as U-235 and Pu-249 has been required. In this case, Gd2O3 is used as a burnable poison to suppress the initial excess reactivity of the core. It is used as form of solid solution in fuel matrix or rod type (Gd2O3 or Gd2O3-ZrO2) in duplex type fuel. To compare to the solid solution type fuel, duplex type fuel has advantage of lower centerline temperature and fission gas release, and no degradation of thermal conductivity because of Gd-free in fuel matrix. However, at elevated temperature, the compressive and tensile stresses and gap variation occurred in the fuel and Gd2O3 (or Gd2O3-ZrO2) rod due to the different thermal expansion in each material. Information on the oxidation behavior of Zircaloy-4 is necessary for an evaluation of its stability during an irradiation. The thermal expansion of the ZrO2-20 mol% Gd2O3 pellet has been studied by X-ray diffraction in the temperature range from 307 to 1273 K. The thermal expansion coefficients and density variations with temperature were calculated from the thermal expansion data. As the temperature increases from 307 K to 1273 K, the lattice parameter of ZrO2-20 mol%Gd2O3 pellet increases from 0.51633 nm to 0.52136 nm. For the temperature range from 307 to 1273 K, the value of the average linear thermal expansion coefficient of the ZrO2-20 mol% Gd2O3 pellet is 1.009 10-5 K-1. The thermal expansion of ZrO2-20 mol%Gd2O3 pellet is similar to that of ZrO2, however, higher than it of Gd2O3. As the temperature increases to 1273 K, the density of ZrO2-20 mol%Gd2O3 pellet decreases to 97.06 % of the initial density at 307 K.

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