Investigation of High-Temperature Uranium-Dioxide Kernel Creep in Nuclear Reactors

The operation of a high-temperature fuel rod with a fuel kernel consisting of uranium dioxide is accompanied by significant changes in the initial structure of the fuel – a multi-zone dioxide structure with different grain size and shape (growth of initially uniaxial grains, formation of a columnar structure) can form in the transverse section of the kernel. For low level of stress appearing in the fuel kernel of such a fuel rod, the creep rate ξ of uranium dioxide is proportional to the stress σ(ξ ~ Bσ), where the creep coefficient B for a specified range of stress depends on the grain size. A method is described for performing reactor tests on model fuel rods that makes it possible to determine the integral coefficient of creep of a fuel kernel, which depends on the temperature distribution and the size and shape of the formed grains. The use of this coefficient greatly simplifies the computational modeling of the useful-life behavior of a high-temperature fuel rod. This method obviates the need for post-reactor studies of fuel-kernel structure. It is most effective when used in combination with neutron-diffraction analysis during irradiation for fast processing of fuel rods.