2, Purdue University, West Lafayette, Indiana, United States
3, Belgian Nuclear Research Centre SCK-CEN, Mol, , Belgium
The goal of this project is to understand the evolution and manifestation of microstructural features in metallic alloy nuclear fuels through a separate effects or parametric test. These are often used to uncover the underlying influence a particular phenomenon or property has on a more complex system into which it is integrated. Such is the situation with the behavior of nuclear fuel under irradiation with respect to phenomena such as grain refinement, fission gas bubble behavior, and element redistribution, all of which are a function of fission rate, fission density, temperature, and material composition. DISECT consists of four uranium-zirconium (U-Zr) low enriched uranium (LEU) fuel assemblies with samples ranging from 6 to 30 weight percent Zr. The U-Zr samples are being fabricated at Idaho National Laboratory (INL) by arc-casting short rods, sectioning the casting into buttons, hot and cold rolling these to thickness, and annealing. These will then be shaped and sealed in a mated zirconium shell that will provide both the vessel for sample retention and the thermal barrier necessary to control fuel temperature. Each assembly is equipped with in-pile instrumentation to monitor sample temperature during irradiation in Belgian Reactor 2 (BR2) operated by Studiecentrum voor Kernenergie (SCK). This novel approach to the experimental design is necessary to target specific temperatures (300-800 C), fission densities (2-6% atomic BU), and fission rates (200-750 W/cc) throughout irradiation without convoluting additional influences such as phase transitions and constituent redistribution. The effects of these well controlled experimental parameters will be used to understand the radiation-induced microstructural changes. As such, the pre-irradiation characterization of the microstructure is a crucial component to this experiment. These activities, discussed herein, include chemical analysis, sample mounting and preparation, optical microscopy, scanning electron microscopy (SEM), wavelength-dispersive X-ray spectroscopy, and transmission electron microscopy.