25 Laser-Based CharacterizationTechniques The Laser-Based Characterization group within INL’s MS&E department has contributed significantly to the foundation of a new field of mechanical characterization termed laser resonant ultrasonic spectroscopy.This new characterization technique is uniquely suited to monitor real-time changes in deformation- driven microstructure evolution. Hot cell variants of these instruments have been developed to measure elastic properties of highly radioactive materials. Currently one such instrument is being used to map the elastic constants of the U-Zr fuel system as a function of composition and temperature. Laser-based instrumentation under development within INL’s MS&E department are described below. TheThermal Conductivity Microscope (TCM) provides a non-contacting, nondestructive means for acquiring thermal conductivity information.The operational principle of the TCM was first developed by the Laser-Based Characterization group at INL.The ability to make single-sided measurements and resolution at the nanometer-micron scale are two of theTCM’s defining characteristics. Combined, these attributes fill an important capability gap associated with current measurement technologies.This instrument, as originally designed, has provided several first-of-a-kind thermal conductivity measurements of irradiated oxide fuels. Of particular note is work involving proton- irradiated uranium oxide where the damage layer extends only a few microns below the surface.TheTCM also has application beyond nuclear materials. Unlike other industry measurement standards, it can provide depth-resolved measurements of conductivity which are crucial for relating microstructure (irradiated or otherwise) to conductivity. Currently theTCM is being transitioned from a lab-based instrument into a field-deployable instrument for the thermal properties hot cell at INL’s Irradiated Materials Characterization Laboratory. Interest in theTCM is growing as the nuclear fuels research community starts to understand its utility for obtaining spatially resolved measurements on fragmented fuel. Development of a Picosecond Ultrasonics Facility has led to an internationally recognized fundamental study of acoustic wave interaction with individual microstructural features such as grain boundaries. Recently this program produced the first images of subsurface grain microstructure in uranium oxide using depth-resolved picosecond ultrasonics.The ability to monitor the response of subsurface grain boundaries to external stimuli holds the potential to significantly enhance fundamental research for energy and other materials. 3-D Quantitative Microstructural Analysis Capability 3-D microstructural analysis capabilities evolved out of the Nuclear Graphite R&D Program’s need to characterize the unique pore structures of various nuclear-grade graphites. Image analysis code was originally developed to characterize the effective gas transport rates through graphite materials. The code has ultimately been expanded to benefit programmatic research across INL. Research programs throughout INL have used these 3-D analysis capabilities, including the Advanced Gas Reactor Fuels Program, the Transient ReactorTest (TREAT) facility Low- enriched Uranium Conversion Program, the Biomass Conversion Program, and the Armor Research Program. Collaborators within Oak Ridge National Laboratory’s Materials Science andTechnology Division also have used INL’s 3-D characterization capabilities. Casting Capability for Metal Fuel and Alloys This lab-scale casting resource is used to develop methodologies for casting uranium alloy fuel rods and plates using surrogate materials.This capability is used to investigate new metal alloys with applications where low electrical conductivity or long-term microstructural stability are necessary. In combination with the analytical capabilities of the CCL (described on previous page) relatively large matrices of experimental alloys can be cast efficiently and their characteristics measured (diffusivity, phase change, thermal expansion, resistivity, oxidation rate, strength and modulus). Once a relationship is established between the alloying concentrations and material properties, it would be possible to specify an alloy composition to produce desired properties.