Featured Application: Quantitative characterization of the fuel to cladding interface in a nuclear fuel plate is being developed to qualify the fuel fabrication process as well as the fuel performance during irradiation.Abstract: To predict the performance of nuclear fuels and materials, irradiated fuel plates must be characterized efficiently and accurately in highly radioactive environments. The characterization must take place remotely and work in settings largely inhospitable to modern digital instrumentation. Characterization techniques based on non-contacting laser sensing methods enable remote operation in a robust manner within a hot-cell environment. Laser characterization instrumentation can offer high spatial resolution and remain effective for scanning large areas. A laser shock (LS) system is currently being developed as a post-irradiation examination (PIE) technique in the hot fuel examination facility (HFEF) at the Idaho National Laboratory (INL). The laser shock technique will characterize material properties and failure loads/mechanisms in various composite components and materials such as plate fuel and next-generation fuel forms in high radiation areas. The laser shock-technique induces large amplitude shock waves to mechanically characterize interfaces such as the fuel-clad bond. As part of the laser shock system, a laser-based ultrasonic C-scan system will be used to detect and characterize debonding caused by the application of the laser shock. The laser shock system has been used to characterize the resulting bond strength within plate fuels which have been fabricated using different fabrication processes. The results of this study will be to select the fabrication process that provides the strongest interface.Appl. Sci. 2019, 9, 249 2 of 16 fuels and irradiated fuels. A quantitative measure of the bond strength at the fuel interfaces will permit the qualification of the LEU fuel and the understanding of its performance for use in research reactors.The advancement of newly developed fuels for performance, safety and nuclear safe guard applications requires the means to characterize the performance of reactor plate fuels. Irradiated plate fuels must be tested in a high-rad environment. The plate fuel characterization is performed remotely and in a hostile environment to sensors and electronic instrumentation. Laser-based techniques have the capability to be remote and robust within a hot-cell environment. Laser-based characterization techniques provide valuable spatial resolution appropriate for scanning and imaging large areas. The Idaho National Laboratory (INL) is designing a laser shock characterization system that will examine irradiated fuel plates within a hot cell. The laser shock system is comprised of a laser shock subsystem and laser-based ultrasonic C-scan system (LUT). The LS and LUT subsystems will be integrated into a single system located at the same hot-cell window. The LS subsystem is designed to characterize interface strength and the LUT is designed to ultrasonically char...

The laser shock system uses acoustic shockwaves to measure the interface strength of newly designed nuclear fuel plates. The quantitative measurement of interface strength will help understand fuel performance during irradiation. The laser shock technique imparts laser energy into a plate that then creates an acoustic shockwave. The amount of energy in the plate is proportional to the surface velocities measured on the back side of the plate. An accurate determination of surface velocity will enable better fuel performance predictions. The focus of this paper is on the implementation of a Photonic Doppler Velocimeter to corroborate the Fabry-Perot measurements from the laser shock system. Currently, a Fabry-Perot velocimeter takes the velocity measurements that are converted in stress. We have designed and implemented a Photonic Doppler Velocimeter to corroborate the Fabry-Perot measurements, which we discuss here along with implementing the short time fast Fourier transform to demodulate the heterodyne beat frequency into velocities. The Photonic Doppler Velocimeter has successfully corroborated the Fabry-Perot measurements.