Remote Fiber-Based Velocimeter for Interface-Strength Measurements

Understanding the performance of nuclear reactor plate fuels is essential to the development of new fuel systems. The condition of pre- and post-irradiation plates must be characterized effectively and efficiently before and after irradiation within a high rad environment. Characterization work after irradiation must be performed remotely, in an environment hostile to instrumentation. Laser-based characterization methods provide a capability to be robust within a hot-cell environment. Laser-based characterization can provide high spatial resolution appropriate for scanning and imaging large areas. Idaho National Laboratory is developing a laser-shock system for use in the post-irradiation examination station of the Hot Fuel Examination Facility. This laser-shock system is used to characterize the strength of bonds between fuel and cladding and between cladding and cladding. The technique induces large-amplitude shockwaves to mechanically characterize interfaces between the materials. As the shockwave propagates as a compressional wave through the fuel plate to the free (unconfined) backside surface, it is reflected back through the test plate as a rarefaction (tensile) wave. This wave is the physical mechanism that induces internal delamination failure. However, accurate measurement of surface velocity to quantify the energy traveling through the interfaces to the back surface of the fuel plate was complicated by the original fiber-based velocimeter design, which was biased by parasitic back reflections. This paper discusses the discovery of the back-reflection issue and the design changes to resolve the issue. Supporting data will be presented.