# Interface Characterization within a Nuclear Fuel Plate
## 1 Introduction  
The United States High Performance Research Reactor (USHPRR) Fuel Development (FD) pillar is tasked with the development and qualification of a novel high density U-Mo alloy based fuel which will enable USHPRR conversions to low-enriched uranium (LEU). The notable FD undertakings include the demonstration of novel fuel that passes the operational safety, dimensional stability, thermal stability, and other requirements of the applicable regulatory agency. The main FD project objective is to advance the technical means necessary to replace highly enriched uranium (HEU) fuel with LEU fuel in research and test reactors. The use of LEU fuel must be done without significant penalties in performance, economics, or safety of the reactors. FD is focused on a milestone to convert all designated research reactors, foreign and domestic, to LEU fuel.  
Irradiated fuel testing is the only effective method to assess the behavior of new fuels. A common reason for fuel failure in a reactor is the debonding of the fuel from Al cladding. The void initiated by a debond generates a localized rise in temperature that may cause fuel failure by melting the cladding. The LS characterization technique will characterize bond strength at the fuel-clad interface in freshfuels 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 characterize/image irradiated material.  
Laser-based characterization of base monolithic U-10 Mo fuel is being conducted by the USHPRR Fuel Qualification project to support fabrication development and ensure the fuel maintains mechanical integrity and does not delaminate during normal operating conditions. Characterization involves laser shock experiments, combined with laser-based ultrasonic scanning, to evaluate the bonding integrity and relative strength of interfaces within fuel plates. This paper discusses fresh fuel studies that were carried out on a series of fuel plates manufactured at Los Alamos National Laboratory in which various controlled levels of interfacial contamination were intentionally introduced into the fuel plates during fabrication in order to affect the bond strength adversely. Additional scoping studies were conducted on several developmental fuel plates supplied by the USHPRR Fuel Fabrication Pillar in which the Zr diffusion barrier was applied to the U-Mo foils by electroplating and plasma spraying. The electroplating and plasma spraying processes are being evaluated as potential alternatives to the baseline co-rolling fabrication process.