As part of a Westinghouse Atomic Power Division (WAPD) program, a study was made of methods by which nondestructive inspections of the core-to-clad bonds in completed, flat-plate fuel assemblies could be made. Normally, these inspections are made on single fuel elements by frost testing or ultrasonic methods. However, none of these techniques, as usually applied, could be used on complete subassemblies because they are not usable in long thin passages. Therefore, it was necessary to develop a new inspection method.