Present status of oxide thickness measurement on irradiated fuel rods using eddy current technique

In the inspection of fuel cladding tubes used for nuclear power generation, the application of eddy current flaw detection technique has been advanced. At present, in the quality inspection of Zircaloy cladding tubes in the production process of the cladding tubes and fuel assemblies, ultrasonic flaw detection method has been used, but the flaw detection if irradiated fuel rods in power stations has been carried out by eddy current method. Because the irradiated fuel rods having high radioactivity are handled in the hot cells isolated with thick concrete walls, the equipment arranged in the cells must be small, and easy to be handled with manipulators and other remotely operated jigs. Recently, the development of the techniques for measuring the thickness of the zirconium oxide film formed on the surfaces of fuel cladding tubes and channel boxes has been advanced in various countries. In order to heighten the burnup of fuel and to extend the service life of fuel, the state of oxidation of fuel must be grasped in detail. The principle of the measurement, the equipment and the method of measurement are reported. (Kako, I.)