Non destructive oxide thickness measurement for BWR fuel rods∼Development of crud removal technique and measurement results∼

It is well known that crud deposits form on the BWR fuel surfaces. These deposits contain some tenacious crud which cannot be easily removed. This residual crud results in significant errors during the oxide thickness measurement using ECT (eddy current test) methods. To prevent such errors NFI, with help from TEPCO and JAEA, developed a technique that can remove tenacious crud without damaging the oxide film on the BWR fuel cladding. Using this developed technique, the oxide thickness measured by ECT agrees closely with metallographic examination results. As a result, data regarding the oxide thickness of high burn up fuels were successfully obtained using this developed technique during the poolside examination of the fuel. The measured oxide thicknesses were low, i.e. around 10μm. These data corresponded closely with the measurements previously obtained by metallographic examinations of the Japanese BWR fuels. In addition, data were acquired to verify the higher corrosion rates for fuel rod cladding with low Fe and low Sicontent after long irradiation periods