Ultrasonic systems for high-accuracy thickness measurement of fuel bundle bearing pads and shield plug crimps

The performance of two ultrasonic systems, remotely operated in high radiation environment, are presented. The first system is used to measure the bearing pad height of radioactive fuel bundles located in the irradiated fuel bays, at Darlington NGS. The system was designed and commissioned to achieve an accuracy of ± 20 μm. The repeatability of results is within ± 10 μm uniformity band. The measurements are independent of testing speed, water temperature, bundle temperature, pencil geometry. Possibilities and limitations of the UT system are also presented and some improved alternatives are proposed. The second system was developed for measuring the crimp height of shield plugs (special iron casting) at Bruce B - Mark Ill development. The accuracy of measurements is ± 50 μm, with a repeatability of ± 25 μm. The results are independent of shield plug thickness variation and ovality, crimp off-set and heavy-water temperature. (author)