Recent development of post-irradiation examination techniques at NFD

Various kinds of techniques have been developed and applied to the post-irradiation examination (PIE) of irradiated fuels and other materials at the NFD Hot Laboratory. Among these, the following three techniques, recently put to practical use, are described. (1) Restoration of destructively tested fuel rod. A technique to restore puncture tested and sectioned fuel rods has been developed. Those fuels and decladded UO2 particles, used together with fresh cladding tubes, were TIG welded to complete fuel rods and reassembled into a standard 8x8 fuel bundle. After PIE completion, this procedure would be helpful in regard to licensing for transportation to, and handling in, the reprocessing plant. (2) Oxide thickness measurement. A non-destructive method for measuring water side corrosion in Zry-2 cladding tubes has been developed. The frequency of 0.5 MHsub(z) was chosen for exciting eddy current in the lift-off method. Comparison between the values obtained in a destructive test and this non-destructive method showed good agreement for oxide layer thicknesses ranging 10μm to 150μm. (3) Specimen preparation. Structural materials and core components have a variety of shapes. A technique to prepare mechanical test specimens from those irradiated materials has been developed. A typical procedure for the tensile test coupon made out of thick stainless steel tubing was as follows: a) cutting it to an appropriate size of arc shape using a diamond saw, b) punching to a coupon, and c) finishing by a milling machine to remove the work hardened layer of the material. (author)