RETENTION CHARACTERISTICS OF FISSION GAS IN AN IRRADIATED OXIDE FUEL

摘要

In this work, the retention characteristics of fission gas in an irradiated oxide fuel along the axial direction of a fuel rod were investigated using a simple and fast experimental procedure. In addition to the fission gas measurements, other destructive and non-destructive post irradiation examination (PIE) tests were conducted to review their impact on the gas retention. A lead rod was extracted from a lead test assembly(LTA), which was irradiated to 56.9 MWd/kgU during three irradiation cycles for a total exposure of 1406 effective full power days(EFPD). Around 0.1 g of oxide fuel fragments was randomly collected from the four sampling positions of the fuel rod, and they were individually fused with metallic fluxes to extract the retained krypton and xenon. According to the measurement results, the retained krypton and xenon concentration ranges were 0.114 cc/gU-0.139 cc/gU and 1.073 cc/gU-1.338 cc/gU, respectively, and their retention percentage after normalization of the sample local burnup showed a decreasing trend as the axial height of the fuel rod increased. The water-side oxide layer thickness scope of the tested fuel clads measured by an observation of the optical microscope images was 13 μm-42 μm, and the thickness was increased along the axial height of the rod. The amount of released krypton and xenon into the rod-free volume was measured as 5.70 cc and 54.6 cc at 0°C, 1atm, respectively, by a rod puncturing/collection procedure, which corresponds to a 1.94% fractional fission gas release(FFGR) referring to fission gas generation(FGG) by a code calculation.