DEUTERIUM RADIAL REDISTRIBUTION IN ZR-LINER CLADDING TUBES

Hydrogen isotopes in fuel cladding of nuclear power reactor are of muc h interest in relation to the secondary hydriding of claddings, tritiu m content in spent fuels, and other issues. Using nuclear reaction ana lysis (NRA), we performed out-of-reactor analysis on the radial distri bution of deuterium in Zr-liner zircaloy-2 claddings. Three specimens of the cladding were thermally charged with deuterium gas at 673 K in advance. One was quenched in water (sample 1) and the others were grad ually cooled to 433 K (samples 2 and 3). The NRA showed that the radia l distribution of deuterium was flat from the inside to the outside in the sample 1 tube. As diffusion of deuterium is much restricted after quenching, the distribution observed is considered to be the same as that before quenching. In samples 2 and 3, on the other hand, a sharp peak was formed in the zirconium liner near the Zr-zircaloy-2 interfac e. The peak concentration in the liner was several times as large as t hat in zircaloy-2. This indicated that the migration towards Zr-liner in the gradual cooling resulted in the redistribution of deuterium. Th e redistribution can be explained by a slight difference in tbe termin al solubility of deuterium in the two materials, Zr and zircaloy-2. Th e large effect of this slight difference on the redistribution of hydr ogen isotopes is also discussed.