Deuterium radial redistribution in Zr-liner cladding tubes

Abstract

Hydrogen isotopes in fuel cladding of nuclear power reactor are of much interest in relation to the secondary hydriding of claddings, tritium content in spent fuels, and other issues. Using nuclear reaction analysis (NRA), we performed out-of-reactor analysis on the radial distribution 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 gradually cooled to 433 K (samples 2 and 3). The NRA showed that the radial 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 interface. The peak concentration in the liner was several times as large as that in zircaloy-2. This indicated that the migration towards Zr-liner in the gradual cooling resulted in the redistribution of deuterium. The redistribution can be explained by a slight difference in the terminal solubility of deuterium in the two materials, Zr and zircaloy-2. The large effect of this slight difference on the redistribution of hydrogen isotopes is also discussed.