Evaluation of FP behavior and O/M ratio in FBR fuel irradiated to high burnup

Sato, Isamu; Yamamoto, Kazuya ; Kajitani, Yukio

The O/M ratio of fuel is related with most of fuel properties, especially it is important to evaluate radial O/M ratio distribution of fuel irradiated to high burnup in order to predict change of the properties. In this work, the radial O/M ratio distribution of irradiated FBR fuels was measured and evaluated. The fuels are irradiated in "JOYO", which were irradiated to the highest burnup(ca. 13at%). In this study, an indirect method, REDOX of Mo was used to obtain radial O/M ratio distribution, in which oxygen potential in fuel was determined by measuring oxidation and reduction states of Mo existing as a fission product (FP) in fuel. Oxygen potential distribution in fuel was determined from temperature profile and measured Mo distribution in fuel. O/M ratio distribution in fuel was evaluated from the oxygen potential, based on Catlow theory. The obtained O/M ratio distribution in fuel was compared with one calculated using Aitken model, which explains oxygen migration in fuel. Consequently, it was shown that the oxygen migration mechanism in high burnup fuel might differ from one suggested by Aitken and it might be necessary to take into consideration the effect of burnup on heat oftransport in oxygen thermal diffusion.