Abstract
In order to elucidate fuel wash-out behavior after the degraded secondary failure of BWR fuel rods, corrosion experiments in high temperature and high pressure water of 340°C and 15 MPa were conducted for UO2 and UO2−10 wt%Gd2O3 fuel pellets with different grain sizes, which had been irradiated in a commercial BWR or a test reactor (burnup: 32–34 GWd/tU). The fuel corrosion was characterized by the occurrence of microcracks along the grain boundaries due to preferential U4O9 formation, and became noticeable in the oxygenated water of more than several ppm dissolved oxygen concentration. The grain boundary penetration depths for the irradiated pellets were approximately equivalent to, or somewhat deeper than the values for previous unirradiated pellets reported by the present authors. Consequently, fuel irradiation, i.e., accumulation of fission products had no significant effect o n the fuel corrosion. Enlarging grain size and 10 wt% Gd2O3 doping distinctly improved the corrosion resistance. The 85Kr release into the hot water, which had been accumulated in the grain boundaries during base irradiation, increased linearly with corrosion penetration depth.
Published Version
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