Double diffusive dissolution model of UO pellet in molten Zr cladding

伊藤 あゆみ*; 山下 晋   ; 田崎 雄大 ; 垣内 一雄 ; 小林 能直*

Ito, Ayumi*; Yamashita, Susumu; Tasaki, Yudai; Kakiuchi, Kazuo; Kobayashi, Yoshinao*

The rapid dissolution of UO in molten Zr that could occur during fuel-cladding liquefaction at high temperatures and its kinetics were reformulated considering the convective mass transfer and the chemical effect at the UO/Zr interface. The mass transfer coefficient of U was obtained as a correlation including the aspect ratio term by CFD analysis. To explain the gap between the rapid dissolution rate observed in the experiments and the density-driven convective mass transfer, we introduced an idea in which the eutectic melting at the UO/Zr interface promotes the grain detachment owing to infiltration of the U-Zr-O liquid into the UO grain boundaries. The developed model was validated with UO-Zr crucible experiments at 2273 and 2373 K. The calculated mass percentage ratios of U/Zr agreed with the measurements and the transition times from rapid saturation to precipitation were consistent with the metallographic observations.