Phase-field analysis for diffusion couple between UO and Zr

Nishida, Yuki*; Tsukada, Yuki*; Koyama, Toshiyuki*; Kurata, Masaki 

In a severe accident of light water reactors, interaction layers are formed between UO pellet and Zry cladding in the beginning stage. The melting temperature of a part of layers are rather lower than that of Zry cladding. In the present study, a base MPFM model was developed for understanding solid-solid diffusion and layer formation between UO and Zr, which are major constituents of pellet and cladding, respectively. Then, liquefaction condition of each layer was discussed using MPFM model. Model calculation indicates that meta-stable liquid phase is possibly formed in intermediate stage of mutual diffusion even at 1773 K, which is far lower than melting temperature of Zry. Also, in case of mutual diffusion between UO and Zr, spinodal separation of each phase potentially accerelates the layer formation.