Modeling of chemical interactions of fuel rod materials at high temperatures I. Simultaneous dissolution of UO 2 and ZrO 2 by molten Zr in an oxidizing atmosphere

Abstract

Investigations and modeling of high-temperature processes associated with the oxidation of UZrO molten mixtures under various conditions of severe accidents (intact heated fuel rods or relocating melt) are presented on the basis of a thorough analysis of metallographic post-test examination data obtained in the fuel bundle CORA experiments. In Part I a model of simultaneous dissolution of solid UO 2 and ZrO 2 phases by molten Zr in an oxidizing atmosphere (steam) is presented. This modeling is performed on the basis of the generalization of a previously developed model of UO 2 dissolution by molten Zr taking into account the chemical dissolution by convectively stirring melt of a ZrO 2 layer interacting with steam. The model describes the complicated kinetics of these interactions accompanied by precipitation of a ceramic (U, Zr)O 2− x phase in the bulk of the liquid. This process finally leads to complete conversion of the melt into the (U, Zr)O 2− x layer located between UO 2 fuel and ZrO 2 shell. Such a three-layer structure was regularly observed in the CORA post-test metallographic examinations of fuel rods heated above the melting point of Zr cladding ( T ≥ 1950°C).