High temperature reactions of UO2, ZrO2, B4C, CaO, and SiO2 under reducing and oxidizing atmospheres

Uranium and several other radioactive materials reacted with zircaloy (Zry) and/or its oxide, ZrO2, presented in the fuel cladding, to form fuel debris at the Fukushima Daiichi Nuclear Power Station in 2011. Under very high temperature conditions, the melt core, mainly consisting of the control rods (stainless steel rod filled with B4C) and fuel assembly (UO2 and Zry) materials, was solidified at the lower head of the pressure vessel. In addition, the melt core was also solidified at the lower head of the pedestal reacted with cement materials (CaO and SiO2). In order to forward a safe and controlled decommissioning process, structural and thermodynamic estimations of the fuel debris under various atmospheric conditions such as reducing and oxidizing atmospheres have been conducted. In the present study, the local structure of basic uranium/zirconium compounds has been characterized under different treatment conditions in the presence of B4C, CaO and SiO2 in atmospheric conditions with different temperatures ranging from 1473 to 1873 K. These reactions are of specific interest to the interaction between nuclear fuel and cladding tube materials.