Simulation with the HITO code of the interaction of Zircaloy with uranium dioxide and steam at high temperatures

In a hypothetical severe fuel damage accident the Zircaloy (Zry) cladding may react, on its internal face, with the UO2 fuel and, on the external face, with steam. These reactions result in the formation of ZrO2, various oxygen stabilized α-Zr(O) phases and a (U, Zr) alloy. The HITO (High Temperature Oxidation) code describes both internal and external oxidation of the Zry cladding. The diffusion equations of oxygen in the various reaction layers are solved by an implicit finite differences method. Experimental results of isothermal and transient experiments are used to check the code. Comparison between the experimental data and the results calculated with the HITO code shows a good agreement. (orig.)