Abstract The results of former isothermal UO2/Zircaloy interaction experiments were corrected by introducing the actual annealing temperatures and reaction times. This was accomplished by comparison of the ZrO2 and α-Z(O) reaction layer thickness of the UO2/Zircaloy interaction experiments with those of Zircaloy/cladding oxidation experiments performed under well controlled temperature conditions. The reactions occurring during heatup and cooldown were included in the so-called isothermal annealing time. The corrected Arrhenius equations were then used to determine the effective oxygen diffusion coefficients in the various phases. A good agreement between the experimental data and the results of the model was achieved using the new effective diffusion coefficients along with functions fitted for the oxygen concentrations at the phase boundaries. Both sets of functions will also allow the calculation of the UO2/Zircaloy interaction during temperature transients.