The authors have investigated the effect of oxygen, steam, and nitrogen on the reaction kinetics of zirconium alloys for several years. A model describing the influence of the flow rates of the reacting gases on the reaction kinetics was developed. It is well known that the presence of nitrogen in steam atmospheres can increase the reaction rate of zirconium alloys. Precipitation of zirconium nitrides results in the formation of a pronounced crack structure in the oxide layer. Such an open crack network in the oxide scale enhances the hydrogen uptake of the remaining metallic zirconium alloy detectable by neutron imaging methods. In situ neutron radiography investigations of the reaction of Zircaloy-4 in nitrogen/steam and air/steam atmospheres were performed to get more information about the reaction mechanisms and kinetics. The experiments were performed in the temperature range of 800 to 1,100°C with constant partial pressures of the gas components but varying total gas flow rates. Tests in pure steam were performed under similar conditions as a reference. The paper describes the in situ neutron radiography experiments and analyzes the results of these laboratory and radiography investigations. The reactions occur mostly as the model predicted. However, discrepancies to the model predictions were found partially at higher temperatures. This shows that additional parameters influencing the reaction behavior have to be included in the model.