In this study, we investigated the chemical interaction behavior of metal fuels such as U, U–5 wt.%Zr and U–10 wt.%Zr with T91 steel at high temperature using differential thermal analysis (DTA) and differential scanning calorimetry (DSC) simulating the event of a transient condition. The DTA experiments reveal the presence of a very strong exothermic reaction between T91 and metal fuels at around 1100^oC. The temperature of the reaction shifts towards higher side with increase in Zr content of the alloy. Further analysis confirms that the reaction is the result of an eutectic reaction involving the formation of UFe₂. The microstructure of the reaction zone has been evaluated with the help of SEM and EPMA. The enthalpy of the above mentioned exothermic reaction was found decreasing with increase in Zr content.