The rod ejection accident in a pressurized water reactor and the control rod drop accident in a boiling water reactor are analyzed in this paper, both in a best-estimate (realistic) and a conservative manner. CORETRAN, a modern three-dimensional time-dependent nodal code, is used for all simulations. In all considered cases, the resulting peak fuel enthalpy is far less than the current licensing limit of 180 cal/g. The advantage of using a three-dimensional code over the classical point-kinetics approach can be summarized: The power peak is nominally a factor of 10 times lower, and the pulse is 10 times wider. Therefore, a three-dimensional approach predicts a much milder event. Sensitivity studies were performed to identify the influence of several parameters on the reactivity insertion simulations.