AbstractA dynamic void quality perturbation model has been developed to improve the capabilities of the NUFREQ code with respect to local void perturbation calculations. The present model calculates the local void perturbation in terms of the local quality perturbation, the dynamic drift flux parameters, and the transient time. In addition, the model evaluates the void reactivity feedback and the boiling channel nuclear reactor feedback. Depending on the flow regime, this model can predict the local void fraction perturbation in horizontal (CANDU reactors) and vertical channels (light water reactors). Numerical results revealed that this model enhanced the capabilities of the NUFREQ code and improved its accuracy in predicting the lower natural frequency as well as the system frequency response at higher frequencies.