The development of an improved model to determine the dynamic response of the primary heat transport pump during severe transients in a Canada deuterium uranium reactor is presented. A lumped parameter model is proposed. A control volume formulation is employed for centrifugal pumps. The mathematical formulation of this model is based on mass, momentum, and energy balances as well as on Euler’s Theory of Turbomachines. Several constitutive relationships are adopted in the model to describe three-dimensional effects. In addition, the proposed model includes the consequent effect of different flow regimes and the slip between the two phases. Numerical results indicated that the proposed model favorably predicted the pump response and compared well with other pump-related models (Aerojet Nuclear Company) in the literature as well as in the experimental data.