A predictive transient one-dimensional rotodynamic pump model is currently developed into the CATHARE-3 thermal-hydraulic system code at CEA Saclay, France. Flow is computed in each part of the pump (suction, impeller, diffuser, volute and discharge pipe) based on the definition of a mean stream line. Several cells are used to mesh each part of the rotodynamic pump, which makes this model different from usually called “1D models”. In this study, the model is tested on a medium specific speed centrifugal pump in every operating modes encountered in the first quadrant (positive flow rate and rotational speed). A flow rate evolution is performed at the nominal rotational speed and also at rotational speed equal to zero in order to produce complete first quadrant homologous curves. Relative discrepancy between computation and experiment is respectively less than 10% and 15% on the whole obtained homologous head and torque curves.