The long-term, safe, and reliable operation of a reactor coolant pump is vital for the safety of a nuclear reactor. In the case of a station blackout or power failure to the pump, the inertia of rotating parts of the pump should provide sufficient pumping capacity or flow rate to remove decay heat to ensure the safety of the reactor. An accurate flow coastdown analysis is required for the design and manufacture of reactor coolant pumps. In this paper a mathematical model is formulated to study flow coastdown of CHASNUPP-2, which is a pressurized water reactor. Frictional losses in the pump are also incorporated in the model to get accurate results. Two important parameters of the model are inertia of the pump impeller and inertia of the coolant, which are related to each other in the form of effective energy ratio. The effective energy ratio is made variable in order to accurately model the flow coastdown transient. The model is solved numerically to get flow coastdown curves and the comparison of the theoretical and experimental results shows a good agreement between them.
