Pressurized water reactor core thermal-hydraulics model for flow coastdown transient

The flow coastdown transient analysis is crucial for the design and safety analysis of a nuclear reactor because, in such an event, the core cooling depends upon flywheel inertia of reactor coolant pumps. In this paper, the results of real time flow coastdown transient initiated by power failure to the reactor coolant pumps on the CHASHMA Nuclear Power Plant Unit-2 (CHASNUPP-2) are presented. To examine the effect of thermal-hydraulics parameters, a mathematical model of core thermal-hydraulics for the flow of coastdown transient has been developed. The resulting equations are solved analytically for a pressurized water reactor. The accuracy of the model depends on the core time constant tau, which has been computed to be 9.28 s for CHASNUPP-2, the calculation methodology is described in the paper. The results are compared with the transient data, good agreement is found between the model prediction and the flow coastdown transient data. It is inferred that the coastdown flow rate is effective in removing the stored heat in the core.