Modeling of flow coastdown transient of a reactor coolant system under different pump failures

Abstract

The flow coastdown transient calculation is important for the safety analysis of a nuclear reactor. An accurate transient analysis during coastdown is necessary and important for the design and manufacture of a reactor coolant pump, since only the reliable work of reactor coolant pumps can guarantee the safety of a nuclear power plant during this important period.In the present work, mathematical models are solved for the non-dimensional transient flow rates in four loops and a reactor core under different power failures of reactor coolant pumps. Python 3.6, high level programming language, is used to solve the mathematical equations of core thermal-hydraulics for the flow coastdown transient. A standard 4-Loop Westinghouse design pressurized water reactor is used in the analysis. Three cases are studied; failure of one of the four pumps, sequential failure of the four pumps and simultaneous failure of the four pumps due to loss of off-site power. The important parameters for the safety analysis of the reactor are flow coastdown time, flow rates, and coolant temperature. The model results for a single pump failure are compared with the published experimental data during flow coastdown of Qinshan reactor coolant pump. The comparison results show acceptable agreements. Sensitivity analyses for two different parameters during flow coastdown transient are investigated. These two parameters are the fluid inertia ratio, α and core time constant, τ. Effects of each of the parameters on the flow coastdown transient, are given separately.