Development of an improved non-equilibrium multi-region model for pressurized water reactor pressurizer

Highlights: • A non-equilibrium multi-region model of pressurizer in PWR is developed. • The model do not need the knowledge of the surge flow distribution. • Mesh-independent solutions can be obtained in the model. • The model is verified with the Shippingport pressurizer loss-of-load experiments. - Abstract: This paper presents an improved non-equilibrium multi-region model for accurate prediction of pressure in the pressurizer of pressurized water reactor under transient conditions. The pressurizer model consists of three layers: a liquid layer, a saturated layer and a vapor layer. Each layer is further meshed into several control volumes (regions). The mathematical model derived from the mass and energy conservations describes most of the important thermal-hydraulics phenomena that occur in the pressurizer: bulk evaporation (bubble rise), bulk condensation (condensate fall) and spray condensation. The surge flow caused by the temperature change of the primary coolant is treated as the external boundary condition. To obtain the numerical solutions, the control equations of this model are first transformed into a set of linear equations, which is subsequently solved by the Gauss-Jordan elimination with partial pivoting. The mesh-independent solutions of the pressure of this model are in good agreement with the Shippingport pressurizer loss-of-load experiments. Moreover, the transient flow field of the pressurizer is analyzed. Unlike most of the previous models that require changing the empirically-determined surge flow distribution coefficient(s) to match the experiment data, this model does not need the knowledge of the surge flow distribution. And unlike the previous non-equilibrium multi-region model, this model can obtain the mesh-independent solutions.