Research on wall-to-vapor convective heat transfer model in reflooding phase of typical PWR based on RELAP5

This paper evaluates the rationality of RELAP5 reflood models based on the reflooding experiments FLECHT SEASET. The calculated results show that the current version of RELAP5 underestimates the peak clad temperature when simulating the low flooding rate test. Combined the characteristics of the reflooding phase of typical PWR and considered the vapor flow state and rod bundle configuration effects, the wall-to-vapor convective heat transfer model is modified. A new wall-to-vapor convective heat transfer model is established for the simulation of the typical PWR reflooding phase. Through the validation of this new model by comparing the calculation results of peak clad temperature from original code and modified code, it can be concluded that the new model is reasonable. (authors)