Development of analytical models for the natural circulation behavior of a full-scale PWR fuel assembly

Abstract

During a loss-of-coolant accident in spent fuel pools, the fuel assembly will be exposed to the air environment and decay heat will be removed through the natural circulation of air. In this study, the Darcy-Forchheimer model was revised based on experiment to predict the pressure drop of the fuel assembly. Based on the ideal gas hypothesis, this paper also established analytical prediction models to estimate the natural circulation flow rate and the maximum cladding temperature of the fuel assembly. The model can accurately prediction of the flow rate of the fuel assembly under different heating powers. Through this model, it is found that with the increase of heating power, the natural circulation flow of air first increases and then decreases, and reaches the maximum when the power is about 2000 W. Meanwhile, lowering the environment temperature can significantly reduce the maximum cladding temperature of the fuel assembly.