Numerical scaling assessment on natural circulation in Core Makeup Tank

Abstract

To assess the impact of the wall-stored energy on natural circulation in the Core Make-up Tank (CMT) system in advanced PWR design, the Hierarchical Two-Tiered Scaling (H2TS) method was applied to scaling effects in the corresponding transient process. The models were simulated with the Relap5 code under different scales, and the transient scaling distortion for the key parameters and the similarity criteria numbers were evaluated. The results show that the wall-stored energy can affect the natural circulation in CMT, and remarkably delay the dropping of the mass flow rate at the second stage, but does not affect the time for the thermal stratification to penetrate the CMT. As far as the key parameters dominating natural circulation are concerned, the different scaled-down models can simulate the prototype process with acceptable deviations throughout the CMT cooling period. The evolution of the wall-stored energy in the model and the prototype can be in good agreement by selecting appropriate similarity criteria numbers. However, large deviations of some similarity criteria numbers may occur due to the great change of thermophysical properties.