Dynamic characteristics and scaling distortion of gravity-driven draining process in Core Makeup Tank

Abstract

The transient process of the gravity-driven draining in the core make-up tank (CMT) system will be affected by the wall-stored energy, which will lead to the deviation of experimental results based on scaled-down test facilities. In order to understand the corresponding mechanism, the Hierarchical Two-Tiered Scaling (H2TS) method was adopted to scaling effects. The Relap5 code was used to simulate the gravity-driven draining process of the models with different scaling sizes, and the transient scaling distortion were evaluated. It was found that all the dynamic distortions of the similarity criterion numbers increase with the decreasing of the scaling size. Among the two key criterion numbers that dominate the wall heat transfer, the distortion of the condensation number is very small while that of the heat conduction number is larger. Under all scaled-down cases, the water level in CMT drops slightly slower than that under the prototype case, and the smaller the length scale is, the slower the dropping speed is. Under all cases, the discharging mass flow rate decreases gradually with time, and the dynamic processes of fluid temperature and solid temperature between the model and the prototype are basically the same under the condition of equal physical properties.