An assessment of scaling methods for ECC behavior in downcomer of UPTF with RELAP5 code

Abstract

Various experimental investigations in scaled-down test facilities have been conducted to observe the ECC behaviors during a Large-Break Loss of Coolant Accident (LBLOCA). The ability of the scaling method to describe the similarity between the prototype and the scaled models required validation. In this paper, a series of simulations were performed to investigate the characteristics of ECC penetration in UPTF and the models scaled by four scaling methods including three-level scaling method, linear method, modified linear method and Hierarchical Two-tiered Scaling (H2TS) method. The ECC behaviors, such as the inventory and pressure in lower plenum, steam mass flow at the break, have been analyzed. And the applicability of the scaling method has been evaluated based on the analysis of the ECC behaviors in both of the prototype and scaled models. The results showed that the transient process in the model scaled by H2TS method with aspect ratio of 1.87 and modified linear was in good agreement with the prototype during ECC injection. Moreover, in order to investigate the effect of the aspect ratio, different aspect ratio in H2TS method was applied to scale the model and the inventory in the lower plenum between the UPTF and the model has been compared. In addition, the modified Wallis correlation for CCFL accounting for the condensation effect has been performed.