DSS application on single-phase natural circulation in a simple rectangular loop

Scaling analysis is widely used in the design of nuclear reactor passive safety systems to ensure those scaled-down test facilities can accurately capture important phenomena in a full-scale prototype. In this study, the transient scaling distortion of a single-phase natural circulation system was evaluated using the new Dynamical System Scaling (DSS) method. For convenience of comparison, the conventional Hierarchical Two-Tiered Scaling (H2TS) method, based on the initial static characteristic values, was applied first to determine the system scaling ratios. The different scaled-down cases based on the two methods were calculated with the Relap5 computational code. The results show that two different scaling number groups can be obtained based on the traditional H2TS method and the new DSS identity method, and both of the methods can effectively model the single phase natural circulation in a simple loop. The relative scaling distortion of the transient mass flow rate fluctuated sharply at the initial stage, when the power input increased step-wise, but gradually grew afterwards. In addition, with a smaller power ratio, the DSS identity method was more helpful for the scaled-down facility design.