Dynamic scaling characteristics of single-phase natural circulation based on different strain transformations

To understand the dynamical system scaling (DSS) analysis theory, the applicability of DSS β- and ω-strain transformation methods for the scaling analysis of complex loops was explored. A simplified model consisting of two loops was established based on the primary and secondary sides of a nuclear reactor, and β- and ω-strain transformation methods were used to analyze the single-phase natural circulation in the primary circuit. For comparison with the traditional method, simplified DSS β- and ω-strain methods were developed based on the standard scaling criterion. The strain parameters in these four methods were modified to form multiple groups of scaled-down cases. The transient process of the natural circulation was simulated using the Relap5 code, and the variation in the dynamic flow characteristics with the strain numbers was obtained using different scaling methods. The results show that both the simplified and standard DSS methods can simulate the dynamic characteristics of natural circulation in the primary circuit. The scaled-down cases in the simplified method exhibit the same geometric scaling and correspond to small core power ratios. By contrast, different scaled-down cases in the standard DSS method correspond to different geometric scaling criteria and require more power. The dynamic process of natural circulation can be simulated more accurately using the standard DSS method.