Dynamical system scaling of integral natural circulation experiments for fluoride-salt cooled reactors

The Dynamical System Scaling (DSS) method developed by Reyes et al. adds a new dimension to scaling of integral systems where distortion estimates are given as functions of time rather than as static values. The distortion is an important parameter describing a scaled experiment because it evaluates the extent to which results from the experiment can be used to conclude characteristics of the prototype. The DSS method is applied in this paper to develop the scaling criteria for a two-loop natural circulation transient in the Mark 1 Pebble-Bed Fluoride- Salt-Cooled High Temperature Reactor (Mk1 PB-FHR). The necessary steps to perform an optimization study to determine a hypothetical DSS-scaled facility that can be used to validate natural circulation behavior in the primary and secondary loops of the Mk1 PB-FHR are then described in detail. This application of the DSS method to an integral system with multiple loops, where the systems code RELAP5-3D is used to generate model and prototype data, reveals the added complexities associated with the DSS method, while providing the framework to connect the DSS method to a systems code. In particular, the added difficulty of employing a systems code, rather than a numerical solution to governing equations, is addressed by the development of a simple iteration algorithm to determine model parameters needed for the optimization study. The Compact Integral Effects Test (CIET) facility at the University of California-Berkeley, completed in 2014, has successfully validated natural circulation behavior of the Mk1 PB-FHR. This experimental facility was scaled based on the Hierarchical Two-Tiered Scaling (H2TS) method, and allows the application of the DSS method to be compared to the H2TS method, as the DSS method is applied in this paper to the same transient in the same reactor that is modeled by CIET.