Scaling and distortion analysis using a simple natural circulation loop for FHR development

Abstract Integral effects tests (IETs) using simulant fluids are expected to play an important role in code validation for Fluoride-salt-cooled High-temperature Reactors (FHRs). In this work, a scaling analysis is conducted for a natural circulation loop to simulate expected behaviors in FHRs. Based on the dimensionless governing equations and the derived non-dimensional numbers, similarity criteria are developed for the natural circulation loop. A prototypical natural circulation loop is identified and several ideally scaled models, using the simulant fluid Dowtherm A and the prototypic fluid FLiBe, are designed based on the developed scaling criteria. Steady-state and transient analyses are performed using RELAP5-3D for both the prototypical and scaled models to evaluate whether the scaling criteria is maintained in the models. The model using Dowtherm A and reduced-height, reduced-area scaling replicates the dynamic response of the prototype highly consistently, with the maximum error less than 0.1%. The Dowtherm A simulant performs better than the FLiBe in the scaled models, especially in the reduction of scaling distortion caused by the parasitic heat loss.