Scaling methodology and transient distortion evaluation for loop-type sodium-cooled fast reactors

For loop-type sodium-cooled fast reactors employing the sodium-sodium-air configuration, the primary natural circulation path constitutes a single closed loop. While this design facilitates scaled integral tests for validating natural circulation capability, existing methodologies lack dedicated research systematically incorporating the unique characteristics of loop-type SFRs. The scaling criteria were derived through dynamical system scaling modified by the Favre-averaging method. Incorporating the characteristics of loop-type SFR components, the parameter determination methodology was established and subsequently validated using the FFTF reactor as the representative case. The prototypic numerical model was established and validated against the Benchmark for FFTF LOFWOS Test #13, subsequently serving as the foundation for model scaling. Numerical comparisons between the scaled and prototype models were performed for three operational regimes: initial forced circulation steady-state, stable natural circulation, and transient response during LOFWOS Test #13. The analysis investigated three frictional resistance correction approaches and two intermediate heat exchanger parameter design methods, evaluating the impacts on transient process. The transient distortions among different schemes were quantified by the time-value-difference dynamic time warping distortion evaluation code. This study confirms the theoretical feasibility of performing scaled sodium tests for loop-type SFRs with the proposed scaling and distortion evaluation methodology, while also revealing additional distortion factors requiring consideration in practical scaled test implementation.