Development of 1D-CFD coupling method for natural circulation analyses through benchmark analyses of shutdown heat removal tests in EBR-II

At the Japan Atomic Energy Agency, a multilevel simulation (MLS) system, which enables consistent evaluation from whole plant behavior to local phenomena in the plant components, is being developed to attempt plant design and enhance the safety of sodium-cooled fast reactors. Whole plant and local multidimensional thermal–hydraulic behaviors were evaluated by coupling the in-house one-dimensional plant dynamics analysis code named Super-COPD (1D) and the computational fluid dynamics (CFD) code of ANSYS Fluent. Both codes were coupled and controlled using a Python script-based program. In this study, numerical analyses of the protected and unprotected loss-of-flow tests: SHRT-17 and SHRT-45R, conducted in EBR-II, were performed to validate the coupling method in the MLS system. In the analyses, the cold pool, upper plenum, and Z-shaped pipe connecting the upper plenum and intermediate heat exchanger were modeled by the CFD code. The flow network model for the 1D contained components in the primary heat transport system. By comparing the results of the 1D-CFD coupled analyses with those of standalone analyses using the 1D code and measured data, the validity of the 1D-CFD coupling method for plant dynamics behavior was confirmed. Through numerical analyses, thermal stratification, which is difficult to evaluate using only the 1D code, was clarified in the region modeled by the CFD code. Furthermore, the temperature profiles along the thermocouple trees installed in the upper plenum and cold pool were almost reproduced.