A multi-scale CFD-system coupled code for transient analysis of the passive residual heat removal system of MHTGR

•DOM method was finally adopted for coupling.•A multi-scale CFD-system coupled code for the PRHRS of HTR-10 was developed.•Transient characteristics of the PRHRS during the startup process were calculated.•The computational results are in good agreement with the experimental results.•Radiation heat transfer plays a very important role in the heat removal process.