Severe accident is complex coupling processes involving multiple components, phases, and physical fields, and related research is a complex and challenging systematic engineering project. In recent years, relevant scientific research institutions have placed greater emphasis on the development of integrated analysis codes for severe accident in order to address the issue of program autonomy, and modular severe accident analysis program (MOSAP) is one of them independently developed by Xi'an Jiaotong University, China.

This study aims to validate the early in-vessel phenomenon analysis model of the self-developed integrated analysis code MOSAP for severe accident.

The MOSAP code and the internationally recognized severe accident analysis code were used to model and calculate experiments on international standard questions ISP31 and ISP46. The calculation results of fuel and control rod temperature, hydrogen production, and major radioactive nuclide release rates obtained by the MOSAP were compared and analyzed with experimental and internationally recognized code calculation results.

The results show that the MOSAP calculation results are in good agreement with the experimental and internationally recognized code calculation results, and the deviation between the main parameter calculation values and the experimental values is within 20%.

The self-developed code MOSAP can simulate the early in-vessel phenomena of severe accident such as core overheating, fuel, cladding, and control rod oxidation, as well as fission product release.