Abstract: Analyses of representative accident scenarios are imperative to assess and evaluate the inherent safety features of a prismatic modular high temperature gascooled reactor (HTGR). The accident progression of a HTGR is typically characterized by the coupling of multiphysics phenomena. However, computational codes available for the HTGR accident analyses are still relatively rare at present, especially those dedicated to the prismatictype core design. In addition, many of these codes are either lumpedparameter that cannot give the detailed threedimension (3D) distributions of key variables (e.g. fuel temperature), or are incapable of capturing the coupling of major phenomena. As a consequence, a generic CFD code, i.e. COMSOL multiphysics, was employed in this work to create a detailed 3D geometry representing the reactor, including fuel assemblies containing fuel and coolant channels, graphite moderator blocks, side reflector as well as the reactor pressure vessel. Specifically, the passive residual heat removal system (RCCS) was simply treated as a convective boundary condition due to the lack of detailed design scheme right now. A point kinetics module was prepared in this work using C++ language to account for the transient neutron kinetics. The Gear algorithm was applied to numerically solve the system of equations of the point kinetics, given that the stiffness is relatively large. The C++ was then compiled into dynamic link library (DLL), which was accessed by the COMSOL simulation in the form of an external function, with the fuel and moderator temperatures evaluated by COMSOL as input arguments. The steady state under normal operation condition was first calculated, which served as the initial condition for the subsequent transient analyses for three selected typical accidents, including pressurized loss of forced cooling (PLOFC), PLOFC without scram (PLOFC+ATWS), and reactivity insertion without scram (RIA+ATWS) accidents. Finally, sensitivity analysis was carried out on the effect of radiative emissivity between reactor pressure wall and RCCS. The simulation results show that the peak fuel temperature throughout the whole accident progression is remained far below its upper limit value (1 620 ℃) with a considerably large margin, implying that the integrity of fuel assemblies can be successfully guaranteed under the accident scenarios concerned in the present work. Moreover, enhancement of the RCCS heat removal capacity can significantly relief the accident consequence for PLOFC accident but lead to an inverse trend for ATWS accident, which underlines the importance of further comprehensive analysis and modeling validation. To conclude, the computational model developed in this work along with the derived results can serve as the starting point for future development of the accident analysis tool, which is applicable for the incoming indepth safety analysis and assessment works.