Three-dimensional modeling and loss-of-coolant accident analysis of high temperature gas cooled reactor

•Three-dimensional model is established for the core of HTR.•3D model is validated by comparing the calculated results with THERMIX software.•Effects of convection heat-transfer among pebble bed, sidewall and cold-gas plenum is considered.•Different operating conditions including rated power and accidents are simulated and studied. The high temperature gas-cooled reactor (HTR) is well known due to its prominent inherent safety, high efficiency and low carbon environmental protection. Accurate and reliable thermal hydraulic analysis is of great significance to the system design of HTR. Based on the coolant flow and heat transfer process in the core, this study establishes a three-dimensional coupled model for the core of HTR, and the temperature variation in the core is simulated. The model is verified by comparing the calculated results with those published data by THERMIX software. After that, the models are employed to study thermal hydraulic characteristics under the loss of coolant accident. The results show that the maximum relative error of the calculated results with published data are 2.1% under full power, the three-dimensional model can be employed to simulate the flow and heat transfer process in the primary circuit of HTR. The calculation of 50% of full power shows that the model fully considers the influence of convective heat transfer and radiative heat transfer between the core of the pebble bed and the core side wall and the cold air chamber, making numerical calculations closer to actual condition. It is found when approximately 20% of the coolant is lost, the outlet temperature of helium reaches 1140 K, which exceeds the helium outlet temperature limit (1126 K). In addition, the inherent safety of an HTR be verified under transient conditions of natural convection.