Conceptual design for a small modular district heating reactor for Mongolia

► We performed design study of a small, modular district heating reactor with passive safety features for long core life. ► The design concept was based on the high temperature gas-cooled reactor (HTGR). ► The core dimensions chosen were 8m diameter and 8m height with 330MWth of power. ► The proposed reactor with 20wt% of uranium enrichment can be critical around 16years. ► It is possible to remove decay heat without any active cooling system after the shutdown. The energy demand in Mongolia is expected to increase in the near future. The purpose of the present study was to design a small, modular district heating reactor with passive safety features for long core life to meet the country’s expected energy demand. The design concept was based on the advanced and well-proven technology of the high temperature gas-cooled reactor (HTGR) idea. The reactor size was roughly estimated without any active cooling system to remove the decay heat, and the optimal core dimensions chosen were 8m diameter and 8m height with 330MWth of power. Fundamental analyses of the reactor for criticality and burnup were performed by using continuous energy Monte Carlo code MVP 2.0, and the proposed reactor with 20wt% of uranium enrichment can be critical around 16years. The initial effective neutron multiplication factor can be suppressed to 1.1351 when there are 9 burnable poison (BP) rods with 12wt% of boron carbide in B4C/C composite and 10wt% of 10B per assembly.