Modular high-temperature gas-cooled reactor (MHTGR) is being developed under the Next Generation Nuclear Plant Program in nuclear engineering studies. As the world searches for an energy source with high energy density, clean, abundant, and storable nature to avoid global warming issues, MHTGR seems to be a promising solution, particularly the possibility of producing hydrogen. Studying and developing safety analyses are required for the optimum design and safety of the MHTGR systems. The focus of several researchers, in previous years, has been directed in conducting investigations on natural convection heat transfer and flow dynamics in diverse geometries and operating conditions of MHTGR. The implementation of natural convection in nuclear reactors comes in the form of an engineered feature in accomplishing passive safety. In this review article, a comprehensive literature review has been introduced about the current status of the MHTGR. As part of an effort to understand the current status of the MHTGR safety analysis technology, this article introduced the MHTGR phenomena identification and event categorization and acceptance criteria.