Abstract: Background: Initial event analysis is the beginning of the reactor nuclear safety analysis and probabilistic safety assessment, and plays a key role in these analyses. At present, the initial event analysis evaluation method and experience are mainly used for the water reactors. There is hardly any analysis method and theory for the initial event analysis of the solid thorium molten salt reactor. However, with the research of molten salt reactor and the reactor progress of probabilistic safety assessment (PSA), initial event analysis has become increasingly important. Purpose: On the one hand, by carrying on the preliminary exploration research for the TMSR-SF1 (Thorium Molten Salt Reactor, Solid Fuel #1) initial event analysis, to determine TMSR-SF1 initial events of potential, causes radioactive release, and give the TMSR-SF1 initial event lists. On the other hand, the aim is to group the determinate initial events. Methods: First of all, we used the master logic diagram (MLD) analysis method, and referenced the initial event lists of pressurized water reactor, the fluoride-salt-cooled high-temperature reactor (FHR), the high temperature gas cooled reactor and the sodium cooled fast reactor, to carry on the TMSR-SF1 preliminary analysis and research of initial events and main external events. Then, the accident type classification method was applied to group theTMSR-SF1 preliminary determinate initial events. Results: Through the MLD analysis, we determined the preliminary initial event lists for TMSR-SF1 which contain 37 initial events, and given 6 class accident types of TMSR-SF1 initial events. Conclusion: This study provides basic foundation for the TMSR-SF1 PSA accident sequence analysis of the next step, and gives an important support for the integrity of the molten salt reactor safety analysis.

Key words: Solid thorium molten salt reactor, Probabilistic safety assessment (PSA), Master logic diagram, Initial event analysis