Abstract: The initial events analysis is the basis of probabilistic safety analysis. Quantitative evaluation of the initial events is the precondition for probabilistic safety analysis to obtain quantitative risk results. Combination of engineering evaluation and deductive analysis is used to identify the initial events of typical uranium purification and conversion facilities. According to the similarities and differences of facility safety protection measures, the initial events are categorized into five groups, and the UF₆ leakage is the main concern in uranium purification and conversion facility. Event tree for accident sequence analysis was used to obtain UF₆ leakage events sequence and the corresponding frequency.

Key words: uranium conversion, initial event, accident sequence, probability analysis