Abstract: Almost all spent fuel reprocessing facilities have adopted Purex process. The red oil explosion is a great concern in safety study of spent fuel reprocessing facilities adopting Purex process. The event tree and fault tree analysis was performed for the red oil explosion of a medium level radioactive waste liquid evaporator for the collective decontamination and separation cycle segment in a representative reprocessing facility in this paper. The results show that the occurrence frequency of a red oil explosion is extremely low, and human errors and common cause failures are major causes to a red oil explosion. Therefore, some relevant measures should be taken to prevent such accidents.