The purpose of this internal hazards analysis is to identify and document the internal hazards and potential initiating events associated with preclosure operations of the repository at Yucca Mountain. Internal hazards are those hazards presented by the operation of the facility and by its associated processes that can potentially lead to a radioactive release or cause a radiological hazard. In contrast to external hazards, internal hazards do not involve natural phenomena and external man-made hazards. This internal hazards analysis was performed in support of the preclosure safety analysis and the License Application for the Yucca Mountain Project. The methodology for this analysis provides a systematic means to identify internal hazards and potential initiating events that may result in a radiological hazard or radiological release during the repository preclosure period.