Nuclear criticality safety lessons learned from the Rocky Flats Plant fires

The Rocky Flats Plant had significant fire events in the years 1957 and 1969 that incurred millions of dollars in damages and suspended plutonium processing operations for months. In each event, firefighters were trained in criticality safety and attempted to extinguish the fires using approved dry extinguishers. When these efforts proved ineffective, the firefighters were forced to extinguish using water. The report on investigation of fire by the Atomic Energy Commission (AEC) capture the details of the event, including the resulting material form and configuration of plutonium that had been treated with fire water. When performing criticality safety analyses, all credible normal and abnormal conditions must be analyzed and remain subcritical. Water ingress due to a fire is a commonly considered abnormal condition when evaluating a fissionable material operation. At the Los Alamos National Laboratory (LANL), several criticality safety evaluations rely on verbiage from the AEC fire reports to analyze the credibility and/or subcriticality of fire-related conditions for the abnormal condition of a fire. The analyses that reference the AEC reports are inconsistent in approach and level of rigor. It is important to derive lessons learned from historical events of consequence in fissionable material processing for consistent and thorough safety analysis development. The events of this fire are evaluated to provide technical guidance on utilization of the lessons learned for modern fissionable material handling facilities. (author)