Design improvements to the High Flux Isotope Reactor for safety enhancement

The High Flux Isotope Reactor (HFIR) at the Oak Ridge National Laboratory (ORNL) was shut down in late 1986 for a reevaluation of the integrity of the pressure vessel because the radiation damage rate appeared to be greater than expected. The U.S. Department of Energy (DOE) reviewed the reevaluation and a subsequent ORNL proposal for a 10-yr life extension of the vessel as well as the overall design and safety of the HFIR. In response to recommendations by the DOE-appointed review committees, ORNL performed a probabilistic risk assessment (PRA) to help identify and prioritize plant safety upgrades. Related studies performed before reactor restart included the internal-events PRA, the potential for and consequences of loss-of-coolant accidents (LOCAs), seismic upgrades, and decay heat removal. Ongoing programs to ensure that the level of safety continues to improve include an update of the internal-events PRA, an external-events PRA, additional LOCA studies, and implementation of an environmental qualification program. HFIR was restarted in April 1989 and is expected to be operational for an additional 10 effective full-power years.