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.