Loss-of-coolant accident analyses have been completed for the High-Flux Isotope Reactor safety analysis report. More than 100 simulations have been performed using the RELAP5/MOD2.5 computer program. The RELAP5 input model used for the simulations is quite detailed, including 17 parallel channels in the core region, the three active heat exchanger cells, the pressurizing system, and the secondary cooling system. Special models are developed to represent the effects of shrinkage in the primary coolant pressure boundary and cavitation of the primary coolant pumps. Six locations in the primary coolant system are selected as pipe break sites to determine the worst-case scenario. At each of the locations, simulations are completed for a range of break diameters. The reactor is assumed to survive the transient as long as the hot-spot heat flux remains below the flow excursion limit. In addition to the baseline simulations, extensive parametric simulations are conducted to ensure that the modeling assumptions used are conservative. For a break diameter of 5.1 cm at any of the six locations in the system, the hot-spot heat flux remains beneath this limit, and furthermore, no boiling occurs in the fuel region. A summary table for all results is presented, and results are discussed in detail for the worst-case 5.1-cm break scenario.