Nuclear operation of HRE-2 began in December, 1957. In January, 1960, the reactor was shut down for repair and modifications of the core tank. During this two-year period, operation of HRE-2 went far toward attaining the original goals of the experiment. It was possible to operate continuously for periods of up to three months; with the exception of the core tank, the life of components exceeded expectations. The maintenance which was required was shown to be practicable. Continuous removal of neutron poisons during operation and excellent containment of radioactivity were demonstrated. The general corrosion rate proved to be moderate to low. Although the experience was generally good, at some operating conditions fuel solution instability was observed when the reactor was operated at power. Uranium which separated as a result of the solution instability sometimes caused reactivity excursions. Uranium deposits in the core led to hot spots and two holes were melted in the thin Zircaloy-2 tank which separated the core and the blanket. Core modifications were designed to alleviate the conditions which led to fuel instability, and future operation will test the effectiveness of the changes.