[en] The unirradiated tensile properties of two different heats of Hycon 3HP trademark CuNiBe (HT Temper) have been measured over the temperature range of 20-500 degrees C for longitudinal and long transverse orientations. The room temperature electrical conductivity has also been measured for both heats. Both heats exhibited a very good combination of strength and conductivity at room temperature. The strength remained relatively high at all test temperatures, with a yield strength of 420-520 MPa at 500 degrees C. However, low levels of ductility (<5% uniform elongation) were observed at test temperatures above 200-250 degrees C, due to flow localization adjacent to grain boundaries. Fission neutron irradiation to a dose of ∼0.7 dpa at temperatures between 100 and 240 degrees C produced a slight increase in strength and a significant decrease in ductility. The measured tensile elongation increased with increasing irradiation temperature, with a uniform elongation of ∼3.3% observed at 240 degrees C. The electrical conductivity decreased slightly following irradiation, due to the presence of defect clusters and Ni, Zn, Co transmutation products. The data indicate that CuNiBe alloys have irradiated tensile and electrical properties comparable or superior to CuCrZr and oxide dispersion strengthened copper at temperatures <250 degrees C, and may be suitable for certain fusion energy structural applications