The effect of low-temperature (T{sub irr} less than 0.3. T{sub melt}) irradiation on the tensile properties of copper and precipitation-hardened (PH) and dispersion-strengthened (DS) copper alloys was investigated. Samples were irradiated with fission neutrons at temperatures of 80 to 200{degrees}C to doses of 0.6 to 5 dpa. Irradiation at temperatures <150{degrees}C resulted in significant hardening and accompanying embrittlement in all of the materials. By comparing the present results with literature data, it is concluded that severe radiation embrittlement occurs in copper alloys irradiated at temperatures {le}I00{degrees}C for doses above {approximately} 0.01 to 0.1 dpa. On the other hand, irradiation at temperatures above 150{degrees}C causes only moderate embrittlement for doses up to {approximately}5 dpa. It is recommended that the minimum operating temperature for copper alloys intended for structural applications in fusion energy systems should be 150{degrees}C, unless uniform elongations <I% can be accomodated in the design
