The systematic research of in-reactor creep regularities for different purity polycrystalline copper and elaboration of the related theoretical model are discussed. The stress and temperature dependence of the in-reactor and thermal creep rates of pure copper and temperature dependence of the in-reactor and thermal creep rates of technical copper have been analyzed. It is shown that for each of the materials studied there is a temperature region where an abnormal reduction of the creep rate with increasing temperature takes place. A creep model based on dislocations sliding and thermoactivation overcoming of barriers by them is suggested. It is shown that the model well describes the conduct peculiarities of the in-reactor and thermal creep rates of copper in different temperature-strength conditions. The reasons for the abnormal temperature dependence of the creep rate in the intermediate temperature region are discussed.