Generalized creep model of Zircaloy-4 cladding tubes

Zircaloy-4 cladding tubes with different area reductions at the final cold working were subjected to creep testing at temperatures of 350 to 500 degrees C. The creep testing was carried out mainly at the biaxial stress state. The creep rate and creep strain of the Zircaloy-4 cladding tube increased with increasing area reduction at the final cold working. The creep model was derived to cover the effect of area reduction and then verified by using supplementary creep data obtained at 350 degrees C and 138 MPa. Furthermore, this generalized creep model was verified to well describe the thermal creep of Duplex tubes and low Sn Zircaloy-3 tubes. The creep rate of Zircaloy-4 cladding tubes followed the exponential stress dependence, not the power law creep. The creep activation energy was determined to be 60 kcal/mol, leading to the conclusion that creep is controlled by dislocation creep. Thus, it is suggested that the increase of creep rates and creep strains with the increase in cold working is due to an enhanced climb rate arising from the increased concentration of vacancy. (C) 1997 Elsevier Science B.V.