Irradiation-induced microstructural changes in Zr-1% Sn-1% Nb-0.4% Fe

The high resistance to nodular corrosion and irradiation-induced creep and growth shown by Zr-1% Sn-1% Nb-0.4% Fe compared with Zircaloy or binary ZrNb alloys requires a scientific explanation of the alloy's irradiation stability through analysis of its changes in microstructure and phases during irradiation. The evolution of its microstructure and phase composition was studied by irradiating specimens of channel and cladding tubes at 300 to 350°C and neutron fluences up to 4.1 × 1026n m−2 (E > 0.1MeV). Microstructural changes were also analyzed in a pressure tube that had operated in an RBMK-1500 for 5.5. years. In irradiated Zr-1% Sn-1% Nb-0.4% Fe second phase precipitates are subject to transformation and changes are observed in particle composition, size and shape. In the microstructure of the irradiated alloy matrix, dislocation loops of the 〈a〉-type prevail while dislocations of the 〈c〉-type, which dominate in Zircaloy and ZrNb alloys are absent. Microstructural characteristics of alloy microstructure were quantitatively assessed and consideration was given to the interrelationship between alloy microstructure evolution and the kinetics of property changes under neutron irradiation.