4.02 – Radiation Damage in Austenitic Steels

Austenitic stainless steels used as fuel cladding or structural components in various reactor types must often withstand an exceptionally strenuous and challenging environment, even in the absence of neutron irradiation. In addition to the environmental challenges associated with surviving prolonged exposure to high temperature and corrosive media, exposure to displacive neutron irradiation pushes steels into a progressive nonequilibrium evolution involving generation of completely new microstructural components unique to the radiation environment and new phase structures driven by diffusional processes that operate only during irradiation. The result of such microstructural and microchemical alteration is often the production of an alloy that cannot be found on an equilibrium diagram. Concurrent with this evolution on the microscopic scale are macroscopic changes in physical and mechanical properties, and most importantly, changes in dimensional stability that are outside the realm of normal engineering experience. Such changes can strongly affect the structural integrity and limit the in-reactor lifetime of structural steels. While reviews of this type usually focus primarily on the displacive aspects of neutron irradiation and perhaps confine the review to one or two types of reactor, it is necessary in this review to give equal attention to the transmutation aspects of irradiation for the full range of neutron flux-spectral environments. This review first focuses on identifying the important characteristics of various reactor environments, then addresses the microscopic aspects of neutron-induced alteration, and finally moves to cover the macroscopic consequences of these alterations.