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Commercial ferritic and austenitic steels are the predominant materials used in both fossil and nuclear power plants; the significant difference in nuclear plants is the exposure to neutron fluence. Three aspects of material behavior are reviewed: (1) the role of residual elements on radiation damage of steels used for water reactor pressure vessels, (2) influence of neutron-gamma flux and water reactor coolant on stress corrosion, and (3) neutron-induced swelling and void formation in austenitic stainless steels in fast reactors.

Stainless steels represent one of the major groups of structural and fuel cladding materials used in nuclear reactors. These steels have been used extensively in civilian power reactors. This paper reviews the performance of ferritic, martensitic, austenitic, and precipitation hardening stainless steels when exposed to neutrons, and the effects of reactor environment, whether water, gas, or liquid metal. The effects of neutron irradiation on the mechanical properties of stainless steels are examined. Generally, exposure to neutron flux increases the yield strength substantially more than it does the ultimate tensile strength. This is accompanied by marked decreases in ductility. Uniform elongation becomes extremely small after exposures in the range 1020 to 1021 nvt. The dynamic properties of the stainless steels such as creep, stress rupture, and low cycle fatigue are reviewed, based on the limited data available. The effects of stress application to stainless steels while exposed to neutrons are also discussed. Specific consideration is given to surface corrosion, oxidation, and stress corrosion where the neutron induced heat flux plays a major role. Potential limitations to the use of these steels by such reactions are considered, as are possible solutions to the problems. Certain indirect effects of a neutron environment such as thermal cycling due to varying gamma flux during reactor startup and shutdown and the deleterious effects of such cycling are considered in structural components and in fuel cladding. Other indirect effects unique to nuclear reactors such as the interaction of fuel with stainless cladding are discussed briefly.

Materials selection for liquid metal fast breeder reactor (LMFBR) primary systems including the vessel, piping, heat exchanger, steam generator, core internals, and fuel cladding is reviewed on the basis of a logic chain. Based on this approach the austenitic stainless steels appear to be the most acceptable candidates for first generation demonstration LMFBRs. However, several real or potential problems exist with these or other materials when exposed to the LMFBR environment including temperature, neutron fluence and sodium. Specific problems discussed are creep-fatigue interactions resulting in reduced component life, sigma or chi phase embrittlement, thermal sensitization, possible stress corrosion, and void formation and swelling of core internals and fuel cladding when exposed to high neutron fluences at proposed reactor temperatures. tf4h\^ j §.