TEM [transmission electron microscopy], APFIM [atom-probe field ion microscopy], and SANS [small-angle neutron scattering] examination of aged duplex stainless steel components from some decommissioned reactors

Cast stainless steels, composed of duplex phases of austenite and ferrite, are used extensively in nuclear reactors because of their superior strength, weldability, resistance to stress corrosion cracking, and soundness of casting. For example, cast stainless steels are used for primary coiling pipes of pressurized water reactors (PWRs), and valves and pump casings of PWRs and boiling water reactors (BWRs), the structural integrity of which is vital for safe operation of the reactors. In the present investigation, microstructural characteristics of several long-term-aged field components from two decommissioned reactors have been examined by transmission electron microscopy (TEM), atom-probe field ion microscopy (APFIM), and small-angle neutron scattering (SANS) techniques to establish the embrittlement mechanisms for the reactor-aged material. The results have then been compared to those of the laboratory-aged specimens obtained for the temperature range between 300 and 450 degree C. The chemical compositions and ferrite contents of the reactor components are listed. KRB BWR (located in Gundremmingen, Federal Republic of Germany) had been in service for ∼12 yr, and the Shippingport PWR (near Pittsburgh, Pennsylvania) had operated for ∼22 yr