The integrity of reactor internal components made of austenitic stainless steel welds with a duplex structure can potentially be affected by thermal aging and/or neutron irradiation induced embrittlement. There have not been sufficient studies on the long-term service performance of SS welds in light water reactors. In this study, thermal aging was performed at 400 °C for up to 2220 h on a 308L weld, and the irradiation was conducted in the Halden reactor at ~315 °C to 0.08 dpa (5.6 × 1019 n/cm2, E > 1 meV). The microstructural evolution of the ferrite phase was characterized using atom probe tomography (APT) and auxiliary transmission electron microscope studies. Spinodal decomposition and Ni-Mn-Si solute clusters were observed in both the thermally aged and neutron irradiated 308L welds. As compared with thermal aging, low dose neutron irradiation induced similar spinodal decomposition with slightly larger concentration wavelength and amplitude. The solute clusters in irradiated ferrite phase also show a larger mean size, a wider size distribution, but a lower number density as compared with those in thermally aged ferrite phase. In addition, the neutron irradiation significantly promotes segregation of trace elements, particularly phosphorus, at the Ni-Mn-Si solute clusters.
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This research was sponsored by the U. S. NRC under contract #NRC-HQ-14-G-0014. This work was also partially supported by the U.S. Department of Energy, Office of Nuclear Energy under DOE Idaho Operations Office Contract DE-AC07-051d14517, as part of an ATR National Scientific User Facility experiment. The authors would like to thank Joanna Taylor, Jatuporn Burns and Dr. Yaqiao Wu for their invaluable assistance at the CAES facility.
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