b'Nuclear Science User Facilities Short CommunicationsCharacterization of Grain Boundaries of Alloy X-750 and SS 304Irradiated in Experimental Breeder Reactor-IILingfeng HeIdaho National LaboratoryLingfeng.He@inl.govT at the selected grain boundary was his project investigates the dose rate effect on the microstructuralconducted on a LEAP 4000X HR at the evolution of stainless steels,Center for Advanced Energy Studies which is currently not well understood.(CAES) Microscopy and Characterization Moreover, this project also tries toSuite (MaCS). STEM, TEM, and APT characterize the elemental segregationdata were then combined to achieve behavior at different types of grainbetter understanding of the irradiated boundaries and establish the possiblemicrostructure and microchemistry.relationship between elementalResultssegregation and grain boundary strengthSTEM data on the irradiated micro-as part of an Idaho National Laboratorystructure, including the size and (INL) Laboratory-Directed Researchnumber density of voids, Frank loops, and Development project. The grainand gamma-prime precipitates were boundary strength will be measuredgathered as well as APT data. APT data using similar setup as previous studieson microchemistry at different types of [1,2]. The specimens were chosengrain boundaries. The irradiated micro-from the NSUF library [3]. For bothstructures of stainless steel (SS) 304 and unirradiated and irradiated specimens,nickel-base alloy X-750 were compared focused ion beam (FIB) was usedto existing data in literature of similar to prepare site-specific lamellae foralloys irradiated at different dose rates.characterization by transmission electron microscopy (TEM). The Titan ScanningOur results show [4] that dose rate TEM (STEM) at the Irradiated Materialshas a significant effect on the loop size Characterization Laboratory (IMCL),and density in SS 304 i.e., lower dose equipped with ChemiSTEM technologyrate leads to larger loop size but lower was used to quantify radiation-inducedloop density. Besides dislocation loops, defects (i.e., dislocation loops, voids,voids were also found in SS 304 [4]. and precipitates) and the segregationNi and Si segregation was identified at at defect sinks (dislocations and grainthe void-matrix interface, and (Ni,Si)-boundaries). Electron backscatterrich clusters were also identified. The diffraction (EBSD) was carried out toHyperSpy non-negative matrix factor-distinguish different types of grainization (NMF) multivariate statistical boundaries. Atom probe tomographyanalysis (MVSA) was used to better (APT) measurement of the segregationquantify the Ni and Si content in the (Ni,Si)-rich clusters.54'