NSUF 19-1721: Nanoscale analysis of Mn-Si-Ni phase in neutron irradiated T91 at 320C
The fuel cladding material of Generation IV nuclear reactors experience extreme temperatures, radiation damage, and coolant-interactions, which limit the window-of-operation. T91 ferritic-martensitic steel is a candidate for the fuel cladding material. Irradiation is the driving force for microstructural and microchemical evolution that has direct impact on the mechanical performance, which limits the advanced reactor structural components.
One of the defining microstructural features that results from irradiation of T91 is the formation of nanosized Mn-Si-Ni rich precipitates (ppts). These ppts act as obstacles to dislocation glide, increasing both its strength and susceptibility to embrittlement. Thus, understanding how these ppts form as a function of dose and temperature could have direct impact in our understanding and predictability of the materials performance during service.
High temperature analysis of these ppts have been investigated between 400-650C however low temperature (<320C) irradiation studies are rarely found in literature. The nucleation and evolution of these ppts at temperatures below 320C are not well understood, and it is clear that they impose a major effect on the material’s embrittlement. Therefore, the first scientific output is understanding the effect of low temperature embrittlement phenomena of T91 at the nanoscale is essential to fill this knowledge gap. Atom probe tomography and nanoindentation techniques, selected to perform the proposed research, are ideal to explore this aspect.
The second scientific output is that T91 steel has already been irradiated with Fe4+ ions at 300 oC with a dose ranging from 0.4 dpa to 25 dpa at the Dalton Cumbrian Facility, UK. Initial atom probe results show the evolution of these ppts as a function of dose. Ion irradiation is a useful tool to understand the effects of radiation damage, however further validation is required to determine whether ion irradiation could be used as a surrogate for neutron irradiation. Direct comparison between the ion and neutron irradiated samples could provide evidence for this possible validation.
The requested neutron irradiated samples are: T91 1005-2008-139, 1.82 dpa at 319 oC and T91 1109-2008-139, 6.65 dpa at 318.50-320.50C.
The methods employed within this study are three: Dual Focused Ion Beam microscope at CAES to produce atom probe samples; Local Electrode Atom Probe (LEAP) 4000X HR at CAES; and Nanoindentation equipment at CAES (TI-950 Triboindenter, Hysitron)
We request: 6 full days on the FIB to produce all the atom probe; 10 full days on the LEAP 4000X HR; 3 full days on the nanoidentor.
Prior to the FIB work, the neutron-irradiated samples require to be polished to Electron Backscatter Diffraction (EBSD). This requirement is to ensure optimal surface quality for the FIB and near surface nanoindentation (any rough surface will invalidate the indentation results). The typical polishing route would be mechanical polishing form 300 git Silicon Carbide papers to 1um diamond with a 10-minute colloidal silica finish polishing stage. Thus, 1 day is required for INL staff to prepare these samples prior to shipment to CAES before FIB work is conducted.
Additional Info
| Field | Value |
|---|---|
| Abstract | The fuel cladding material of Generation IV nuclear reactors experience extreme temperatures, radiation damage, and coolant-interactions, which limit the window-of-operation. T91 ferritic-martensitic steel is a candidate for the fuel cladding material. Irradiation is the driving force for microstructural and microchemical evolution that has direct impact on the mechanical performance, which limits the advanced reactor structural components. One of the defining microstructural features that results from irradiation of T91 is the formation of nanosized Mn-Si-Ni rich precipitates (ppts). These ppts act as obstacles to dislocation glide, increasing both its strength and susceptibility to embrittlement. Thus, understanding how these ppts form as a function of dose and temperature could have direct impact in our understanding and predictability of the materials performance during service. High temperature analysis of these ppts have been investigated between 400-650C however low temperature (<320C) irradiation studies are rarely found in literature. The nucleation and evolution of these ppts at temperatures below 320C are not well understood, and it is clear that they impose a major effect on the material’s embrittlement. Therefore, the first scientific output is understanding the effect of low temperature embrittlement phenomena of T91 at the nanoscale is essential to fill this knowledge gap. Atom probe tomography and nanoindentation techniques, selected to perform the proposed research, are ideal to explore this aspect. The second scientific output is that T91 steel has already been irradiated with Fe4+ ions at 300 oC with a dose ranging from 0.4 dpa to 25 dpa at the Dalton Cumbrian Facility, UK. Initial atom probe results show the evolution of these ppts as a function of dose. Ion irradiation is a useful tool to understand the effects of radiation damage, however further validation is required to determine whether ion irradiation could be used as a surrogate for neutron irradiation. Direct comparison between the ion and neutron irradiated samples could provide evidence for this possible validation. The requested neutron irradiated samples are: T91 1005-2008-139, 1.82 dpa at 319 oC and T91 1109-2008-139, 6.65 dpa at 318.50-320.50C. The methods employed within this study are three: Dual Focused Ion Beam microscope at CAES to produce atom probe samples; Local Electrode Atom Probe (LEAP) 4000X HR at CAES; and Nanoindentation equipment at CAES (TI-950 Triboindenter, Hysitron) We request: 6 full days on the FIB to produce all the atom probe; 10 full days on the LEAP 4000X HR; 3 full days on the nanoidentor. Prior to the FIB work, the neutron-irradiated samples require to be polished to Electron Backscatter Diffraction (EBSD). This requirement is to ensure optimal surface quality for the FIB and near surface nanoindentation (any rough surface will invalidate the indentation results). The typical polishing route would be mechanical polishing form 300 git Silicon Carbide papers to 1um diamond with a 10-minute colloidal silica finish polishing stage. Thus, 1 day is required for INL staff to prepare these samples prior to shipment to CAES before FIB work is conducted. |
| Award Announced Date | 2019-05-14T14:00:08.047 |
| Awarded Institution | Center for Advanced Energy Studies |
| Facility | Microscopy and Characterization Suite |
| Facility Tech Lead | Alina Zackrone, Yaqiao Wu |
| Irradiation Facility | None |
| PI | Thomas Davis |
| PI Email | [email protected] |
| Project Type | RTE |
| RTE Number | 1721 |