NSUF 15-567: Characterisation of Irradiation-Induced Nanoscale Features in Model RPV Steels using Advanced Analytical Electron Microscopy
This project addresses the physical microstructural changes that have occurred in model RPV steels as a result of neutron-irradiation in ATR, which have led to significant hardening and embrittlement. Specifically, this project will utilise previously-irradiated model steels from the UCSB-1 experiment at ATR to examine the nanoscale irradiation-induced features formed during high fluence irradiation (~1.1 X 10E21 n/cm2; ~ 1.7 dpa) at 290°C. As plant lifetimes are extended beyond the original license period, it is important to understand the nature and development of these irradiation-induced features as well as other defects that may form during high fluence, high flux irradiation. This proposal has three objectives: 1) High resolution micro-chemical characterisation of the irradiation-induced solute-containing features using the FEI Titan G2 80-200 S/TEM with Super X (4 Si Drift Detectors) and a Gatan Quantum 965 EELS for nm-scale EDX and EELS spectrum imaging. The capability for tilting the FIB “lift out” specimens will permit limited TEM-based tomographic evaluation for feature morphology. Furthermore, these techniques will also be applied to assess any segregation irradiation-induced defects, such as dislocation loops, etc. 2) Detailed Electron Diffraction characterisation of the nanoscale hardening features. As these solute-enriched features develop during neutron irradiation, they may develop into discrete nano-precipitates. Thus, careful electron diffraction analysis using high dynamic range digital image plates will enable the detection of weak diffraction reflections that conventional CCD cameras are unable to detect. To date, only limited efforts have been made to apply this methodology to study the nanoscale features. 3) Characterisation of high fluence/high flux irradiation-induced defects. Careful bright-field and weak-beam dark-field TEM imaging techniques will be used to identify irradiation-induced dislocation loops and other defects. By coupling the care weak-beam microscopy with the spectrum imaging capability, it may be possible to determine a relationship between defect type and segregation. To-date, clear evidence of such irradiation-induced defect analysis has been somewhat limited for RPV steels. This research has the potential to impact our understanding of the nature of the irradiation-induced solute-enriched hardening features – particularly for low Cu steel. The potentially complex nature of the solute-enriched features in high Cu model steels can be compared with the well-defined precipitates formed in long-term thermally-aged (365°C) Fe-Cu-Ni-Mn alloys. These results, coupled with the characterisation of irradiation-induced defects, can assist in the refinement of new predictive models for embrittlement, elucidating the complex nature of the solute-enriched features, and providing evidence for a continuum of "features" that develop as a function of neutron fluence. This project will be performed over a 6 to 9 month period ( June 2015 – Jan 2016/March 2016) depending upon the arrival of the specimens in Manchester.
Additional Info
| Field | Value |
|---|---|
| Abstract | This project addresses the physical microstructural changes that have occurred in model RPV steels as a result of neutron-irradiation in ATR, which have led to significant hardening and embrittlement. Specifically, this project will utilise previously-irradiated model steels from the UCSB-1 experiment at ATR to examine the nanoscale irradiation-induced features formed during high fluence irradiation (~1.1 X 10E21 n/cm2; ~ 1.7 dpa) at 290°C. As plant lifetimes are extended beyond the original license period, it is important to understand the nature and development of these irradiation-induced features as well as other defects that may form during high fluence, high flux irradiation. This proposal has three objectives: 1) High resolution micro-chemical characterisation of the irradiation-induced solute-containing features using the FEI Titan G2 80-200 S/TEM with Super X (4 Si Drift Detectors) and a Gatan Quantum 965 EELS for nm-scale EDX and EELS spectrum imaging. The capability for tilting the FIB “lift out” specimens will permit limited TEM-based tomographic evaluation for feature morphology. Furthermore, these techniques will also be applied to assess any segregation irradiation-induced defects, such as dislocation loops, etc. 2) Detailed Electron Diffraction characterisation of the nanoscale hardening features. As these solute-enriched features develop during neutron irradiation, they may develop into discrete nano-precipitates. Thus, careful electron diffraction analysis using high dynamic range digital image plates will enable the detection of weak diffraction reflections that conventional CCD cameras are unable to detect. To date, only limited efforts have been made to apply this methodology to study the nanoscale features. 3) Characterisation of high fluence/high flux irradiation-induced defects. Careful bright-field and weak-beam dark-field TEM imaging techniques will be used to identify irradiation-induced dislocation loops and other defects. By coupling the care weak-beam microscopy with the spectrum imaging capability, it may be possible to determine a relationship between defect type and segregation. To-date, clear evidence of such irradiation-induced defect analysis has been somewhat limited for RPV steels. This research has the potential to impact our understanding of the nature of the irradiation-induced solute-enriched hardening features – particularly for low Cu steel. The potentially complex nature of the solute-enriched features in high Cu model steels can be compared with the well-defined precipitates formed in long-term thermally-aged (365°C) Fe-Cu-Ni-Mn alloys. These results, coupled with the characterisation of irradiation-induced defects, can assist in the refinement of new predictive models for embrittlement, elucidating the complex nature of the solute-enriched features, and providing evidence for a continuum of "features" that develop as a function of neutron fluence. This project will be performed over a 6 to 9 month period ( June 2015 – Jan 2016/March 2016) depending upon the arrival of the specimens in Manchester. |
| Award Announced Date | 2015-04-22T00:00:00 |
| Awarded Institution | None |
| Facility | None |
| Facility Tech Lead | Yaqiao Wu |
| Irradiation Facility | None |
| PI | Grace Burke |
| PI Email | [email protected] |
| Project Type | RTE |
| RTE Number | 567 |