NSUF 20-2929: Effects of cold rolling and induction casting on the microstructural evolution in irradiated uranium-10wt.% molybdenum (U-Mo) alloys
The purpose of this project is to study the effects of cold rolling and induction casting on the microstructural evolution in irradiated uranium-10wt.% molybdenum (U-Mo) alloys. A U-Mo alloy monolithic fuel plate is fabricated by casting, hot rolling, cold rolling, and hot isostatic pressing (HIP) processes. Research has extensively been carried out for HIP-processed U-Mo alloy fuel plates irradiated to high burn-up. However, there is a lack of knowledge of the microstructural evolution under low fluence irradiation of the non-HIPed U-Mo alloys. This includes the rolled alloy foil, as well as the U-Mo alloy fuel that is cast into a slug form without rolling, which is a more suitable geometry for other advanced reactor fuel types. Both fabrication techniques have unique as-fabricated microstructures, including varying grain morphology, texture, and dislocation density. During the cold-rolling fabrication process, a high density of dislocations and additional grain boundaries is produced. These mechanically-induced defects may act as sinks (interstitials) and nucleation sites (voids and fission gas bubbles) for the irradiation-induced defects, leading to different microstructures under irradiation. Moreover, since the fuels are irradiated at relatively low temperatures (< 350°C), irradiation-enhanced diffusion may also affect the defect evolution. It is hypothesized that the density of irradiation-induced defects in the U-Mo alloy depends on various aspects, including the initial microstructure, as well as irradiation temperature, fluence, and flux. Transmission electron microscopy (TEM), including bright-field (DF)/dark-field (DF) imaging, selected area electron diffraction (SAED), and energy dispersive spectroscopy-scanning transmission electron microscopy (EDS-STEM), will be used to characterize the unirradiated and irradiated U-10 Mo as-cast and as-rolled foils. BF/DF imaging will provide the information on the overall microstructures in the unirradiated and irradiated alloys. BF/DF imaging will be also used to calculate a density/size of irradiation-induced defects, and to identify the types of defects. An existence of voids and fission gas bubbles will be confirmed by BF imaging, and the types of dislocation loops will be identified by weak beam DF using two beam condition. Presence of decomposed phases and its crystal structure will be identified by EDS-STEM and SAED, respectively. Finally, the types of nanoscale precipitates/clusters will be identified by HRTEM. It is proposed that FIB and TEM (BF/DF, SAED, HRTEM, and EDS-STEM) are used for 1 week, respectively. This research will help fuel designers to optimize fabrication techniques (e.g. rolling versus casting), as well as to tune irradiation-induced defect densities and phase decomposition under irradiation. Although the U-Mo alloy was chosen for this study, this knowledge can be applied to other fuel systems that exhibit similar phase transitions and/or fabrication techniques. In addition, the results will provide valuable input parameters into U-Mo fuel behavior models. By combining the previous data from synchrotron x-ray techniques with the newly proposed electron microscopy work, the fidelity of the fuel performance models will be improved.
Additional Info
| Field | Value |
|---|---|
| Abstract | The purpose of this project is to study the effects of cold rolling and induction casting on the microstructural evolution in irradiated uranium-10wt.% molybdenum (U-Mo) alloys. A U-Mo alloy monolithic fuel plate is fabricated by casting, hot rolling, cold rolling, and hot isostatic pressing (HIP) processes. Research has extensively been carried out for HIP-processed U-Mo alloy fuel plates irradiated to high burn-up. However, there is a lack of knowledge of the microstructural evolution under low fluence irradiation of the non-HIPed U-Mo alloys. This includes the rolled alloy foil, as well as the U-Mo alloy fuel that is cast into a slug form without rolling, which is a more suitable geometry for other advanced reactor fuel types. Both fabrication techniques have unique as-fabricated microstructures, including varying grain morphology, texture, and dislocation density. During the cold-rolling fabrication process, a high density of dislocations and additional grain boundaries is produced. These mechanically-induced defects may act as sinks (interstitials) and nucleation sites (voids and fission gas bubbles) for the irradiation-induced defects, leading to different microstructures under irradiation. Moreover, since the fuels are irradiated at relatively low temperatures (< 350°C), irradiation-enhanced diffusion may also affect the defect evolution. It is hypothesized that the density of irradiation-induced defects in the U-Mo alloy depends on various aspects, including the initial microstructure, as well as irradiation temperature, fluence, and flux. Transmission electron microscopy (TEM), including bright-field (DF)/dark-field (DF) imaging, selected area electron diffraction (SAED), and energy dispersive spectroscopy-scanning transmission electron microscopy (EDS-STEM), will be used to characterize the unirradiated and irradiated U-10 Mo as-cast and as-rolled foils. BF/DF imaging will provide the information on the overall microstructures in the unirradiated and irradiated alloys. BF/DF imaging will be also used to calculate a density/size of irradiation-induced defects, and to identify the types of defects. An existence of voids and fission gas bubbles will be confirmed by BF imaging, and the types of dislocation loops will be identified by weak beam DF using two beam condition. Presence of decomposed phases and its crystal structure will be identified by EDS-STEM and SAED, respectively. Finally, the types of nanoscale precipitates/clusters will be identified by HRTEM. It is proposed that FIB and TEM (BF/DF, SAED, HRTEM, and EDS-STEM) are used for 1 week, respectively. This research will help fuel designers to optimize fabrication techniques (e.g. rolling versus casting), as well as to tune irradiation-induced defect densities and phase decomposition under irradiation. Although the U-Mo alloy was chosen for this study, this knowledge can be applied to other fuel systems that exhibit similar phase transitions and/or fabrication techniques. In addition, the results will provide valuable input parameters into U-Mo fuel behavior models. By combining the previous data from synchrotron x-ray techniques with the newly proposed electron microscopy work, the fidelity of the fuel performance models will be improved. |
| Award Announced Date | 2020-02-05T14:10:30.34 |
| Awarded Institution | None |
| Facility | None |
| Facility Tech Lead | Alina Zackrone |
| Irradiation Facility | None |
| PI | Gyuchul Park |
| PI Email | [email protected] |
| Project Type | RTE |
| RTE Number | 2929 |