NSUF 19-1730: The microstructure characterization of 21Cr32Ni model austenitic alloy irradiated at BOR60 reactor
Understanding the irradiation behavior of the materials at high dose is crucial for the development of advanced reactors where the level of radiation damage is expected to reach more than ~200 dpa (displacements per atom). However, neutron irradiation experiments take years of irradiation to reach the desired dose levels. Also, these irradiation experiments are expensive and often require special handling of the radioactive samples with dedicated instruments for characterization. A promising solution is to use heavy-ion irradiation to simulate neutron irradiation. Because the damage rate in heavy ion irradiation is ~100-1000 times higher than the damage rate in neutron irradiation, the experimental time can be reduced from years to hours and days. In addition, the lack of radioactivity provides more flexibility to the users for post-irradiation characterization. To use energetic heavy ions it is necessary to take into account its differences from neutron irradiation such as higher damage rates and the lack of helium. Therefore, in order to reliably use ion irradiation simulations to predict high dose materials behavior in reactors, it is necessary to demonstrate that the ion irradiated micro-structures closely reproduce the micro-structure in neutron irradiated environment. The proposed work is a part of multi-institutional research project that has the ultimate goal of emulating the micro-structural evolution of the candidate materials at high doses in future reactor systems as best as possible using ion irradiation. Within this scope, a comprehensive set of irradiation experiments were designed and have been performed using both ions and neutrons.The neutron irradiation experiments have been conducted in the BOR60 fast reactor in Russia while the ion irradiation experiments have been conducted at the Michigan Ion Beam Laboratory. The irradiation parameters such as dose, irradiation temperature and the amount of helium injection used in the ion irradiation experiments were selected to mimic the conditions prevalent in the BOR60 reactor. The ion irradiation temperature was higher than that for neutron irradiation to compensate for the higher displacement rate in that case. The amount of helium generated in the materials of interest was estimated using both the SPECTER computer code and the neutron flux information received from BOR60. Although the spectrum is fast, calculations show that He is generated to the level of 1 He ppm/dpa. Several candidate alloys with analogous model alloys were irradiated together. The model alloys used in this project are chemically analogous, but compositionally simpler than the commercial candidate alloys proposed for future advanced nuclear reactors, serving therefore as reference to the analogous commercial alloys. The commercial alloy 800H is considered as one of the primary candidate material of reactor internals in advanced reactor systems, and the 21Cr32Ni alloy used in this project is an analogous model alloy.Previous work from our group includes the characterization of the irradiated 21Cr32Ni alloy microstructure irradiated to 17 dpa with a dual beam ion (5 MeV Fe++ and co-injected helium). As mentioned above, the irradiation doses used in these experiments are similar to those achieved in BOR60 reactor. The amount of helium generation in 21Cr32Ni model alloy and alloy 800H for a given BOR60 neutron flux was calculated to be ~17 appm after 17 dpa using SPECTER, thus one helium ppm per dpa. This was the target value used as reference in these dual ion irradiation experiments. The dual ion beam irradiation study showed that the simultaneous injection of 17 appm helium to into a 21Cr32Ni model alloy sample promoted void nucleation in its microstructure and resulted in higher swelling than seen in samples those irradiated with the a single beam. In the current proposal, we intend to characterize 21Cr32Ni austenitic model alloys irradiated in BOR-60 reactor to nominal doses of 17 dpa and 35 dpa at 386°C using TEM and compare with those irradiated with dual beam ions that were already characterized. For this purpose, TEM samples will be prepared using FIB from the bulk materials already available at ORNL with the technical assistance of LAMDA staff. FIB technique was chosen instead of electro polishing because it is also the method used for preparing ion irradiated sample as it allows provide precise control of the sample location and a more direct comparison. Also it produces a low radioactivity sample because of the small volume. In contrast, electropolishing does not always produce a usable sample and because of its larger volume will be considerably more radioactive. To be able to optimize ion irradiation parameters to reproduce the neutron irradiated microstructure as best as possible, we intend to characterize the neutron irradiated samples. The comparison of the ion and neutron irradiated microstructures will be done by comparing the appropriate measures of the irradiation induced features that can best describe the final state of the irradiated microstructure. For example, for the case of mechanical properties, the measures are dislocation morphology, dislocation loops, their habit planes, burger’s vectors, and average sizes and densities; for the case of swelling, the measures are the size, size distribution and density of the voids and for the case of micro-chemical changes, the measures are grain boundary segregation, and any precipitate formation. Irradiation-induced defects such as dislocation loops and cavities will be analyzed using bright-field/dark-field and their size distribution and density will be calculated by measuring the foil thickness. Segregation and precipitation behavior will be analyzed using energy dispersive X-ray spectroscopy in TEM. The results obtained in these experiments will help to optimize the experimental parameters which will be compared with a dual beam ion irradiated microstructure that were already characterized to optimize ion irradiation parameters to simulate neutron irradiation.
Additional Info
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| Abstract | Understanding the irradiation behavior of the materials at high dose is crucial for the development of advanced reactors where the level of radiation damage is expected to reach more than ~200 dpa (displacements per atom). However, neutron irradiation experiments take years of irradiation to reach the desired dose levels. Also, these irradiation experiments are expensive and often require special handling of the radioactive samples with dedicated instruments for characterization. A promising solution is to use heavy-ion irradiation to simulate neutron irradiation. Because the damage rate in heavy ion irradiation is ~100-1000 times higher than the damage rate in neutron irradiation, the experimental time can be reduced from years to hours and days. In addition, the lack of radioactivity provides more flexibility to the users for post-irradiation characterization. To use energetic heavy ions it is necessary to take into account its differences from neutron irradiation such as higher damage rates and the lack of helium. Therefore, in order to reliably use ion irradiation simulations to predict high dose materials behavior in reactors, it is necessary to demonstrate that the ion irradiated micro-structures closely reproduce the micro-structure in neutron irradiated environment. The proposed work is a part of multi-institutional research project that has the ultimate goal of emulating the micro-structural evolution of the candidate materials at high doses in future reactor systems as best as possible using ion irradiation. Within this scope, a comprehensive set of irradiation experiments were designed and have been performed using both ions and neutrons.The neutron irradiation experiments have been conducted in the BOR60 fast reactor in Russia while the ion irradiation experiments have been conducted at the Michigan Ion Beam Laboratory. The irradiation parameters such as dose, irradiation temperature and the amount of helium injection used in the ion irradiation experiments were selected to mimic the conditions prevalent in the BOR60 reactor. The ion irradiation temperature was higher than that for neutron irradiation to compensate for the higher displacement rate in that case. The amount of helium generated in the materials of interest was estimated using both the SPECTER computer code and the neutron flux information received from BOR60. Although the spectrum is fast, calculations show that He is generated to the level of 1 He ppm/dpa. Several candidate alloys with analogous model alloys were irradiated together. The model alloys used in this project are chemically analogous, but compositionally simpler than the commercial candidate alloys proposed for future advanced nuclear reactors, serving therefore as reference to the analogous commercial alloys. The commercial alloy 800H is considered as one of the primary candidate material of reactor internals in advanced reactor systems, and the 21Cr32Ni alloy used in this project is an analogous model alloy.Previous work from our group includes the characterization of the irradiated 21Cr32Ni alloy microstructure irradiated to 17 dpa with a dual beam ion (5 MeV Fe++ and co-injected helium). As mentioned above, the irradiation doses used in these experiments are similar to those achieved in BOR60 reactor. The amount of helium generation in 21Cr32Ni model alloy and alloy 800H for a given BOR60 neutron flux was calculated to be ~17 appm after 17 dpa using SPECTER, thus one helium ppm per dpa. This was the target value used as reference in these dual ion irradiation experiments. The dual ion beam irradiation study showed that the simultaneous injection of 17 appm helium to into a 21Cr32Ni model alloy sample promoted void nucleation in its microstructure and resulted in higher swelling than seen in samples those irradiated with the a single beam. In the current proposal, we intend to characterize 21Cr32Ni austenitic model alloys irradiated in BOR-60 reactor to nominal doses of 17 dpa and 35 dpa at 386°C using TEM and compare with those irradiated with dual beam ions that were already characterized. For this purpose, TEM samples will be prepared using FIB from the bulk materials already available at ORNL with the technical assistance of LAMDA staff. FIB technique was chosen instead of electro polishing because it is also the method used for preparing ion irradiated sample as it allows provide precise control of the sample location and a more direct comparison. Also it produces a low radioactivity sample because of the small volume. In contrast, electropolishing does not always produce a usable sample and because of its larger volume will be considerably more radioactive. To be able to optimize ion irradiation parameters to reproduce the neutron irradiated microstructure as best as possible, we intend to characterize the neutron irradiated samples. The comparison of the ion and neutron irradiated microstructures will be done by comparing the appropriate measures of the irradiation induced features that can best describe the final state of the irradiated microstructure. For example, for the case of mechanical properties, the measures are dislocation morphology, dislocation loops, their habit planes, burger’s vectors, and average sizes and densities; for the case of swelling, the measures are the size, size distribution and density of the voids and for the case of micro-chemical changes, the measures are grain boundary segregation, and any precipitate formation. Irradiation-induced defects such as dislocation loops and cavities will be analyzed using bright-field/dark-field and their size distribution and density will be calculated by measuring the foil thickness. Segregation and precipitation behavior will be analyzed using energy dispersive X-ray spectroscopy in TEM. The results obtained in these experiments will help to optimize the experimental parameters which will be compared with a dual beam ion irradiated microstructure that were already characterized to optimize ion irradiation parameters to simulate neutron irradiation. |
| Award Announced Date | 2019-05-14T15:50:18.957 |
| Awarded Institution | None |
| Facility | None |
| Facility Tech Lead | Kory Linton |
| Irradiation Facility | None |
| PI | Muhammet Ayanoglu |
| PI Email | [email protected] |
| Project Type | RTE |
| RTE Number | 1730 |