NSUF 10-253: Radiation-induced segregation/depletion at grain boundaries in neutron irradiated 304SS at low dose rates
Radiation-induced segregation/depletion (RIS/RID) and its deleterious impact on properties in austenitic stainless steels have been studied extensively, particularly at high dose rates (typically >10-4dpa/s). However, validation of life-extension plans for light water reactors and future applications in advanced fission and fusion reactors require input data on the effects of high fluence obtained at low dose rate on the microstructure and mechanical properties of austenitic stainless steels. We therefore propose to characterize the microstructural changes induced by irradiation up to high doses at low dose rate in hex blocks irradiated in the EBR-II fast reactor located in Idaho Falls, Idaho. The material of interest is an annealed 304 stainless steel neutron irradiated in the reflector and blanket region in the temperature range of 375- 400oC to a maximum of 32 dpa at 2.3.10-7 and an additional 0.9dpa at 3.4 10-9dpa/s with variations in temperature and dose rates depending on the blocks location with respect to the core. Allen (J. Nuclear Mat. 2008) investigated a 304 stainless steel irradiated in the EBR-II at 379oC to 19.5dpa at 2-4.10-8 dpa/s, finding a strong dependence of RIS on dose rate. Precipitation of carbides and alpha phase were also reported after irradiation at low dose rates in 304 steels, with a strong effect on the segregation behavior at surrounding grain boundaries. Previous analyses of the hex block have also shown non uniform swelling depending on the block position in the reactor as well as the formation of a thin ferrite layer at the sodium-wetted surfaces. This investigation will therefore focus on the analysis of selected areas within the blocks to sample different dose rates and temperatures. The overall microstructure (voids, phases, second phases, grain structure), defect character (loop density and spatial distribution), as well as the atomic scale analysis of grain boundary chemistry will be characterized using analytical electron microscopy and atom-probe tomography. The synergy or competition between the development of radiation induced segregation at grain boundaries and the nucleation of second phases and voids and proximity to the sodiumwetted surface will be considered. Resources to perform this work are available at Idaho National Laboratory and associated facilities (post examination equipment for sample preparation, scanning electron microscopy with energy dispersive spectroscopy, electron back scattered diffraction, transmission electron microscopy, analytical electron microscopy and atom-probe tomography). A good portion of a PhD student time will be dedicated to this project and the project is therefore expected to last 3 years. The impact of this work will be measured with the delivery of a detailed understanding of the chemical changes that occurred in the 304 SS as function of location within the hex blocks and therefore as function of temperature gradients and dose rate. The results will complete the limited amount of existing data on irradiated stainless steels irradiated at low dose rates, provide new methods for grain boundary analysis and further insights in the mechanisms of radiation-induced segregation and depletion in these
Additional Info
| Field | Value |
|---|---|
| Abstract | Radiation-induced segregation/depletion (RIS/RID) and its deleterious impact on properties in austenitic stainless steels have been studied extensively, particularly at high dose rates (typically >10-4dpa/s). However, validation of life-extension plans for light water reactors and future applications in advanced fission and fusion reactors require input data on the effects of high fluence obtained at low dose rate on the microstructure and mechanical properties of austenitic stainless steels. We therefore propose to characterize the microstructural changes induced by irradiation up to high doses at low dose rate in hex blocks irradiated in the EBR-II fast reactor located in Idaho Falls, Idaho. The material of interest is an annealed 304 stainless steel neutron irradiated in the reflector and blanket region in the temperature range of 375- 400oC to a maximum of 32 dpa at 2.3.10-7 and an additional 0.9dpa at 3.4 10-9dpa/s with variations in temperature and dose rates depending on the blocks location with respect to the core. Allen (J. Nuclear Mat. 2008) investigated a 304 stainless steel irradiated in the EBR-II at 379oC to 19.5dpa at 2-4.10-8 dpa/s, finding a strong dependence of RIS on dose rate. Precipitation of carbides and alpha phase were also reported after irradiation at low dose rates in 304 steels, with a strong effect on the segregation behavior at surrounding grain boundaries. Previous analyses of the hex block have also shown non uniform swelling depending on the block position in the reactor as well as the formation of a thin ferrite layer at the sodium-wetted surfaces. This investigation will therefore focus on the analysis of selected areas within the blocks to sample different dose rates and temperatures. The overall microstructure (voids, phases, second phases, grain structure), defect character (loop density and spatial distribution), as well as the atomic scale analysis of grain boundary chemistry will be characterized using analytical electron microscopy and atom-probe tomography. The synergy or competition between the development of radiation induced segregation at grain boundaries and the nucleation of second phases and voids and proximity to the sodiumwetted surface will be considered. Resources to perform this work are available at Idaho National Laboratory and associated facilities (post examination equipment for sample preparation, scanning electron microscopy with energy dispersive spectroscopy, electron back scattered diffraction, transmission electron microscopy, analytical electron microscopy and atom-probe tomography). A good portion of a PhD student time will be dedicated to this project and the project is therefore expected to last 3 years. The impact of this work will be measured with the delivery of a detailed understanding of the chemical changes that occurred in the 304 SS as function of location within the hex blocks and therefore as function of temperature gradients and dose rate. The results will complete the limited amount of existing data on irradiated stainless steels irradiated at low dose rates, provide new methods for grain boundary analysis and further insights in the mechanisms of radiation-induced segregation and depletion in these |
| Award Announced Date | 2010-06-09T00:00:00 |
| Awarded Institution | University of Wisconsin |
| Facility | University of Wisconsin Ion Beam Laboratory |
| Facility Tech Lead | Alina Zackrone, Kevin Field, Kory Linton, Kumar Sridharan, Yaqiao Wu |
| Irradiation Facility | None |
| PI | Emmanuelle Marquis |
| PI Email | [email protected] |
| Project Type | PIE Only |
| RTE Number | 253 |