NSUF 17-908: Radiation induced segregation and phase separation in neutron irradiated FeCrAl alloys
The objective of this project is to understand the radiation induced segregation and phase separation behavior of FeCrAl alloys. FeCrAl alloys are proposed to replace Zr alloy nuclear fuel claddings in the current fleet of light water reactors, as part of a proposed accident tolerant fuel (ATF) design. Understanding microstructural and microchemical evolution of these alloys under irradiation is a key step toward commercial deployment of ATF technologies, but the radiation-induced segregation (RIS) behavior in these materials has been under-studied and is not well understood. Recent results from a neutron-irradiated commercial Fe-13Cr-4Al alloy indicate an irradiation-induced Cr-Fe-Cr multi-layered chemical enrichment profile at the grain boundary, accompanying the well-known irradiation-enhanced a-a' phase separation. In the proposed work, we seek to attain a mechanistic understanding of these two phenomena, and hypothesize that they are both diffusion-controlled mechanisms. Furthermore, RIS could lead to significant depletion of Cr, causing to preferential grain boundary attack under normal operation. Hence, a critical need exists to confirm whether RIS in FeCrAl is a diffusion-controlled phenomenon and to define its bounding conditions.
We propose to conduct a scanning transmission electron microscopy (STEM) characterization study of irradiated FeCrAl alloys, to ascertain RIS and phase separation behaviors as a function of three parameters: irradiation temperature, Cr composition, and Al composition. We will study high value specimens that were irradiated in the High Flux Isotope Reactor, specifically, FeCrAl alloys C06M, C35M, C36M and C37M irradiated to 195°C, 364°C, and 559°C at damage doses of 1.8-1.9 dpa. These conditions are relevant to early-life conditions of light water reactors (200-330°C), and the highest temperature, 559°C, resides outside the expected temperature range for a-a' phase separation thereby enabling determination of any synergies between a-a' phase separation and RIS. We are requesting access to ORNL LAMDA for 6 days of focused ion beam (FIB) time to prepare lamella, and 10 days of STEM time to conduct large-area chemical mapping of edge-on grain boundaries with very high-efficiency, high-speed energy dispersive x-ray spectroscopy (EDS). The data we will generate can be leveraged to validate ATF microstructure models in MARMOT as well as more classical rate theory models. The project outcome is a systematic and mechanistic understanding of RIS and phase separation in FeCrAl alloys; the broader impact of this work is that it will enable a science-based design and selection of FeCrAl alloys to maximize microchemical stability under irradiation.
Additional Info
| Field | Value |
|---|---|
| Abstract | The objective of this project is to understand the radiation induced segregation and phase separation behavior of FeCrAl alloys. FeCrAl alloys are proposed to replace Zr alloy nuclear fuel claddings in the current fleet of light water reactors, as part of a proposed accident tolerant fuel (ATF) design. Understanding microstructural and microchemical evolution of these alloys under irradiation is a key step toward commercial deployment of ATF technologies, but the radiation-induced segregation (RIS) behavior in these materials has been under-studied and is not well understood. Recent results from a neutron-irradiated commercial Fe-13Cr-4Al alloy indicate an irradiation-induced Cr-Fe-Cr multi-layered chemical enrichment profile at the grain boundary, accompanying the well-known irradiation-enhanced a-a' phase separation. In the proposed work, we seek to attain a mechanistic understanding of these two phenomena, and hypothesize that they are both diffusion-controlled mechanisms. Furthermore, RIS could lead to significant depletion of Cr, causing to preferential grain boundary attack under normal operation. Hence, a critical need exists to confirm whether RIS in FeCrAl is a diffusion-controlled phenomenon and to define its bounding conditions. We propose to conduct a scanning transmission electron microscopy (STEM) characterization study of irradiated FeCrAl alloys, to ascertain RIS and phase separation behaviors as a function of three parameters: irradiation temperature, Cr composition, and Al composition. We will study high value specimens that were irradiated in the High Flux Isotope Reactor, specifically, FeCrAl alloys C06M, C35M, C36M and C37M irradiated to 195°C, 364°C, and 559°C at damage doses of 1.8-1.9 dpa. These conditions are relevant to early-life conditions of light water reactors (200-330°C), and the highest temperature, 559°C, resides outside the expected temperature range for a-a' phase separation thereby enabling determination of any synergies between a-a' phase separation and RIS. We are requesting access to ORNL LAMDA for 6 days of focused ion beam (FIB) time to prepare lamella, and 10 days of STEM time to conduct large-area chemical mapping of edge-on grain boundaries with very high-efficiency, high-speed energy dispersive x-ray spectroscopy (EDS). The data we will generate can be leveraged to validate ATF microstructure models in MARMOT as well as more classical rate theory models. The project outcome is a systematic and mechanistic understanding of RIS and phase separation in FeCrAl alloys; the broader impact of this work is that it will enable a science-based design and selection of FeCrAl alloys to maximize microchemical stability under irradiation. |
| Award Announced Date | 2017-04-26T10:06:12.98 |
| Awarded Institution | None |
| Facility | None |
| Facility Tech Lead | Kory Linton |
| Irradiation Facility | None |
| PI | Janelle Wharry |
| PI Email | [email protected] |
| Project Type | RTE |
| RTE Number | 908 |