NSUF 23-4629: Atom probe characterization of HT-9 as a function of neutron irradiation temperature
Ferritic-martensitic (F-M) steels are being considered as candidate in-core structural materials for fast reactors and advanced LWR due to their excellent resistance to radiation-induced void swelling, microstructural stability, thermal conductivity, and superior irradiation creep properties. HT-9 being the first-generation F-M steel has a relatively large irradiation mechanical and microstructural database. HT-9 was selected as the fuel clad and duct material in FFTF and EBR-II, and it is still the first-choice candidate core material for several advanced reactor concepts due to its service performance and the relatively large database on it. Currently, commercial nuclear power companies such as TerraPower has rejuvenated the manufacturing of HT-9.
To address the issue of low-temperature (~425°C) neutron irradiation hardening and embrittlement, it is necessary to conduct systematic investigations on the mechanical behavior and microstructure of HT-9 with slight variations in chemical composition and heat treatment over a wide range of doses and temperatures. Three HT-9 heats (ORNL, LANL and EBR II) with variations in manufacturing process, chemical composition and heat treatment were neutron irradiated (~4 dpa) in the ATR at different temperatures (241C-469C), as a part of the UW-Madison NSUF pilot irradiation experiment. Our team recently won RTE awards (#1687 and #4201) and completed microhardness testing, tensile testing, SEM and EBSD characterization of unirradiated and HT-9 variants (~4 dpa) as a function of irradiation temperature. Maximum impact of this work will be obtained by performing TEM and APT characterization of these neutron irradiated samples present at PNNL to correlate the measured hardening with microstructural features.
We propose to employ the APT technique to enhance the understanding of the underlying mechanisms for α′ and Ni/Mn/Si precipitation evolution in HT-9 upon neutron irradiation. The objective of this RTE proposal is to evaluate the formation of α′ and Ni/Mn/Si precipitation in neutron irradiated (~4 dpa) HT-9 as a function of irradiation temperature (241°C, 291°C, 388°C and 469°C). Considering RTE funding availability, we limited the number of samples to five (control: 1; irradiated: 4), by choosing one HT-9 heat (ORNL variant; 11.6Cr-1Mo-0.5W-0.5Ni-0.3V; HT: 1060°C/60 min/air cooled; 730°C/120 min/air cooled) to study a range of temperatures that is relevant for alpha prime precipitation studies and LWR/advanced reactor applications. To achieve this objective, we will utilize APT to determine the size, number density, and chemical composition of the α′ and Ni/Mn/Si precipitates. To understand the contributions to irradiation hardening, the dispersed barrier-hardening model will be employed to determine the changes in yield strength induced by each type of obstacles, and then compare the measured hardening (tensile and microhardness data from previously funded RTE #1687) with microstructure-deduced hardening contributions obtained from APT (proposed RTE; α’ and G phases) and TEM studies (ongoing work). By doing this work, our team can contribute to filling the gap in the literature on understanding the irradiation effects on HT-9 and F-M steels in general.
The project performance (sample preparation, APT characterization, and analysis) is expected to take place during June 2023 – Feb 2024 and will result in one conference presentation and one journal article publication.
Additional Info
| Field | Value |
|---|---|
| Abstract | Ferritic-martensitic (F-M) steels are being considered as candidate in-core structural materials for fast reactors and advanced LWR due to their excellent resistance to radiation-induced void swelling, microstructural stability, thermal conductivity, and superior irradiation creep properties. HT-9 being the first-generation F-M steel has a relatively large irradiation mechanical and microstructural database. HT-9 was selected as the fuel clad and duct material in FFTF and EBR-II, and it is still the first-choice candidate core material for several advanced reactor concepts due to its service performance and the relatively large database on it. Currently, commercial nuclear power companies such as TerraPower has rejuvenated the manufacturing of HT-9. To address the issue of low-temperature (~425°C) neutron irradiation hardening and embrittlement, it is necessary to conduct systematic investigations on the mechanical behavior and microstructure of HT-9 with slight variations in chemical composition and heat treatment over a wide range of doses and temperatures. Three HT-9 heats (ORNL, LANL and EBR II) with variations in manufacturing process, chemical composition and heat treatment were neutron irradiated (~4 dpa) in the ATR at different temperatures (241C-469C), as a part of the UW-Madison NSUF pilot irradiation experiment. Our team recently won RTE awards (#1687 and #4201) and completed microhardness testing, tensile testing, SEM and EBSD characterization of unirradiated and HT-9 variants (~4 dpa) as a function of irradiation temperature. Maximum impact of this work will be obtained by performing TEM and APT characterization of these neutron irradiated samples present at PNNL to correlate the measured hardening with microstructural features. We propose to employ the APT technique to enhance the understanding of the underlying mechanisms for α′ and Ni/Mn/Si precipitation evolution in HT-9 upon neutron irradiation. The objective of this RTE proposal is to evaluate the formation of α′ and Ni/Mn/Si precipitation in neutron irradiated (~4 dpa) HT-9 as a function of irradiation temperature (241°C, 291°C, 388°C and 469°C). Considering RTE funding availability, we limited the number of samples to five (control: 1; irradiated: 4), by choosing one HT-9 heat (ORNL variant; 11.6Cr-1Mo-0.5W-0.5Ni-0.3V; HT: 1060°C/60 min/air cooled; 730°C/120 min/air cooled) to study a range of temperatures that is relevant for alpha prime precipitation studies and LWR/advanced reactor applications. To achieve this objective, we will utilize APT to determine the size, number density, and chemical composition of the α′ and Ni/Mn/Si precipitates. To understand the contributions to irradiation hardening, the dispersed barrier-hardening model will be employed to determine the changes in yield strength induced by each type of obstacles, and then compare the measured hardening (tensile and microhardness data from previously funded RTE #1687) with microstructure-deduced hardening contributions obtained from APT (proposed RTE; α’ and G phases) and TEM studies (ongoing work). By doing this work, our team can contribute to filling the gap in the literature on understanding the irradiation effects on HT-9 and F-M steels in general. The project performance (sample preparation, APT characterization, and analysis) is expected to take place during June 2023 – Feb 2024 and will result in one conference presentation and one journal article publication. |
| Award Announced Date | 2023-06-01T09:06:08.547 |
| Awarded Institution | None |
| Facility | None |
| Facility Tech Lead | Stuart Maloy, Yaqiao Wu |
| Irradiation Facility | None |
| PI | Ramprashad Prabhakaran |
| PI Email | [email protected] |
| Project Type | RTE |
| RTE Number | None |