NSUF 18-1590: 3D Microstructural Assessment of Irradiated and Control U-10Zr Fuels

Mechanistic Fuel Failure-3 (MFF-3) include U-10wt%Zr (U-10Zr) fuels that are sodium bonded to HT9 cladding with a smear density of 75% and maximum burnup of 13.5 at %. Although early PIE of U-10Zr fuels from EBR-II provided a suggestive correlation between phase transformations and porosity via BSE-SEM imaging, there is a lack of detailed understanding on the crystal structure of the phases, grain size distribution, phase distribution, and constituent re-distribution. There have been several postulations regarding the effects of a-U, ß-U, y-(U, Zr) and d-UZr2 phase transformations in the irradiated fuel. Although transmission electron microscope (TEM) assessment of major phases at different regions of the irradiated fuel via recently awarded Rapid Turnaround Experiments (RTE) will provide a detailed analysis on phases present at different regions of the fuel, there still exists a knowledge gap on phase distribution, grain size distribution, and constituent re-distribution on a microscopic scale on these fuels. Additionally, there is lack of critical assessment on the deviations in microstructure between irradiated MFF-3 and unirradiated control fuel to accurately describe the microstructural alterations from irradiation. To effectively compare the microstructural changes between different regions of the irradiated fuel, we propose the lift-out focused ion beam (FIB) milled blocks of size (100x100x50) µm and subjugation of these blocks to multiple electron backscatter diffraction (EBSD) and EDS scans for 3D assessment. The scans acquired will also be compared to the unirradiated control fuel. For this work, it is proposed that 4 FIB-blocks of (100x100x50) µm in size are to be milled and lifted out from the irradiated and un-irradiated fuels samples (3 from Irradiated fuel at region: A, B, and C, and 1 from un-irradiated control fuel). After the fabrication of FIB milled blocks, they are lifted out and attached to copper grids. The blocks are then tilted appropriately to acquire BSE images, and EBSD/EDS maps. The procedure is then followed by milling off a small layer from the top of the FIB blocks by using the Ga dual beam in the FIB-SEM, and repeating the initial steps of acquiring BSE image, EBSD, and EDS maps. These steps are then repeated sequentially layer by layer to eventually acquire 3D-EBSD and EDS data sets. The EBSD scans will ideally possess an approximate scan window size of (100x50) µm with a step size of 500 nm for 10 sections. Comparing 3D-EBSD and EDS data to reconstructed tomography data will facilitate in providing a robust 3D analysis of the fuel with high data fidelity. Additional information that can be acquired by a comparison between EBSD and EDS to synchrotron tomography data also include effect of phases on the morphology of cavities, and assessment of local swelling in fuels. This work in co-relation to the synchrotron tomography experiments at ANL, and recently awarded RTE for TEM assessment of fuels will also be the first ever quantitative 3D assessment on microstructural changes in irradiated U-10Zr fuels.

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필드	값
Abstract	Mechanistic Fuel Failure-3 (MFF-3) include U-10wt%Zr (U-10Zr) fuels that are sodium bonded to HT9 cladding with a smear density of 75% and maximum burnup of 13.5 at %. Although early PIE of U-10Zr fuels from EBR-II provided a suggestive correlation between phase transformations and porosity via BSE-SEM imaging, there is a lack of detailed understanding on the crystal structure of the phases, grain size distribution, phase distribution, and constituent re-distribution. There have been several postulations regarding the effects of a-U, ß-U, y-(U, Zr) and d-UZr2 phase transformations in the irradiated fuel. Although transmission electron microscope (TEM) assessment of major phases at different regions of the irradiated fuel via recently awarded Rapid Turnaround Experiments (RTE) will provide a detailed analysis on phases present at different regions of the fuel, there still exists a knowledge gap on phase distribution, grain size distribution, and constituent re-distribution on a microscopic scale on these fuels. Additionally, there is lack of critical assessment on the deviations in microstructure between irradiated MFF-3 and unirradiated control fuel to accurately describe the microstructural alterations from irradiation. To effectively compare the microstructural changes between different regions of the irradiated fuel, we propose the lift-out focused ion beam (FIB) milled blocks of size (100x100x50) µm and subjugation of these blocks to multiple electron backscatter diffraction (EBSD) and EDS scans for 3D assessment. The scans acquired will also be compared to the unirradiated control fuel. For this work, it is proposed that 4 FIB-blocks of (100x100x50) µm in size are to be milled and lifted out from the irradiated and un-irradiated fuels samples (3 from Irradiated fuel at region: A, B, and C, and 1 from un-irradiated control fuel). After the fabrication of FIB milled blocks, they are lifted out and attached to copper grids. The blocks are then tilted appropriately to acquire BSE images, and EBSD/EDS maps. The procedure is then followed by milling off a small layer from the top of the FIB blocks by using the Ga dual beam in the FIB-SEM, and repeating the initial steps of acquiring BSE image, EBSD, and EDS maps. These steps are then repeated sequentially layer by layer to eventually acquire 3D-EBSD and EDS data sets. The EBSD scans will ideally possess an approximate scan window size of (100x50) µm with a step size of 500 nm for 10 sections. Comparing 3D-EBSD and EDS data to reconstructed tomography data will facilitate in providing a robust 3D analysis of the fuel with high data fidelity. Additional information that can be acquired by a comparison between EBSD and EDS to synchrotron tomography data also include effect of phases on the morphology of cavities, and assessment of local swelling in fuels. This work in co-relation to the synchrotron tomography experiments at ANL, and recently awarded RTE for TEM assessment of fuels will also be the first ever quantitative 3D assessment on microstructural changes in irradiated U-10Zr fuels.
Award Announced Date	2018-09-17T12:08:35.257
Awarded Institution	Idaho National Laboratory
Facility	Advanced Test Reactor
Facility Tech Lead	Alina Zackrone
Irradiation Facility	None
PI	Jonova Thomas
PI Email	[email protected]
Project Type	RTE
RTE Number	1590