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FIGURE 4 Demonstration of laser profilometry system precision and repeatability ona .5 mm gauge block. Color maps of laser scans ona 4 xX 4 mm region are taken using a step size of (A) 25 um and (B) 100 um. Furthermore, consecutive scans of the same area using 100 um step sizes are shown in (C) as scan-to-scan variation in thickness measurements.

Figure 4 Demonstration of laser profilometry system precision and repeatability ona .5 mm gauge block. Color maps of laser scans ona 4 xX 4 mm region are taken using a step size of (A) 25 um and (B) 100 um. Furthermore, consecutive scans of the same area using 100 um step sizes are shown in (C) as scan-to-scan variation in thickness measurements.

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rod was then cut into .7-.9mm disks vis electro-discharge machining. All U feedstocks were enriched with 1.22-1.24% 235). The two U-10Mo batches, U -10Mo 2002 and U-10Mo 2003, contained 9.99 wt % total Mo. The two U-17Mo batches, U-17Mo 2004 and U-17Mo 2005, contained 16.8 wt % total Mo. Finally, samples were transported to ORNL for characterization and assembly of the irradiation test. HFIR contains a variety of target loading positions that can be used to achieve a variety of goals, depending on required flux, specimen size, neutron energy, and so on. The MiniFuel system was designed for insertion into the Inner Small Vertical Experimental Facility (VXF) target position, which is indicated with an arrow and label at the top of the HFIR schematic in Figure 1 and has an approximate thermal neutron flux of about 5 x 10'* cm™ s7! (Petrie et al., 2019). In this work, three of the nine available target positions in the MiniFuel were loaded with three different target assemblies, each of which contained six U-Mo disks in separate capsules, as shown in Figure 1. Specific positions of each were chosen to achieve the desired irradiation conditions provided in Table 1. The intended doses were achieved by removing each target assembly after the appropriate number of HFIR cycles.
rod was then cut into .7-.9mm disks vis electro-discharge machining. All U feedstocks were enriched with 1.22-1.24% 235). The two U-10Mo batches, U -10Mo 2002 and U-10Mo 2003, contained 9.99 wt % total Mo. The two U-17Mo batches, U-17Mo 2004 and U-17Mo 2005, contained 16.8 wt % total Mo. Finally, samples were transported to ORNL for characterization and assembly of the irradiation test. HFIR contains a variety of target loading positions that can be used to achieve a variety of goals, depending on required flux, specimen size, neutron energy, and so on. The MiniFuel system was designed for insertion into the Inner Small Vertical Experimental Facility (VXF) target position, which is indicated with an arrow and label at the top of the HFIR schematic in Figure 1 and has an approximate thermal neutron flux of about 5 x 10'* cm™ s7! (Petrie et al., 2019). In this work, three of the nine available target positions in the MiniFuel were loaded with three different target assemblies, each of which contained six U-Mo disks in separate capsules, as shown in Figure 1. Specific positions of each were chosen to achieve the desired irradiation conditions provided in Table 1. The intended doses were achieved by removing each target assembly after the appropriate number of HFIR cycles.
Schematic of HFIR core and MiniFuel assembly relevant to this U-Mo irradiation. The MiniFuel assembly was inserted in the Inner Small VXF target position, as indicated. Adapted with permission from Petrie et al. (Petrie et al., 2019).
Schematic of HFIR core and MiniFuel assembly relevant to this U-Mo irradiation. The MiniFuel assembly was inserted in the Inner Small VXF target position, as indicated. Adapted with permission from Petrie et al. (Petrie et al., 2019).
Process diagram for laser profilometry measurements (A) dual-laser data acquisition across MiniFuel disk specimen, (B) data import and visualization, and (C) volume rendering. 4 Results and discussion allows direct thickness to be measured without assumptions intrinsic to the caliper or depth-microscopy techniques. Primary uncertainties involve resolution (i.e, edge effects due to XY step resolution and laser spot size), data filtering, and volume rendering algorithms. 4.1 Preirradiation characterization 4.1.1 Laser profilometry height and uncertainty evaluation
Process diagram for laser profilometry measurements (A) dual-laser data acquisition across MiniFuel disk specimen, (B) data import and visualization, and (C) volume rendering. 4 Results and discussion allows direct thickness to be measured without assumptions intrinsic to the caliper or depth-microscopy techniques. Primary uncertainties involve resolution (i.e, edge effects due to XY step resolution and laser spot size), data filtering, and volume rendering algorithms. 4.1 Preirradiation characterization 4.1.1 Laser profilometry height and uncertainty evaluation
temperature). Practically, however, the laser profilometry system can capture local thickness variations across the gauge block. These variations are on the order of only a few micrometers, but scans using a step size of 25 (Figure 4A) and 100 um (Figure 4B) can resolve these nuanced thickness gradients across the gauge block surface. This shows the high accuracy of the laser system. Conversely, five consecutive scans of the same area are compared as thickness histograms in Figure 4C. The average thickness of these five scans is approximately 498 zm with a standard deviation of 320 nm, but each sequential scan shows a trend for decreasing average thickness. This trend is due to a slight hysteresis in stage position caused by a lack of precision translating encoder values to dimensional translations. The result is a slight change in the center of the field of view during repeated scans, which leads to a slight change in average thickness. This phenomenon is less concerning for single scans with a small step size than for scans with large jumps in XY coordinates. By understanding and controlling these stage artifacts, laser-based dimensional measurements can significantly improve postirradiation volume measurements. Because these gauge blocks are used for calibration, the uncertainty associated with the laser profiling system is estimated to be 3 um. Compared to the 700-900 um heights of the sample, a 3 ym uncertainty results in <.5% overall height error for the present samples. For a cubic, y-U, crystal, the swelling is isotropic and thus swelling can be measured either with full volume change, or, with only height change following irradiation.
temperature). Practically, however, the laser profilometry system can capture local thickness variations across the gauge block. These variations are on the order of only a few micrometers, but scans using a step size of 25 (Figure 4A) and 100 um (Figure 4B) can resolve these nuanced thickness gradients across the gauge block surface. This shows the high accuracy of the laser system. Conversely, five consecutive scans of the same area are compared as thickness histograms in Figure 4C. The average thickness of these five scans is approximately 498 zm with a standard deviation of 320 nm, but each sequential scan shows a trend for decreasing average thickness. This trend is due to a slight hysteresis in stage position caused by a lack of precision translating encoder values to dimensional translations. The result is a slight change in the center of the field of view during repeated scans, which leads to a slight change in average thickness. This phenomenon is less concerning for single scans with a small step size than for scans with large jumps in XY coordinates. By understanding and controlling these stage artifacts, laser-based dimensional measurements can significantly improve postirradiation volume measurements. Because these gauge blocks are used for calibration, the uncertainty associated with the laser profiling system is estimated to be 3 um. Compared to the 700-900 um heights of the sample, a 3 ym uncertainty results in <.5% overall height error for the present samples. For a cubic, y-U, crystal, the swelling is isotropic and thus swelling can be measured either with full volume change, or, with only height change following irradiation.
TABLE 2 Sample geometric density and bulk porosity based on sample dimensions measured by calipers and the Keyence Macroscope
TABLE 2 Sample geometric density and bulk porosity based on sample dimensions measured by calipers and the Keyence Macroscope
TABLE 3 Local porosity and precipitate characteristics, as determined by data from Slice-and-View operations. surface area divided by the surface area of a perfect sphere with the same volume (Wadell, 1932). Pores comprised much more of the local volume and were either small, <.005 um? spheres or larger voids. The larger voids comprised nearly the entirety of the porosity and were less spherical. In contrast, precipitates were more numerous, smaller, and more elongated on average than the voids. Because of the local nature of the Slice-and-View operation, the results in Table 3 may not be characteristic of the distribution of pores and precipitates throughout all samples. However, these results are consistent with the general microscopy of the samples. The geometry of each identified defect is provided in the Supplementary Table S1.
TABLE 3 Local porosity and precipitate characteristics, as determined by data from Slice-and-View operations. surface area divided by the surface area of a perfect sphere with the same volume (Wadell, 1932). Pores comprised much more of the local volume and were either small, <.005 um? spheres or larger voids. The larger voids comprised nearly the entirety of the porosity and were less spherical. In contrast, precipitates were more numerous, smaller, and more elongated on average than the voids. Because of the local nature of the Slice-and-View operation, the results in Table 3 may not be characteristic of the distribution of pores and precipitates throughout all samples. However, these results are consistent with the general microscopy of the samples. The geometry of each identified defect is provided in the Supplementary Table S1.
(A) XRD spectra for each of the four batches of U-Mo alloys, and (B) lattice parameters calculated from (A) using Rietveld refinement. Each curve in (A) is labeled with the relevant sample name and overlaid with the y-U and Si standard peak locations. In (B), calculated parameters are given as a function of Mo content in atom percent. In both concentrations, both batches overlap one another, but the points can be discerned upon close inspection.
(A) XRD spectra for each of the four batches of U-Mo alloys, and (B) lattice parameters calculated from (A) using Rietveld refinement. Each curve in (A) is labeled with the relevant sample name and overlaid with the y-U and Si standard peak locations. In (B), calculated parameters are given as a function of Mo content in atom percent. In both concentrations, both batches overlap one another, but the points can be discerned upon close inspection.
(A) Hardness and (B) modulus of each of the U-Mo alloys sorted by batch with concentration noted. The parameters were obtained by averaging the sample data after indenting between 900 and 1,000 nm into the material.
(A) Hardness and (B) modulus of each of the U-Mo alloys sorted by batch with concentration noted. The parameters were obtained by averaging the sample data after indenting between 900 and 1,000 nm into the material.
Representative BSE images of each U-Mo alloy at low (A,C,E,G) and high (B,D,F,H) magnifications. Voids and recessed regions appear as blackened areas. Darker areas are regions of lower electron density. Red arrows indicate locations where darker banded regions intersect.
Representative BSE images of each U-Mo alloy at low (A,C,E,G) and high (B,D,F,H) magnifications. Voids and recessed regions appear as blackened areas. Darker areas are regions of lower electron density. Red arrows indicate locations where darker banded regions intersect.
FIGURE 8 Summary of the EDS-calculated (A) U and (B) Mo concentrations in each set of U-Mo samples. The red squares, black triangles, and green oentagons represent the concentration average in the low concentration regions, in the bulk, and at the point of maximum concentration, respectively.
FIGURE 8 Summary of the EDS-calculated (A) U and (B) Mo concentrations in each set of U-Mo samples. The red squares, black triangles, and green oentagons represent the concentration average in the low concentration regions, in the bulk, and at the point of maximum concentration, respectively.
TEM-EDS line scans of the U-10Mo 2002 sample indicating that the precipitates feature a lack of Mo but still contain high concentrations of U in addition to N and O. Linescans (B, D) were produced by averages of the map data across the specific regions shown in (A,C), using a line step size of 8.5 nm.
TEM-EDS line scans of the U-10Mo 2002 sample indicating that the precipitates feature a lack of Mo but still contain high concentrations of U in addition to N and O. Linescans (B, D) were produced by averages of the map data across the specific regions shown in (A,C), using a line step size of 8.5 nm.
BISON-predicted strains of U-10Mo disks compared with fission density and average disk temperature. The strains shown include (A) thermal expansion strain (B) gaseous fission product swelling strain, (C) solid fission product swelling strain (D) creep-induced strain, (E) permanent strain caused by swelling and creep, and (F) total strain caused by thermal expansion, swelling, and creep.
BISON-predicted strains of U-10Mo disks compared with fission density and average disk temperature. The strains shown include (A) thermal expansion strain (B) gaseous fission product swelling strain, (C) solid fission product swelling strain (D) creep-induced strain, (E) permanent strain caused by swelling and creep, and (F) total strain caused by thermal expansion, swelling, and creep.
Intensity curves for the W disks for (A) 800 frames at 8 s/frame from the radial, top, and bottom segmented edges and (B) all four collection conditions near the radial edge.
Intensity curves for the W disks for (A) 800 frames at 8 s/frame from the radial, top, and bottom segmented edges and (B) all four collection conditions near the radial edge.
Projected error in swelling determination as a function of potential swelling using six measurement scenarios. Pre-test and Post-test refer to measurements before and after the irradiation, respectively. Macroscope refers to the Keyence 3D macroscope, calipers refers to manual measurements with calipers, and profilometer refers to the laser profilometer. Errors were estimated from repeated sampling.
Projected error in swelling determination as a function of potential swelling using six measurement scenarios. Pre-test and Post-test refer to measurements before and after the irradiation, respectively. Macroscope refers to the Keyence 3D macroscope, calipers refers to manual measurements with calipers, and profilometer refers to the laser profilometer. Errors were estimated from repeated sampling.
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