Letter Report Documenting Progress of Second Generation ATF FeCrAl Alloy Fabrication

Material Selection for Accident Tolerant Fuel Cladding

“…Additions of Mo and Si and variations with C and Nb, among other elements have been investigated and processed by different methods, as noted in the previous section. These composition and thermal mechanical strategies to obtain improved microstructures and secondary phases that pin grain boundaries (e.g., Laves phase with Nb in C135Nb [34] ) have successfully increased the yield strength by 30 to 100 pct compared to the initial Fe-13Cr-5Al composition, while maintaining ductility similar to the commercial APMT alloy, Figure 7. A higher strength alloy allows for a thinner cladding wall, which minimizes the neutronics penalty for FeCrAl compared to Zr-based cladding.…”

Database on Performance of Neutron Irradiated FeCrAl Alloys

“…Generation I alloys are ORNL developed model FeCrAl alloys with Y additions used to screen primary composition effects (Cr and Al) on radiation tolerance, as well as other key performance aspects such as welding [21], oxidation [4,9,22], burst behavior [23], and corrosion [24]. Generation I alloys are otherwise referenced as B-series alloys or model alloys in previous reports [3,[5][6][7][8][9][10][11][12][13][14][15][16]. Generation II alloys are ORNL developed FeCrAl alloys with Y additions that also include additional minor alloying elements such as Mo, Nb, Si, and/or C. Minor alloy additions and further refinement in thermomechanical processing for Generation II alloys means generally a higher strength alloy at elevated temperatures compared to Generation I alloys with identical or similar Cr and/or Al contents [3].…”

“…The form factor must satisfy 4 5 = 0, 7 = 1, while 8 5 approaches 1 for large 5. These boundary conditions give unique solutions for radius (7) and the leading coefficient, 9 : , from which / and V can then be determined based on the assumption that precipitate volumes are spherical.…”

“…Phase I was based around exploratory studies of the Fe-Cr-Al design space and focused primarily on assessment of how various aspects of alloy performance were affected by major alloying element composition. The alloys utilized for these investigations were simple FeCrAl-Y model alloys and are typically regarded as Generation I FeCrAl alloys within reporting [3,[5][6][7][8][9][10][11][12][13][14][15][16]. These Phase I alloys have demonstrated that higher Cr and Al contents are generally more desirable for maximizing corrosion and/or oxidation resistance but too much of either can limit alloy applications; excessive Cr additions increase the formation of embrittling Cr-rich αʹ precipitates [17][18][19], while high Al content results in failure during the seamless tube extrusion process required for LWR cladding fabrication [20].…”

“…Computational thermodynamics models were utilized to guide minor alloying additions in order to enhance material strength while maintaining adequate high temperature oxidation resistance and good fabricability for thin-walled tube extrusion by commercial manufacturers. Summaries of the Generation II ATF FeCrAl alloys down-selection and design process can be found in previously published reports [3,[5][6][7][8][9][10][11][12][13][14][15][16]. These engineering alloys are currently undergoing irradiation in the High Flux Isotope Reactor (HFIR) at ORNL, with a subset of low-fluence specimens recently becoming available for analysis.…”