Postirradiation examinations of U-Pu-Zr fuel elements from subassemblies X419 and X419A

Performance of U-Pu-Zr fuel cast into zirconium molds

“…This is probably the characteristic of the Zr-sheathed fuel that restricted axial elongation. The Pu-containing slugs (both Zr-sheathed and standard-cast) exhibited less elongation than the binary slugs, consistent with previously reported results [6,7] (this distinction is observed in elements irradiated at higher fuel temperatures). Hofman, et al [7] suggested that higher Pu alloys exhibit less axial elongation because the three microstructural zones that form during irradiation have different swelling and diffusion properties that lead to higher radial swelling.…”

“…The two ternary elements did have slightly higher gas release fractions than did the binary elements. Although a similar relation between Pu content and fractional gas release has been previously reported [6], only a small number of elements were examined for the present work, so the relation observed here may be anomalous.…”

“…Hofman, et al [7] suggested that higher Pu alloys exhibit less axial elongation because the three microstructural zones that form during irradiation have different swelling and diffusion properties that lead to higher radial swelling. Faster radial swelling causes the fuel slug to contact the cladding sooner in life than is the case for lower Pu alloys, and fuel-claddlng contact restricts axial elongation [6].…”

Thermal hydraulic aspects of an unconventional liquid metal reactor

“…It is believed that this restructuring of the fuel takes places shortly after irradiation and does not affect the fuel behavior in a negative way [30,19]. Table 2.2 shows the concentrations of uranium, plutonium and zirconium after irradiation [28,29]. This restructuring is also believed to be the cause of the cracks that appear on the outer surface of the fuel 130].…”

“…The postirradiation examination of metallic fuels with different Pu concen trations (0, 8, 19 % weight fraction) after 1.9% and 3.0% burnup shows that fuel cracking is not very important in low plutonium content fuel elements i28,29]. Since fuel element cracking also reduces the amount of fission gas retained in the fuel, the U-8Pu-10Zr element had more fission gas retained than the U-19Pu-10Zr element [28,29].…”