Residual Stress Measurements in Welded and Plastically Deformed Target Structural Materials

Transmutation of spent nuclear fuels (SNF) is currently being considered to transform long-lived isotopes to species with relatively short half-lives and reduced radioactivity through capture and decay of minor actinides and fission products. This process is intended for geologic disposal of SNF for shorter durations in the proposed repository at the Yucca Mountain site. The structural material (Type 304L stainless steel/Alloy EP-823) surrounding the transmutation target will be subjected to welding operation and plastic deformation during fabrication, which could induce residual stresses in it. Destructive ring-core, and nondestructive x-ray diffraction, neutron diffraction, and positron annihilation spectroscopic techniques were used to evaluate residual stresses in welded and cold-worked specimens of both materials. The results indicate that, in general, for a welded specimen consisting of Alloy EP-823 and Type 304L stainless steel on opposite sides, compressive and tensile residual stresses were observed in the former and latter materials, respectively. However, a welded specimen consisting of only Alloy EP-823 on both sides showed tensile residual stresses. The extent of residual stresses in cold-worked specimens was enhanced with increased level of cold-reduction. In case of a bent specimen, compressive and tensile residual stresses were noticed in the convex and concave sides, respectively