Assessing Residual Strains in Nuclear Power Reactor Internal Components Weld Mockups of Nickel Alloys Using EBSD

Abstract

The most common failure mode of commercial nuclear reactor internal components is environmentally assisted cracking (EAC). Environmentally cracking is promoted by the simultaneous effects of three affecting variables, namely (1) presence of tensile stresses and strains, (2) and aggressive environment and (3) a susceptible microstructure. If one or more of these affecting variables are removed, cracking will not occur or propagate. For example, EAC susceptibility and growth rate will be minimized if the residual tensile stresses or strains are controlled. Similarly, EAC may be minimized by controlling the chemistry of the weld metal, for example by increasing the content of chromium in the weld metal. The objective of the current research was to complete laboratory weldments of 76 mm thick plates of Alloy 600 using weld metal with three different compositions. Electron backscatter diffraction (EBSD) results of cross sections of the weld showed that approximately 10 to 15% of residual plastic strain existed at near the root of the weld and in the middle section (at approximately 38 mm); however, lower residual plastic strain existed near the top of the weld (last passes).