Small Angle Neutron Scattering Study of Linde 80 RPV Welds

Small angle neutron scattering (SANS) results are presented for Linde 80 welds irradiated, as part of the B&W Owners Group Integrated Surveillance Program, at low fluxes (< 10¹⁵ n/m²-s) to fluences from 0.29 to 3.5x10²³ n/m² (E > 1 MeV) at irradiation temperatures from 276 to 292°C. The welds all contain about 0.6 Ni (all composition units are in wt.%), 0.009 to 0.18 P and 0.05 to 0.28 Cu. In the welds with significant amounts of copper (> 0.2 Cu) the measured defect scattering cross sections were consistent with either: a) copper rich precipitates (CRPs) alloyed with manganese and nickel; or b) dominant CRP scattering, plus a weak contribution from so-called matrix defect features. Similar weak scattering was observed in a low copper (0.06 Cu) weld. The identity of matrix defect features cannot be determined from the SANS data alone, but the scattering is consistent with the presence of subnanometer vacancy cluster-solute complexes. The general character of the CRPs, and the trends in their number density, volume fraction and average radius as a function of fluence and irradiation temperature, are very similar to those observed in a wide range of pressure vessel-type steels irradiated in test reactors at intermediate to high flux. The SANS data in the surveillance welds is also in unity with: a) thermodynamic-kinetic radiation enhanced diffusion models of CRP evolution; b) mechanical property changes, including predictions of the correlations of the surveillance data base; and c) an atomic scale, atom probe field ion microscopy study into the nanostructure-chemistry of a CRP.