Irradiation-induced structural changes in surveillance material of VVER 440-type weld metal

The irradiation-induced microstructural changes in surveillance materials o f the VVER 440-type weld metal Sv-10KhMFT were investigated by small angle neutron scattering (SANS) and anomalous small angle X-ray scattering (SAXS) . Due to the high fluence, a strong effect was found in the SANS experiment . No significant effect of the irradiation is detected by SAXS. The reason for this discrepancy is the different scattering contrast of irradiation-in duced defects for neutrons and X-rays. An analysis of the SAXS shows that t he scattering intensity is mainly caused by vanadium-containing (VC) precip itates and grain boundaries. Both types of scattering defects are hardly ch anged by irradiation. Neutron irradiation rather produces additional scatte ring defects of a few nanometers in size. Assuming these defects are cluste rs containing copper and other foreign atoms with a composition according t o results of atom probe field ion microscopy (APFIM) investigations, both t he high SANS and the low SAXS effect can be explained. (C) 2000 Elsevier Sc ience B.V. All rights reserved.