Analysis of SANS measurements on highly irradiated15H2MFA steel

A 15H2MFA type VVER440 RPV forging material in the unirradiated reference condition and three different irradiation conditions (samples : A; B and C) up to neutron fluences of 2.94x1e20, 9.52x1e20 and 14.5x1e20 cm-2 (E> 0.5 MeV), respectively, were investigated by SANS at the Budapest Research Reactor. The size distributions of the clusters were calculated using the indirect Fourier transform method. The absolute value of volume fraction of clusters is estimated under the assumption that the clusters are non-magnetic scatterers. The nuclear scattering contrast can vary for different irradiation levels. Differences in scaling of both magnetic and nuclear size distributions give a hint of different cluster composition. Information about the cluster composition is included in the A-ratio. Primary, the A-ratio was defined by the ratio of the SANS intensities perpendicular and parallel to the magnetic field direction. In practice, we observe a Q-dependence of the A-ratio.
We observed a difference are in the scaling of the magnetic and nuclear size distributions. The reason of this difference is discussed.