A study of the mechanisms for the irradiation embrittlement of reactor pressure vessel steels

Irradiation damage particles were detected by small angle neutron scattering and positron annihilation techniques in two RPV steels. The particle radii were 8Â and 14Â prior to heat treatments for the plate and weldment, respectively; annealing leads to coarsening in the weldment, the volume fraction remains essentially constant at ~0.14%. The model of copper-rich precipitates ‘diluted’ by Mn atoms or, alternatively, by vacancy agglomerates is consistent with the neutron scattering data, the presence of simple voids in the weldment would contradict the positron results. Preliminary results on these steels and also on related alloys by methods ‘new’ in this field are reported.