SANS investigation of low alloy steels in neutron irradiated, annealed, and reirradiated conditions

Small Angle Neutron Scattering (SANS) experiments were made on several low alloy steels and submerged-arc welds prototypic of nuclear reactor vessel construction. To characterize radiation-enhanced and/or radiation-induced precipitation contributing to mechanical property changes observed in tensile and notch ductility tests of the materials. They were irradiated in UBR Test Reactor. Some of the samples were examined in the 288[degree]C reirradiated (I) condition; others were examined in the postirradiation annealed (IA) condition and in the 288[degree]C irradiated (IAR) condition. Experimental variables included material composition (primarily %Cu, %P, %Ni content), postirradiation annealing temperature (454[degree]C and 399[degree]C), reirradiation fluence level, and neutron-fluence rate ([approximately]0.08, 0.7, and 9 [times] 10[sup 12] n/cm[sup 2]-s[sup [minus]1], E > 1 MeV). The apparent influence of the described variables on size, number density, and composition of Cu-rich precipitates was the primary focus of the SANS analyses. SANS observations are related to measured notch ductility and tensile property changes, with a view toward mechanistic explanation of the observed mechanical property trends for I, IA, and IAR conditions.