Investigations of void formation in neutron irradiated iron and F82H steel

In the present work pure iron and low activation steel F82H have been neutron irradiated at temperatures in the interval 50 deg. C - 350 deg. C to a dose of 0.23 dpa (displacements per atom). The formation of defects has been investigated by the use of positron annihilation spectroscopy (PAS). In addition iron has been irradiated to different doses in the range 0.01 - 0.4 dpa at 50 deg. C and 100 deg. C and the dose dependence of the electrical conductivity determined. The results demonstrated that the formation of voids takes place during neutron irradiation of pure iron in the whole temperature range. For irradiation temperatures of 50 deg. C and 100 deg. C also a high density of micro-voids was observed. Voids and micro-voids were also detected in low activation F82H steel for a low irradiation temperature (50 deg. C), while for irradiation close to the temperature of annealing stage V (250 deg. C), no voids or micro-voids could be detected. Surprisingly, irradiation at the higher temperature of 350 deg. C again resulted in void formation. The annealing behaviour of iron irradiated at 50 deg. C and at 100 deg. C did not show any significant difference. Coarsening of the microvoids and void population takes place below stage V by migration and coalescence of the micro-voids and voids. The dose dependence of the electrical conductivity of iron showed a lower conductivity for the specimens irradiated at 50 deg. C than at 100 deg. C. This has been associated with the segregation of carbon at about 70 deg. C where carbon becomes mobile. (au)