The evolution of the microstructure of Cr16–Ni19 steel under neutron irradiation at initial stage of radiation swelling

Microstructural studies of samples made from different sections of fuel element cladding were carried out after irradiation to damaging doses from 0.3 to 48.5 dpa in a fast neutron reactor with sodium coolant. The microstructure characteristics of samples irradiated with different rates of generation of atomic displacements and cut out from sections with close irradiation temperatures were studied. For each sample, histograms of void size distribution were constructed, which were described by unimodal lognormal distributions. Three types of voids were identified: "small", "medium-sized" and "large", the dependences of the change in the average size and concentration of voids of each type depending on the rate of generation of atomic displacements were traced. The characteristics of the dislocation structure and phase composition of the samples irradiated with different rates of generation of atomic displacements were determined.