Samples of 16Cr - 15 Ni - 3 Mo - 1Ti steel were irradiated to a fast neutron fluence of 1.5 ∙ 10¹⁸ cm^-2 and 1.5 ∙ 10¹⁹ cm^-2 (E>0.1 MeV) in the IVV - 2M reactor and investigated by transmission electron microscopy methods. Electron microscopy patterns were obtained. It was shown that the size distribution of clusters had a form close to a Gaussian after irradiation to a fluence of 1.5 ∙ 10¹⁸ n∙cm^-2. There were several peaks in the distribution histogram of the sample irradiated to 1.5∙10¹⁹ n∙cm^-2.

The formation of the low temperature irradiation clusters in austenitic steel was analyzed with a model of displacement cascades overlapping under cryogenic neutron irradiation. All the clusters formed were differentiated into two groups: low-temperature radiation clusters formed by not overlapped displacement cascades (LTRC - 1) and radiation clusters formed by overlapped cascade regions (LTRC - 2). Analytical expressions were obtained to describe the relationships of the average dimensions of LTRC of both groups and the dynamics of cluster accumulation.