The kinetics of helium release from irradiated samples of austenitic steels OKh16N15M3B and OKh16N15M3BR

Samples of a heat-resistant austenitic steel (both boron free and with 0.005% by weight boron added) were irradiated in the active zone of Reactor WWR-M with a neutron flux of $\text{4 × 10}{}^{13}\text{n/cm}{}^2\text{· s (E ? 3 MeV)}$ and $\text{6 × 10}{}^{13}\text{n/cm}{}^2\text{· s (E ? 0.03 eV)}$ at fixed temperatures in the range of 600°C to 850°C. The neutron fluence was 6 to $\text{8 × 10}{}^{19}\text{n/cm}{}^2$. For the study of the helium release kinetics the samples were annealed with a constant heat-up rate. The experimental equipment and procedure were described previously. Most of the helium (70 to 90%) is released at temperatures of 1420 to 1490°C. This is connected with the melting of the samples. Helium release during the annealing in the range 20 to 1300°C is observed in the form of seven peaks on the curve of gas-release rate. Attempts to interpret the helium diffusion mechanism of each stage is given by determination of the activation energies and other data. Irradiation in a helium atmosphere leads to penetration of helium into the samples, which is proportional to the external gas density. A significant intensification of the generation of helium cavities occurs at irradiation temperatures of 750 to 850°C.