Degradation in mechanical properties of stainless steels C0.12Cr18Ni10Ti and C0.08Cr16Ni11Mo3 Materials for hexagonal ducts of spent fuel assemblies from the BN-350 fast neutron reactor

This paper discusses results of studying the structural behavior of the hexagonal assembly ducts of the BN-350 fast neutron reactor after irradiation in sodium and subsequent water storage at the reactor. Maximum irradiation dose for different ducts varied from similar to 11 dpa for an assembly on the core periphery to similar to 55 dpa for one at core center. The irradiation dose rate for various assemblies and along each assembly varied from similar to 10(-8) dpa/s to 10(-6) dpa/s, and temperature of irradiation ranged from 280 degrees C to 400 degrees C. The changes in microstructure and physico-mechanical properties of 12Cr18Ni10Ti and 08Cr16Ni11Mo3 steels were studied from 50 x 10 x 2 mm samples cut from the assembly ducts at various locations. Changes in microstructure and phase composition were studied by optical microscopy, transmission electron microscopy (TEM) and scanning electron microscopy (SEM), as well as X-ray structure analysis. Mechanical tensile tests and microhardness measurements were performed. For each location on the ducts values of the hydrostatic density (HD) and the transmutation He content, which are dependent on damage dose and temperature, were also determined. The paper describes the dependence of swelling on dose, dose rate, and temperature for both steels, as well as the dependence of yield stress, ultimate strength, and uniform and total elongation, on these parameters.