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The economics and safety of reactors can be affected by the diffusion of fission products into graphite. Xenon (Xe) fission products diffusing into graphite is the most critical neutron absorber and poison that can slow down or stop the chain reaction. The transport parameters for inhibiting the xenon diffusion in graphite are therefore an important scientific problem. Self-sintered nanopore-isotropic (~40 nm) graphite (SSNG) derived from green pitch coke can decrease Xe diffusion into graphite. In this study, the surface morphology and microstructural evolution in graphite before and after irradiation, as well as after annealing, were studied with different characterization methods. A method for the measurement of diffusion coefficients of fission products' diffusion in graphite using Rutherford backscattering spectrometry (RBS) was also reported. The SSNG substrates were implanted with Xe at a dose of 4.8 × 1015 ions/cm2 and energy of 7 MeV. The RT-implanted samples were annealed in a vacuum at 650 °C for 9 h. The implanted and annealed samples were characterized using RBS. The diffusion coefficient D (Xe, 650 °C) was 6.49 × 10−20 m2/s. The results indicate SSNG's excellent ability to inhibit Xe diffusion and are significant for designing and evaluating the safety of nuclear reactors. [ABSTRACT FROM AUTHOR]

The massive molten salt-graphite interface produced by liquid infiltration or vapor penetration in a molten salt reactor suggests the importance of irradiation-induced mixing and diffusion. We employed He+ ion beam irradiation to simulate neutron irradiation-induced mixing of Na and K in graphite. The depth distributions of both Na and K were measured by RBS (Rutherford backscattering spectrometry) and XPS (X-ray photoelectron spectroscopy) depth profiling. Both the mixing rate and the diffusion rates of the Na and K mark layers in the graphite induced by the ion beam irradiation were calculated. The results indicate that the diffusion rates of Na and K in the graphite reflector and/or moderator were several hundred nanometers per dpa irradiation dose. This could induce a change in the properties and cohesion of graphite. [ABSTRACT FROM AUTHOR]

Nickel-based alloys as candidate materials for Thorium Molten Salt Reactor (TMSR), need to be used under high temperature in molten salt environment. In order to ensure the safety of the reactor running, it is necessary to study the elemental move characteristic of nickel-based alloys in the high temperature molten salts. In this work, the scanning nuclear microprobe at Fudan University was applied to study the elemental move. The Nickel-based alloy samples were corroded by molten salt at different temperatures. The element concentrations in the Nickel-based alloys samples were determined by the scanning nuclear microprobe. Micro-PIXE results showed that the element concentrations changed from the interior to the exterior of the alloy samples after the corrosion. [ABSTRACT FROM AUTHOR]