Radiation Damage In The Novel High Silicon Reduced Activation Ferritic-martensitic Steel

Accelerator-Driven sub-critical System (ADS) is regarded as a best way to handle nuclear wastes. Because of intensive irradiation, high temperature and severe corrosion, ADS held out several hash terms for its structural materials. Material problem is one of the key factors restricting the development of advanced nuclear energy systems. Radiation damage processes can cause a series of structural and mechanical property changes in materials, such as irradiation creep, high temperature Helium embrittlement, phase and dimensional instabilities. These phenomena present a real difficulty in operating reactors safely and economically.Regarding the properties of good swelling resistance, low activation, mature industrial manufacture, reduced activation ferritic/martensitic steels are considered as the primary candidate structural materials for GEN Ⅳ fission and fusion demonstration reactors. Due to the lack of the reactor with a corresponding neutron energy spectrum, it is difficult to evaluate the materials effectively in a short time by use of the available material test reactors. Fortunately, energetic ion irradiation provides a low-cost and rapid means of elucidating mechanisms and screening materials for the most important variables. Therefore, energetic ion irradiation experiments can be carried out as an effective complement.As one promising structural material candidate for the accelerator-driven system project in China, a type of reduced activation ferritic/martensitic steel, the novel high silicon (NHS) steel, was cooperatively developed by the Institute of Modern Physics and Institute of Metal Research, CAS. In this thesis, research on radiation damage resistance and defects formation in the near surface region of NHS steel under different temperatures was carried out by means of energetic ion irradiation.l.The NHS steel was irradiated by helium ions at room temperature (RT),300℃, 450℃and750℃.Helium-implantation was performed at a material research terminal chamber of320kV multi-discipline research platform for highly charged ions. The He-implantation induced microstructural changes in the NHS steel were measured by the DBS and TEM. DBS results show distribution of defects in the near-surface of NHS steel is different among all the samples and the transition temperature for the different controlling mechanism of He may be located between300℃and450℃.And, TEM results were confirmed our analysis of the DBS results.2. Another irradiation experiment was carried out at a high temperature and in the stress materials research terminal chamber of the sector focus cyclotron (SFC)in the Laboratory of Heavy Ion Research Facility in Lanzhou (HIRFL), China. The NHS steel is irradiated by196MeV Kr-ion at temperatures of RT、450and550℃.The cavity swelling in the irradiated NHS specimens is investigated by means of transmission electron microscopy (TEM) with cross sectional technique. For comparison, home-made RAFM steel and commercial steel T91were also irradiated by Kr ions under the same conditions and analyzed by TEM. For home-made RAFM and T91steels irradiated at450℃, both large size and bimodal size distribution of the cavity are found in their peak damage regions, whereas NHS steel exhibits good swelling resistance at different irradiation temperatures. Maybe, Si plays an important role in suppressing the cavity swelling. In addition, defects in the near-surface region of NHS steel were examined by DBS and CEMS. CEMS results show that phase transition is not occurred and the crystallinity of the sample irradiated at450℃is less disordered than the other case. DBS results show vacancies formed by thermal activation is dominated at relative higher irradiation temperatures. As the temperature increase, recombination between vacancies and self-interstitial atoms will become noticeable.