| Accelerator-driven subcritical system (ADS) is a new generation of nuclear reactor systems, used for the proliferation of nuclear fuel and transmutation of nuclear waste. Lead-bismuth eutectic (LBE) is accepted as coolant and target candidate material of ADS for its nice thermodynamic and chemical properties. The concentration of dissolved oxygen in liquid lead-bismuth eutectic directly affect the liquid metal thermal hydraulics performance and material compatibility. Therefore, control of oxygen concentration in the liquid lead-bismuth eutectic is one of the key technologies to ensure the future ADS reactor operation. Concentration of dissolved oxygen in liquid lead-bismuth eutectic needs to be controlled in a certain range in order to form an effective anti-corrosive metal oxide layer on structure material surface and avoid excess oxygen to form lead oxide or other impurities. Research on oxygen control technology in the lead-bismuth eutectic is of important scientific significance and application value for LBE used in the ADS succesfully.After sufficient investigations at home and abroad, gase-phase oxygen control technology which has been widely studied and applied around the world has been in-depth experiment research in this research. It carried out based on the self-developed static and flowing lead-bismuth oxygen monitoring and control device. The contents of experiment were typical factors of gase-phase oxygen control influence on the variation of the oxygen concentration. In influence factors, gas injection parameters was related to gase-phase oxygen control itself, lead-bismuth eutectic temperature and flow rate was related to typical experiment conditions for lead-bismuth reactor. Quantitative factors for oxygen control and more systematic study was benefit to develop oxygen control technology as well as to provide credible data for reactor applications in the future.Exploration of gas injection parameters influence on the oxygen concentration variation, mainly containing the injection gas composition, gas injection flow and gas injection mode three influence factors in total.1) In the injection gas composition research, H2/O2and H2/H2O ratio ways of oxygen control were studied respectively with change of gas composition. H2/O2way showed low O2content gas composition was benefit for stability control of oxygen. H2/H2O proportional control oxygen showed that the proportion of gas can achieve different oxygen concentration control, and demonstrated more stability than H2/O2way.2) In the gas injection flow impact studies, the experimental results showed that the oxygen concentration change rate was accelerated with increasing gas flow, in which the process of dissolving oxygen was most obviously. The results showed oxygen concentration stepwise changed for effect of chemical reaction of Fe3O4, NiCr2O4, PbO and other oxides in lead-bismuth eutectic. At the same time, Fe, Cr, Ni and Pb elements chemical reaction were also effect by the gas flow.3) Gas injection mode affect results showed, the bubble gas mode was more significant way to enhance the rate of change of oxygen concentration than cover gas injection, mainly due to the mode of bubble increasing the gas-liquid contact area. Experimental results of gas injection parameters effected on the change of oxygen concentration showed the law of the gas factor effect on oxygen concentration and the physical and chemical reaction mechanism, provide experimental data to support and reference for the oxygen gas control technology.In the research on typical operating conditions of lead-bismuth eutectic reactor, the variation of the oxygen concentration changed with different temperatures and lead-bismuth eutectic flow velocity, different temperature and gas flow in a typical flow velocity. In static conditions with the temperature range of450-600℃, the temperature rises accelerated the rate of oxygen change during the oxygen consumption process apparently, while showed deceleration effect in oxygen dissolving process. The reason may be temperature rise accelerated oxygen dissolving and the oxide decomposition reaction in the oxygen consumption process, but deaccelerated oxide formation. In the LBE flow affect results with0.1-0.3m/s flow velocity range, increase of flow velocity accelerated the change rate of oxygen concentration during the overall reaction, and the oxygen diffusion speed, NiO, NiCr2O4oxide chemical reaction respectively, but deaccelerated Fe oxide formation in the process of oxygen dissolving process. Compared to the static results, the performance of the NiO effect in the flow condition may be Ni element dissolution for fluid scouring action. At low flow velocity, the oxygen concentration showed significant fluctuation in low oxygen range with Fe/Fe3O4equilibrium, which maybe Fe, Ni and other elements content increased by flow condition and formed the oxide local residual. The fluctuation was not obvious with velocity increase, which accelerated the reaction uniformity. In specific flow velocity of0.3m/s,450-550℃range of temperature results showed, temperature rise accelerated the overall rate of oxygen dissolving process, which was different from the static condition of deacceleration effect. The reason maybe flow velocity effected the reaction more than temperature. Temperature rise accelerated the oxygen consumption process, especially for the reaction uniformity in the low oxygen concentration. In specific flow velocity of0.3m/s, gas flow increase accelerated overall reaction process and reaction uniformity. The above results showed that the temperature rise accelerated oxygen consumption process and deaccelerated oxygen dissolving process in static condition. With increase of lead-bismuth eutectic flow velocity, oxygen change rate was accelerate in oxygen dissolving process and oxygen consumption process. In the flow condition, the flow velocity accelerated Fe, Ni and other elements of dissolution erosion phenomenon. The oxide of these elements could cause oxygen fluctuation obviously at low flow velocity and low oxygen range. Therefore, in the actual conditions, it would be necessary to remove impurity to ensure oxygen control uniformity.Different factors impact on the oxygen concentration change, revealed the oxygen concentration variation regulation with different parameters in the oxygen control process. It has a certain significance for application of oxygen control technology. At the same time it provided experimental support and data reference for oxygen control system design parameters and the actual operation in large-scale experimental apparatus even lead-bismuth reactor in the future. |
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