【作者】 张敏；

【导师】 黄群英；

【作者基本信息】 中国科学技术大学 ， 核燃料循环与材料， 2013， 博士

【摘要】 加速器驱动次临界系统(Accelerator Driven Sub-critical system, ADS)目前被认为是可进行放射性核废料嬗变的潜在最有效的途径之一。液态铅铋合金是ADS散裂靶及次临界堆冷却剂的首选材料。铅铋合金在应用中存在诸多关键问题,其中液态铅铋合金中的氧浓度测量与控制直接影响液态金属热工水力学性能及其与材料的相容性而成为ADS研究的关键技术之一。液态铅铋中溶解氧的含量需要控制在一定范围,以在结构材料表面形成有效的抗腐蚀金属氧化层的同时,又避免氧过量而形成氧化铅等杂质。因此,开展氧控技术的研究为铅铋合金在ADS中的成功应用具有重要的科学意义和应用价值。在充分调研国内外氧控技术研究现状的基础上,利用自主研发的静态和流动铅铋氧测控装置,对国际上研究最为广泛的气相氧控技术开展了深入研究,包括气相氧控本身涉及到注气参数对氧控过程中氧浓度变化的影响,及与铅铋堆典型实验工况相关的铅铋温度、铅铋流速等因素的影响规律。对氧控影响因素定量而较为系统的研究为掌握气相氧控技术以及在未来反应堆中的应用提供了可信的数据支持。在对注气参数对氧浓度变化规律探索中,主要从注气成分、注气流量和注气方式三方面影响因素展开实验研究：1)在注气成分影响研究中,对H2/O2法和H2/H2O比例两种氧控方法分别进行不同气体成分的实验研究。其中H2/O2方法控氧结果显示,低O2含量气体成分补氧利于控氧稳定性；H2/H2O比例控氧结果显示,改变气体比例可实现不同氧浓度控制,且较H2/O2方法控氧更稳定。2)在注气流量影响研究中,实验结果显示,增大气体流量加速氧浓度变化速率,其中对补氧过程影响最为明显；同时结果中显示出铅铋合金中Fe3O4、NiCr2O4、PbO等氧化物反应令氧浓度呈阶段变化趋势,气体流量对各阶段氧浓度变化速率的影响也反映出对Fe、Cr、Ni、Pb等元素化学反应的影响规律。3)在注气方式影响实验结果中,鼓入与覆盖气体注入方式比较,氧浓度变化显著,主要原因为鼓入气体增加了气液接触面积。注气参数对氧浓度变化影响的实验结果显示了气体因素对氧浓度的影响规律以及物理化学反应机制,为气相氧控技术的应用提供了实验数据支持与参考。在对铅铋堆典型工况相关的铅铋温度、铅铋流速等因素影响研究中,研究了不同温度、不同流速、典型流速下温度改变以及气体流量改变等实验工况下氧浓度的变化规律。静态工况下温度变化结果显示,在450-600℃范围内,温度升高对加速耗氧过程变化速率明显而对补氧过程表现为减速作用,可能原因为温度升高加速氧扩散,同时对耗氧过程中氧化物分解反应有促进作用,但对补氧过程中金属元素的氧化放热反应有一定的抑制效应。铅铋流速影响大小的实验结果分析显示,0.1-0.3m/s流速范围内,流速增大将会加速整体反应过程氧浓度变化速率,其中对加速氧扩散以及NiO、NiCr2O4氧化物反应作用明显,但不利于Fe元素在补氧过程中氧化物的形成。与静态结果相比,流动状态下表现出NiO的影响,可能是流动冲刷作用加速Ni元素溶解的结果；低流速下在低氧区Fe3O4生成边界附近表现出明显的氧浓度波动现象,这可能是流动加速Fe、Ni等金属元素溶解,形成的氧化物在低流速状态下易形成局部残存所致,流速越大影响越不明显,因此流速增大加速反应的均匀性。特定流速0.3m/s温度变化的实验结果显示,450-550℃范围内,温度升高整体上加速了补氧过程速率,与静态过程中温度减缓效应不同,可能原因为流速加速较温度减缓效应显著；温度升高加速耗氧过程整体反应速率,尤其在低氧区域内加速反应均匀性尤为显著。特定流速0.3m/s气体流量变化的实验结果显示,气体流量增大同样加速氧浓度变化速率与反应的均匀性。上述结果显示,温度升高加速耗氧过程反应,但减缓补氧过程速率；流速增大对补氧耗氧过程均有明显促进作用,而流速冲刷加速Fe、Ni等元素的溶解现象较明显,易在低氧区域出现氧浓度波动现象,流速越小、温度越低则波动幅度越大,因此在实际流动工况下为保证氧控的均匀性,可引入杂质的纯化操作。不同因素对氧浓度变化影响研究,揭示了不同参数对氧控过程中氧浓度变化规律,对氧控技术的应用具有一定的指导意义,同时为大型铅铋实验装置乃至未来堆中的氧控系统参数设计以及实际工况的运行提供了实验支持和数据参考。更多还原

【Abstract】 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.更多还原