高温气冷堆用石墨摩擦性能研究

采用标准摩擦试验机研究了3种石墨(兰州石墨、上海三高石墨和IG-11)的摩擦性能,并用电子扫描显微镜分析了摩擦表面。试验的环境气氛为氦气和空气。研究结果表明:在相同载荷作用下,3种石墨在不同环境气氛中表现出不同的摩擦性能。当滑动速度较大时,在空气环境中的摩擦系数高低依次为兰州石墨>上海三高石墨>IG-11;在氦气环境中的摩擦系数则为上海三高石墨>IG-11>兰州石墨。     

高温气冷堆用国产石墨的摩擦性能

对国产细颗粒石墨和粗颗粒石墨在室温、400℃空气和氦气中的摩擦性能进行了试验。试验发现,摩擦系数随滑动速度的增加而增加,存在临界滑动速度。氦气环境对细颗粒石墨的摩擦系数有影响,对粗颗粒石墨的摩擦系数没有影响。400℃氦气下,粗颗粒石墨的摩擦系数比室温空气下的摩擦系数小,细颗粒石墨的摩擦系数小,细颗粒石墨的摩擦系比室温空气下的摩擦系数小。     

高温气冷堆用石墨材料的氧化性能研究

高温气冷堆均选用石墨材料作为结构材料和慢化剂.在反应堆的运行过程中,由于冷却剂中含有的氧化性气体杂质以及可能发生的进水事故和进气事故,会发生石墨材料的氧化,进而影响反应堆的正常运行和安全.本文主要对近期反应堆用石墨材料的氧化研究进行综合评述,并在此基础上,指出今后需要进一步研究的内容.     

HTR-PM高温气冷示范堆堆芯石墨粉尘产生量估算

在球床式高温气冷堆堆芯内,影响石墨球摩擦磨损率的关键条件为载荷与温度。此前,中国辐射防护研究院研究了载荷对石墨球摩擦磨损性能的影响,得到了石墨球磨损率与载荷的关系。本文在此基础上进一步研究了温度对石墨球磨损率的影响,通过拟合得到了石墨球磨损率与石墨球所受载荷、温度之间的关系式,结合HTR-PM高温气冷示范堆内燃料元件所受载荷和温度的分布情况,计算得出石墨球之间摩擦产生的石墨粉尘量约为14.01 g/d(5.1 kg/a)。     

高温气冷堆用石墨材料氧化行为研究进展

核级石墨是高温气冷堆重要的慢化剂、反射层和结构材料,其氧化腐蚀性能对反应堆安全运行至关重要,因此已成为核材料学科的研究热点之一。本文综述了国内外在核级石墨氧化腐蚀领域的研究现状,总结了核石墨氧化的化学动力学模型、失重率影响因子模型以及模拟计算模型,提出了高温气冷堆用石墨材料氧化腐蚀的研究方向。     

石墨粉尘通过高温气冷堆堆芯球床结构的运动行为研究

高温气冷堆在运行过程中产生带有放射性的石墨粉尘,对反应堆的运行安全和环境安全造成一定影响。本文选取二维球床流场,采用离散相模型分析了堆芯球床结构对石墨粉尘颗粒的扩散和沉积的影响。计算结果表明:球床结构能有效阻碍石墨粉尘颗粒的扩散;沉积在球床结构上的石墨粉尘颗粒数目随堆芯内氦气流速的增加而增大,而由于受到颗粒惯性及热泳力的作用其增长趋势逐渐放缓;石墨粉尘颗粒在球床结构上的沉积效率随粒径的逐渐增加呈现"几乎不变-快速增长-缓速增长"的态势。     

高温气冷堆石墨构件的碰撞力学行为研究

高温气冷堆的反射层和隔热层主要由数量庞大的石墨砖和碳砖组成,在地震或冲击载荷作用下,部件之间可能发生滑移和碰撞,影响其结构完整性。简化的数值分析模型是研究这种大规模散体结构的重要手段,而其中模拟碰撞的非线性连接单元参数对分析的收敛性和结果的准确性至关重要。本文对高温气冷堆中石墨构件的3种典型碰撞形式进行了实验研究,测量得到了各碰撞模式下碰撞时间和恢复系数与碰撞速度的关系。针对碰撞实验中边界条件与堆内实际构件的差别,采用商业有限元分析软件ABAQUS对不同碰撞形式进行了数值分析,进一步获得了更为准确的碰撞特性,并通过改进的Hertz碰撞模型对实验和数值结果进行分析,得出了非线性碰撞连接单元的等效刚度系数和等效阻尼系数。最后利用数值分析方法进行了与堆内构件设计相关的质量和间隙尺寸对碰撞单元等效刚度系数和等效阻尼系数的详细研究,为高温气冷堆石墨和碳堆内构件的设计提供参考。     

高温气冷堆吸收球压碎力模型的计算与研究

吸收球停堆系统是10 MW高温气冷堆的第二停堆系统。吸收球为含25%B₄C的石墨小球,B₄C弥散分布在石墨基体上。压碎力是吸收球的一重要性能指标,与球直径密切相关。采用石墨球模拟高温气冷堆吸收球,研究了石墨球直径和密度对压碎力的影响规律。选用3种不同密度的石墨,加工成5种不同直径的小球,进行压碎实验。研究结果表明：球的压碎力与直径的平方成正比;直径一定时,石墨球的密度越大,压碎力越大。提高石墨球的密度是提高压碎力的有效途径。     

输送速度对高温气冷堆燃料装卸系统提升段石墨球磨损性能的影响

搭建了高温气冷堆燃料装卸系统提升段石墨球磨损性能研究的实验平台,研究了10 MW高温气冷堆(HTR-10)堆用石墨球在氮气气体输送条件下与不锈钢提升管的摩擦磨损性能,重点考察了石墨球输送速度对其磨损率的影响。结果表明:石墨球在不锈钢提升管中的磨损与石墨球的输送速度存在明显的线性关系,速度越高磨损率越大;石墨球的磨损属磨粒磨损,磨损以硬质不锈钢表面粗糙峰对石墨材料的切削作用为主,磨损率较大。     

Effects of reaction temperature and inlet oxidizing gas flow rate on IG-110 graphite oxidation used in HTR-PM

The oxidation behavior of a selected nuclear graphite (IG-110) used in Pebble-bed Module High Temperature gas-cooled Reactor was investigated under the condition of air ingress accident. The oblate rectangular specimen was oxidized by oxidant gas with oxygen mole fraction of 20% and flow rates of 125–500 ml/min at temperature of 400–1200?°C. Experiment results indicate that the oxidation behavior can also be classified into three regimes according to temperature. The regime I at 400–550?°C has lower apparent activation energies of 75.57–138.59 kJ/mol when the gas flow rate is 125–500 ml/min. In the regime II at 600–900?°C, the oxidation rate restricted by the oxygen supply to graphite is almost stable with the increase of temperature. In the regime III above 900?°C, the oxidation rate increases obviously with the increase of temperature. With the increase of inlet gas flow from 125 to 500 ml/min, the apparent activation energy in regime I is increased and the stableness of oxidation rate in regime II is reduced.     

Experimental study on the adsorption and desorption of tritium in the graphite materials for HTR-PM

Tritium behavior in the reactor such as production, diffusion and release are accompanied by their adsorption and desorption in graphite materials, which are essential to the safety of high temperature gas cooled reactor (HTGR). In order to study this important issue, hydrogen instead of tritium is experimentally used in this work and justified viable by theory. By performing multiple sets of comparative experiments, the features of hydrogen adsorption and desorption behavior changing by adsorption temperature and time in typical graphites used in HTR-PM (High Temperature Gas Cooled Reactor – Pebble Bed Module), i.e. reflective layer, fuel element and boron carbon bricks, have been observed and analyzed. Furthermore, the adsorption rates of hydrogen in the three materials as above at different conditions are also given. Based on the experimental results, tritium behavior in the HTR-PM was inferred and estimated, which is significant for the further study on the mechanism of tritium transport.     

Control rod drive for high temperature gas cooled reactor

This control rod drive is developed for HTR-10 high temperature gas cooled test reactor.The stepmotor is prefered to improve positioning of the control rod and the scram behavior.The preliminary test in 1600170 ambient temperature shows that the selected stepmotor and transmission system can meet the main operation function requirements of HTR-10.     

Application of CANDLE burnup to block-type high temperature gas cooled reactor

The CANDLE burnup strategy, where the distributions of fuel nuclide densities, neutron flux, and power density move with the same constant speed and without any change in their shapes, is applied to the block-type high temperature gas cooled reactor. If it is successful, a burnup control rod can be eliminated, and several merits are expected. This burnup may be realized by enriched uranium and burnable poison with large neutron absorption cross-section. With the fuel enrichment of 15%, gadolinium concentration of 3.0%, and fuel cell pitch of 6.6 cm, the CANDLE burnup is realized with the burning region moving speed of 29 cm/year and the axial half-width of power density distribution of 1.5 m. When the concentration of natural gadolinium is higher, the burning region moving speed becomes slower and the burnup becomes higher, though the effective neutron multiplication factor becomes smaller. When U-235 enrichment is higher, the effective neutron multiplication factor becomes larger, the speed becomes slower, and the burnup becomes higher. When the pitch is wider, the effective neutron multiplication factor becomes larger, the speed becomes faster, and the burnup becomes higher.     

Simulation study on candle burnup applied to block-type high temperature gas cooled reactor

The CANDLE burnup is a new reactor burnup concept, where the distributions of fuel nuclide densities, neutron flux, and power density move with the same constant speed along the core axis from bottom to top (or from top to bottom) of the core and without any change in their shapes. It can be applied easily to a block-type high temperature gas cooled reactor (HTGR) using an appropriate burnable poison with a high neutron absorption cross section mixed with uranium oxide fuel. In this study, natural gadolinium is used as burnable poison. In the present paper, the simulation of the burnup for the steady state and the startup is performed.

For the steady state simulation with direct solutions of steady state nuclide densities as inputs, the difference between the results of the steady state analysis and the simulation analysis is very small. It confirms that the steady state analysis is correct. When the initial core is constructed from easily available nuclides, the simulation result gives a reactivity change of 1.7% at a burnup time of 0.7 years.     

Dynamical reliability of the passive system in the very high temperature gas cooled reactor

A dynamic safety assessment has been developed for the passive system in the very high temperature gas cooled reactor (VHTR), when the operational data are insufficient. It was required to make use of the characteristics of the reactor in order to compensate for the data shortage and to treat the propagation of incidents. Therefore, this paper focuses on the failure frequency construction of the basic events and the advanced method of treating the propagation. The mass flow rate caused by the natural circulation in the passive system is related to the fuel temperature which affects the failure fraction of the fuel. These features are utilized for finding the failure frequency of the basic event. The non-linear string logic is used due to the simple and tractable algorithm of the passive system instead of the tree concept which is used in the event-fault tree based decision making. The time feedback is applied to the string concept, where the time weighting is adjusted by the operator’s judgment. Results are obtained for four cases. Among them, two cases are non-linear transition features of the events using feedback. The other two cases are based on linear propagations, which construct the characteristics of the dynamic resistance–stress method (DRSM). Using the string algorithm, one can successfully perform safety assessment for any other advanced reactor such as the VHTR.     

高温气冷实验堆燃料元件双向探测器的研制

介绍了高温气冷实验堆燃料元件双向探测器的基本原理和实现方法。它以两个并联的感应线圈为敏感元件,通过双通道法采集信号,以８９Ｃ５１单片机为处理核心,系统软件采用循环扫描输入端口的方式获取过球信号,经智能分析、判断,实现了燃料元件的双向检测。     

高温气冷堆新燃料运输货包的撞击事故分析

介绍了高温气冷堆新燃料运输货包严重撞击事故的仿真计算分析方法。根据实际货包结构及运输条件,确定了分析的严重撞击事故景象。通过有限元法计算分析了货包在不同姿态、不同速度下的碰撞结果,给出了容器不同部分及所装载的燃料组件的损坏情况。在此基础上,计算了严重事故景象下有效增殖因子k_eff。     

Effect of temperature on graphite oxidation behavior

The temperature dependence of oxidation behavior for the graphite IG-11, used in the HTR-10, was investigated by thermogravimetric analysis in the temperature range of 400–1200 °C. The oxidant was dry air (water content <2 ppm) with a flow rate of 20 ml/min. The oxidation time was 4 h. The oxidation results exhibited three regimes: in the 400–600 °C range, the activation energy was 158.56 kJ/mol and oxidation was controlled by chemical reaction; in the 600–800 °C range, the activation energy was 72.01 kJ/mol and oxidation kinetics were controlled by in-pore diffusion; when the temperature was over 800 °C, the activation energy was very low and oxidation was controlled by the boundary layer. Due to CO production, the oxidation rate increased at high temperatures. The effect of burn-off on activation energy was also investigated. In the 600–800 °C range, the activation energy decreased with burn-off. Results of low temperature tests were very dispersible because the oxidation behavior at low temperatures is sensitive to inhomogeneous distribution of any impurity, and some impurities can catalyse graphite oxidation.