【作者】 陈艳；

【导师】 李向阳； 李涛；

【作者基本信息】 南华大学 ， 安全工程（专业学位）， 2022， 硕士

【摘要】 铀尾矿库是核燃料循环系统中含有放射性废物体积最庞大的贮放地点,是一个长期存在的、潜在的重大危险源和放射性污染源。铀尾矿库主要构建物中最关键的就是铀尾矿库坝体,坝体一旦发生事故,内部放射性铀尾砂会有倾泻而出的可能性。因此铀尾矿库坝体的安全问题一直受到国家和企业的密切关注。湖南某铀尾矿库位于浏阳-衡阳-永州断裂带,其内部存在着一条中生界—新生界侵入的火山岩脉,是一种较为复杂的地质结构,这种地质条件和环境条件使得该地区具有发生破坏性地震的可能性。作为贮存铀尾矿砂的铀尾矿库如何保证在地震条件下安全运行以及防止放射性铀尾砂和含铀废水泄露已成为关键问题。传统的铀尾矿库坝体稳定性评价指标主要包括安全系数和永久位移;其中安全系数又包括平均安全系数和最小安全系数等。边坡、坝体在地震作用下,其内部切应力不断变化,用传统评价指标可能会过于保守或者高估整体稳定性。但是氡气和传统评价指标则不一样,它很敏感,极容易受到周围环境的影响而发生改变。氡从铀尾砂源内持续不断的析出,周围条件发生变化时,结构内部会随之产生相应的变化,比如孔隙率、湿度等发生变化或者出现裂隙、坍塌、沉降,此时氡也会随之响应,氡浓度和氡析出率都会发生改变;因此本文提出利用氡气测量技术来评价铀尾矿库坝体在地震下稳定性。以南方某铀尾矿库坝体作为实验原型,通过工程实地考察和现场取铀尾砂试样,堆筑与原型铀尾矿库坝体相似的缩尺模型,进而基于地震模拟振动台开展振动台试验。通过振动台向缩尺模型施加不同峰值加速度——0.2271～1.1357g模拟微震和强震,振动前后测量氡浓度,计算氡析出率,分析表面裂隙变化,以达到利用氡气测量技术评价坝体稳定性的目的。同时,地震过程中监测不同点加速度、坝体表面位移、内部位移,以验证用氡气测量技术评价铀尾矿库坝体稳定性的可行性。主要工作和研究成果如下所示:（1）测量地震前后氡析出变化,分析氡浓度、氡析出率与铀尾矿库坝体表面裂隙变化。根据氡析出与裂隙的变化特征分为三个阶段,阶段Ⅰ（0～0.6813g）,坝体表面无明显变化,氡析出从0.180Bq·m^-2·s^-1增大到0.714 Bq·m^-2·s^-1。阶段Ⅱ（0.6813～0.9087g）,坝体表面开始有泥块滑落,出现不明显的裂隙,然后微观裂隙聚集、扩展形成局部宏观裂缝,裂隙最先出现在坝体顶部;氡析出率从0.714Bq·m^-2·s^-1增加到1.112 Bq·m^-2·s^-1。阶段Ⅲ（0.9087～1.1357g）,裂缝进一步发育,布满整个坝体表面,表面被分为14个小区块,同时坝体出现沉降和隆起,导致裂隙一侧高于一侧。氡析出率增大为1.356Bq·m^-2·s^-1,但是增长速度变缓。当峰值加速度小于0.6813g时,铀尾矿库坝体处于稳定状态,峰值加速度继续增大,坝体出现裂隙,氡析出率增大到0.553 Bq·m^-2·s^-1,坝体处于失稳状态。（2）为验证氡气测量方法评价铀尾矿库坝体稳定性的可行性,进行了铀尾矿库坝体动力响应研究。发现在地震峰值加速度为0.6813g时,PGA放大系数变化出现拐点,内部水平向位移出现转折点,此时氡析出率为0.714 Bq·m^-2·s^-1。坝体内部出现损伤,表面开始出现微裂隙。此时坝体已受到振动损伤,整体稳定性降低,但是此时坝体仍处于稳定状态。当峰值加速度继续增大时,氡析出率进一步增大,PGA放大系数也逐渐变大,表面裂隙发育贯通,坝体开始出现沉降,此时铀尾矿库坝体已处于失稳状态。因此可以判定基于氡气测量方法评价铀尾矿库坝体稳定性是可行的,并且可以初步判定,当表面氡析出率达到0.553 Bq·m^-2·s^-1到0.714 Bq·m^-2·s^-1时,铀尾矿库坝体稳定性就会开始降低,需要对坝体进行加固措施,防治进一步失去稳定性而发生事故。（3）通过数值模拟软件COMSOL对铀尾矿库坝体在不同峰值加速度下的加速度响应、位移和Von Mises应力进行了分析.发现7组峰值加速度下的铀尾矿库坝体加速度响应都体现出了加速度放大效应和高程效应,前期变化较小,在0.9087g开始时放大效应会更加明显。铀尾矿库坝体表面最大位移会随着地震时步而逐渐增大,峰值加速度越大,位移值也越大。永久位移主要出现在铀尾矿库坝体顶部和1/2高程处,大小呈同心圆式分布。最先在坝体顶部出现裂缝,然后逐渐发育。Von Mises应力最大出现在初期坝内侧坡脚位置,此处最容易发生失效。振动台试验结果与数值模拟结果会有些许不同,但是两者响应规律和总体变化趋势都一致。更多还原

【Abstract】 Uranium tailings pond is the largest radioactive waste storage site in the nuclear fuel cycle system It is a long-standing and potential major hazard source and radioactive pollution source.The dam of uranium tailings pond is one of the main structures of uranium tailings pond,and its safety has been closely concerned by the state and enterprises.A uranium tailings pond in Hunan province is located in the Liuyang-Hengyang-Yongzhou fault zone.There are Mesozoic Cenozoic intrusive volcanic dikes in it.The structure is complex and has the environmental conditions for destructive earthquakes.As a storage of uranium tailings,how to ensure the safe operation under earthquake conditions and prevent the leakage of radioactive materials has become an urgent problem to be solved.The traditional stability evaluation tracer of uranium tailings dam mainly include safety factor and permanent displacement;The safety factor includes average safety factor and minimum safety factor.Under the action of earthquake,the internal shear stress of slope and dam is constantly changing.Using traditional evaluation tracer may be too conservative or overestimate the overall stability.However,radon is different from the traditional evaluation tracer.It is a very sensitive index,which is very vulnerable to the influence of the surrounding environment.Radon continuously exhalates from the uranium tailings source.When the surrounding conditions change,corresponding changes will occur in the structure,such as changes in porosity and humidity,cracks or collapse and settlement.At this time,radon will also respond,and radon concentration and radon exhalation rate will change.Therefore,radon measurement technology can be used to evaluate the stability of uranium tailings dam.Therefore,this paper proposes to use radon measurement technology to evaluate the stability of uranium tailings pond under earthquake.In this paper,a uranium tailings pond in South China is taken as the experimental prototype.Through engineering field investigation and on-site sampling of uranium tailings,a scaled model similar to the dam of the prototype uranium tailings pond is built,and then the shaking table test is carried out.By applying different peak accelerations 0.2271～1.1357g to the scale model to simulate micro earthquakes and strong earthquakes,measure radon concentration before and after vibration,calculate radon exhalation rate,and analyze the changes of surface cracks,so as to judge the stability of dam by radon measurement technology.At the same time,the acceleration of different points,the surface displacement and internal displacement of the dam are monitored during the earthquake to verify the feasibility of radon measurement technology to determine the stability of uranium tailings pond.The main work and research results are as follows:（1）The variation of radon exhalation before and after earthquake is measured,and the variation of radon concentration,radon exhalation rate and surface cracks of uranium tailings dam are analyzed.According to the variation characteristics of radon exhalation and cracks,it is divided into three stages.In stage I（0～0.6813g）,there is no obvious change on the dam surface,and radon exhalation increases from 0.180 Bq·m^-2·s^-1 to 0.714Bq·m^-2·s^-1.In stage II（0.6813～0.9087g）,mud blocks began to slide on the surface of the dam,and there were no obvious cracks on the surface,and then the micro cracks gathered and expanded to form local macro cracks,which first appeared on the top of the dam;Radon exhalation rate increased from 0.714 Bq·m^-2·s^-1 to 1.112 Bq·m^-2·s^-1.In stage III（0.9087～1.1357g）,the cracks are further developed,grow laterally and widen vertically,covering the whole dam surface.The surface is divided into 14small blocks.At the same time,the dam has settlement and uplift,resulting in one side of the crack being higher than the other side.The radon exhalation rate increases to 1.356 Bq·m^-2·s^-1,but the growth rate slows down.When the peak acceleration is less than 0.6813g,the dam of uranium tailings pond is in a stable state,the peak acceleration continues to increase,cracks appear in the dam,the radon exhalation rate increases to 0.553Bq·m^-2·s^-1,and the dam is in an unstable state.（2）In order to verify the feasibility of radon measurement method to evaluate the stability of uranium tailings dam,the dynamic response of uranium tailings dam was studied.It is found that when the seismic peak acceleration is 0.6813g,there is an inflection point in the change of PGA amplification coefficient and a turning point in the internal horizontal displacement.At this time,the radon exhalation rate is0.714Bq·m^-2·s^-1.Damage occurred inside the dam and microcracks began to appear on the surface.At this time,the dam has been damaged by vibration and the overall stability has been reduced,but the dam is still in a stable state.When the peak acceleration continues to increase,the radon exhalation rate further increases,the PGA amplification factor also gradually increases,the surface cracks are developed and connected,and the dam begins to settle.At this time,the dam of uranium tailings pond is in an unstable state.Therefore,it can be determined that it is feasible to evaluate the stability of uranium tailings dam based on radon measurement method,and it can be preliminarily determined that when the surface radon exhalation rate reaches 0.553 Bq·m^-2·s^-1to 0.714 Bq·m^-2·s^-1,the stability of uranium tailings dam will begin to decrease,and reinforcement measures need to be taken to prevent further loss of stability and accidents.（3）The dynamic response of a uranium tailings pond under different peak accelerations is modeled and analyzed using numerical simulation,which includes acceleration response,displacement,and von Mises stress.The acceleration response of the uranium tailings dam under seven different peak accelerations reflects the acceleration amplification effect and the elevation effect.The early stage change is minor,and the amplification impact will be more noticeable towards the beginning of0.9087g.The maximum displacement of the uranium tailings pond dam surface will steadily grow with each earthquake time step.The larger the displacement,the greater the peak acceleration.The permanent displacement occurs primarily at the top and one-half elevation of the uranium tailings dam,and its size is dispersed in a concentric circle.Cracks first appear on the top of the dam and then extend gradually.The maximum von Mises stress occurs at the inner slope toe of the initial dam,where failure is most likely to occur.The shaking table test findings deviate somewhat from the numerical simulation results,but their overall variation law and response displacement are consistent.更多还原