强震下核电厂大型冷却塔倒塌致灾害与控制

Large scale cooling towers with their heights more than 200 m adjacent to nuclear islands in nuclear power plants (NPPs) can collapse under strong earthquakes. The collapse may trigger a series of disasters including severe ground vibration and, consequently, detrimentally affect nuclear-related facilities, possibly resulting in a nuclear accident. This proposal focuses on the disaster process of “assumption→initiation→spread→control”, using a combined research methods of “test investigation + analysis model + numerical simulation” based on logical understanding of “first mechanism/law, then disaster control”. The purpose of this study is to in-deep understand the collapse modes and collapse mechanisms of large scale cooling towers, to reveal the propagation laws of vibration waves, and to propose a comprehensive approach of disaster control. First, collapse mechanisms of cooling towers under strong earthquakes are studied by means of shaking table tests and numerical simulation. Then, the characteristics and laws of vibration excitation and vibration propagation are investigated using block-to-ground impact tests, analysis models and numerical simulation. Finally, an application-oriented approach for disaster control and NPP planning is proposed in various aspects, e.g., controlling collapse modes, reducing initial vibration, attenuating vibration propagation, appropriately spacing between cooling towers and the nuclear island. In particular, this proposal open up a new research field of “collapse-related disasters and disaster mitigation” with wide application.

核电厂核岛附近的大型冷却塔（高度超200米）在强震作用下可能倒塌。倒塌引起的地面剧烈振动等一系列次生灾害危害核相关的仪器设备，可能引发核安全事故。本研究以灾害场景的“假设→产生→扩散→控制”为认识主线，采用“试验+分析模型+数值模拟”的研究手段，遵循“先机理/规律认识，后灾害控制”的认知逻辑，开展复杂问题的科学研究。项目旨在揭示强震下大型冷却塔倒塌形态和机理，认识倒塌引起土体振动规律，提出核电厂倒塌致灾害的控制方法。首先，进行强震下大型冷却塔倒塌振动台试验与数值模拟，阐述倒塌机理。然后，进行块体-地面碰撞试验与数值模拟，认识振动及其传播的特点与规律。最后，从控制塔倒塌形态、减弱触地振动、减弱塔-核岛间振动传播、确定塔-核岛合理间距等方面集成提炼，提出核电厂倒塌灾害控制方法和防灾规划建议。研究涉足“结构倒塌致灾害及其控制”这一全新研究领域，具有成果普适、需求迫切、研究连贯的特点。

针对内陆核电站大型冷却塔在强震下倒塌及引发的地面振动次生灾害，遵循“灾害产生→灾害扩散→灾害控制”的认知逻辑开展科学研究。认识强震下大型冷却塔动力反应与倒塌形态，揭示倒塌机理。认识大型冷却塔倒塌致土体振动与规律。提出核电厂倒塌灾害控制方法与区域防灾规划建议。. 得到的主要结论和取得的创新性成果如下：（1）在地震作用下，冷却塔常常发生“整体下坐式倒塌”。即初始破坏出现在柱子顶端附近，之后上部壳体在重力作用下逐渐压溃剩余的斜支柱，壳体倾斜地向地面整体下坐。在与地面碰撞过程中，壳体解体。（2）开展配筋混凝土块体碰撞问题的试验和数值模拟研究，建立了混凝土块体碰撞冲量模型，模型考虑了初始碰撞速度、配筋率、块体质量、块体质量比、混凝土抗压强度和初始碰撞夹角等影响因素。（3）影响冷却塔倒塌引发的地面振动的因素有：塔型、倒塌形态、外部作用、土体刚度、距离。（4）采用广义极值概率模型，给出具备不同保证率冷却塔倒塌致地面振动反应谱。对85%保证率的反应谱进行包络处理，得到了综合考虑各种影响因素的地面振动反应谱推荐表达式。（5）深入研究了四种减振措施的减振效果，分别是主动隔振沟、被动隔振沟、泡沫混凝土垫层和薄壁圆钢管垫层，推荐采用密度300 kg/m3的泡沫混凝土垫层，其减振效果最好。（6）从控制塔倒塌形态、减弱触地振动、减弱塔-核岛间振动传播、确定塔-核岛合理间距四个方面，提出核电厂倒塌灾害控制方法与区域防灾规划建议。