基于纤维混凝土强度时效特性的核废料贮存容器可靠度分析

发布时间：2018-04-02 18:05

  本文选题：混杂纤维混凝土　切入点：蠕变特性　出处：《东北大学》2014年博士论文

【摘要】：贮存低、中放核废料的混凝土容器在服役期300年内,持续承受衰变热产生的温度应力,长期的温度-荷载耦合作用使混凝土材料性能劣化、强度下降。我国现役的混凝土核废料贮存容器为1989年开发的科研成果,材料为普通混凝土,设计时并未充分考虑温度应力对容器的长期影响,造成现已投入使用的贮存容器表面出现龟裂现象。本文采用聚丙烯-玄武岩纤维混凝土改进贮存容器材料,充分考虑纤维混凝土蠕变特性引起的材料强度衰减及热-力耦合作用下贮存容器的时变受力特征,评估贮存容器在服役过程中的可靠度。论文的主要研究内容如下：考虑纤维的掺量和长度因素,进行9种配合比混凝土坍落度、抗压强度和抗渗性能试验的研究；分析聚丙烯、玄武岩纤维对混凝土工作性能、力学性能和耐久性能的增强机理；依据纤维对混凝土影响的显著性确定纤维混凝土核废料贮存容器的材料构成。以混凝土单轴压缩蠕变试验为基础,对比分析蠕变曲线特征确定伯格斯模型描述普通、纤维混凝土蠕变特性具有良好的适应性。采用最小二乘法利用蠕变曲线反分析得到伯格斯模型参数,建立一维情况下的普通、纤维混凝土本构方程。进而针对由蠕变本构方程求解时变强度的理论方法进行系统的研究,通过引入蠕变柔量建立长期弹模与弹性模量的关系,根据规范和试验数据确定抗压强度与弹性模量的关系方程,基于弹模与强度的时间关系相似性导出时变抗压、抗拉强度的理论公式。时变强度分析结果显示,300年内本文配比纤维混凝土的抗压强度和抗拉强度均大于普通混凝土,差异随时间下降。采用电热系统代替核废料衰变热,模拟混凝土核废料贮存容器的工作状态,通过加热-测温装置获取容器内部实际温度分布。利用MATLAB编程BP神经网络程序,以实测温度为依据反分析混凝土的热工参数,并应用后验差检验方法对分析结果进行评价。根据核废料贮存容器的实际工作状态确定初始条件和边界条件,分析三维模型温度场随时间的分布,进而求得贮存容器内部的温度应力。通过对径向、环向、轴向应力和第一第三主应力的时间关系分析,得到混凝土核废料贮存容器服役期内最不利受力情况,为可靠度分析提供受力参考。基于混凝土蠕变特性,考虑温度对混凝土强度的影响,对现有一般大气条件下的混凝土强度经时变化模型进行修正,得到可以定量反应大气环境、温度效应和持续荷载作用对混凝土强度影响的综合模型。综合考虑混凝土强度和热工参数取值的不确定性,通过蒙特卡洛数值模拟分析得到纤维混凝土核废料贮存容器的失效概率。
[Abstract]:The concrete container with low storage and intermediate release of nuclear waste continuously withstands the temperature stress produced by decay heat during the service period of 300 years. The long-term temperature-load coupling effect results in the deterioration of concrete material performance and the decrease of strength.The existing concrete nuclear waste storage container in our country is a scientific research achievement developed in 1989, and the material is ordinary concrete. The long-term effect of temperature stress on the vessel is not fully considered in the design.Causes the storage container surface to appear the crack phenomenon now in use.In this paper, polypropylene basalt fiber reinforced concrete is used to improve the storage vessel material, and the time-varying force characteristics of storage vessel due to the creep characteristics of fiber reinforced concrete are fully considered.Assess the reliability of storage containers during service.The main contents of this paper are as follows: considering the factors of fiber content and length, the slump, compressive strength and impermeability of 9 kinds of mixed concrete are studied, and the working performance of polypropylene and basalt fiber to concrete is analyzed.The reinforcement mechanism of mechanical properties and durability and the material composition of fiber-reinforced concrete nuclear waste storage vessel are determined according to the significance of fiber to concrete.On the basis of uniaxial compression creep test of concrete, the creep characteristics of fiber reinforced concrete (FRC) are proved to be of good adaptability by comparing and analyzing the creep curve characteristics of Boggs model.By using the least square method, the parameters of the Bergs model are obtained by using the back analysis of creep curve, and the constitutive equations of ordinary fiber reinforced concrete in one dimension are established.Then the relationship between long-term modulus of elasticity and elastic modulus is established by introducing creep flexibility into the theoretical method of solving time-varying strength by creep constitutive equation.The relation equation between compressive strength and elastic modulus is determined according to the criterion and test data. Based on the similarity of time relation between elastic modulus and strength, the theoretical formulas of time-varying compressive and tensile strength are derived.The results of time-varying strength analysis show that the compressive strength and tensile strength of fiber reinforced concrete in this paper are higher than those of ordinary concrete in 300 years, and the difference decreases with time.Instead of nuclear waste decay heat, electric heating system is used to simulate the working state of concrete nuclear waste storage vessel, and the actual temperature distribution inside the vessel is obtained by heating and temperature measuring device.BP neural network program programmed by MATLAB is used to inverse analyze the thermal parameters of concrete based on the measured temperature, and the results of the analysis are evaluated by the method of posteriori difference test.According to the actual working state of the nuclear waste storage vessel, the initial conditions and boundary conditions are determined, and the temperature field distribution with time in the three-dimensional model is analyzed, and the temperature stress inside the storage vessel is obtained.Through the time relation analysis of radial, circumferential, axial stress and the first and third principal stress, the most unfavorable stress during the service period of concrete nuclear waste storage vessel is obtained, which provides a force reference for reliability analysis.Based on the creep characteristics of concrete and considering the influence of temperature on the strength of concrete, the time-varying model of concrete strength under general atmospheric conditions is modified, and the atmospheric environment can be quantitatively reflected.A comprehensive model of the effect of temperature effect and continuous load on concrete strength.Considering the uncertainty of concrete strength and thermal parameters, the failure probability of fiber reinforced concrete nuclear waste storage vessel is obtained by Monte Carlo numerical simulation.
【学位授予单位】：东北大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TL942;TU528.57
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本文编号：1701504