中低温固化环氧树脂配方体系研究方法探讨

介绍了中低温固化环氧树脂配方体系的研究方法.该方法适用于具有特殊要求的大预应力湿法缠绕成型的碳纤维复合材料薄壁内衬筒体工件.从碳纤维复合材料设计指标如复合材料横向拉伸、纤维体积含量等出发,理论推导了树脂基体的断裂延伸率和拉伸强度,并对方法研究中的难点进行分析,提出配方研制中应考虑的原则和研制思路,重点介绍配方体系化学流变工艺适用性预测方法和固化工艺制度的制订方法.     

高温气冷堆用碳毡材料导热系数测量及反问题计算

碳纤维材料已成为核能、航天等领域不可或缺的重要功能材料,在高温气冷堆及其相关实验中需要使用大量碳纤维保温材料。但由于目前测试方法的限制,相关材料物性参数测量数据严重不足,尤其是缺乏高温1000℃以上的热物性参数,致其使用受到限制。为此,清华大学核能与新能源技术研究院研制了模拟高温气冷堆温度、环境氛围的材料测试装置,可提供1600℃以下的材料性能测试。根据该装置一次典型实验过程的测量数据,详细介绍了采用非线性导热反问题方法确定材料温度相关导热系数的完整过程和具体算法。提出了一种依据稳态、非稳态热传导原理求解反问题的简明算法,该方法既可单独使用,也可为其他反问题算法提供良好的迭代初值。实验确定了高温气冷堆用碳毡保温材料在1600℃以下的导热系数,将为高温气冷堆相关实验和其他特高温条件下的应用提供重要参考。     

TRISO燃料颗粒等效导热系数理论模型研究

三层各向同性碳包覆（TRISO）燃料颗粒由核芯和4层包覆层组成,具有良好的裂变产物包容能力,其等效导热系数是计算弥散微封装燃料等效导热系数的重要基础。本文首先从球坐标下基本导热方程出发,基于多相固体宏观等效导热理论,建立了TRISO燃料颗粒等效导热系数理论计算模型;然后,结合固-固二元复合材料等效导热系数Chiew-Glandt模型分析了锆基微封装燃料（M3）芯体等效导热系数。结果表明,本文开发的模型可有效模拟TRISO燃料等效导热系数。基于开发的TRISO等效导热系数模型计算获得了全陶瓷微封装燃料（FCM）的等效导热系数。      

固-固二元复合材料等效导热系数模型研究综述及评价

等效导热系数（ETC）是表征复合材料导热性能的重要参数，与连续相导热系数k_c、分散相导热系数k_d、分散相填充率ø、分散相形状及排列方式等密切相关。因此，复合材料等效导热系数的预测是一个非常复杂的过程。虽然目前存在多种复合材料等效导热系数计算模型，但这些模型在预测固 固二元复合材料等效导热系数时仍存在较大的不确定性，因此，应根据不同的应用工况选择预测精度较高的等效导热系数计算模型。本文首先总结了目前广泛应用的颗粒状分散相固-固二元复合材料等效导热系数预测方法，包括已有经验或理论模型、最小热阻法、热阻网络法、数值模拟方法、渐进均匀化方法、逾渗理论方法等，然后基于国内外开展的固-固二元复合材料等效导热系数实验或数值模拟结果，综合评价已有经验或理论模型，给出不同应用工况下预测精度较高的等效导热系数经验或理论模型。     

固-固二元复合材料等效导热系数模型研究综述及评价

等效导热系数(ETC)是表征复合材料导热性能的重要参数,与连续相导热系数k_c、分散相导热系数k_d、分散相填充率?、分散相形状及排列方式等密切相关。因此,复合材料等效导热系数的预测是一个非常复杂的过程。虽然目前存在多种复合材料等效导热系数计算模型,但这些模型在预测固-固二元复合材料等效导热系数时仍存在较大的不确定性,因此,应根据不同的应用工况选择预测精度较高的等效导热系数计算模型。本文首先总结了目前广泛应用的颗粒状分散相固-固二元复合材料等效导热系数预测方法,包括已有经验或理论模型、最小热阻法、热阻网络法、数值模拟方法、渐进均匀化方法、逾渗理论方法等,然后基于国内外开展的固-固二元复合材料等效导热系数实验或数值模拟结果,综合评价已有经验或理论模型,给出不同应用工况下预测精度较高的等效导热系数经验或理论模型。     

二次侧非能动余热排出系统传热能力试验研究

通过搭建试验装置,针对二次侧非能动余热排出系统（ASP）,开展了试验研究。本文对ASP整体性能响应和稳态特性试验研究的试验装置、试验工况、试验结果进行了介绍。试验结果表明,在模拟事故工况下,ASP可稳定建立自然循环,并将回路热量导出,保证系统整体安全性;稳态特性试验中,回路压力为8 MPa时,可导出设计热量,且随压力的升高,导热能力增大,水箱温度对于换热影响较小。     

高放废物地质处置库热学分析的参数敏感性研究

应用FLAC3D软件建立高放废物地质处置库热学分析的简化计算模型,选择影响处置库温度场的包括材料热学参数、几何参数以及时间参数在内的16个关键参数,以膨润土内表面峰值温度(该物理量是高放废物地质处置库热学设计计算中作为温度准则的物理量)为参数敏感性分析的目标物理量,通过热学计算开展参数敏感性分析。在参数敏感性分析中,将参数敏感程度划分为高、中、低三等。分析表明:4个参数(膨润土导热系数、膨润土厚度、围岩导热系数、高放废物中间贮存时间)为高敏感度参数,2个参数(散热材料厚度、回填材料厚度)为中度敏感性参数,其它10个参数(高放玻璃固化废物体、外包装容器、散热材料、回填材料的导热系数与比热,以及膨润土与围岩的比热)为低敏感度参数。通过分析可以得到如下结论:在设计高放废物地质处置库时,对膨润土及围岩导热系数的测试应力求准确,对测试结果数据认真分析,确保为设计计算提供合理的输入参数;在确保膨润土满足工艺要求功能的前提下,宜尽量减小膨润土的厚度;按照本文热学分析模型初步估算,我国高放废物至少需要中间贮存20 a以上。     

EAST-NBI偏转磁体线圈水冷能力分析与测试研究

偏转磁体是中性束注入器的关键部件之一,它安装在中性束注入器真空室内部。为适应核聚变研究装置对中性束注入器高能量、长脉冲、稳态运行的要求,对其偏转磁体原先励磁线圈的水冷系统进行了分析,提出增加水冷抽头的方法完成了改进设计,并对改进前后线圈的冷却能力进行了实验测试。测试结果显示,当中性束注入器长脉冲稳态运行时,改进后的水冷结构能及时带走偏转磁体励磁线圈产生的热量;冷却水的进出口水温差约21 oC;偏转磁体线圈导体表面的温度约45 oC;改进设计水冷系统性能得到优化,满足了EAST-NBI高参数、稳态运行的要求。     

真空石墨加热器温度场数值模拟与分析

石墨加热器是测量球床堆芯等效导热系数实验的关键部件,加热器温度场对系统安全及数据准确性有重要影响。本文基于Fluent计算平台,分别采用DTRM模型、P1模型、ROSSELAND模型、DO模型对真空保护环境下的石墨加热器温度场进行数值模拟,确定适合真空保护石墨加热器温度场的计算方法并讨论石墨导热系数、表面发射率对温度场分布的影响。比较分析表明：DO模型计算得到的温度分布较为接近真实情况,导热系数小于35W/(m•K)时,最高温度对其敏感;导热系数大于35W/(m•K)时,其对加热体最高温度影响较小,最高温度较为稳定。     

微型反应堆卸料装置设计及可靠性分析

微型反应堆（简称“微堆”）低浓化及退役都包含乏燃料卸出的操作,而保证乏燃料安全卸出的关键设备之一就是卸料装置。现有的卸料装置在操作过程中会破坏微堆堆筒体密封性,并且无法恢复,但微堆低浓化后还需利用原有堆筒体进行装料运行,所以本文在此需求的基础上设计了一套新型的卸料装置,可在不分离筒节、不破坏筒体完整性及密封性的前提下完成卸料操作。新设计的卸料装置包含卸料操作工具和辅助机械装置两部分。卸料操作工具通过小盖开口即可实现燃料组件的抓取,实施吊装。卸出的微堆乏燃料具有很高的放射性,卸料操作工具配合辅助机械装置,可实现远距离起升平移的操作,这种设计便于屏蔽,同时可有效降低工作人员所受辐射剂量。对该卸料装置进行计算和可靠性分析,结果表明其强度远大于实际使用载荷,安全可靠,能较好地满足微堆使用需求。新型微堆卸料装置具有经济性好、易制备、易操作的特点,下一步将在国内外微堆低浓化卸料或退役中推广应用。     

Conjugate heat transfer and thermoelastic analysis of heat-generating rods

The exact mathematical formulation and solution of a number of problems dealing with temperatures and stress fields in canned cylinders with arbitrary internal power distribution and fully developed axial turbulent flow are discussed. The problem areas are: (1) the exact linear, thermal, thermoelastic and mechanical stress analysis for a rod in symmetric flow with general integral end force/displacement relations; (2) heat transfer from a clad cylinder with a symmetric heating and temperature dependent conductivity; and (3) asymptotic linear thermal analysis of a rod and associated sub-channel from a square or triangular array.     

Analysis of (n, 2n) Cross Sections at 14.7 MeV in Region of Rare-Earths

Heat transfer by simultaneous conduction and radiation through ceramic fiber insulation is studied experimentally. The temperature profiles and the effective thermal conductivity are determined over a wide range of porosities of the insulation and of temperature provided at the hot boundary.

The resulting data are analyzed in detail to gain an understanding of the mechanism of heat transfer through such medium. A semi-empirical formula is derived for quantitatively predicting the thermal performance of ceramic fiber insulation. The formula incorporates as parameters the porosity and temperatures of the hot and cold boundaries.     

Thermal properties of redeposition layers in the JT-60U divertor region

Thermal properties of the redeposition layer on the inner plate of the W-shaped divertor of JT-60U have been measured with laser flash method so as to estimate transient heat loads onto the divertor. Morphology analysis of the redeposition layer was conducted with a scanning electron microscope. Measurement of a redeposition layer sample of more than 200 μm thick, which had been produced near the most frequent striking point, showed following results: (1) the bulk density of the redeposition layer is about half of that of carbon fiber composite material; (2) the specific heat of the layer is roughly equal to that of the isotropic graphite; (3) the thermal conductivity of the redeposition layer is two orders of magnitude smaller than that of the carbon fiber composite. This low thermal conductivity of the redeposition layer is considered to be caused by a low graphitization degree of the redeposition layer. The difference between the divertor heat loads and the loss of the plasma stored energy becomes smaller taking account of thermal properties of the redeposition layer on the inner divertor, whereas estimated heat loads due to the ELMs is still larger than the loss. This is probably caused by the poloidal distribution of the thermal properties.     

Transient Temperature Response of an Annular Flow with Step Change in Heat Generating Rod

An analysis is made on the transient temperature response of fluid and of heat generating rod in the case of annular flow. Special consideration is given to the effects of the rod heat capacity and radial thermal conduction in the rod during the transient.

The analysis is based on the following assumptions: (1) Initially the system has a uniform temperature distribution, and the rod undergoes a step change in heat generation; (2) the temperature of the fluid entering the annular space is kept constant; (3) the velocity distribution of fluid is uniform; (4) all physical properties remain unchanged during the transient; (5) axial thermal conduction in the rod is neglected in comparison with that in the radial direction; (6) axial thermal conduction in the fluid is neglected in comparison with axial thermal convection.

The present result is compared with values by quasi-static solution for various heat transfer parameters.     

The variance of the temperature distribution in a reactor cell

Local variations in fuel packing density, fuel enrichment, bond-gap thickness, surface asperities, etc. give rise to potentially significant deviations in the temperature distribution in a reactor cell. Treating the second moments of the statistical variations of the fuel thermal conductivity, gap conductance, heat transfer coefficient from can to bulk coolant, etc. by means of specific variances the standard deviation of the temperature distribution is calculated. To account for the temperature dependence of the fuel thermal conductivity and to remover non-linearities in the equations describing the temperature deviations, a linearization approximation is adopted and the resulting equations are solved by means of an expansion over azimuthal harmonics utilizing radially dependent coefficients. In the main text, axial conduction effects are neglected in order to simplify algebraic expressions; however, in Appendix I it is shown how an expansion over axial harmonics enables the inclusion of axial conduction which is important in describing strong localized deviations. It is demonstrated that the standard deviation of a quantity that is a linear combination of the harmonics of the temperature has a variance that contains no cross-correlation between different harmonics.     

A parametric analysis of heat transfer in composite nuclear fuels

The composite nuclear fuel described in this paper consists of a heat generating fuel matrix containing cylindrical metal and fibers uniformly aligned throughout the matrix. Exact analytical solutions were found for temperature distributions in the fiber and matrix for a composite cell modeled as concentric cylinders. A parametric study is presented of composite overall thermal conductivities and temperature distributions as a function of fiber-to-matrix conductivity ratios, cell length-to-radius ratios, and fiber-to-cell radius ratios. For composite cells in which length-to-radius ratios exceed 10, axial temperature distributions may be calculated assuming a homogeneous material.     

Analytical Modelling of Overpack of Enriched Uranium Hexafluoride Package in a Fire Event

Abstract

A fissile package must be subjected to a fire test at 800°C for 30 min. For a package that contains enriched uranium hexafluoride (UF₆), the temperature of the contents has to be kept below 121°C in order to avoid rupture of the 30B cylinder. A previous study on heat transfer mechanisms in an enriched UF₆ package type ‘DOT-21PF-1’ found that decomposed gas with a temperature of around 100°C generated from heated penolic foam thermal insulator was a major heat source heating the cylinder in the initial period of the fire test, in addition to the heat conducted from the outer surface through the thermal insulator into the interior of the package. Mitsubishi Materiass Corporation has developed a new packaging for enriched UF₆ ‘MST-30’ that also uses phenolic foam as the thermal insulator, and has pelformdd a fire test at 800°C for 30 min, which also indicated the temperature history of the package interior affected by heating from the decomposed gas. In this study, a laboratory test was carried out to identify the kind of gas generated from the heated phenoiic foam. The test found that the decomposed gas was water vapour. Since water vapour has a large latent heat, it has a large heat transfer coefficient when it condenses on a cool surface. By taking the water vapour heating mechanssm into account, an analytical model was developed for MST-30 to simulate the measured cylinder temperature history. Analytical models for evaluaiing the cylinder temperature under the 800°C/30 min fire test considering conservativeness are also presented.     

高温球床壁面区域有效导热系数模型优化

有效导热系数用来表征高温气冷球床堆堆芯综合传热能力,提高球床有效导热系数的预测精度对于高温气冷球床堆的热工设计和安全分析十分重要。为了优化球床壁面区域有效导热系数模型,本文针对无序石墨球床有效导热系数开展数值研究,分析了无序堆积球床主体区域、近壁面区域以及壁面区域有效导热系数的分布特性。结果表明：壁面区域有效导热系数相对于主体区域和近壁面区域显著降低,其平均降幅约为22%。因此引入了修正系数C_w对ZBS模型在壁面区域进行优化,对于球床主体区域及近壁面区域修正系数C_w=1,对于壁面区域,修正系数C_w=0.78。通过与前期无序球床实验数据和南非HTTU实验数据的对比,验证了优化后的ZBS模型能较好地预测球床壁面区域有效导热系数。     

Transient thermal stresses and displacements in a transversely isotropic semi-infinite circular cylinder subjected to an arbitrary surface heat generation and a convective heat loss

The transient thermal stresses and displacements in a traction-free, transversely isotropic, semi-infinite circular cylinder subjected to a convective heat loss on the end surface is analyzed by means of a set of stress functions and a generalized Fourier-integral representation for exponential function.The purpose of this paper is to present the results of theoretical analysis which considers the effects of the thermal and elastic anisotropes of the material properties on the thermal stresses and displacements in the transversely isotropic, semi-infinite circular cylinder due to an arbitrary cylindrical surface heat generation.A detailed numerical result of the thermal stresses and displacements is given for various values of the ratios of the thermal conductivity coefficients, Young's moduli and linear thermal expansion coefficients in the axial and radial directions and it is demonstrated that the sensivity of the maximum stress and displacement to the anisotropy of the thermal conductivity coefficient is significant.