乏燃料运输容器事故工况密封分析研究

目的 为防止放射性物质泄漏,要求乏燃料运输容器在事故工况下保证容器的密封。通过对乏燃料运输容器比例容器事故工况密封分析研究,为乏燃料运输容器密封分析提供依据。方法 为验证假想事故工况乏燃料运输容器的密封性,采用LS-DYNA分析软件,开展乏燃料运输容器比例容器9 m跌落分析,提取密封螺栓跌落过程中的载荷时程和密封面分离量,并在比例容器跌落试验后开展气密性能试验。结果 跌落分析结果表明,比例容器内、外盖在跌落过程中,密封螺栓应力满足限值要求;内、外盖密封面最大分离量小于密封结构有效回弹量。同时跌落后容器的气密性检查试验结果表明其密封性能良好。结论 乏燃料运输容器比例容器的跌落密封分析和气密性试验结果表明,在事故工况下乏燃料运输容器货包能够保证密封要求,该分析方法可用于乏燃料运输容器事故工况的密封分析。     

事故工况下乏燃料运输容器跌落分析

目的验证乏燃料运输容器本体、内外盖、吊篮和螺栓及其运输包装设计,在事故工况中以最危险角度从9 m高度自由跌落至水平的刚性地面过程中,是否满足GB 11806《放射性物质安全运输规定》的规范要求。方法采用LS-DYNA进行有限元仿真模拟跌落过程以代替跌落试验,开展乏燃料运输容器9 m自由跌落冲击分析,并根据ASME规范第III卷规定的应力限值对容器本体、内外盖、吊篮和螺栓进行应力校核。结果应力校核结果显示,乏燃料运输容器本体、内外盖、吊篮和螺栓满足设计强度要求。结论该乏燃料运输容器本体、内外盖、吊篮和螺栓及其运输包装设计满足GB 11806规范要求。     

燃料运输容器跌落姿态分析技术

目的总结燃料运输容器跌落分析流程,设计合理的姿态分析方案,通过分析使燃料运输容器设计满足GB 11806规定的跌落试验要求。方法使用动力有限元方法对新燃料运输容器进行多姿态多工况的跌落分析,并根据试验结果对分析结果进行验证,将分析和试验经验总结成完整的分析流程。结果通过分析,新燃料运输容器在正常运输条件下的最不利跌落姿态为9°小角度跌落,该工况下容器外壳最大变形量为49 mm。事故运输条件下最不利跌落姿态为正向垂直跌落,燃料组件最大冲击力为1.78 MN。结合分析和试验结果总结了容器最不利跌落姿态的分析流程和技术要点。结论结合分析和试验结果,得到了新燃料运输容器各跌落试验的最不利跌落姿态,并总结了燃料运输容器跌落分析的通用流程。     

乏燃料运输容器减震器应用及研究现状

目的 了解国内外乏燃料运输容器减震器的成熟结构形式,分析应用技术的主要特点,整理现有减震器缓冲材料的材料特性和研究现状,为国内减震器设计发展提供一定参考。方法 综述国内外代表性乏燃料运输容器的减震器应用现状,分析现有缓冲材料的优缺点和结构设计方面的注意事项。结果 目前,国内外乏燃料运输容器多采用木材填充的壳式减震器,在填充材料方面,聚氨酯泡沫、蜂窝铝等工程材料也有应用,此外泡沫铝、碳泡沫、双向瓦楞蜂窝铝等新型材料也被研究用作减震器缓冲材料。结论 建议继续增加对新型缓冲材料以及对减震器结构设计的研究,以满足未来国内大型乏燃料运输容器的应用需要,同时建议注重减震器产品的适配性和兼容性,开发系列化产品。     

某乏燃料运输容器减震器设计及验证

目的 研发用于某运输容器的减震器,同时探究减震器尺寸和填充材料的分散性对减震器设计的影响。方法 开展减震器尺寸对运输容器减震效果的分析计算,通过木材抗压强度试验获取木材压缩强度分散性,并使用有限元方法对运输容器进行9 m过重心角跌落分析,并进行9 m过重心角跌落测试验证。结果 一般来说减震器尺寸越大,其吸收能量越多,但其尺寸超过某临界点后减震效果反而下降;低抗压强度的填充木材吸能力不如较高抗压强度的,但填充木材抗压强度较大时,减震器偏硬会导致较大的容器刚体加速度。结论 该减震器设计合理,满足规范要求。填充木材的力学性能分散性,偏大或偏小都会对设计产生影响,因此,使用木材作为缓冲填充材料,设计时需要充分考虑木材压缩强度分散性对缓冲效果的影响。     

核乏燃料运输容器减震器填充材料研究进展

目的综述以木材、聚氨酯泡沫、蜂窝铝作为核乏燃料运输容器减震器填充材料的性能。方法通过对3种填充材料的减震器进行受载分析,然后对3种填充材料的力学性能进行验证。结果将3种材料作为核乏燃料减震器填充材料具有可行性,还列出了3种材料的不足之处。结论工业上对有着优秀能量吸收、限制过载、质轻且受环境变化影较小的核乏燃料运输容器减震器填充材料有着迫切需求。之后提出将2种材料(泡沫铝和双向瓦楞蜂窝铝)作为减震器的填充材料,并分析了2种材料的特点与吸能特性,证明了其作为减震器填充材料的合理性与可行性。     

新燃料运输容器运输多根小型组件的跌落分析

目的 通过跌落分析，确认STC容器可用于运输多根小型组件。方法 设计一个可装载多根小型组件的运输内胆，并从外形尺寸、质量、安装方式、重心位置等维度对内胆组件和新燃料组件进行比较，从而明确运输多根小型组件时STC容器的跌落姿态——与运输新燃料组件时一致。最后，比较STC容器在装载2种组件时的跌落分析。结果 跌落分析表明，在各种工况下的跌落中，相较于运输新燃料组件，STC容器运输多根小型组件的变形量要小。结论 通过内容物比对和跌落分析，证明了STC容器不仅可用于运输新燃料组件，还可以用于运输多根小型组件。该运输方案满足了跌落验收标准，确保了容器在各工况下跌落的闭合状态，从而提高了设计效率，节约了研制成本。     

乏燃料容器设计中组件包壳的氢脆特性影响分析

目的针对高燃耗乏燃料在干法运输条件下存在的包壳脆性变化,探讨其对我国现阶段乏燃料运输及容器安全研究中以“组件结构保持完整”作为设计基准所带来的影响和考虑。方法结合锆包壳氢化物韧脆转变的机理,针对乏燃料离堆和运输过程对包壳性能变化进行分析,并根据美国“ISG-11”等技术导则中提出的判别准则,探讨事故载荷下高燃耗乏燃料包壳结构性能的变化。结果通常认为2G乏燃料不需要考虑其材料氢脆影响问题,而高燃耗的3G乏燃料则必须综合评价离堆及后续干法运输过程中各种因素变化对其性能的影响,以判断包壳的峰值温度、韧脆转变温度和温度变化幅度等是否会对事故工况下“其结构始终保持完整”的设计基准造成影响。结论随着我国进入3G高燃耗乏燃料密集运输的时代,在乏燃料运输容器设计及运输安全分析时更应充分考虑包壳材料氢脆特性影响下的乏燃料结构在事故载荷下的保持能力。     

缓冲包装跌落仿真误差分析

目的研究Ansys/LS-DYNA DTM模块跌落仿真分析与经典缓冲包装设计方法之间的误差,并分析阻尼及摩擦因数对仿真结果的影响。方法基于经典缓冲包装设计方法,分别设计线弹性与双线性材料为缓冲材料的产品-衬垫系统;利用Ansys/LS-DYNA DTM模块对线弹性与双线性缓冲材料的产品-衬垫系统进行跌落分析,对比分析理论设计与仿真分析结果。结果对于线弹性材料与双线性缓冲材料的产品-衬垫系统,Ansys/LS-DYNA DTM模块跌落仿真分析与经典缓冲包装理论设计之间的误差均在5%以内。系统阻尼的增加导致所受最大冲击加速度减小;摩擦因数对所受最大冲击加速度影响较小;线性粘滞系数的增加导致所受最大冲击加速度增加。结论对于一般的工程应用,Ansys/LS-DYNA DTM模块跌落仿真分析方法与经典缓冲包装设计方法之间的误差在允许范围内。     

新燃料运输容器聚氨酯泡沫填充材料性能研究

目的对新燃料运输容器聚氨酯泡沫填充材料进行性能测试、寿命预测,验证其是否满足新燃料运输容器设计性能要求和使用寿命要求。方法分别测试填充在新燃料运输容器不同区域的硬质聚氨酯泡沫的压缩性能、吸水性能、阻燃性能、隔热性能,并利用热重分析方法研究硬质聚氨酯泡沫填充材料的热老化性能,预测寿命。结果根据测试结果,研制的硬质聚氨酯泡沫能够满足新燃料运输容器填充材料的设计性能要求和使用寿命要求,在最高正常使用温度38℃条件下,预测其寿命为34年。结论在新燃料组件正常运输工况和事故运输工况条件下,硬质聚氨酯泡沫填充材料均能对燃料组件起到良好的保护作用,为实现新燃料运输容器国产化奠定了基础。     

Ⅰ-Ⅱ复合型裂纹脆性断裂的最小J_2准则

实际工程的结构中,裂纹多处于复合型状态,因此复合型裂纹断裂的理论研究有着更为重要的理论意义和实用价值。本文以Ⅰ-Ⅱ复合型裂纹为研究对象,将偏应力张量的第二不变量2J作为判定依据,预测了裂纹起裂的角度以及开裂荷载,并与一些实验数据进行了比较,符合得也较好。计算结果进一步表明了在裂纹起裂引起的应变能转化过程中,起主要作用的是形状改变比能这一事实,由此得出了另一个结论是在裂纹尖端,平行于裂纹方向的应力级数展开式中非奇异项对裂纹的开裂角度以及开裂荷载是有影响的。     

Three-dimensional numerical investigation of brittle bond fracture

A fracture mechanics based analysis of interface bond failure is presented. The bond edge is regarded as an interface crack front loaded under combined mode 1, 2 and 3 loading, and results are obtained for the critical stress for initiation of bond failure and the location along the bond edge where failure is initiated. A numerical procedure is formulated to study the propagation of the interface crack following initiation. Assuming that the crack propagates at the interface, a criterion for propagation is formulated, and it is shown that the crack front shape predicted is consistent with the basic interface fracture mechanics assuming quasi-static crack propagation. Results for the bond strength are presented for different fracture criteria and different bond shapes.     

A new method to estimate the plane strain fracture toughness of materials

Although the testing method for fracture toughness K_IC has been implemented for decades, the strict specimen size requirements make it difficult to get the accurate K_IC for the high‐toughness materials. In this study, different specimen sizes of high‐strength steels were adopted in fracture toughness testing. Through the observations on the fracture surfaces of the K_IC specimen, it is shown that the fracture energy can be divided into 2 distinct parts: (1) the energy for flat fracture and (2) the energy for shear fracture. According to the energy criterion, the K_IC values can be acquired by small‐size specimens through derivation. The results reveal that the estimated toughness value is consistent with the experimental data. The new method would be widely applied to predict the fracture toughness of metallic materials with small‐size specimens.     

Calibration procedures for a computational model of ductile fracture

A recent extension of the Gurson constitutive model of damage and failure of ductile structural alloys accounts for localization and crack formation under shearing as well as tension. When properly calibrated against a basic set of experiments, this model has the potential to predict the emergence and propagation of cracks over a wide range of stress states. This paper addresses procedures for calibrating the damage parameters of the extended constitutive model. The procedures are demonstrated for DH36 steel using data from three tests: (i) tension of a round bar, (ii) mode I cracking in a compact tension specimen, and (iii) shear localization and mode II cracking in a shear-off specimen. The computational model is then used to study the emergence of the cup-cone fracture mode in the neck of a round tensile bar. Ductility of a notched round bar provides additional validation.     

On the failure of cracks under mixed-mode loads

Fracture of plates containing a crack under mixed-mode, I and II, loading conditions is investigated. Fracture mechanisms are first examined from fracture surface morphology to correlate with the macroscopic fracture behavior. Two distinct features are observed and they are typical of shear and tensile types of failure. From this correlation, a fracture criterion based on the competition of the attainment of a tensile fracturing stress σ_{_C} and a shear fracturing stress τ_{_C} at a fixed distance around the crack tip is proposed. Material ductility is incorporated using τ_{_C}/σ_{_C} determined from classical material failure theories. The type of fracture is predicted by comparing τ_{_max}/σ_{_max} at r=r_{_C} for a given mixed mode loading to the material ductility_{τ_C/σ_C} , i.e. τ_{_max}/σ_{_max})<(τ_{_C} /σ_{_C}) for tensile type of fracture and (τ_{_max}/σ_{_max}) r (τ_{_C}/ σ_{_C}) for shear type of fracture. It is found that, for typical engineering structural metals with certain ductility, (1) crack propagation initiates according to the maximum hoop stress criterion when the the mode mixity is near mode I and according to the maximum shear stress criterion when the mode mixity is near mode II, and (2) the transition of the failure from tensile to shear type can be predicted by the proposed criterion. For brittle materials the maximum hoop (opening) stress always reaches the tensile fracturing stress before the maximum shear stress reaches the shear fracturing stress of the material at a crack tip. Therefore, specimens made of brittle materials tend to fail under the maximum hoop stress criterion, as demonstrated by Erdogan and Sih (1963) and others. This revised version was published online in August 2006 with corrections to the Cover Date.     

不同形态铁素体试样低温断裂行为的研究

采用热模拟方法,模拟不同形态的针状铁素体、板条状铁素体和魏氏组织的试样,测定试样的断裂参量,发现不同形态伯铁素体具有不同的解理断裂应力σｆ,而且韧性高的σｆ也高;断口分析结果也表明,不同的铁素体具有不同的断口特征。低温下解理断裂的发生满足两个条件;切应力达到临界的切应力;正应力达到解理断裂应力。     

Discrete fractal fracture mechanics

A modification of the classical theory of brittle fracture of solids is offered by relating discrete nature of crack propagation to the fractal geometry of the crack. The new model incorporates all previously considered theories of fracture processes, in particular the Griffith [Griffith AA. The phenomenon of rupture and flow in solids. Philos Trans Roy Soc Lond 1921;A221:163-398] theory, its contemporary extension known as LEFM and the most recently developed Quantized Fracture Mechanics (QFM) by Pugno and Ruoff [Pugno N, Ruoff RS. Quantized fracture mechanics. Philos Mag 2004;84(27):2829-45]. Using an equivalent smooth blunt crack for a given fractal crack, we find that assuming that radius of curvature of the blunt crack is a material property, the crack roughens while propagating. In other words, fractal dimension at the crack tip is a monotonically increasing function of the nominal crack length, i.e., the presence of the Mirror-Mist-Hackle phenomenon is analytically demonstrated.     

Evaluation of the fracture toughness properties of polytetrafluoroethylene

Polytetrafluoroethylene (PTFE) (Dupont Tradename Teflon) is a common polymer with many structural applications including sheet, gaskets, bearing pads, piston rings and diaphragms. The interest here developed because this polymer is being considered as the major component of a newly proposed `reactive' material with a possible application as a projectile to replace common inertial projectiles. Little mechanical property data is available on this material since it is commonly used only as a coating material with the dominant properties being its low friction coefficient and high application temperature. Previous work (Joyce, 2003) on commercially available sheet PTFE material has demonstrated the applicability of the normalization method of ASTM E1820 (1999), the elastic-plastic fracture toughness standard to develop fracture toughness properties of this material over a range of test temperatures and loading rates. Additional work on the aluminum filled `reactive' derivative of the basic PTFE polymer (Joyce and Joyce, 2004) has also recently been completed. In this work, standard ASTM E1820 fracture toughness specimens machined from sintered pucks of PTFE were tested at four test temperatures and at a range of test rates to determine the J _Ic and J resistance curve characteristics of the PTFE material. The major results are that while crack extension is difficult at standard laboratory loading rates at ambient (21 °C) temperature or above, for temperatures slightly below ambient or for elevated loading rates, a rapid degradation of fracture resistance occurs and cracking occurs in a ductile or even nearly brittle manner.     

Prediction of the Brittle Fracture Toughness of Neutron-Irradiated Reactor Pressure-Vessel Steels. Part 1

The irradiation effect on the temperature dependence of the brittle fracture toughness of reactor pressure-vessel steels is simulated using the probabilistic model for the fracture-toughness prediction, which was proposed by the authors earlier. The paper analyzes the irradiation effect on the parameters controlling the plastic deformation and brittle fracture of reactor pressure-vessel steels. We consider the mechanisms of microcrack nucleation in nonirradiated, irradiated, and post-irradiation-annealed reactor pressure-vessel steels.     

Fracture resistance of 8 mol% yttria stabilized zirconia

Anin situ technique for the assessment of fracture resistance employing double cantilever beam (DCB) specimens was developed in the present study. The side-grooved DCB specimens were loaded with pure bending moments in a specially designed and fabricated test fixture which went inside the specimen chamber of a scanning electron microscope. The study as conducted on a 8 mol% fully stabilized cubic phase yttria (Y₂O₃) stabilized zirconia (YSZ) ceramic. The powder processed sheets were sintered at 1600°C for 2 h in a zirconia tube furnace. The mode I applied energy release rate, G_I was determined for both pure YSZ and treated YSZ. Two sets of experiments were conducted for the complete characterization of the ceramics. Three fracture toughness values were determined for the pure and treated ceramics, viz. (i) at the onset of the crack initiation,G _ic, (ii) at the arrest of a subcritical crack, G_ia and (iii) at the onset of the fast fracture,G _if. Two analyses of the experimental data were carried out, viz. method of extrapolation and statistical analysis. In case of the pure YSZ, a transgranular mode of the stable crack growth was identified to be predominant. The porous coating treatment appeared to have positive effects as the crack initiation resistance increased due to electrode layers. The stable crack growth behaviours of the ceramics were investigated by monitoring the crack growth velocity as a function of appliedG values. The results obtained were of direct significance in designing and fabrication of SOFC stacks.