Investigation of the internal friction increase caused by temperature changes in polycrystalline uranium specimens

The increase in the internal friction with time in heating at different rates was measured with respect to the damping of torsional vibrations during the heating of specimens. Specimens of -phase quenched, - and -phase annealed, and recrystallized polycrystalline uranium were investigated. It is shown that the rate of the internal friction rise in specimens gradually decreases in time and that the internal friction increment attains a limiting value, the magnitude of which is approximately proportional to the specimen heating rate. The internal friction increment is related to stresses which arise in the specimen due to the anisotropic thermal expansion coefficient when the temperature changes. The reduction in internal stresses, which is either due to an increase in the grain size to a magnitude comparable to the diameter of the specimen under investigation or the formation of a predominant orientation in specimens, results in a reduction of the internal friction increment. During the heating process, also macroscopic shearing deformation occurs in the specimen. Such an increase in internal friction in heating was also observed in a thermally anisotropic metal, such as zinc; it was not observed in metals with isotropic thermal expansion coefficients — aluminum and molybdenum.     

Internal friction in uranium

Studies have been made of the temperature dependence of internal friction and the shear modulus in uranium. The internal friction in uranium depends on the heat treatment and is reduced after annealing in the ß and regions. During polymorphous transformations the internal friction changes its value isothermally. The transitions ß and ß are accompanied by a reduction in the internal friction and ß and ß by an increase in the internal friction. Each polymorphous modification of uranium in the temperature ranges for its existence has its own value of internal friction.     

Dissipative heating in a coated viscoelastic cylinder

The thermomechanical responses of a long coated hollow cylinder made of viscoelastic material subjected to cyclic presure fluctuations at high frequency are studied. The accumulation of the continuous energy dissipation induces a significant temperature increase in the material which affects the material behavior and hence the structural response. The paper adopts a numerical approach with the intention of studying the effect of coating. It is found that the coating has little effect on the dissipative heating due to internal pressure fluctuation. However, the heating effect can be greatly reduced when the cyclic pressure is applied on the outside surface.     

The effect of certain cycle parameters on the efficiency of a nuclear gas turbine unit

The effect is analyzed of the increase of the effective pressure ratio, the regeneration factors, the initial gas pressure, temperature of the fuel element cladding, hydraulic resistance of the gas circuit on the internal efficiency of a nuclear gas turbine unit, taking into account the characteristics of the active zone of the reactor. The results are given of the effect on the efficiency of a nuclear gas turbine unit (NGTU) of the intermediate heating and cooling of the gas. A possible circuit for a NTGU is discussed, with one intermediate heating and three-stage cooling of the gas;Translated from Atomnaya Énergiya, Vol. 20, No. 5, pp. 412–415, May, 1966.     

The effect of azimuthal temperature distribution on the ballooning and rupture behavior of Zircaloy-4 cladding tube under transient-heating conditions

For the purpose of investigating the effect of azimuthal temperature distribution on the ballooning and rupture behavior of Zircaloy-4 (Zry-4) cladding tube, laboratory-scale experiments on non-irradiated Zry-4 cladding tube specimens were performed under transient-heating conditions which simulate loss-of-coolant accident (LOCA) conditions by using an external heating method, and the data obtained were compared to those from a previous study, where an internal heating method was used. The maximum circumferential strains of the cladding tube specimens were firstly divided by the engineering hoop stress. The divided maximum circumferential strains, ks, of the previous study, which used the internal heating method, were then corrected based on the azimuthal temperature difference (ATD) in the cladding tube specimen. The ks for the external heating method which was used in this study agreed fairly well with the corrected ks obtained in the previous study which employed the internal heating method in the burst temperature range below ～1200 K. Also, the area of rupture opening tended to increase with increasing of the value which is defined as the engineering hoop stress multiplied by the maximum circumferential strain. From the results obtained in this study, it was suggested that the maximum circumferential strain and the size of rupture opening of a cladding tube under LOCA-simulated conditions can be estimated mainly by using the engineering hoop stress, the maximum circumferential strain, and ATD in the cladding tube specimen, irrespective of heating methods.     

Transient thermal stresses in a bonded composite hollow circular cylinder under symmetrical temperature distribution

A general treatise for the transient thermal stress problem of a composite circular cylinder made by bonding is described under a symmetrical temperature distribution. Analysis is developed by stress function method by the aid of Laplace transforms. Numerical examples are illustrated for the hollow composite cylinder with several radius-ratios made by the different materials due to transient heating at the internal surface by liquid.     

球床模块堆停堆后自然对流传热特性数值研究

对冷却流体在球床模块堆内燃料颗粒填充区域中的流动和传热过程进行了研究.数值模拟突然停堆后燃料颗粒区在温差作用下的自然对流过程,分析了瑞利数Ra对燃料填充区域内流场、温度场和局部努塞尔数Nu以及壁面摩擦阻力系数的影响.计算结果表明:当球床模块堆突然停堆时燃料填充区域可形成加热壁面流体上升流动、冷却壁面下降流动的自然循环流动;随着Ra数增大,回流中心向上移动;沿轴向壁面局部Nusselt数和摩擦阻力系数存在极值,并且极值点随Ra数增大而向上移动;与氮气相比,氦气作为冷却介质停堆后具有更均匀的堆芯轴向温度分布.     

托卡马克等离子体中快粒子触发的高频鱼骨模不稳定性研究

本文考虑托卡马克等离子体中快粒子的空间密度分布剖面,在中性束及电子回旋共振加热的条件下,建立了研究鱼骨模的色散关系并对鱼骨模作了数值研究。结果表明:快粒子对内扭曲模有致稳作用,且在近轴加热条件下可激发高频鱼骨模,其频率与快粒子的环向进动频率一致。鱼骨模的增长率与快粒子的密度梯度有关,一般随密度梯度的增加而增大。在高比压区间,勉强通行快粒子可驱动鱼骨模进入第二稳定区,在该区域鱼骨模是稳定的。     

Use of the α → β quartz transition to monitor the temperature increase produced by a proton microbeam

Ion microbeams induce in certain cases local heating of a sample under investigation, especially in insulators. To obtain experimental values of this temperature increase, we used a quartz sample which presents its own internal thermometer with the α → β transition observed at 573°C. At this temperature, the transition is easily observed from the rapid variation of the bubble size contained in a melted inclusion trapped in the quartz. We measured the temperature increase produced by a 3 MeV proton microbeam. For this purpose, the nuclear microprobe chamber was equipped with a sample heating stage. The decrease of the power injected by the heater element (beam on) required to observe the transition has been interpreted as a local increase of the temperature under microbeam exposure.     

Friction and wear of Inconel 690 and Inconel 600 for steam generator tube in room temperature water

In the steam generators of nuclear power plants, the flow of cooling water can cause the tubes to vibrate, resulting in fretting wear damage due to contacts between these tubes and their supports. The tubes are made of Inconel 690 and Inconel 600 and the supports are made of STS 304. In this paper, fretting wear tests in water were performed using the materials Inconel 690 and Inconel 600 in contact with STS 304. Fretting tests using a cross-cylinder type set up were conducted under various vibrating amplitudes and applied normal loads in order to measure friction forces and wear volumes. Also, conventional sliding tests using a pin-on-disk type set up were carried out to compare these test results.In the fretting tests, friction force was found to be strongly dependent on normal load and vibrating amplitude. Coefficients of friction decreased with an increase in the normal load and a decrease in the vibrating amplitude applied. Also, the wear of Inconel 600 and Inconel 690 was predicted using a work rate model. Depending on the normal load and vibrating amplitude applied, distinctively different wear mechanisms and often drastically different wear rates occurred. It was found that the fretting wear coefficients for Inconel 600 and Inconel 690 were 9.3×10⁻¹⁵ and 16.2×10⁻¹⁵ Pa⁻¹, respectively. This study shows that Inconel 690 can result in lesser friction forces and exhibits less wear resistance than Inconel 600 in room temperature water.     

Vibrations of probe used for the defect detection of helical heating tubes in a fast breeder reactor: Part 2. Vibration analysis and numerical simulations

A detection of a defect of a helical heating tube installed in the fast breeder reactor “Monju” in Japan is done by a feeding of an eddy current testing (ECT) probe with magnetic sensor into the tube. An undesirable vibration of the ECT probe always happens under a certain condition and makes the inspection difficult. Several characteristics of the vibration have been made clear by some experiments using a mock-up, but the essential factor of the vibration is still unclear. In this paper, a numerical simulation of the vibration is implemented on the assumption that the vibration is caused by Coulomb friction. An analytical model, which is obtained as a lumped mass model, is a large-scale non-linear vibration system and many computational costs are ordinarily required to carry out the simulations. The Transfer Influence Coefficient Method is applied so that the simulation is efficiently carried out. The results of simulation qualitatively agree well with the experimental results. It confirms the validity of the assumption that the vibration is caused by Coulomb friction.     

LOCA工况下环形燃料元件外包壳鼓胀爆破试验研究

为获得环形燃料元件外包壳在压水堆冷却剂丧失事故（LOCA）工况下鼓胀爆破温度和应变的经验关系式，为设计计算提供必要的输入，并初步评价其LOCA工况下的鼓胀爆破性能，在堆外对其开展了LOCA工况下的鼓胀爆破试验研究。在不同的升温速率和内压下，蒸汽环境中，以外表面红外加热的方式对环形燃料元件外包壳进行了鼓胀爆破试验。总结了试验得到的经验关系式，分析了试验中爆破温度和应变的影响因素，并将试验结果与美国核管理委员会出版的NUREG0630中的结果进行对比，验证了试验结果的合理性。获得的试验数据可用于环形燃料的设计、计算和改进。     

A numerical investigation of SBLOCA scenario in nuclear heating reactor

Small break loss of coolant accident (SBLOCA) is one of the most important severe accidents in nuclear heating reactor. Nuclear heating reactor designed by Tsinghua University, whose primary loop is integrated layout and designed without main pump. The initial water volume in the reactor vessel is important to determine whether the reactor will be cooled or not as no safety injection system is designed for coolant makeup during the whole scenario. This paper simulates SBLOCA in nuclear heating reactor based on RELAP5. Transient behavior of relevant thermal parameters is specifically analyzed. Moreover, investigation also has been made on SBLOCA scenario based on different residual heat removal correlations and found the long-term residual heat removal capacity is decisive in determining the loss of coolant. The mathematical form of residual heat removal correlation is specifically deducted and can be widely applied to different situations. The envelope line that differentiates the region whether the core is safe or not under different maximum PRHRS capacity is also given.     

Development of debris bed cooling evaluation code,DPCOOL, based on heating porous media submerged in two-phase pool

ABSTRACT

A framework of the modular code system, THERMOS, aiming to evaluate cooling of a debris bed having complex configurations was introduced with a focus on one of the major modules, DPCOOL, which models heating or non-heating porous media of particulate debris in a two-phase pool. In DPCOOL, pool and debris bed regions are discretized in a three-dimensional Cartesian coordinate system. A pool region is formulated based on the two-fluid model. A two-phase flow in the debris bed region is formulated based on the Tung & Dhir model with modifications for smaller particles proposed by Schmidt. In order to synthesize the momentum equations of the two regions, interpolation factors as piecewise linear functions of porosity are introduced. The interfacial friction model was validated based on Chu’s test using a debris bed composed of non-heating SUS spheres in a water pool with air injection from below where the net water flow in the layer became zero so that pressure loss of the layer was governed by interfacial friction. The sum of the two-phase flow friction and the interfacial friction models was validated based on top flooding and bottom flooding tests conducted in IKE’s DEBRIS test facility loaded with mixed steel and alumina spheres that were heated by an induction coil system.     

Study theoretically on two-phase circulation flow characteristics under ERVC condition in advanced PWR

For the problem of two-phase natural circulation flow in gap clearance between reactor vessel lower head and insulator in the condition of severe accident, one-dimensional steady-state natural flow analysis code was written by utilizing FORTRAN. Based on the code, the effects of different correlations for friction coefficient and the number of nodes of heating section on mass flow rate of two-phase natural circulation flow were studied. And the results are compared with that of Chinese REPEC experiment and simulation using RELAP5 program so as to verify the rationality and correctness of the code. Based on the experiment data, simulation results and the model, friction coefficient and the void fraction condition under ERVC correlation are obtained by fitting. The results calculated by the model using fitting friction coefficient correlation agree well with ULPU V test data. Furthermore, the effect of power, pressure, inlet area, gap diameter, flooding level and inlet water subcooling on mass flow rate and void fraction of two-phase natural circulation were studied utilizing this code.     

Formation of Electron Internal Transport Barrier in Edge Plasma of Small Size Divertor Tokamak

The formation of electron internal transport barrier (EITB) during using counter-neutral beam injection (NBI) heating in the edge plasma of small size divertor tokamak can be simulated by using fluid transport code B2SOLPS0.5.2D. The results of simulations give us the following: (1) Plasma heating with counter-neutral beam injection leads to, strong, parabola type electron internal transport barrier (EITB) was formed in the edge plasma of small size divertor tokamak. (2) In case of plasma heating by counter-neutral beam injection, the radial electric field shear (E _r –gradient) was increased, while electron transport coefficients were reduced in conjunction with the formation of electron internal transport barrier (EITB). (3) The plasma heating by counter-neutral beam injection play significantly role in redistribution of parallel (toroidal) velocity in edge plasma of small size divertor tokamak.     

矩形窄缝通道内单相水流动特性研究

通过理论分析,得到了计算矩形窄缝通道单相层流摩阻系数的公式。对小高宽比矩形窄缝通道内的流动特性进行了实验研究,结果表明：矩形窄缝通道内单相摩阻系数随Re变化的曲线和圆管有相同的趋势,但圆管流动摩阻公式不适用于矩形窄缝通道。矩形通道内摩阻系数与Re和通道截面高宽比有关,通道高宽比越小,摩阻系数越大。实验结果和理论推导结论一致。从截面湿周和切向应力两方面解释了高宽比对矩形窄缝通道内单相水层流摩阻特性的影响机理。     

High-temperature internal friction in polycrystalline Zirconium and Zircaloy-4

The data on the high-temperature internal friction of zirconium and zirconium alloys are reviewed and new results on zirconium and Zircaloy-4, measured at low and at intermediate frequencies, are presented. It is shown that the damping spectrum of pure zirconium, for annealed polycrystals, shows a peak probably related to relaxation of grain or subgrain boundaries. The data on Zircaloy-4 show two peaks: one near the grain-boundary peak in the pure metal and another one at a higher temperature. Possible mechanisms for these peaks are discussed. Finally, the high-temperature internal friction background of zirconium and zirconium alloys is analyzed and, for Zircaloy-4, the apparent activation enthalpy is found to be related to the grain size.     

圆管通道底部再淹没过程实验研究

为验证和优化再淹没模型,通过实验研究了圆管通道内再淹没阶段流动换热特性,获得了不同工况下壁面温度的变化规律,实验工况范围为：入口冷却剂流速3~15 cm/s、入口过冷度15~75 ℃、初始壁面峰值温度340~600 ℃、实验压力0.2~0.4 MPa、加热功率1.3~2.3 kW/m。分析了初始壁温、冷却剂入口温度、入口流速及加热功率对骤冷时刻与骤冷温度的影响。结果表明,骤冷时刻与骤冷温度均随初始壁温、冷却剂入口温度以及加热功率的增加而增加,随入口冷却剂流速的增加而减小。