An improved interface model for molten corium-concrete interaction

In the field of research for Severe Accidents of PWRs, calculation results are needed to estimate when corium achieves basemat melt-through. In this framework, knowledge of the heat transfer coefficient as well as the temperature at the interface between the melt and the solid are key issues. It has been previously emphasized that physico-chemistry of the melt (composition) affects the temperature. However, the effect of gas sparging and liquid concrete release on the mechanical stability of the solid layer and on the interface temperature has not been analysed in detail. ARTEMIS 1D tests were launched to analyse the phenomenology at the interface. A general conclusion for all these tests is that a solid medium enriched in refractory species exists at the interface between the pool and the concrete.Tests 2 and 6, which are close to reactor representative conditions, could be well described with the assumption T_interface = T_liquidus. The analysis of tests 3 and 4 revealed that the interfacial medium is thicker by a factor of 4-5 times than calculated with the assumption of pure conduction heat transfer. Detailed analysis leads to the conclusion that the interfacial medium is made of a porous layer of refractory particles embedded in a liquid phase. The liquid density difference, between the porous medium and chimneys, results in recirculation of the liquid in the porous layer. This recirculation is responsible for a convective contribution to heat transfer through the porous layer. The convective heat flux is partly linked to cooling of the recirculating liquid, but also to its partial solidification. The solidification results in gradual plugging and enrichment of the porous layer in refractory species and in the increase of the resistance to heat transfer. The phenomena have been modelled and ARTEMIS tests 3 and 4 are well reproduced. The complete plugging of the porous medium, associated with thermodynamic equilibrium at the interface between the solid medium and the pool leads naturally to the solid crust model implemented in TOLBIAC-ICB. The latter model appears, thus, as a simplification of the porous medium approach described here.Thick interfacial layers, which have composition between refractory and corium mixture, have been observed in ACE and MACE tests with LCS (Limestone-Common Sand) or Limestone concrete and can be explained with the proposed model approach. For siliceous concrete, convection within a porous medium is not possible due to the large viscosity.     

碳化硅基新型包覆燃料颗粒的设计及制备

TRISO型包覆燃料颗粒可将核裂变产生的气体、固体裂变产物束缚在燃料颗粒内部,是高温气冷堆安全性的重要保障。为满足未来超高温气冷堆在更高温度及更高燃耗条件下对燃料元件的要求,需对传统TRISO颗粒进行优化和改进。基于包覆颗粒的破损机制,设计了两种SiC基新型包覆颗粒,一种采用疏松SiC层替代疏松热解炭层,包覆层由内而外依次为疏松SiC层、内致密热解炭层、致密SiC层、外致密热解炭层;另一种为全SiC包覆结构,包覆层由内而外依次为内层疏松SiC层、SiC过渡层、外层致密SiC层。根据结构设计,采用流化床化学气相沉积法实验探索了疏松SiC的形成机制及包覆工艺条件,并利用SEM、XRD等进行材料分析,最终成功实现了两种新型包覆颗粒的大规模制备。更进一步,提出了全SiC基燃料元件的概念,并制备了球形和柱形全SiC基模拟燃料元件。     

The cyclic nature of corrosion of zircaloy-4 in 633 K water

Optical and electron microscopic examination of cathodic-vacuum-etched cross-sections of corrosion films on zircaloy-4, produced during 108.86-Ms (1260-day) tests in 633 K water, revealed alternate dense columnar-grained layers and narrow porous layers lying parallel to the metal surface, but no through-thickness openings except at corners. Correlation of layer structures with corrosion test data indicates that the corrosion process consists of repeated cycles of cube-root kinetics. During each cycle, a new protective layer grows at the metal-oxide interface. At a critical thickness, the layer suddenly becomes non-protective, causing transition to the initially rapid corrosion rate of a new cycle. Porous layers mark the location of the interface at the time of each transition. Variations in post-transition corrosion rates are related to variations in the cube-root rate constant, average film density, and critical layer thickness. A stress-controlled corrosion mechanism is proposed.     

颗粒尺寸分析仪法测量包覆颗粒疏松层密度的研究

包覆燃料颗粒的质量对于高温气冷堆安全运行起着重要作用。低密度热解炭层作为包覆的第一层非常关键,关系到包覆燃料颗粒和燃料元件的性能质量。本文介绍一种用颗粒尺寸分析仪测量疏松热解炭层密度的方法,该方法采用颗粒尺寸分析仪测量包覆前后颗粒的直径,再结合天平称得包覆前后颗粒的质量,经过计算得到包覆燃料颗粒疏松热解炭层的密度。对该方法测量包覆燃料颗粒疏松层密度的测量精度进行了验证。结果表明,该方法的测量精度满足测试要求,且该方法快速、便捷,适于工程应用。     

阳极氧化法制备多孔硅中的正电子湮没及扫描电子显微镜研究

用正电子湮没技术和扫描电子显微镜研究研究了阳极氧法法制备的多孔硅材料。正电以实验表明,随着阳极氧化时间的延长,平均寿命值增大,空位缺陷增多,长寿命成分较少。扫描电子显微显示,在阳极氧化过程中有尺寸为几μｍ的单晶球形成。     

非饱和水通过双层孔隙介质渗流的定量实验

非饱和水通过双层孔隙介质的渗流对于放射性废物近地表处置库的顶盖设计具有重要意义。本文主要介绍非饱和水通过以黄土（细颗粒）和石英砂（粗颗粒）组成的双层孔隙介质渗流定量实验的装置、方法及其结果。从实验结果可见：黄土中的非饱和水在下渗过程中遇到石英砂层时，即使石英砂层很薄，且粒度很小，下渗水也发生绕流现象；相对绕流量的大小随水的喷淋强度的增大而减小，随石英砂层厚度的增加而增加。另外，实验发现，相当部分的绕流水是紧石英砂层的下表面运动的。由实验结果推断，在石英砂粒径0.2-0.45mm、埋深20cm情况下，不起绕流作用的石英砂层厚度≤1mm；对于≥2mm厚的石英砂层，相对绕流量达100％的喷淋强度需低于5mm/d。     

A mathematical model for crevice corrosion under porous deposits

A model has been developed to investigate the corrosion of steels in a thin, narrow crevice formed between the metal surface and an oxygen-permeable, porous deposit. A thin electrolyte layer exists within the deposit, due to geochemical fluids dripping onto a deposit-covered surface or due to the adsorption of moisture by a hygroscopic deposit. Mass transfer by diffusion and ion migration is considered in both the electrolyte films inside and outside of the crevice. The main reactions considered are the anodic dissolution of the alloy substrate, hydrolysis of the alloying element cations, dissociation of water, and the cathodic reduction of oxygen, hydrogen ion, and water. Special attention has been given to the role of parameters connected with the porous layer (porosity, tortuosity, and the layer thickness) on the rate of crevice corrosion. It is shown that the cavity acts as an ‘electrochemical amplifier’ from the point of view of the concentration of aggressive anions that leads to increasing of corrosion rate and to a higher probability of pit nucleation within the crevice.     

Transient response simulation of gas separation membrane module for an atmosphere detritiation system

Transient response of a gas separation membrane module for the atmosphere detritiation system was numerically simulated with a mass transfer model. The module contains thousands of hollow fiber type polyimide membranes. The simulation model took into account permeation of water vapor through the dense layer of the membrane, diffusive transfer through the porous support layer and adsorption/desorption of water vapor into the matrix of the porous layer. The slow responses of the water vapor concentration in the retentate and the permeation rate were well reproduced by the present simulation, and transient changes in a follow fiber membrane were investigated in detail. The inventory and the mean residence time of water vapor at 303 K were estimated for the commercial membrane module (UMS-B2, Ube industries, Ltd.) as 5.7 × 10^?3 mol and 380 s, respectively.     

氢同位素色谱分析研究进展

对氢同位素色谱分析研究进展进行了综述,内容主要包括分析原理、材料研究与分析柱研制。材料研究主要包括改性材料的负载量、阳离子种类、阴离子种类。分析柱研制在材料研究的基础上进行,根据测试需求,在材料性质、柱型、柱长等方面进行设计,优选出适合于具体使用场景的建议柱型。无过渡金属磁性催化作用的氧化铝PLOT(porous layer open tubular)柱,适用于氢同位素的正-仲态分离;含过渡金属磁性催化作用的氧化铝色谱柱,适用于氢同位素的分子态分离。一般地,PLOT柱使用寿命较短,但其适用于快速分析;微填充柱分析时间较长,但性能稳定性较好。有序介孔材料(OMMs),具有较大比表面积,通过调节介孔孔径有望提升氢同位素低温分离性能;过渡金属离子(如Cu(Ⅰ))对氢分子的Kubas作用,有望实现氢同位素常温洗脱分离。     

双层孔隙介质中非饱和渗流的水势分布与变化

水势反映土壤水的能态,而水势梯度则是决定水流方向和速度的重要因素。本文主要介绍非饱和水通过以黄土(细颗粒)和石英砂(粗颗粒)组成的双层孔隙介质渗流的水势分布和变化的实验方法和主要实验结果,用以进一步分析解释以前工作中观察到的非饱和水在双层孔隙介质中的绕流现象。实验结果表明：在喷水强度一定情况下,石英砂层中的水势随石英砂层厚度的增加而减小;在石英砂层厚度一定情况下,石英砂层中的水势随喷水强度的增加而增大;石英砂层上方的水部分通过石英砂层向下流动,部分绕过石英砂层向下流动;绕过石英砂层的水部分地紧贴石英砂层下表面向石英砂层下方的黄土中流动。这是一些值得进一步探讨的现象。     

Experimental study on in-vessel debris coolability in ALPHA program

In-vessel debris coolability experiments were performed in ALPHA program at JAERI. Aluminum oxide (Al₂O₃) produced by a thermite reaction was used as a debris simulant. Approximately 30 and 50 kg of Al₂O₃ were poured into a pool of nearly saturated water at the ambient pressure of approximately 1.3 MPa formed in a lower head experimental vessel. The post-test visual observation and measurement using an ultrasonic technique indicated the formation of a thin porous layer at the vicinity of the surface of the solidified Al₂O₃ and the interfacial gap between the solidified Al₂O₃ and the lower head experimental vessel wall. Thermal transient characteristics on the lower head experimental vessel wall observed in the experiments implied that the interfacial gap and the thin porous layer in the solidified Al₂O₃ layer acted as a thermal resistance during the initial heat-up stage, and water subsequently penetrated into the interfacial gap to effectively cool the lower head experimental vessel wall. The maximum heat flux removed from the experimental vessel was ranged from approximately 190 to 360 kW m⁻² while the temperature of the vessel wall decreased rapidly.     

Fatigue testing of metallurgically-bonded EBR-II superheater tubes

Fatigue crack growth tests were performed on 2¼Cr–1Mo steel specimens machined from ex-service experimental breeder reactor-II (EBR-II) superheater duplex tubes. The tubes had been metallurgically-bonded with a 100 μm thick Ni layer; the specimens incorporated this bond layer. Fatigue crack growth tests were performed at room temperature in air and at 400 °C in air and humid Ar; cracks were grown at varied levels of constant ΔK. In all conditions the presence of the Ni bond layer was found to result in a net retardation of growth as the crack passed through the layer. The mechanism of retardation was identified as a disruption of crack planarity and uniformity after passing through the porous bond layer. Full crack arrest was only observed in a single test performed at near-threshold ΔK level (12 MPa√m) at 400 °C. In this case the crack tip was blunted by oxidation of the base steel at the steel–nickel interface.     

Microscopic thermal characterization of HTR particle layers

This paper presents thermal diffusivity measurements of HTR fuel particle pyrolytic carbon layers at room temperature. The photoreflectance microscopy (PM) technique is used to characterize particle layers at a microscopic scale. Nevertheless, buffer layer needs a particular analysis due to its porous structure. Indeed, measurements by PM on this material only permit to obtain the thermal diffusivity of the solid skeleton, whose homogeneous zones surface does not exceed 100 μm². These characteristics make, on the one hand, delicate the use of PM, and on the other hand, require the use of a numerical homogenization technique. This model takes into account the properties of gas confined in the pores, to simulate the conduction heat flux traveling through the layer in relation with its microstructure and to estimate an effective thermal conductivity of the entire layer. This approach is validated by infrared microscopy measurement of the effective thermal diffusivity of the especially elaborated thicker buffer layer. Last, the first tests to characterize the silicon carbide layer are presented.     

Porous silicon-based passivation and gettering in polycrystalline silicon solar cells

In this work, we report on the effect of introducing a superficial porous silicon (PS) layer on the electrical characteristics of polycrystalline silicon solar cells. The PS layer was formed using a vapour etching (VE)-based method. In addition to its known anti-reflecting action, the forming hydrogen-rich PS layer acts as a passivating agent for the surface of the cell. As a result we found an improvement of the I–V characteristics in dark conditions and AM1 illumination. We show that when the formation of a superficial PS layer is followed by a heat treatment, gettering of impurities from the polycrystalline silicon material is possible. After the removal of the PS layer and the formation of the photovoltaic (PV) structure, we observed an increase of the light-beam-induced-current (LBIC) for treatment temperatures not exceeding 900 °C. An improvement of the bulk minority carrier diffusion length and the grain boundary (GB) recombination velocity were observed as the temperature rises, although a global decrease of the LBIC current was observed for temperatures greater than 900 °C.     

Transient Behaviors of Gas in Thermal Insulation Media at Rapid Depressurization

Thermal insulation systems are often used to high-temperature gas cooled reactors.

In this paper, transient behavior of the gas flow in thermal insulation media was systematically analyzed in the case of sudden decrease in a coolant pressure. The structure of these systems is capable of substituting for the simplified model that the gas in a containment filled with porous insulation media exhausts from a balancing hole to main flow duct. In the case of rapid depressurization, these behaviors were calculated by using equations of continuity and motion based on the Darcy flow model with area ratio of a balancing hole and permeability of porous insulation media as parameters. The transient pressure difference of a hot liner wall between the main flow helium and the insulation layer induced at depressurization was numerically analyzed. It was revealed from analytical results that transient behaviors were strongly influenced by prescribed parameters, and experimental results can be explained by using the analytical model.     

Analysis of porous silicon

Porous silicon, suitable after oxidation for dielectric isolation, has been produced successfully by anodizing silicon in strong HF. The oxidized layer has been shown to have promise in device manufacture, providing high packing densities and radiation hardness. Anodizing has been carried out using both single and double cells, following the effects of current density. HF concentration and silicon resistivity. The resultant porous layers have been characterised with respect to composition and structure. The materials produced differ considerably in lattice strain, composition and reactivities. Prompt radiation analyses ¹⁹F(p,αγ), ¹⁶O(d,α), ¹²C(d,p), are useful for monitoring the anodizing procedures and subsequent oxidation: currently, interest centres on the mechanistic information obtained. RBS analysis using α-particles gives a much lower Si response from porous than from bulk silicon. Glancing angle proton recoil analyses reveal considerable quantities of hydrogen in the porous layers. These mutually consistent findings have considerable mechanistic significance; extensive Si-H bonding occurs following a 2 equivalent Faradaic process.     

The quenching behavior of aqueous nanofluids around rods with high temperature

The quenching behavior of aqueous nanofluids containing various volume fractions of Al₂O₃, SiO₂, TiO₂ and CuO nanoparticles is experimentally investigated around high temperature brass rod (diameter 20 mm × 75 mm). The experiments are performed at saturated conditions under atmospheric pressure. The results show that the quenching process is strongly dependent on the kind of nanoparticle, as well as its volume fraction. Although it is not observed from the first run in nanofluids, the quenching time is considerably shortened during the repetitive quenching tests. After the repetition tests in nanofluids, a nanoparticles porous layer occurs on the quenched surface and thus, the film boiling vanishes. The surface contact angles and the surface roughness of the quenched surfaces are measured. The results show that contact angles decreases and the surface roughness increases. It can be concluded that the primary reason of critical heat flux enhancement is the change of the surface characteristics due to the porous layer. In addition, the results also showed that there is no significant change in the nucleate boiling heat transfer.     

1993 National Symposium on Atomic Energy,Tokyo, Japan

A steady-state simulation model of the gas separation system using a hollow-filament type membrane has been proposed. The mass transfer coefficients in the non-porous thin layer, in the porous support layer of the membrane and in the boundary layer of the membrane surface are estimated in the model. The four types of flow patterns: cross flow, mixing flow, concurrent flow and counter current flow, are also considered in the model. The mass transfer through the non-porous thin layer of the membrane controls the overall mass transfer by ~99%. The experimental observations of TPL (Tritium Process Laboratory in JAERI) for N₂–H₂ and Air—H₂ systems agreed with the calculated results of the cross flow under a set of typical conditions (disposal volume of 2.78×10^?3 Nm³/s, feed-side pressure of 3.44×10⁵Pa, and permeated-side pressure of 1.07×10⁴ Pa). The validity of the simulation method was thus proved. For Air-H₂-H₂O system also, the recovery ratios calculated for H₂ are in good agreement with the experimental observations. However, the calculated recovery ratios of water vapor were slightly smaller than the experimental observations. This discrepancy may result from the difference in separation mechanism between H₂ and water vapor, or the construction change of membrane caused by the existence of water vapor.     

Experimental Study on Transient Behaviors of Gas in Thermal Insulation Media at Rapid Depressurization

Thermal insulation system is often used to high temperature gas-cooled reactors. In the present paper, transient behavior of the gas flow in thermal insulation media is experimentally studied in the case of sudden decrease of coolant pressure. The structure of these systems is capable of substituting for the simplified model that the gas in a container filled with porous insulation media exhausts from a balancing hole to the main flow. In the case of rapid depressurization, transient behaviors are measured by pressure sensors along an axial direction of the insulation layer, changing experimental parameters such as pressure gradient, opening of a balancing hole and packed density. The induced pressure is measured along the axial direction of the insulation layer. The induced pressure difference and the peak value of pressure difference are summarized with parameters. Lastly, a satisfactory agreement between experimantal and analytical results is obtained for several specified cases of testing.     

快速响应PNIPA／Fe3O4复合凝胶辐射制备与性能研究

采用化学共沉淀法制备了四氧化三铁粒子,以N-异丙基丙烯酰胺（NIPA）、N,N-亚甲基双丙烯酰胺（MBA）和聚乙二醇（PEG）为原料,以60Coγ,射线为放射源,辐照聚合制备了多孔PNIPA／Fe3O4复合水凝胶,并对其温度敏感性、平衡溶胀率进行了表征。研究发现：磁性四氧化三铁纳米粒子在凝胶中分散均匀;凝胶具有明显的温度敏感性;致孔剂的添加提高了水凝胶的平衡溶胀率,多孔复合水凝胶失水率达96％,比普通磁性水凝胶失水率提高了约76％;致孔剂的添加使复合凝胶的最低临界相转变温度由34℃升高至37℃左右。