液态铅铋合金回路氧输运特性的数值研究

为研究液态铅铋合金（LBE）冷却剂系统气态氧控装置——膨胀箱中覆盖气体的氧输运特性,利用计算流体动力学（CFD）软件ANSYS Fluent对氧输运进行了数值计算。根据覆盖气体流动特性和混合气体中低氧分压特点,对膨胀箱气相空间进行简化,将气-液交界面视为氧浓度恒定的自由表面边界,采用组分输运模型计算气体和液态LBE之间传质后的液态LBE氧浓度。结果表明,传质系数随液态LBE入口流速增大而增大,液态LBE入口流速增大则膨胀箱内气-液对流强度增加,有利于增强膨胀箱的氧输运;膨胀箱中液态LBE温度越高,则氧输运的平均传质系数越大;在液态LBE入口流速一定时,平均传质系数可表示为温度的递增函数。在饱和氧浓度阈值内,入口氧浓度和气-液交界面氧浓度不影响膨胀箱的传质系数,对液态LBE回路的氧浓度控制有利。本研究定量获得了使液态LBE回路处于合理氧浓度范围内的操作条件,为实验及系统设计提供数据参考。     

Behavior of steels in flowing liquid PbBi eutectic alloy at 420-600 °C after 4000-7200 h

This paper presents the results of steel exposure up to 7200 h in flowing LBE at elevated temperatures and is a follow-up paper of that with results of an exposure of up to 2000 h. The examined AISI 316 L, 1.4970 austenitic and MANET 10Cr martensitic steels are suitable as a structural material in LBE (liquid eutectic Pb₄₅Bi₅₅) up to 550 °C, if 10⁻⁶ wt% of oxygen is dissolved in the LBE. The martensitic steel develops a thick magnetite and spinel layer while the austenites have thin spinel surface layers at 420 °C and thick oxide scales like the martensitic steel at 550 °C. The oxide scales protect the steels from dissolution attack by LBE during the whole test period of 7200 h. Oxide scales that spall off are replaced by new protective ones. At 600 °C severe attack occurs already after 2000 and 4000 h of exposure. Steels with 8-15 wt% Al alloyed into the surface suffer no corrosion attack at all experimental temperatures and exposure times.     

Mass transfer of iron impurities in LBE loops under non-isothermal flow conditions

Lead-bismuth eutectic (LBE) regained interest as a target and a nuclear coolant in nuclear applications. However, the corrosion of the structural materials such as ferritic/martensitic and austenitic stainless steels remains a major issue. Usually, their corrosion behavior measured as the mass transfer by dissolution/precipitation of metal solutes in non-isothermal flowing LBE is tested in loop systems. The exposures usually last for several thousand hours but, to date, almost no reliable long-term experience is reported. A mass transfer model based on species conversion and experimentally verified flow parameters is proposed and applied to predict the corrosion rate of iron solute at dissolved oxygen levels typical for active oxygen control in LBE. The sensitivity of the model indicates that iron diffusion seems to play a decisive role.     

铅铋合金中Bi/Bi_2O_3型氧传感器准确性及稳定性测试研究

液态铅铋合金(LBE)中溶解氧浓度的精确测量是实现LBE中氧浓度控制的前提。本文用一自主研制的Bi/Bi2O3型氧传感器来测量LBE氧浓度,在静态氧饱和的LBE中分别进行了准确性及稳定性测试。准确性测试结果表明,在340~480℃范围内氧传感器电动势实验曲线随温度的变化与理论曲线一致,电动势绝对误差最大为-2.6 mV;稳定性测试结果表明,在450℃、50h内电动势绝对误差为-1.4mV,波动为4mV。     

Oxygen measurements in stagnant lead-bismuth eutectic using electrochemical sensors

Sensors are the major part of an active oxygen control system (OCS) to be used in ADS reactors employing lead bismuth eutectic (LBE). We tested Pt/air and Bi/Bi₂O₃ probes based on yttria-stabilized zirconia (YSZ) solid electrolytes. The sensors were calibrated by evaluating the electromotive force (EMF) - temperature dependencies in oxygen un-/saturated stagnant LBE compared to the van’t-Hoff’s isotherm. Also, probe kinetics while changing the H₂/H₂O ratio was studied. Typical, reproducible curves are presented confirming attainment of oxygen equilibrium between the fluids. The sensor outputs are deterministic, predictable. Exceptional small drifts were due to interfacial kinetics, not to the sensors behavior. Simultaneous testing of several probes in one melt was performed. The sensors seemed to be qualified for large scale use.     

Corrosion behaviour of stainless steels in flowing LBE at low and high oxygen concentration

The corrosion behaviours of austenitic steel AISI 316L and martensitic steel T91 were investigated in flowing lead-bismuth eutectic (LBE) at 400 °C. The tests were performed in the LECOR and CHEOPE III loops, which stood for the low oxygen concentration and high oxygen concentration in LBE, respectively. The results obtained shows that steels were affected by dissolution at the condition of low oxygen concentration (C_[O2] = 10⁻⁸-10⁻¹⁰ wt%) and were oxidized at the condition of high oxygen concentration (C_[O2] = 10⁻⁵-10⁻⁶ wt%). The oxide layers detected are able to protect the steels from dissolution in LBE. Under the test condition adopted, the austenitic steel behaved more resistant to corrosion induced by LBE than the martensitic steel.     

Effect of the presence of In and Sn in the oxygen chemistry in molten 44.5% lead-55.5% bismuth alloy

The oxygen activity and its control is a key parameter in the use of molten lead-bismuth eutectic LBE in accelerator-driven systems (ADS) reactors. The presence of pollutants in the molten alloy, such as metallic impurities dissolved from the structural material or from other sources, can modify the oxygen chemistry in the molten alloy. For this reason, the oxygen activity in molten LBE has been studied under the presence of In and Sn as a metallic impurities. All the experiments were performed with a shift of the covering gas from a reductive environment (Ar + 10% H₂) to air (20% O₂). These covering gas conditions were used to enable measurement of the electrochemical potential of the sensor in a low oxygen environment and under oxygen saturation conditions of the molten alloy (Me/LBE). All of the tests were performed at 500 °C and in stagnant conditions in an autoclave.     

On the kinetics of LME for the ferritic-martensitic steel T91 immersed in liquid PbBi eutectic

Use of heavy liquid metals (HLM), such as the Lead-Bismuth eutectic (LBE), is foreseen for targets and coolants in the newly designed accelerator driven systems (ADS). However, most of the structural materials suffer severe damage when in contact with the HLM. In particular, the simultaneous presence of load and environment can induce a phenomenon named Liquid Metal Embrittlement (LME) in the reference material (ferritic-martensitic steel T91). This phenomenon could give rise to high crack growth rates and the abrupt collapse of the structural material.In this study the effect of LBE on the crack growth rate of the T91 steel was evaluated. The effect of pre-exposure to flowing LBE was considered and assessed in terms of crack growth rates and fracture surface appearance.It was concluded that if conditions for wetting were reached during exposure in LBE, e.g. by dissolution or rupture of protective oxide layers, LME was likely to occur under stress, at 300 °C, regardless of the LBE chemistry.     

Thermal-hydraulic performance of heavy liquid metal in straight-tube and U-tube heat exchangers

Motivated by an increased interest in heavy liquid metal (lead or lead alloy) cooled fast reactors (LFR) and accelerator-driven system (ADS), the present paper presents a study on resistance characteristics and heat transfer performance of liquid lead bismuth eutectic (LBE) flow through a straight-tube heat exchanger and a U-tube heat exchanger. The investigation is performed on the TALL test facility at KTH. The heat exchangers have counter-current flow arrangement, and are made from a pair of 1-m-long concentric ducts, with the LBE flowing in the inner tube of 10 mm I.D. and the secondary coolant flowing in the annulus. The inlet temperature of LBE into the heat exchangers is from 200 °C to 450 °C with temperature drops from 0 °C to 100 °C within the LBE flow range of Re = 10⁴-10⁵. Analysis of the experimental results obtained provides a basic understanding and quantification of the regimes of lead-bismuth flow and heat transfer through a straight tube and a U-shaped tube. The unique data base also serves as benchmark and improvement for system thermal-hydraulic codes (e.g. RELAP, TRAC/AAA) whose development and testing were dominantly driven by applications in water-cooled systems. Lessons and insights learnt from the study and recommendations for the heat exchanger selection are discussed.     

High temperature oxidation of Fe-9Cr-1Mo steel in stagnant liquid lead-bismuth at several temperatures and for different lead contents in the liquid alloy

This research project deals with the feasibility studies concerning the construction of an hybrid reactor for the transmutation of long-lived radioactive wastes. In this context, the liquid lead-bismuth eutectic (LBE) is considered to be a good candidate for the spallation target material needed for the neutrons production necessary to the transmutation. In this hybrid reactor, the LBE, which is enclosed in a T91 (Fe-9%Cr) steel container, can induce corrosion concerns. If the oxygen content dissolved in Pb-Bi is higher than the needed content for magnetite formation, corrosion proceeds by oxidation of the steel. Previously, specific results were reported, obtained in stagnant liquid LBE at 470 °C. An analytical model taking into account the oxide layer structure has been carried out. It involves iron, oxygen and chromium bulk diffusion and diffusion via preferential paths such as liquid lead-bismuth nano-channels incorporated in the oxide layer structure and grain boundaries. In this paper, experimental results on corrosion kinetics, obtained at different temperatures with different percentages of lead in the lead-bismuth alloy, are presented. The model, adapted to the different experimental conditions, is compared to these kinetics and to experimental points coming from the literature at different temperatures in LBE, in pure lead and in pure bismuth.     

Measurement technique developments for LBE flows

We report on the development of measurement techniques for flows in lead-bismuth eutectic alloys (LBE). This paper covers the test results of newly developed contactless flow rate sensors as well as the development and test of the LIDAR technique for operational free surface level detection. The flow rate sensors are based on the flow-induced disturbance of an externally applied AC magnetic field which manifests itself by a modified amplitude or a modified phase of the AC field. Another concept of a force-free contactless flow meter uses a single cylindrical permanent magnet. The electromagnetic torque on the magnet caused by the liquid metal flow sets the magnet into rotation. The operation of those sensors has been demonstrated at liquid metal test loops for which comparative flow rate measurements are available, as well as at the LBE loops THESYS at KIT and WEBEXPIR at SCK-CEN. For the level detection a commercial LIDAR system was successfully tested at the WEBEXPIR facility in Mol and the THEADES loop in Karlsruhe.     

Corrosion behaviors of US steels in flowing lead-bismuth eutectic (LBE)

Corrosion tests of several US martensitic and austenitic steels were performed in a forced circulation lead-bismuth eutectic non-isothermal loop at the Institute of Physics and Power Engineering (IPPE), Russia. Tube and rod specimens of austenitic steels 316/316L, D-9, and martensitic steels HT-9, T-410 were inserted in the loop. Experiments were carried out simultaneously at 460 °C and 550 °C for 1000, 2000 and 3000 h. The flow velocity at the test sections was 1.9 m/s and the oxygen concentration in LBE was in the range of 0.03-0.05 wppm. The results showed that at 460 °C, all the test steels have satisfactory corrosion resistance: a thin protective oxide layer formed on the steel surfaces and no observable dissolution of steel components occurred. At 550 °C, rod specimens suffered rather severe local liquid metal corrosion and slot corrosion; while tube specimens were subject to oxidation and formed double-layer oxide films that can be roughly described as a porous Fe₃O₄ outer layer over a chrome-rich spinel inner layer. Neglecting the mass transfer corrosion effects by the flowing LBE, calculations based on Wagner’s theory reproduce the experimental results on the oxide thickness, indicating that the oxide growth mechanism of steels in LBE is similar to that of steels in air/steam, with slight modification by dissolution and oxide dissociation at the liquid metal interface.     

Fundamental data: Solubility of nickel and oxygen and diffusivity of iron and oxygen in molten LBE

Experiments for determining nickel solubility limit and iron diffusion coefficient are presented and their results are discussed. Nickel solubility limit is determined by two methods: ex situ by solid sampling followed by ICP-AES analysis and in situ by Laser Induced Breakdown Spectroscopy and their results are compared. The iron diffusion coefficient is obtained using the technique of rotating specimen dissolution.Also a method to determine the oxygen solubility and diffusivity in LBE is developed and results at 460, 500 and 540 °C are presented. It is based on the following electrochemical cell: O₂ (reference mixture), Pt //YSZ//O₂ (LBE) which can work as an oxygen sensor or as a coulometric pump.     

Data acquisition and control system for lead-bismuth loop KYLIN-Ⅱ-M

Among different heavy liquid metals(HLMs), lead-bismuth eutectic(LBE) is considered at present as a potential candidate for the coolant of new generation fast reactors(critical and subcritical) and for liquid spallation neutron sources and accelerator driven systems(ADS). A high temperature liquid LBE loop, KYLIN-II-M,has been built to study the characteristics of corrosion and fluidity of LBE at the Institute of Nuclear Energy Safety Technology. However, due to the sensors and execution components of the loop work at high temperatures and in severely corrosive environments, the reliability and security of the data acquisition and control system(DACS) of KYLIN-II-M face challenges during the loop operation. In order to meet the urgent needs for KYLIN-II-M’s long-term stable operation, a virtualization and redundancy control system has been developed.The onsite operation result shows that the DACS is stable and reliable. In this paper, the experimental results are described in detail.     

Corrosion experiments and materials developed for the Japanese HLM systems

The static corrosion tests in lead-bismuth eutectic (LBE) were conducted from 450 °C to 600 °C to understand corrosion behavior and develop corrosion resistant materials for heavy liquid metal systems. While increase of Cr content in steels enhances corrosion resistance in LBE, the effect approaches a constant value above 12 wt% of Cr. Corrosion depth in LBE increases with increasing temperature and corrosion attack becomes severe above 550 °C even under the condition of high oxygen concentration. Nickel dissolution and Pb-Bi penetration occur in 316SS and JPCA above 550 °C under the condition of high oxygen concentration. When oxygen concentration decreases below the level of Fe oxide formation, corrosion attack on these steels also becomes violent due to dissolution of various elements and grain boundary corrosion. Whereas additions of 1.5 wt% Si to T91 and 2.5 wt% Si to 316SS improve corrosion resistance, the effect is insufficient taking fluctuation of oxygen concentration in LBE into consideration. Furthermore, addition of 1.5 wt% Si to T91 causes rise in DBTT. A new coating method using Al, Ti and Fe powders produces corrosion resistant coating layers on 316SS. The coating layers containing 6-8 wt% Al exhibit good corrosion resistance at 550 °C for 3000 h in LBE containing 10⁻⁶-10⁻⁴ wt% of oxygen.     

Electrochemical oxygen sensors for on-line monitoring in lead-bismuth alloys: status of development

This paper presents the state of development of oxygen sensors based on the electromotive force (emf) measurement at null current, using yttria stabilized zirconia as solid electrolyte for application in liquid lead-bismuth eutectic (LBE), which is envisaged as a nuclear coolant or as a spallation target in accelerator driven system (ADS) for nuclear waste transmutation. The assembly procedure, the calibration method, as well as the summary of the various validation tests undergone in both static and loop facilities are presented so as to define a real state of achievement and the basics needs for further studies. The sensors are efficient, accurate, rapid and reliable for research loops. However, the poor mechanical resistance as well as the effect of traces of impurities, promoting an increasing time-drift under certain conditions, are to be further studied to improve the sensor reliability for a nuclear use. The oxygen and chromium solubilities were reassessed in the process of the sensor testing, those relations are also given and discussed.     

Active oxygen control by a PbO mass exchanger in the liquid lead–bismuth eutectic loop: MEXICO

Accurate control of dissolved oxygen concentration is crucial in order to use liquid lead alloys as a coolant of advanced nuclear systems. An oxygen control system based on PbO mass exchanger (PbO MX) technology was implemented in order to control the dissolved oxygen concentration in the liquid lead--bismuth eutectic (LBE) loop MEXICO. The oxygen control system consisted of a packed bed of PbO spheres, an oxygen sensor and a pneumatic control valve. The concentration of dissolved oxygen in the loop was controlled by regulating the LBE flow through the PbO MX using a proportional–integral–derivative (PID) controller with feedback from the oxygen sensor. Highly accurate control of the dissolved oxygen concentration in the loop was achieved by this system.     

Performance of oxygen sensor in lead–bismuth at high temperature

Performance of yttria-stabilized zirconia solid electrolyte oxygen sensor with a reference electrode of Bi/Bi₂O₃ was investigated. The oxygen sensor was tested in alumina vessel in order to prevent generating of impurities. The oxygen potential in the melt was controlled by injecting steam–hydrogen gas mixture (P_H2/P_H2O) into stagnant LBE. The electromotive force (EMF) of the sensor was compared with the theoretical EMF derived from the Nernst equation at various LBE temperatures (550–700 °C). The influences of various injection gas temperatures (200–500 °C) on the sensor output were also investigated. It was found that the sensor signals of the oxygen potential in LBE have not been affected by the injection gas temperature. The results also showed that the measured EMFs were in good agreement with the theoretical values of the EMF. The material aspects were investigated as well. The SEM (Scanning Electron Microscope) devices were used to analyze the cross-section of oxygen sensors after the exposition to LBE at 700 °C for 1000 h. The SEM micrograph showed that the yttria-stabilized zirconia solid electrolyte had an excellent corrosion resistance to the high temperature LBE as the working fluid and high temperature bismuth as the reference fluid.     

A lattice Boltzmann modeling of corrosion behavior and oxygen transport in the natural convection lead-alloy flow

Corrosion of structural materials presents a critical challenge in the use of lead–bismuth eutectic (LBE) or liquid lead as a nuclear coolant in accelerator-driven systems and advanced reactors. Actively controlling the oxygen concentration in LBE has been proved to be effective to mitigate corrosion under certain conditions. For mixing the oxygen uniformly and quickly, natural convection is proposed to enhance the oxygen transport. In the present study, a lattice Boltzmman simulation of coupled natural convection and lead bismuth eutectic flow in a simplified container was carried out to study characteristics of the oxygen transport and corrosion behaviors. It is assumed that the corrosion product (mainly iron) concentration is at its equilibrium level at the wall. The wall boundary condition for the mass transfer of corrosion production was taken based on the active-oxygen-control model. To examine the effect of different nature convection flow patterns on corrosion behavior and oxygen transport, three heating cases, which correspond to one-, two- and four-vortex flow patterns, are examined. Both of the local and average Sherwood number at the wall, distribution of corrosion product and oxygen, and oxygen diffusion time are analyzed. Some useful information was obtained to understand the mechanism of corrosion behavior and oxygen transport in the LBE system.