液态铅铋回路设计研制与材料腐蚀实验初步研究

铅铋合金共晶体是加速器驱动次临界系统(ADS)重要的散裂靶材料和冷却剂候选材料,也是先进快中子堆的重要冷却剂材料,液态铅铋回路是开展液态铅铋合金相关技术研究的必备实验平台。FDS团队正在设计研制KYLIN系列铅铋实验回路,本文基于中国首座热对流铅铋回路KYLIN-Ⅰ开展了马氏体钢T92、CLAM和奥氏体钢316L在480℃下,流速为0.14 m/s的饱和氧浓度铅铋中的腐蚀实验研究。初步实验结果显示,三种实验材料均发生氧化腐蚀。     

Simulation study of steels corrosion phenomenon in liquid lead–bismuth cooled reactors using molecular dynamics methods

Corrosion phenomena of stainless steel in liquid lead–bismuth as a coolant in nuclear fast breeder reactor are a field which is intensively investigated by the researchers in the recent year. We try to study this corrosion phenomena by computer simulation using molecular dynamics methods. The initial positions of the system were taken from the crystal structure data including the cell parameters and the types of the crystal. In this simulation, interatomic potential between Fe–Fe, Pb–Pb, Bi–Bi, Ni–Ni and Cr–Cr was assumed to follow Lennard–Jones potential. The Lennard–Jones potential parameters have been derived by fitting the data available in the literature. Nickel and chromium atoms were substituted into Fe crystal with the percentage of 10% and 16% to construct systems like SS 316. Molecular dynamics simulation has been done by interfacing iron and steel with liquid lead and liquid lead–bismuth in several temperatures. The result of this simulation showed that lead atoms can diffuse into Fe–10%Ni–16%Cr about 1.18 Å at 773 K while in Fe–10%Ni and Fe–16%Cr about 7.25 Å and 11.08 Å, respectively.     

Alkaline extraction of polonium from liquid lead bismuth eutectic

The production of highly radiotoxic polonium isotopes poses serious safety concerns for the development of future nuclear systems cooled by lead bismuth eutectic (LBE). In this paper it is shown that polonium can be extracted efficiently from LBE using a mixture of alkaline metal hydroxides (NaOH + KOH) in a temperature range between 180 and 350 °C. The extraction ratio was analyzed for different temperatures, gas blankets and phase ratios. A strong dependence of the extraction performance on the redox properties of the cover gas was found. While hydrogen facilitates the removal of polonium, oxygen has a negative influence on the extraction. These findings open new possibilities to back up the safety of future LBE based nuclear facilities.     

AFM and MFM characterization of oxide layers grown on stainless steels in lead bismuth eutectic

Fast reactors and spallation neutron sources may use lead bismuth eutectic (LBE) as a coolant. Its thermal physical and neutronic properties make it a high performance nuclear coolant and spallation target. The main disadvantage of LBE is that it is corrosive to most steels and container materials. Active control of oxygen in LBE will allow the growth of protective oxides on steels to mitigate corrosion. To understand corrosion and oxidation of candidate materials in this environment and to establish a solid scientific basis the surface structure, composition, and properties should be investigated carefully at the smallest scale. Atomic force microscopy (AFM) is a powerful tool to map out properties and structure on surfaces of virtually any material. This paper is a summary of the results from AFM measurements on ferritic/martensitic (HT-9) and austenitic (D9) steels that are candidates for liquid metal cooled reactors.     

Review of liquid metal corrosion issues for potential containment materials for liquid lead and lead–bismuth eutectic spallation targets as a neutron source

Lead (Pb) and lead–bismuth eutectic (44Pb–56Bi) have been the two primary candidate liquid metal target materials for the production of spallation neutrons. Selection of a container material for the liquid metal target will greatly affect the lifetime and safety of the target subsystem. For the liquid lead target, niobium–1 wt% zirconium (Nb–1Zr) is a candidate containment material for liquid lead, but its poor oxidation resistance has been a major concern. In this paper, the oxidation rate of Nb–1Zr was studied based on the calculations of thickness loss resulting from oxidation. According to these calculations, it appeared that uncoated Nb–1Zr may be used for a 1-year operation at 900°C at P_O2=1×10^–6 Torr, but the same material may not be used in argon with 5-ppm oxygen. Coating technologies to reduce the oxidation of Nb–1Zr are reviewed, as are other candidate refractory metals such as molybdenum, tantalum, and tungsten. For the liquid lead–bismuth eutectic target, three candidate containment materials are suggested, based on a literature survey of the materials’ compatibility and proton irradiation tests: Croloy 2-1/4, modified 9Cr–1Mo, and 12Cr–1Mo (HT-9) steel. These materials seem to be used only if the lead–bismuth is thoroughly deoxidized and treated with zirconium and magnesium.     

Preliminary study on the measurement technology of oxygen concentration in liquid lead bismuth

液态铅铋合金是加速器驱动次临界系统(ADS)中散裂靶兼冷却剂的主要候选材料.氧浓度是影响液态铅铋合金(LBE)对结构材料腐蚀的关键因素,而氧传感器是实现液态铅铋合金中氧浓度精确测量的重要部件,本研究设计研制了一种液态铅铋系统氧传感器并基于自主研制的高温液态铅铋合金氧测控预研平台,初步开展了氧饱和LBE中的氧浓度测量实验.实验结果显示,300～400℃的氧饱和LBE中,氧传感器的电压信号(E)随温度(T)变化的实验曲线与理论曲线变化趋势相吻合;相对于300℃＜T＜350℃温度范围,氧传感器在350℃＜ T＜400℃范围内的测量性能更好,仪器本身的系统误差约为17mV.     

Corrosion, Al containing corrosion barriers and mechanical properties of steels foreseen as structural materials in liquid lead alloy cooled nuclear systems

A key problem in development of heavy liquid metal cooled nuclear energy and transmutation reactors is the corrosion of structural and fuel. Above 500 °C steels have to be protected by stable, thin oxide scales. A well understood measure is alloying of stable oxide formers into the surface. Two methods, alloying an Al layer into the steel surface using pulsed electron beams (GESA - gepulste Elektronenstrahlanlage) and coating the surface with an Al-alloy with subsequent GESA treatment are applied. In the range of 4-10 wt% Al on the surface a stable thin alumina scale is formed by Al diffusion to the surface and selective oxidation. The alumina scale grows only very slowly and prevents migration of oxygen into the steel as well as migration of steel components onto the surface. A number of corrosion experiments showed the good protective behaviour of Al scales in LBE with 10⁻⁶ wt% oxygen up to 650 °C and for exposure times up to 10,000 h. Furthermore the influence of parameters like stresses in the cladding wall, creep behaviour, different flow velocities of the LBE and changing temperatures and oxygen concentrations in LBE is discussed. This paper will provide an overview on the activities concerning Pb-PbBi corrosion and corrosion protection performed at the Institute of Pulsed Power and Microwave Technology (IHM) at the KIT.     

Compatibility of martensitic/austenitic steel welds with liquid lead bismuth eutectic environment

The high-chromium ferritic/martensitic steel T91 and the austenitic stainless steel 316L are to be used in contact with liquid lead-bismuth eutectic (LBE), under high irradiation doses. Both tungsten inert gas (TIG) and electron beam (EB) T91/316L welds have been examined by means of metallography, scanning electron microscopy (SEM-EDX), Vickers hardness measurements and tensile testing both in inert gas and in LBE. Although the T91/316L TIG weld has very good mechanical properties when tested in air, its properties decline sharply when tested in LBE. This degradation in mechanical properties is attributed to the liquid metal embrittlement of the 309 buttering used in TIG welding of T91/316L welds. In contrast to mixed T91/316L TIG welding, the mixed T91/316L EB weld was performed without buttering. The mechanical behaviour of the T91/316L EB weld was very good in air after post weld heat treatment but deteriorated when tested in LBE.     

The influence of proton irradiation on the corrosion of HT-9 during immersion in lead bismuth eutectic

The impedance properties of the oxide on the martensitic-ferritic steel HT-9 were characterized during proton irradiation at the LANSCE WNR facility. Prior to the irradiation experiment, samples were pre-oxidized in moist air resulting in an oxide scale that was on the order of 3 μm thick. Samples were then irradiated during immersion in 473 K lead-bismuth eutectic at a proton current of approximately 63 nA. To assess corrosion rate in real-time, a sinusoidal voltage perturbation was applied across the oxide surface as a function of frequency and the corresponding current response was measured. This method yielded values of oxide impedance which were used in conjunction with Wagner’s oxidation theory to calculate corrosion rate. In general, proton irradiation was associated with an increase in corrosion rate.     

Long term corrosion on T91 and AISI1 316L steel in flowing lead alloy and corrosion protection barrier development: Experiments and models

Considering the status of knowledge on corrosion and corrosion protection and especially the need for long term compatibility data of structural materials in HLM a set of experiments to generate reliable long term data was defined and performed. The long term corrosion behaviour of the two structural materials foreseen in ADS, 316L and T91, was investigated in the design relevant temperature field, i.e. from 300 to 550 °C. The operational window of the two steels in this temperature range was identified and all oxidation data were used to develop and validate the models of oxide scale growth in PbBi. A mechanistic model capable to predict the oxidation rate applying some experimentally fitted parameters has been developed. This model assumes parabolic oxidation and might be used for design and safety relevant investigations in future. Studies on corrosion barrier development allowed to define the required Al content for the formation of thin alumina scales in LBE. These results as well as future steps and required improvements are discussed. Variation of experimental conditions clearly showed that specific care has to be taken with respect to local flow conditions and oxygen concentrations.     

Behavior of pressure-vessel steels exposed to hydrogen from corrosion and environment

Examples reflecting materials performance under service conditions are used to illustrate the potential deterioration of pressure–vessel steels exposed to hydrogen under varying corrosion and stress conditions. The fundamental reactions of hydrogen attack at elevated temperatures and pressures, of hydrogen-induced cracking, and of various types of hydrogen-induced stress corrosion cracking are discussed. Steel selection possibilities, constructional and processing parameters, corrosive-medium influences, and protective measures are presented.     

中国低活化马氏体钢CLAM在液态锂铅中腐蚀的初步实验研究

液态金属锂铅包层是最具发展潜力的聚变堆包层之一,其首选结构材料为低活化铁素体/马氏体钢,而它与液态锂铅的相容性是聚变堆材料研究领域的关键问题之一.本文介绍中国低活化马氏体钢CLAM在液态金属锂铅回路DRAGON-1热对流工况下的实验情况及500 h 480 ℃下初步腐蚀实验结果,并与同样工况下316L奥氏体钢腐蚀结果进行了对比分析.结果显示CLAM钢与液态锂铅的相容性优于316L钢.     

Intergranular stress corrosion cracking initiation model of austenite stainless steels used in BWRs for optimized water chemistry control

A calculation model on intergranular stress corrosion cracking (IGSCC) initiation time of materials used in boiling water reactors (BWRs) has been developed to evaluate effectiveness of water chemistry control for mitigation of the IGSCC. The model was composed of four terms which determine passive film break time: (1) a chemical term based on electrochemical corrosion potential (ECP) and impurity concentration; (2) a mechanical term based on strain rate; (3) a material term based on sensitization; and (4) an irradiation term based on acceleration of corrosion by γ-rays and neutron irradiation. The contribution of the chemical term in the passive film break was calculated based on a deterministic local corrosion model. Then, the local corrosion model was modified by adding mechanical acceleration of the film rupture to treat the IGSCC phenomenon. The model could reproduce the behavioral tendency seen in the slow strain rate tensile test on high carbon contents with sensitization heat treatment (for example, 620°C × 24 h). Under BWR operating conditions, IGSCC initiation time could be extended by a factor of 5 by lowering the electric conductivity from 1.0 to 0.06 μS/cm. If the ECP was reduced below the critical potential by a mitigation method, the IGSCC initiation time was predicted to become sufficiently long for pipings and components.     

Thermodynamic properties of actinides and fission products in liquid bismuth

A critical review on the fundamental properties (solubility, activity coefficients and stable metallic compounds) of actinides and rare earth fission products in liquid bismuth is conducted in this study. The available data are summarized and analyzed. New temperature-dependent correlations, which extend the available data to a broader range of applications, are developed based on existing data from different sources when multiple measurements are available. Analysis of the data shows the strong correlations between some properties (solubility and activity coefficients) and the atomic numbers of the elements.     

Mechanical properties of martensitic steels after exposure to flowing liquid metals

This paper describes the tensile test results of martensitic steels EUROFER 97 and T91 after exposure to flowing Pb-17Li and Pb-55.5Bi alloy, respectively. The corrosion tests were performed in LIFUS II loop (Pb-17Li) and LECOR loop (Pb-55.5Bi) located in the ENEA Brasimone Center. Tensile test were carried in SYNTECH test machine under Ar atmosphere with an extension rate of 2 mm/min, and test temperature for EUROFER and T91 steels were at 480 and 400 °C respectively. The exposure of EUROFER steel to the liquid Pb-17Li did not affect its mechanical properties, while the ductility of T91 steel was deteriorated after exposed to flowing liquid Pb-55.5Bi.     

Effect of corrosion potential on the corrosion fatigue crack growth behaviour of low-alloy steels in high-temperature water

The low-frequency corrosion fatigue (CF) crack growth behaviour of different low-alloy reactor pressure vessel steels was characterized under simulated boiling water reactor conditions by cyclic fatigue tests with pre-cracked fracture mechanics specimens. The experiments were performed in the temperature range of 240-288 °C with different loading parameters at different electrochemical corrosion potentials (ECPs). Modern high-temperature water loops, on-line crack growth monitoring (DCPD) and fractographical analysis by SEM were used to quantify the cracking response. In this paper the effect of ECP on the CF crack growth behaviour is discussed and compared with the crack growth model of General Electric (GE). The ECP mainly affected the transition from fast (‘high-sulphur’) to slow (‘low-sulphur’) CF crack growth, which appeared as critical frequencies ν_crit = f(ΔK, R, ECP) and ΔK-thresholds ΔK_EAC = f(ν, R, ECP) in the cycle-based form and as a critical air fatigue crack growth rate da/dt_Air,crit in the time-domain form. The critical crack growth rates, frequencies, and ΔK_EAC-thresholds were shifted to lower values with increasing ECP. The CF crack growth rates of all materials were conservatively covered by the ‘high-sulphur’ CF line of the GE-model for all investigated temperatures and frequencies. Under most system conditions, the model seems to reasonably well predict the experimentally observed parameter trends. Only under highly oxidizing conditions (ECP ? 0 mV_SHE) and slow strain rates/low loading frequencies the GE-model does not conservatively cover the experimentally gathered crack growth rate data. Based on the GE-model and the observed cracking behaviour a simple time-domain superposition-model could be used to develop improved reference CF crack growth curves for codes.     

Surface modification/alloying using intense pulsed electron beam as a tool for improving the corrosion resistance of steels exposed to heavy liquid metals

The alloying of steel surface with aluminum (Al) using Microsecond-pulsed Intense Electron Beams (MIEB-Al) was developed and optimized in order to be used for improving the corrosion resistance of the 316, 1.4970 and T91 steels, exposed to liquid Pb and Pb-Bi-eutectic. The procedure consists in two steps: (i) coating the steel surface with Al or an Al-containing alloy layer and (ii) melting the coating layer and the steel surface layer using intense pulsed electron beam. In order to cover the steel surface with an homogeneous and crack-free Al-alloyed layer, the following experimental conditions are required: Al coating thickness range 5-10 μm, electron kinetic energy 120 keV; pulse duration 30 μs; energy density 40-45 J/cm²; number of pulses 2-3.Using the mentioned procedure, the corrosion resistance of the 316, T91 and 1.4970 steels, exposed to Pb and Pb-Bi-eutectic with different oxygen concentrations and under different temperatures, was considerably improved due to the formation of a thin alumina layer (which thickness is lower than 1 μm for all the tested temperatures and durations) acting as an anti-corrosion barrier.     

Compatibility of surface-coated steels, refractory metals and ceramics to high temperature lead–bismuth eutectic

Compatibility of cladding material with lead–bismuth eutectic at temperature higher than 650 °C is one of the most crucial issues for feasibility of lead–bismuth-cooled fast reactors with cycle efficiency as high as 40%. In order to search for corrosion-resistant materials with lead–bismuth eutectic at temperature higher than 650 °C, surface-coated steels, some refractory metals and various ceramics were tested by means of stirred-type corrosion test. Lead–bismuth was heated up to 700 °C electrically in an alumina crucible, and oxygen concentration in the lead–bismuth was adequately controlled by injection of argon, steam and hydrogen gas mixture into the lead–bismuth. Specimens of aluminum–iron-alloy-surface-coated steels, refractory metals and ceramics including SiC/SiC composites were immersed in the stirred lead–bismuth for 1000 h. It was found that the surface-coated steels showed good compatibility with the lead–bismuth due to formation of a thin and stable protection layer on the surfaces. Tungsten and molybdenum exhibited high corrosion resistance. On the other hand, niobium is not a reliable material for the high temperature LBE. SiC and Ti₃SiC₂ also exhibited high corrosion resistance. On the other hand, the physical performance of the SiC/SiC composite must be improved especially by minimizing the porosity.