Liquid Lead-bismuth Eutectic Alloy Research Articles

Statistical in situ scanning electron microscopy investigation on the failure of oxide scales

AbstractOxide scales play a pivotal role in obstructing surface chemical and electrochemical reactions, hence hindering chemo‐mechanical effects such as liquid metal embrittlement of steels. Therefore, the critical conditions and failure mechanism of the oxide film are of major interest in the safe service of steels. Though in situ microscopic methods may directly visualize the failure mechanism, they are often challenged by the lack of statistically reliable evaluation of the critical conditions. Here, by combining in situ scanning electron microscopy with a tapered specimen tensile test in a single experiment, we uniquely achieve a mechanistic study with statistically reliable quantification of the critical strains for each step of the dynamic process of film rupture. This is demonstrated with the oxide films formed on a ferrite–martensite steel in liquid lead–bismuth eutectic alloy at elevated temperatures, with in situ results falling right into the predictions of the statistical analysis. Explicitly, the integrated experimental methodology may facilitate the materials genome engineering of steels with superior service performance.

A Review of Corrosion Behavior of Structural Steel in Liquid Lead–Bismuth Eutectic

Liquid lead–bismuth eutectic alloy is one of the candidate coolants for fourth-generation nuclear power systems because of its good physical and chemical properties, neutron economic performance, and safety. However, the compatibility between the coolant and structural steel is still the main factor restricting its large-scale industrial application in the nuclear energy field. Structural steel in a liquid lead–bismuth eutectic alloy for a long time would cause severe corrosion. The erosion of structural steel by high-flow-rate liquid lead–bismuth alloy will lead to a more complex corrosion process. This paper mainly reviews the corrosion characteristics of liquid lead–bismuth and the corrosion behavior of structural steel in liquid lead-bismuth eutectic. The main methods of inhibiting liquid lead–bismuth corrosion are summarized, and future research directions are suggested.

Electrochemical separation of Gadolinium from variable valence europium in molten LiCl-KCl via liquid LBE alloy electrode

The highly effective separation of two adjacent rare earth is significant to the rare earth and nuclear industries. This paper investigates the highly effective separation of Gd over Eu using liquid lead–bismuth eutectic (LBE) alloy cathode in molten LiCl-KCl-EuCl3-GdCl3 by pulse potential electrolysis (PPE). Underpotential deposition of Eu and Gd is observed on the LBE alloy, with a depolarization value far greater than that of the liquid Pb electrode. Furthermore, the higher exchange current density and the lower activation energy of the electrode reaction indicate that the LBE alloy cathode has higher kinetic performance than the liquid Pb. Then, the practical electro-separation in LiCl-KCl-EuCl3-GdCl3 systems is carried out by applying different electrolysis technology. The effects of varying electrolysis methods and parameters on separation factor (SF), extraction efficiency, cathode product morphology, and crystal size are studied and compared. The results show that both the extraction efficiency and the separation factor obtained by the PPE are the largest. The calculated extraction efficiency of Gd and the actual separation factor SFGd/Eu of Gd/Eu could be up to 99.1 % and 759, respectively.

Microstructural investigation and identification of intermetallic σ-phase in solution annealed 316L-type austenitic stainless steel

MYRRHA (Multi-purpose hYbrid Research Reactor for High-tech Applications) is an accelerator driven system, currently under development at SCK CEN in Mol, Belgium. This nuclear system will use liquid Lead-Bismuth eutectic alloy as a spallation target for fast neutron production and as coolant. The ideal structural material for a liquid metal cooled reactor should be unsusceptible to both liquid metal embrittlement and liquid metal corrosion, while possessing high toughness. Nuclear grade austenitic stainless steels similar to AISI 316L have therefore been chosen as the main candidate structural materials for MYRRHA. In the framework of the qualification of those candidates, a specific batch of this material has shown unexpectedly poor mechanical properties, which triggered the need of in-depth microstructural analysis. The behaviour was attributed to the unexpected and undesired presence of intermetallic σ-phase. The σ-phase was identified with a high confidence by combining the data for chemical composition from energy-dispersive X-ray spectroscopy and crystallographic information from electron backscatter diffraction by comparing simulated Kikuchi diffraction patterns with experimentally recorded ones. At first sight the optical appearance of σ-phase resembles δ-ferrite islands, which results in the risk of overlooking this when only classical material qualification methods are used. When left undetected, testing this material including the brittle σ-phase in a liquid metal environment, in combination with miniature mechanical test specimens, could lead to misinterpretation of embrittlement of the austenitic matrix.

Effect of Relative Flow Velocity on Corrosion Behavior of High Nitrogen Austenitic Stainless Steel in Liquid Lead-bismuth Eutectic Alloy

Effect of Relative Flow Velocity on Corrosion Behavior of High Nitrogen Austenitic Stainless Steel in Liquid Lead-bismuth Eutectic Alloy

Design and economic analysis of a novel hybrid nuclear-solar complementary power system for power generation and desalination

In this study, a novel nuclear-solar complementary power (NSCP) system using heavy liquid metal is proposed for electricity and freshwater productions. A small nuclear reactor and a solar tower receiver are integrated in this multi-energy complementary system. Liquid lead-bismuth eutectic alloy is utilized as the heat transfer medium in the solar energy block. The Ebsilon software is used to model the NSCP system. The design point behaviour estimate results show that the electric power and electric efficiency of the NSCP system are 318.8 MW and 39.3%. The solar power capacity proportion is 43.5%. The freshwater daily output of the NSCP system is 3891.8 t. The exergy evaluation results reveal that the solar tower receiver has the maximum exergy loss (345.81 MW) with the exergy efficiency of 46.2%. The annual operation behaviour analysis results of the NSCP system reveal that under the assumed operation strategy, high power generation capacity factors can be achieved. The economic investigation results show that the levelized cost of electricity of the NSCP system is 0.0517 $∙(kWh)−1. Compared with a desalination system driven by a coal-fired power plant, the desalination block of the NSCP system can have an annual cost saving of 680423.0 $.

Effect of Nanostructured Surface on the Corrosion Behavior of RAFM Steels

This study investigated the effect of a preformed nanostructured surface on the corrosion behavior of 9Cr2WVTa reduced activation ferritic/martensitic (RAFM) steel and 9Cr+AlSi steel (9Cr2WVTa with the 0.12 wt.% Al and 0.68 wt.% Si addition) at 700 °C in air and at 550 °C in liquid lead–bismuth eutectic (LBE) alloys. The nanostructured surface layer was fabricated by surface mechanical rolling treatment (SMRT). The results showed that the SMRT 9Cr+AlSi sample has a lower oxidation rate than the SMRT 9Cr2WVTa steel at 700 °C in air, due to the faster diffusion rates of Al, Cr and Si in the nanostructure and a higher diffusion driving force increased by Cr. The SMRT 9Cr+AlSi sample at 550 °C in oxygen-saturated LBE alloy also had a higher oxidation rate, due to the formation of Al and Si oxides in the internal oxide layer.

Enhanced oxidation resistance of a reduced activation ferritic/martensitic steel in liquid Pb-Bi eutectic alloy by preforming a gradient nanostructured surface layer

A gradient nanostructured (GNS) surface layer with a thickness of ∼250 μm was produced on an 11Cr-WVTaSi reduced activation ferritic/martensitic (RAFM) steel by means of surface mechanical rolling treatment (SMRT). The mean grain size was ∼53 nm at the topmost surface layer and increased gradually with increasing depth. The oxidation behavior of the GNS sample was compared with that of the coarse-grained counterpart in an oxygen-saturated liquid lead-bismuth eutectic (LBE) alloy at 550 °C. The results showed that the oxidation resistance of the GNS sample was significantly enhanced in the liquid LBE alloy after different immersion times up to 3500 h. This was mostly due to the accelerated formation of a dense and protective spinel scale enriched with Si and Mn on the GNS sample.

Cavitation erosion behavior of CLAM steel weld joint in liquid lead-bismuth eutectic alloy

The cavitation erosion of weld joint and base metal of China low activation martensitic (CLAM) steel in liquid lead-bismuth eutectic alloy (LBE) at 550 °C was investigated to simulate the cavitation erosion of the first wall and the nuclear main pump impeller in the accelerator driven sub-critical system (ADS). A suit of ultrasonic cavitation facility was self-designed to study the cavitation erosion. By studying the surface micro topography, roughness and mean pit depth of the tested specimens, it was found that some crater clusters and large scale cracks appeared on the tested specimen surface after the formation of numerous single craters, and the base metal exhibited much better cavitation erosion resistance than the weld bead due to the difference in their mechanical properties and microstructures. In addition, by comparing the results of static corrosion and cavitation erosion, it could be concluded that the cavitation erosion and the dissolution and oxidation corrosion in liquid LBE would accelerate mutually.

The comparative analysis on thermal storage systems for solar power with direct steam generation

Two sensible heat storage systems and two latent heat storage systems, in which liquid lead-bismuth eutectic alloy (LBE) is selected as sensible heat storage medium and sodium nitrate is selected as phase change storage material, are investigated for concentrated solar power (CSP) with direct steam generation (DSG) in the present work. The temperature pinch point likely occurs in sensible heat storage system, which restricts the optimization space. The temperature difference distributes more uniformly in latent heat storage system than in sensible heat storage system, and the outlet temperature of steam is far higher in latent heat storage system than in sensible heat storage system. The exergy efficiency is more two times in latent heat storage system than in sensible heat storage system. The three-tank latent heat storage system has the most flexible and effective performance among the four storage systems.

Ultrasonic cavitation erosion of 316L steel weld joint in liquid Pb-Bi eutectic alloy at 550 °C

Liquid lead-bismuth eutectic alloy (LBE) is applied in the Accelerator Driven transmutation System (ADS) as the high-power spallation neutron targets and coolant. A 19.2kHz ultrasonic device was deployed in liquid LBE at 550°C to induce short and long period cavitation erosion damage on the surface of weld joint, SEM and Atomic force microscopy (AFM) were used to map out the surface properties, and Energy Dispersive Spectrometer (EDS) was applied to the qualitative and quantitative analysis of elements in the micro region of the surface. The erosion mechanism for how the cavitation erosion evolved by studying the element changes, their morphology evolution, the surface hardness and the roughness evolution, was proposed. The results showed that the pits, caters and cracks appeared gradually on the erode surface after a period of cavitation. The surface roughness increased along with exposure time. Work hardening by the bubbles impact in the incubation stage strengthened the cavitation resistance efficiently. The dissolution and oxidation corrosion and cavitation erosion that simultaneously happened in liquid LBE accelerated corrosion-erosion process, and these two processes combined to cause more serious damage on the material surface. Contrast to the performance of weld metal, base metal exhibited a much better cavitation resistance.

Effects of iron and chromium on the dynamic properties of oxygen in liquid lead–bismuth eutectic alloy

Ab initio molecular dynamics simulations were performed to investigate the effects of iron (Fe) and chromium (Cr) on the dynamic behaviour of oxygen in liquid lead–bismuth eutectic (LBE). The results indicated that oxygen atoms could be strongly attracted towards Fe and Cr atoms, forming metal oxide complexes dominated by Fe3O4 and Cr2O3. These oxide complexes could retard oxygen diffusion and reduce the concentration of free oxygen in LBE, thereby leading to an increase in the output of oxygen sensor in experiments. Besides, the diffusivities of Fe and Cr in LBE were obtained at different temperatures.

The heat transfer mechanism study of three-tank latent heat storage system based on entransy theory

A three-tank latent heat storage system in which liquid lead–bismuth eutectic alloy (LBE) is used as sensible heat storage medium, and sodium nitrate is selected as the phase change material (PCM), is proposed in the present work. The performance of thermal storage system depends chiefly upon the heat transfer performance at superheated steam stage, and the mass flow rate of LBE can be adjustable to accommodate the specific heat change of water/steam. There exists an optimal mass flow rate ratio to maximize the performance of storage system. Generally, the more uniform the temperature difference distribution is, the higher the thermal performance of the storage system. The optimal mass flow rate of liquid LBE appears under constant mass flow rate ratio condition, in which the entransy and exergy rises of steam reach the maximum. The increasing number of transfer units at superheated steam stage improves the thermal storage performance monotonously. The exergy efficiency of this storage system runs at more than 80% through proper parameters setting.

Brittle fracture of T91 steel in liquid lead–bismuth eutectic alloy

The mechanical behaviour of the T91 martensitic steel has been studied in liquid lead–bismuth eutectic (LBE) and in inert atmosphere. Several conditions were considered to point out the most sensitive embrittling factors. Smooth and notched specimens were employed for respectively monotonic and cyclic loadings.The present investigation showed that T91 appeared in general as a ductile material, and became brittle in the considered conditions only if at least tests were performed in LBE. It turns out that the loading rate appeared as a critical parameter for the occurrence of liquid metal embrittlement of T91 in LBE. For the standard heat treatment condition, loading monotonically the T91 very slowly instead of rapidly in LBE resulted in brittle fracture. Also, under cyclic loading, the crack propagated in a brittle manner in LBE.

The impact of the composition of structural steels on their corrosion stability in liquid Pb–Bi at 500 and 400 °C with different oxygen concentrations

In recent years, heavy liquid metals have found exercise as possible coolants and targets in the conversion of radioactive elements in accelerator driven systems (ADS). Liquid lead–bismuth eutectic alloy is one of candidates for this using tanks to its suitable nuclear and physical properties. Performed examination was aimed at research of compatibility choice materials for parts of ADS with liquid Pb–Bi eutectic alloy, influence of composition choice materials on their corrosion resistance, influence of temperature and oxygen content. We performed corrosion tests of 1000 h each on approximately 20 types of structural steels (austenitic, ferritic and martensitic) in convection loops with flowing Pb–Bi at 500 and 400 °C and using different oxygen concentrations. The impact of Fe, Cr, Ni, Mn, Si, Al and Mo content on the corrosion stability of these steels was measured without and after preliminary passivation through creating thin spinel or oxide layers on their surface.