Liquid Liquid Lead-bismuth Eutectic Research Articles

In-situ measurement of hydrogen isotope behavior in high temperature LBE: Diffusivity, permeability, and solubility

The Lead-Bismuth Fast Reactor (LBR) emerges as a promising concept due to its superior neutron economy, chemical stability, and thermal properties. From the nuclear safety standpoint, the focus has predominantly been on the behavior of 210Po and other fission products, while the issue of tritium in LBRs has not been sufficiently addressed due to the inconvenience of tritium experiments. Formation of tritium/helium bubbles induces significant local stress and volume expansion, leading to hardening and embrittlement of structural materials, thus expediting their degradation through irradiation effects. Current understanding of tritium transport within liquid Lead-Bismuth Eutectic (LBE) remains incomplete. To bridge this gap, a novel device employing the "permeation pot" method has been developed for the first experimental quantification of diffusivity, permeability, and solubility of hydrogen isotopes in liquid LBE. Notably, hydrogen diffusivity in this medium is found to be three to four orders of magnitude greater than in conventional 316L stainless steel structural material. Furthermore, the temperature-dependence of diffusivity in liquid metals is minimal compared to solids, as indicated by the activation energy. Conversely, solubility in 316L significantly surpasses that in LBE by three to four orders of magnitude. This discrepancy accelerates the tritium release from LBE to structural material, leading to the failure of the structural material.

Insights into fatigue crack propagation mechanism of T91 steel in liquid lead-bismuth eutectic at 150–450 °C

The fatigue crack growth (FCG) behaviors of T91 steel in oxygen-saturated liquid lead–bismuth eutectic (LBE) at 150–450 °C were investigated. The FCG rate increased gradually with the increase of temperature at 150–350 °C, is firstly low at 450 °C and then comparable with that at 350 °C. The macroscopic trans-granular cracks preferentially propagated along the deformation-induced low-angle grain boundaries (LAGBs) near the crack tip at the microscopic scale. Intergranular precipitation-enhanced wetting of matrix by liquid LBE results in the reduction of atomic bonding force and formation of micro-cracks along the LAGBs, which triggers brittle cracking.

Numerical simulation and model development of drag coefficient of bubbles in gas-liquid metal two-phase flow

The occurrence of a steam generator tube rupture (SGTR) accident in a lead-bismuth cooled fast reactor results in the formation of steam bubbles in the liquid lead-bismuth eutectic (LBE). This may degrade heat transfer and power transients in the reactor core due to the migration and accumulation of steam bubbles. To investigate the dynamics of steam bubbles flowing in liquid LBE, it is essential to develop an accurate model for the bubble drag coefficient. In this paper, a three-dimensional numerical model is first established to simulate the injection of high-pressure steam bubbles into a high-temperature LBE molten pool. The model is based on the CLSVOF method. By analyzing the trajectory, velocity, and diameter of bubbles, and combining them with the force equilibrium equation for bubbles, the values of the drag coefficient for bubbles are determined. On this basis, the suitability of current empirical drag models for bubble migration in LBE is evaluated. Finally, the optimal drag coefficient model is selected and further improved. Results reveal that the prediction error of the optimized model for the bubble drag coefficient in liquid LBE is within ±15 %.

Corrosion behavior of magnetron sputtering Fe31Cr20Al17Ti16Nb16 high entropy coating in liquid lead-bismuth eutectic with different oxygen concentration at 500 °C

The major concern of the structure integrity of lead cooled reactor is the corrosion behavior of fuel cladding and other core internal materials. Magnetron sputtering technology is adopted as an surface coating method to improve the corrosion resistance of nuclear fuel cladding exposed to liquid lead-bismuth eutectic (LBE). Fe31Cr20Al17Ti16Nb16 high entropy alloy (HEA) coatings were prepared on tubular ferritic/martensitic (F/M) steel which is the candidate fuel cladding material, and the corrosion behaviors of Fe31Cr20Al17Ti16Nb16 coatings in LBE are investigated in this work. F/M steel specimens with Fe31Cr20Al17Ti16Nb16 coatings were exposed to 500 °C stagnant liquid LBE with oxygen concentration of Co ≈ 1 × 10−4 wt% and Co ≈ 1 × 10−7 wt% for 1000 h respectively. The primary findings suggest that the oxygen content of LBE mainly affects the morphology of duplex oxide layers generated during corrosion process, which resulting from the different inward diffusion flux of oxygen. In oxygen-saturated (Co ≈ 1 × 10−4 wt%) LBE, the overall oxide layer exhibits bulging and incompact morphology and infiltration of Pb is probed at inner Cr2O3 oxide layer, larger-sized cavities (the observed maximum dimension reaches 233.5 nm) distribute close to the outer Fe3O4/FeCr2O4 layer; In oxygen-depleted (Co ≈ 1 × 10−7 wt%) LBE, duplex oxide layer presents relatively dense and uniform state, tiny cavities (observed maximum dimension is 38.3 nm) dispersing at the internal of oxide areas. Corrosion rates of the Fe31Cr20Al17Ti16Nb16 coatings under two oxygen situations are 2 orders of magnitude lower than uncoated F/M steel under same exposure condition, the oxide layers with better uniformity and density produced in Co ≈ 1 × 10−7 wt% LBE indicating the better application advantage of Fe31Cr20Al17Ti16Nb16 coatings in oxygen-depleted LBE.

Corrosion effect analysis on thermal-hydraulics of LBE/water spiral tube steam generator under oxygen-controlled environment

The advancement of utilizing liquid Lead-Bismuth Eutectic (LBE) as a cooling medium is hindered by its pronounced corrosive properties. The impact of LBE corrosion on the performance of heat exchangers is significant over the long term, however, this aspect has been largely overlooked in previous studies. Historically, there has been a dearth of LBE corrosion models that account for flow accelerated corrosion. Concurrently, precise numerical models and coupling methods for comprehending the interplay between LBE corrosion and thermal-hydraulics have not been developed. Nevertheless, these contents are pivotal for the advancement of liquid LBE cooling mediums. To delve into the flow and heat transfer characteristics of heat exchangers subjected to LBE corrosion, enhancements were made to capture the accelerated removal effect of LBE corrosion flow. Subsequently, a bidirectional coupling model encompassing LBE corrosion and flow heat transfer was formulated. The Computational Fluid Dynamics (CFD) method was employed to simulate the corrosion and flow heat transfer in a spiral tube steam generator under conditions of saturated oxygen concentration and an oxygen-controlled environment. The results indicate that the corrosion of liquid LBE forms an oxidation layer, which hinders the heat transfer in the spiral tube steam generator. This leads to a significant increase in the wall friction coefficient and a decrease in the surface Nusselt number. However, it does not have a significant effect on the water side evaporation process of the spiral tube steam generator. The implementation of an oxygen-controlled environment can effectively reduce the influence of LBE corrosion on the flow heat transfer of the spiral tube steam generator. Especially under high temperature conditions, it can reduce the near wall temperature of LBE change by up to 57.5% and the outlet temperature change by up to 61.5%. The oxygen-controlled environment results in prolonged local hypoxia time, with a more pronounced effect at higher temperatures.

Development of an accelerator-based neutron source to prototype Mo-99 production, part I: A liquid LBE windowless target

Molybdenum-99 (Mo-99)’s decay product, technetium-99 (Tc-99 m), is one of the most critical isotopes for medical diagnostics. To provide U.S. domestic supply of Mo-99 without using high-enriched uranium (HEU), a subcritical uranium target assembly (UTA) is irradiated by an accelerator-based neutron source to create Mo-99 through fission. This study discusses the development of the accelerator-based neutron source. The high-energy electrons from the accelerator irradiate a liquid lead-bismuth eutectic (LBE) target to produce neutrons. Part I of this work focuses on numerical and experimental analysis towards the development of a liquid LBE windowless target. Unlike the existing windowless targets in literature, the current design creates a vertical free surface for a beam to irradiate. First, a hydrodynamic analysis of the LBE windowless target is performed. Simplified analytical calculations are assisted by 2D computational fluid dynamics (CFD) simulations to design the target, with the focus on eliminating recirculation zones and avoiding cavitation. With the optimized geometry, the experimental study is performed to investigate the flow hydrodynamics using liquid LBE. The experiments (1) compare pressure drop in the system to correlation predictions; (2) visualize the free surface liquid LBE flow from the beam view; (3) validate the LBE flow profile using temperature sensitive paint from the side view; and (4) validate the liquid LBE film thickness using gamma densitometer measurements. Second, the power handling capability of the designed windowless target is investigated. The divider plate in the current design is susceptible to overheating due to the thin LBE film in front. As LBE erosion and corrosion is likely to occur at an LBE velocity of 2.0 m/s and temperature above 500 °C, a power limit of 10 kW of beam power was established to prevent this corrosion from occurring, which is calculated by a Nusselt number correlation. The divider plate surface temperature at 10 kW agrees well with the 3D CFD simulation results. Part I demonstrates the fundamental physics in liquid LBE windowless target design and associated testing. A companion paper, Part II will demonstrate how to couple this windowless target into the Mo-99 production system, including an accelerator system operating under an ultra-high vacuum and the UTA cooled by water at room temperature.

Development of an accelerator-based neutron source to prototype Mo-99 production, Part II: A liquid LBE loop under a high vacuum

To provide US domestic supply of Mo-99 without using high-enriched uranium (HEU), a subcritical uranium target assembly (UTA) is irradiated by an accelerator-based neutron source to create Mo-99 through fission. Part I of this work discusses the design of a liquid lead–bismuth eutectic (LBE) windowless target for an accelerator-based neutron source development. Part II discusses how to couple this windowless target to an accelerator operating at an ultra-high vacuum and the subcritical UTA cooled by water at room temperature.Due to the windowless design of the target, the liquid LBE flow shares an ultra-high vacuum (<1.3 × 10−7 Pa or 10−9 Torr) space with the accelerator. As a result of this shared vacuum space, the LBE system must operate at a high vacuum (10−3 ∼ 10−6 Pa or 10−5 ∼ 10−8 Torr). A magnetic rotary motion feedthrough unit utilizes magnetic fluid to allow rotation of the pump while maintaining a high vacuum environment. Prior to testing the LBE system under vacuum, a pump curve measurement is performed to estimate flowrate in the system. This measurement also generates data on orifice loss coefficients, which are compared to correlations in literature. The second experiment investigates vacuum level in the LBE system during operation. High vacuum is maintained (10−3 ∼ 10−5 Pa or 10−5 ∼ 10−7 Torr) during system operation, and a residual gas analyzer (RGA) scan shows that partial pressures of residual gases in the LBE system lower over the duration of LBE system operations. The third experiment investigates the gravity driven liquid LBE flowing out of the target chamber in the return line, which is partially full. If the liquid LBE is not drained quickly enough, flooding in the target chamber could occur. The coefficient n in the Manning equation is found to be around 0.008 s/m1/3. The last experiment performed is a demonstration that a vacuum jacket could provide sufficient thermal insulation to allow coupling between 300 °C LBE loop and a water tank at room temperature. The results from these experiments have influenced the development of the neutron source for the future commercial scale Mo-99 production system.

Fracture behaviors of modified 9Cr-1Mo steels in liquid lead–bismuth eutectic immersion environment using in-situ testing technique

The 9Cr-1Mo ferrite/martensite steel stands as a crucial candidate material for structural use in lead-cooled fast reactors. However, its susceptibility to embrittlement in liquid lead–bismuth eutectic (LBE) alloy represents a significant hurdle that hinders its widespread application. In this paper, two modified 9Cr-1Mo steels, designated as A-type steel and B-type steel, were proposed by adding aluminum and silicon elements, respectively. To examine the embrittlement caused by liquid LBE the uniaxial tensile tests were conducted on the original T91 steel, A-type steel, and B-type steel in liquid LBE at temperatures of 180 °C, 350 °C and 450 °C. Then, based on the proposed in-situ testing method and compliance method, the fracture properties (J-R curves and the crack initiation fracture toughness) of the above 9Cr-1Mo steels were analyzed at different temperatures. Results showed that the yield stress, tensile strength, and elongation of the modified 9Cr-1Mo steels are higher than those of the original T91 steel, but the A-type steel and B-type steel exhibit different mechanical responses with temperature changes. Moreover, with the increase of temperature, the fracture toughness of T91 steel and B-type steel significantly decreases, but the A-type steel decreases first and then increases. There is no doubt that the crack initiation fracture toughness of the modified 9Cr-1Mo steels is higher than that of the original T91 steel in all tested temperature ranges. Finally, combined with fractographic analysis, the effects of liquid LBE at various temperatures on the embrittlement mechanism of 9Cr-1Mo steels were discussed.

Precipitation characteristics and growth mechanism of Fe and Cr from liquid lead-bismuth eutectic by quenching in liquid nitrogen

The compatibility of structural steels with liquid lead-bismuth eutectic (LBE) restricts the development of the lead-cooled fast reactor (LFR) and the accelerator driven sub-critical (ADS) system. During the reactor operation, alloying elements in steel can dissolve into LBE. The dissolved alloying elements could precipitate in cold parts of the reactor due to the decrease in solubility, which can cause pipe clogging and worsen heat transfer. Therefore, it is necessary to study their precipitation characteristics to provide a reference for the filtration process. In this paper, Fe, Cr, and a mixture of Fe and Cr were added to liquid LBE at 1173 K and quenched in liquid nitrogen to study their precipitation characteristics. The scanning electron microscope (SEM) and field-emission scanning electron microscope (FESEM) were used to analyze the morphology, and the phase structure was identified by an X-ray diffractometer. The chemical compositions of precipitates were analyzed by an energy dispersive spectrometer (EDS, Esprit Compact, Bruker) and an electron probe microanalyzer (EPMA, EPMA-8050 G, Shimadzu). The solid-liquid interface structure and growth mechanism of precipitates were also discussed. The difference in growth mechanisms resulted in various morphologies for the precipitates. There were three morphologies of precipitates: faceted dendrite, polyhedron (cube, octahedron, and hopper), and seaweed dendrite. All the precipitates in LBE have a faceted growth character except the seaweed dendrites, irrespective of their morphology. The growth of Fe, Cr, and Cr-Fe faceted dendrites originated from continuous growth followed by lateral growth. On the contrary, the cubic and octahedral precipitates were controlled by the spiral growth mechanism, and the growth mechanism of hopper crystals was two-dimensional nucleation. The formation of seaweed dendrites was caused by a strong local undercooling of nonfaceted dendrites.

Corrosion behaviors of ODS-FeCrAl in oxygen-saturated lead-bismuth eutectic at 550°C: Effects of grain boundaries and minor elements

Long-term corrosion behavior of ODS-FeCrAl tube was investigated in oxygen-saturated static liquid lead-bismuth eutectic (LBE) at 550 °C. Different densities of sub-grain boundaries (sub-GBs) lead to different corrosion behaviors on the inside and outside surfaces of the tube. The oxide film formed on the inside surface consists of Fe3O4, Fe-Cr-Al spinel and Al2O3, and on the outside surface consists of Fe-Cr-Al spinel rich in Cr&Al and Al2O3. Excessively high density of sub-GBs accelerates the oxidation rate. The precipitation of W&Ti promotes the formation of Cr-rich and Al-rich oxides. The corrosion mechanism of ODS-FeCrAl in liquid LBE is discussed.

Numerical study on dissolution characteristics of solid-phase oxygen control in liquid LBE systems based on the porous media model

For the proper design and operation of lead oxide mass exchanger (PbO MX), the dissolution kinetics of PbO in flowing liquid Lead-bismuth eutectic (LBE) needs to be determined. A computational fluid dynamics (CFD) method of the PbO MX was established. The solid-phase oxygen control part of the MX is PbO spheres packed bed, which is regarded as a porous media in the simulation calculation. The oxygen mass transfer process between PbO spheres packed bed and liquid LBE was simulated by a porous media model with the species transport model. The relationship between the dissolution rate of MX and the flow rate, temperature and initial oxygen concentration is predicted. The dissolution rate of PbO increases exponentially with increasing temperature of LBE. Besides, the dissolution rate of oxygen is positively correlated with the LBE flow velocity. In the specific oxygen concentration range, the MX inlet oxygen concentration has little effect on the dissolution rate. The smaller the porosity of PbO spheres packed bed has, the smaller the dissolution rate of oxygen is. Furthermore, when the porosity is constant, the dissolution rate of oxygen increases with the increase of the height of the packed bed of PbO spheres.

Performance of potentiometric oxygen sensors with LSCF electrode in lead–bismuth eutectic loop

Oxygen sensors are the major part of the active oxygen control system (OCS) to be used in the liquid lead–bismuth eutectic (LBE) system. In this paper, the electromotive force (EMF) measured by yttria stabilized zirconia (YSZ) solid electrolyte sensor with LSCF (lanthanum strontium cobalt ferrite)/air reference electrode in static oxygen saturated LBE is used to obtain relationship between EMF and temperature. The EMF output by oxygen sensors is deterministic and predictable. At the same time, the performance of oxygen sensors in flow loop of liquid LBE were also studied. EMF output curves of oxygen sensors corresponding to the operation of consuming dissolved oxygen are given. It is proved that the LSCF/air sensor can be used to monitor oxygen concentration in non-isothermal LBE systems.

A comparative study on the corrosion performance of four FeCrAl alloys with different Cr contents in contact with oxygen-saturated LBE

The corrosion behavior of a series of FeCrAl alloys with four Cr contents was investigated in static oxygen-saturated liquid lead–bismuth eutectic (LBE) at 600 °C for 720 h. The oxidation layer had a triple-layered structure composed of an external magnetite layer, a middle Fe–Cr spinel layer, and an inner oxide zone. Characterization of the FeCrAl alloys after corrosion in the static liquid LBE showed that the corrosion behavior was dependent on the Cr content. The corrosion appearances and mechanisms were studied, and the oxygen diffusion processes that may have occurred during corrosion were discussed.

Numerical simulation of corrosion phenomena in oxygen-controlled environment for a horizontal lead-bismuth reactor core

In order to explore the core corrosion characteristics of horizontal lead-bismuth reactor in oxygen-controlled environment, a liquid lead-bismuth eutectic (LBE) corrosion model including the growth and removal process of oxide layer was established in this paper. The coupling method of double-layered oxidation model and computational fluid dynamics (CFD) was used to simulate the long-term oxidation corrosion of horizontal LBE reactor core numerically. The results show that the average total oxide layer thickness of fuel rod surface is 1.59 μm, and the thickest oxide layer is 3.48 μm on the fuel rod surface at the core outlet after 20,000 h. The fuel rods maintain a double-layer oxide layer structure. The growth rate and removal rate of the oxide layer on fuel rod surface increase with the increase of inlet temperature and the decrease of inlet flow rate. The growth rate of the oxide layer on fuel rod surface increases with the increase of inlet oxygen concentration, while the removal rate decreases. At higher temperature above 420℃, lower flow velocity below 0.25 m/s and lower oxygen concentration below 2 × 10−8wt%, the magnetite layer will first be completely removed from the surface of the fuel rods at the core outlet. The liquid LBE oxidation corrosion model and coupled CFD method presented in this paper can be used for numerical simulation of oxidation corrosion in different units of LBE cooling system.

Preparation of CMAS, LZS glass-ceramics and study of the glass ceramics anti-corrosion properties in liquid leadbismuth eutectic at 500°C

Liquid lead-bismuth eutectic (LBE) was an important candidate material for the fourth generation reactor coolant. Its high temperature and heavy metal corrosion conditions put forward higher requirements for the corrosion resistance of reactor structural materials. As a new kind of special material, glass-ceramic material, which possesses the excellent properties of glass and ceramics, has good mechanical property, wear-resisting property and corrosion resistance. The LBE corrosion behavior of glass-ceramics at typical operating temperatures of nuclear reactors was investigated. The lead bismuth corrosion test was carried out under the condition of oxygen saturation at 500°C for 500h. The lead bismuth corrosion resistance of the two glass ceramic samples in static LBE was analyzed by means of scanning electron microscope (SEM) and X-ray diffraction (XRD). After 500 h corrosion in oxygen saturated liquid LBE at 500°C, there was no obvious corrosion on the surface of CMAS glass ceramics. Its dense microstructure and stable phase composition effectively prevented the penetration of Pb and Bi elements, and had good resistance to corrosion; The surface of LZS glass ceramics was covered with a layer of loose and porous compounds, and the thickness of the corrosion zone was 10 μm, which occurred a certain degree of lead-bismuth corrosion, and its corrosion resistance was poor. The results showed that under the same corrosion conditions, no lead bismuth corrosion behavior was found on the surface of CaO-MgO-Al2O3-SiO2 (CMAS) glass-ceramic, while there was a corrosion layer with a thickness of about 10 μm on the surface of Li2O-ZnO-SiO2 (LZS) glass-ceramic, indicating that the lead bismuth corrosion resistance of CMAS glass ceramics was significantly better than that of LZS glass ceramics.

Impact of Bi content on the accuracy of oxygen concentration measurements in liquid Pb–Bi alloys

Accurate measurements of the oxygen concentration in liquid lead-bismuth eutectic (LBE) alloys are essential for ensuring optimum cooling conditions in heavy liquid metal coolant fast reactors. However, while unavoidable variations in the Bi contents of these alloys can affect the accuracy of these measurements, this issue has not yet been rigorously evaluated. The present work addresses this issue by evaluating variations in oxygen concentration measurements obtained experimentally for oxygen-saturated liquid LBE alloys with different Bi contents at different temperatures using a solid electrolyte oxygen sensor. Theoretical relationships are established between sensor voltage, oxygen concentration, temperature, and Bi content under the applied experimental conditions, and excellent agreement is obtained between the experimental and theoretical results. The theoretical relationships establish that the voltage decreases by about 1 mV for every 1 wt% increase in Bi content at a temperature of 400 °C. At a fixed voltage, with the increase of T, the influence of the Bi content on the CO calculation results gradually increased. Finally, the impact of varying Bi contents on the accuracy of oxygen concentration measurements is evaluated under practical reactor operation conditions, and higher requirements for the control of dissolved oxygen in LBE-cooled fast reactors are proposed.

High corrosion resistance of twin boundaries in medium-entropy alloy exposed to liquid lead-bismuth eutectic at 500 °C: Mechanism exploration by both experiment and first-principles calculation

The present study discovered the twin boundaries (TBs) of CoCrNi medium-entropy alloy (MEA) exhibited high corrosion resistance to liquid lead-bismuth eutectic (LBE) at 500 °C with 5 × 10−7 mass% dissolved oxygen. The grain boundaries (GBs) were corroded by LBE, forming brittle Bi3Ni phases in LBE interior and at the LBE/CoCrNi interface. First-principles calculation indicated that the Bi diffusion energy barriers at GBs and TBs were 0.69 eV and 1.52 eV, respectively. The high diffusion barrier for Bi atom in CoCrNi MEA contributed to the high corrosion resistance of TBs in the liquid LBE.

Numerical study on the heat transfer characteristics of a liquid lead–bismuth eutectic in a D-type channel

A printed circuit heat exchanger (PCHE) can offer superior performance in area concentration and heat transfer efficiency. A PCHE with a liquid lead–bismuth eutectic (LBE) and supercritical carbon dioxide as working media can use these materials as intermediate heat exchangers in lead–bismuth eutectic-cooled reactors to reduce facility size and improve economy. To ensure the reliability of a numerical simulation for a liquid LBE in PCHE channels, the flow and heat transfer characteristics of a liquid LBE were investigated in a single D-type channel. The existing turbulent Prandtl number (Prt) models and the shear‒stress transport (SST) k−ω model were evaluated first by using experimental liquid metal data. Then, a suitable Prt model was proposed for the numerical simulation of the liquid LBE. Finally, the flow and heat transfer characteristics of the liquid LBE were studied in D-type straight channels and D-type zigzag channels. The study presented the effects of flow velocity, wall heat flux, equivalent diameter and zigzag channel angle on the flow resistance and heat transfer characteristics. Meanwhile, a heat transfer correlation suitable for a D-type straight channel was also proposed. The research results in this paper lay a good foundation for the development of PCHEs with an LBE as the working fluid.

Performance of the new ferritic/martensitic steel SIMP against liquid lead‐bismuth eutectic corrosion: Comparison with T91 and 316L steels

AbstractThe degradation of structural materials caused by the corrosion of liquid lead‐bismuth eutectic (LBE), the coolant of lead‐cooled fast reactors (LFRs), has become one of the limiting factors for the development of LFRs. In this study, LFR structural candidates SIMP and T91 ferritic/martensitic steels and 316L austenitic stainless steel were selected to conduct corrosion experiments at different durations (120–1218 h) in oxygen‐saturated liquid LBE at 550°C. It was found that the austenitic stainless steel 316L has the best resistance to LBE corrosion due to its high Cr content, which allows dense Fe–Cr spinel with high Cr content to be generated in oxygen‐containing LBE, slowing down the oxidation rate. However, a certain degree of dissolution corrosion occurred in the early stages of corrosion in 316L steel, which disappeared with the increase of time. The ferritic/martensitic steel SIMP has better oxidation resistance than T91 due to its higher Si content, which results in a more compact inner oxide layer of SIMP steel, thus impeding the diffusion of Fe and O ions more effectively.

Corrosion behavior of T91 steel in liquid lead-bismuth eutectic at 550 °C: Effects of exposure time and dissolved oxygen concentration

Long-term corrosion behavior of T91 steel was investigated in 550 °C static liquid lead-bismuth eutectic (LBE) at different dissolved oxygen (DO) concentration. It was found that the oxide film formed in the oxygen-saturated LBE consists of iron-lead composite oxide, Fe3O4, Fe-Cr spinel and an inner oxidation zone (IOZ). The IOZ is composed of matrix and FeCr2O4 which follows orientation relationships with the matrix. The thickness of oxide film significantly reduces at DO= 1.26 × 10−6 wt %. Dissolution corrosion and intergranular penetration of Pb-Bi were observed at DO≤ 1.41 × 10−8 wt %. The corrosion mechanism of T91 steel in liquid LBE is discussed.