The composition of the cover gas above liquid lead-bismuth eutectic (LBE) is studied in nitrogen and argon atmospheres to evaluate the feasibility of using nitrogen as main cover gas in LBE cooled nuclear systems. A mass spectrometer is coupled to a reactor vessel setup to study online the speciation from contacting different cover gas environments with LBE. The experiments are performed in representative conditions for MYRRHA and reveal that little interactions occur between nitrogen and LBE in a temperature range between 200 and 450 degrees C. NO and NH3 are the only N-containing species detected in amounts similar to those of the reference measurements. Using mass spectrometry (MS), a clear and fast dissolution of O2 from the cover gas into the LBE is observed upon contacting N2 enriched with oxygen. Changes in the LBE-cover gas interface morphology could be linked to the observed evolution of the oxygen content in the gas exit stream. Thermodynamic calculations are performed to serve as guidance for the experimental campaign and the species formed in the chemical equilibria calculations are in line with the experimental results.

We propose a new electrochemical method for the measurement of the solubility product of the oxide of a metal impurity, in a liquid metal solvent that is less easily oxidized than the metal impurity. When a known amount of oxygen is continuously added into the liquid metal by coulometric titration, the dissolved metal impurity reacts with the added dissolved oxygen, forming a metal oxide. By measuring the concentration of dissolved oxygen in the liquid metal solvent during the titration, the solubility product of the impurity metal oxide in the liquid metal solvent can be derived. From this solubility product, using thermochemical data of the known chemical species involved in the oxidation reaction, i.e. Sieverts' constant of dissolved oxygen in the liquid metal solvent and the Gibbs free energy of formation of the impurity metal oxide, the elemental solubility of the metallic impurity element in the liquid metal solvent can be derived as well. In this work, we validate the method by measuring the solubility product of magnetite (Fe3O4) in molten lead-bismuth eutectic alloy (LBE), in the temperature range of 723-826 K.

The dissolved oxygen concentration must be well controlled in liquid Pb for use as a primary coolant of fast spectrum nuclear reactors. We have measured fundamental data of oxygen in liquid Pb. The Sieverts constant and solubility of oxygen were measured by coulometric titration. Thermal cycling of liquid Pb allowed a quantification of the excess oxygen above solubility required to initiate solid PbO nucleation, which is the metastable limit in liquid Pb. The data obtained in this study are as follows:

Oxygen control is one of the key technologies to limit corrosion or coolant oxidation in lead bismuth eutectic cooled nuclear reactors. In this paper, we show that a stirred bubble column reactor can be an efficient tool for addition and extraction of dissolved oxygen from lead-bismuth eutectic. The design criteria and the resulting layout of the HELIOS3 reactor are detailed and typical results obtained are described. Dissolved oxygen extraction rates are only given at high oxygen activity, as dissolved corrosion products and oxides can strongly influence the rate of addition or extraction of dissolved oxygen at low oxygen activity.

Detection and characterisation of voids in heavy liquid metals (HLM) is required for next generation nuclear reactor systems. However, its determination presents a challenge owing to their opaque nature and the high temperatures involved. Therefore, tools are needed that can be used to capture local, quantitative information at relevant nuclear operating conditions. In this work, the feasibility of using optical fibre sensors for the measurement of void fractions in liquid metals is presented. Since the functioning of optical probes is usually explained by a crude on-off model, the complexity of both the optical response and the hydrodynamic tip interface interactions often remain hidden to new users. To clarify this point, well-controlled lab-scale experiments dealing with the response of three concept probe tip geometries are presented. Analysis of the obtained signal transients is used to provide guidelines for effective data processing. To conclusively demonstrate the principle, an optimal prototype system successfully determined the local void fraction and frequency in a pilot-scale reactor using liquid lead bismuth eutectic (LBE) as working fluid. The information obtained by the optical sensor allows for validation of computational fluid dynamics (CFD) models to aid the design of LBE-based nuclear reactors, as well as for other liquid metal gas systems in general.

•Dissolved oxygen is removed from LBE using a PbO cold trap for LBE.•PbO particles formed in LBE are captured on stainless steel filter discs.•Oxygen removal proceeds by PbO particle capture followed by growth.•The rate of oxygen removal from the system depends on the PbO growth rate.

Control of the dissolved oxygen concentration is crucial for the use of liquid lead bismuth eutectic (LBE) as a coolant of advanced nuclear reactors. An electrochemical oxygen pumping (EOP) system was applied to a non-isothermal liquid LBE loop in order to evaluate its capability to control oxygen in 700 liters of flowing LBE. Oxygen pumps were fabricated using one end closed tube of yttria partially stabilized zirconia (YPSZ) as the solid electrolyte and LSCF (lanthanum strontium cobalt ferrite) as electrode. The oxygen transfer through the oxygen pump was regulated by controlling the applied electric current using a PID controller with feedback from a potentiometric oxygen sensor. The oxygen was added to or removed from the LBE by oxygen pumps depending on target oxygen concentration and a process value given by the oxygen sensor. At low oxygen concentrations, oxygen removal rates were limited by oxygen mass transfer. This limitation could be overcome by operating the pumps above the decomposition potential of zirconia. (C) 2019 The Electrochemical Society.

Lead oxide (PbO) formation can occur in Lead-Bismuth Eutectic (LBE)-cooled nuclear systems in case of oxygen ingress or temperature decrease of the coolant beyond the normal operation ranges. In the present work the formation of lead oxide in an actively cooled LBE flow is studied. Computational fluid dynamics (CFD) is used to predict the nucleation, growth and dissolution of PbO particles. Solid oxide particles are modeled as a pseudocontinuous phase, using the Kinetic Theory of Granular Flow (KTGF) to account for particle-flow interaction. The particle size distribution (PSD) is accounted for using Population Balance Equations/Models (PBE/PBM). The results obtained from the model are qualitatively in good agreement with experimental results obtained in the MEXICO loop at SCK.CEN. The calculated PSD reveals that the majority of the oxide particles are expected to be in the sub-micron range. Experimental results indicate that in the studied conditions PbO nucleates in the LBE bulk leading to suspended particles in the LBE flow.

An increased interest in the use of liquid metals for novel energy conversion systems is present today. The Accelerator Driven System (ADS) called MYRRHA under design at the Belgian Nuclear Research Centre (SCK-CEN) is an example of such an innovative system. The use of Lead-Bismuth Eutectic (LBE) as a coolant for this reactor implies that an accurate knowledge on the chemical properties of the coolant needs to be available. An important factor is the risk of coolant oxidation due to oxygen ingress in the system. Although the formation of lead oxide (PbO) is well understood, the deposition mechanism and kinetics are not yet studied. In this work the deposition mechanism of PbO on 316L stainless steel is investigated. The evolution of the dissolved oxygen concentration during thermal cycling of LBE indicates that fouling of isothermal surfaces by PbO can only proceed by particle deposition. On the other hand, the fouling of non-isothermal surfaces by PbO is dominated by crystallization fouling. A real-time measurement of the PbO deposition rate shows an asymptotic behavior of PbO crystallization fouling. By predicting the onset of PbO nucleation and subsequent growth, a kinetic model for the crystallization fouling is put forward. Quantitative agreement between deposition rate predictions and validation measurements is obtained around 673 K.

Liquid lead-bismuth eutectic (LBE) is an important candidate to become the primary coolant of future, generation IV, nuclear fast reactors and Accelerator Driven System (ADS) concepts. One of the main challenges with the use of LBE as a coolant is to avoid its oxidation which results in solid lead oxide (PbO) precipitation. The chemical equilibria governing PbO formation are well understood. However, insufficient kinetic information is currently available for the development of LBE-based nuclear technology. Here, we report the results of experiments in which the nucleation, growth and dissolution of PbO in LBE during temperature cycling are measured by monitoring dissolved oxygen using potentiometric oxygen sensors. The metastable region, above which PbO nucleation can occur, has been determined under conditions relevant for the operation of LBE cooled nuclear systems and was found to be independent of setup geometry and thus thought to be widely applicable. A kinetic model to describe formation and dissolution of PbO particles in LBE is proposed, based on Classical Nucleation Theory (CNT) combined with mass transfer limited growth and dissolution. This model can accurately predict the experimentally observed changes in oxygen concentration due to nucleation, growth and dissolution of PbO, using the effective interfacial energy of a PbO nucleus in LBE as a fitting parameter. The results are invaluable to evaluate the consequences of oxygen ingress in LBE cooled nuclear systems under normal operating and accidental conditions and form the basis for the development of cold trap technology to avoid PbO formation in the primary reactor circuit.

Iron released by steel corrosion was found to be a key impurity in reactions with dissolved oxygen in liquid lead-bismuth eutectic alloys. The iron-oxygen-magnetite equilibrium was characterized, allowing the quantification of phenomena that are important for long-term operation of lead-alloy based installations such as corrosion rate control and management of precipitates.

Accurate knowledge of polonium evaporation from lead–bismuth eutectic (LBE) is crucial for the design of accelerator driven nuclear systems in which LBE is used as target material or coolant. In this work we investigated the relation between the oxygen content and its distribution in liquid LBE samples and polonium evaporation from these samples at 400 °C. A fraction of the polonium was rapidly released, and we found a correlation between the amount of this fast-released polonium and the amount of oxygen concentrated in an oxide layer on top of the LBE sample. A qualitative model describing the polonium evaporation behavior in relation to oxygen content and distribution in polonium-doped LBE samples is outlined.

It is widely recognized that the control of the activity of dissolved oxygen is essential for the use of lead–bismuth eutectic (LBE) as primary coolant for nuclear systems. A lead oxide mass exchanger (PbO MX) comprised of a packed bed of lead oxide spheres is a promising solution to regulate the dissolved oxygen activity in the LBE. In order to design and operate a PbO MX properly, the dissolution kinetics of PbO in flowing LBE should be determined. A high-fidelity Computational Fluid Dynamic (CFD) model of solid-to-liquid mass transfer has been developed to determine the mass transfer coefficient of a PbO MX in flowing LBE. We validated the developed CFD model against experimental data obtained from the LBE test loop CRAFT, at SCK•CEN. The model is in good agreement with the experimental data. The effect of the channel to particle diameter ratio (R) on the mass transfer coefficient was evaluated by using the validated model. A mass transfer correlation for PbO MX was obtained, in terms of the Sherwood number, by fitting the simulation results for the general case of a random packed bed with a porosity of about 0.4.

Potentiometric oxygen sensors with LBE/PbO and In/In2O3 reference electrodes coupled with yttria partially stabilized zirconia (YPSZ) have been developed for use in liquid lead-bismuth eutectic (LBE) over the temperature range from 200 to 450°C. The performance of sensors with LBE/PbO and In/In2O3 reference electrodes was evaluated comparing the oxygen activity measured in oxygen saturated LBE (from 200 to 450°C) with these sensors to the one measured by sensors with Bi/Bi2O3 and air/LSM (strontium-doped lanthanum manganite) electrodes, using same solid electrolyte and measurement setup. The sensors with LBE/PbO and In/In2O3 reference electrode performed well down to 200°C while the sensor with Bi/Bi2O3 showed significant deviations at 200°C.

Previous thermal hydraulic experiments with flowing lead bismuth eutectic (LBE) in the MYRRHA/XT-ADS windowless spallation target mock-up installed at the THEADES loop at the Karlsruher Institut fur Technologie have shown that the LBE flow in the target mock-up behaves as a vacuum pump. An experimental setup is built and tested at the THEADES loop for quantification of this effect. In this paper, experimental evidence shows that the vacuum effect of flowing LBE at 200 degrees C, under MYRRHA like geometry and nominal LBE flow conditions, leads to an equivalent vacuum pumping speed for nitrogen gas of the order of 1 l/s. This is sufficient to reduce the vacuum pressure in the target zone below 10(-3) mbar. (C) 2013 Elsevier B.V. All rights reserved.

Understanding polonium evaporation from lead-bismuth eutectic (LBE) is required for the design of nuclear installations that use liquid LBE as coolant or spallation target. In the present study we measured the time-dependent release of polonium from LBE samples in Ar/5 %H 2 and Ar between room temperature and 500 °C. Our experiments revealed that the majority of polonium in the samples evaporated according to established temperature correlations for the Henry constant of polonium in LBE. However a small fraction of polonium in the LBE behaved differently, causing a relatively large but transient polonium release at the start of evaporation experiments. We showed that this volatile fraction of polonium was located near the sample surface and was formed after prolonged exposure of the samples to air at room temperature. We speculate that the peculiar evaporation behavior of this surface polonium is caused by enrichment and association with an oxide layer.

•We developed an oxygen control system by using electrochemical oxygen pump for use in liquid LBE.•The oxygen pump was fabricated using partially stabilized zirconia and LSM–GDC composite.•Highly accurate control of the oxygen concentration in the LBE was achieved by the system.•The feasibility of using the pumping system for measuring corrosion kinetics of structural steels in liquid LBE was also demonstrated.

Qualitative and quantitative understanding of Po volatilization under different conditions is of key importance for safety assessments of lead-bismuth eutectic (LBE) based nuclear reactors, spallation targets and accelerator driven systems. In this work we explore the possibilities of the transpiration method in combination with simple models to study the equilibrium and kinetics of Po evaporation from highly diluted solutions in lead-bismuth eutectic between 600 and 1000 degrees C in Ar/5% H-2 and Ar. On the basis of evaporation experiments at various carrier gas flow rates, we identified the conditions of vapor saturation allowing the determination of equilibrium constants. From the limiting behavior at high flow rates, values for the maximal evaporation rate of Po from LBE were estimated. Measurements of evaporation as a function of time were consistent with the assumption that polonium dissolved in LBE obeys Henry's law. A theoretical analysis furthermore suggested that diffusion of polonium in LBE was not a rate limiting factor for evaporation under vapor saturation conditions. Newly determined values for the Henry constant of Po in LBE between 600 and 1000 degrees C were consistent with previously derived correlations.