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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 pseudo-continuous 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.

To support the design of an external filtering and conditioning system for the lead-bismuth cooled MYRRHA reactor, the formation and transport of iron oxide particles from corrosion products in the reactor primary system have been investigated for normal operating conditions. The regions of the reactor with the highest probability of oxide formation are identified by a local chemical equilibrium model for magnetite formation. This analysis reveals that magnetite precipitation generally occurs in regions with large temperature gradients. For the specific case of the MYRRHA reactor, these regions correspond to the transition region between the barrel and the upper plenum, mainly at the location of the holes in the top part of the barrel. The transport behaviour of solid oxides from these regions is then investigated with a multi-phase Euler-Lagrange particle tracking model of the MYRRHA primary system. The simulations show that the majority of large oxide particles (above 100 µm) will eventually move to the free surface without passing through the reactor core, thereby allowing their removal by an external filtering system with surface extraction. This indicates that such large particles present a minimal risk for sudden core blockage, which does not compromise reactor safety. On the other hand, particles below a threshold diameter identified at 40 µm cannot be efficiently filtered out by an external system since the majority follows the carrier liquid and re-enters the core during each LBE flow-through cycle. The continuous purification of the coolant is therefore necessary to avoid undesired build-up of suspended particles in the primary system. A preliminary design value of the required mass flow rate through the filters is identified with the support of numerical simulations.

Corrosion of steels in lead bismuth eutectic (LBE) cooled reactors can be mitigated by forming a protective oxide layer on the steel surfaces. The amount of oxygen necessary to ensure continuous oxide layer formation on fuel cladding depends on the characteristics of the steel and on the local temperature, local oxygen concentration and velocity of the LBE in contact with the steel. The most critical areas from a corrosion point of view are high temperature and low oxygen concentration regions. Wire-wrapped fuel assemblies (FAs) which are foreseen to be used in LBE cooled reactors, are characterized by hot spots and quasi-stagnant areas where oxygen could be depleted. Experimental measurements to verify whether the oxygen concentration in those critical areas is sufficiently elevated for oxide layer formation, are practically impossible. This information can be however obtained by numerical modeling. This paper focuses on the development of a numerical model of oxygen mass transfer in a 19-pin scaled fuel assembly (FA) representative of the MYRRHA reactor core. Oxidation of steels and oxygen transport from the bulk of the LBE to the surface of steels were simulated simultaneously. The simulations provide a local oxygen concentration mapping at steel/LBE interface enabling to identify the regions of the core which could be prone to corrosion due to oxygen depleted LBE. Operation recommendations for the MYRRHA reactor were given based on the simulation results.

Lead-Bismuth Eutectic (LBE) is an interesting candidate as coolant for future Accelerator Driven Systems (ADS) and Generation IV (Gen. IV) nuclear power plants. A well-known issue of liquid metal coolants is the need for coolant chemistry control and continuous purification. This paper presents a purification strategy for control of the dissolved oxygen content in LBE by means of a LBE cold trap. Although cold traps have been explored in the past for Sodium Fast Reactors (SFR) and more recently for lead-lithium (PbLi), advances on cold trapping for LBE are lacking behind. Formation of lead oxide (PbO) is promoted in a non-isothermal purification device (cold trap) to lower the dissolved oxygen concentration present in the liquid metal. Attachment of PbO particles to the stainless steel filter material is observed and continuous growth of captured PbO consumes oxygen from the liquid metal melt. A long-term purification campaign of more than one month is presented to demonstrate the increase in cold trap effectiveness with loading.

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.

Potentiometric oxygen sensors with metal–metal oxide reference electrodes including Cu/Cu 2 O, Ni/NiO and Fe/Fe 3 O 4 were tested in oxygen saturated lead–bismuth eutectic (LBE) over the temperature range from 200 to 450 °C to assess their minimum operating temperature limit. The performance of sensors with the three reference electrodes was compared to that of a sensor with air/lanthanum strontium manganese oxide (LSM) reference electrode using the same solid electrolyte material and measurement setup. The sensor with Cu/Cu 2 O reference electrode performed well down to 200 °C in oxygen saturated LBE, while those with Ni/NiO and Fe/Fe 3 O 4 showed significant deviations from expected values below 300 °C. Furthermore, the sensor with Cu/Cu 2 O electrode showed a response to temperature variations as fast as that of the air/LSM electrode over the entire temperature range of interest in liquid LBE.

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.

The development of integrated numerical codes based on Computational Fluid Dynamics (CFD) and high-fidelity chemical reaction modules, offers the opportunity of an accurate simulation of turbulent reactive transport in nuclear reactors. This is invaluable in the optimization of coolant chemistry for the safe operation of nuclear reactors. The aim of this article is to develop a multi-physics simulation tool, where the chemical equilibrium solver and database of the commercial HSC-Chemistry software are integrated with the widely used CFD code ANSYS FLUENT. The assumption of local chemical equilibrium is used for a coupled simulation. The coupling procedure between codes is performed by a sequential operator-splitting approach. In this framework, the HSC equilibrium solver is called sequentially from each cell of the FLUENT computational domain whose composition has changed from equilibrium. Both iterative and non-iterative time marching algorithms are implemented and can be selected, depending on the problem under investigation. Communication between the codes is handled by a custom-designed object-oriented coupler class. A compiled-linked-in integration between FLUENT, the coupler class and HSC is designed, in order to minimize CPU time by exchanging data directly in the main memory. The coupled simulator is verified and preliminary validated with examples of chemical systems relevant for Gen. IV nuclear reactors cooled by lead-bismuth eutectic (LBE). The tool shows good performances in terms of numerical accuracy and computational speed. Its complete functionality is then illustrated with an application related to localized-corrosion modeling in flowing LBE. This application showed that the integrated code based on FLUENT and HSC is a promising tool for a wide range of applications involving reactive transport simulations.

Electrochemical oxygen pumping method was applied in order to control the dissolved oxygen concentration in liquid lead–bismuth eutectic (LBE). The oxygen pump was fabricated using yttria partially stabilized zirconia (YPSZ) as a solid electrolyte and LSM (strontium-doped lanthanum manganite)–GDC (gadolinium-doped ceria) composite as a cathode. An oxygen control system, comprising of the oxygen pump, an oxygen sensor and a DC current source as well as a proportional-integral-derivative (PID) controller for the current control, was applied to regulate the dissolved oxygen concentration in liquid LBE. Highly accurate control of the oxygen concentration was achieved by this system. In addition, the feasibility of using the pumping system for measuring corrosion kinetics of structural steels in liquid LBE was demonstrated.

The evaporation of Po from its dilute solution in liquid lead–bismuth eutectic (LBE) was determined between 700 and 1000 °C in Ar/5%H2 by the transpiration method. Concurrent measurements of the evaporation of LBE could be well reproduced by calculations using literature data, confirming conditions of equilibrium and convective vapor transport in our transpiration method experiments. This allowed to model the Po evaporation data and extract accurate temperature correlations for the Henry constant for Po dissolved in LBE at two different Po concentrations. Extrapolations of the new correlations were in excellent agreement with existing data at lower temperature.

The evaporation behavior of polonium as one of the most hazardous radionuclides produced in spallation based neutron sources with liquid lead–bismuth targets has been quantified in this study. The normalized apparent vapor pressure, i.e. the Henry constant of polonium over liquid lead–bismuth eutectic was determined in the temperature range relevant for operation of such targets, i.e. 164–500 °C. For comparison and better fundamental understanding, the Henry constant of polonium over pure liquid bismuth was determined in a temperature range of 300–500 °C. The Henry constants of polonium in this temperature range were found to be orders of magnitude higher than expected from earlier studies at higher temperatures. Possible mechanisms responsible for this unexpected behavior are discussed.

Potentiometric oxygen sensors fabricated with yttria partially stabilized zirconia (YPSZ) and a Bi/Bi2O3 reference electrode were tested in oxygen saturated lead–bismuth eutectic (LBE) and oxygen saturated tin (Sn), respectively, in order to estimate the accuracy of the oxygen sensors prior to applying them to R&D work for MYRRHA. The accuracy of these sensors was estimated in the temperature range of 673–733 K by measuring the electromotive force (emf) of eight sensors. The standard deviation on the measured emf data was about 0.79 mV in the case of oxygen saturated LBE and was about 1.25 mV in the case of oxygen saturated Sn. These values result in a standard deviation of 4% on the oxygen concentration in LBE which is calculated from the measured emf.

Zeogrids and Zeotiles are hierarchical materials built from assembled MFI zeolite precursor units. Permanent secondary porosity in these materials is obtained through self assembly of nanoparticles encountered in MFI zeolite synthesis in the presence of supramolecular templates. Hereon, the aggregated species are termed nanoslabs. Zeogrids are layered materials with lateral spacings between nanoslabs creating galleries qualifying as supermicropores. Zeotiles present a diversity of tridimensional nanoslab assemblies with mesopores. Zeotile-1, -4 and -6 are hexagonal mesostructures. Zeotile-1 has triangular and hexagonal channels; Zeotile-4 has hexagonal channels interconnected via slits. Zeotile-2 has a cubic structure with gyroid type mesoporosity. The behavior of Zeogrids and Zeotiles in adsorption, membrane and chromatographic separation and catalysis has been characterized and compared with zeolites and mesoporous materials derived from unstructured silica sources. Shape selectivity was detected via adsorption of n- and iso-alkanes. The mesoporosity of Zeotiles can be exploited in chromatographic separation of biomolecules. Zeotiles present attractive separation properties relevant to CO2 sequestration. Because of its facile synthesis procedure without hydrothermal steps Zeogrid is convenient for membrane synthesis. The performance of Zeogrid membrane in gas separation, nanofiltration and pervaporation is reported. In the Beckmann rearrangement of cyclohexanone oxime Zeogrids and Zeotiles display a catalytic activity characteristic of silicalite-1 zeolites. Introduction of acidity and redox catalytic activity can be achieved via incorporation of Al and Ti atoms in the nanoslabs during synthesis. Zeogrids are active in hydrocracking, catalytic cracking, alkylation and epoxidation reactions. Zeogrids and Zeotiles often behave differently from ordered mesoporous materials as well as from zeolites and present a valuable extension of the family of hierarchical silicate based materials.

Researchers in need of an ordered nanoporous material tend to rely on the original synthesis protocols which often demand hydrothermal synthesis and involve harsh chemical conditions, expensive sacrificial templates and long synthesis times. Considerable efforts have been invested in developing new pathways to simplify synthesis procedures. While in the area of zeolites even with optimum templates intrinsic energy barriers of the crystallization process obstruct the development of easy room temperature synthesis, the synthesis of ordered mesoporous materials and metal organic frameworks (MOFs) are examples of materials for which synthesis can be rationalized and simplified. One key element for the development of room temperature synthesis is the selection of highly efficient templates.

Hexagonal mesoporous solids were synthesized from solutions containing TS-1 seeds. The products were characterized by XRD, nitrogen and argon physisorption, TEM, TG/DTA of template decomposition (also after extraction of the mesopore template), UV–Vis and IR spectroscopy, and XANES at the TiK edge. Their catalytic activities were assessed for cyclohexene epoxidation in hydrophilic and hydrophobic environment (CH3OH/water, with H2O2 oxidant, and decane, with tert-butyl hydro-peroxide oxidant, respectively) and for n-hexene epoxidation in hydrophilic environment. The mesopore system was clearly documented by XRD, physisorption measurements, and TEM, whereas evidence for micropores by physisorption proved elusive. However, the micropore template was detected in the solids by TG/DTA even after extraction of the mesopore template, and among the Ti sites, which were confirmed to be tetrahedrally coordinated by UV–Vis and XANES, a clear majority was able to coordinate two water molecules. It was concluded that the pore walls had been built up from nanoparticulate TS-1 precursors resulting in walls of ca. 1.5 nm thickness, which resemble rather the exterior layers of a TS-1 crystallite than its (hydrophobic) interior. In cyclohexene epoxidation, the micro-mesophases were by 1–2 orders of magnitude more active than TS-1 and outperformed also Ti-MCM-41, at similar selectivity in hydrophobic medium. With 1-hexene in hydrophilic medium, however, the micro-mesophases failed completely whereas TS-1 exhibited high activity.

Ordered mesoporous materials with specific microporosity in the mesopore walls can be assembled by a secondary templating synthesis departing from a clear subcolloidal suspension dedicated to the tetrapropylammonium (TPA) mediated synthesis of colloidal Silicalite-1. A typical member of this material family is Zeotile-2. Zeotile-2 is mesostructurally similar to the cubic MCM-48 material with exceptional long-range order of the mesostructure. Zeotile-2 samples in which the TPA was either left or evacuated were prepared by leaching in boiling ethanolic acetic acid and calcination. The evacuation of the TPA gave rise to a substantial micropore volume revealed with nitrogen adsorption isotherms. The mesoporosity was independent of the presence of the TPA. Molecular separations of isooctane/octane mixtures illustrated the occurrence of molecular shape selectivity similar to MFI-type zeolites.