Heavy Liquid Metal Coolant Research Articles

Reaction Capsule Design for Interaction of Heavy Liquid Metal Coolant, Fuel Cladding, and Simulated JOG Phase at Accident Conditions

High temperature corrosion of fuel cladding material (15-15Ti) in high burn-up situations has been an important topic for molten metal-cooled Gen-IV reactors. The present study aims to investigate the simultaneous impact of liquid lead (coolant side) and cesium molybdate (fuel side) on the cladding tube material. A capsule was designed and built for experiments between 600 °C and 1000 °C. In order to simulate a cladding breach scenario, a notch design on the cladding tube was investigated pre- and postexposure. Material thinning by corrosion and leaching at temperatures ≥ 900 °C caused breaches at the notches after 168 h exposure. The temperature dependent cladding thinning phenomenon was used for kinetic interpretation. As the first of a two-part study, this paper will focus on the exposure capsule performance, including metallographic cross-section preparation and preliminary results on the interface chemistry.

Advancement Toward the Experimental Measurement of the Lead–Bismuth Eutectic Thermal Properties Using Differential Scanning Calorimetry Technique

Abstract The differential scanning calorimetry (DSC) method has recently emerged as a sophisticated and precise technique for promising contributions to the thermal analysis of various materials, including heavy liquid metal (HLM) coolants. However, there is a lack of experimental studies on the thermal properties of lead-based fluids, such as lead–bismuth eutectic (LBE) and lead–lithium eutectic, which are potential candidates for use as coolants, breeders, and neutron multipliers in advanced nuclear systems like the fourth-generation lead-cooled fast reactor. The available experimental data on the thermal properties of LBE and other lead-based fluids is limited, and the measurements have significant uncertainty. In addition, the composition of components used in the previous studies is inconsistent, and the environmental conditions were often unknown. Therefore, to fill these gaps and advance the thermal properties measurement technique for heavy liquid metal coolants, ENEA Brasimone, in collaboration with DICI-UNIPI, has installed a DSC instrument setup. The experiments performed at the installed DSC setup are focused on measuring some essential thermal properties of LBE using DSC. The experience gained from this work will facilitate the measurement of other fluids based on lead alloy, especially lead–lithium eutectic, a potential candidate for breeder, coolant, and neutron multiplier in demonstration power plant fusion reactors. This study represents the first effort to advance the DSC approach for accurately measuring the thermal characteristics of heavy liquid metals that are highly reactive, such as lead–lithium, which has significant potential in advanced nuclear systems.

Heavy liquid metal cooled fast reactors: peculiarities and development status of the major projects

Fast reactors with heavy liquid metal coolant (lead or eutectic bismuth-lead alloy) are one of the most advanced technologies capable to address the accumulated world nuclear energy issues. This innovative power technology is being developed in Russia, the USA, China and the European Union. Russia is the leader since it has focused on this topic for a number of decades. First concrete started to be poured in June 2021 to form the foundation of the Russian BREST-OD-300 lead cooled reactor scheduled to be started up in 2026. Attention is also given to the development status of the Chinese CLEAR reactor series. A large scope of R&D has been undertaken, and large-scale nonnuclear experimental facilities are under construction. International Euro-US consortiums for the development of the ALFRED, PLFR and MYRRHA reactors do not expect any unsolvable technical issues either and are currently formulating requirements to the test facilities and candidate materials and technologies required for further activities.

Model of interaction of a steam-water cavity with a molten metal near a solid wall

To evaluate the consequences of an accidental rupture of a steam generator heat exchange tube in a reactor with a heavy liquid metal coolant, a mathematical model of the interaction of a steam-water cavity with molten metal near a solid wall was developed. The melt flow is considered as a potential flow of an incompressible fluid. The heat exchange between the melt and the steam-water mixture is not taken into account. The steam-water mixture is modeled by an equilibrium two-phase model. It is believed that the evolution of the steam-water cavity is an isentropic process. The numerical implementation of the mathematical model was performed using the boundary element method. Verification of the developed model using a numerical solution of a spherically symmetric problem of the interaction of a spherical steam-water cavity with a melt in infinite space, obtained using the Rayleigh-Plesset equation, showed good agreement between the solutions obtained by different methods. Using the developed model, a test calculation of the interaction of a steam-water cavity with the surrounding molten metal near a solid wall was performed. Analysis of the calculation revealed several stages of this interaction

The Current State of Development and Prospects for the Creation of Sensors of Thermodynamic Activity of Oxygen in Relation to Reactor Units with a Heavy Liquid Metal Coolant

Successful development of the world nuclear energy is not possible without a transition to a new technological platform. The most promising nuclear technology for this today seems to be fast reactors cooled by liquid metal coolants. In 2021, the construction of the world’s first nuclear power plant with a fast reactor BREST-OD-300 began in the city of Seversk, Russia. This reactor, having a number of innovative solutions, uses liquid lead as the primary coolant. Lead belongs to the class of heavy liquid metal coolants and is similar in technological properties to the Pb-Bi eutectic alloy. Since the 60s of the last century, special attention has been paid to the substantiation of the operability and safety of heavy liquid metal coolants in Russia. The key element of the technology of such a coolant is the thermodynamic oxygen activity sensor, which controls the oxidation potential of the coolant and ensures the cleanliness and corrosion resistance of the circuit. This article provides an overview of the main design solutions proposed for the oxygen activity sensor, their analysis is given, and proposals for the development of an improved sensor design that would meet the requirements of large-scale nuclear power are considered.

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.

Corrosion behaviour of P-91 steel and type 316 LN stainless steel with and without a ceramic coating in the lead with oxygen at 550°C

The corrosion issues of structural materials in a molten lead environment are the major problem for the heavy liquid metal coolants (Pb, Pb-Li or Pb-Bi eutectic) based future advanced nuclear reactors. The present study focused on providing understanding to the corrosion and its mechanisms of P-91 steel and type 316LN stainless steel (SS) in as received and 50% Al2O3 - 50% Y2O3 Atmospheric Plasma Spray (APS) coated conditions in the molten lead with 10−5 wt.% oxygen at 550 °C for different exposure durations. The uncoated P-91 steel revealed an increase in dissolution attack with time and formation of magnetite (Fe3O4) and spinel oxides (FeCr2O4) as corrosion layer. The microstructural cross-sectional examination of type 316LN SS showed that the penetration depth difference was not significant between 1500 h and 2000 h, and the corrosion rate is faster in the initial period of molten lead exposure and slows down with time. Ferritization occurs in the Ni and Cr depleted outer surface regions. The post molten lead exposure characterization revealed the dominant corrosion mechanism as dissolution and oxidation without phase transformation for P-91 steel, whereas the dissolution mechanism led to phase transformation in 316LN SS. The protective alumina-yttria coated P-91 steel served better in the molten lead, but the coated 316LN SS exhibited coating compatibility issues by crack formation and delamination, which is attributed to the high coefficient of thermal expansion of type 316LN SS substrate. The work provides a new understanding of the corrosion mechanism of ceramic composite coated P-91 steel and type 316LN SS in a molten lead environment for different exposure durations.

Lagrangian Investigation of Convective Mass Transfer of Dissolved Elements at Specimen Boundaries in a Flowing Molten Lead Loop

Mass transfer is the dominant mode of structural material corrosion in energy systems employing heavy liquid metal coolant such as lead-cooled reactors. Modeling efforts in the literature have focused on materials science aspects, such as diffusive transport of alloying elements in structural materials and oxide layers, oxide layer growth and erosion, and species dissolution at the interface, but they have overlooked convective transport which is often represented by simplified one-dimensional models with no transverse convection. Here, within a Lagrangian framework, we particularly study the convective transport of dissolved elements at specimen boundaries in a flowing molten lead loop. Three-dimensional transient Reynolds-averaged Navier-Stokes simulations coupled with particle transport are carried out to compare convective transport in lead and other coolants, such as lead-bismuth eutectic, pressurized water, and sodium. Transverse convection in the narrow test section is observed to occur at a timescale comparable to longitudinal (downstream) transport and removal of particles from the test section, which highlights the need for three-dimensional modeling in the present setup. The effects of temperature, surface roughness, and mean flow velocity on convective transport in lead are investigated. While mean flow velocity is the dominant variable affecting convective mass transfer, increased surface roughness and reduced temperature are also shown herein to moderately enhance convective transfer.

ДИССОЦИАЦИЯ ОКСИДОВ ЖЕЛЕЗА В РАСПЛАВАХ ТЯЖЕЛЫХ МЕТАЛЛОВ

At present, the problem of providing corrosion resistance of steels in heavy liquid metal coolants is solved by forming and maintaining protective oxide films on the surfaces of structural steels. However, oxide films are not absolutely impermeable barriers for the components of steels (primarily iron), which, as a result of diffusion processes, inevitably enter the coolant and can interact with oxygen to form solid-phase oxides. Within the framework of this work, a method is considered for obtaining the numerical values of the quantities characterizing the processes of dissociation of iron oxides as a function of temperature and oxygen potential of HLMC. The performed calculations made it possible to obtain specific numerical values of the limiting solubilities of iron oxides as a function of the temperature and the initial state of the coolant with respect to iron and oxygen impurities, and also made it possible to obtain numerical values of other thermodynamic parameters characterizing the current and limiting state of HLMC. The considered approach is of a general nature and can be used in experimental studies of the kinetic and thermodynamic characteristics of the dissociation processes of compounds in liquid metals.

Features of methods for monitoring the fuel cladding tightness in lead-cooled fast breeder reactors

To timely detect failed fuel elements, a reactor plant should be equipped with a fuel cladding tightness monitoring system (FCTMS). In reactors using a heavy liquid-metal coolant (HLMC), the most efficient way to monitor the fuel cladding tightness is by detecting gaseous fission products (GFP). The article describes the basic principles of constructing a FCTMS in liquid-metal-cooled reactors based on the detection of fission products and delayed neutrons. It is noted that in a reactor plant using a HLMC the fuel cladding tightness is the most efficiently monitored by detecting GFPs. The authors analyze various aspects of the behavior of fission products in a liquid-metal-cooled reactor, such as the movement of GFPs in dissolved and bubble form along the circuit, the sorption of volatile FPs in the lead coolant (LC) and on the surfaces of structural elements, degassing of the GFPs dissolved in the LC, and filtration of cover gas from aerosol particles of different nature. In addition, a general description is given of the conditions for the transfer of GFPs in a LC environment of the reactor being developed. Finally, a mathematical model is presented that makes it possible to determine the calculated activity of reference radionuclides in each reactor unit at any time after the fuel element tightness failure. Based on this model, methods for monitoring the fuel cladding tightness by the gas activity in the gas volumes of the reactor plant will be proposed.

Measurements of pitch-off diameter of gas bubbles in liquid metal

To determine the separation diameter of bubbles in a liquid metal melt, an original technique based on the conductivity method is proposed. A thin electrode is installed in the center of the outflow channel, and the separation of bubbles is determined by closing and opening the electrical circuit. In this way, the separation frequency of the bubbles and their volume can be determined. Additional studies are carried out on a transparent liquid (water). It is shown that the presence of an electrode has little effect on the process of bubble detachment. The processing data of high-speed video filming and the proposed method in a transparent liquid coincide with high accuracy. Measurements of the frequency of bubble detachment in melts of the Rose and lead alloy are carried out. The results obtained are used to tune two-phase flow models when simulating fast neutron reactors with heavy liquid metal coolants.

Numerical investigation on the hydraulic loss correlation of ring-type spacer grids

An accurate prediction of the pressure drop along the flow paths is crucial in the design of advanced passive systems cooled by heavy liquid metal coolants. To date, a generic pressure drop correlation over spacer grids by Rehme has been applied extensively, which was obtained from substantial experimental data with multiple types of components. However, a few experimental studies have reported that the correlation may give large discrepancies. To provide a more reliable correlation for ring-type spacer grids, the current numerical study aims at figuring out the most critical factor among four hypothetical parameters, namely the flow area blockage ratio, number of fuel rods, type of fluid, and thickness of the spacer grid in the flow direction. Through a set of computational fluid dynamics simulations, we observed that the flow area blockage ratio dominantly influences the pressure loss characteristics, and thus its dependence should be more emphasized, whereas the other parameters have little impact. Hence, we suggest a new correlation for the drag coefficient as CB = Cv,m/ε2.7, where Cv,m is formulated by a nonlinear fit of simulation data such that Cv,m = −11.33 ln(0.02 ln(Reb)).

ИССЛЕДОВАНИЕ ХАРАКТЕРИСТИК ГРАНУЛ ОКСИДА СВИНЦА ПОСЛЕ ДЛИТЕЛЬНОЙ ВЫДЕРЖКИ В ЖИДКОМ СВИНЦЕ

In order to ensure the safe operation of reactor installations under development with heavy liquid metal coolants (HLMC), such as lead and lead-bismuth, it is necessary to address issues related to the control and regulation of the oxygen potential of the coolant. This is necessary to maintain the normalized range of dissolved oxygen concentrations to ensure the conditions for the formation and maintenance of the integrity of protective oxide coatings on structural materials, as well as to prevent the formation of oxide slags from the coolant during the operation of the reactor plant. Specialists of IPPE have developed a method and a means of solid-phase regulation of the thermo-dynamic activity of oxygen in HLMC. In mass transfer devices developed for the implementation of the solid-phase method of controlled feeding of a heavy liquid metal coolant with dissolved oxygen, lead oxide granules are used as a filler. One of the important issues in substantiating the reliability of mass transfer devices is the question of the constancy of the mechanical properties and chemical composition of lead oxide granules after their prolonged stay under the level of a heavy liquid metal coolant at operating temperature. The lead oxide granules were aged in a sealed container filled with lead. The tank was equipped with the necessary means to control the temperature of the lead and the pressure of the protective gas (argon). The article presents the results of experimental studies of lead oxide granules after their exposure in a lead melt at a temperature of (420±10) °C in a non-carbon mode for 6000 hours. To investigate the characteristics of the lead oxide pellets, a batch of pellets was excavated after 500, 750, 1000, 1750, 2500, 3000, 4500 and 6000 hours from the start of the tests. For the pellets from each recess, the following studies were performed: - pellet density measurements; - measurement of breaking forces of lead oxide granules; - determination of pellet impact strength; - chemical analysis of granule composition.

РАСЧЕТНО-АНАЛИТИЧЕСКИЕ ИССЛЕДОВАНИЯ ОБРАЗОВАНИЯ И НАКОПЛЕНИЯ ОТЛОЖЕНИЙ В КОНТУРЕ С ТЖМТ В РАМКАХ СОГЛАСОВАННОЙ МОДЕЛИ ПРОТЕКАНИЯ ФИЗИКО-ХИМИЧЕСКИХ ПРОЦЕССОВ

An engineering model has been analyzed for a self-consistent calculation of the growth of an oxide film in circulation circuits with a heavy liquid metal coolant and concentrations of impurities (oxygen, iron, and magnetite) from the point of view of a possible uncertainty in determining the oxygen activity. The modeling of thermohydraulic and physicochemical processes is based on solving the associated three-dimensional equations of hydrodynamics, heat transfer, convective-diffusive transport, and the formation of chemically interacting impurity components in the coolant volume and on the surface of steels. The yield of iron and the formation of magnetite are due precisely to the specifics of self-consistent physicochemical processes in the oxide film and at the interface. There have been conducted model calculations of the influence of the uncertainty of oxygen activity on the speed and the integral yield of iron, which under the given conditions of the oxygen regime after an interaction with oxygen causes the appearance of magnetite. It has been numerically demonstrated that in the saturation mode there is a model-independent characteristic, which is determined by the parabolic constant and thickness of the oxide film characteristic of steel.

СОВРЕМЕННОЕ СОСТОЯНИЕ И ЗАДАЧИ РАЗРАБОТОК ПО ТЕХНОЛОГИИ ТЯЖЁЛЫХ ЖИДКОМЕТАЛЛИЧЕСКИХ ТЕПЛОНОСИТЕЛЕЙ (Pb, Pb-Bi)

The technology of heavy liquid metal coolant (HLMC) is an important part of the safety system for the operation of reactor facilities with HLMC at all stages of their life cycle: from the preparation of a coolant and loading into the reactor to the decommissioning of the reactor facility (RF). The technology of heavy liquid metal coolant is a set of measures that allow: - to prepare the coolant for filling in the primary circuit of the RF; - to maintain the conditions in the coolant to ensure the corrosion resistance of structural steels; - to perform the coolant cleaning from solid-phase slags both based on lead oxides and based on oxides of structural steel components; - to clean the protective gas from coolant aerosols and corrosion products; - to perform the diagnostics of the contour state. HLMC technology includes both methods of performing technological operations, as well as special equipment, controls, and analysis methods. To date, a significant amount of research and development work has been carried out for the implementation of HLMC in the “BREST-OD-300” and special-purpose RF. The report paper presents the achievements in the field of HLMC technology in recent years of the work of the staff of IPPE JSC.

ПОДДЕРЖАНИЕ КАЧЕСТВА СВИНЕЦСОДЕРЖАЩИХ ТЕПЛОНОСИТЕЛЕЙ В ПЕРСПЕКТИВНЫХ ТЕХНОЛОГИЯХ ПЕРЕРАБОТКИ ОРГАНИЧЕСКОГО И НЕОРГАНИЧЕСКОГО СЫРЬЯ

The unique properties of heavy liquid metal coolants (low chemical activity when interacting with air, organic compounds, water and water vapor, high boiling point, low vapor pressure) allow them to be used both in the first circuits of fast neutron reactor plants and in heat exchangers used for processing various organic and inorganic raw materials. Such devices can be either recuperative or mixing type. The latter additionally have the following advantages: lower cost and simplicity of construction; no heat transfer surfaces that can be subject to corrosion and contamination; reduced dimensions due to a larger specific heat transfer surface. The greatest degree of study relates to liquid metal pyrolysis of solid substances, direct contact distillation of aqueous solutions without preliminary preparation, improving the efficiency of continuous casting machines due to the replacement of water with lead-bismuth eutectic. The results of research in support of the above processes are presented. The methods of maintaining the quality of lead-containing heat carriers do not have fundamental differences for the conditions of reactor installations and in relation to promising technologies for processing organic and inorganic raw materials. At the same time, the requirements for devices for implementing these methods in promising technologies for processing various raw materials are significantly lower: in general, a sensor for measuring the thermodynamic activity of oxygen and a device for entering gas (hydrogen-containing or oxygen-containing) mixtures in the coolants.

Modeling of Gas-Phase Transport in Heavy Liquid-Metal Coolant Flow in the HYDRA-IBRAE/LM Thermohydraulic Code

Approaches to modeling gas-phase transport in heavy liquid-metal coolant flow in the HYDRA-IBRAE/LM code, which is actual for safety validation of nuclear reactors with a leak in the steam-generator tubes, are examined. A hierarchy of models for determining the dispersed-particle size that are implemented in the code for bubble flow is presented: empirical correlation, transport equation for the density of the interfacial surface area, and kinetic equation for the particle-size distribution function. The results of test calculations are presented.

ОЦЕНКА НИЗКОКИСЛОРОДНОЙ ГРАНИЦЫ СУЩЕСТВОВАНИЯ ПЛЮМБОФЕРРИТНЫХ ФАЗ В РАСПЛАВЕ СВИНЦА

At present, installations with heavy liquid metal coolants (HLMC) based on lead melts are considered as promising nuclear power plants, since these coolants have a number of advantages over alkali metals and other coolants. A feature of heavy liquid metals is their rather high corrosivity towards structural materials; however, at present this problem has been partially solved due to the formation of protective oxide coatings on the surfaces of steels based on oxides of metal components of structural steels. This determines the main tasks of modern HLMC technology, which are to provide conditions for the formation and maintenance of oxide layers with optimal protective properties on the surfaces of structural steels. The success of solving these problems in the general case depends on an adequate representation and quantitative description of the properties of the system “liquid metal melt - oxide phase”. In this work, we consider the questions of the possibility of the formation of plumboferrite phases in liquid lead, their composition and thermodynamic properties.

Radionuclide Chemistry in Nuclear Facilities Based on Heavy Liquid Metal Coolants: Past, Present and Future.

Heavy liquid metals such as lead and lead bismuth eutectic (LBE) are considered as spallation target material for next-generation neutron sources and as coolant of fast spectrum nuclear reactors that are developed to facilitate more efficient use of nuclear fuel as well as transmutation of long-lived nuclear waste. During the operation of such facilities, the heavy liquid metal will be activated by nuclear reactions. Additionally, fission product radionuclides may be introduced into the liquid metal from leaking fuel pins or by fission of the target nuclei in spallation. The chemical behaviour of these radioactive contaminants in the liquid metal - especially their immediate volatilization or volatilization of formed secondary compounds - may affect the safety of such facilities. The present article summarizes the activities of PSI's Laboratory of Radiochemistry towards a better understanding of the chemistry of potentially hazardous radionuclides in LBE and discusses aspects that need to be addressed in future to support the licensing of heavy liquid metal-based nuclear facilities.

Integrated researches of topical problems of fast reactors thermal physics

The results of actual studies are presented to justify the thermophysical characteristics and safety of fast reactors with sodium and lead coolants. The influence of a stratified coolant flow on the formation of velocity and temperature fields in a fast reactor vessel with a sodium coolant is shown. The development of the degradation of the fuel assembly during the development of a severe accident with the loss of sodium flow rate in a fast reactor, the blockage of the cross sections of the fuel assembly and the release of marker materials beyond it are demonstrated. The expediency of the combined sodium purification system built into the reactor vessel is shown, in which “cold traps” are an indispensable element, and “hot traps” provide accelerated oxygen purification during operation of the NPP in nominal regime. The results of studies of a large-modular sodium-water steam are presented. As applied to a reactor with a lead coolant, the influence of spacer grids on heat transfer in a fuel assembly of the core is shown. On the model of the steam generator of the reactor installation with lead coolant, it was found that the values of the steam temperature at the outlet of both collectors coincide. The temperature of lead at the exit from the lowering section and in the main path of lead is coincides also. The state and prospects of the development of technology for heavy liquid metal coolants are analyzed. The principle possibility of providing the required parameters of a high-temperature fast reactor with a sodium coolant for the production of hydrogen is shown. The problems of further thermophysical research are analyzed.