Sergey Yakush

• PhD, Dr. Sci
• Head of Department at Russian Academy of Sciences

Mixtures of hydrogen with common hydrocarbon fuels are considered viable for reducing carbon footprint in modern industry, power production, and transportation. The addition of hydrogen alters the kinetics and thermophysical properties of the mixtures, as well as the composition and properties of combustion products, requiring detailed research int...

Experiments on the melting and regression of a slab-shaped paraffin sample in a hot gas flow are conducted in a wide range of gas temperature, pressure, and mass flow rate in order to establish a parametric dependence of the regression rate on the operating conditions and process parameters. In some tests, ignition of the fuel vapor and droplets oc...

The hydrodynamic and thermal interaction of water with the high-temperature melt of a heavy metal was studied via the Volume-of-Fluid (VOF) method formulated for three immiscible phases (liquid melt, water, and water vapor), with account for phase changes. The VOF method relies on a first-principle description of phase interactions, including drag,...

The model of interaction of a water jet with a melt was validated using experimental data from experiments in which a water jet was injected into a vessel filled with a melt of a eutectic alloy of lead and bismuth. The model is based on the VOF method for immiscible liquids. In the experiments, the experimental data of which were used to validate t...

One of the possible consequences of a severe accident at a nuclear power plant with a pressurized water reactor is a steam explosion that occurs as a result of the interaction of a high-temperature melt of core materials with water and can lead to the failure of the containment. The paper considers the initial stage of the steam explosion (premixin...

The article considers the existing models and correlations for describing heat transfer during film boiling. Film boiling is an important thermophysical process that determines the course of interaction of the melt of reactor core materials with the coolant, which can potentially occur during a severe accident at a nuclear power plant with a pressu...

The impingement of a short-duration water jet on a pool of molten Rose’s metal is studied experimentally herein. Short-duration water jet impacting on the free surface of a molten metal pool with a temperature of 300 °C are generated with a pneumatic water delivery system, with two-camera high-speed video registration. A total of 14 experimental se...

Multi-parameter study on the subsonic equilibrium air plasma flows in the cylindrical discharge channel of an induction RF-plasmatron IPG-3 with the maximum operating power of 1 MW is presented. Simulations are carried out by numerical solution of full Navier–Stokes equations coupled with a two-dimensional equation for high-frequency electric field...

In the present work, the effect of a noncondensable gas on the collapse of a hot bubble in cold water was studied. It is assumed that the bubble consists of a gas mixture of steam, which can condense on cold water, and a noncondensable gas. The dynamics of the bubble was modeled by the integral equations of mass and energy supplemented by the steam...

Flame interaction with obstacles can affect significantly its behavior due to flame front wrinkling, changes in the flame front surface area, and momentum and heat losses. Experimental and theoretical studies in this area are primarily connected with flame acceleration and deflagration to detonation transition. This work is devoted to studying lami...

Gas-phase combustion of methylmethacrylate (MMA) monomer is an essential stage of solid polymethylmethacrylate (PMMA) combustion, which is of interest in many applications. A skeletal kinetic scheme for MMA combustion in air is proposed including 44 irreversible elementary reactions for 29 species. The mechanism is derived from the reduced kinetic...

На основе численного решения уравнений многокомпонентного реагирующего газа в приближении малых чисел Маха представлена вычислительная модель горения предварительно перемешанной смеси в узком зазоре между параллельными пластинами. Применяется алгоритм поблочного адаптивного измельчения сетки, позволяющий достигать высокого разрешения в областях рез...

Splashes of high-temperature melt spreading over a water pool bottom can be a reason for the formation of a zone where melt, water and steam are mixed, providing conditions for powerful steam explosions. The paper considers the formation of melt splashes arising from the impact of a water jet on the surface of the melt. Numerical simulations are pe...

The influence of bubbles of hot non-condensable gas formed at the interface between the melt and water on the formation of a mixture of melt with water capable of producing steam explosions is considered. The dynamics of such a bubble in subcooled water is analyzed numerically in a one-dimensional spherically symmetric approximation. It is shown th...

A collapse of the vapour film separating a hot melt droplet from the surrounding water due to sudden ambient pressure rise is considered. The pressure peak causes a direct contact between water and melt, leading to significant disturbances of the melt droplet surface. Results of numerical simulations performed by the VOF method are presented. Param...

200°С) капли воды диаметром D = 0.42 см со скоростью U = 3.3 м/с, впервые прослежены методами фото-и видеорегистрации. В режиме образования всплеска группы мелких капелек воды последовательно выбрасываются с вершин шипов на пелене вокруг области первичного контакта, затем с шипов на кромке слоя растекания воды. Далее капельки воды выле-тают вертика...

Changes in the composition of groups of droplets (sprays) emitted by a drop of water 0.42 cm in diameter at a velocity of 3.3 m/s falling into a crucible with a metal melt (Rose alloy at a temperature of 200 ° C) were traced by photo and video recording for the first time. In the splash formation mode, groups of small water droplets are subsequentl...

Results of numerical modeling of solid fuel melting and shedding by hot gas flow are presented. The computational model is based on the Volume-of-Fluid approach, implemented on a two-dimensional Cartesian grid, with one-equation turbulence model. Simulations are presented for a slab of wax interacting with a parallel gas flow, with the properties t...

Featured Application Nuclear safety, stratified steam explosion. Abstract Small-scale experimental studies of melt splashing upon the impact of water are presented here, with a focus on the fluid dynamics and thermal aspects of these interactions. Gravity-accelerated droplets and forced short-duration water jets interacted with liquid Rose’s alloy...

The paper is devoted to numerical study of the influence of the initial shape of a vapor bubble on the surface impact of the water jet emerging due to the bubble collapse. This problem is relevant to spreading of high-temperature melt under a layer of subcooled water. The vapor bubbles formed on the melt-water interface, upon complete penetration i...

As a pre-requisite for powerful steam explosion following the spread of molten high-temperature material over the bottom of water pool, a premixed zone must be formed with certain contents of melt, water, and vapour. Experimental observations indicate that melt spreading is featured by the formation of periodic melt splashes which can be responsibl...

Numerical simulations are performed for a spherical bubble containing hot vapor in subcooled water. Unlike conventional cavitation problems, the initial pressure in the bubble and surrounding liquid are equal to each other. The physical mechanism for the appearance of pressure difference driving the bubble collapse is rapid cooling and condensation...

Collapse of a hot vapour bubble captured by subcooled water can produce a cumulative jet similar to that appearing in cavitating flows. In the context of stratified steam explosions following spreading of hot melt under a water layer, impact of the water jets can be a reason for melt splashes promoting the mixing of cold and hot liquids necessary f...

Collapse of superheated vapor bubbles in subcooled water is studied from the viewpoint of possible mechanisms of premixed zone formation in stratified vapor explosions. Numerical modeling is performed for spherically symmetric bubble collapse in subcooled water, with different initial vapor superheats. The kinetic energy of liquid flow generated du...

A computational model of low-melting solid fuel regression in the combustion chamber of hybrid rocket engine is presented. The numerical model is based on a system of governing equations with simple effective viscosity model accounting for turbulence the gas phase. The numerical model takes into account heating of the solid fuel by the heat flux fr...

The paper discusses the physical background of explosive phenomena caused by internal energy release in substances undergoing liquid-to-vapor phase transition. Two types of “physical” explosions are discussed: the boiling liquid expanding vapor explosion arising upon catastrophic failure of high-pressure vessels and known as one of major hazards in...

A two-dimensional three-phase mathematical model of forest fires constructed by the method of averaging over the height of the forest fuel layer is considered. The gas phase in the model is described by gas dynamics equations with the k − ε turbulence model and the eddy breakup model to describe the rate of turbulent combustion and the rate of heat...

Выполнен анализ недавних экспериментов по исследованию стратифицированных паровых взрывов с использованием так называемых частичных адиабат Гюгонио. Под последними понимаются кривые, которые получаются в результате решения соотношения Гюгонио, однако, в данном случае смягчается требование о полной фрагментации расплава и его перемешивания с охладит...

A multiphase model for steam explosion is considered, with assumption of mechanical equilibrium between water and vapor phases in the mixture, but with non-equilibrium drag and heat exchange with high-temperature melt droplets taken into account. Governing equations are formulated and solved numerically. Simulations of pressure waves following ther...

Stability of combustion in solid fuel scramjets is contingent upon proper geometry of fuel grain and availability of a flame holder. Flame stabilization is achieved in the recirculation zone developing due to sudden expansion behind the inlet. Previous experimental and theoretical works suggest that there exists an optimum range of length-to-diamet...

Detailed comparison of numerical results obtained for IPG−4 plasmatron (base case), IPG − 3H hypothetical plasmatron and IPG − 3 real plasmatron is provided to estimate the accuracy of the similarity conditions and the applicability of that conditions for the pair of IPG − 4 and IPG − 3 plasmatrons. IPG − 3H hypothetical plasmatron is geometrically...

This work is motivated by the problem of restraining temperature escalation inside a porous heat-releasing media submerged in a pool of liquid coolant. When coolant temperature reaches saturation, boiling begins in the bulk of the porous bed, with void generation rate determined by the heating power. Amount of void determines hydrostatic pressure d...

Recent experimental results on stratified steam explosion are analyzed by the model of “non-ideal” thermal detonation based upon Hugoniot relations, with factors taking into account incomplete melt fragmentation and participation of liquid coolant. The pressure behind the shock wave and conversion ratio are obtained as functions of the mass fractio...

Lead-cooled fast reactors have several advantages in comparison to thermal neutron reactors and sodium-cooled fast reactors. Despite the considerable interest of international nuclear power community to this technology, safety issues associated with possible chain rupture of steam generator tubes initiated by rupture of a single tube in the tube bu...

Experimental results on laminar propane flames propagating in a narrow gap between parallel glass plates are presented. Development and evolution of cellular flame structure is demonstrated by video and long-exposure photo recordings for stoichiometric and fuel-rich mixtures with equivalence ratio of 1.0:1.25. It is shown that in narrow gaps the la...

Software was developed to calculate electric field amplitude in the induction plasmatron discharge channel in framework of 2D model with far field boundary conditions. This code was integrated with the solver for Navier-Stokes equations for plasma flow in the plasmatron channel. Numerical simulation of inductively coupled plasma flow was carried ou...

A computational model is presented for a solid-fuel ramjet engine with an axisymmetric combustion channel in a fuel grain containing a wider section near the air inlet. The latter part of the channel serves as a flame holder where a recirculation zone develops providing necessary combustion stabilization. The model is based on RANS equations, with...

Flash evaporation of a superheated water droplet in heavy liquid metal coolant (lead) is considered, in application to the analysis of a lead-cooled fast reactor steam generator tube rupture accident. The model is based on thermodynamic equilibrium formulation for the expanding water-steam mixture and inviscid compressible formulation for the surro...

On the basis of a multistep kinetic mechanism for flame inhibition by organophosphorus compounds including more than 200 reactions, a skeletal mechanism for flame inhibition by trimethylphosphate was developed. The mechanism consists of 22 irreversible elementary reactions, involving 9 phosphorus-containing species. Selection of the crucial steps w...

A modified two-dimensional two-phase mathematical model of forest wildfires propagation is considered. The model is based on the averaging of three-dimensional equations of two-phase medium over the height of the forest fuel (FF) layer and it includes the (k‒ε)-turbulence model with additional turbulence production and dissipation terms in the fore...

Combustion stability problem for solid fuel ramjet engine is considered. Stabilization is achieved due to the presence of a wider section in the combustion channel near the air inlet. In this part, playing the role of flame holder, a recirculation zone develops which increases the residence time of combustion products in contrast to the straight pa...

A numerical model for boil-up of superheated liquid following loss of containment and expansion of two-phase mixture into the atmosphere is proposed and applied to evaluation of blast effects of Boiling Liquid Expanding Vapor Explosions (BLEVEs). The model assumes that the mixture in the two-phase cloud stays in thermodynamic equilibrium during exp...

Filtration processes which accompany the cyclic operation of the oil production well with variable bottom hole pressure are considered. The task is solved in the axis-symmetrical formulation for a layered nonuniform oil reservoir with highly and lowly permeable layers. The distributions of oil saturation are calculated for the stationary and cyclic...

Nordic-type boiling water reactors employ melt fragmentation, quenching, and long term cooling of the debris bed in a deep pool of water under the reactor vessel as a severe accident (SA) mitigation strategy. The height and shape of the bed are among the most important factors that determine if decay heat can be removed from the porous debris bed b...

Termination of severe accident progression by core debris cooling in a deep pool of water under reactor vessel is considered in several designs of light water reactors. However, success of this accident mitigation strategy is contingent upon the effectiveness of heat removal by natural circulation from the debris bed. It is assumed that a porous be...

Debris bed formation and coolability are studied by DECOSIM code. Main physical mechanisms affecting dispersed particle spreading in the course of melt-water interaction are considered, and their relevance to the formation of porous debris bed in various melt ejection modes is discussed. Numerical simulations of gradually growing and instantly form...

Melt fragmentation, quenching and long term coolability in a deep pool of water under reactor vessel are employed as a severe accident mitigation strategy in several designs of light water reactors. Success of the strategy is contingent upon effectiveness of natural circulation in removing the decay heat generated by the porous debris bed. Geometri...

Several designs of light water reactors consider melt fragmentation and cooling of corium debris bed in a deep pool as important part of their severe accident management strategies. Traditional approach to assessment of debris coolability is based on the bed dryout criterion. However, this is the most conservative criterion which doesn't take into...

In the case of severe accident in Nordic boiling water reactors (BWR), core melt is poured into a deep pool of water located under the reactor. The severe accident management (SAM) strategy involves complex and coupled physical phenomena of melt-coolant-structure interactions sensitive to the transient accident scenarios. Success of the strategy is...

SOCRAT-BN is a software package to simulate design and severe accidents of sodium-cooled fast reactors. The package consists of modules for calculating damage to the reactor's core, thermohydraulic processes and neutron physics. The thermohydraulic module has been developed to calculate one-and two-phase flows in channels with complex geometry. The...

One-dimensional coolability problem for a flat homogeneous heat-releasing debris bed is considered, with the critical conditions for steady-state cooling characterized by the Dryout Heat Flux (DHF). DHF is determined for top-fed and bottom-fed debris beds from several two-phase models differing by the treatment of porous and interphase drag. Aleato...

Cumulation of shock snd detonation waves was considered. Computations were carried out by use of second-order central-difference scheme. Cumulation of waves in cone region with scales of 1 meter was studied. Pictures of flow in shock and detonation waves during different time moments were obtained as well as time dependences and maximum pressures f...

SOCRAT-BN is a software package to simulate design and severe accidents of sodium-cooled fast reactors. The package consists of modules for calculating damage to the reactor’s core, thermohydraulic processes and neutron physics. The thermohydraulic module has been developed to calculate one- and two-phase flows in channels with different geometry a...

Coolability of an ex-vessel debris bed in severe accident conditions is considered from the risk perspective. The concept of “load versus capacity” is employed to quantify the probability of failure (local dryout). Possible choices of “load” and “capacity” in terms of heat fluxes, thermal power or melt mass are discussed. Results of Monte Carlo sim...

Fire risk for building occupants is determined by the time required for safe egress and the time at which untenable conditions develop in building rooms or on the egress routes. In the present study, the CFAST zone model is applied to the simulation of fire development and smoke propagation in multiroom buildings, with the aim of studying the sensi...

Results of recent verification studies of VAPEX-M module intended for the calculation of fuel-coolant interaction (FCI) are presented. The mathematical model and correlations for the main physical processes are described. Comparisons of calculated results with three series of FCI experiments (MAGICO-2000, QUEOS, FARO) are presented. It is shown tha...

In the conditions where the oxygen supply into the fire compartment is insufficient to maintain steady combustion (underventilated fires), the flame becomes essentially transient and can be thrown out of the ventilation opening. In this paper, experimental and computational studies on burner and pool compartment fires with limited ventilation in a...

Modeling of industrial accidents with liquefied toxic and flammable gases is considered. Propagation of nonreacting heavy gas clouds over complex terrains is described by a two-dimensional model with averaging over the cloud height. A numerical simulation of a toxic accident initiated by the release of chlorine in the urban environment has been per...