Development of a Multiphase Particle Method for Melt-Jet Breakup Behavior of Molten Core in Severe Accident

Abstract In a hypothetical severe accident in a light water reactor (LWR) nuclear power plant, there is a possibility that molten core released from the reactor vessel gets in contact with water in the containment vessel. In this so-called fuel-coolant interactions (FCIs) process, the melt jet will breakup into fragments, which is one of the important factors for a steam explosion, as a potential threat to the integrity of the containment vessel. The particle method could directly and easily capture the large deformed interfaces by particle motions, benefiting from its Lagrangian description and meshless framework. In order to investigate the melt-jet breakup with solidification processes, a multiphase particle method with arbitrary high order scheme is presented in this study. In addition, an interfacial particle shifting scheme is developed to suppress the unnatural particle penetration between different phases. The convergence rate with different order is firstly confirmed by a verification test in terms of both explicit and implicit calculations. Then, a transient heat conduction between two materials is carried out and quite good results are obtained. After that, a rising bubble benchmark is performed to show the feasibility of modelling for deformation and collapse. Improvements of clear interface are indicated compared with previous reported results. Two important multiphase instabilities, namely the Rayleigh-Taylor instability and the Kelvin-Helmholtz instability, are studied since they play important roles during the melt-jet breakup. The results achieved so far indicate that the developed particle method is capable to analyze the melt-jet breakup with heat transfer.

Download Full-text

Numerical Simulation of Corium Jet Breakup During Fuel-Coolant Interaction Based on the ALISA Test Performed at KROTOS Test Facility

Volume 8: Computational Fluid Dynamics (CFD); Nuclear Education and Public Acceptance ◽

10.1115/icone26-81818 ◽

2018 ◽

Author(s):

Pei Shen ◽

Wenzhong Zhou

Keyword(s):

Numerical Simulation ◽

Steam Explosion ◽

Field Method ◽

Severe Accident ◽

Phase Field Method ◽

Test Facility ◽

Jet Breakup ◽

Jet Behavior ◽

Jet Fragmentation ◽

Explosion Test

Steam explosion is one of the consequences of fuel-coolant interactions in a severe accident. Melt jet fragmentation, which is the key phenomenon during steam explosion, has not been clarified sufficiently which prevents the precise prediction of steam explosion. The focus of this paper is on the numerical simulation of the melt jet behavior falling into a coolant pool in order to get a qualitative and quantitative understanding of initial premixing stage of fuel-coolant interaction. The objective of our first phase is the simulation of the fragmentation process and the estimation of the jet breakup length. A commercial CFD code COMSOL is used for the 2D numerical analysis employing the phase field method. The simulation condition is similar to our steam explosion test supported by the ALISA (Access to Large Infrastructure for Severe Accidents) project between European Union and China, and carried out in the KROTOS test facility at CEA, France. The simulation result is in relatively good agreement with the experimental data. Then the effect of the initial jet velocity, the jet diameter and the instability theory are presented. The preliminary data of melt jet fragmentation is helpful to understand the premixing stage of the fuel-coolant interaction.

Download Full-text

Optimization of Moving Particle Semi-Implicit (MPS) Method and Studying of Flow Instability

Volume 8: Computational Fluid Dynamics (CFD); Nuclear Education and Public Acceptance ◽

10.1115/icone26-81948 ◽

2018 ◽

Author(s):

Kailun Guo ◽

Ronghua Chen ◽

Suizheng Qiu ◽

Wenxi Tian ◽

Guanghui Su ◽

...

Keyword(s):

Multiphase Flows ◽

Flow Instability ◽

Free Particle ◽

Particle Method ◽

Severe Accident ◽

Particle Methods ◽

Two Phase ◽

Mps Method ◽

Viscosity Term ◽

Moving Particle

Multiphase flow widely exists in the nature and engineering. The two-phase flow is the highlight of the studies about the flow in the vessel and steam explosion in nuclear severe accidents. The Moving Particle Semi-implicit (MPS) method is a fully-Lagrangian particle method without grid mesh which focuses on tracking the single particle and concerns with its movement. It has advantages in tracking complex multiphase flows compared with gird methods, and thus shows great potential in predicting multiphase flows. The objective of this thesis is to develop a general multiphase particle method based on the original MPS method and thus this work is of great significance for improving the numerical method for simulating the instability in reactor severe accident and two-phase flows in vessel. This research is intended to provide a study of the instability based on the MPS method. Latest achievements of mesh-free particle methods in instability are researched and a new multiphase MPS method, which is based on the original one, for simulating instability has been developed and validated. Based on referring to other researchers’ papers, the Pressure Poisson Equation (PPE), the viscosity term, the free surface particle determination part and the surface tension model are optimized or added. The numerical simulation on stratification behavior of two immiscible flows is carried out and results are analyzed after data processing. It is proved that the improved MPS method is more accurate than the original method in analysis of multiphase flows. In this paper, the main purposes are simulating and discussing Rayleigh-Taylor (R-T) instability and Kelvin-Helmholtz (K-H) instability. R-T and K-H instability play an important role in the mixing process of many layered flows. R-T instability occurs when a lower density fluid is supported by another density higher fluid or higher density fluid is accelerated by lower density fluid, and the resulting small perturbation increases and eventually forms turbulence. K-H instability is a small disturbance for two different densities, such as waves, at the interface of the two-phase fluid after giving a fixed acceleration in the fluid. Turbulence generated by R-T instability and K-H instability has an important effect in applications such as astrophysics, geophysics, and nuclear science.

Download Full-text

3D Simulation of Molten Metal Freezing Behaviour Using Finite Volume Particle Method

18th International Conference on Nuclear Engineering: Volume 2 ◽

10.1115/icone18-29198 ◽

2010 ◽

Author(s):

Rida S. N. Mahmudah ◽

Masahiro Kumabe ◽

Takahito Suzuki ◽

LianCheng Guo ◽

Koji Morita ◽

...

Keyword(s):

Molten Metal ◽

Finite Volume ◽

Particle Method ◽

Metal Structure ◽

Freezing Behavior ◽

Severe Accident ◽

Particle Methods ◽

Freezing Process ◽

Penetration Length ◽

Moving Particle

Understanding the freezing behavior of molten metal in flow channels is of importance for severe accident analysis of liquid metal reactors. In order to simulate its fundamental behavior, a 3D fluid dynamics code was developed using Finite Volume Particle (FVP) method, which is one of the moving particle methods. This method, which is fully Lagrangian particle method, assumes that each moving particle occupies certain volume. The governing equations that determine the phase change process are solved by discretizing its gradient and Laplacian terms with the moving particles. The motions of each particle and heat transfer between particles are calculated through interaction with its neighboring particles. A series of experiments for fundamental freezing behavior of molten metal during penetration on to a metal structure was also performed to provide data for the validation of the developed code. The comparison between simulation and experimental results indicates that the present 3D code using the FVP method can successfully reproduce the observed freezing process such as molten metal temperature profile, frozen molten metal shape and its penetration length on the metal structure.

Download Full-text

Development of Numerical Simulation for Jet Breakup Behavior in Complicated Structure of BWR Lower Plenum: 1 — Preliminary Analysis of Jet Breakup Behavior in Complicated Structure by TPFIT

Volume 6: Beyond Design Basis Events; Student Paper Competition ◽

10.1115/icone21-15744 ◽

2013 ◽

Author(s):

Takayuki Suzuki ◽

Hiroyuki Yoshida ◽

Fumihisa Nagase ◽

Yutaka Abe ◽

Akiko Kaneko

Keyword(s):

High Speed ◽

Measured Data ◽

Severe Accident ◽

Interface Tracking ◽

Phase Flow ◽

Complicated Structure ◽

Support Plate ◽

Jet Breakup ◽

Multi Phase ◽

Developing Method

In order to improve the safety of Boiling Water Reactor (BWR), it is required to know the behavior of the plant when an accident occurred as can be seen at Fukushima Daiichi nuclear power plant accident. Especially, it is important to estimate the behavior of molten core jet in the lower part of the containment vessel at severe accident. In the BWR lower plenum, the flow characteristics of molten core jet are affected by many complicated structures, such as control rod guide tubes, instrument guide tubes and core support plate. However, it is difficult to evaluate these effects on molten core jet experimentally. Therefore, we considered that multi-phase computational fluid dynamics approach is the best way to estimate the effects on molten core jet by complicated structure. The objective of this study is to develop the evaluation method for the flow characteristic of molten core jet including the effects of the complicated structures in the lower plenum. So we are developing a simulation method to estimate the behavior of molten core jet falling down through the core support plate to the lower plenum of the BWR. The method has been developed based on interface tracking method code TPFIT (Two Phase Flow simulation code with Interface Tracking). To verify and validate the applicability of the developed method in detail, it is necessary to obtain the experimental data that can be compared with detailed numerical results by the TPFIT. Thus, in this study, we are carrying out experimental works by use of multi-phase flow visualization technique. In the experiments, time series of interface shapes are observed by high speed camera and velocity profiles in/out of the jet will be measured by the PIV method. In this paper, the outline of the developing method based on the TPFIT was explained. And, the developing method was applied to preliminary experiment with/without modeled complicated structures. As the results, predicted interface shapes were almost agreed with measured data. However, predicted falling down velocity of the jet was lower than measured data. We considered causes of this underestimation and improved the method and simulation conditions to resolve this problem.

Download Full-text

Numerical Simulation of Liquid Jet Behavior in Shallow Pool by Interface Tracking Method

Volume 1: Beyond Design Basis; Codes and Standards; Computational Fluid Dynamics (CFD); Decontamination and Decommissioning; Nuclear Fuel and Engineering; Nuclear Plant Engineering ◽

10.1115/icone2020-16213 ◽

2020 ◽

Author(s):

Takayuki Suzuki ◽

Hiroyuki Yoshida ◽

Naoki Horiguchi ◽

Sota Yamamura ◽

Yutaka Abe

Keyword(s):

Numerical Simulation ◽

Hydrodynamic Interaction ◽

Reactor Vessel ◽

Severe Accident ◽

Water Pool ◽

Molten Material ◽

Jet Breakup ◽

Jet Behavior ◽

Lattice Resolution ◽

Core Materials

Abstract In the severe accident (SA) of nuclear reactors, fuel and components melt, and melted materials fall to a lower part of a reactor vessel. In the lower part of a reactor vessel, in some sections of the SAs, it is considered that there is a water pool. Then, the melted core materials fall into a water pool in the lower plenum as a jet. The molten material jet is broken up, and heat transfer between molten material and coolant may occur. This process is called a fuel-coolant interaction (FCI). FCI is one of the important phenomena to consider the coolability and distribution of core materials. In this study, the numerical simulation of jet breakup phenomena with a shallow pool was performed by using the developed method (TPFIT). We try to understand the hydrodynamic interaction under various, such as penetration, reach to the bottom, spread, accumulation of the molten material jet. Also, we evaluated a detailed jet spread behavior and examined the influence of lattice resolution and the contact angle. Furthermore, the diameters of atomized droplets were evaluated by using numerical simulation data.

Download Full-text

Numerical Investigation of Melt Jet Breakup With Different Shapes in Water Pool

Volume 6: Thermal-Hydraulics ◽

10.1115/icone25-67611 ◽

2017 ◽

Author(s):

Hui Cheng ◽

Jiyun Zhao

Keyword(s):

Surface Area ◽

Steam Explosion ◽

Nuclear Power ◽

3D Model ◽

Severe Accident ◽

Interface Surface ◽

Jet Breakup ◽

Different Shapes ◽

Interface Surface Area ◽

2D Model

During a severe accident in nuclear power plant, core damage may occur due to decay heat and molten fuel can pour into and interact with water resulting in steam explosion. The energetics of steam explosion strongly depends on the initial premixing stage during which the molten fuel undergoes a coarse fragmentation process, which determines the surface area for fuel-coolant contact and heat transfer. Extensive research has been done to understand the premixing stage, however, most of the studies are focused on the cylindrical jet interaction with water. In fact, during core melt, the molten fuel may pour near the edge of core, so the shapes and size of melt jet may differ significantly based on specific conditions. In this paper, numerically study on the melt jet breakup with different shapes in pool water are conducted, such as elliptical shape with VOF method. Firstly, the deformation of molten jet under the same conditions in 2D model is compared with 3D model and shows that the breakup of 3D model is quite different from 2D model, the integration of 3D model is maintained much better than 2D model. Then the characteristics of breakup of elliptic cylindrical melt jet are analyzed and compared with cylindrical melt jet. The results shows that the interface surface area of elliptic cylindrical jet is nearly twice the cylindrical jet.

Download Full-text

Simulation of Liquid Jet Breakup of a Swirl-Type Fuel Injector for Automobile Engines

Volume 1: Symposia, Parts A and B ◽

10.1115/fedsm2007-37010 ◽

2007 ◽

Cited By ~ 3

Author(s):

Eiji Ishii ◽

Toru Ishikawa ◽

Yoshiyuki Tanabe

Keyword(s):

Water Column ◽

Grid Method ◽

Particle Method ◽

Engine Fuel ◽

Fuel Injector ◽

Free Surfaces ◽

Scale Free ◽

Multi Scale ◽

Jet Breakup ◽

Automobile Engines

To simulate multi-scale free surfaces, we developed a hybrid particle/grid method by which the free surfaces within sub-grid regions are simulated by the particle method, and other regions are simulated with the grid method. The particle method uses two types of particles to model gas and liquid fluids in order to simulate the interaction between them. We tested the new method on fragmentation of a water column, and the predicted configurations of the water column are consistent with measurements of Koshizuka and Oka. We also simulated the fuel spray near the outlet of an automobile-engine fuel injector and found that this method qualitatively simulated the breakup of the liquid film.

Download Full-text