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Matjaž Leskovar - One of the best experts on this subject based on the ideXlab platform.
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Investigation of Steam Explosion duration in stratified configuration
Nuclear Engineering and Design, 2019Co-Authors: Matjaž Leskovar, Mitja Uršič, Vasilij Centrih, Janez KokaljAbstract:Abstract A Steam Explosion is an energetic fuel-coolant interaction process, which may occur during a severe reactor accident when the molten core comes into contact with the coolant water. In the stratified melt-coolant configurations, where the corium melt is released in a shallow water pool or in an initially dry cavity later flooded with coolant water, the melt-water interaction may occur on the interface between the bottom melt layer and the upper water layer. It was long believed that stratified melt-water conditions cannot generate strong explosive interactions, because it was assumed that there is no significant premixing of melt and coolant water prior to the shock wave propagation. However, the recently performed experiments in the PULiMS and SES (KTH, Sweden) facilities with corium simulant materials revealed that strong Steam Explosions may spontaneously develop also in a stratified melt-water configuration, where a formation of a considerable melt-water premixed layer was observed. Understanding the premixture formation mechanisms is crucial for predicting the stratified Steam Explosion energetics. One of the external indicators of the way the melt and water are mixed during the stratified Steam Explosion process is the Explosion duration. In the article, the duration of the stratified Steam Explosion is studied by the analysis of experimental observations in the PULiMS and SES tests using simulation results obtained with the MC3D code (IRSN, France). The Explosion characteristics are analysed by varying the available melt mass in the premixed layer, the triggering position, the melt droplet diameter, the void fraction in the premixed layer, the void fraction in the water above the premixed layer and the size of the fine fragments. The analysis showed that longer Explosion duration for the experiments with strong Explosions cannot be predicted solely by varying the premixed layer conditions. A significant increase of the Explosion duration could be obtained only by increasing the size of the fine fragments, which depends on the nature of the Explosion. Thus the observed discrepancies between the experimental results and simulations can be explained by the fact that in strong stratified Steam Explosions there is also significant melt-water layer mixing during the Explosion propagation.
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Influence of corium composition on ex-vessel Steam Explosion
Annals of Nuclear Energy, 2019Co-Authors: Tomaž Skobe, Matjaž LeskovarAbstract:Abstract The worst event that could happen in a nuclear power plant is a severe accident. If during such accident the corium melt comes into contact with the coolant water, a Steam Explosion may occur. At some stage of the accident progression, the primary system and the containment integrity of the nuclear power plant are jeopardized. In the article, the material influence of the oxide and metal corium on the ex-vessel Steam Explosion is investigated. The main purpose of the research work was a comparative analysis of different scenarios of Steam Explosion in the flooded reactor cavity. The purpose was to determine the influence of the material properties of the melt (comparison of oxide and metallic melt) and the oxidation of the metallic melt on the Steam Explosion strength. A PWR ex-vessel Steam Explosion study was carried out with the MC3D computer code. A premixing simulation and an Explosion simulation were performed for each type of the corium. The Explosion was triggered at the time of melt bottom contact. The global jet breakup model was used to simulate the premixing simulations. In the first part comparative calculations with oxide corium and oxide corium with prescribed thermal properties of metal corium are presented to find the isolated influence of thermal properties. The analysis of PWR ex-vessel Steam Explosion with oxide corium was already performed in the past ( Leskovar and Ursic, 2014 ), but in this paper the comparative calculations with oxide corium and oxide corium with prescribed thermal properties of metal corium are presented for the first time. The purpose was to determine the differences in premixing and the Steam Explosion strength at simulations considering solely the different thermal properties of the oxide and metal corium. In the second part of the paper the influence of the metal corium oxidation on the ex-vessel Steam Explosion is presented. Due to the focusing effect the reactor vessel would most likely fail at the side and the outflow of metal corium would occur. First of all it was necessary to collect material properties of metal corium. The ex-vessel Steam Explosion was investigated and discussed by varying the metal corium oxidation rate. Additionally, based on experimental findings, the hydrogen film hypothesis for oxidation is presented. In this paper the calculations with properties of metal corium are presented for the first time. With the comparison of the simulation results the influence of the corium composition on the strength of the Steam Explosion is analysed. The simulation results revealed that with metal corium the strength of the Steam Explosion is in some cases higher than with oxide corium.
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Estimation of pressure loads during ex-vessel Steam Explosion
ICONE-16, 2017Co-Authors: Matjaž LeskovarAbstract:An ex-vessel Steam Explosion may occur when, during a severe reactor accident, the reactor vessel fails and the molten core pours into the water in the reactor cavity. A Steam Explosion is a fuel coolant interaction process where the heat transfer from the melt to water is so intense and rapid that the timescale for heat transfer is shorter than the timescale for pressure relief. This can lead to the formation of shock waves and production of missiles that may endanger surrounding structures. A strong enough Steam Explosion in a nuclear power plant could jeopardize the containment integrity and so lead to a direct release of radioactive material to the environment. In the paper, different scenarios of ex-vessel Steam Explosions in a typical pressurized water reactor cavity are analyzed with the code MC3D, which is being developed for the simulation of fuel-coolant interactions. A comprehensive parametric study was performed varying the location of the melt release (central and side melt pours), the cavity water sub-cooling, the primary system overpressure at vessel failure and the triggering time for Explosion calculations. The main purpose of the study was to determine the most challenging ex-vessel Steam Explosion cases in a typical pressurized water reactor and to estimate the expected pressure loadings on the cavity walls. Special attention was given to melt droplets freezing, which may significantly influence the outcome of the fuel-coolant interaction process. The performed analysis shows that for some ex-vessel Steam Explosion scenarios much higher pressure loads are predicted than obtained in the OECD program SERENA Phase 1. Copyright © 2008 by ASME.
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Modeling of Steam Explosion in partially flooded PWR reactor cavity
2005 Summer Heat Transfer Conference (HT2005) : 2005 ASME/Pacific Rim Technical Conference and Exhibition on Integration and Packaging of MEMS, NEMS, 2017Co-Authors: Leon Cizelj, Matjaž Leskovar, Boštjan KončarAbstract:When the hot molten core comes into contact with the water in the reactor cavity a Steam Explosion can occur. The Steam Explosion might be triggered during some scenarios of severe nuclear reactor accidents, when extremely hot molten nuclear fuel interacts with the coolant water. A highly energetic Steam Explosion in a nuclear power plant could cause the containment failure and the release of radioactive fission products to the environment. The purpose of the performed analysis is to provide a first estimation of the expected pressure loadings on the typical PWR cavity structures during a Steam Explosion. To achieve this, the fit-for-purpose Steam Explosion model is proposed, followed by a Computational Fluid Dynamics (CFD) analysis. In the present work two Steam Explosion scenarios in the partially flooded Pressurized Water Reactor (PWR) cavity were simulated with the general purpose code CFX-5 [1] to estimate pressure loadings on cavity walls. Copyright © 2005 by ASME.
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Analysis of oxidation influence on Steam Explosion energetics
Annals of Nuclear Energy, 2016Co-Authors: Matjaž Leskovar, Vasilij Centrih, Mitja UršičAbstract:Abstract When during a severe reactor accident the corium melt comes into contact with the coolant water a Steam Explosion may occur. If non-oxidized zirconium is present in the corium melt the oxidation of zirconium may significantly affect the Steam Explosion energetics, as observed in experiments. In the ZREX experiments the Steam Explosion strength was largely increased by the oxidation of zirconium, whereas in the recently performed OECD SERENA project KROTOS and TROI experiments it seems that the oxidation had an inhibiting effect. To find out the reasons for this qualitatively different behavior, the experimental results were investigated in comparison and computer simulations were performed. In the article, the performed analysis of the influence of oxidation on the Steam Explosion energetics is presented and discussed. Based on the experimental findings, the hydrogen film hypothesis is proposed, claiming that only a limiting amount of zirconium may be oxidized during the premixing phase in sub-cooled water conditions and that the remaining non-oxidized zirconium is available for the oxidation in the Explosion phase. Various computer simulations were performed with the MC3D code to support the hypothesis and to get additional insight. It may be concluded that the proposed hypothesis qualitatively explains the observed experimental findings.
Hongzhang Chen - One of the best experts on this subject based on the ideXlab platform.
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Steam Explosion as a Hydrothermal Pretreatment in the Biorefinery Concept
Hydrothermal Processing in Biorefineries, 2017Co-Authors: Hongzhang Chen, Wenjie SuiAbstract:Steam Explosion is one of the leading and most promising hydrothermal pretreatment for lignocellulose biorefinery. In the biorefinery concept, this monograph chapter systematically elaborates the basic principles, derived technologies, and process integration of Steam Explosion biorefinery techniques in development. The theoretical bases of Steam Explosion technology were elucidated from the transfer rules and hydrothermal mechanism during the multistage pretreatment process. Based on the cognition of Steam Explosion process and heterogeneity of lignocellulosic feedstock, a series of novel Steam Explosion-derived biorefinery techniques were explored to achieve the efficient fractionation and conversion of biomass components. Their integrated industrial biorefinery chain was further interpreted by a typical ethanol production demonstration project, in order to boost the development of Steam Explosion technology from biorefinery engineering. It is anticipated to have some guiding meaning for the better interpretation and application of Steam Explosion biorefinery techniques in both the experimental research and industrial production.
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physical structure changes of solid medium by Steam Explosion sterilization
Bioresource Technology, 2016Co-Authors: Zhimin Zhao, Lan Wang, Hongzhang ChenAbstract:Physical structure changes of solid medium were investigated to reveal effects of Steam Explosion sterilization on solid-state fermentation (SSF). Results indicated that Steam Explosion changed the structure of solid medium at both molecular and three-dimensional structural levels, which exposed hydrophilic groups and enlarged pores and cavities. It was interesting to find that pores where capillary water located were the active sites for SSF, due to the close relationship among capillary water relaxation time, specific surface area and fermentation performance. Therefore, Steam Explosion sterilization increased the effective contact area for microbial cells on solid medium, which contributed to improving SSF performance. Combined with the previous research, mechanisms of SSF improvement by Steam Explosion sterilization contained both chemical and physical effects. (C) 2015 Elsevier Ltd. All rights reserved.
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Effects of water states on Steam Explosion of lignocellulosic biomass.
Bioresource technology, 2015Co-Authors: Wenjie Sui, Hongzhang ChenAbstract:The work aimed to identify the complexity and roles of water states in Steam Explosion process of corn stalk to enhance the treatment efficiency. Results showed that two main water states with different mobility existed in corn stalk and influenced Steam Explosion treatment. By correlating dynamic water states data to feedstock mechanical properties and treatment process characteristics, the bound water being the excellent plasticizer that reduced the mechanical strength of fibers by over 30%, was conducive to treatment; while, the free water presenting buffering effects in treatment by hindering heat transfer which was reflected by the increase of temperature rising time by 1.29 folds and Steam consumption by 2.18 folds, was not conducive. The distinguished point of these two waters was fiber saturated point. By considering treatment efficacy and energy consumption, the significance of fiber saturated point was highlighted as the optimal water states for Steam Explosion of corn stalk.
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study on loading coefficient in Steam Explosion process of corn stalk
Bioresource Technology, 2015Co-Authors: Wenjie Sui, Hongzhang ChenAbstract:The object of this work was to evaluate the effect of loading coefficient on Steam Explosion process and efficacy of corn stalk. Loading coefficient's relation with loading pattern and material property was first revealed, then its effect on transfer process and pretreatment efficacy of Steam Explosion was assessed by established models and enzymatic hydrolysis tests, respectively, in order to propose its optimization strategy for improving the process economy. Results showed that loading coefficient was mainly determined by loading pattern, moisture content and chip size. Both compact loading pattern and low moisture content improved the energy efficiency of Steam Explosion pretreatment and overall sugar yield of pretreated materials, indicating that they are desirable to improve the process economy. Pretreatment of small chip size showed opposite effects in pretreatment energy efficiency and enzymatic hydrolysis performance, thus its optimization should be balanced in investigated aspects according to further techno-economical evaluation. (C) 2014 Elsevier Ltd. All rights reserved.
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Water transfer in Steam Explosion process of corn stalk
Industrial Crops and Products, 2015Co-Authors: Wenjie Sui, Hongzhang ChenAbstract:Steam Explosion is one of the leading and most promising biorefinery technologies for lignocellulosic biomass. Water as the only transfer medium participated in Steam Explosion process is closely correlated with refining efficacy and energy consumption, while researches on Steam Explosion are neglected from transfer mechanism. In this work, from water transfer perspective, Steam Explosion process was innovatively divided into four specific stages and the multi-stage mass transfer model of Steam Explosion process was firstly established. From this model, quantitative relation of water composition in each stage and final water content formula were evaluated, which is efficient to guide the process energy efficiency with several proposed regulation strategies. By combining transfer process simulation with pretreatment efficacy evaluation, much water in feedstock presented a buffering effect on reaction and transfer issues during Steam Explosion process, thereby weakening the actual severity of treatment. 40% water content of cellulosic biomass was optimized from the compromise between treatment efficacy and energy efficiency. The yield of overall glucose through pretreatment and enzymatic hydrolysis was increased by over 20% with a potential cost savings of Steam consumption by simply coordinating water content of cellulosic biomass prior to Steam Explosion treatment. Thus, results in the work emphasize the water transfer and regulation during Steam Explosion process on understanding water reaction mechanism, enhancing pretreatment efficacy and saving energy, leading to more efficient use of biomass. (C) 2015 Elsevier B.V. All rights reserved.
Luiz Pereira Ramos - One of the best experts on this subject based on the ideXlab platform.
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the effect of Steam Explosion on the production of sugarcane bagasse polyester composites
Composites Part A-applied Science and Manufacturing, 2011Co-Authors: Ricardo José Brugnago, Kestur Gundappa Satyanarayana, Fernando Wypych, Luiz Pereira RamosAbstract:Abstract This paper describes a pretreatment option to sugarcane bagasse fibers for their use in composite preparation with unsaturated polyester. Sugarcane bagasse fibers modified by (i) Steam Explosion and (ii) alkali washing after Steam Explosion, along with (iii) as-received bagasse fibers were characterized. Steam Explosion significantly reduced the amount of hemicelluloses and acid-soluble lignin of bagasse fibers, while acid-insoluble lignin increased proportionally. Alkaline washing of Steam-exploded fibers removed nearly 60% of their acid-insoluble lignin. Polyester matrix composites containing 10 wt.% of these fibers were prepared by compression molding. Density, thermal stability, water absorption and thermomechanical analysis of the composites containing Steam Explosion treated bagasse fibers showed improvement in these properties over those of the untreated fiber containing composite. These are explained in terms of the chemical modifications that occurred due to the Steam Explosion treatments.
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The effect of Steam Explosion on the production of sugarcane bagasse/polyester composites
Composites Part A: Applied Science and Manufacturing, 2011Co-Authors: Ricardo José Brugnago, Kestur Gundappa Satyanarayana, Fernando Wypych, Luiz Pereira RamosAbstract:Abstract This paper describes a pretreatment option to sugarcane bagasse fibers for their use in composite preparation with unsaturated polyester. Sugarcane bagasse fibers modified by (i) Steam Explosion and (ii) alkali washing after Steam Explosion, along with (iii) as-received bagasse fibers were characterized. Steam Explosion significantly reduced the amount of hemicelluloses and acid-soluble lignin of bagasse fibers, while acid-insoluble lignin increased proportionally. Alkaline washing of Steam-exploded fibers removed nearly 60% of their acid-insoluble lignin. Polyester matrix composites containing 10 wt.% of these fibers were prepared by compression molding. Density, thermal stability, water absorption and thermomechanical analysis of the composites containing Steam Explosion treated bagasse fibers showed improvement in these properties over those of the untreated fiber containing composite. These are explained in terms of the chemical modifications that occurred due to the Steam Explosion treatments.
Wenjie Sui - One of the best experts on this subject based on the ideXlab platform.
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Steam Explosion as a Hydrothermal Pretreatment in the Biorefinery Concept
Hydrothermal Processing in Biorefineries, 2017Co-Authors: Hongzhang Chen, Wenjie SuiAbstract:Steam Explosion is one of the leading and most promising hydrothermal pretreatment for lignocellulose biorefinery. In the biorefinery concept, this monograph chapter systematically elaborates the basic principles, derived technologies, and process integration of Steam Explosion biorefinery techniques in development. The theoretical bases of Steam Explosion technology were elucidated from the transfer rules and hydrothermal mechanism during the multistage pretreatment process. Based on the cognition of Steam Explosion process and heterogeneity of lignocellulosic feedstock, a series of novel Steam Explosion-derived biorefinery techniques were explored to achieve the efficient fractionation and conversion of biomass components. Their integrated industrial biorefinery chain was further interpreted by a typical ethanol production demonstration project, in order to boost the development of Steam Explosion technology from biorefinery engineering. It is anticipated to have some guiding meaning for the better interpretation and application of Steam Explosion biorefinery techniques in both the experimental research and industrial production.
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Effects of water states on Steam Explosion of lignocellulosic biomass.
Bioresource technology, 2015Co-Authors: Wenjie Sui, Hongzhang ChenAbstract:The work aimed to identify the complexity and roles of water states in Steam Explosion process of corn stalk to enhance the treatment efficiency. Results showed that two main water states with different mobility existed in corn stalk and influenced Steam Explosion treatment. By correlating dynamic water states data to feedstock mechanical properties and treatment process characteristics, the bound water being the excellent plasticizer that reduced the mechanical strength of fibers by over 30%, was conducive to treatment; while, the free water presenting buffering effects in treatment by hindering heat transfer which was reflected by the increase of temperature rising time by 1.29 folds and Steam consumption by 2.18 folds, was not conducive. The distinguished point of these two waters was fiber saturated point. By considering treatment efficacy and energy consumption, the significance of fiber saturated point was highlighted as the optimal water states for Steam Explosion of corn stalk.
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study on loading coefficient in Steam Explosion process of corn stalk
Bioresource Technology, 2015Co-Authors: Wenjie Sui, Hongzhang ChenAbstract:The object of this work was to evaluate the effect of loading coefficient on Steam Explosion process and efficacy of corn stalk. Loading coefficient's relation with loading pattern and material property was first revealed, then its effect on transfer process and pretreatment efficacy of Steam Explosion was assessed by established models and enzymatic hydrolysis tests, respectively, in order to propose its optimization strategy for improving the process economy. Results showed that loading coefficient was mainly determined by loading pattern, moisture content and chip size. Both compact loading pattern and low moisture content improved the energy efficiency of Steam Explosion pretreatment and overall sugar yield of pretreated materials, indicating that they are desirable to improve the process economy. Pretreatment of small chip size showed opposite effects in pretreatment energy efficiency and enzymatic hydrolysis performance, thus its optimization should be balanced in investigated aspects according to further techno-economical evaluation. (C) 2014 Elsevier Ltd. All rights reserved.
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Water transfer in Steam Explosion process of corn stalk
Industrial Crops and Products, 2015Co-Authors: Wenjie Sui, Hongzhang ChenAbstract:Steam Explosion is one of the leading and most promising biorefinery technologies for lignocellulosic biomass. Water as the only transfer medium participated in Steam Explosion process is closely correlated with refining efficacy and energy consumption, while researches on Steam Explosion are neglected from transfer mechanism. In this work, from water transfer perspective, Steam Explosion process was innovatively divided into four specific stages and the multi-stage mass transfer model of Steam Explosion process was firstly established. From this model, quantitative relation of water composition in each stage and final water content formula were evaluated, which is efficient to guide the process energy efficiency with several proposed regulation strategies. By combining transfer process simulation with pretreatment efficacy evaluation, much water in feedstock presented a buffering effect on reaction and transfer issues during Steam Explosion process, thereby weakening the actual severity of treatment. 40% water content of cellulosic biomass was optimized from the compromise between treatment efficacy and energy efficiency. The yield of overall glucose through pretreatment and enzymatic hydrolysis was increased by over 20% with a potential cost savings of Steam consumption by simply coordinating water content of cellulosic biomass prior to Steam Explosion treatment. Thus, results in the work emphasize the water transfer and regulation during Steam Explosion process on understanding water reaction mechanism, enhancing pretreatment efficacy and saving energy, leading to more efficient use of biomass. (C) 2015 Elsevier B.V. All rights reserved.
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Multi-stage energy analysis of Steam Explosion process
Chemical Engineering Science, 2014Co-Authors: Wenjie Sui, Hongzhang ChenAbstract:Owing to the deficiency of investigating Steam Explosion on energy utilization, in this study, we analyze the heat transfer mechanism and energy consumption of Steam Explosion process. Based on years of research, we propose that energy consumption of Steam Explosion not only involves holding pressure and instantaneous decompression stages but also the upward stage of pressure. On this basis, a multi-stage heat transfer model of Steam Explosion process integrating technical features is established. Results reveal the significance of pressure boost stage which contributes the vast majority of total energy consumption. The amount of Steam consumption per unit mass of dry materials m′ is presented to quantitatively evaluate the energy consumption under various factors, in which initial moisture content is considered as the most important factor. Several rational operational strategies for improving energy efficiency are proposed including controlling low moisture content of materials (
Michael L. Corradini - One of the best experts on this subject based on the ideXlab platform.
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Stratified Steam Explosion energetics
Nuclear Engineering and Technology, 2019Co-Authors: Jun Wang, Michael L. CorradiniAbstract:Abstract Vapor Explosions can be classified in terms of modes of contact between the hot molten fuel and the coolant, since different contact modes may affect fuel-coolant mixing and subsequent vapor Explosion energetics. It is generally accepted that most vapor Explosion phenomena fall into three different modes of contact; fuel pouring into coolant, coolant injection into fuel and stratified fuel-coolant layers. In this study, we review previous stratified Steam Explosion experiments as well as recent experiments performed at the KTH in Sweden. While experiments with prototypic reactor materials are minimal, we do note that generally the energetics is limited for the stratified mode of contact. When the fuel mass involved in a Steam Explosion in a stratified geometry is compared to a pool geometry based on geometrical aspects, one can conclude that there is a very limited set of conditions (when melt jet diameter is small) under which a Steam Explosion is more energetic in a stratified geometry. However, under these limited conditions the absolute energetic Explosion output would still be small because the total fuel mass involved would be limited.
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analysis of the dynamic pressure from ex vessel Steam Explosion for pressurized water reactor
Progress in Nuclear Energy, 2017Co-Authors: Ronghua Chen, Jun Wang, Suizheng Qiu, Michael L. CorradiniAbstract:Abstract In a nuclear reactor severe accident, the molten core debris may cause Steam Explosion when contacting with water in the reactor cavity below the reactor pressure vessel (RPV), which can endanger the containment integrity of the nuclear power plant. In this study, the improved FCI computer code TEXAS-VI considering solidification effects and the original code TEXAS-V were used to analyze the TROI TS-3 test as a benchmark experiment. Then a series of ex-vessel Steam Explosion simulations were performed. In the experimental comparison, the melt penetration (leading front position in the coolant) in TS-3 was well predicted by TEXAS. The pressure at different positions simulated by TEXAS-VI was notably lower than that of TEXAS-V, but in good agreement with the experiment results. The simulation results showed that the modeling of corium solidification during the mixing process and the breakup criteria in TEXAS-VI largely mitigates the rapid breakup, thereby affecting the Steam Explosion. Our study continued by using TEXAS-VI to analyze ex-vessel Steam Explosion energetics for a range of different initial conditions, with the aim to examine the impact of the fuel melt initial diameter and velocity. For conservative estimation, the cross sectional area ratio of the fuel-coolant mixing region to the injected corium was set to maximize the peak Explosion impulse based on a number of parametric calculations. In scope of this study conditions, the larger the diameter and the initial injected velocity of corium were, the larger the maximum pressure and the liquid kinetic energy from the Steam Explosion were. The void fraction can influence the fragmentation rate during the Explosion stage and mitigate the propagation of the pressure pulse during the propagation stage. The liquid kinetic energy would be affected by the pressure from the Steam Explosion and the void fraction at the end of mixing stage.
