PARAMETER DEPENDENCE OF STEAM EXPLOSION LOADS AND PROPOSAL OF A SIMPLE EVALUATION METHOD

Kiyofumi Moriyama,박현선 한국원자력학회 2015 Nuclear Engineering and Technology Vol.47 No.7

The energetic steam explosion caused by contact between the high temperature moltencore and water is one of the phenomena that may threaten the integrity of the containmentvessel during severe accidents of light water reactors (LWRs). We examined thedependence of steam explosion loads in a typical reactor cavity geometry on selectedmodel parameters and initial/boundary conditions by using a steam explosion simulationcode, JASMINE, developed at Japan Atomic Energy Agency (JAEA). Among the parameters,we put an emphasis on the water pool depth that has significance in terms of accidentmitigation strategies including cavity flooding. The results showed a strong correlationbetween the load and the premixed mass, defined as the mass of the molten material inlow void zones (void fraction < 0.75). The jet diameter and velocity that comprise the flowrate were the primary factors to determine the premixed mass and the load. The waterpool depth also showed a significant impact. The energy conversion ratio based on theenthalpy in the premixed mass was in a narrow range ~4%. Based on this observation, weproposed a simplified method for evaluation of the steam explosion load. The resultsshowed fair agreement with JASMINE.

Simulation of melt jet breakup experiments by JASMINE with an empirical correlation for melt particle size distribution

Moriyama, Kiyofumi,Park, Hyun Sun Atomic Energy Society of Japan 2016 Journal of nuclear science and technology Vol.53 No.10

<P>We modified JASMINE code, a fuel-coolant interaction simulation code developed at Japan Atomic Energy Agency (JAEA), to extend the applicability for ex-vessel melt coolability assessment. The modification included addition of a melt particle size distribution model based on an empirical correlation and a simple non-local radiation heat transfer model, improvement in the treatment of melt particle generation, and re-agglomeration of settled particles. The modified code was tested by simulating melt jet breakup experiments, namely selected cases of ALPHA/GPM series with alumina-zirconia mixture and steel melt by JAEA, and FARO experiments with urania-zirconia mixture by Joint Research Center Ispra. Simulation results showed that the code reproduces the experimental results well for the cases with a deep subcooled water pool where the melt breaks up completely. On the other hand, significant underestimation of heat removal from the melt and overestimation of agglomeration of settled melt was encountered for conditions with a shallow or saturation temperature water pool. The melt agglomeration behavior in the simulation was sensitive to model parameters on the agglomeration criterion and heat transfer depending on conditions.</P>

Sensitivity and uncertainty analyses of ex-vessel molten core cooling in a flooded cavity during a severe accident

Hwang, Byoungcheol,Moriyama, Kiyofumi,Hwang, Gisuk,Kaviany, Massoud,Lee, Mooneon,Kim, Eunho,Park, Hyun Sun Elsevier 2018 Nuclear engineering and design Vol.328 No.-

<P><B>Abstract</B></P> <P>Sensitivity and uncertainty analyses of molten core cooling under the ex-vessel phase of a severe accident of a light water reactor was performed with the COOLAP-I (COOLability Analysis Program-I) model, a parametric model considering one-dimensional heat transfer of a porous debris particle bed, covering a broad range of phenomena from the melt jet release to the long-term cooling process. COOLAP-I improved the previous version by including particle generation by the fuel-coolant interaction (FCI), and internal heat generation by the decay heat. With nine representative input parameters, an uncertainty analysis using Latin hypercube sampling (LHS) method with 300 samples were conducted, and the cooling characteristics such as total enthalpy, maximum temperature, decay heat ratio, and cake (a lump of connected particles) fraction, were examined for the elapsed time of up to 50 h. This analysis demonstrates the impacts of the water pool depth, the jet breakup-related parameters, and the accumulation area of the debris particles on the cake formation by particle agglomeration and analyzes the long-term coolability of debris particle bed in plant scale conditions.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The numerical approach for ex-vessel corium coolability is suggested. </LI> <LI> The sensitivity tests and uncertainty analyses were performed based on APR1400. </LI> <LI> The parameter importance analysis based on the condition of melt jet fully-fragmentation was performed. </LI> </UL> </P>

FARO tests corium-melt cooling in water pool: Roles of melt superheat and sintering in sediment

Hwang, Gisuk,Kaviany, Massoud,Moriyama, Kiyofumi,Park, Hyun Sun,Hwang, Byoungcheol,Lee, Mooneon,Kim, Eunho,Park, Jin Ho,Nasersharifi, Yahya Elsevier 2016 Nuclear engineering and design Vol.305 No.-

<P><B>Abstract</B></P> <P>The FARO tests have aimed at understanding an important severe accident mitigation action in a light water reactor when the accident progresses from the reactor pressure vessel boundary. These tests have aimed to measure the coolability of a molten core material (corium) gravity dispersed as jet into a water pool, quantifying the loose particle diameter distribution and fraction converted to cake under range of initial melt superheat and pool temperature and depth. Under complete hydrodynamic breakup of corium and consequent sedimentation in the pool, the initially superheated corium can result in debris bed consisting of discrete solid particles (loose debris) and/or a solid cake at the bottom of the pool. The success of the debris bed coolability requires cooling of the cake, and this is controlled by the large internal resistance. We postulate that the corium cake forms when there is a remelting part in the sediment. We show that even though a solid shell forms around the melt particles transiting in the water pool due to film-boiling heat transfer, the superheated melt allows remelting of the large particles in the sediment (depending on the water temperature and the transit time) using the COOLAP (Coolability Analysis with Parametric fuel-cooant interaction models) code. With this remelting and its liquid-phase sintering of the non-remelted particles, we predict the fraction of the melt particles converting to a cake through liquid sintering. Our predictions are in good agreement with the existing results of the FARO experiments. We address only those experiments with pool depths sufficient/exceeding the length required for complete breakup of the molten jet. Our analysis of the fate of molten corium aimed at devising the effective scenarios for its safe cooling in the containment so that predicted the minimum pool depth for no cake formation as functions of the melt superheat and water (subcooled/saturation) temperatures.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The numerical approach for FARO experimental data is suggested. </LI> <LI> The cooling mechanism of ex-vessel corium is suggested. </LI> <LI> The predicted minimum pool depth for no cake formation is suggested. </LI> </UL> </P>

CFD-DEM 알고리즘 기반의 층수내 입자의 거동 및 침적에 대한 특성 분석

황병철(Byoungcheol Hwang),Kiyofumi Moriyama,박현선(Hyun Sun Park),김무환(Moo Hwan Kim) 대한기계학회 2017 대한기계학회 춘추학술대회 Vol.2017 No.11

The Discrete Element Method (DEM) algorithm adopts the simplified model for particle-particle interaction, to simulate massive particle flows in various engineering applications including powder technology, food engineering, civil engineering, and more. However, in the special condition like the fluid flow affects largely on the trajectory of a solid particle such as mineral processing, fluidized bed, or bubble column reactor, the analysis for fluid regime is a key parameter which can be calculated by the Computational Fluid Dynamics (CFD). In this research, the numerical analysis based on the CFD-DEM algorithm to simulate the particle sedimentation under a continuous liquid medium was performed. The spherical particles are initially settled at the funnel above a cylindrical liquid (water) pool. The particles are gravitationally settled on the catcher plate located at the bottom of test section. For the validation of the analysis, the experimental results performed with three types of particles (i.e., Al₂O₃, ZrO₂, Stainless steel) with two sizes of 4, and 6 mm were compared. The resulting parameters related to the particle sedimentation characteristics such as the settling time, the particle velocity, and the particle distribution were examined which showed a good agreement.

마이크로 구조 표면에서의 임계열유속 증진에 관한 실험적 연구

김설하(Kim Seol Ha),Kiyofumi Moriyama,박현선(Hyunsun Park),김무환(Moo Hwan Kim) 대한기계학회 2014 대한기계학회 춘추학술대회 Vol.2014 No.11

It is well known that microstructures of a heating surface significantly enhances critical heat flux (CHF) of pool boiling due to the surface roughness-amplified capillary force. We suggest the limitation of the capillary effect induced by the surface roughness, by modelling a capillary wicking flow and a permeable liquid flow on the microstructured surface. Then, the critical size of microstructure for CHF delay were calculated, and evaluated in pool boiling experiments on the microfabricated structured surfaces. The experimental results also demonstrated that the CHF enhancement by roughness was limited by the permeable liquid flow, rewetting performance through structured surface.

Influence of particle morphology on pressure gradients of single-phase air flow in the mono-size non-spherical particle beds

Park, Jin Ho,Lee, Mooneon,Moriyama, Kiyofumi,Kim, Moo Hwan,Park, Hyun Sun Elsevier 2018 Annals of nuclear energy Vol.115 No.-

<P><B>Abstract</B></P> <P>Adequate equivalent diameters for non-spherical particles in predicting the pressure drop of fluid flow through particle beds were pursued. A series of experiments to measure the pressure drop of single-phase air flow through particle beds were performed using three kinds of spherical particles (2, 3.5 and 5 mm diameter) and four kinds of cylindrical particles. The experimental data were utilized for evaluating previous models and for proposing a new model, a modified Wu et al. (2008) model with an alternative Ergun constant for the viscous energy loss term.</P> <P>The proposed model agreed well with the pressure drop of single-phase flow through spherical particle beds within 10% in average. The experimental data for cylindrical particle beds also agreed well with the proposed model within 16% in average by applying the equivalent diameter proposed by Li and Ma (2011) as a characteristic size of non-spherical particles.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The pressure drops of air flows through particle beds were measured. </LI> <LI> The adequacy of Ergun constants was evaluated. </LI> <LI> The adequacy of effective diameters for non-spherical particles was evaluated. </LI> <LI> A improved pressure drop model for single-phase fluid in particle beds was proposed. </LI> </UL> </P>

Penetration of Isothermal Plunging Jet into Denser Liquid

Hyun Sun Park,Norihiro Yamano,Kiyofumi Moriyama,Yu Maruyama,Yanhua Yang,Anhar R. Antariksawan,Jun Sugimoto,Sadao Fujii 대한기계학회 1998 KSME/JSME THERMAL and FLUID Engineering Conference Vol.1 No.1

Study on Subcooled Water Injection into Molten Material

Hyun Sun Park,Norihiro Yamano,Kiyofumi Moriyama,Yu Maruyama,Yanhua Yang,Jun Sugimoto 대한기계학회 1998 Heat transter conference Vol.6 No.1

Effects of heat flux on dropwise condensation on a superhydrophobic surface

황경원,DongHyun Kim,HangJin Jo,박현선,Kiyofumi Moriyama,Moo Hwan Kim 대한기계학회 2016 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.30 No.5

The condensation heat transfer efficiencies of superhydrophobic surfaces that have ~160° contact angle under atmospheric conditions were investigated experimentally. The departing diameter and the contact angle hysteresis of droplets were measured by capturing front and tilted side views of condensation phenomena with a high speed camera and an endoscope, respectively. Condensation behaviors on the surface were observed at the micro-scale using an Environmental scanning electron microscope (ESEM). Apparently-spherical droplets formed at very low heat flux q″ ~20 kW/m 2 but hemispherical droplets formed at high q″ ~440 kW/m 2 . At high q″, heat transfer coefficients were lower on the superhydrophobic surface than on a hydrophobic surface although the superhydrophobic surface is water repellent so droplets roll off. The results of contact angle hysteresis and ESEM image revealed that the reduced heat transfer of the surface can be attributed to the large size of departing droplets caused by adhesive condensed droplets at nucleation sites. The results suggest that the effect of q″ or degree of sub-cooling of a condensation wall determine the droplet shape, which is closely related to removal rates of condensates and finally to the heat transfer coefficient.