Kyushu University Academic Staff Educational and Research Activities Database
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Koji Morita Last modified date:2021.10.26

Graduate School
Undergraduate School

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Nuclear Energy System Research Group, Department of Applied Quantum Physics and Nuclear Engineering .
Academic Degree
Doctor of Engineering
Country of degree conferring institution (Overseas)
Field of Specialization
Nuclear Engineering
Total Priod of education and research career in the foreign country
Outline Activities
I am conducting education and research on the development of attractive nuclear energy systems such as future nuclear reactors with excellent safety and reliability, as well as on issues that arise in the use of nuclear energy and their solutions. Through theoretical and numerical simulations, and basic experiments, I am engaged in advanced research on the fundamental physical phenomena involved in nuclear energy systems, and on the development of technologies for these systems from the viewpoint of engineering systems. Based on thermal hydraulics, nuclear safety engineering, etc., the department strives to develop human resources who can flexibly respond to various social demands for future nuclear energy systems by acquiring basic and applied skills.
Research Interests
  • Clarification of thermal-hydraulic phenomena and development of mechanistic models for IVR (In-Vessel Retention) of core melts
    keyword : In-Vessel Retention, multi-phase flow, next-generation nuclear reactor
  • Development of passive safety systems to prevent severe accidents
    keyword : severe accident, passive safety, next-generation nuclear reactor
  • Validation and sophistication of reactor safety analysis codes
    keyword : severe accident, safety assessment, code validation
  • Development of technology for numerical simulation of multicomponent multiphase flow phenomena
    keyword : multi-phase flow, numerical simulation, computational fluid dynamics
  • Clarification of damaged core and source term behaviors under severe accident conditions
    keyword : severe accident, core damage accident, source terms
Current and Past Project
  • R&D of Next Generation Methods for Fast Reactor Safety Analysis with Advanced Computational Science
  • A reserach project entitled 'Clarification of key thermal-hydraulic phenomena in severe transeint of accelerator driven systems' which forms part of the IAEA's Co-ordinated Research Project in 'Studies of advanced reactor technology options for effective incineration of radioactive waste'.
Academic Activities
1. Introduction to Transport Phenomena.
1. H. Yamano, S. Fujita, Y. Tobita, K. Kamiyama, Sa. Kondo, K. Morita, M. Sugaya, M. Mizuno, S. Hosono, T. Kondo, SIMMER-IV: Three Dimensional Computer Program for LMFR Core Disruptive Accident Analysis -Version 2.A Model Summary and Program Description -, Japan Nuclear Cycle Development Institute, JNC TN9400 2003-070, 2003.08.
2. H. Yamano, S. Fujita, Y. Tobita, K. Kamiyama, Sa. Kondo, K. Morita, E. A. Fischer, D. J. Brear, N. Shirakawa, X. Cao, M. Sugaya, M. Mizuno, S. Hosono, T. Kondo, W. Maschek, E. Kiefhaber, G. Buckel, A. Rineiski, M. Flad, T. Suzuki, P. Coste, S. Pigny, J. L, SIMMER-III: A Computer Program for LMFR Core Disruptive Accident Analysis -Version 3.A Model Summary and Program Description -, Japan Nuclear Cycle Development Institute, JNC TN9400 2003-071, 2003.08.
3. K. Morita, H. Yamano, Y. Tobita, Sa. Kondo, SIMMER-III/IV Heat- and Mass-Transfer Model - Model and Method Description -, Japan Nuclear Cycle Development Institute, JNC TN9400 2003-047, 2003.07.
4. K. Morita, Y. Tobita, Sa. Kondo, E. A. Fischer, SIMMER-III Analytic Thermophysical Property Model, Japan Nuclear Cycle Development Institute, JNC TN9400 2000-004, 1999.05.
5. K. Morita, Y. Tobita, Sa. Kondo, E. A. Fischer, K. Thurnay, SIMMER-III Analytic Equation-of-State Model, Japan Nuclear Cycle Development Institute, JNC TN9400 2000-005, 1999.05.
1. Xiaoxing Liu, Koji Morita, Shuai Zhang, An ALE pairwise-relaxing meshless method for compressible flows, Journal of Computational Physics, 10.1016/, 387, 1-13, 2019.06, In this paper, we present a pairwise-relaxing meshless (PRM) method for solving the Euler equations of compressible flows within the Arbitrary Lagrangian Eulerian (ALE) framework. Derived from the moving particle semi-implicit (MPS) method and the finite volume particle (FVP) method, the PRM approximates the derivatives from the value defined at the midpoint of each interacting particle pairs through a kernel-based formulation. Pairwise-relaxing constants are introduced to the kernels to provide degree of freedom to enforce the Taylor-series consistency condition while mass, momentum and energy are conserved exactly. An upwind high-order reconstruction scheme via a corrective procedure and variable cut-off radius is also developed for this PRM method. The HLLC approximate Riemann solver is adopted to solve Riemann problem. One and two-dimensional numerical tests are presented to demonstrate the performance of the PRM method..
2. Koji Morita, Tatsuya Matsumoto, Shinpei Nishi, Tatsuya Nishikido, Songbai Cheng, Hirotaka Tagami, Tohru Suzuki, Yoshiharu Tobita, A new empirical model for self-leveling behavior of cylindrical particle beds, journal of nuclear science and technology, 10.1080/00223131.2015.1126204, 53, 5, 713-725, 2016.05, During the material relocation phase of core disruptive accidents in sodium-cooled fast reactors, the rapid quenching and fragmentation of molten materials discharged from the reactor core into the lower plenum region can lead to the formation of debris beds. Coolant boiling may lead to leveling of the mound-shaped beds, which changes both the beds' coolability with decay heat in the fuel and the neutronic characteristics. In this study, a series of experiments using simulant materials were performed to develop an experimental database of self-leveling processes of particle beds in a cylindrical system. To simulate the coolant boiling in the beds in the experiments, a gas injection method was used to percolate nitrogen gas uniformly through the base of a bed with a conical-shaped mound. Time variations in bed height during the self-leveling process were measured for different particle sizes, densities and sphericities, and gas injection velocities. Using a dimensional analysis approach, a new model was proposed. This model correlates the experimental data on transient bed height with an empirical equation using a characteristic time for self-leveling development and an equilibrium bed height. The proposed model reasonably predicts the self-leveling development of particle beds..
3. K. MORITA, S. ZHANG, S. KOSHIZUKA, Y. TOBITA, H. YAMANO, N. SHIRAKAWA, F. INOUE, H. YUGO, M. NAITOH, H. OKADA, Y. YAMAMOTO, M. HIMI, E. HIRANO, S. SHIMIZU, M. OUE, Detailed Analyses of Key Phenomena in Core Disruptive Accidents of Sodium-cooled Fast Reactors by the COMPASS Code, Nuclear Engineering and Design, 241, 12, 4672-4681, 2011.12.
4. B. ZHANG, T. HARADA, D. HIRAHARA, T. MATSUMOTO, K. MORITA, K. FUKUDA, H. YAMANO, T. SUZUKI, Y. TOBITA, Self-Leveling Onset Criteria in Debris Beds, J. Nuclear Science and Technology, 47, 4, 384-395, 2010.04.
5. M. Kabir HOSSAIN, Y. HIMURO, K. MORITA, K. NAKAGAWA, T. MATSUMOTO, K. FUKUDA, W. MASCHEK, Simulation of Molten Metal Penetration and Freezing Behavior in a Seven-pin Bundle Experiment, J. Nuclear Science and Technology, Vol.46, No.8, pp.799-808, 2009.08.
6. S. ZHANG, S. KUWABARA, T. SUZUKI, Y. KAWANO, K. MORITA, K. FUKUDA, Simulation of Solid–fluid Mixture Flow Using Moving Particle Methods, J. Computational Physics, Vol.228, Issue 7, pp.2552-2565, 2009.04.
7. M. Mizanur RAHMAN, Yoshiyuki EGE, Koji MORITA, Kiyoshi NAKAGAWA, Kenji FUKUDA, Werner MASCHEK, Simulation of Molten Metal Freezing Behavior onto a Structure, Nuclear Engineering and Design, Vol.238, Issue 10, pp.2706-2717, 2008.10.
8. Koji MORITA, Tatsuya MATSUMOTO, Kenji FUKUDA, Yoshiharu TOBITA, Hidemasa YAMANO, Ikken SATO, Experimental Verification of the Fast Reactor Safety Analysis Code SIMMER-III for Transient Bubble Behavior with Condensation, Nuclear Engineering and Design, Vol.238, Issue 1, pp.49-56, 2008.01.
9. Ping LIU, Satoshi YASUNAKA, Tatsuya MATSUMOTO, Koji MORITA, Kenji FUKUDA, Hidemasa YAMANO, Yoshiharu TOBITA, Dynamic Behavior of a Solid Particle Bed in a Liquid Pool, SIMMER-III Code Verification, Nuclear Engineering and Design, Vol.237, No.5, pp.524-535, 2007.03.
10. Koji Morita, Wernar Maschek, Michael Flad, Yoshiharu Tobita, Hidemasa Yamano, Thermophysical Properties of Lead-bismuth Eutectic for Use in Reactor Safety Analysis, J. Nuclear Science and Technology, Vol.43, No. 5, pp.1-11, 2006.05.
11. Shuai Zhang, Koji Morita, Kenji Fukuda, Noriyuki Shirakawa, An Improved MPS Method for Numerical Simulations of Convective Heat Transfer Problems, Int. J. Numerical Methods in Fluids, Vol.51, No. 1, pp. 31-47, 2006.05.
12. Ping Liu, Satoshi Yasunaka, Tatsuya Matsumoto, Koji Morita, Kenji Fukuda, Yoshiharu Tobita, Simulation of the Dynamic Behavior of the Solid Particle Bed in a Liquid Pool: Sensitivity of the Particle Jamming and Particle Viscosity Models, J. Nuclear Science and Technology, Vol.43, No. 2, pp.140-149, 2006.02.
13. K. Morita, T. Matsumoto, R. Akasaka, K. Fukuda, T. Suzuki, Y. Tobita, H. Yamano, Sa. Kondo, Development of multicomponent vaporization/condensation model for a reactor safety analysis code SIMMER-III: Theoretical modeling and basic verification, Nuclear Engineering and Design, 10.1016/S0029-5493(02)00351-5, 220, 3, 224-239, Vol. 220, No. 3, pp. 224-239, 2003.01.
14. K. Morita, Sa. Kondo, Y. Tobita, D. J. Brear, SIMMER-III Applications to Fuel-Coolant Interactions, Nuclear Engineering and Design, Vol. 189, pp. 337-357, 1999.01.
15. K. Morita, E. A. Fischer, K. Thurnay, Thermodynamic Properties and Equations of State for Fast Reactor Safety Analysis Part II: Properties of Fast Reactor Materials, Nuclear Engineering and Design, Vol. 183, No. 3, pp. 193-211, 1998.01.
16. K. Morita, E. A. Fischer, Thermodynamic Properties and Equations of State for Fast Reactor Safety Analysis Part I: Analytic Equation-of-State Model, Nuclear Engineering and Design, Vol. 183, No. 3, pp. 177-191, 1998.01.
Works, Software and Database
1. .
Membership in Academic Society
  • The Japanese Society for Multiphase Flow
  • Atomic Energy Society of Japan
  • The Japan Society of Mechanical Engineers
Educational Activities
Classes in Graduate School of Engineering:
- Nuclear Safety Engineering,
- Multiphase Flow Science in Energy Engineering,
- Nuclear Fuel Cycle Experiment II,
- Research Project in Nuclear Energy System C,
- Nuclear Energy System Laboratory C,
- Independent Study and Seminar in Nuclear Energy System C,
- Colloquium on Nuclear Energy System C,
- International Environmental System Engineering 3, and
- International Environmental System Engineering 5

Classes in Undergraduate School of Engineering:
- Exercises in Fundamental Physics IB,
- Thermodynamics,
- Introduction to Nuclear Reactor Engineering,
- Seminar of Applied Quantum Physics II and III,
- Engineering Analysis and Design, and
- Bachelor Research Work in Energy Science and Engineering
Other Educational Activities
  • 2013.12.
  • 2011.02.
  • 2009.11.