中法核工程与技术学院核声论坛（总第155期）

报告人简介About the speaker：

Yokoyama Ryo graduated from University of Tokyo, now he is the Assistant Professor of University of Tokyo.

Professional Experience is as follows.

2021-2022: Research Assistant, University of Tokyo, Japan

2022-2024: Research Fellow, Japan Society for Promotion of Science (JSPS), Japan

2022-2023: Researcher, Commissariat à l’énergie atomique et aux énergies alternatives (CEA), Cadarache IRESNE・LEAG, France

2023: Researcher, Université de Lorraine, LEMTA, France

2023: Designated Young Researcher, International Atomic Energy Agency (IAEA), Decommissioning and Environmental Remediation, Austria 

2024-(2029): Assistant Professor, Nuclear Professional School, University of Tokyo, Japan

报告摘要Abstract:

With the lessons learned from the Fukushima Daiichi Nuclear Power Plant (1F) accident, understanding nuclear severe accidents has become a top priority for improving the safety systems of nuclear power plants. Due to the challenges of conducting scalable experiments, there is increasing attention on robust simulations capable of handling multi-physics phenomena. In this seminar, I will introduce a novel Lagrangian particle method, "Moving Particle Hydrodynamics" (MPH), and its application to nuclear severe accidents.

The mathematical formulation of the MPH method, which models incompressible fluids, rigid bodies, and elastic bodies, will be presented. The discretized formulation follows fundamental physical laws such as mass conservation, linear and angular momentum conservation, and the second law of thermodynamics. The results of this method have been verified and validated through both fundamental experiments and theory.

As part of its application to severe accidents, the MPH method has been used in several large-scale experiments, including the VULCANO experiments conducted at CEA and debris bed formation experiments at Sun Yat-Sen University. The simulation results show promising outcomes. For the VULCANO experiments, the simulation successfully reproduced the gliding motion of highly viscous corium spreading and its termination. In the debris bed formation experiments, the simulation results indicated that the debris bed size governs pool convection behavior, consistent with experimental findings.

Finally, the MPH method has been extended to real-scale calculations for 1F, aiming to provide the best estimate of fuel debris distribution. In the case of Unit 3, the sedimentation of debris is predicted due to the combination of highly viscous corium relocation and rapid cooling from strong boiling heat transfer, vapor heat transfer, and radiation. For Unit 1, significant corium spreading and Molten Corium-Concrete Interaction (MCCI) are predicted due to insufficient cooling, regardless of the corium's shear viscosity.

Overall, these results demonstrate the robustness and potential of the MPH method to be applied to various nuclear severe accident scenarios.