Session: 11-02 Severe accident mitigation phenomena

Paper Number: 136038

136038 - Study on the Remelting Process of the Debris Bed in the Lower Head of Reactor Pressure Vessel Based on Lattice Boltzmann Method 

Abstract: 

The retention of core melt (corium) in the lower head of the reactor pressure vessel (RPV) has been considered as a severe accident management strategy to maintain the reactor pressure vessel (RPV) integrity of a light water reactor. The corium behavior (debris bed formation, debris remelting, molten pool convection and physicochemical reactions) in the lower head plays an important role in severe accident progression. To study the debris bed remelting process in the lower head of the reactor pressure vessel, as well to explore the influence of external cooling on the debris bed remelting process, the Lattice Boltzmann Method (LBM) is employed to simulate the remelting process of the debris bed.

The Lattice Boltzmann Method, as a powerful numerical method for simulating fluid flow and complex physical processes, has been widely used in the solution of solid-liquid phase change problems in recent years due to its advantages in parallel computing and its ability to well implement the moving boundary problem of mass conservation. In the present study, the modification of the temperature equilibrium distribution function is proposed to simulate the phase change process between the oxidic corium phase and the liquid metal phases. Thermal Lattice Boltzmann Method (TLBM) based on total enthalpy is adopted to handle the latent heat in the phase change process, and the Immersed Boundary Method (IBM) is used to account for the velocity and boundary conditions of the solid-liquid phase interface. For the velocity field and temperature field in the simulation domain, the Multiple Relaxation Time (MRT) collision scheme is adopted based on TLBM. Finally, the accuracy of the model is verified by the heat melting verification model in the semi-infinite space, and then this model is used to simulate the remelting process of the debris bed. In addition, the calculation results from the present LBM model are also compared with the experimental data based on the COREM experimental system which is design and constructed to investigate the melting process of a debris bed packed with multi-component particles. The COREM experiment uses employs octanol and Wood's alloy as the metal phase and oxide phase in the debris bed, respectively, and employs the induction heating to simulate the decay heat in the debris bed. During the tests, a temperature-measuring optical fiber (a kind of optical temperature sensor) is used to measure the wall temperature, and a high-definition camera is used to record the melting process. The simulation results and experimental results have good consistency in data such as wall temperature distribution. In addition, the natural convection phenomenon during the melting process is also being successfully simulated.

Presenting Author: Shang Shi Xi‘an Jiaotong University

Presenting Author Biography: Shang Shi received the bachelor's degree from Xi’an Jiaotong University. He is currently working toward the master’s degree in the State Key Laboratory of Multiphase Flow in Power Engineering at Xi’an Jiaotong University. His primary research focus is on numerical simulation.

Authors:

Shang Shi Xi‘an Jiaotong University
Liangxing Li Xi'an Jiaotong University
Weimin Ma Royal Institute of Technology
Xiao Zeng China Nuclear Power Engineering Co., LTD.
Yidan Yuan China Nuclear Power Engineering Co., LTD
Zhenxin Lei Xi‘an Jiaotong University
Zutao Xiang Xi‘an Jiaotong University
Xiangyang Xu Xi‘an Jiaotong University