Experimental study and simulation of metallic melt infiltration into porous media

by Liang Chen (KTH Physics)

Tuesday 10 Jun 2025, 09:00 → 12:00 Europe/Stockholm

FA31 (AlbaNova Main Building)

Abstract

Modeling corium melt infiltration into porous debris beds is crucial for predicting and mitigating severe accidents in nuclear power plants. A comprehensive understanding of melt infiltration requires both experimental and numerical approaches. 

Experimentally, two key studies are conducted: One quantifies the wettability of various surfaces by metallic melt, while the other examines one-dimensional melt infiltration dynamics in porous media composed of corresponding materials (MRSPOD-1D). The results indicate that wettability significantly influences infiltration dynamics, with wettable surfaces facilitating initial infiltration and non-wettable surfaces impeding it. 

Numerically, a multiscale modeling framework is employed, spanning from an interface- resolved (pore-scale) method to a space-averaged (macroscopic) approach. The numerical study of this thesis first focuses on developing and validating a pore-scale numerical model that simulates molten metal relocation using interface tracking methods. The model integrates the Level-Set (LS) method to track the metal-gas interface and the enthalpy-porosity approach to account for phase changes. Validation is performed using REMCOD-E8 and REMCOD-E9 experimental data. 

Building on the experimental and pore-scale findings, a macroscopic model is developed by coupling the LS method with the Brinkman equations. The macroscopic model is validated against MRSPOD-1D and REMCOD experiments and further assessed through comparisons with pore-scale simulations. 

The multiscale modeling approach reveals the complex interplay among particle surface wettability, pore size, the melt pressure head, melt superheat, and particulate bed temperature on the dynamics of the melt infiltration: (1) enhanced surface wettability consistently promotes melt infiltration and heat transfer across all Bond numbers, though it can also trigger early solidification, particularly at low Bond numbers; (2) melt infiltration becomes more sensitive to the wettability as pore size decreases, occurring in non-wettable media only when melt pressure overcomes capillary resistance, while this sensitivity diminishes as pore size increases; (3) at high Bond numbers, infiltration rates strongly depend on the initial melt pressure head, which drives faster infiltration until the melt layer atop the bed is depleted; (4) higher initial particulate bed temperatures and melt superheat enhance infiltration, whereas lower temperatures may cause solidification arrest, indicating that additional heat sources in reactor-relevant scenarios could promote remelting and facilitate deeper infiltration; (5) pore-scale simulations more accurately capture infiltration dynamics when solidification occurs, whereas both pore-scale and macroscopic models yield comparable results in high-temperature cases without solidification. 

This thesis advances the understanding of melt infiltration mechanisms and provides validated tools for severe accident modeling, which are critical for enhancing severe accident management strategies.