Numerical modelling of metallic melt damage in contemporary tokamaks and future fusion reactors
Abstract
The provision of plasma-facing components (PFCs) with sufficient lifetime constitutes one of the major remaining technological challenges in the development of magnetic confinement fusion reactors. In ITER, under construction, and DEMO, undergoing its conceptual design phase, the PFC integrity is primarily threatened by fast transient power loading owing to MHD instabilities such as edge-localized modes, vertical displacement events or major disruptions. The extreme heat loads will generate melt that will be subject to strong volumetric forces that will displace the material, causing large-scale deformations that may severely compromise power handling. Moreover, off normal events can be accompanied by the production of relativistic intense runaway electron (RE) beams that may lead to deep melting and even PFC explosions. Hence, reliable modelling of melt and explosive events as well as assessment of their consequences constitute a key topic in fusion research.
The MEMENTO code, developed and maintained by our group, is the only worldwide code capable of simulating the self-consistent motion of induced metallic melts coupled with the thermoelectric response of large-area wetted PFCs. It solves the incompressible resistive thermoelectric MHD set of equations within the shallow water approximation coupled with the heat convection-diffusion equation. Its predictive capability has been successfully tested in multiple experiments that deliberately achieved PFC melting in a controlled manner and has been exclusively employed for melt predictions in ITER & DEMO. Benchmarking experiments concerned different plasma heat loads, tokamaks, materials, geometries, cooling types and electrical connections. These validation activities have been funded by EUROfusion, ITER and VR.
We request computational resources necessary for:
• benchmarking of MEMENTO against controlled experiments on sustained melt bridging of castellated tungsten (W) PFCs. Particularly, the ASDEX Upgrade H-mode sloped exposure originally scheduled for 2025, postponed for 2026;
• benchmarking of MEMENTO against controlled experiments on melt motion in tungsten heavy alloy (WHA) PFCs. Particularly, the ASDEX Upgrade H-mode leading edge exposure proposed for 2026;
• predictive runs of MEMENTO for the damage of W limiters under different transient event scenarios in DEMO;
• predictive runs of Geant4-MEMENTO for the thermal response of W limiters under different runaway electron scenarios in DEMO;
• final benchmarking of Geant4-LSDYNA for the modelling of the thermomechanical response (including fragmentation) of graphite PFCs against controlled runaway electron driven damage experiments in DIII-D;
• extension of the Geant4-LSDYNA workflow for runaway electron induced fragmentation from brittle (graphite) to ductile materials (tungsten). Particularly, addition of: (i) mesh deletion owing to vaporization, (ii) multi-phase equation-of-state, (iii) advanced material strength models;
• first benchmarking of Geant4-MEMENTO for the thermal response and the Geant4-LSDYNA for the thermomechaniscal response against controlled runaway electron impact experiments on instrumented W tiles: (i) an experiment performed in WEST in 2025, (ii) an experiment proposed for ASDEX Upgrade in 2026, (iii) an experiment proposed for DIII-D in 2026;
• predictive runs of Geant4-LSDYNA for the thermomechanical response for different runaway electron impact scsenarios in ITER;
• modelling of tritiated boron dust self-charging with Geant4.
