FESTIM v2.0: Upgraded framework for multi-species hydrogen transport and enhanced performance

TL;DR

FESTIM v2.0 tackles the challenge of accurately modelling hydrogen isotope transport in fusion-relevant materials by delivering a modular, multi-species finite element framework built on DOLFINx. The paper details architectural redesigns that separate physics per subdomain, introduce comprehensive reaction networks (including trapping, isotope exchange, and decay), and provide flexible interface and boundary condition treatments (DG/Nitsche and penalty methods) for robust multi-material simulations. It also demonstrates substantial performance gains over the previous version and highlights interoperability with external solvers for multiphysics workflows, including coupling with CFD and neutronics codes via dedicatedOpenMC2DOLFINX and foam2dolfinx tools. Collectively, FESTIM v2.0 offers a scalable, sustainable platform enabling high-fidelity hydrogen transport studies across scientific and engineering applications, with verified V&V resources and active community support for ongoing development.

Abstract

FESTIM is an open-source finite element framework for modelling the transport of hydrogen isotopes in materials. It provides a flexible and extensible tool for simulating diffusion, trapping, surface interactions, and other processes that govern hydrogen behaviour. This paper presents FESTIM v2.0, a major release that broadens both the physical scope and the software infrastructure of the framework. On the physics side, the formulation adopts a modular structure that supports multi-species transport, advanced trapping and reaction schemes, isotope exchange, decay, and advection. Interface and boundary conditions have been generalised, and interoperability with external solvers enables multiphysics workflows, including coupling with fluid dynamics and neutron transport codes. On the software side, FESTIM v2.0 has been migrated to DOLFINx, the next-generation FEniCS platform, providing improved performance, interoperability, and long-term sustainability. Taken together, these advances position FESTIM v2.0 as a versatile platform for investigating hydrogen transport in materials across scientific and engineering applications.

Figures (7)

• Figure 1: Illustration of how external meshes can be generated and integrated in FESTIM. A user can interact with FESTIM through any of the supported input formats in DOLFINx. Additionally, meshio can be used to convert files from other formats to XDMF, which can then be read into FESTIM.
• Figure 2: Influence of advection on species transport in diffusion- and advection-dominated regimes.
• Figure 3: Multi-material test case hydrogen field solution
• Figure 4: Comparison of average runtimes for the Diffusion: multi-material benchmark case delaporte-mathurin_festim_2024-1 using FESTIM v1 and v2.0 with different interface treatments. Results are averaged over ten runs.
• Figure 5: Fields passed between OpenMC, OpenFOAM, and FESTIM using the openmc2dolfinx and foam2dolfinx packages. This setup demonstrates FESTIM's extensibility and its ability to interoperate with specialised solvers in multi-physics workflows.