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

FESTIM is an open-source finite element framework for modelling the transport of hydrogen isotopes in materials. This paper presents FESTIM v2.0, a major release that broadens the framework’s physical scope and software infrastructure. The new formulation supports fully coupled multi-species transport, advanced trapping and reaction networks, isotope exchange, decay, advection, and generalised treatments of interfaces and boundaries. FESTIM v2.0 is built on DOLFINx, providing improved scalability, interoperability, and long-term sustainability. Performance benchmarks on representative multi-material diffusion problems show speedups of up to approximately 15× relative to FESTIM v1, enabling more efficient engineering-scale, multiphysics simulations. The framework is designed for applications ranging from laboratory-scale permeation experiments to component-level analyses relevant to fusion fuel-cycle technologies. Together, these advances establish FESTIM v2.0 as a versatile and efficient platform for hydrogen transport modelling in complex materials systems.