Influence of barrier materials on tritium permeation in the EU-DEMO fusion reactor

Abstract

In the EU-DEMOWater-Cooled Lithium Lead (WCLL) breeding blanket concept, controlling tritium permeation from the breeder material (PbLi) to the cooling water, through the structural steel EUROFER97, is a critical challenge to ensure both reactor safety and fuel cycle efficiency. To mitigate tritium losses, permeation barrier (PB) materials are being actively investigated, either as thin coatings or as bulk resistive interlayers. In this context, the development of advanced numerical tools capable of accurately describing the coupled physical phenomena governing tritium transport is of paramount importance. In this thesis, a Computational Fluid Dynamics (CFD) based numerical model is developed and implemented within the open-source OpenFOAM framework to improve the understanding of tritium transport phenomena in the presence of permeation barriers in representative WCLL blanket geometries. The model builds upon an existing solver for transient, buoyant and turbulent flowswithconjugateheattransfer, andincorporatesnewcapabilities to describe tritium mass transport. These include dedicated boundary conditions accounting for concentration discontinuities at interfaces between materials with different solubilities, as well as dissociation and recombination processes at fluid–solid surfaces. Three PB materials are investigated: iron, currently considered as the reference design option, and two alternative ceramic materials, Al2O3 and B4C. The model is first validated against a reference case of tritium permeation through a composite membrane reported in the literature, showing excellent agreement. It is subsequently applied to reduced and full-scale WCLL elementary cell configurations to quantify tritium losses to the cooling water. The results indicate a permeation reduction of up to two and six orders of magnitudefor Al2O3 andB4C,respectively, compared to the reference case without a permeation barrier. Overall, the proposed modelling framework demonstrates strong potential as a robust tool to support tritium transport analyses and the design and safety optimization of breeding blankets in future fusion reactors.