This paper presents the application of the image-based finite element method (IBFEM) to quantify the impact of micro-structure caused by manufacturing processes on the performance of fusion energy heat exchangers. The components, containing tungsten, were imaged with high-power lab-based X-ray CT and neutron CT. Volume data was converted into part-specific IBFEM meshes using the software ScanIP. The open source software ParaFEM was used to simulate the microstructurally faithful models using boundary conditions to simulate the extreme environment within a nuclear fusion reactor. By comparison with design-based simulations the impact of minor deviations from the design introduced during manufacturing were estimated. By digitally testing ‘real’ components, results can be interrogated through the sample’s full volume. This provides more sophisticated information than pass/fail experimental tests which can be used to rate components in a manner similar to material purity for optimised usage.