The thermal performance of a carbon fibre composite-copper monoblock, a sub-component of a fusionreactor divertor, was investigated by finite element analysis. High-accuracy simulations were createdusing an emerging technique, image-based finite element modelling, which converts X-ray tomogra-phy data into micro-structurally faithful models, capturing details such as manufacturing defects. Forvalidation, a case study was performed where the thermal analysis by laser flash of a carbon fibre composite-copper disc was simulated such that computational and experimental results could be compared directly. Results showed that a high resolution image-based simulation (102 million elements of32 m width) provided increased accuracy over a low resolution image-based simulation (0.6 million ele-ments of 194 m width) and idealised computer aided design simulations. Using this technique to analysea monoblock mock-up, it was possible to detect and quantify the effects of debonding regions at the carbonfibre composite-copper interface likely to impact both component performance and expected lifetime.These features would not have been accounted for in idealised computer aided design simulations.© 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license(http://creativecommons.org/licenses/by/4.0/).