Analysis of a tile repair technique based on brazing process for ITER First Wall

•Suitable repair techniques are explored for the ITER first wall manufactured by Europe.•The work is focused on total replacement of the damaged tile.•A brazing process is proposed avoiding high temperatures.•Detailed thermal steady state and transient analyses that simulate the brazing process.•Key parameters are proposed looking for an optimization of the process. The European ITER First Wall panel design relies on a HIP based manufacturing sequence. However, failures of the bond to the beryllium tile might occur during the fabrication and under high heat flux qualification. A dedicated project has been stablished between UKAEA/CCFE and F4E aiming to identify suitable repair techniques. One of the most promising identified techniques consists of a total replacement of the tile, which would be joined again with a brazing process specifically designed for this purpose. A proper replacement and repair of the tile imply a final good quality of the new bond without damaging the rest of the component. This means that the repairing brazing process has to: avoid degradation on CuCrZr base material, limit the surface beryllium tile temperature, limit the temperature and heat exposure to the neighbouring tiles, etc. The complexity of this method has required crucial engineering analyses. The goal of the work here presented is to describe those analyses as well as the methods for finally finding the right brazing process that would be compatible with the challenging requirements. Two different approaches based on thermal assessment are proposed (supported with analytical and finite element modelling): first, a steady-state thermal analysis explores possible thermo-hydraulic conditions (via the pre-existing cooling channels) as well as the influence of the thermal contact conductance on the thermal behaviour of the component; secondly, a detailed thermal transient analysis allows reproducing in detail the brazing process following the consequences on the thermal distribution through the component. By combining these analyses with manufacturing aspects, the right parameters controlling the process (heat flux, hydraulic conditions and braze temperature) are found. Although the predictions and conclusions require experimental benchmarking, this work has provided a strong indication of the feasibility of the proposed technique.