Finite element modelling of the corrosion of stainless steels/CuCrZr for STEP

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The STEP programme roadmap is very tight, with a need to down select materials in the next few years, before build can begin in 2032, if the programme is to deliver by 2040. There is a need to select the materials that will carry coolant to remove reactor heat, which might be stainless steels, as used in many fission plants, and also proposed for ITER, using boronated coolant water.To achieve the ambitious goals for fusion state-of-the art corrosion modelling capabilities will be needed to support experiments. This project will use phase field approaches embedded in finite element models, being developed at Imperial College, jointly by the Martinez-Paneda and Wenman groups to model corrosion development (including microstructure, electrolyte ion concentrations, pit nucleation and growth and transition to stress corrosion cracks). The work will use either or both the COMSOL and ABAQUS finite element codes. The current models build on the work of Turnbull et al. (2008). that showed that pit growth in stainless steels can be explained by the development of plastic strains at the pit sides that lead to oxide fracture and increase the corrosion rate of the underlying metal. These models have very recently been enhanced further to by addition of electrolyte ion concentrations and thus can be used to model a range of coolant chemistries and then can be further advanced by addition of microstructure via crystal plasticity approaches allowing the effects of localised stress/strains, due to crystal orientation, to be considered in the corrosion process. The models, whilst initially tested on stainless steels can be developed further/adapted to other coolant/materials combinations such as CuCrZr or martensitic/ferritic steels as proposed for STEP.