SiC fuel cladding: Macroscopic effects of radiation on mechanical and thermal properties from microstructural-scale characterisation and modelling

Silicon carbide is a candidate material for accident tolerant fuel cladding applications in nuclear power reactors due to its good neutronic performance for light water reactors, high temperature strength, exceptional stability under irradiation, and reduced oxidation compared to conventional Zircaloy fuel cladding under accident conditions. The development and investigation of these materials is particularly important in the light of the Fukushima event and the subsequent emphasis on Accident Tolerant Fuel concepts (ATF).

Recent efforts have attempted to model the behaviour of several SiC-based cladding designs under realistic LWR operating conditions, and give predictions of stresses and failure probabilities throughout the fuel life. These models treat the very complex, highly structured SiC-SiC composite as a homogenous material. This assumption seriously limits the applicability and accuracy of these models and such models cannot be used effectively to optimize the cladding macro and microstructure.

In order to design these materials to produce the best possible performance, a more refined model is needed representing accurately the composite microstructure and the behaviour of the various components For such a comprehensive model, the material properties of the constituent components of the composites, their mutual interfaces, and the way these respond to irradiation, are needed as input parameters.

This project aims to develop localized materials assessment techniques to directly measure mechanical and thermal properties of the individual constituents of SiC-based claddings at the relevant micro-scale, before and after irradiation, in order to provide input parameters for a comprehensive model which will be developed and validated in this program.

Since the Fukushima incident in 2011 there has been a widespread effort to increase the safety of nuclear fission reactors in extreme-incident conditions. In particular development of accident tolerant fuel claddings has been identified as a priority. Silicon carbide composites are being investigated for these applications due to good neutronic performance, high temperature strength, exceptional stability under irradiation, and in particular, from the safety perspective, its reduced oxidation compared to conventional Zircaloy under accident conditions. This grant will accelerate the development and deployment of SiC/SiC fuel cladding allowing for safer nuclear fission reactors. The development of safer nuclear power stations will encourage their further deployment in an effort to combat climate change through a reduction in greenhouse gas emissions. This will have a wide reaching positive impact on the global population.

Within the UK, SiC/SiC materials are of interest to a large range of companies, including: large global nuclear power suppliers such as EdF-who will be the end users; SME's who work on producing SiC materials such as ATL, High Wycombe; and national laboratories such as NNL and CCFE, who have interests in deploying SiC materials in other nuclear applications such as nuclear fusion. We will work with ISIS innovation, the University of Oxford's Technology Transfer Department, if appropriate to exploit any commercial potential of our findings. In addition the testing techniques and modelling methodologies developed in high temperature micro-fracture testing are of interest to leading UK companies such as Rolls Royce's in their development of high temperature turbine materials for aerospace applications. These companies are already involved in supporting nuclear research at Oxford University and we will disseminate results from this project through our regular meetings with them and through the small focussed workshop meetings (see "academic beneficiaries" section)