Atomic-Scale Characterisation of Reactor Pressure Steels

The reactor pressure vessel (RPV) is a safety critical component of a nuclear fission reactor. Hence, the long-term stability, strength and toughness of RPV steels are of vital importance for the power-generating industry. The main experimental technique to be used will be atom probe tomography. This cutting edge microscopy technique enables a three-dimensional, atom-by-atom characterisation of the microstructure of the steel, providing unique insight into the fundamental mechanisms of solute clustering and the resulting embrittlement. Additional experimental work will involve electron microscopy and mechanical property measurements. This research is critical both for the predicting the safe operating lifetimes of existing fission plants, and also in the design and manufacture of new reactors, such as Small Modular Reactors, in the UK.

This is project will enable ongoing collaboration between Oxford and Rolls Royce. The current ageing experiments (approaching 5 years of continuous thermal treatments) will be continued with removal from furnaces and testing/examination of aged samples at suitable intervals. Current mechanistic understanding is that any nano-scale precipitation will be more likely found either on dislocations or grain boundaries. Because of this more emphasis will be placed on grain boundary behaviour and in particular the segregation of elements such as phosphorus, as well as Ni/Mn/Cu. This will require greater use of instruments other than atom probe, such as Focused Ion Beam (FIB) to generate site specific specimen, and Transmission Kikuchi Diffraction (TKD) to characterise the crystallographic misorientation of the grain boundaries.

The project also represents an opportunity to continue to collaborate with the Odette Group at UCSB. This collaboration has enabled access to neutron irradiated samples for complementary analysis to our thermally aged counterparts. This has previously led to opportunities to use the facilities at Idaho National Laboratory for the characterisation of active materials. However, it now presents the possibility to exploit the expertise and capabilities at the Culham Centre for Fusion Energy (CCFE) Materials Research Laboratory.

The capability for 3D chemically-resolved atomic imaging has exciting implications for unlocking microstructure-property relationships critical to design of new materials, developing processing routes, understanding in-service performance and degradation/failure mechanisms in harsh environments. This research into structural materials for GenIV Small Modular Reactors, will also contribute to safety critical monitoring of reactor steels.

As such, this project is directly relevant to multiple EPSRC themes such as Physical Sciences, Manufacturing the Future, Engineering and Energy, across research areas: Nuclear Fission (Maintain), Materials for Energy Applications (Grow), Materials Engineering-Metals and Alloys (Maintain). It falls under the EPSRC themes of a Productive and Resilient Nation, contributing to the renaissance of nuclear research in the UK.