Understanding Irradiation Embrittlement of Reactor Pressure Vessel Steels Using Micromechanical Methods and Atom Probe Tomography

This project is a collaboration with our industrial partner Rolls Royce. The development of Small Modular Reactors has the potential to play an important part in the UK’s industrial strategy and to tackling the green energy grand challenge.  However, the design, build and maintenance of next generation nuclear reactors must be underpinned by new research into ageing and degradation of the structural materials.

In particular, the reactor pressure vessel (RPV) is a critical component of a nuclear fission reactor. Hence, understanding evolution of the long-term microstructural stability, strength and toughness of RPV steels subject to the harsh reactor environment is of vital importance for the power-generating industry. The exposure of RPV steels to neutron irradiation gives rise to irradiation-enhanced diffusion, rearrangement of solute atoms and consequently, a degradation of the mechanical properties. This typically results in irradiation hardening and embrittlement which limits the lifetime of nuclear-power plants. An improved understanding the of the underlying causes of embrittlement would enable the better estimates for safe operating conditions and aid the development of materials with increased resistance to irradiation embrittlement.

Specifically, in this project atom probe tomography (APT) and nanoindentation will be combined for the study of systematic set of thermally aged and/or irradiated RPV steels. APT provides three-dimensional, atom-by-atom imaging of the steel  microstructure, offering unique insight into the still poorly understood fundamental mechanisms of nickel-manganese-silicon solute cluster formation and evolution.  Moreover, nanoindentation is a non-destructive micromechanical technique that enables the measurement of irradiation induced hardness, and thus embrittlement, on a length-scale comparable to that of the microstructure, whilst reducing the volume of radioactive material that is required for testing. Combining these techniques will enable new understanding of the role these microstructural features play in irradiation embrittlement.

Specimens of the irradiated steel will be prepared for characterisation at the UKAEA Materials Research Facility and APT will be undertaken at the new Nuclear Materials Atom Probe Facility (NuMAP) in the Materials Department in Oxford.

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