Modelling radiation resistant low activation High Entropy Alloys

The UK Government policy is that nuclear energy has an important role to play in providing an energy future that is safe and low carbon with minimal waste production; for example, the Government's "Nuclear Sector Deal" paper published this summer has as a priority "a long-term vision of innovation-led growth that delivers successively lower generation costs and a 20% reduction in decommissioning costs to the taxpayer".
In 2018, the UK derived ~20% of its electrical power from nuclear reactors and it is likely that demand for electrical energy will only increase, e.g., through the electrification of transport. In the short term, small-modular reactors (SMR) and Gen-III technologies may be utilised to meet demand. The development of radiation-resistant alloys for use in next-generation nuclear reactors will help sustain and expand the UK's capacity to build advanced power plants, with the ability to deliver reliable low-carbon energy. With Materials science highlighted as the key challenge in the 2016 EPSRC Independent Review of Fission and Fusion, this project will aim at addressing the functional materials challenge using advanced computer modelling and simulation.

Therefore in this project, atomistic models High Entropy Alloys (HEAs) will be developed and the models used to investigate the mechanical and thermal properties of specific low activation (i.e. they do not become highly radioactive for long periods) HEAs. HEAs are novel alloys where no single metallic element dominates and four or more elements are used in near equal atomic ratios. HEAs are currently the subject of a significant international research effort due to their reported superior mechanical properties compared to conventional alloys, such as excellent hardness and high temperature strength and stability. They have therefore excellent potential for nuclear applications provided they do not become active under irradiation.

Various theoretical models based on ab initio techniques will be implemented to investigate mechanical and thermal properties and these will be compared to experiment. However the system sizes that can be studied using ab initio methods are necessarily small due to computing limitations and so a second aim of the project is to study larger systems through the use of multi scale modelling by linking the ab initio results with a classical potential formalism. This will allow the alloy behaviour under irradiation also to be investigated and the results compared with other more conventional materials.

The project will concentrate on the investigation of reduced activation HEAs specifically those comprising of TiVZrTa and VWMoCr and TiVCrMnFe, which will be considered in a related experimental programme but the techniques that will be developed and used will have a general application to other complex alloys and therefore potentially wide use outside the nuclear area.

In 2018, the UK derived ~20% of its electrical power from nuclear reactors. The demand for electrical energy will only increase, e.g., through the electrification of transport. In the short term, small-modular reactors (SMR) and Gen-III technologies may be utilised to meet demand. However, in a future in where nuclear waste is minimised and fuels other than uranium utilised, new Gen-IV and fusion reactors need to be developed. Such reactors will only be built with the help of new materials that can operate in more extreme environments than currently.
One family of materials that is showing great promise are the High Entropy Alloys (HEAs). They are a relatively new class of materials and therefore there is a limited understanding of the electronic, elastic and thermodynamic stability properties.
In this project we aim to bring a range of advanced computational methods to develop a better understanding of the structure - property relationship of complex High Entropy Alloys. These HEAs are inherently complex in nature with 4 or more elements in the compilation e.g. VWMoCr or TiZrHfTa.

The main economic impact will occur in conjunction with the associated experimental programme, which will be involved in producing the low activation alloys. The ability to scale up the most successful alloys into commercial quantities has a large economic potential. The modelling proposed in the project will facilitate the development of these materials in the laboratory and therefore bring the objective of commercial alloy production closer.
The work is focussed towards understanding low activation materials with potential use in the nuclear industry so as a result the work will have impact with commercial organisations such as National Nuclear Laboratories, EDF, Rolls-Royce plc, AREVA who will benefit, not only from the results of the project in identifying new materials for nuclear applications but also through the skills acquired by the personnel working on the project. The work will have impact with the nuclear energy agency (NEA) of the OECD, who will benefit through the PI's interaction with the structural materials modelling group of the NEA. The work will also be publicised at the annual UK nuclear academics meeting.
Another direct output will be highly skilled researchers who have developed multidisciplinary skills in the nuclear modelling area. The appointed PDRA will directly help in the supervision of PhD students working in the area adding further impact through the training of new researchers.
Impact will be achieved not only through publication in top international journals, the usual presentations at important international meetings such as the US Materials Research Symposia, held in Boston each Fall, but also through the development of a web site, promotional materials, preprint archives and small intense workshops with leading international experts.