Mesoscale finite element phase field modelling of liquid lithium corrosion of steels

Liquid lithium is a proposed coolant for the STEP fusion reactor because of its ability to remove heat efficiently, as a liquid metal, but with the added advantage that Li can breed tritium from neutron interactions. One of the proposed materials that the liquid lithium will be in contact with is grade P91 steels. These steels have been used extensively in the fossil fuels and nuclear industry and they have both reasonable corrosion/oxidation resistance due to the Cr present but more importantly have high creep strength at elevated temperatures required by STEP. P91 grades are ferritic-martensitic steels with a highly complex microstructure that contains a variety of both precipitates and inclusions. These are well known to influence the creep properties but are likely to have a role to play in the corrosion of the steel by liquid lithium. At Imperial we have recently been developing a model, within the finite element phase field method framework, that can generate polarisation curves similar to those observed experimentally during the measurements of corroding metals. These models will be developed to study single grain, bi-crystals and grains with a single second phase particle embedded, of the various types found in P91 steels, to assess which particles are critical in the presence of Li and control the corrosion behaviour of these steels. These models will be developed in parallel with the localised corrosion experiments that will take place at UKAEA of P91 steels in liquid lithium. The models once developed for simple cases will also attempt (subject to experimental data availability) to include the effect of radiation damage through hardening and potentially grain boundary chemical segregation effects in these steels on the corrosion behaviour in liquid Li.

It cannot be overstated how important reducing CO2 emissions are in both electricity production for homes and industry but also in reducing road pollution by replacing petrol/diesel cars with electric cars in the next 20 years. These ambitions will require a large growth in electricity production from low carbon sources that are both reliable and secure and must include nuclear power in this energy mix. Such a future will empower the vision of a prosperous, secure nation with clean energy. To do this the UK needs more than 100 PhD level people per year to enter the nuclear industry. This CDT will impact this vision by producing 70, or more, both highly and broadly trained scientists and engineers, in nuclear power technologies, capable of leading the UK new build and decommissioning programmes for future decades. These students will have experience of international nuclear facilities e.g. ANSTO, ICN Pitesti, Oak Ridge, Mol, as well as a UK wide perspective that covers aspects of nuclear from its history, economics, policy, safety and regulation together with the technical understanding of reactor physics, thermal hydraulics, materials, fuel cycle, waste and decommissioning and new reactor designs. These individuals will have the skill set to lead the industry forward and make the UK competitive in a global new build market worth an estimated £1.2tn. Equally important is reducing the costs of future UK projects e.g. Wylfa, Sizewell C by 30%, to allow the industry and new build programme to grow, which will be worth £75bn domestically and employ tens of thousands per project.

We will deliver a series of bespoke training courses, including on-line e-learning courses, in Nuclear Fuel Cycle, Waste and Decommissioning; Policy and Regulation; Nuclear Safety Management; Materials for Reactor Systems, Innovation in Nuclear Technology; Reactor Operation and Design and Responsible Research. These courses can be used more widely than just the CDT educating students in other CDTs with a need for nuclear skills, other university courses related to nuclear energy and possibly for industry as continual professional development courses and will impact the proposed Level 8 Apprenticeship schemes the nuclear industry are pursuing to fill the high level skills gap.

The CDT will deliver world-class research in a broad field of nuclear disciplines and disseminate this work through outreach to the public and media, international conferences, published journal articles and conference proceedings. It will produce patents where appropriate and deliver impact through start-up companies, aided by Imperial Innovations, who have a track record of turning research ideas into real solutions. By working and listening to industry, and through the close relationships supervisory staff have with industrial counterparts, we can deliver projects that directly impact on the business of the sponsors and their research strategies. There is already a track record of this in the current CDT in both fission and fusion fields. For example there is a student (Richard Pearson) helping Tokamak Energy engage with new technologies as part of his PhD in the ICO CDT and as a result Tokamak Energy are offering the new CDT up to 5 studentships.

Another impact we expect is an increasing number of female students in the CDT who will impact the industry as future leaders to help the nuclear sector reach its target of 40% by 2030.
The last major impact of the CDT will be in its broadening scope from the previous CDT. The nuclear industry needs to embrace innovation in areas such as big data analytics and robotics to help it meet its cost reduction targets and the CDT will help the industry engage with these areas e.g. through the Bristol robotics hub or Big Data Institute at Imperial.

All this will be delivered at a remarkable value to both government and the industry with direct funding from industry matching the levels of investment from EPSRC.