ZrO2-corrosion-layers and their grain boundary networks

Zr-alloys are used for nuclear fuel cladding in water-cooled reactors. These alloys corrode in contact with their local-environment, e.g. hot water and steam (Féron 2012). Initially oxidation rapidly results in the formation of a zirconium oxide layer that reduces the oxidation rate. The migration of charged species in the oxide layer is largely controlled by the microstructure (Garner et al. 2015, 2017) and grain boundary network of the oxide layer (Gertsman et al. 1997).
Initially a non-equilibrium tetragonal phase close to the metal-oxide interface. However as the Oxide layer gains thickness the location of the reaction interface between metal and oxide are further from the surface. The compressive stress in the oxide layer decrease with distance from the metal/oxide interface to eventually be insufficient to stabilise the tetragonal phase. It transforms to monoclinic ZrO2, which is the stable phase at atmospheric pressure and temperature below 1500 K.

In this challenging project, we aim at characterizing the behaviour of different grain boundary networks using state-of-the-art meso- to nano-scale characterisation techniques including transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD) techniques. We will experimentally alter Zr-alloys and investigate how this affects the formation and microstructural properties of the resulting Zr-oxide layers. Eventually the experimental data will be used to explore the microstructures using different modelling approaches.

References:
Féron, D. (2012) Preface. In Nuclear Corrosion Science and Engineering pp. xxvii-xxix. Elsevier.
Garner, A., Hu, J., Harte, A., Frankel, P., Grovenor, C., Lozano-Perez, S., and Preuss, M. (2015) The effect of Sn concentration on oxide texture and microstructure formation in zirconium alloys. Acta Materialia, 99, 259-272.
Garner, A., Frankel, P., Partezana, J., and Preuss, M. (2017) The effect of substrate texture and oxidation temperature on oxide texture development in zirconium alloys. Journal of Nuclear Materials, 484, 347-356.
Gertsman, V.Y., Zhilyaev, A.P., and Szpunar, J.A. (1997) Grain boundary misorientation distributions in monoclinic zirconia. Modelling and Simulation in Materials Science and Engineering, 5, 35-52.

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.