Thermal transient effects in fusion front wall/breeder blanket components

The high operating temperatures and nuclear radiation within a fusion reactor can significantly change the microstructure of its components, which in turn can change the material properties and mechanical behaviour. The materials chosen for fusion reactors have been specifically engineered to reduce the amount of induced radiation, but it is also important to understand how such materials will behave when exposed to the high temperatures of the fusion plasma. The plasma in a fusion reactor can reach temperatures of millions of degrees, and is kept controlled during operation using focused magnetic fields for containment. However, in the event of a loss of this containment it is possible for the plasma to contact with wall, leading to dramatic increases in temperature over short periods of time. The thermal transients will heat reactor materials above their desired operating conditions for very short spells but many times during operation. This could produce undesired and unpredicted microstructural evolution in components. This project would build on work at Bristol that has shown that even short periods high temperature (~750C) exposure can cause significant microstructural degradation of the Eurofer-97 stainless steel material used for structural support and cooling pipes [1]. This could affect mechanical properties and corrosion resistance, in turn leading to a shortening of component life. This PhD project will study the effect of very short-term thermal excursions on fusion front wall, divertor and breeder blanket materials and assess their effect on the microstructure and corrosion behaviour of the material.
The student will build on existing experimental research at Bristol using a custom design vacuum laser exposure rig, that can expose materials to controlled thermal pulses for short (1-10s) thermal spikes using a CO2 laser. The student will adapt this experimental rig to enable faster cooling rates and shorter thermal spikes to more closely simulate the conditions of a plasma excursion. The system will then be used to study the microstructural evolution behaviour of fusion materials after repeated short-term thermal exposure. The project will investigate the thermal evolution and potential impacts from high numbers (reactor relevant) of thermal cycling above the desired operating temperatures on FW materials (e.g. ODS steel) and/or breeder substrate (Eu97) close to FW and interface joint. To get
the appropriate cycling rates (with fast cooling rates), investment in a new rig will likely by required. But such a rig could be used for other fusion relevant projects.
Thermally exposed specimens will be characterised using scanning and transmission electron microscopy, x-ray diffraction and tomography to observe the change in the material microstructure with increasing heat exposure, and determine if any embrittlement or change in mechanical properties occur that might cause problems if used in a fusion reactor. The student will also compare experimental results to computational simulations of the phase diagram using CALPHAD-based modelling. There may also be opportunities to combine thermal exposures with the effects of irradiation and stress, and to assess similar conditions in weldments.

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.