Joining refractory metals for nuclear fusion applications

Typically components in a fusion reactor need to be made of a variety of different materials to cope with the diverse range of demands placed on the component by fusion reactor conditions, including 14 MeV neutron irradiation, high temperatures, plasma exposure and pulsed operations. In current reactors typically tungsten is used in the divertor region, with more structural components being made from steels. However, moving forward for the UK Atomic Atomic Energy Authority 'STEP' (Spherical Tokamak for Energy Production) programme, tungsten and various other refractory alloys are not only being considered for the divertor, but also for the first wall and structural components with complex geometries. In order to use tungsten or other refractory metals in these areas, it will be important to be able to develop techniques to join tungsten components together, while maintaining structural integrity and dealing with issues such as the brittle nature of tungsten. This project will investigate joining of tungsten or other STEP relevant alloys using welding processes such as electron beam or arc welding. The welds will be characterised via a variety of techniques including microscopy, hardness testing and in-situ neutron diffraction techniques. The response to the welds to irradiation damage can also be investigated.
There will also be the possible addition of computed tomography (CT), using in-situ mechanical testing experiments to investigate the mechanical behaviours of the welds. The project will be based at the University of Manchester and also make use of the National Lab Facilities at Diamond Light Source (DLS) and ISIS, supervised by Dr. Aneeqa Khan at the University of Manchester at Harwell and Dr. Ed Pickering and Dr. John Francis at the University of Manchester. The project will also work closely with the Materials Technology group at UKAEA.

The objectives of the project will be to:
Produce refractory metal welds
Characterize the as-welded behaviour of a variety of refractory metal welds
Measure the levels of residual stress present in the as-welded materials
Investigate how the mechanical behaviour changes following irradiation and/or thermal exposure.

Identifying a sustainable energy supply is one of the biggest challenges facing humanity. Fusion energy has great potential to make a major contribution to the baseload supply - it produces no greenhouse gases, has abundant fuel and limited waste. Furthermore, the UK is amongst the world leaders in the endeavour to commercialise fusion, with a rapidly growing fusion technology and physics programme undertaken at UKAEA within the Culham Centre for Fusion Energy (CCFE). With the construction of ITER - the 15Bn Euro international fusion energy research facility - expected to be completed in the middle of the 2020's, we are taking a huge step towards fusion power. ITER is designed to address all the science and many of the technology issues required to inform the design of the first demonstration reactors, called DEMO. It is also providing a vehicle to upskill industry through the multi-million pound high-tech contracts it places, including in the UK.
ITER embodies the magnetic confinement approach to fusion (MCF). An alternative approach is inertial fusion energy (IFE), where small pellets of fuel are compressed and heated to fusion conditions by an intense driver, typically high-power lasers. While ignition was anticipated on the world's most advanced laser fusion facility, NIF (US), it did not happen; the research effort is now focused on understanding why not and the consequences for IFE, as well as alternative IFE schemes to that employed on NIF.

Our CDT is designed to ensure that the UK is well positioned to exploit ITER and next generation laser facilities to maximise their benefit to the UK and indeed international fusion effort. There are a number of beneficiaries to our training programme: (1) CCFE and the national fusion programme will benefit by employing our trained students who will be well- equipped to play leading roles in the international exploitation of ITER and DEMO design; (2) industry will be able to recruit our students, providing companies with fusion experience as part of the evolution necessary to prepare to build the first demonstration power plants; (3) Government will benefit from a cadre of fusion experts to advise on its role in the international fusion programme, as well as to deliver that programme; (4) the UK requires laser plasma physicists to understand why NIF has not achieved ignition and identify a pathway to inertial fusion energy.

As well as these core fusion impacts, there are impacts in related disciplines. (1) Some of our students will be trained in low temperature plasmas, which also have technological applications in a wide range of sectors including advanced manufacturing and spacecraft/satellite propulsion; (2) our training in materials science has close synergies with the advances in the fission programme and so has impacts there; (3) AWE require expertise in materials science and high energy density plasma physics as part of the national security and non-proliferation strategy; (4) the students we train in socio-economic aspects of fusion will be in a position to help guide policy across a range of areas that fusion science and technology touches; (5) those students involved in inertial fusion will be equipped to advance basic science understanding across a range of applications involving extreme states of matter, such as laboratory astrophysics and equations of state at extreme pressures, positioning the UK to win time on the emerging next generation of international laser facilities; (6) our training in advanced instrumentation and control impacts many sectors in industry as well as academia (eg astrophysics); (7) finally, high performance computing underpins much of our plasma and materials science, and our students' skills in advanced software are valued by many companies in sectors such as nuclear, fluid dynamics and finance.