Joining tungsten for nuclear fusion applications

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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. Initial electron beam welds in 2.5mm thick tungsten plates have bene produced at NAMRC. This project will follow on from this, investigating 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/other fusion relevant 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 Harwell, supervised by Dr. Aneeqa Khan at the University of Manchester, Dr Anastasia Vasileiou and Dr. John Francis at the University of Manchester. The project will also work closely with materials technology and joining groups at UKAEA.The objectives of the project will be to:Characterize the as-welded behaviour of a variety of refractory metal weldsMeasure the levels of residual stress present in the as-welded materialsInvestigate how the mechanical behaviour changes following irradiation and/or thermal exposure.