Culham scientists are taking part in a five-year, £7 million collaborative project to help develop materials for fusion and fission reactors of the future.
Nuclear fusion and advanced 'Generation IV' fission power plants could form a large part of the UK's long-term electricity supply. In order to do so, however, materials science problems, many of which are common to both technologies, must be solved.
The structural materials from which the power plants' core components will be built must have high strength and toughness at high temperatures, and retain good mechanical properties and thermal conductivity for decades despite being subjected to radiation damage from high-energy neutrons. The neutrons knock atoms from their positions, scrambling the materials' carefully-designed microstructures, and produce many small crystal defects which make the materials harder and more brittle. Fusion neutrons, unlike those in current nuclear power plants, also have enough energy to give rise to transmutation reactions: this causes three problems. First, many elements ordinarily used in strong alloys cannot be used, because their transmutation products are highly radioactive for thousands of years, so alternative alloy compositions must be designed using a very restricted range of elements. Second, even 'safe' elements like tungsten and tantalum transmute into other elements under fusion neutron bombardment, so that the composition of the alloys changes continuously. Thirdly, helium is produced embrittling the materials.
The new project is led by the University of Oxford and involves Liverpool and Salford Universities, Rolls Royce in the UK and CEA in France, as well as CCFE. It will use computer modelling to predict the formation of defects during irradiation of candidate materials, which will be examined using advanced microscopical techniques and tested using novel micromechanical methods. The experiments will use ion irradiated specimens where the ion irradiation affects only extremely thin layers of the material (1/1000 mm thick). CCFE's contribution will be primarily in the modelling area, drawing on the specialist expertise gained from materials studies for the UK and EURATOM fusion programme.
The work, made possible by a grant from the Engineering and Physical Sciences Research Council, will greatly add to understanding of structural integrity issues which underpin development of alloys for high-flux, high-temperature neutron environments. It should therefore significantly speed development of the new types of steel and tungsten-based materials that are essential for the commercial realisation of fusion and new-generation fission power. It will also help the UK to lead scientific research in new materials and to train experts for future fission and fusion programmes.