Fast reactors have the unique ability to be sustainable by, not only being able to generate their own fuel, but through being able to burn minor actinides to reduce the quantity and radiotoxicity of nuclear wastes. The latter ability enables fast reactors to not only burn the minor actinides produced by themselves but, in addition, the minor actinides arising from legacy wastes and thermal reactors in the nuclear park. This proposal concentrates on the gas-cooled fast reactor (GFR) with a view to developing the GFR as a more sustainable version of the very high temperature reactor (VHTR). The design goals for GFR are ambitious, aiming, initially, for a core outlet temperature of around 850 deg.C, a compact core with a power density of about 100MWth/m3, a low enough plutonium inventory to allow wide deployment, a self-sustaining core in terms of plutonium consumption, and a proliferation resistant core by not using specific plutonium breeding elements. This project will contribute Euratom’s contribution to the Generation IV system research programme. As such, it is strongly aligned with the goals and structure of the latter. In addition this project fulfills an objective of thestrategic research agenda of the European Sustainable Nuclear Energy Technology platform, for GFR to be developed as one of the longer-term alternatives to the sodium cooled fast reactor. The work of this project is aligned with the viability phase of the Generation IV GFR system which concludes at the end of 2012. As such this is a three year project and its objective is to contribute to the demonstration of the viability of the GFR system with regard to deployment as a commercial sustainable nuclear energy system. As well as contributing to Generation IV GFR research, this project provides the Euratom representation on the GFR System Steering Committee and the two project management boards (PMBs), namely, the Conceptual Design and Safety PMB and the Fuel and Core Materials PMB