N. Taylor

European DEMO design strategy and consequences for materials

Demonstrating the production of net electricity and operating with a closed fuel-cycle remain unarguably the crucial steps towards the exploitation of fusion power. These are the aims of a demonstration fusion reactor (DEMO) proposed to be built after ITER. This paper briefly describes the DEMO design options that are being considered in Europe for the current conceptual design studies as part of the Roadmap to Fusion Electricity Horizon 2020. These are not intended to represent fixed and exclusive design choices but rather ‘proxies’ of possible plant design options to be used to identify generic design/material issues that need to be resolved in future fusion reactor systems. The materials nuclear design requirements and the effects of radiation damage are briefly analysed with emphasis on a pulsed ‘low extrapolation’ system, which is being used for the initial design integration studies, based as far as possible on mature technologies and reliable regimes of operation (to be extrapolated from the ITER experience), and on the use of materials suitable for the expected level of neutron fluence. The main technical issues arising from the plasma and nuclear loads and the effects of radiation damage particularly on the structural and heat sink materials of the vessel and in-vessel components are critically discussed. The need to establish realistic target performance and a development schedule for near-term electricity production tends to favour more conservative technology choices. The readiness of the technical (physics and technology) assumptions that are being made is expected to be an important factor for the selection of the technical features of the device.

Safety and licensing of nuclear facilities for fusion

Nuclear fusion facilities of the future will need authorization for their construction, commissioning and operation. This licensing by a nuclear regulator will require, as for any other nuclear facility, that the design conforms to regulations and high safety standards, and that it is demonstrated that all necessary safety provisions are incorporated in the design. A safety culture is required throughout the facility lifetime - starting at the conceptual design stage - and this must include clear top-level safety objectives that cascade down to detailed safety requirements at the component level. ITER has already achieved an important step by obtaining the license to construct. Lessons learned during this licensing process should be applied to DEMO and other future nuclear fusion facilities. Additional safety issues may arise as the result of large-scale tritium breeding and other design variations such as the selected materials. As well as developments in the design of fusion systems, the evolving expectations of nuclear regulators has also to be taken into account.

Analysis of ITER Magnet in Safety-Related Fault Condition—Case Study for PF3

The ITER magnet system contains stored energy, 41 GJ in the toroidal field system and up to ~10 GJ in the poloidal field (PF)/central solenoid system during plasma operation. A quench in the ITER magnet is regarded as a normal event, and the ITER magnet system has a redundant quench detection system and a reliable fast discharge system in order to achieve low probability of unmitigated quench and its propagation in the ITER magnet system. An electrical circuit model is developed by using a circuit simulator in order to estimate the arc power during fault conditions. The ANSYS 3-D model of the magnet, including electrical, thermal, and arcing inside the coil, is being constructed to analyze the thermal and electrical behavior of the magnet in an unmitigated quench. In this paper, thermal analyses of the fault condition related to the PF coil and impacts to the vacuum vessel are reported.