Neutronics assessment of EU DEMO alternative divertor configurations

Highlights: • First neutronics assessment of alternative divertor configurations in DEMO. • Shielding proposals to reduce TF coil heat loads and neutron streaming. • DPA, helium production and to assess material damage and lifetimes of components. • MCNP model constructed for SN, SX and XD divertor configurations. • Tritium breeding ratio (TBR) calculated for SN, SX and XD divertor configurations. As a demonstration fusion power plant, EU DEMO has to prove the maturity of fusion technology and its viability for electricity production. The central requirements for DEMO rest on its capability to generate significant net electric power to the grid (300 MW to 500 MW) safely and consistently. Plant availability and lifetime will approach that of a commercial fusion power plant. Operating at such regimes presents many complex challenges, of which one is plasma exhaust. To mitigate the risk that the implementation in preceding experimental devices, namely ITER, does not extrapolate to the requirement of DEMO, alternative solutions must be sought. The investigation of alternative divertor configurations was born out of this motive, seeking to resolve a 'critical' challenge for the realisation of DEMO. In this paper, we study the neutronics performance of three concepts: Single Null (SN), Super-X (SX) and X-divertor (XD). This is the first time a preliminary analysis of alternative configurations to the SN baseline has been performed. The shielding proposals and design recommendations presented herein should be integrated with other engineering and physics constraints in future iterations of the chosen divertor concept.