Shielding concept and neutronic assessment of the DEMO lower remote handling and pumping ports

•Several iterations of the lower port of the EU DEMO were analyzed in terms of neutronic performance.•Lower port is challenging due to space constraints and the requirement to provide large opening for vacuum pumping.•Significant progress was made but further optimizations are needed. Within the EUROfusion Power Plant Physics and Technology Department the DEMOnstrational fusion power plant (DEMO) is being developed. One of the fundamental challenges is the integration of ports in the vacuum vessel. The lower port of the DEMO machine is particularly challenging due to tight space constraints imposed by the toroidal field (TF) coils and the requirement to provide a large open duct through both the divertor and inside the port to enable for vacuum pumping. In addition, feeding pipes of divertor and tritium breeding blanket need to be integrated and access space must be provided for various remote handling operations. Several neutronics requirements need to be fulfilled, e.g. the nuclear heating of the superconducting TF coils and the gamma radiation levels inside the cryostat need to be limited to reduce occupational exposure to personnel during maintenance, and the irradiation damage and neutron heating in different components need to be considered in the design and limited. The results of neutronic analyses show that further shielding optimization is needed as maximum TF coil heating is still 5× the design limit and the SDDR values orders of magnitude above the target values inside the lower port duct. With this in mind the direction of future design developments is discussed.