Neutronics studies on the European DEMO divertor target supports

• Neutrons degrade materials, risking divertor reliability. • Supporting target material: Eurofer, CuCrZr, and SS316Ti assessed. • CuCrZr shows +11 % higher nuclear heating than others. • Neutron flux and damage in Eurofer barely affected by target. • Eurofer is more attractive than CuCrZr and SS316Ti from activation point of view. The divertor is a key in-vessel component of the DEMO reactor, responsible for power exhaust and impurity control under severe irradiation and high nuclear load conditions. Neutron interactions cause heat generation, transmutation, material damage, and activation, leading to potential degradation of mechanical integrity and functional performance. To ensure reliable operation, accurate assessment of the divertor’s nuclear response is essential. This study investigates and compares three candidate materials for the divertor target supports: Eurofer, considered the reference structural material; CuCrZr, selected for its high heat removal capability; and SS316Ti, widely used in fission applications for its swelling resistance. Three-dimensional neutronics and activation analyses were conducted using the MCNP5 Monte Carlo code and the FISPACT-II inventory code, based on the latest DEMO Water-Cooled Lithium Lead (WCLL) divertor design. The results provide insights into nuclear heating, radiation damage, gas production, and long-term activation, offering guidance for material selection in future DEMO divertor developments. Results include neutron flux, nuclear heating, absorbed dose, radiation damage, and gas production (He and H). CuCrZr target supports show a nuclear power deposition about 17 MW higher than steels, with peak heating exceeding 10 W/cm³. SS316Ti presents lower heating (below 10 W/cm³) and moderate activation levels. Damage in Eurofer ranges from 0.01 to 5.5 dpa/FPY, with localized peaks below the baffle regions, while H and He production reach 170 and 110 appm/FPY in the most exposed areas. The divertor exhibits good global shielding, with vessel damage remaining below 2.75 dpa over 30 FPY. Post-shutdown activation analyses confirm Eurofer as the most favourable option, whereas Ni, Co, and Nb impurities in CuCrZr and SS316Ti result in higher long-term activity. Overall, these comprehensive neutronics and activation studies provide essential guidance for the material selection and optimization of the DEMO divertor design.