Analysis of radiation environment at divertor in helical reactor FFHR-d1

• Neutronics environments at divertors have been evaluated in the FFHR-d1 design.
• Divertors can be placed behind blankets and radiation shields in helical reactors.
• Damages at the outboard and inboard divertors are ∼0.16 and ∼1.6 dpa/year.
• The damages at the inboard divertors could be suppressed by further design efforts.
• Copper materials could be adopted for cooling tubes of the divertors in FFHR-d1.

Neutron transport calculations with a three-dimensional model of the helical reactor FFHR-d1 have been performed for the accurate analysis of neutronics environment in the divertor areas. Based on the obtained neutron spectra, magnitudes of irradiation damage, contact dose rates and decay heat have been evaluated mainly for Fe, W and Cu. Since divertors can be placed behind radiation shields in helical reactors, magnitudes of damage and radioactivation at the outboard divertors are almost two orders lower than those at blanket first walls. Cu materials could be used as a cooling channel material of the outboard divertors. In contrast, the magnitudes at the inboard divertors are only one order lower compared with those at the first walls due to the limited space at the inboard side. Damage on Cu is evaluated to be ∼10 dpa after 6 years operation. Further efforts in divertor development and reactor design could suppress the magnitude of damage to less than half for adoption of Cu materials for the inboard divertors.