Neutronic Calculations for a Magnetic Fusion Energy Reactor with Liquid Protection for the First Wall

Liquids may be used between the magnetic confined fusion plasma and the first wall of the plasma chamber to reduce the material damage through displacements per atom (dpa) and helium gas production. This could extend the lifetime of the first wall in a magnetic fusion energy (MFE) reactor to a plant lifetime of ~30 yr.

Neutronic calculations are carried out in S₁₆P₃ approximation for a typical HYLIFE-II blanket geometry, an inertial fusion energy (IFE) reactor design. This provides a comparison of the damage data between compressed and uncompressed targets, for IFE and MFE applications, respectively, by using Flibe (Li₂BeF₄), natural lithium, and Li₁₇Pb₈₃ eutectic as both coolant and wall protection. In the consideration of mainline design criteria, including sufficient tritium breeding ratio (TBR = 1.1), material protection (dpa < 100 and He < 500 parts per million by atom in 30 yr of operation), and shallow burial index, coolant zone thickness values are found to be 60 cm for Flibe, 171 cm for natural lithium, and 158 cm for Li₁₇Pb₈₃ with Type 304 stainless steel (SS-304) as structural material.

Material damage investigations are extended to structural materials made of SiC and graphite for the same blanket to obtain waste material suitable for shallow burial after decommissioning of the power plant.

The dpa values and helium production rates in graphite are comparable to those in SS-304. However, they are higher in SiC than in SS-304 and graphite.

The average neutron heating density in the external 1.6-mm-thick SS-304 shell of the investigated blanket beyond the SiO₂ insulation foam decreases rapidly with increasing thickness of the Flibe coolant. With DR = 60 and 80 cm, it becomes only 594 and 95 W/cm³, respectively. The design limit for heat generation density in superconducting coils for magnetic fusion is 80 W/cm³. A very important result of this work is that a blanket with liquid-curtain protection would not require extra shielding for superconducting coils around the fusion plasma chamber. This could result in an important simplification of the design.