Fusion energy is the ultimate energy to cover Mankind’s energy needs forever. However, taming the fusion energy is the greatest technological challenge the humanity is facing. Development of structural materials to withstand against the extreme conditions in the course of fusion power plant operation is one of the toughest nuts to be cracked. A great number of structural materials have been investigated for f usion reactor applications, such as steels (austenitic stainless steels and ferritic/martensitic steels), vanadium alloys, refractory metals and alloys (niobium alloys, tantalum alloys, chromium and chromium alloys, molybdenum alloys, tungsten and tungsten alloys), and composites (SiC f /SiC and Carbon Fibre Composite CFC composites).
Steels have extensive technological data base and significantly lower cost compared to other refractory metals and alloys. Ferritic steels and modified austenitic stainless (Ni and Mo free) have relatively low residual radioactivity. However, steels cannot withstand high neutron wall loads to build an economically competitive fusion reactor. Some refractory metals and alloys (niobium alloys, tantalum alloys, molybde num alloys, tungsten and tungsten alloys) can withstand high neutron wall loads. But, in addition to their very limited technological data base, they have high residual radioactivity and prohibitively high production costs.
A protective, flowing liquid zone to protect the first wall of a fusion reactor from direct exposure to the fusion reaction products could extend the lifetime of the first wall to the expected lifetime of the fusion reactor. In that context, a fusion fission (hybrid) with a multi layered spherical blanket has been investigated, which is composed of a first wall made of oxide dispersed steel (ODS, 2 cm); neutron multiplier and coolant zone made of LiPb; ODS separator (2 cm); a m olten salt FLIBE coolant and fission zone; ODS separator (2 cm ); graphite reflector. Calculations are conducted for a liquid wall with variable thickness, containing Flibe + heavy metal salt (UF 4 or ThF 4 ) is used for first wall protection. The content of heavy metal salt is chosen as 4 and 12 mol%. A flowing wall wit h a thickness of ~ 60 cm can extend the lifetime of the solid first wall structure to a plant lifetime of 30 years for 9Cr 2WVTa and V 4Cr 4Ti, whereas the SiC f /SiC composite as first wall needs a flowing wall with a thickness of ~ 85 cm to maintain the ra diation damage limit.