The European reference reduced-activation ferritic/martensitic steel, designed from the ground up for fusion blanket structures where neutron activation must be minimized.
EUROFER97 is a reduced-activation ferritic/martensitic (RAFM) steel developed by the European fusion program as the baseline structural material for DEMO-class breeding blankets. It belongs to the 9Cr-1W family of steels, engineered to replace conventional high-chromium steels by substituting molten-salt-reactor-legacy elements (molybdenum, niobium, nickel) with low-activation alternatives (tungsten, tantalum, vanadium) so that activated components can qualify for shallow land burial within approximately 100 years after shutdown.1
The nominal composition of EUROFER97 is Fe-9Cr-1.1W-0.2V-0.12Ta-0.11C (wt%). The 9% chromium content provides oxidation resistance and stabilizes the body-centered cubic (bcc) ferritic/martensitic microstructure after normalizing at ~980 °C and tempering at ~760 °C. Tungsten and tantalum serve as solid-solution and precipitation strengtheners, respectively, replacing the molybdenum and niobium found in conventional power-plant steels like Grade 91.2
EUROFER97 provides reliable mechanical properties from roughly 250 °C to 550 °C. The lower bound is set by irradiation hardening and embrittlement: below ~250 °C, displacement damage from 14.1 MeV neutrons drives the ductile-to-brittle transition temperature (DBTT) upward, creating a risk of brittle fracture in a pressurized blanket structure. The upper bound is set by thermal creep: above ~550 °C, the tempered martensite microstructure is insufficiently creep-resistant for the multi-year service lives required in a power plant. This 300-degree operating window is a significant design constraint that drives helium-cooled blanket concepts toward higher-pressure, lower-temperature regimes.3
Neutron irradiation produces both displacement damage (measured in dpa) and transmutation helium in RAFM steels. At the fusion-relevant ratio of ~10 appm He per dpa, helium accumulates at grain boundaries and precipitate interfaces, potentially exacerbating high-temperature embrittlement. Because no existing neutron source fully replicates the fusion spectrum, the irradiation database for EUROFER97 relies on a combination of fission-reactor campaigns (HFR Petten, BOR-60), spallation-source experiments (SINQ), and ion-beam surrogate studies. The planned IFMIF-DONES facility is specifically designed to close this qualification gap with a Li(d,xn) neutron source matching the D-T energy spectrum up to ~50 dpa.4
Research on next-generation variants aims to widen the operating window. Oxide-dispersion-strengthened (ODS) EUROFER incorporates nanoscale Y2O3 particles that pin dislocations and grain boundaries, raising the creep limit toward 650 °C. Castable nanostructured alloy (CNA) variants seek similar improvements through thermomechanical processing without the powder-metallurgy route that makes ODS steels difficult to fabricate and join.
In the European DEMO design, EUROFER97 forms the structural backbone of both the Helium-Cooled Pebble Bed (HCPB) and the Water-Cooled Lithium-Lead (WCLL) blanket concepts. Thousands of tonnes of the steel will be required, making industrial-scale production, welding qualification, and post-irradiation waste management central programmatic milestones.