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Reduced-Activation Ferritic-Martensitic (RAFM) Steel

The structural steel designed for fusion reactors — engineered to avoid long-lived radioactive isotopes so that activated components can be recycled after 50–100 years of cooling.

Reviewed Last reviewed: 9 Aug 2026 · Category: Fuels & Materials

What Is RAFM Steel?

Reduced-activation ferritic-martensitic (RAFM) steels are specialized structural alloys developed specifically for fusion reactor components. They are based on 8–9% chromium martensitic steels (similar to power-plant steels like P91) but with strict substitutions: molybdenum is replaced by tungsten, niobium by tantalum, and nickel, cobalt, and copper are minimized. These substitutions ensure that under 14 MeV neutron irradiation, the steel produces only short-lived radioactive isotopes.[1]

Reduced activation = recyclable: After ~100 years of cooling, a RAFM steel component from a fusion reactor will have radioactivity levels low enough for hands-on recycling or disposal as low-level waste. Conventional stainless steels (316L) would require ~10,000 years. This is a fundamental advantage of fusion over fission — no geological repository is needed.

Key Alloys

EUROFER97: The European reference alloy (Fe-9Cr-1W-0.2V-0.07Ta), developed at KIT and produced in industrial quantities. EUROFER97 is the baseline structural material for the European DEMO and ITER Test Blanket Modules. F82H: The Japanese reference (Fe-8Cr-2W-0.2V-0.04Ta), developed at JAEA. CLAM: The Chinese reference alloy. All three are broadly similar in composition and properties.[2]

Limitations

RAFM steels have an upper operating temperature limit of ~550°C (creep) and a lower limit of ~350°C (irradiation hardening and embrittlement). This limits the thermodynamic efficiency of the power cycle. Higher-temperature alternatives (ODS steels, SiC/SiC composites, vanadium alloys) are being developed for next-generation designs but are far less mature.[3]

Sources

  1. Zinkle, S.J. and Snead, L.L. "Designing radiation resistance in materials for fusion energy." Annual Review of Materials Research, 44, 241–267, 2014.
  2. Tavassoli, A.A. et al. "Current status and recent research achievements in ferritic/martensitic steels." Journal of Nuclear Materials, 329–333, 257–262, 2004.
  3. Tanigawa, H. et al. "Development of benchmark reduced activation ferritic/martensitic steels for fusion energy applications." Nuclear Fusion, 57, 092004, 2017.

Related

Blanket Neutron Activation ITER Test Blanket Module ODS Steel SiC/SiC Composite