The innermost material surface of a fusion reactor facing the plasma — subjected to extreme heat flux, neutron bombardment, and plasma erosion, making it one of the most demanding materials challenges in engineering.
ReviewedLast reviewed: 9 Aug 2026·Category: Glossary
Definition
The first wall is the plasma-facing surface of the blanket structure in a magnetic confinement fusion device. It directly faces the fusion plasma and must withstand heat fluxes of 0.1–1 MW/m² during normal operation, with transient loads from ELMs and disruptions reaching tens of MW/m².[1]
Material choices: Current first-wall materials include tungsten (W) and beryllium (Be). ITER uses beryllium for the main chamber first wall and tungsten for the divertor. DEMO and future reactors are expected to use tungsten throughout, as beryllium’s low melting point and toxicity make it less suitable for power-plant conditions.
Requirements
The first wall must: (1) conduct heat efficiently to the coolant; (2) resist erosion from plasma particle bombardment (sputtering); (3) withstand neutron damage accumulating to 50–150 dpa; (4) minimize tritium retention; and (5) be compatible with remote-handling replacement, since it will become radioactive and require periodic replacement (every 2–5 years in a power plant).[2]
Challenges
No material simultaneously satisfies all first-wall requirements under prototypic fusion conditions. Tungsten is the leading candidate due to its high melting point (3422°C), low sputtering yield, and low tritium retention, but it becomes brittle under neutron irradiation and is difficult to machine and join.[3]
Sources
Federici, G. et al. "European DEMO design strategy and consequences for materials." Nuclear Fusion, 57, 092002, 2017.
Rieth, M. et al. "Recent progress in research on tungsten materials for nuclear fusion applications in Europe." Journal of Nuclear Materials, 432, 482–500, 2013.
Zinkle, S.J. and Was, G.S. "Materials challenges in nuclear energy." Acta Materialia, 61, 735–758, 2013.