Reducing tritium permeation in nuclear fusion applications

Tritium permeation is a challenge for inertial confinement fusion experiments at the Laboratory for Laser Energetics and the National Ignition Facility, as well as for fusion energy research and development conducted in national laboratories, universities and fusion startup companies worldwide. Standard stainless steel alloys used as structural materials in these experiments become radioactive when bombarded with neutrons, but alternative materials that bypass this radioactivity, like reduced activation ferritic martensite (RAFM), are more susceptible to tritium permeation. This does not just cost researchers valuable tritium; it also contributes to the formation of radioactive waste.

This is why Bentley et al. explored new methods to create tritium permeation barriers (TPBs) using atomic layer deposition (ALD).

Losses via permeation into structural components are problematic because we need all of that tritium for the fusion reaction, [and] because tritium itself is radioactive, permeation requires that we use double containment and implement strict safety protocols for handling tritium,” said author Zachary Robinson.

The researchers used ALD alumina coatings on RAFM substrates to test their effectiveness on the permeation of deuterium — tritium’s nonradioactive cousin, an isotope of hydrogen with one neutron instead of tritium’s two.

With a thickness of about 10 nanometers, alumina coatings created an effective permeation barrier, reducing deuterium permeation by up to a factor of 35. Moreover, the coatings fundamentally altered the permeation process, changing the limiting step from the molecule’s motion through the barrier to the molecule’s breakdown.

The researchers say with further confirmation, ALD can be used anywhere that handles tritium.

“This work established the potential for TPBs on fusion-relevant substructures,” said Robinson. “In order to realize this, we need to extend the work to 3D geometries — i.e. actually coat tubing and tritium containers with ALD alumina films and test those materials extensively with tritium.”

Source: “Atomic layer deposition of alumina films on reduced-activation ferritic-martensitic steel for nuclear fusion applications,” by Soren Bentley, Jim Johnson, Alexander C. Kozen, Jeffrey M. Woodward, Jianing Sun, Rashad Ahmadov, Josh Ruby, Mark D. Wittman, Salvatore Scarantino, Greg Amos, Matthew Sharpe, and Zachary R. Robinson, Journal of Vacuum Science & Technology A (2026). The article can be accessed at https://doi.org/10.1116/6.0005729 .

This paper is part of the Atomic Layer Deposition (ALD) Collection, learn more here .