As fusion developers race toward commercial reactors, Canadian researchers are studying what materials could best contain the challenging fusion fuel ingredient - tritium.

Tritium is responsible for the glowing red light in exit signs above doorways, the hands and numbers on glow-in-the-dark wristwatches, and the way-finding lines along either side of an airplane aisle. And, if you ask scientists from around the world, it also has the very real potential to help enable fusion energy in the future.

Given its proven ability to generate a lot of energy when fused with deuterium (another hydrogen isotope), tritium is one of the ingredients scientists intend to leverage to recreate nuclear fusion, the type of reaction that fuels the Sun's ability to endlessly produce heat and light, here on Earth.

Fusion reactors offer not only the promise of generating large amounts of low-carbon energy, but also the advantage of producing far less long-lived radioactive waste than conventional nuclear fission technologies. However, realizing this potential involves overcoming significant technical challenges. Among these is the difficulty of designing systems capable of containing fusion fuels, such as hydrogen isotopes, that can readily migrate through even nano-scale gaps within materials.

That's why scientists at Canada's national nuclear laboratory are testing how these fuel ingredients, namely tritium and deuterium, interact and potentially diffuse through materials at elevated temperatures. Ultimately, their work will help inform policies on the materials used to design and build deuterium-tritium fusion systems in Canada.

"We're interested in the radioactive hydrogen isotope, tritium, because it has a tendency to slip right through metals, like water through a sieve, especially at the elevated temperatures found in the systems adjacent to the fusion reactor," says hydrogen research scientist, Julien Lang.

To run these systems safely and efficiently, we need to be able to contain tritium, he explains. Otherwise, the valuable fuel needed to sustain the reaction is lost over time, and can potentially increase the radiological exposure for nuclear energy workers.

So, the team is putting materials to the test.

They're using an experimental system (or rig) that heats the materials in contact with tritium to temperatures required for the fuel cycle loop in a fusion reactor to operate - including the detritiation system and tritium storage system. They are then tracking how fast the tritium passes (or permeates) through specific metals.

Scientists heated a tube of INCOLOY Alloy 800 to 850 o C in their newly-upgraded system that tracks how tritium moves through materials.

Current testing is focused on one of the most common types of stainless steel (grade 304), the standard material for these systems, at temperatures ranging from 250 ^o C to 950 ^o C. This initial testing has shown just how fast tritium permeation happens. At 850° C, tritium diffuses through a one-millimetre-thick stainless steel wall in about two minutes.

And tritium permeation in minutes is not sustainable.

"If fusion reactors are to exist, they will need operators and maintenance and this means people in the building and on the floor that can't be exposed to radiation hazards," says Lang. "More importantly, a fusion reactor will not be able to sustain its reaction if the tritium fueling it permeates through steel walls."

For the CNL team, it's particularly exciting to be building an in-house capability with their own experimental system and procedure. It will enable them to develop a reliable database to compare materials appropriately - an essential step, given that the data currently available on tritium permeation is not precise or accurate.

Beyond the technical advances, the team is motivated by the broader impact of their work, contributing to research that is helping move Canada closer to a whole new world of nuclear energy.

"It's really encouraging to be undertaking this level of research that has captured the attention of many international collaborators," says nanomaterials scientist, Larissa Jorge. "It gives meaning and purpose to the work we are doing."

As the global investment in fusion continues, this research strengthens Canada's role in assessing material performance and opens new opportunities for international collaborations and partnerships in fusion energy.

This research is funded by Atomic Energy of Canada Limited's (AECL) Federal Nuclear Science & Technology (FNST) Work Plan, which connects federal organizations, departments, and agencies to the nuclear science expertise and facilities we have at Chalk River Laboratories.

Under the FNST Work Plan, researchers at Canadian Nuclear Laboratories (CNL) carry out projects to support the Canadian government's core responsibilities and priorities across the areas of health, safety and security, energy, and the environment.