Detritiation facility reopens at Culham

In the last three years of plasma operations, the Joint European Torus's (JET's) deuterium-tritium experiments resulted in residual tritium being retained within the tokamak's walls and internal components. This reflected the isotope's tendency to permeate into materials during high-powered fusion operations. Understanding how much tritium is retained within the materials, and how much can be removed through thermal treatment, will be essential in developing a waste management strategy for the JET Decommissioning and Repurposing (JDR) programme.

By recovering tritium, UKAEA's waste teams can greatly reduce disposal costs for materials such as tungsten, beryllium, Inconel, steel, copper and carbon-fibre composite. When they are initially removed from JET, these materials are classified as intermediate-level waste. By removing tritium, they can be reclassified as low-level waste, which is up to ten times less expensive to dispose of, or even to be recycled into future fusion or fission machines.

Experimental trials on tiles and components removed from JET in late 2024 showed that they can be treated without prior disassembly. The trials also demonstrated that mixed material streams can also be processed simultaneously, replicating what would happen in an industrial-scale treatment facility. To remove the retained tritium, the materials are heated to elevated temperatures in the Materials Detritiation Facility (MDF) furnace under carefully controlled conditions designed to minimise oxidation. Limiting oxidation improves the efficiency of the process, reducing maintenance requirements, and helps to ensure the process remains safe and effective.

Tritium released during heating is carried from the furnace by the process gas stream and passed through a catalyst that converts gaseous tritium species into tritiated water, enabling its efficient capture. Once the furnace has cooled, the thermally treated contents are taken out and subjected to destructive sampling for further analysis. In addition to this thermal treatment, gram-scale samples from JET are being analysed to determine concentrations of other radionuclides and to quantify the amount of tritium remaining in the materials after treatment.

_{Materials after being processed in the Materials Detritiation Facility (Image: UKAEA)}

"Successful processing of these samples gives us access to evidence that has simply not been available before, allowing us to better understand the nature of JET materials and the challenges associated with their long-term management," said Xavier Lefebvre, head of waste at JET Decommissioning and Repurposing. "The insights gained from this work have the potential to fundamentally influence the future waste strategy for JDR, reducing uncertainty and enabling more informed decisions on waste treatment, packaging, disposal routes and decommissioning planning. By improving the evidence base that underpins these decisions, the work may also demonstrate more proportionate waste management solutions and a better understanding of long-term liabilities.

"It is an excellent example of how innovation, scientific ambition and operation can come together to deliver benefits not just for today's programme, but for the future of fusion decommissioning."

The MDF will remove retained tritium from materials and reduce the volume of higher-activity waste requiring specialist management on site, UKAEA said. As well as processing its own legacy waste, UKAEA said the MDF is available for use by companies and organisations undertaking similar cutting-edge research in waste and materials management.

About JET

JET was a tokamak fusion system with a doughnut-shaped vacuum chamber where, under the influence of extreme heat and pressure, gaseous hydrogen fuel becomes a plasma. The charged particles of the plasma can be shaped and controlled by massive magnetic coils placed around the vessel to confine the hot plasma away from the vessel walls. It was the only tokamak fusion machine in operation capable of handling tritium fuel, and was a key device in preparations for the multinational ITER fusion research project which is currently under construction in southern France.

JET was a European project built and used collaboratively by European researchers. It is now owned, and in its last years operated by, the UKAEA, and used by scientists from 28 European countries to conduct research into the potential for carbon-free fusion energy in the future through work coordinated by the EUROfusion consortium. The tokamak's first deuterium-tritium experiments took place in 1997.

JET's final experiments using deuterium and tritium fuel were conducted over seven weeks from August to October 2023, ahead of its retirement following its final pulse in December. During those experiments, JET produced the largest amount of energy achieved in a fusion experiment, breaking its own record set in 2021. Following its retirement JET has moved on to repurposing and decommissioning, a process expected to last until about 2040, and which is seen as providing further opportunities to discover and develop new technologies and skills for future fusion.

JET is now in the early stages of being decommissioned and repurposed by the UKAEA, under the JDR programme.