SPECIAL REPORT | MANAGING TRITIUM
Tritium takes centre stage
Behind plans to breed tritium in fusion reactors are decades of experience in understanding tritium’s characteristics, plus a variety of options for extracting it from the ‘blanket’.
FUSION REACTOR DESIGNS THAT ARE fuelled by deuterium and tritium often include a lithium ‘blanket’ around the fusion site. This is where the necessary tritium fuel is ‘bred’: neutron bombardment causes the lithium to decay to tritium, which is extracted from the ‘blanket’ and ultimately recycled into the fusion reaction. This cosy description masks a complex process in which the tritium being managed is not only a radiological hazard but a chemical hazard as well. Specific risks come with its nature as an isotope of hydrogen, but there are also physical hazards as it causes embrittlement in container materials, either due to radiological effects or due to the emergence of helium as a decay product.
Chemical interactions The safe and secure management of tritium has been a nuclear industry focus for many decades. The US Atomic Energy Act of 1954, as amended (AEA) lists tritium as an “other” category of accountable nuclear material. Under this designation it must be controlled and accounted for financial and nuclear materials management purposes and protected in a manner consistent with its strategic and monetary importance. In the US the reportable quantity of tritium is one gramme, except for tritium contained in water
used as a moderator in a nuclear reactor, which is not an accountable nuclear material. DOE requires tritium facilities with more than reportable 1 gramme quantity of tritium to establish material control and accountability systems to provide accurate nuclear materials inventory information while transactions exceeding the threshold must also be reported. Hydrogen and tritium handling infrastructure typically
uses Type 300-series austenitic stainless steels, due to their resistance to hydrogen isotope embrittlement. A 2021 paper in Fusion Engineering and Design: ‘Tritium embrittlement of austenitic stainless-steel tubing at low helium contents, by Timothy M. Krentz , Joseph A. Ronevich, Dorian K. Balch, Chris San Marchi’ discusses the effect of tritium and notes that there is some information on the performance of various alloys and some relationships have been established, such as correlation of embrittlement with hydrogen content and a positive effect of increasing nickel content. However, “there has been a lack of systematic studies focused on the effect that microstructural variation has on susceptibility to hydrogen embrittlement”. Type 300-series austenitic stainless steels also have the
advantage that they can be welded – the preferred joining strategy, as it is generally less leak prone than mechanical
Above: Neutron bombardment causes the lithium to decay to tritium, which is extracted from the lithium ‘blanket’ surrounding a fusion reactor
36 | September 2025 |
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