The supply of tritium fuel is an enormous problem for mainstream fusion reactors, probably a show-stopper. Surprisingly, fusion advocates often say that the fuel is abundant and an advantage of fusion. In reality, the opposite is the case for tritium and propaganda on this issue contain much misinformation as described in the references at the bottom of this pages. A single fusion power plant, with electrical output 1 GigaWatt, would consume about 60 kg/year of tritium but, currently, only about 0.5 kg/year is produced worldwide.
A mis-leading feature of propaganda from fusion advocates of fusion are statements that the fuel is abondance in the sea, however, in all the oceans of the world there is about 30 kg of tritium.
The figure below from the paper by Ohms et al., shows the distribution of tritium in the world's oceans (as heavy water HTO). The concentration is highest in the northern hemisphere because the main source is the atmospheric nuclear tests in the 1950s and 1960s. About 10% of the tritium in the sea is constantly replenished from generation by cosmic rays in the atmosphere.
Mean tritium concentrations measure in the oceans between 0 and 500 m depth. The unit are tritium units, 1 tritium atom per 1018 hydrogen atoms, and the data are corrected for decay to year 2016
Decay of tritium levels in measurements from North Atlantic.
The decay of tritium with a half-life of 12.3 years (5% per year), indicated in the plot above for the tritium in the oceans, is a major problem for all sources of tritium.
A claim on the website of the private company Commonwealth Fusion Systems that "One glass of water will provide enough fusion fuel for one person's lifetime". The data above shows that one glass of water taken from the sea offshore from Boston would contain 3 million tritium atoms which is enough to heat the glass of water by fusion reactions by 0.0004°C. Clearly the propaganda claim is wrong.
No tritium is commercially extracted from the sea and all commercial supplies come from fission reactors, largely CANDU reactors which have D2O as moderator. The current world stock of tritium is around 25kg which will increase slowly until the CANDU reactors reach the end of their operational lives. From then on, the radioactive tritium will decay away at a rate of 5% per year. When the ITER project starts fusion operations around 2035, it will consume the major fraction of the world stock. The figure below shows an estimated evolution of the world stock of tritium.
Projection of world civil tritium supplies in coming decades.
Due to the impossibility of external supply, fusion reactors must regenerate tritium. This process involves three separate aspects, all very difficult to achieve:
Two of these aspects are covered on this page. The aspect of tritium breeding is covered in the page: Breeder Blanket where possible values for the Tritium Breeding Ratio (TBR) are given.
According to the estimates described above estimates, by 2050 when the construction of the first fusion power plants might start, world tritium stock could be less than a few kg. Even if the tritium breeding process actually works in practice an initial start-up inventory for each reactor is required.
The paper by Kovari et al., explores various options to start-up commercial fusion reactors. In theory, a lack of tritium could be overcome at any time, since it can be generated in a fission reactor, but any claimed advantages of replacing fission with fusion clearly are not valid if fission reactors must be built to supply the fusion fuel. The Kovari paper considers different scenarios with less than 50% tritium at start-up. The table below gives the fusion power for various tritium %. The figure gives the number of years to produce enough tritium to make a 50% tritium fraction as a function of initial tritium inventory.
|Tritium %||Fusion power (MW)|
Start-up with deuterium rich fuel, power at different tritium percentage (from Kovari et al).
Time to reach 50% tritium percentage with different starting tritium inventory (from Kovari et al)
The paper calculates the cost of making tritium with this methodology at $2 billion per kg of tritium saved at start-up, not economically sensible.
If somehow a start-up inventory is obtained, the regeneration processes would be very complex. The first complexity is that after injection into the reactor only a few percent of the tritium is actually burnt and the un-burnt fuel must be recuperated, purified and re-injected. The regeneration of tritium in the breeder blanket is whole other pathway in the complete fuel cycle. The figure below, from the paper: Abdou et al. (2021), illustrates the complexities in the tritium system.
Fuel cycle: Tritium injected into plasma but not burnt, passes into an exhaust or is trapped on plasma facing surfaces. Neutrons from fusion interact in the blanket and regenerate tritium.
The tritium has four routes in the system:
Abdou et al. have developed a dynamic model to evaluate the requirement to achieve tritium self-sufficiency. The model considers several parameters, including:
The figure shows the required Tritium Breeding Ratio (TBR) for various tritium processing time, tp , in the plasma exhaust, as a function of ηf fb.
The estimates of TBR possible with existing technologies are in the range 1.05 - 1.15 and indicated by the green bands in the plot. The conclusion is that with the ITER "state-of-the-art" parameters (fuelling efficiency, ηf <25%; plasma burn fraction, fb=0.35%; tp=several hours), self-sufficiency is not possible and much higher values of these parameters are needed beyond what seems currently possible.
The two papers discussed in this section indicate that the actions needed to obtain tritium for a commercial fusion power plant would either be uneconomic, very difficult or politically unacceptable.
Without tritium fuel, the question arises as whether alternative fuels are possible. The alternatives are considered in the page: Alternative Approaches with the conclusion they are also, in practice, not possible.
A series of articles on the website of Steven Krivit at: The New Energy Times, Fusion Fuel Exposé, gives examples of the propaganda used to mis-lead the general public on the tritium supply situation. An excellent treatment of the supply issue of tritium, as well as lithium and other rare minerals for use in a fusion reactor, is given in the book of L.J. Reinders. There is an excellent article by Daniel Clery in Science: Fusion power may run out of fuel before it even gets started.