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Given a successful deuterium-tritium fusion reactor such as that conceived by ITER, could the world's energy needs theoretically be met without the input of any petroleum or natural gas products?

Deuterium is currently typically produced by the girdler sulfide process from seawater which requires a natural gas input, although methods involving electrolysis or distillation are known.

Lithium is currently mined, although there are methods known of extracting it from seawater.

Could the extractions of these elements be powered exclusively from the energy produced by fusion reactors in the future? This would leave seawater and the reserve of lithium from the earth's crust as the only fuel sources (or just seawater, if we are extracting the lithium from it).

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The energy cost of obtaining Deuterium and Lithium is minimal compared to the energy released by the fusion process. There are many references that provide relevant information but a sensible one to refer to is the official ITER site "Fusion for energy". Fusion for Energy (F4E) is the European Union’s Joint Undertaking for ITER and the Development of Fusion Energy.

On their understanding fusion page they say:

A 1,000-megawatt electric fusion power plant would consume around 100 kg of deuterium and three tonnes of natural lithium in a year whilst generating 7 billion kilowatt-hour. To generate the same amount of electricity, a coal-fired power plant would need around 1.5 million tonnes of coal.

and

If used to fuel a fusion power station, the lithium in one laptop battery, complemented with half a bath of water, would produce the same amount of electricity as burning 40 tonnes of coal.
(eg ~= 8000 dollars at 5c/kWh wholesale or 40,000 dollars at NZ 25c/kWh retail).

However what is required is Tritium - Lithium is simply an easily obtained precursor. Obtaining Tritium from Lithium is the "hard part" and while it is proposed that this step be incorporated in the ITER system, and is liable to succeed if ITER succeeds, the process is at this stage "theoretical and experimental".

Tritium can be, and currently is, bred from Lithium using fast neutrons from existing reactors, the amount obtained in this manner is enough to initiate a national or international fusion energy system but nowhere near enough to sustain it. What is essential is the "breeding" of the essential Tritium from Lithium using a suitable source of fast neutrons from the ITER process itself

ITER's own site, in the section Tritium Breeding says

... While deuterium can be extracted from seawater in virtually boundless quantities, the supply of tritium is limited, estimated currently at twenty kilos. .... tritium can be produced within the tokamak when neutrons escaping the plasma interact with a specific element—lithium—contained in the blanket. This concept ... is an important one for the future needs of a large-scale fusion power plant.

ITER will procure the tritium "fuel" necessary for its expected 20-year lifetime from the global inventory. But for DEMO, the next step on the way to commercial fusion power, about 300g of tritium will be required per day to produce 800 MW of electrical power. No sufficient external source of tritium exists for fusion energy development beyond ITER, making the successful development of tritium breeding essential for the future of fusion energy.

ITER will provide a unique opportunity to test mockups of breeding blankets, called Test Blanket Modules (TBM), in a real fusion environment. Within these test blankets, viable techniques for ensuring tritium breeding self-sufficiency will be explored.

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How Tritium is obtained at present:

Construction & Operation of a Tritium Extraction Facility at the Savannah River Site
Final Environmental Impact Statement DOE/EIS-0271 1999 - 140 page pdf

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With respect to generating hydrocarbons from "other sources of cheap energy"

Yes. The process could be totally "geologically stored hydrocarbon" free, which I think is the 'spirit' of what you are asking.

Once you achieve "energy too cheap to meter" [tm] (2nd time lucky perhaps) you can produce hydrocarbons from current biological waste - or from newly grown feedstock if you so desired. Various people have demonstrated 'just about anything organic' to petroleum products converters. Videos of some such are available on you-tube - caveat emptor as ever, and I knew a man in Louisiana who I have lost touch with who was doing just this several years ago, and having a lot of trouble interesting anyone in the process.

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  • $\begingroup$ Thank you for you answer. I am looking more for an energy accounting answer. Ie - a fusion reactor could theoretically produce xx MW of electricity from xx units of fuel, the fuel takes xx MW to produce xx units of fuel from seawater, etc. $\endgroup$
    – Steve M
    Aug 8 '15 at 15:31
  • $\begingroup$ @SteveM I don't understand what you want. Russell's "too cheap to meter" scenario is effectively "more energy than we can use." That pretty much means that at that point anything that makes sense to do with electricity will be done with electricity. That doesn't mean that there aren't situations where hydrocarbons make sense. $\endgroup$
    – hazzey
    Aug 9 '15 at 1:24
  • $\begingroup$ @SteveM Answer updated. If ITER works it will be necessary to establish viable means of breeding Tritium from Lithium using neutrons from the fusion process. This is the 'hard and expensive part' compared to which the costs and efforts of Lithium and Deuterium procurement are minimal. $\endgroup$ Aug 9 '15 at 5:33

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