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First, sorry for bad English.

If the fusion become a viable energy source, and used extensively, it will have impact on the amount of hydrogen in our environment? Unlike pollution by carbon dioxide, turn hydrogen into helium and it can not be broken again, photosynthesis is the molecular level, fission with hellium? then we would not be destroying the source of life on the planet? Creating more and more unbreakable Helium?

Nuclear fission has its radioactive waste and would never be feasible for home use because of the radiation, but dreamed cold fusion could move cars without immediate impact on the environment.

If what do I think is right, millions of cars creating helium would surely kill the planet in a few centuries.

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    $\begingroup$ Run some numbers... If by centuries you actually mean billions of years you might be right... $\endgroup$
    – Jon Custer
    Feb 16 '16 at 1:41
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    $\begingroup$ We won't be running out of hydrogen, but we may run short on lithium after a couple million years... :-) $\endgroup$
    – CuriousOne
    Feb 16 '16 at 1:55
  • $\begingroup$ I've done these calculations in the past - but it's easy enough to look them up, and they are summarized below. $\endgroup$ Feb 16 '16 at 1:57
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Hydrogen fusion as proposed today is based on deuterium, a stable isotope of hydrogen. It is extracted from sea water in the form of "heavy water" molecules. About 1 water molecule in 3,200 contains deuterium.

See https://en.wikipedia.org/wiki/Heavy_water#Production

You can calculate the energy gain from converting two molecules of HD (hydrogen plus deuterium) into a single atom of He (helium) by taking the difference in their measured masses (mass deficit), and convert this to energy via E=mc^2.

The helium produced would rapidly escape the atmosphere because it is so light - the motion in the upper atmosphere, due to its mass and the temperature, is greater than the planetary escape velocity, so it is quickly lost. See Can Helium Disappear from Earth?. So we don't need to worry overly much about becoming high-pitched singers!

This leaves the question of how long will our supply of deuterium last? It depends upon our rate of energy usage,it would last 1,000 million years. Or so calculated this article which appeared in New Scientist on January 24,1957, p. 36: https://books.google.com/books?id=idzeW5i68UYC&lpg=PA1&pg=PA35#v=onepage&q&f=false

So we should be OK.

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  • $\begingroup$ Fusion reactors fuse DT, not HD. Tritium has to be bred from Lithium. $\endgroup$
    – CuriousOne
    Feb 16 '16 at 2:07
  • $\begingroup$ Fusion reactors could also fuse DD, but the DT fusion is energetically preferred. $\endgroup$ Feb 16 '16 at 3:07
  • $\begingroup$ DT is the most efficient, but is not the only possible path. Here we're just talking about how long the hydrogen lasts. Next question would be when does the lithium run out! $\endgroup$ Feb 16 '16 at 3:13

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