Since it looks like they’re going to be building a fusion reactor in either Japan or France, I got to wondering about this.
Fusion reactors fuse 4 hydrogen atoms into a helium atom, right?
The article said “no greenhouse gasses” are produced but does this mean massive amounts of helium will be released into the atmosphere?
Will we all be talking funny in 30 years?
They likely want to fuse two deuterium atoms. Deuterium is a hydrogen with a neutron in addition to the proton as the nucleus.
Any escaped helium would fairly quickly drift into the upper atmosphere. If you want to talk funny, you’ll still have to inhale from a balloon.
Fusion of light hydrogen into helium barely works under stellar-core conditions. It has nothing to do with any fusion reactor whose design consists of more than handwaving. The article says that:
which, of course, means deuterium. Either the proposed reactor is a D-D reactor (at which idea I laugh scornfully) or Ms. Kerr completely missed the need for tritium (which must be bred from lithium). Given the general tone of the article, I’d guess the latter.
The article doesn’t mention the power rating of the reactor, but a good-sized fossil-fuel or fission reactor runs about 1GW. The D-T reaction produces, IIRC, about 14.1 MeV per fusion (and helium nucleus produced). 1 eV = 1.602x10[sup]-19[/sup] J; 1 J/s = 1 watt, so at 100% efficiency and 100% uptime the plant would produce about 90 tonnes/year of helium (assuming that I haven’t baked the dog on the arithmetic, always a possibility). Of course, the plant will have neither 100% efficiency nor 100% uptime; insert your own numbers here. Whatever they are, however, only a Greenpeacenik could say that “massive amounts of helium will be released”.
Okay, I’ll insert my own numbers, say 50% efficiency and 100% uptime (downtime wouldn’t have any emissions would it?). Only 180 tons per gigawatt year, that’s nothin’.
But if this catches on and another 1,000 reactors are built all over the world (how many fission reactors are there now?) then we’re looking at 180,000 tons per year. How much helium is in the atmosphere now? How long would it take at that rate to increase the total helium by 1%?
Thanks for the replies
The Bulletin of the Atomic Scientists says that as of 12/1998 there were 429 fission reactors worldwide, producing in excess of 345 GW of electricity.
The total mass of the Earth’s atmosphere is estimated at 5.29x10[sup]15[/sup] tonnes. Assuming that we have fusion reactors producing 180,000 tonnes/year of helium, and assuming that none of that helium escapes to space (which it surely will, but I don’t know off-hand how to go about calculating the escape rate), it would take 2.94x10[sup]10[/sup] years to make the atmosphere 1% helium (from which we may deduce that the description of Mote Prime in The Mote in God’s Eye has more than a little hand-waving in it).
Helium now accounts, IIRC, for about 5x10[sup]-4[/sup]% of the atmosphere (more or less; when we’re talking about trace constituents like that, you have to give me an order of magnitude or two 
), so doubling its concentration (with the assumptions supra) would take only 147,000 years. The Sierra Club’s anti-fusion demo is next Friday.
Well, back to the OP, and doing some handwaving to presume the fusion reactors work, the reaction would happen in an enclosed vessel, so the operator could capture the helium and sell it to a cryonics lab or to Goodyear – if the price is right.
We should ask how much helium DO we vent into the atmosphere in any given year already. Right now the helium we use is obtained as a byproduct of natural gas extraction (it’s generated by radioactive decay in rocks, and got trapped by the same nonpermeable rock pockets that trap natural gas) and some of it may be getting vented rather than captured (if it’s not worth the driller’s cost) but all of what does get used is eventually released. As mentioned, He flies up into the upper atmosphere quite quickly.
I thought that very light gasses such as Hydrogen and Helium dissipated into space rather than persisting in the atmosphere?
They do. That infinitesimal amt. that’s currently there is on its way out to space as we speak.