

Fusion reactors, here we come!





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RE: Doesn't the Sun
By nrb on 5/26/2006 8:22:39 AM , Rating: 2
Isn't the sun run on fusion?
Yeah - but would you want to stand really close to the Sun? ;-)

Actually we will definitely never be able to duplicate on Earth the type of fusion that happens in the Sun. In the core of the Sun regular Hydrogen is converted to Helium. The best we could even theoretically do is to convert Deuterium (heavy hydrogen) to Helium. This produces far less energy, and Deuterium is far less common than regular Hydrogen. There is a reasonable amount of it in seawater, but extracting it isn't cheap.

RE: Doesn't the Sun
By beemercer on 5/26/2006 5:22:28 PM , Rating: 3
-It is also possible to run the D-T reaction; this is the easiest to achieve:
D + T ? 4He + n
n + 6Li ? T + 4He
n + 7Li ? T + 4He + n
-Or the p-11B fuel cycle; no neutrons;
p + 11B ? 3 4He

*Lifted from wikipedia

RE: Doesn't the Sun
By shecknoscopy on 5/26/2006 6:58:25 PM , Rating: 2
So, a synthesis that doesn't yield free neutrons effectively eliminates the neutron-caused radioactive waste that's casually mentioned in the other posts here. Namely, that starting with non-radioactive materials, free neutrons (which can't be controlled with electric or magnetic fields, owing to their lack of charge or manipulable dipole) would irradiate the walls of the reactor. Small fluxes are bad enough, but prolonged exposure to intense neutron radiation would begin to decay the very nuclear structure of the materials lining the reactor itself, converting harmless building materials into nuclear waste.

This is, as many people have pointed out, of substantially lower ecological impact than the type of waste generated by fission reactors. And, as a political side-note - and considering the embroiled debate surrounding Iran's nuclear program - I'll add that another benefit of these fusion reactors is that they are distinctly removed in imput materials, design and output than are fusion bombs. Hence there would be no debate as to the ultimate directive of a given facility: weapon or energy-production. Another plus there.

However, the low-or-no neutron flux reactions outlined here require the enrichment and isolation of either various lithium or Boron isotopes, or a stable proton source. While not making the reactor radioactive (or as radioactive - there's still the pesky gamma and x-ray problem), it adds the difficulties of needing to purify less abundant, and more dangerous fuel sources. One of the beauties of the D+T reaction is that it requries little purification to make the original fuels, and at least one of the reaction products is totally harmless. This is no longer the case for the Li or B reactions, and now requires extensively waste-producing processes to make the fuel in the first place. We're not quite back at Square One, but we're closer.

BUT the big problem is that all of this is really moot. The problem so far with fusion is that, though the reaction ultimately produces energy, the energetic barrier to starting this reaction - the so-called activation energy - has, to date, been higher than the amount of energy produced. That is, a Tokomak reactor, operating for 10 hours, would produce enough energy to run Tokyo for a day. But in order to run it for 10 hours, we needed to put in 1.05 day's worth of Tokyo-energy (a standard SI unit, I assure you), to get the reaction started. So, we're in the hole.

Seriously; until someone can get a reactor that actually yields a net profit on energy production, all of this debate is purely academic. For the moment, we've not found the would-be "methedone" for our "oil addiction."

I like to inhale the oil, myself. Get skeeved out by needles.

RE: Doesn't the Sun
By beemercer on 5/27/2006 1:52:23 PM , Rating: 3
Good job summing it up

