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> Also, you can't make small scale fusion power plants. If the reactor was the size of a light bulb and produced 40w of power you would still need several feet

by waps 12y ago

> Also, you can't make small scale fusion power plants. If the reactor was the size of a light bulb and produced 40w of power you would still need several feet of shielding to avoid killing anyone in the area and that shielding would vary quickly become extremely radioactive. Fission is low energy in comparison. http://en.wikipedia.org/wiki/List_of_coal_power_stations http://en.wikipedia.org/wiki/List_of_coal_power_stations over 5+ GW of thermal power. Google "aneutronic fusion". Granted, ITER will never support it, but that's just another reason to try other things. ITER makes everything radioactive, but aside from that being the easiest reaction there is no good reason for doing that. As for the size of fusion reactors, go to your nearest (big) hospital. They have a football-sized one in the radiology department. The box it's in is fridge-sized. A Farnsworth-Hirsh fusor to be exact. It will be shielded, because it's using DT fusion. If you really knew what you were doing you could get it to fuse p+B11 and it would produce electrons, but it would defeat the point for the hospital, as it's neutron radiation is exactly why they have it. Now granted this reactor has a q value of 0.02 or so. But if there were a smart way to get it to a q of 100 or so that would almost be your lightbulb example. Get it to work on p-B11 and ...

Retric 12y ago
There is no such thing as neurotic fusion. Best case neutrons carry 1% of the total released energy, but if a 100w light bulb produced 1w of unshielded 2.5MeV neutrons it would quickly give everyone in a fairly large room a lethal radiation dose. Edit: For the morbidly curious 1w / (3 x 10 -13)j/electron = 3.3e+12 electrons. 10M from the device you have a sphere with a surface area of 1256m^2. http://miscpartsmanuals3.tpub.com/TM-55-315/TM-55-3150021.htm http://miscpartsmanuals3.tpub.com/TM-55-315/TM-55-3150021.ht... 1 rem (neutrons/cm2) from 2.5 MeV neutrons = 3* 10^6 neutrons / cm^2. 100 rem received over a short time period are likely to cause acute radiation syndrome (ARS), possibly leading to death within weeks if left untreated. So, 3 * 10^6 * 100 * 100^2 * 1256 = ~4 * 10^ 15 electrons would kill ~1/2 the people standing within 30 feet in ~10 minutes. And far less time than that to start handing out cancers left and right. And at 10 feet that's ~60 seconds. (Assuming I did not mess up...) PS: It's far safer to spread the same dose over longer periods of time. But, if your working near a useful fusion device it needs to be heavily shielded.
- pdonis 12y ago
  I assume you mean "aneutronic fusion". There are a number of fusion reactions that do not yield neutrons: http://en.wikipedia.org/wiki/Nuclear_fusion#Criteria_and_candidates_for_terrestrial_reactions http://en.wikipedia.org/wiki/Nuclear_fusion#Criteria_and_can... They are harder to initiate than the D-T reaction, which is why they're not the ones being tried first for fusion-generated electricity; but they're perfectly good fusion reactions which have been observed in experiments.
  - Retric 12y ago
    There are fusion paths that don't result in neutrons but you don't get to limit yourself to just those path's. Consider DD fusion > 50%He + 50%T but you don't get to keep the T in a thermal DD plasma so you need to also look at DT's paths.
    - pdonis 12y ago
      > you don't get to limit yourself to just those path's You do if you're using fuel for which there are no possible paths that result in neutrons. For example, He-3, proton-lithium-6, or proton-boron-11.
      - Retric 12y ago
        proton-whatever also gives you some proton-proton fusion so now you have deuterium which is not so clean. Let alone p whatever the walls of your chamber are. Still, if your going to pretend we can do anything harder harder than DT or perhaps DD your might as well go for p+p as it's fairly 'clean' and the fuel is plentiful.
        pdonis 12y ago
        p+p is a lot harder to initiate than any of the reactions listed on the Wikipedia page I linked to. The only reason it happens in stars is that gravitational confinement makes stellar cores much, much denser than plasmas we can produce on Earth. It's not going to happen in an Earthbound reactor using proton (+ something else) fuel. You're right that there will be some fuel particles that escape confinement and react with the chamber walls; but proper confinement makes this effect very small, much smaller than the numbers you were quoting for radiation exposure, which are based on using fuels that produce neutrons as reaction products. Neutron's can't be confined in a plasma because they're uncharged, so they immediately escape and hit the chamber walls. Protons, and other fuel particles, don't have that problem since they're charged and can be confined (if they couldn't be you wouldn't be able to make the reactor work at all).

by waps 12y ago

Retric 12y ago

There is no such thing as neurotic fusion. Best case neutrons carry 1% of the total released energy, but if a 100w light bulb produced 1w of unshielded 2.5MeV neutrons it would quickly give everyone in a fairly large room a lethal radiation dose. Edit: For the morbidly curious 1w / (3 x 10 -13)j/electron = 3.3e+12 electrons. 10M from the device you have a sphere with a surface area of 1256m^2. http://miscpartsmanuals3.tpub.com/TM-55-315/TM-55-3150021.htm http://miscpartsmanuals3.tpub.com/TM-55-315/TM-55-3150021.ht... 1 rem (neutrons/cm2) from 2.5 MeV neutrons = 3* 10^6 neutrons / cm^2. 100 rem received over a short time period are likely to cause acute radiation syndrome (ARS), possibly leading to death within weeks if left untreated. So, 3 * 10^6 * 100 * 100^2 * 1256 = ~4 * 10^ 15 electrons would kill ~1/2 the people standing within 30 feet in ~10 minutes. And far less time than that to start handing out cancers left and right. And at 10 feet that's ~60 seconds. (Assuming I did not mess up...) PS: It's far safer to spread the same dose over longer periods of time. But, if your working near a useful fusion device it needs to be heavily shielded.

pdonis 12y ago
I assume you mean "aneutronic fusion". There are a number of fusion reactions that do not yield neutrons: http://en.wikipedia.org/wiki/Nuclear_fusion#Criteria_and_candidates_for_terrestrial_reactions http://en.wikipedia.org/wiki/Nuclear_fusion#Criteria_and_can... They are harder to initiate than the D-T reaction, which is why they're not the ones being tried first for fusion-generated electricity; but they're perfectly good fusion reactions which have been observed in experiments.
- Retric 12y ago
  There are fusion paths that don't result in neutrons but you don't get to limit yourself to just those path's. Consider DD fusion > 50%He + 50%T but you don't get to keep the T in a thermal DD plasma so you need to also look at DT's paths.
  - pdonis 12y ago
    > you don't get to limit yourself to just those path's You do if you're using fuel for which there are no possible paths that result in neutrons. For example, He-3, proton-lithium-6, or proton-boron-11.
    - Retric 12y ago
      proton-whatever also gives you some proton-proton fusion so now you have deuterium which is not so clean. Let alone p whatever the walls of your chamber are. Still, if your going to pretend we can do anything harder harder than DT or perhaps DD your might as well go for p+p as it's fairly 'clean' and the fuel is plentiful.
      - pdonis 12y ago
        p+p is a lot harder to initiate than any of the reactions listed on the Wikipedia page I linked to. The only reason it happens in stars is that gravitational confinement makes stellar cores much, much denser than plasmas we can produce on Earth. It's not going to happen in an Earthbound reactor using proton (+ something else) fuel. You're right that there will be some fuel particles that escape confinement and react with the chamber walls; but proper confinement makes this effect very small, much smaller than the numbers you were quoting for radiation exposure, which are based on using fuels that produce neutrons as reaction products. Neutron's can't be confined in a plasma because they're uncharged, so they immediately escape and hit the chamber walls. Protons, and other fuel particles, don't have that problem since they're charged and can be confined (if they couldn't be you wouldn't be able to make the reactor work at all).