4 ms·

I'm a bit skeptical about the claim "it doesn't produce dangerous, long-term toxic waste." I'm no expert but I've read that fusion reactors will be producing ma

by Elrac 12y ago

I'm a bit skeptical about the claim "it doesn't produce dangerous, long-term toxic waste." I'm no expert but I've read that fusion reactors will be producing massive amounts of neutron radiation (like the neutron bomb, AKA the "real estate bomb," heh!) which ends up absorbed by the cladding of the reactor chamber and converts it to partly radioactive isotopes. A consequence is that the reaction chamber walls lose their physical integrity, i.e. become brittle, so leaving them in place is not an option. Thus, when operating a fusion reactor, you're constantly forced to replace crunchy, fusion-baked, radioactive reactor wall debris with newly built wall plates. I admit to having no idea about which isotopes would be produced and what their half-life would be. If anyone can shed some light or correct me, I'd be indebted.

lotsofmangos 12y ago
"I'm no expert but I've read", is probably one of the most dangerous phrases in the entire English language. That said, I'm no expert but I've read that the half life of the stuff it irradiates is pretty short, so you only need to store it for a hundred years or so rather than 10,000. So no ray-cats are needed. http://emperorx.bandcamp.com/album/10000-year-earworm-to-discourage-settlement-near-nuclear-waste-repositories http://emperorx.bandcamp.com/album/10000-year-earworm-to-dis...
- Elrac 12y ago
  I hoped to limit the impact of my speculation by being humble about my state of knowledge. Anyway, more information is good, and that's one less thing for me to lose sleep over. Thanks!
  - the8472 12y ago
    >I hoped to limit the impact of my speculation by being humble You could have requested information instead. Otherwise people may feel compelled[1] to "fix" your half-baked knowledge by argumenting ferociously instead of just presenting knowledge. [1] http://xkcd.com/386/ http://xkcd.com/386/
    - DennisP 12y ago
      Cunningham's Law: The best way to get the right answer on the Internet is not to ask a question, it's to post the wrong answer. http://meta.wikimedia.org/wiki/Cunningham%27s_Law http://meta.wikimedia.org/wiki/Cunningham%27s_Law
Tuna-Fish 12y ago
Most fusion reactor designs intend the vast majority of those neutrons to be absorbed by a cladding of lithium for tritium breeding. Lithium being bombarded by neutrons does not produce dangerous long-lasting isotopes.
- Elrac 12y ago
  Pretty clever of them! Thanks for the heads up.
the8472 12y ago
It largely depends on the elements used for the inner reactor walls and there is ongoing research to find good candidate materials[1]. Yes, radioactive waste will be produced - unless an aneutronic fusion process can be handled - but the goal is to have low-halftime waste that is manageable and does not have to be contained for millions of years. And fission reactors also have this problem to some degree, although their neutron radiation has very different energy profiles compared to fusion. When they are dismantled their reactor cores also have to be treated as waste. But unlike fusion plants you have to deal with the structural materials AND the actual spent fuel. So fusion plants will generally be better than fission, no matter what you end up doing. Additionally the high energy neutrons of fusion reactors may prove useful to transmutate radioactive waste from fission plants so they might actually lead to a net reduction in radioactive waste. [1] http://en.wikipedia.org/wiki/International_Fusion_Materials_Irradiation_Facility http://en.wikipedia.org/wiki/International_Fusion_Materials_...
- Elrac 12y ago
  The argument about the fuel not turning into nuclear waste is compelling. So we're talking about less radioactive material with a shorter half-life. Win-win!
  - xorcist 12y ago
    Depends on what you mean with "less", especially since as far as I understand no one is close to a economically viable solution yet. But shorter half-life is most likely true.
DennisP 12y ago
Here's an article that quotes a fusion researcher saying there'd be much less waste from fusion, and it would stop being significantly radioactive after 50 to 100 years: http://www.wm.edu/news/stories/2012/safer,-more-efficient,-fusion-generated-electricity-is-on-the-horizon123.php http://www.wm.edu/news/stories/2012/safer,-more-efficient,-f... That's a researcher working in mainstream fusion, so that would be for deuterium-tritium fuel, which is the easiest but produces very high-energy neutrons. More advanced fuels are mostly aneutronic. Helion is attempting D-D/D-He3, which would release only 6% of its energy as neutron radiation. Tri-Alpha and LPP are attempting boron fusion, for which neutron radiation is only 1% of the released energy.
- Elrac 12y ago
  The "state of the art" looks a bit chaotic to people looking in from the outside, what with the variety of approaches being tested. But this is exactly how progress is made in science! I'm glad to see that neutron blasting is being taken into consideration. I suppose not wasting most of your energy output as destructive radiation makes excellent sense economically, too. Thanks!
  - DennisP 12y ago
    With D-T the neutrons do heat a fluid, so it's not like the energy is wasted. For example, General Fusion would use them to heat a mixture of molten lead and lithium (the latter for breeding more tritium), which would heat water for a steam turbine. But aneutronic fuels put most of their energy into fast-moving charged particles, which lets you extract electric power without using a turbine.
snarfy 12y ago
Boron + Hydrogen = 3 helium. No neutrons are produced.
- jwilliams 12y ago
  As a very rough generalization this is true – in the detail you'll see neutrons are still produced. Just a significantly lower percentage (Aneutronic fusion is defined as less than 1% of total energy as neutrons). It's still enough that it needs to be moderated.

by Elrac 12y ago

lotsofmangos 12y ago

"I'm no expert but I've read", is probably one of the most dangerous phrases in the entire English language. That said, I'm no expert but I've read that the half life of the stuff it irradiates is pretty short, so you only need to store it for a hundred years or so rather than 10,000. So no ray-cats are needed. http://emperorx.bandcamp.com/album/10000-year-earworm-to-discourage-settlement-near-nuclear-waste-repositories http://emperorx.bandcamp.com/album/10000-year-earworm-to-dis...

Elrac 12y ago
I hoped to limit the impact of my speculation by being humble about my state of knowledge. Anyway, more information is good, and that's one less thing for me to lose sleep over. Thanks!
- the8472 12y ago
  >I hoped to limit the impact of my speculation by being humble You could have requested information instead. Otherwise people may feel compelled[1] to "fix" your half-baked knowledge by argumenting ferociously instead of just presenting knowledge. [1] http://xkcd.com/386/ http://xkcd.com/386/
  - DennisP 12y ago
    Cunningham's Law: The best way to get the right answer on the Internet is not to ask a question, it's to post the wrong answer. http://meta.wikimedia.org/wiki/Cunningham%27s_Law http://meta.wikimedia.org/wiki/Cunningham%27s_Law

Tuna-Fish 12y ago

Most fusion reactor designs intend the vast majority of those neutrons to be absorbed by a cladding of lithium for tritium breeding. Lithium being bombarded by neutrons does not produce dangerous long-lasting isotopes.

Elrac 12y ago
Pretty clever of them! Thanks for the heads up.

the8472 12y ago

It largely depends on the elements used for the inner reactor walls and there is ongoing research to find good candidate materials[1]. Yes, radioactive waste will be produced - unless an aneutronic fusion process can be handled - but the goal is to have low-halftime waste that is manageable and does not have to be contained for millions of years. And fission reactors also have this problem to some degree, although their neutron radiation has very different energy profiles compared to fusion. When they are dismantled their reactor cores also have to be treated as waste. But unlike fusion plants you have to deal with the structural materials AND the actual spent fuel. So fusion plants will generally be better than fission, no matter what you end up doing. Additionally the high energy neutrons of fusion reactors may prove useful to transmutate radioactive waste from fission plants so they might actually lead to a net reduction in radioactive waste. [1] http://en.wikipedia.org/wiki/International_Fusion_Materials_Irradiation_Facility http://en.wikipedia.org/wiki/International_Fusion_Materials_...

Elrac 12y ago
The argument about the fuel not turning into nuclear waste is compelling. So we're talking about less radioactive material with a shorter half-life. Win-win!
- xorcist 12y ago
  Depends on what you mean with "less", especially since as far as I understand no one is close to a economically viable solution yet. But shorter half-life is most likely true.

DennisP 12y ago

Here's an article that quotes a fusion researcher saying there'd be much less waste from fusion, and it would stop being significantly radioactive after 50 to 100 years: http://www.wm.edu/news/stories/2012/safer,-more-efficient,-fusion-generated-electricity-is-on-the-horizon123.php http://www.wm.edu/news/stories/2012/safer,-more-efficient,-f... That's a researcher working in mainstream fusion, so that would be for deuterium-tritium fuel, which is the easiest but produces very high-energy neutrons. More advanced fuels are mostly aneutronic. Helion is attempting D-D/D-He3, which would release only 6% of its energy as neutron radiation. Tri-Alpha and LPP are attempting boron fusion, for which neutron radiation is only 1% of the released energy.

Elrac 12y ago
The "state of the art" looks a bit chaotic to people looking in from the outside, what with the variety of approaches being tested. But this is exactly how progress is made in science! I'm glad to see that neutron blasting is being taken into consideration. I suppose not wasting most of your energy output as destructive radiation makes excellent sense economically, too. Thanks!
- DennisP 12y ago
  With D-T the neutrons do heat a fluid, so it's not like the energy is wasted. For example, General Fusion would use them to heat a mixture of molten lead and lithium (the latter for breeding more tritium), which would heat water for a steam turbine. But aneutronic fuels put most of their energy into fast-moving charged particles, which lets you extract electric power without using a turbine.

snarfy 12y ago

Boron + Hydrogen = 3 helium. No neutrons are produced.

jwilliams 12y ago
As a very rough generalization this is true – in the detail you'll see neutrons are still produced. Just a significantly lower percentage (Aneutronic fusion is defined as less than 1% of total energy as neutrons). It's still enough that it needs to be moderated.