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Very interesting. What about the high-energy neutrons produced by D+T fusion though? Wouldn't they escape the magnetic containment?

bostik 11y ago
Yes. They are also a major source of excess energy once the reaction becomes self sufficient. Capture the high-energy neutrons in a suitable material and it heats up. Use heat exchangers to run turbines, produce electricity. If you read up on fusion energy, you'll soon encounter the note that fusion reactor waste is short-lived and therefore easier to manage + store than fission reactor waste. The material used to capture neutrons is transmuted to radioactive isotopes, but due to the choice of materials* used the half-life of those isotopes is pretty low. Yes, it also means that the fusion reactor waste is more energetic and more active radiation source than fission waste. But because it's going to become safe in just a couple of hundred years, it causes much less of a headache in terms of storage. *: We don't necessarily know what the radioactive isotopes will be. I think the jury and researchers are still out on that one but I dare say it's guaranteed that the neutron absorbent will NOT be uranium or radium.
- danmaz74 11y ago
  To clarify, when talking about the neutrons I wasn't thinking about the radioactive waste problem, but about keeping the superconductor's temperature low. I just took a look at the Iter schema and noticed that there is a "blanket" that covers the interior surface of the vacuum vessel exactly to absorb the neutrons. The vessel then has a water cooling system. At this point, I was also wondering if you have any idea about how much of the heat transfer from the plasma to the vessel would be be through those neutrons (ie if it's the main heat transfer medium).
  - bostik 11y ago
    By my understanding practically all of the generated energy is due to neutrons hitting the containment vessel. Highly energetic neutron, impacting solid matter, will generate quite a bit of heat in the violent collision. I found one fairly decent source [0] which goes into somewhat greater detail. It's worth noting that if you follow the link to first page of the series, that page explicitly states that what fusion reactors call "neutron flux" would be called "heat flux" in traditional reactors. And it makes sense even when thinking logically. Energy and matter are interchangeable, and the reactor turns matter into energy; majority of matter escaping from the fusion reactor will be helium and neutrons. These particles interacting with external solid matter turns kinetic energy into heat. That's the power plant's heat source. Now, as to the fraction of heat transferred by neutrons compared to that transferred by the newly formed helium - I have no idea. 0: http://www.visionofearth.org/industry/fusion/how-do-we-turn-nuclear-fusion-energy-into-electricity/ http://www.visionofearth.org/industry/fusion/how-do-we-turn-...
    - danmaz74 11y ago
      Thanks for the update :) Regarding helium, considering that it's plasma we're talking about, I think it can't escape at all - the separated nuclei and electrons should be contained by the magnetic field.

bostik 11y ago

Yes. They are also a major source of excess energy once the reaction becomes self sufficient. Capture the high-energy neutrons in a suitable material and it heats up. Use heat exchangers to run turbines, produce electricity. If you read up on fusion energy, you'll soon encounter the note that fusion reactor waste is short-lived and therefore easier to manage + store than fission reactor waste. The material used to capture neutrons is transmuted to radioactive isotopes, but due to the choice of materials* used the half-life of those isotopes is pretty low. Yes, it also means that the fusion reactor waste is more energetic and more active radiation source than fission waste. But because it's going to become safe in just a couple of hundred years, it causes much less of a headache in terms of storage. *: We don't necessarily know what the radioactive isotopes will be. I think the jury and researchers are still out on that one but I dare say it's guaranteed that the neutron absorbent will NOT be uranium or radium.

danmaz74 11y ago
To clarify, when talking about the neutrons I wasn't thinking about the radioactive waste problem, but about keeping the superconductor's temperature low. I just took a look at the Iter schema and noticed that there is a "blanket" that covers the interior surface of the vacuum vessel exactly to absorb the neutrons. The vessel then has a water cooling system. At this point, I was also wondering if you have any idea about how much of the heat transfer from the plasma to the vessel would be be through those neutrons (ie if it's the main heat transfer medium).
- bostik 11y ago
  By my understanding practically all of the generated energy is due to neutrons hitting the containment vessel. Highly energetic neutron, impacting solid matter, will generate quite a bit of heat in the violent collision. I found one fairly decent source [0] which goes into somewhat greater detail. It's worth noting that if you follow the link to first page of the series, that page explicitly states that what fusion reactors call "neutron flux" would be called "heat flux" in traditional reactors. And it makes sense even when thinking logically. Energy and matter are interchangeable, and the reactor turns matter into energy; majority of matter escaping from the fusion reactor will be helium and neutrons. These particles interacting with external solid matter turns kinetic energy into heat. That's the power plant's heat source. Now, as to the fraction of heat transferred by neutrons compared to that transferred by the newly formed helium - I have no idea. 0: http://www.visionofearth.org/industry/fusion/how-do-we-turn-nuclear-fusion-energy-into-electricity/ http://www.visionofearth.org/industry/fusion/how-do-we-turn-...
  - danmaz74 11y ago
    Thanks for the update :) Regarding helium, considering that it's plasma we're talking about, I think it can't escape at all - the separated nuclei and electrons should be contained by the magnetic field.