5 ms·

It’s worth making a few notes: 1. ITER is a political beast, not a practical one. 2. These are problems with D-T fusion, not all fusion, although... 3. Aneut

It’s worth making a few notes: 1. ITER is a political beast, not a practical one. 2. These are problems with D-T fusion, not all fusion, although... 3. Aneutronic fusion isn’t even on the remote horizon. Fusion has incredible potential, but probably not for anyone alive today.

ZenoArrow 9y ago
Regarding point 2, the only drawback I'm aware of with D-T fusion is that it still produces nuclear waste (whereas aneutronic fusion produces zero/close to zero nuclear waste), however the nuclear waste produced by D-T fusion is said to be: * Smaller in size than the nuclear waste produced by the current approaches to nuclear fission. * Has a shorter half life than spent nuclear fission fuel, meaning that it doesn't take as long before it's safe to take it out of storage. Aside from nuclear waste, are there other drawbacks to D-T fusion that people should be aware of?
- DennisP 9y ago
  Concern about tritium leaks, the need for tritium breeding which limits how fast you can build new reactors, hard neutron radiation that theoretically could be used to breed fissiles (but only if you have a high-enough tritium breeding ratio to keep the reactor fueled, despite not using all your neutrons for that), and the need for a steam turbine, which means you're not going to achieve the extremely low costs that may be achievable with aneutronic fusion. Which doesn't mean D-T is hopeless, just not as good as aneutronic. I've seen fusion scientists say the waste from D-T reactors would only need to be contained for several decades.
  - ZenoArrow 9y ago
    > "the need for a steam turbine" Where's the steam turbine in the following fusion approach? https://en.wikipedia.org/wiki/Dense_plasma_focus https://en.wikipedia.org/wiki/Dense_plasma_focus https://lppfusion.com/fusion-power/dpf-device/ https://lppfusion.com/fusion-power/dpf-device/
    - DennisP 9y ago
      Exactly, that one's aneutronic.
      - ZenoArrow 9y ago
        It can use both D-T and pB11. The majority of tests to date have been with D-T. It's best not to confuse the reactor design with the target fuel.
        DennisP 9y ago
        Actually pure deuterium in the tests so far. But the design explicitly targets boron fusion. If it were adapted to D-T, then it would in fact need a steam turbine. The great thing about pB11 is that most of the energy output is fast-moving charged particles, and that's not true of D-T.
- IntronExon 9y ago
  Sputtering of the metal in the reactor due to fast neutrons, leading to embrittlement, large amounts of neutron activated waste, and an unreasonable maintenance schedule. Lost energy due to said neutrons. Plus all of what has been said before me by DennisP.
simias 9y ago
>1. ITER is a political beast, not a practical one. Can you expand on that? Whose politics and for what purpose?
- IntronExon 9y ago
  Sure, these are two good sources for thst. In depth: http://ffden-2.phys.uaf.edu/feb.7.03.pdf http://ffden-2.phys.uaf.edu/feb.7.03.pdf Light: https://www.nytimes.com/2017/03/27/science/fusion-power-plant-iter-france.html https://www.nytimes.com/2017/03/27/science/fusion-power-plan... In short it was originally Cold War politics to get some international cooperation going around energy. Over time it morphed into a pissing/$$$ contest between nations involved.
- loopbit 9y ago
  I'm not an expert and all of this happened almost 20 years ago, but I do remember avidly reading about ITER around 2001-2003, when the project was more or less agreed between all parties. Wikipedia[0] has a short paragraph on the history and I'd say that any project involving so many different countries and governments (and bureaucracies!) is a red-tape hell. Just choosing the location was a long and difficult process[1]. Canada proposed a location but later pulled out, Japan put a lot of pressure to get it built there. Even within Europe it caused a political "war" between France and Spain, both proposing different sites. First the EU decided to back France and it was finally agreed upon as the final location. From what I remember, many people complained about the decision. Japan felt left out and was offered 20% of the research personnel. The infrastructures in France had to be built from the ground up even before the actual work to build the plant could start, the area didn't even have big enough roads to bring all the materials, which in turn delayed the works and increased the costs (something that wouldn't have happened in Spain or Japan, no idea about Canada). [0] https://en.wikipedia.org/wiki/ITER#Organization_history https://en.wikipedia.org/wiki/ITER#Organization_history [1] https://en.wikipedia.org/wiki/ITER#Location https://en.wikipedia.org/wiki/ITER#Location
DennisP 9y ago
There are several aneutronic fusion projects. The biggest is Tri Alpha, with over $500 million invested. They proved stable plasma in 2015 at 10 million degrees, and just completed a new reactor they plan to take to 100 million degrees; according to their model, the plasma should get more stable at higher temperatures. If it turns out that way, pumping up the heating to boron fusion temperatures is relatively simple, and they have a straightforward path to a practical reactor in 2025 or so. (Source: recent articles plus a presentation I saw from one of their people in 2016) There's a group that thinks a sufficiently powerful petawatt picosecond laser could ignite fusion in a block of boron fuel. This will be testable with an off-the-shelf laser before long; these lasers are improving by a factor of ten every three years. YCombinator has an investment in Helion, which is working on a hybrid D-D/D-He3 reactor (the He3 comes from the D-D reactions), saying only 6% of the energy would be released as neutron radiation. Plus there's LPP, a tiny dark-horse project that will finally get a decent test of their idea this year.
- IntronExon 9y ago
  Like you, I’m hoping for an unforeseen breakthrough, but it seems very unlikely anytime soon. Just containing such an energetic plasma for any length of time past ignition is going to require it’s own set of breakthroughs in materials and manipulation of magnetic fields.
  - DennisP 9y ago
    The temperature would be very high but the amount of energy wouldn't necessarily be remarkable. And for the pulsed designs (laser and LPP), containment time isn't a concern.

ZenoArrow 9y ago

Regarding point 2, the only drawback I'm aware of with D-T fusion is that it still produces nuclear waste (whereas aneutronic fusion produces zero/close to zero nuclear waste), however the nuclear waste produced by D-T fusion is said to be: * Smaller in size than the nuclear waste produced by the current approaches to nuclear fission. * Has a shorter half life than spent nuclear fission fuel, meaning that it doesn't take as long before it's safe to take it out of storage. Aside from nuclear waste, are there other drawbacks to D-T fusion that people should be aware of?

DennisP 9y ago
Concern about tritium leaks, the need for tritium breeding which limits how fast you can build new reactors, hard neutron radiation that theoretically could be used to breed fissiles (but only if you have a high-enough tritium breeding ratio to keep the reactor fueled, despite not using all your neutrons for that), and the need for a steam turbine, which means you're not going to achieve the extremely low costs that may be achievable with aneutronic fusion. Which doesn't mean D-T is hopeless, just not as good as aneutronic. I've seen fusion scientists say the waste from D-T reactors would only need to be contained for several decades.
- ZenoArrow 9y ago
  > "the need for a steam turbine" Where's the steam turbine in the following fusion approach? https://en.wikipedia.org/wiki/Dense_plasma_focus https://en.wikipedia.org/wiki/Dense_plasma_focus https://lppfusion.com/fusion-power/dpf-device/ https://lppfusion.com/fusion-power/dpf-device/
  - DennisP 9y ago
    Exactly, that one's aneutronic.
    - ZenoArrow 9y ago
      It can use both D-T and pB11. The majority of tests to date have been with D-T. It's best not to confuse the reactor design with the target fuel.
      - DennisP 9y ago
        Actually pure deuterium in the tests so far. But the design explicitly targets boron fusion. If it were adapted to D-T, then it would in fact need a steam turbine. The great thing about pB11 is that most of the energy output is fast-moving charged particles, and that's not true of D-T.
IntronExon 9y ago
Sputtering of the metal in the reactor due to fast neutrons, leading to embrittlement, large amounts of neutron activated waste, and an unreasonable maintenance schedule. Lost energy due to said neutrons. Plus all of what has been said before me by DennisP.

simias 9y ago

>1. ITER is a political beast, not a practical one. Can you expand on that? Whose politics and for what purpose?

IntronExon 9y ago
Sure, these are two good sources for thst. In depth: http://ffden-2.phys.uaf.edu/feb.7.03.pdf http://ffden-2.phys.uaf.edu/feb.7.03.pdf Light: https://www.nytimes.com/2017/03/27/science/fusion-power-plant-iter-france.html https://www.nytimes.com/2017/03/27/science/fusion-power-plan... In short it was originally Cold War politics to get some international cooperation going around energy. Over time it morphed into a pissing/$$$ contest between nations involved.
loopbit 9y ago
I'm not an expert and all of this happened almost 20 years ago, but I do remember avidly reading about ITER around 2001-2003, when the project was more or less agreed between all parties. Wikipedia[0] has a short paragraph on the history and I'd say that any project involving so many different countries and governments (and bureaucracies!) is a red-tape hell. Just choosing the location was a long and difficult process[1]. Canada proposed a location but later pulled out, Japan put a lot of pressure to get it built there. Even within Europe it caused a political "war" between France and Spain, both proposing different sites. First the EU decided to back France and it was finally agreed upon as the final location. From what I remember, many people complained about the decision. Japan felt left out and was offered 20% of the research personnel. The infrastructures in France had to be built from the ground up even before the actual work to build the plant could start, the area didn't even have big enough roads to bring all the materials, which in turn delayed the works and increased the costs (something that wouldn't have happened in Spain or Japan, no idea about Canada). [0] https://en.wikipedia.org/wiki/ITER#Organization_history https://en.wikipedia.org/wiki/ITER#Organization_history [1] https://en.wikipedia.org/wiki/ITER#Location https://en.wikipedia.org/wiki/ITER#Location

DennisP 9y ago

There are several aneutronic fusion projects. The biggest is Tri Alpha, with over $500 million invested. They proved stable plasma in 2015 at 10 million degrees, and just completed a new reactor they plan to take to 100 million degrees; according to their model, the plasma should get more stable at higher temperatures. If it turns out that way, pumping up the heating to boron fusion temperatures is relatively simple, and they have a straightforward path to a practical reactor in 2025 or so. (Source: recent articles plus a presentation I saw from one of their people in 2016) There's a group that thinks a sufficiently powerful petawatt picosecond laser could ignite fusion in a block of boron fuel. This will be testable with an off-the-shelf laser before long; these lasers are improving by a factor of ten every three years. YCombinator has an investment in Helion, which is working on a hybrid D-D/D-He3 reactor (the He3 comes from the D-D reactions), saying only 6% of the energy would be released as neutron radiation. Plus there's LPP, a tiny dark-horse project that will finally get a decent test of their idea this year.

IntronExon 9y ago
Like you, I’m hoping for an unforeseen breakthrough, but it seems very unlikely anytime soon. Just containing such an energetic plasma for any length of time past ignition is going to require it’s own set of breakthroughs in materials and manipulation of magnetic fields.
- DennisP 9y ago
  The temperature would be very high but the amount of energy wouldn't necessarily be remarkable. And for the pulsed designs (laser and LPP), containment time isn't a concern.