6 ms·

> What's the catch this time? This is D-T fusion. Which means you have to have T. Which currently comes from fission reactor and has a half life of 15 years.

> What's the catch this time? This is D-T fusion. Which means you have to have T. Which currently comes from fission reactor and has a half life of 15 years. So the plan is to use a molten salt blanket with Be to breed T. But Be isn’t scalable for consumption, so maybe lead eventually. That’s probably do-able, it just slows down the rate new reactors can come online since Pb is not as good a neutron multiplier. Once they breed extra T, they have to capture and refine it. Hydrogen is very corrosive and hard to work with… and T is radioactive hydrogen. Again, probably doable. But guess what? Refining spent nuclear waste in fission reactors is also do-able. It’s also super expensive. And they still need a containment vessel that will withstand the wear and tear from sitting next to a mini hydrogen bomb all day. These challenges are likely all surmountable. But are they surmountable AND cheaper than existing nuclear or other energy sources? Meh?

rnhmjoj 5y ago
> But are they surmountable AND cheaper than existing nuclear or other energy sources? DT fusion solves the two biggest arguments that are always raised by nuclear energy opponents: storage of nuclear waste (it doesn't produce high-level waste) and safety (it's not perfect but it can't explode). I wouldn't call it a "meh", even if it comes off as much more expensive than fission.
- danans 5y ago
  > I wouldn't call it a "meh", even if it comes off as much more expensive than fission. It's not competing with fission, though. It's competing with renewables + storage + load shifting + efficiency. Compared to those, it might indeed be "meh".
  - rnhmjoj 5y ago
    Agreed, but grid and storage technology that will completely solve the renewable intermittence is probably as far in the future as commercial fusion reactors.
    - pfdietz 5y ago
      This is a gross mischaracterization of the situation. There are a wide variety of energy storage schemes that promise to make renewables + storage cheaper than fission, which in turn is likely to be much cheaper than fusion. Simply dumping excess renewable power into a resistively heated thermal mass and using that to drive a power plant is likely to be cheaper than fusion.
    - ncmncm 5y ago
      The only open question about large-scale energy storage is which of many viable alternatives will turn out cheapest, and when their price will bottom out. Battery storage that starts at 1/3 of lithium cost, before price begins to fall, is coming to market. Until prices do start to bottom out, investment in storage is wasteful, so dollars go to generating capacity of known utility. Each square meter of panel that goes online delays climate disaster by a precisely understood amount. Each panel made can go into service almost instantly. No matter how big the project, it can start delivering power anytime. There is no smallest-useful facility, right down to the residential rooftop. Every dollar diverted to Tokamak instead brings climate disaster nearer.
      - deleted 5y ago
        [deleted]
  - UnFleshedOne 5y ago
    In the grid this would take role of coal or gas plants for base load, no?
    - danans 5y ago
      Storage at sufficient scale would supply some of what we refer to as baseload today, much as hydro provides baseload power in many places today.
  - r00fus 5y ago
    For terrestrial operations, sure. But we need to either overcome shielding hurdles with fission or have relatively portable fusion if we're really going to explore our solar system or the stars. Renewables are key to having a sustainable energy economy. Fusion power is what will let us do the drastic things to recover from climate disaster that is already here.
  - jonnycomputer 5y ago
    I am generally in support of solar and wind. But then, people underestimate the environmental destruction those can entail, depending on the site. Yesterday, I saw a hillside in a very rural part of Appalachia covered in solar panels. Nothing grew on the hill. Because, you know, plants would cover up the panels in no-time, so you have to vigorously keep all of it in check, with herbicides. Aside from the loss of potential carbon storage from allowing trees to grow on the hillside, which very well might offset any carbon-related gains from using solar, it's just bad for the ecology (which is exceedingly rich in the vicinity). Any farm typical for the area would be multiples of times better. This is not intended as a rant against solar (again, I'm an enthusiastic supporter), but I'd guess a landscape of fusion generators would take fewer square meters of land than the equivalent using solar. And that is nothing to scoff at.
    - danans 5y ago
      > Aside from the loss of potential carbon storage from allowing trees to grow on the hillside, which very well might offset any carbon-related gains from using solar, It is incredibly unlikely to offset the carbon related gains of solar, because the carbon sequestration efficiency of plants and trees is very low to begin with, far lower than solar's capacity to displace carbon emitted from coal when area is held constant. Sure, it's better to put the solar where there is no existing tree cover, but it seems like most of Appalachia is covered in trees.
      - jonnycomputer 5y ago
        which it should be. carbon is not the only environmental issue we face. appalachia is the main channel of animal migration. its incredible. we should do all we can to protect it's integrity.
        danans 5y ago
        > which it should be. Solar power will never need to remove more than a tiny fraction of tree cover from Appalachia. What's a far bigger threat to the ecosystem, including animal migration, is mountaintop removal for coal mining: https://law.lclark.edu/live/blogs/134-de-regulation-of-mountain-top-removal-mining- https://law.lclark.edu/live/blogs/134-de-regulation-of-mount...
- speed_spread 5y ago
  It sounds like the T production chain might itself be quite messy. Molten isotopes salt and lead? How much of that stuff would you need? What do you do with when it goes bad? It may not go boom Chernobyl-style, but it's still far from the birds-in-the-sky deuterium-from-the-sea fusion dream.
  - scythe 5y ago
    The bad zone of radioactive byproducts is the half life between 10 and 1000000 years. Shorter and you can wait it out. Longer and the activity is low enough to ignore when it's spread out. When designing a fusion reactor, you can usually choose components that won't generate these undesirable nuclides. But in fission, many products are generated, so persistent contamination is practically impossible to avoid.
  - rnhmjoj 5y ago
    > It sounds like the T production chain might itself be quite messy. It is: it's definitely the biggest challenge after plasma confinement. > Molten isotopes salt and lead? There are two main blanket technology in development: ceramic and liquid breeders. They're called breeders but are very different from the kind of breeders you have in a fission reactor. Both are based on converting lithium to tritium by capturing fusion neutrons, but in one case the lithium is in the form of solid pebbles, while in the other, in a molten mixture of lithium-lead (there are no salts AFAIK). To produce more tritium than you start with you also need a neutron multiplier: beryllium in ceramic breeders and lead in liquid breeders. The problem is beryllium is rare (and also toxic): a 500MW reactor needs ~200 kg/year, which is not a lot, but there's very very little beryllium on earth. If you factor in the initial reactor inventory (170 t/reactor) it turns out ubiquitous fusion energy it's not sustainable if we choose beryllium. If you go with lithium-lead you need more material: 3 t/year (but remember lead is a lot heavier and more common too). If you plan to cover the world energy base load with fusion, you would need a lot of lead (~10% world annual production) but it's doable. For me, the biggest problem right now is lithium: DT fusion needs lots of pure ⁶Li, which is extracted by enriching even more natural lithium. If we're not careful enough with recycling it from old batteries, we are likely to exhaust the world resources in a few decades. > What do you do with when it goes bad? It may not go boom Chernobyl-style, but it's still far from the birds-in-the-sky deuterium-from-the-sea fusion dream. The worst case scenario is still the loss of coolant accident (LoCA). The blanket is exposed to a ~2MW/m² heat load from the plasma (in addition to all kind of radiation), so failing to cool adequately a module means it will very rapidly turns into a (radioactive) molten mess that's not easy to handle. Yeah, it's bad but not nearly as bad as the same accident in a fission reactor.
- mordymoop 5y ago
  I had heard that one of the major drawbacks of tokamaks was the incredible temperatures lead to situations where the smallest mechanical failure will lead to an explosion of hot, radioactive gas. Is that not the case?
  - ncmncm 5y ago
    That would be the least of its problems. Costing hundreds or thousands of times as much as solar + storage is a more serious problem. Since it won't be built, that is a theoretical problem. But the project can absorb an unlimited amount of money first.
  - pas 5y ago
    The whole amount of gas in the chamber is just a few grams. Tritium is not pleasant though, but veeeeeeeeery far from anything that could do real harm: https://en.wikipedia.org/wiki/Tritium#Health_risks https://en.wikipedia.org/wiki/Tritium#Health_risks (you'd need to leak a lot of it continuously)
  - rnhmjoj 5y ago
    Temperature is not a very good quantity to gain intuition about plasmas (or heat transfer in general): the temperature of the electrons in a incandescent light bulb is around 10000 K, which seems very hot, but since their density is much lower than the air density, the powers involved are quite small and a light bulb is pretty safe to touch. In the same way, a fusion plasma doesn't hold that much energy because of the extremely low density (4×10^-6 that of air). An explosion (a runaway/chain reaction) is also not possible: the reactor must continuously supplied with fuel or the fusion reactions will stop in a matter of seconds. There are situations which could result in significant damage to the reactor components, but still not a public safety concern. Distruptions are events in which the plasma confinement is lost and a large amount of heat is released that could damage all components that face the plasma, but reactors are designed to withstand this. Another drawback, if you like, are runaway electrons, which are populations of relativistic particles that become unbound and penetrare the vacuum vessel for several mm. Again, this is not a particular issue from a safety point of view, but they can do a lot of damage: if they hit a magnetic coil and cause a loss of the superconductivity state, the coil can heat very rapidily (due to the huge current that goes through it) and potentially melt. Replacing such a coil could cost years of maintenance, for this reason reactors are build with many fallback systems.
- baybal2 5y ago
  > storage of nuclear waste (it doesn't produce high-level waste) It does. You cannnot fuse just D+T, other trace gasses, and lighter isotopes will be present as well.
  - rnhmjoj 5y ago
    No, it doesn't in any significant quantity [1]. Besides, there are practically no high Z elements in a fusion plasma. That's because they emit bremsstrahlung radiation (power grows like Z²) and rapidly cool off the plasma. If the reaction is to be self-sustained, the plasma charge averaged over the density (Zeff) must be kept as close as possible to 1. Considering that there's only a few grams of material in a full reactor, there are virtually no heavy elements. The radiative losses do exist, but are caused by detached atoms from the plasma facing components. Everything close to the plasma is made of light elements and specifically chosen to not produce dangerous radioisotopes when neutron activated: no high-level waste materials, meaning the half-life is lower that 10 years and they can be recycled in around 100 years. [1]: http://www.iter.org/faq#Can_you_declare_fusion_is_really_safe_while_it_uses_huge_amount_of_tritium_generates_strong_neutrons_and_brings_about_huge_amount_of_radiological_waste_ http://www.iter.org/faq#Can_you_declare_fusion_is_really_saf...
- nickik 5y ago
  Very questionable if a fusion reactor is safer then a common molten salt fission reactor. I would argue that is far less likely to 'explode'. And you can burn up the waste majority of that waste, the leftover waste after that would not really a huge issue. Both of these are far more political problems then actual real problems a society based on modern fission would have.
  - Symmetry 5y ago
    The problem with fission reactors in general is that after you stop the chain reaction you've still got a tenth or so of the power output you had when it was on from decay heat for a while and you need a reliable way to get rid of that heat even in the event of a disaster. With fusion the nice thing is that the new heat stops appearing as soon as the reaction stops.
    - nickik 5y ago
      Yes and that is far easier to do then containing a fusion reaction. There are known well understood engineering solution that have been known since the 70s and that work fine. The real danger is the high pressure that PWR are under and the chemical instability of the elements that were put together in those designs. Reactors that are not under pressure and do not have chemical instability that lead to explosive cases have a very contained area of effect even in a worst case.
- lambdatronics 5y ago
  Yeah, but nuclear energy opponents aren't the reason fission isn't getting built -- it's primarily about the cost.
OJFord 5y ago
> This is D-T fusion. Which means you have to have T. For the other uninitiated, (or far enough out of secondary school and didn't take it further!) this seems to refer to Deuterium-Tritium fusion, D & T being the isotopes of hydrogen with an atomic mass of 2 (1 neutron, 'heavy' but stable) and 3 (2 neutrons, radioactive) respectively.
worldvoyageur 5y ago
Tritium is a natural byproduct of CANDU fusion reactors, of which there are some 25 or so in operation globally, mostly in Canada. CANDUs use heavy water as a neutron moderator (D20 instead of H2O), making T2O a natural byproduct. Though most of the reactors do not harvest the tritium, a small number do. CANDU operators have long been ready to make the capital investments in tritium harvesting, once demand materializes. ITER has long been seen as a potential major source of tritium demand.
- anonuser123456 5y ago
  I think the SPARC guys are going to eat all the CANDU tritium before ITER ever gets a chance light up. If we have to scale up fission reactors to produce enough tritium to scale fusion reactors, then don't need the fusion reactors.
  - mlindner 5y ago
    Tritium only has a half life of 12 years. It's not like there's stockpiles of the stuff. It's constantly being produced. Also as mentioned up thread, they'll breed their own Tritium.
- codesnik 5y ago
  (you probably meant to write "CANDU fission reactors")
- snek_case 5y ago
  I'm wondering, fusion reactors themselves produce neutron radiation as a byproduct. Once you have a fusion reactor running, could you use the fusion reactor itself to breed tritium? Also thinking, we target deuterium + tritium fusion because it's the least energy intensive. However, once we have working proof of concept reactors, could we just make them slightly bigger and fuse more abundant molecules/isotopes instead?
  - carbonguy 5y ago
    > Once you have a fusion reactor running, could you use the fusion reactor itself to breed tritium? I'll have to find the citation, but IIRC the answer is "theoretically, yes" - the concept is that molten lithium could be used in a tokamak to absorb neutrons and produce tritium at the same time. EDIT: Here are two citations I was able to find quickly - it looks like one of the ITER experiments will be to validate the concept [1] and that this could also be the way that heat is removed from the reactor. [2] [1] iter.org/mach/TritiumBreeding [2] https://www.euro-fusion.org/faq/top-twenty-faq/what-is-a-lithium-blanket-and-how-does-it-work/ https://www.euro-fusion.org/faq/top-twenty-faq/what-is-a-lit...
mcswell 5y ago
"Hydrogen is very corrosive and hard to work with" Corrosive compared to what? You can put it in a rubber balloon and hand it to a kid. "T is radioactive hydrogen": True, it emits low energy beta radiation, which is an electron, and is stopped by a sheet of paper. I used to have a wrist watch with a tritium dial; I haven't died of cancer yet.
- snek_case 5y ago
  Corrosive is the wrong word, but hydrogen is such a small molecule, it can leak through metals and weaken them, as I understand it. It's hard to contain. https://www.imetllc.com/hydrogen-embrittlement-steel/ https://www.imetllc.com/hydrogen-embrittlement-steel/
- GordonS 5y ago
  > Corrosive compared to what? You can put it in a rubber balloon and hand it to a kid. I've never heard of hydrogen-filled balloons (at least not the kind of balloon you can hand to a kid) - we're you thinking of helium?
  - bjowen 5y ago
    It’s a high-school level laboratory experiment. Nobody’s handing them out at birthday parties[0], but mostly because hydrogen likes to go bang loudly, not because it’s corrosive or toxic or anything. [0] unless Mark Rober is involved in some way.
  - mcswell 5y ago
    I know about helium balloons, but hydrogen is really cheap compared to helium. And it's nowhere near as dangerous as it's made out to be. The Hindenburg burned, it did not explode.
eloff 5y ago
I'm not sure if it would be cheaper, but the potential could be there if there's enough innovation in the space. At least in happy we're exploring all paths and not betting the farm on just one.

rnhmjoj 5y ago

> But are they surmountable AND cheaper than existing nuclear or other energy sources? DT fusion solves the two biggest arguments that are always raised by nuclear energy opponents: storage of nuclear waste (it doesn't produce high-level waste) and safety (it's not perfect but it can't explode). I wouldn't call it a "meh", even if it comes off as much more expensive than fission.

danans 5y ago
> I wouldn't call it a "meh", even if it comes off as much more expensive than fission. It's not competing with fission, though. It's competing with renewables + storage + load shifting + efficiency. Compared to those, it might indeed be "meh".
- rnhmjoj 5y ago
  Agreed, but grid and storage technology that will completely solve the renewable intermittence is probably as far in the future as commercial fusion reactors.
  - pfdietz 5y ago
    This is a gross mischaracterization of the situation. There are a wide variety of energy storage schemes that promise to make renewables + storage cheaper than fission, which in turn is likely to be much cheaper than fusion. Simply dumping excess renewable power into a resistively heated thermal mass and using that to drive a power plant is likely to be cheaper than fusion.
  - ncmncm 5y ago
    The only open question about large-scale energy storage is which of many viable alternatives will turn out cheapest, and when their price will bottom out. Battery storage that starts at 1/3 of lithium cost, before price begins to fall, is coming to market. Until prices do start to bottom out, investment in storage is wasteful, so dollars go to generating capacity of known utility. Each square meter of panel that goes online delays climate disaster by a precisely understood amount. Each panel made can go into service almost instantly. No matter how big the project, it can start delivering power anytime. There is no smallest-useful facility, right down to the residential rooftop. Every dollar diverted to Tokamak instead brings climate disaster nearer.
    - deleted 5y ago
      [deleted]
- UnFleshedOne 5y ago
  In the grid this would take role of coal or gas plants for base load, no?
  - danans 5y ago
    Storage at sufficient scale would supply some of what we refer to as baseload today, much as hydro provides baseload power in many places today.
- r00fus 5y ago
  For terrestrial operations, sure. But we need to either overcome shielding hurdles with fission or have relatively portable fusion if we're really going to explore our solar system or the stars. Renewables are key to having a sustainable energy economy. Fusion power is what will let us do the drastic things to recover from climate disaster that is already here.
- jonnycomputer 5y ago
  I am generally in support of solar and wind. But then, people underestimate the environmental destruction those can entail, depending on the site. Yesterday, I saw a hillside in a very rural part of Appalachia covered in solar panels. Nothing grew on the hill. Because, you know, plants would cover up the panels in no-time, so you have to vigorously keep all of it in check, with herbicides. Aside from the loss of potential carbon storage from allowing trees to grow on the hillside, which very well might offset any carbon-related gains from using solar, it's just bad for the ecology (which is exceedingly rich in the vicinity). Any farm typical for the area would be multiples of times better. This is not intended as a rant against solar (again, I'm an enthusiastic supporter), but I'd guess a landscape of fusion generators would take fewer square meters of land than the equivalent using solar. And that is nothing to scoff at.
  - danans 5y ago
    > Aside from the loss of potential carbon storage from allowing trees to grow on the hillside, which very well might offset any carbon-related gains from using solar, It is incredibly unlikely to offset the carbon related gains of solar, because the carbon sequestration efficiency of plants and trees is very low to begin with, far lower than solar's capacity to displace carbon emitted from coal when area is held constant. Sure, it's better to put the solar where there is no existing tree cover, but it seems like most of Appalachia is covered in trees.
    - jonnycomputer 5y ago
      which it should be. carbon is not the only environmental issue we face. appalachia is the main channel of animal migration. its incredible. we should do all we can to protect it's integrity.
      - danans 5y ago
        > which it should be. Solar power will never need to remove more than a tiny fraction of tree cover from Appalachia. What's a far bigger threat to the ecosystem, including animal migration, is mountaintop removal for coal mining: https://law.lclark.edu/live/blogs/134-de-regulation-of-mountain-top-removal-mining- https://law.lclark.edu/live/blogs/134-de-regulation-of-mount...
speed_spread 5y ago
It sounds like the T production chain might itself be quite messy. Molten isotopes salt and lead? How much of that stuff would you need? What do you do with when it goes bad? It may not go boom Chernobyl-style, but it's still far from the birds-in-the-sky deuterium-from-the-sea fusion dream.
- scythe 5y ago
  The bad zone of radioactive byproducts is the half life between 10 and 1000000 years. Shorter and you can wait it out. Longer and the activity is low enough to ignore when it's spread out. When designing a fusion reactor, you can usually choose components that won't generate these undesirable nuclides. But in fission, many products are generated, so persistent contamination is practically impossible to avoid.
- rnhmjoj 5y ago
  > It sounds like the T production chain might itself be quite messy. It is: it's definitely the biggest challenge after plasma confinement. > Molten isotopes salt and lead? There are two main blanket technology in development: ceramic and liquid breeders. They're called breeders but are very different from the kind of breeders you have in a fission reactor. Both are based on converting lithium to tritium by capturing fusion neutrons, but in one case the lithium is in the form of solid pebbles, while in the other, in a molten mixture of lithium-lead (there are no salts AFAIK). To produce more tritium than you start with you also need a neutron multiplier: beryllium in ceramic breeders and lead in liquid breeders. The problem is beryllium is rare (and also toxic): a 500MW reactor needs ~200 kg/year, which is not a lot, but there's very very little beryllium on earth. If you factor in the initial reactor inventory (170 t/reactor) it turns out ubiquitous fusion energy it's not sustainable if we choose beryllium. If you go with lithium-lead you need more material: 3 t/year (but remember lead is a lot heavier and more common too). If you plan to cover the world energy base load with fusion, you would need a lot of lead (~10% world annual production) but it's doable. For me, the biggest problem right now is lithium: DT fusion needs lots of pure ⁶Li, which is extracted by enriching even more natural lithium. If we're not careful enough with recycling it from old batteries, we are likely to exhaust the world resources in a few decades. > What do you do with when it goes bad? It may not go boom Chernobyl-style, but it's still far from the birds-in-the-sky deuterium-from-the-sea fusion dream. The worst case scenario is still the loss of coolant accident (LoCA). The blanket is exposed to a ~2MW/m² heat load from the plasma (in addition to all kind of radiation), so failing to cool adequately a module means it will very rapidly turns into a (radioactive) molten mess that's not easy to handle. Yeah, it's bad but not nearly as bad as the same accident in a fission reactor.
mordymoop 5y ago
I had heard that one of the major drawbacks of tokamaks was the incredible temperatures lead to situations where the smallest mechanical failure will lead to an explosion of hot, radioactive gas. Is that not the case?
- ncmncm 5y ago
  That would be the least of its problems. Costing hundreds or thousands of times as much as solar + storage is a more serious problem. Since it won't be built, that is a theoretical problem. But the project can absorb an unlimited amount of money first.
- pas 5y ago
  The whole amount of gas in the chamber is just a few grams. Tritium is not pleasant though, but veeeeeeeeery far from anything that could do real harm: https://en.wikipedia.org/wiki/Tritium#Health_risks https://en.wikipedia.org/wiki/Tritium#Health_risks (you'd need to leak a lot of it continuously)
- rnhmjoj 5y ago
  Temperature is not a very good quantity to gain intuition about plasmas (or heat transfer in general): the temperature of the electrons in a incandescent light bulb is around 10000 K, which seems very hot, but since their density is much lower than the air density, the powers involved are quite small and a light bulb is pretty safe to touch. In the same way, a fusion plasma doesn't hold that much energy because of the extremely low density (4×10^-6 that of air). An explosion (a runaway/chain reaction) is also not possible: the reactor must continuously supplied with fuel or the fusion reactions will stop in a matter of seconds. There are situations which could result in significant damage to the reactor components, but still not a public safety concern. Distruptions are events in which the plasma confinement is lost and a large amount of heat is released that could damage all components that face the plasma, but reactors are designed to withstand this. Another drawback, if you like, are runaway electrons, which are populations of relativistic particles that become unbound and penetrare the vacuum vessel for several mm. Again, this is not a particular issue from a safety point of view, but they can do a lot of damage: if they hit a magnetic coil and cause a loss of the superconductivity state, the coil can heat very rapidily (due to the huge current that goes through it) and potentially melt. Replacing such a coil could cost years of maintenance, for this reason reactors are build with many fallback systems.
baybal2 5y ago
> storage of nuclear waste (it doesn't produce high-level waste) It does. You cannnot fuse just D+T, other trace gasses, and lighter isotopes will be present as well.
- rnhmjoj 5y ago
  No, it doesn't in any significant quantity [1]. Besides, there are practically no high Z elements in a fusion plasma. That's because they emit bremsstrahlung radiation (power grows like Z²) and rapidly cool off the plasma. If the reaction is to be self-sustained, the plasma charge averaged over the density (Zeff) must be kept as close as possible to 1. Considering that there's only a few grams of material in a full reactor, there are virtually no heavy elements. The radiative losses do exist, but are caused by detached atoms from the plasma facing components. Everything close to the plasma is made of light elements and specifically chosen to not produce dangerous radioisotopes when neutron activated: no high-level waste materials, meaning the half-life is lower that 10 years and they can be recycled in around 100 years. [1]: http://www.iter.org/faq#Can_you_declare_fusion_is_really_safe_while_it_uses_huge_amount_of_tritium_generates_strong_neutrons_and_brings_about_huge_amount_of_radiological_waste_ http://www.iter.org/faq#Can_you_declare_fusion_is_really_saf...
nickik 5y ago
Very questionable if a fusion reactor is safer then a common molten salt fission reactor. I would argue that is far less likely to 'explode'. And you can burn up the waste majority of that waste, the leftover waste after that would not really a huge issue. Both of these are far more political problems then actual real problems a society based on modern fission would have.
- Symmetry 5y ago
  The problem with fission reactors in general is that after you stop the chain reaction you've still got a tenth or so of the power output you had when it was on from decay heat for a while and you need a reliable way to get rid of that heat even in the event of a disaster. With fusion the nice thing is that the new heat stops appearing as soon as the reaction stops.
  - nickik 5y ago
    Yes and that is far easier to do then containing a fusion reaction. There are known well understood engineering solution that have been known since the 70s and that work fine. The real danger is the high pressure that PWR are under and the chemical instability of the elements that were put together in those designs. Reactors that are not under pressure and do not have chemical instability that lead to explosive cases have a very contained area of effect even in a worst case.
lambdatronics 5y ago
Yeah, but nuclear energy opponents aren't the reason fission isn't getting built -- it's primarily about the cost.

OJFord 5y ago

> This is D-T fusion. Which means you have to have T. For the other uninitiated, (or far enough out of secondary school and didn't take it further!) this seems to refer to Deuterium-Tritium fusion, D & T being the isotopes of hydrogen with an atomic mass of 2 (1 neutron, 'heavy' but stable) and 3 (2 neutrons, radioactive) respectively.

worldvoyageur 5y ago

Tritium is a natural byproduct of CANDU fusion reactors, of which there are some 25 or so in operation globally, mostly in Canada. CANDUs use heavy water as a neutron moderator (D20 instead of H2O), making T2O a natural byproduct. Though most of the reactors do not harvest the tritium, a small number do. CANDU operators have long been ready to make the capital investments in tritium harvesting, once demand materializes. ITER has long been seen as a potential major source of tritium demand.

anonuser123456 5y ago
I think the SPARC guys are going to eat all the CANDU tritium before ITER ever gets a chance light up. If we have to scale up fission reactors to produce enough tritium to scale fusion reactors, then don't need the fusion reactors.
- mlindner 5y ago
  Tritium only has a half life of 12 years. It's not like there's stockpiles of the stuff. It's constantly being produced. Also as mentioned up thread, they'll breed their own Tritium.
codesnik 5y ago
(you probably meant to write "CANDU fission reactors")
snek_case 5y ago
I'm wondering, fusion reactors themselves produce neutron radiation as a byproduct. Once you have a fusion reactor running, could you use the fusion reactor itself to breed tritium? Also thinking, we target deuterium + tritium fusion because it's the least energy intensive. However, once we have working proof of concept reactors, could we just make them slightly bigger and fuse more abundant molecules/isotopes instead?
- carbonguy 5y ago
  > Once you have a fusion reactor running, could you use the fusion reactor itself to breed tritium? I'll have to find the citation, but IIRC the answer is "theoretically, yes" - the concept is that molten lithium could be used in a tokamak to absorb neutrons and produce tritium at the same time. EDIT: Here are two citations I was able to find quickly - it looks like one of the ITER experiments will be to validate the concept [1] and that this could also be the way that heat is removed from the reactor. [2] [1] iter.org/mach/TritiumBreeding [2] https://www.euro-fusion.org/faq/top-twenty-faq/what-is-a-lithium-blanket-and-how-does-it-work/ https://www.euro-fusion.org/faq/top-twenty-faq/what-is-a-lit...

mcswell 5y ago

"Hydrogen is very corrosive and hard to work with" Corrosive compared to what? You can put it in a rubber balloon and hand it to a kid. "T is radioactive hydrogen": True, it emits low energy beta radiation, which is an electron, and is stopped by a sheet of paper. I used to have a wrist watch with a tritium dial; I haven't died of cancer yet.

snek_case 5y ago
Corrosive is the wrong word, but hydrogen is such a small molecule, it can leak through metals and weaken them, as I understand it. It's hard to contain. https://www.imetllc.com/hydrogen-embrittlement-steel/ https://www.imetllc.com/hydrogen-embrittlement-steel/
GordonS 5y ago
> Corrosive compared to what? You can put it in a rubber balloon and hand it to a kid. I've never heard of hydrogen-filled balloons (at least not the kind of balloon you can hand to a kid) - we're you thinking of helium?
- bjowen 5y ago
  It’s a high-school level laboratory experiment. Nobody’s handing them out at birthday parties[0], but mostly because hydrogen likes to go bang loudly, not because it’s corrosive or toxic or anything. [0] unless Mark Rober is involved in some way.
- mcswell 5y ago
  I know about helium balloons, but hydrogen is really cheap compared to helium. And it's nowhere near as dangerous as it's made out to be. The Hindenburg burned, it did not explode.

eloff 5y ago

I'm not sure if it would be cheaper, but the potential could be there if there's enough innovation in the space. At least in happy we're exploring all paths and not betting the farm on just one.