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Neutrons make hardware radioactive. Many on Hacker News fantasize about fusion (not fission) reactors. These fusion reactors will be an intense source of fast

Neutrons make hardware radioactive. Many on Hacker News fantasize about fusion (not fission) reactors. These fusion reactors will be an intense source of fast neutrons. All the hardware in a fusion reactor will become radioactive. Not to mention the gamma rays. If you have to deal with radioactive materials, why not just use fission? After 70 years of working with fission reactors, we know how to build and operate them at 95%+ efficiency. Fission can provide all the power we need. Today there are 440 nuclear fission reactors operating in 32 countries. 20% of America's grid power comes from nuclear fission. If you want to develop energy technology, focus on improving fission. For example, TRISO fuel (https://news.ycombinator.com/item?id=41898377 https://news.ycombinator.com/item?id=41898377) or what Lightbridge is doing (https://www.ltbridge.com/lightbridge-fuel https://www.ltbridge.com/lightbridge-fuel). Hacker News is hostile to fission and defeatist (unable to contemplate innovation in fission technology) but this attitude will gradually change. Quoting John Carmack: "Deuterium fusion would give us a cheap and basically unlimited fuel source with a modest waste stream, but it is an almost comically complex and expensive way to generate heat compared to fission, which is basically 'put these rocks next to each other and they get hot'."

raverbashing 2y ago
Fission is "simple" but it seems every designer in the XX century made it as much complicated as possible for not so great reasons (and don't even get me started on the "let's not use breeding reactors" stuff) Cooling that requires pumps, as an example, should be a non-starter in new projects.
- rob74 2y ago
  The designs are complicated, well, because in practice it's not as simple as "put these rocks next to each other and they get hot". When you put the rocks next to each other, they not only get hot, but also emit some nasty radiation that has to be shielded. And if the rocks get a liiiitle bit too close together, they might explode, which leads to huge headaches for everyone involved, so you'd better make sure that doesn't happen...
  - meindnoch 2y ago
    >And if the rocks get a liiiitle bit too close together, they might explode Impossible. Worst thing that can happen without carefully designed explosive lens is a nuclear fizzle.
    - empath75 2y ago
      There are lots of ways that nuclear plants can explode or fail in otherwise catastrophic ways, it doesn't need to be an atomic explosion.
      - meindnoch 2y ago
        Parent was alluding to a nuclear explosion, not a steam explosion or other type of explosion. Other kinds of explosions have nothing to do with the fissile material ("rocks" in their parlance) being "too close together". Steam explosions in particular are caused by boiling water, due to increased reactor power, or inadequate circulation of coolant. In a nuclear reactor, the fuel cells are held in a fixed matrix, and are not moving an inch closer to each other, whether the reactor is operating normally, or a steam explosion is imminent. In general, nobody was disputing the possibility of steam explosions, or other type of failures at nuclear power plants, thus your comment is besides the point, and irrelevant to this subthread.
- SoftTalker 2y ago
  Weapons proliferation concerns is/was the reason fission power is so complicated.
elashri 2y ago
> we know how to build and operate them at 95%+ efficiency. Fission can provide all the power we need. I am not sure what do you mean by 95%+ efficency here. But if you are talking about the entire process of getting the energy/power from the nuclear reactor this is not possible. You are still limited by carnot cycle. Even the most advanced reactors like HTGRs [1] operate with efficiency about 45%. If you have some other definition of efficiency than the standard then it would be good if you define that. [1] https://en.wikipedia.org/wiki/High-temperature_gas-cooled_reactor https://en.wikipedia.org/wiki/High-temperature_gas-cooled_re...
- atomic128 2y ago
  See discussion of "capacity factor" here: https://news.ycombinator.com/item?id=41858892 https://news.ycombinator.com/item?id=41858892 It's the same as when we talk about the efficiency of a GEMM kernel on a particular piece of hardware. As efficiency approaches 100% the kernel is saturating the hardware's capacity to perform multiply/add.
  - howenterprisey 2y ago
    The term "capacity factor" should generally always be used for that concept, because "efficiency" has its own, different, meaning for power plants.
  - deleted 2y ago
    [deleted]
cosmic_quanta 2y ago
> Neutrons make hardware radioactive True, but two caveats: 1. Neutron bombardment due to fusion makes hardware radioactive for less than 10 years, which isn't great but does not compare to fission waste; 2. Some fusion processes don't emit neutrons (aneutronic fusion). As I understand it, these processes aren't as efficient, but there is the possibility of a tradeoff between generation of ratioactive waste vs. efficiency.
- khuey 2y ago
  Aneutronic fusion is even harder than regular fusion so it's not a realistic solution in any near-term scenario.
  - Symmetry 2y ago
    It has the advantage that the energy it gives off can be be converted directly to electrical energy rather than driving an external heat engine, so despite the greater difficulty of ignition its not obviously a worse choice.
  - fusionadvocate 2y ago
    That is incorrect. Recent advances using attosecond lasers enable new tricks and fusion conditions to be realized tabletop. Search also for plasmonics. Using nano antennas and intense lasers to accelerate protons and electrons in a tabletop device (previously required large machines).
    - ben_w 2y ago
      Fusors already enabled desktop fusion reactors, literally high school science fair projects even a couple of decades back. What stops Fusors and Polywells from having already given us this decades ago with P-B11 etc. is that the cross section for fusing is so much lower than the cross section for elastic scattering, and that elastic scattering loses so much energy to EM via bremsstrahlung.
- adrian_b 2y ago
  > Neutron bombardment due to fusion makes hardware radioactive for less than 10 years Very false. The current design target for fusion reactors is that the materials taken out of the reactor should become "low-level radioactive waste" after being stored for one hundred years. It is acknowledged however that it is likely that a small fraction of the materials will not satisfy the criteria for "low-level radioactive waste" even after one thousand years. For example it is extremely difficult to avoid using carbon in the reactor. Besides various kinds of steels used in reactor components there are now some proposals to replace the tungsten used in the plasma-facing surface with some carbides, for increased endurance. Carbon 14 remains radioactive for thousands of years. There are many commonly used materials for which substitutes must be developed, e.g. new alloys, because otherwise they would produce radioactive isotopes with lifetimes of tens of thousands of years, e.g. there are efforts to develop some stainless steels with chromium and tungsten as a replacement for the normally used steels with chromium and molybdenum, which would generate long-lived radioactive waste. See e.g. the UK governmental report: https://assets.publishing.service.gov.uk/media/61ae4caa8fa8f503780c1ce9/radioactive-wastes-from-fusion-energy-corwm3735-preliminary-paper.pdf https://assets.publishing.service.gov.uk/media/61ae4caa8fa8f...
lupusreal 2y ago
The only hard part of dealing with nuclear waste is the social aspect. If not for that, you can simply and safely dump it into the ocean. Water is excellent shielding and the amount of uranium/etc already dissolved in sea water is absurd. Put it in a stainless steel vessel first if you want most of it to decay before coming into contact with the water, but that's not even necessary.
- perihelions 2y ago
  That doesn't really work because marine life is good at filtering and concentrating a subset of the elements that are in spent nuclear fuel. There are already ocean fish that are too poisonous too safely eat because of (coal-emitted) mercury pollution—and that's only 100,000 tons of mercury, total, in the history of human industry [0]. If you dig in to the hard numbers surrounding spent fuel, it's a much, much more toxic and difficult problem than mercury—diluting it in the oceans is a complete non-starter. [0] https://en.wikipedia.org/wiki/Marine_mercury_pollution https://en.wikipedia.org/wiki/Marine_mercury_pollution
  - meindnoch 2y ago
    Mercury from burning coal is an extremely dilute pollutant. There's zero hope for capturing and containing it. Nuclear waste in contrast is literally just barrels/boxes of stuff. You can pick it up with a forklift and put it inside a sealed container for the next thousand years.
    - cesarb 2y ago
      > Nuclear waste in contrast is literally just barrels/boxes of stuff. You can pick it up with a forklift and put it inside a sealed container for the next thousand years. You can't pick it up with a forklift to put it inside the sealed container. That would make the forklift (and its operator) radioactive. You can only use a forklift after it's already within the sealed container. See for instance this real-life video (shot on a nuclear power station in my country), which shows used nuclear fuel rods being put inside a sealed container for long-term storage: https://www.youtube.com/watch?v=7X5K46ALdD0 https://www.youtube.com/watch?v=7X5K46ALdD0
vilhelm_s 2y ago
The radioactivity generated from neutron activation is low-level, so you don't need to worry about accidents releasing lots of radioactivity, or about how to store waste for a long time. There are a lot of people worrying about those two things for fission reactors. Also, the fuel for fusion reactors is much more plentiful. If we went all in on fission we might run out of easily minable uranium ore in a century or so, so it would be nice to have fusion reactors ready to take over then.
- adrian_b 2y ago
  The radioactivity generated from neutron activation is not at all low-level, because the neutron flux is huge, providing most of the energy generated by the fusion reactor. The intense neutron flux will transmute a very high number of atoms, so when taken out of the reactor all materials are very highly radioactive. What can be hoped is that there may be choices for the materials used in a fusion reactor that will ensure a short enough lifetime for the radioactive isotopes, so that the radioactivity of the contaminated materials will become low-level soon enough. The studies that I have seen have the target that the radioactive waste produced by a fusion reactor should become low-level radioactive waste after one hundred years. To reach this target, many commonly used structural materials, like many types of steel, must be completely avoided, e.g. any steel containing nickel, molybdenum or niobium. Even the carbon from steel is a problem, because the radioactivity of C14 will persist for thousands of years. A smaller fraction of the materials, particularly from highly activated plasma facing and near plasma components, may fail to meet current low-level waste criteria even after one thousand years. See e.g. the report: https://assets.publishing.service.gov.uk/media/61ae4caa8fa8f503780c1ce9/radioactive-wastes-from-fusion-energy-corwm3735-preliminary-paper.pdf https://assets.publishing.service.gov.uk/media/61ae4caa8fa8f...
  - pas 2y ago
    How does the waste distribution and amount compare to fission reactors? (Pressure vessels, spent fuel rods, what else?) If we need to to dump every 50 year a few thousand tons of steel into the old uranium mines that seems like a good deal, no?
deleted 2y ago
[deleted]
_neil 2y ago
You posted this same comment[0] nearly word for word a month ago. Why is that? Not sure why, but “many on hacker news fantasize about fusion (not fission)” stuck in my head. [0] https://news.ycombinator.com/item?id=41677250 https://news.ycombinator.com/item?id=41677250
Borg3 2y ago
Thats least of your problem imo. Neutron corrosion is bigger problem. There is trick to use Lithium shielding, with create Tritium needed for Fussion. But not sure how effective it is, especially for long term reactor lifetime. Those reactors are very expensive, not sure if its worth to shut it down every year and replace entire Li shielding...
- throwup238 2y ago
  I think beryllium is a better candidate. It can be grown as a single crystal and there’s lots of research into using it for shielding in nuclear lightbulb reactors.
  - perihelions 2y ago
    You're overlooking the other requirement of the blanket—that it captures fusion neutrons to breed tritium, and provides a self-sustaining, closed fuel cycle. Lithium is mandatory for a D+T reactor blanket, because of these reactions: https://en.wikipedia.org/wiki/Tritium#Lithium https://en.wikipedia.org/wiki/Tritium#Lithium (Do you have a link about that beryllium nuclear lightbulb rocket? It sounds interesting).
  - LargoLasskhyfv 2y ago
    Who is researching nuclear lightbulb reactors?
    - defrost 2y ago
      Thomas Latham was, in 1991 ... today, not so much. https://ntrs.nasa.gov/api/citations/19920001892/downloads/19920001892.pdf https://ntrs.nasa.gov/api/citations/19920001892/downloads/19... https://arc.aiaa.org/doi/10.2514/6.1991-3512 https://arc.aiaa.org/doi/10.2514/6.1991-3512
  - rnhmjoj 2y ago
    Beryllium is a good plasma facing material (low Z, low retention, low activation) and acts as a neutron multiplier, but it's highly toxic: only a few months ago ITER announced they scrapped the design of the first wall because working with beryllium was causing too many complications and slowing the project even more. It's also so rare to be completely unsuitable for a power plant: a single DEMO-like reactor with a ceramic blanket (HCCB design) would require 70% of the world beryllium output to build and then burn through 200kg/year. Essentially you could only build a couple of these.
jylam 2y ago
I'm not a specialist but here is what I think I know (I'm talking with the point of view of a Frenchman, who consumes most of his electricity from (fission) nuclear power plants): 1/ Uranium is not a renewable (quite the opposite), needs to be mined and treated (which is expensive and very polluting), and not present at the required concentrations in most of the world (this creates geopolitical issues). 2/ Fission nuclear plants require a well functioning [state|government], and no war. A (conventional) strike on a nuclear power plant can have devastating and lasting consequences. Even a random terrorist group can do that. 3/ I've read that "Ultimately, researchers hope to adopt the protium–boron-11 reaction, because it does not directly produce neutrons, although side reactions can" (that's a wikipedia quote, but I've read that already from other sources). So fusion doesn't seem the best option on the short term, because of the complexity and cost of research, but definitely seems to be the very best option in the middle and long term. And we made the short term catastrophic choice already with coal and oil, it'll be good to learn from that. Or maybe I'm totally wrong.
- adrian_b 2y ago
  Deuterium is also not renewable, even if it is more abundant than uranium. The H1-B11 reaction would be a much better energy source than anything else, but for now nobody knows any method to do it. There is no chance to do it by heating, but only by accelerating ions, and it is not known how a high enough reaction rate could be obtained.
  - rnhmjoj 2y ago
    I'm curious, what are you considering for stating that deuterium is not renewable? AFAIK there's an essentially limitless supply in the form of HDO in the oceans[1] and there are cost effective methods[2] to isolate it. [1]: https://en.wikipedia.org/wiki/Semiheavy_water https://en.wikipedia.org/wiki/Semiheavy_water [2]: https://en.wikipedia.org/wiki/Girdler_sulfide_process https://en.wikipedia.org/wiki/Girdler_sulfide_process
    - adrian_b 2y ago
      If you are able to say that there is a limitless amount of deuterium in the oceans, than you can say the same about the amount of uranium in the oceans, even if the amount of dissolved uranium is about one thousand times less. Both the amounts of deuterium and of uranium in the solar system are finite and smaller than of the abundant elements. Moreover, the natural processes that create deuterium and uranium within a normal stellar system are slower than those that destroy them, so there is no chance of their quantities ever increasing. Unlike using other chemical elements to make some stuff, using deuterium or uranium for producing energy destroys them without any means to regenerate them, so it is by definition a non-renewable process. The hydrogen (protium) in the Sun is also non-renewable, but its quantity is enormous in comparison with the amount of deuterium existing on Earth (and the amount of energy that the Sun produces per proton is greater than the amount of energy that can be produced per deuteron). Like deuterium is extracted from sea water, uranium can also be extracted from sea water, where it is one of the most abundant metals, except for the alkali metals and the alkaline earth metals. However the energy required for extracting uranium is significantly higher, due to its much lower concentration than deuterium (though deuterium is difficult to separate due to its similarity with the lighter isotope of hydrogen, while for the uranium ions much more efficient chemical reactions would be possible, which would bind uranium ions without being affected by the other dissolved ions).
UltraSane 2y ago
Exactly. We should be working on making nuclear reactors cost $1/watt to construct. I can't see a technological reason why they couldn't be that cheap to build.
ben_w 2y ago
> Hacker News is hostile to fission and defeatist (unable to contemplate innovation in fission technology) but this attitude will gradually change. Lots of us like fission and think the fears are overestimated. Nevertheless, the observation is that new developments in fission tend to result in the cost increasing, not decreasing. And I say that as someone with a similar mindset regarding fusion, though for different reasons: you can pick aneutronic fusion reactions… but look at what weapons can proliferate with transmutation from the neutrons you can also choose, and ask which governments will turn them down.
fragmede 2y ago
> Many on Hacker News fantasize about fusion (not fission) reactors. These fusion reactors will be an intense source of fast neutrons. All the hardware in a fusion reactor will become radioactive. Not to mention the gamma rays. My personal ideology about fusion aside, it should be mentioned there is an easy fix for these radiation problems. What you do is put the fusion reactor in space, and collect the energy with specialized fusion energy collectors on Earth (or in space). They'll have the problem that they aren't able to collect energy if the fusion reaction is below the horizon, so this design is imperfect, but having the fusion reaction take place in space means you don't have to deal with a radioactive casing by not including it in your fusion reaction space station design because you don't need any. Just a bit of hydrogen, a tiny bit of helium, and a some time.
- koe123 2y ago
  For such an approach I’ve always thought it seemed a risk to launch something like that into the air. E.g. what happens if the rocket explodes while taking off? Or something bad happens when in space? Will it rain nuclear material?
  - fragmede 2y ago
    Obviously you just put the nuclear material inside of the in-flight data recorder so it will survive a rocket failure. If you're being serious, Cassini had those kinds of questions with its launch about its RTG but that didn't have enough nuclear material for it to be a problem. If we were to try and use a fusion reaction in space, we'd probably use the existing one.

raverbashing 2y ago

Fission is "simple" but it seems every designer in the XX century made it as much complicated as possible for not so great reasons (and don't even get me started on the "let's not use breeding reactors" stuff) Cooling that requires pumps, as an example, should be a non-starter in new projects.

rob74 2y ago
The designs are complicated, well, because in practice it's not as simple as "put these rocks next to each other and they get hot". When you put the rocks next to each other, they not only get hot, but also emit some nasty radiation that has to be shielded. And if the rocks get a liiiitle bit too close together, they might explode, which leads to huge headaches for everyone involved, so you'd better make sure that doesn't happen...
- meindnoch 2y ago
  >And if the rocks get a liiiitle bit too close together, they might explode Impossible. Worst thing that can happen without carefully designed explosive lens is a nuclear fizzle.
  - empath75 2y ago
    There are lots of ways that nuclear plants can explode or fail in otherwise catastrophic ways, it doesn't need to be an atomic explosion.
    - meindnoch 2y ago
      Parent was alluding to a nuclear explosion, not a steam explosion or other type of explosion. Other kinds of explosions have nothing to do with the fissile material ("rocks" in their parlance) being "too close together". Steam explosions in particular are caused by boiling water, due to increased reactor power, or inadequate circulation of coolant. In a nuclear reactor, the fuel cells are held in a fixed matrix, and are not moving an inch closer to each other, whether the reactor is operating normally, or a steam explosion is imminent. In general, nobody was disputing the possibility of steam explosions, or other type of failures at nuclear power plants, thus your comment is besides the point, and irrelevant to this subthread.
SoftTalker 2y ago
Weapons proliferation concerns is/was the reason fission power is so complicated.

elashri 2y ago

> we know how to build and operate them at 95%+ efficiency. Fission can provide all the power we need. I am not sure what do you mean by 95%+ efficency here. But if you are talking about the entire process of getting the energy/power from the nuclear reactor this is not possible. You are still limited by carnot cycle. Even the most advanced reactors like HTGRs [1] operate with efficiency about 45%. If you have some other definition of efficiency than the standard then it would be good if you define that. [1] https://en.wikipedia.org/wiki/High-temperature_gas-cooled_reactor https://en.wikipedia.org/wiki/High-temperature_gas-cooled_re...

atomic128 2y ago
See discussion of "capacity factor" here: https://news.ycombinator.com/item?id=41858892 https://news.ycombinator.com/item?id=41858892 It's the same as when we talk about the efficiency of a GEMM kernel on a particular piece of hardware. As efficiency approaches 100% the kernel is saturating the hardware's capacity to perform multiply/add.
- howenterprisey 2y ago
  The term "capacity factor" should generally always be used for that concept, because "efficiency" has its own, different, meaning for power plants.
- deleted 2y ago
  [deleted]

cosmic_quanta 2y ago

> Neutrons make hardware radioactive True, but two caveats: 1. Neutron bombardment due to fusion makes hardware radioactive for less than 10 years, which isn't great but does not compare to fission waste; 2. Some fusion processes don't emit neutrons (aneutronic fusion). As I understand it, these processes aren't as efficient, but there is the possibility of a tradeoff between generation of ratioactive waste vs. efficiency.

khuey 2y ago
Aneutronic fusion is even harder than regular fusion so it's not a realistic solution in any near-term scenario.
- Symmetry 2y ago
  It has the advantage that the energy it gives off can be be converted directly to electrical energy rather than driving an external heat engine, so despite the greater difficulty of ignition its not obviously a worse choice.
- fusionadvocate 2y ago
  That is incorrect. Recent advances using attosecond lasers enable new tricks and fusion conditions to be realized tabletop. Search also for plasmonics. Using nano antennas and intense lasers to accelerate protons and electrons in a tabletop device (previously required large machines).
  - ben_w 2y ago
    Fusors already enabled desktop fusion reactors, literally high school science fair projects even a couple of decades back. What stops Fusors and Polywells from having already given us this decades ago with P-B11 etc. is that the cross section for fusing is so much lower than the cross section for elastic scattering, and that elastic scattering loses so much energy to EM via bremsstrahlung.
adrian_b 2y ago
> Neutron bombardment due to fusion makes hardware radioactive for less than 10 years Very false. The current design target for fusion reactors is that the materials taken out of the reactor should become "low-level radioactive waste" after being stored for one hundred years. It is acknowledged however that it is likely that a small fraction of the materials will not satisfy the criteria for "low-level radioactive waste" even after one thousand years. For example it is extremely difficult to avoid using carbon in the reactor. Besides various kinds of steels used in reactor components there are now some proposals to replace the tungsten used in the plasma-facing surface with some carbides, for increased endurance. Carbon 14 remains radioactive for thousands of years. There are many commonly used materials for which substitutes must be developed, e.g. new alloys, because otherwise they would produce radioactive isotopes with lifetimes of tens of thousands of years, e.g. there are efforts to develop some stainless steels with chromium and tungsten as a replacement for the normally used steels with chromium and molybdenum, which would generate long-lived radioactive waste. See e.g. the UK governmental report: https://assets.publishing.service.gov.uk/media/61ae4caa8fa8f503780c1ce9/radioactive-wastes-from-fusion-energy-corwm3735-preliminary-paper.pdf https://assets.publishing.service.gov.uk/media/61ae4caa8fa8f...

lupusreal 2y ago

The only hard part of dealing with nuclear waste is the social aspect. If not for that, you can simply and safely dump it into the ocean. Water is excellent shielding and the amount of uranium/etc already dissolved in sea water is absurd. Put it in a stainless steel vessel first if you want most of it to decay before coming into contact with the water, but that's not even necessary.

perihelions 2y ago
That doesn't really work because marine life is good at filtering and concentrating a subset of the elements that are in spent nuclear fuel. There are already ocean fish that are too poisonous too safely eat because of (coal-emitted) mercury pollution—and that's only 100,000 tons of mercury, total, in the history of human industry [0]. If you dig in to the hard numbers surrounding spent fuel, it's a much, much more toxic and difficult problem than mercury—diluting it in the oceans is a complete non-starter. [0] https://en.wikipedia.org/wiki/Marine_mercury_pollution https://en.wikipedia.org/wiki/Marine_mercury_pollution
- meindnoch 2y ago
  Mercury from burning coal is an extremely dilute pollutant. There's zero hope for capturing and containing it. Nuclear waste in contrast is literally just barrels/boxes of stuff. You can pick it up with a forklift and put it inside a sealed container for the next thousand years.
  - cesarb 2y ago
    > Nuclear waste in contrast is literally just barrels/boxes of stuff. You can pick it up with a forklift and put it inside a sealed container for the next thousand years. You can't pick it up with a forklift to put it inside the sealed container. That would make the forklift (and its operator) radioactive. You can only use a forklift after it's already within the sealed container. See for instance this real-life video (shot on a nuclear power station in my country), which shows used nuclear fuel rods being put inside a sealed container for long-term storage: https://www.youtube.com/watch?v=7X5K46ALdD0 https://www.youtube.com/watch?v=7X5K46ALdD0

vilhelm_s 2y ago

The radioactivity generated from neutron activation is low-level, so you don't need to worry about accidents releasing lots of radioactivity, or about how to store waste for a long time. There are a lot of people worrying about those two things for fission reactors. Also, the fuel for fusion reactors is much more plentiful. If we went all in on fission we might run out of easily minable uranium ore in a century or so, so it would be nice to have fusion reactors ready to take over then.

adrian_b 2y ago
The radioactivity generated from neutron activation is not at all low-level, because the neutron flux is huge, providing most of the energy generated by the fusion reactor. The intense neutron flux will transmute a very high number of atoms, so when taken out of the reactor all materials are very highly radioactive. What can be hoped is that there may be choices for the materials used in a fusion reactor that will ensure a short enough lifetime for the radioactive isotopes, so that the radioactivity of the contaminated materials will become low-level soon enough. The studies that I have seen have the target that the radioactive waste produced by a fusion reactor should become low-level radioactive waste after one hundred years. To reach this target, many commonly used structural materials, like many types of steel, must be completely avoided, e.g. any steel containing nickel, molybdenum or niobium. Even the carbon from steel is a problem, because the radioactivity of C14 will persist for thousands of years. A smaller fraction of the materials, particularly from highly activated plasma facing and near plasma components, may fail to meet current low-level waste criteria even after one thousand years. See e.g. the report: https://assets.publishing.service.gov.uk/media/61ae4caa8fa8f503780c1ce9/radioactive-wastes-from-fusion-energy-corwm3735-preliminary-paper.pdf https://assets.publishing.service.gov.uk/media/61ae4caa8fa8f...
- pas 2y ago
  How does the waste distribution and amount compare to fission reactors? (Pressure vessels, spent fuel rods, what else?) If we need to to dump every 50 year a few thousand tons of steel into the old uranium mines that seems like a good deal, no?

deleted 2y ago

[deleted]

_neil 2y ago

You posted this same comment[0] nearly word for word a month ago. Why is that? Not sure why, but “many on hacker news fantasize about fusion (not fission)” stuck in my head. [0] https://news.ycombinator.com/item?id=41677250 https://news.ycombinator.com/item?id=41677250

Borg3 2y ago

Thats least of your problem imo. Neutron corrosion is bigger problem. There is trick to use Lithium shielding, with create Tritium needed for Fussion. But not sure how effective it is, especially for long term reactor lifetime. Those reactors are very expensive, not sure if its worth to shut it down every year and replace entire Li shielding...

throwup238 2y ago
I think beryllium is a better candidate. It can be grown as a single crystal and there’s lots of research into using it for shielding in nuclear lightbulb reactors.
- perihelions 2y ago
  You're overlooking the other requirement of the blanket—that it captures fusion neutrons to breed tritium, and provides a self-sustaining, closed fuel cycle. Lithium is mandatory for a D+T reactor blanket, because of these reactions: https://en.wikipedia.org/wiki/Tritium#Lithium https://en.wikipedia.org/wiki/Tritium#Lithium (Do you have a link about that beryllium nuclear lightbulb rocket? It sounds interesting).
- LargoLasskhyfv 2y ago
  Who is researching nuclear lightbulb reactors?
  - defrost 2y ago
    Thomas Latham was, in 1991 ... today, not so much. https://ntrs.nasa.gov/api/citations/19920001892/downloads/19920001892.pdf https://ntrs.nasa.gov/api/citations/19920001892/downloads/19... https://arc.aiaa.org/doi/10.2514/6.1991-3512 https://arc.aiaa.org/doi/10.2514/6.1991-3512
- rnhmjoj 2y ago
  Beryllium is a good plasma facing material (low Z, low retention, low activation) and acts as a neutron multiplier, but it's highly toxic: only a few months ago ITER announced they scrapped the design of the first wall because working with beryllium was causing too many complications and slowing the project even more. It's also so rare to be completely unsuitable for a power plant: a single DEMO-like reactor with a ceramic blanket (HCCB design) would require 70% of the world beryllium output to build and then burn through 200kg/year. Essentially you could only build a couple of these.

jylam 2y ago

I'm not a specialist but here is what I think I know (I'm talking with the point of view of a Frenchman, who consumes most of his electricity from (fission) nuclear power plants): 1/ Uranium is not a renewable (quite the opposite), needs to be mined and treated (which is expensive and very polluting), and not present at the required concentrations in most of the world (this creates geopolitical issues). 2/ Fission nuclear plants require a well functioning [state|government], and no war. A (conventional) strike on a nuclear power plant can have devastating and lasting consequences. Even a random terrorist group can do that. 3/ I've read that "Ultimately, researchers hope to adopt the protium–boron-11 reaction, because it does not directly produce neutrons, although side reactions can" (that's a wikipedia quote, but I've read that already from other sources). So fusion doesn't seem the best option on the short term, because of the complexity and cost of research, but definitely seems to be the very best option in the middle and long term. And we made the short term catastrophic choice already with coal and oil, it'll be good to learn from that. Or maybe I'm totally wrong.

adrian_b 2y ago
Deuterium is also not renewable, even if it is more abundant than uranium. The H1-B11 reaction would be a much better energy source than anything else, but for now nobody knows any method to do it. There is no chance to do it by heating, but only by accelerating ions, and it is not known how a high enough reaction rate could be obtained.
- rnhmjoj 2y ago
  I'm curious, what are you considering for stating that deuterium is not renewable? AFAIK there's an essentially limitless supply in the form of HDO in the oceans[1] and there are cost effective methods[2] to isolate it. [1]: https://en.wikipedia.org/wiki/Semiheavy_water https://en.wikipedia.org/wiki/Semiheavy_water [2]: https://en.wikipedia.org/wiki/Girdler_sulfide_process https://en.wikipedia.org/wiki/Girdler_sulfide_process
  - adrian_b 2y ago
    If you are able to say that there is a limitless amount of deuterium in the oceans, than you can say the same about the amount of uranium in the oceans, even if the amount of dissolved uranium is about one thousand times less. Both the amounts of deuterium and of uranium in the solar system are finite and smaller than of the abundant elements. Moreover, the natural processes that create deuterium and uranium within a normal stellar system are slower than those that destroy them, so there is no chance of their quantities ever increasing. Unlike using other chemical elements to make some stuff, using deuterium or uranium for producing energy destroys them without any means to regenerate them, so it is by definition a non-renewable process. The hydrogen (protium) in the Sun is also non-renewable, but its quantity is enormous in comparison with the amount of deuterium existing on Earth (and the amount of energy that the Sun produces per proton is greater than the amount of energy that can be produced per deuteron). Like deuterium is extracted from sea water, uranium can also be extracted from sea water, where it is one of the most abundant metals, except for the alkali metals and the alkaline earth metals. However the energy required for extracting uranium is significantly higher, due to its much lower concentration than deuterium (though deuterium is difficult to separate due to its similarity with the lighter isotope of hydrogen, while for the uranium ions much more efficient chemical reactions would be possible, which would bind uranium ions without being affected by the other dissolved ions).

UltraSane 2y ago

Exactly. We should be working on making nuclear reactors cost $1/watt to construct. I can't see a technological reason why they couldn't be that cheap to build.

ben_w 2y ago

> Hacker News is hostile to fission and defeatist (unable to contemplate innovation in fission technology) but this attitude will gradually change. Lots of us like fission and think the fears are overestimated. Nevertheless, the observation is that new developments in fission tend to result in the cost increasing, not decreasing. And I say that as someone with a similar mindset regarding fusion, though for different reasons: you can pick aneutronic fusion reactions… but look at what weapons can proliferate with transmutation from the neutrons you can also choose, and ask which governments will turn them down.

fragmede 2y ago

> Many on Hacker News fantasize about fusion (not fission) reactors. These fusion reactors will be an intense source of fast neutrons. All the hardware in a fusion reactor will become radioactive. Not to mention the gamma rays. My personal ideology about fusion aside, it should be mentioned there is an easy fix for these radiation problems. What you do is put the fusion reactor in space, and collect the energy with specialized fusion energy collectors on Earth (or in space). They'll have the problem that they aren't able to collect energy if the fusion reaction is below the horizon, so this design is imperfect, but having the fusion reaction take place in space means you don't have to deal with a radioactive casing by not including it in your fusion reaction space station design because you don't need any. Just a bit of hydrogen, a tiny bit of helium, and a some time.

koe123 2y ago
For such an approach I’ve always thought it seemed a risk to launch something like that into the air. E.g. what happens if the rocket explodes while taking off? Or something bad happens when in space? Will it rain nuclear material?
- fragmede 2y ago
  Obviously you just put the nuclear material inside of the in-flight data recorder so it will survive a rocket failure. If you're being serious, Cassini had those kinds of questions with its launch about its RTG but that didn't have enough nuclear material for it to be a problem. If we were to try and use a fusion reaction in space, we'd probably use the existing one.