3 ms·

> It is likely unachievable anytime in the next half a century. It is very important for this message to get through. Fusion is not "just around the corner".

> It is likely unachievable anytime in the next half a century. It is very important for this message to get through. Fusion is not "just around the corner". By the way, the energy generated by fusion is higher than that generated by fission, but not by a huge amount. Only by a factor of 4. The energy density of Deuterium+Tritium is 337 TJ/kg. The energy density of Uranium is 81 TJ/kg. For comparison, the energy density of methane is 56 MJ/kg or more than 1 million times lower than that of Uranium.

willis936 4y ago
1 kg of deuterium is a lot friendlier to be around and less alarming to find anywhere on the planet than 1 kg of U-235. 1 kg of tritium is a hazard, but it's also more than the global annual production of tritium and any DT reactor would be engineered to have low tritium inventories and a controllable breed rate.
- credit_guy 4y ago
  U-235 has a half life of 700 million years. When it decays, it releases alpha radiation (Helium neclei), which is not that dangerous. As long as you don’t ingest or inhale it, U-235 is harmless. If you do ingest or inhale it, it will probably harm you more because it is a heavy metal than because it is radioactive.
  - willis936 4y ago
    Do you know how many people you can threaten and actually kill with 1 kg of U-235?
    - credit_guy 4y ago
      I don't fully understand where you're going with this question. Maybe you are implying a terrorist could get their hands on 1kg of U-235 and either make a dirty bomb or a nuke. A dirty bomb would not really be more dangerous than a dirty bomb made with Cadmium. As for a nuke, 1kg is well below the minimum necessary to make a nuclear bomb, which is about 15 kg. But that's not the only thing. You need weapons grade Uranium for that, i.e. Uranium where U-235 constitutes at least 85% of the whole. Civilian reactors use Uranium that is enriched to much lower levels. Currently, the vast majority of the civilian reactors use Uranium enriched to 4.5%. A terrorist who gets their hands on that, can forget about building a nuclear bomb, except if they have means to further enrich that Uranium. In other words, if they have centrifuges, like Iran does. I might remind you that Iran is a state, not a single person. In any case, if you have centrifuges, you might as well start with Uranium ore, there's no point in stealing from an existing civilian reactor.
    - MertsA 4y ago
      Basically one. Now if it was 50 kg then you're getting into the realm of criticality.
  - ouid 4y ago
    Unlike in most cases, where there is a conflation of fissile and radioctive substances, I believe that the parent comment was actually referring the the problem that occurs when you allow people to get their hands on too much enriched uranium.
77pt77 4y ago
And it was 50 years away 50 years ago. It's always the same. Reminds me of a well known electric car CEO that says self-driving cars are 3 years away and has been saying that for 10 years.
- headmelted 4y ago
  I mean I sort of see why you’ve been downvoted (this is off-topic and adds nothing to the discussion), but you’re also not wrong. Extraordinary claims require extraordinary evidence, which is a lesson that we learned a million different hard ways and which has been almost completely forgotten.
mlindner 4y ago
> It is very important for this message to get through. Fusion is not "just around the corner". Only if you keep reading articles written by people who don't know what they're talking about. Fusion power break even will happen in roughly 5 years with MIT's/Commonwealth Fusion's SPARC test reactor.

willis936 4y ago

1 kg of deuterium is a lot friendlier to be around and less alarming to find anywhere on the planet than 1 kg of U-235. 1 kg of tritium is a hazard, but it's also more than the global annual production of tritium and any DT reactor would be engineered to have low tritium inventories and a controllable breed rate.

credit_guy 4y ago
U-235 has a half life of 700 million years. When it decays, it releases alpha radiation (Helium neclei), which is not that dangerous. As long as you don’t ingest or inhale it, U-235 is harmless. If you do ingest or inhale it, it will probably harm you more because it is a heavy metal than because it is radioactive.
- willis936 4y ago
  Do you know how many people you can threaten and actually kill with 1 kg of U-235?
  - credit_guy 4y ago
    I don't fully understand where you're going with this question. Maybe you are implying a terrorist could get their hands on 1kg of U-235 and either make a dirty bomb or a nuke. A dirty bomb would not really be more dangerous than a dirty bomb made with Cadmium. As for a nuke, 1kg is well below the minimum necessary to make a nuclear bomb, which is about 15 kg. But that's not the only thing. You need weapons grade Uranium for that, i.e. Uranium where U-235 constitutes at least 85% of the whole. Civilian reactors use Uranium that is enriched to much lower levels. Currently, the vast majority of the civilian reactors use Uranium enriched to 4.5%. A terrorist who gets their hands on that, can forget about building a nuclear bomb, except if they have means to further enrich that Uranium. In other words, if they have centrifuges, like Iran does. I might remind you that Iran is a state, not a single person. In any case, if you have centrifuges, you might as well start with Uranium ore, there's no point in stealing from an existing civilian reactor.
  - MertsA 4y ago
    Basically one. Now if it was 50 kg then you're getting into the realm of criticality.
- ouid 4y ago
  Unlike in most cases, where there is a conflation of fissile and radioctive substances, I believe that the parent comment was actually referring the the problem that occurs when you allow people to get their hands on too much enriched uranium.

77pt77 4y ago

And it was 50 years away 50 years ago. It's always the same. Reminds me of a well known electric car CEO that says self-driving cars are 3 years away and has been saying that for 10 years.

headmelted 4y ago
I mean I sort of see why you’ve been downvoted (this is off-topic and adds nothing to the discussion), but you’re also not wrong. Extraordinary claims require extraordinary evidence, which is a lesson that we learned a million different hard ways and which has been almost completely forgotten.

mlindner 4y ago

> It is very important for this message to get through. Fusion is not "just around the corner". Only if you keep reading articles written by people who don't know what they're talking about. Fusion power break even will happen in roughly 5 years with MIT's/Commonwealth Fusion's SPARC test reactor.