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I am arguing with the sort of vision of fusion power that's presented in popular articles, like the NYT one that started this thread. "Clean power that powers t

I am arguing with the sort of vision of fusion power that's presented in popular articles, like the NYT one that started this thread. "Clean power that powers the Sun" - yup, he said that. A senior scientist who knows the numbers. See below in the thread how relevant this is. "Relies only on seawater as fuel" - check. "Offers no chance of a catastrophic accident" - oh come on, even a coal powerplant offers that. Articles like this are a strawman, and Stewart C. Prager, director of the Princeton Plasma Physics Laboratory, knows better and should be ashamed of himself. To take up just the matter of catastrophic accidents: it is said correctly that a fission powerplant can never explode like a fission bomb - the atoms of fuel are in the wrong arrangement for that. But any continuous system for producing fusion power is theoretically capable of "running away" - it is a self-reinforcing process, after all - and producing an actual nuclear explosion. They will design it to make this spectacularly unlikely? OK, sure they will, but let's not talk about this being danger-free. Or the "fuel from seawater" thing. Seawater contains 3.3 ppb of uranium, and it would be commercially feasible to extract it if the prices were higher. It's actually easier to do this than to design fusion reactors. And you can use more advanced fission cycles, especially the thorium ones, to extend the energy you get out of fission fuels. EDIT: let me clarify the actual quote from Dr. Prager that I am complaining about: Harnessing nuclear fusion, the energy that powers the sun and the stars, has been a goal of physicists worldwide since the 1950s. It is essentially inexhaustible and it can be created using hydrogen isotopes — chemical cousins of hydrogen, like deuterium — that can readily be extracted from seawater. This is so incredibly misleading in many ways, without containing an actual false statement. This kind of manipulation of popular opinion makes me angry. Does anyone want to defend this, even as a popularization?

uvdiv 15y ago
Or the "fuel from seawater" thing. Seawater contains 3.3 ppb of uranium, and it would be commercially feasible to extract it if the prices were higher. ... And you can use more advanced fission cycles, especially the thorium ones, to extend the energy you get out of fission fuels. Indeed. There's about a factor of 100,000x right there -- 500x for increased uranium supply (5e9 tons in oceans, vs. 1e7 tons in "conventional" <$130 kg/ton reserves (IAEA est.)), and 200x for increased fuel efficiency. But any continuous system for producing fusion power is theoretically capable of "running away" - it is a self-reinforcing process, after all - and producing an actual nuclear explosion. Don't think this is true. Fusion plasmas need active confinement -- a hotter plasma is no longer confined, and will no longer fuse. This is so incredibly misleading in many ways, without containing an actual false statement. For example, the limited resource is not deuterium but tritium (a misdirection). The plan to create this is by fissioning lithium, which is actually a rather scarce element (comparable with uranium, ironically). To get more interesting sustainability you need to switch to something like D+D fusion, which is much harder to achieve. http://en.wikipedia.org/wiki/Tritium#Lithium http://en.wikipedia.org/wiki/Tritium#Lithium
- yaakov34 15y ago
  Thanks for the correction about runaway fusion reactions. Does this only prevent it from doing a "Ivy Mike" on us, or can they actually make it passively self-regulating to the point that it can't breach the containment? I still think he is being disingenuous when he says that there is no danger of accident with fusion reactors. Proposed designs have huge irradiated masses and very large neutron fluxes. There is going to be a ton of active safety systems needed, any way you imagine it.
  - uvdiv 15y ago
    There's also the fact that the plasma has extremely low density, so there is very little fuel in the core at a time: "Less than 1g of fusion fuel is present in the Vacuum Vessel at any one moment." http://www.iter.org/mach/fuelcycle http://www.iter.org/mach/fuelcycle
  - teamonkey 15y ago
    If there is any disruption in pressure or temperature required for fusion, the reaction will stop almost instantly. In addition, simply interrupting the flow of fuel will immediately stop the reaction safely. There is no chance at all of meltdown or re-ignition of the fuel.

uvdiv 15y ago

Or the "fuel from seawater" thing. Seawater contains 3.3 ppb of uranium, and it would be commercially feasible to extract it if the prices were higher. ... And you can use more advanced fission cycles, especially the thorium ones, to extend the energy you get out of fission fuels. Indeed. There's about a factor of 100,000x right there -- 500x for increased uranium supply (5e9 tons in oceans, vs. 1e7 tons in "conventional" <$130 kg/ton reserves (IAEA est.)), and 200x for increased fuel efficiency. But any continuous system for producing fusion power is theoretically capable of "running away" - it is a self-reinforcing process, after all - and producing an actual nuclear explosion. Don't think this is true. Fusion plasmas need active confinement -- a hotter plasma is no longer confined, and will no longer fuse. This is so incredibly misleading in many ways, without containing an actual false statement. For example, the limited resource is not deuterium but tritium (a misdirection). The plan to create this is by fissioning lithium, which is actually a rather scarce element (comparable with uranium, ironically). To get more interesting sustainability you need to switch to something like D+D fusion, which is much harder to achieve. http://en.wikipedia.org/wiki/Tritium#Lithium http://en.wikipedia.org/wiki/Tritium#Lithium

yaakov34 15y ago
Thanks for the correction about runaway fusion reactions. Does this only prevent it from doing a "Ivy Mike" on us, or can they actually make it passively self-regulating to the point that it can't breach the containment? I still think he is being disingenuous when he says that there is no danger of accident with fusion reactors. Proposed designs have huge irradiated masses and very large neutron fluxes. There is going to be a ton of active safety systems needed, any way you imagine it.
- uvdiv 15y ago
  There's also the fact that the plasma has extremely low density, so there is very little fuel in the core at a time: "Less than 1g of fusion fuel is present in the Vacuum Vessel at any one moment." http://www.iter.org/mach/fuelcycle http://www.iter.org/mach/fuelcycle
- teamonkey 15y ago
  If there is any disruption in pressure or temperature required for fusion, the reaction will stop almost instantly. In addition, simply interrupting the flow of fuel will immediately stop the reaction safely. There is no chance at all of meltdown or re-ignition of the fuel.