7 ms·

I've seen the scenario you describe as the "fission bridge to fusion" scenario, and as I understand it, a major problem is that it can't be done with existing p

I've seen the scenario you describe as the "fission bridge to fusion" scenario, and as I understand it, a major problem is that it can't be done with existing pressurized light-water reactors. These systems just don't use Uranium very efficiently, they extract a small percentage of the energy from the fuel, and then need to be refueled. This doesn't mean the "fission bridge to fusion" is impossible by any means, but it does mean that significant work needs to be done in developing and commercializing next-generation fission reactors, including breeder reactors, which use much more of the available energy from fuel, and possibly novel reactor designs that can run on reprocessed fuel from LWRs. A political complication is that large-scale commercial nuclear fuel reprocessing represents a nuclear-weapons proliferation risk, and so might imply regulatory burdens, or require international agreements on use and control before it can go forward. Refs: Dim recollection from reading Walter C. Patterson's "Nuclear Power", and some discussion about peak Uranium (https://en.wikipedia.org/wiki/Peak_uranium https://en.wikipedia.org/wiki/Peak_uranium).

aidenn0 4y ago
My understanding is that breeder reactors are politically problematic because of proliferation concerns.
Manuel_D 4y ago
Reprocessing increases net efficiency considerably [1]. Few people do it since uranium is very cheap relative to the amount of energy extracted from it, even without reprocessing. But if fuel ever becomes constrained, reprocessing would become competitive. Nuclear weapons proliferation isn't a risk among most countries that have nuclear generation programs. Heck, most of them already have nuclear weapons. The rest can contract out reprocessing to nuclear-armed countries. 1. https://en.wikipedia.org/wiki/Nuclear_reprocessing https://en.wikipedia.org/wiki/Nuclear_reprocessing
- jhallenworld 4y ago
  Also there are "near-breeder" CANDU heavy water moderated reactors: they are a proven technology that exists today and can use non-enriched uranium. They also in theory can use a plutonium/thorium mixture, so can burn thorium. They are cheaper as far as fuel, but it turns out that fuel didn't become as expensive as anticipated in the 1970s (when it was thought that there would be 1000s of reactors). They are physically larger, so have a higher construction cost that put them at a disadvantage compared to conventional LWRs. The tritium needed for fusion reactors comes from these CANDU reactors (some of the deuterium from the heavy water is converted to tritium, it is collected).
vlovich123 4y ago
Peak uranium isn’t a thing even using today’s inefficient reactors. The key insight is that if you’re using fission to power DAC, then you don’t even need to worry about proliferation. Countries can continue to use coal and oil while nuclear fission is used for DAC. An international agreement that they pay a tax to the countries that do have the capability to do DAC powered by fission. China and USA make up the vast majority of emissions, make up a good chunk of global GDP and both have nuclear power plant capabilities & they're not the only two countries who have that. Yes, there’s an imbalance there to think through but it can be remediated a bit (and mostly it’ll be Brazil and India that we would need to worry about assuming we can get China on board). Certainly better than doing nothing for decades or even a century.
- 7speter 4y ago
  I'm asking because I'm definitely not an expert on this, but if we can't use uranium efficiently, wouldn't that mean the plants would be creating lots of waste they wouldn't if they were more efficient? Would plants that would already be built be upgradable in the case more efficient methods of using uranium come online?
  - vlovich123 4y ago
    You can reprocess “waste” in a breeder reactor. Not sure if plants can be retrofitted with a new generation of reactor, but even if you need a new plant that’s not that big a deal because the waste is still usable fuel (it’s not a use once thing)
    - Maursault 4y ago
      Trouble is, breeder reactors cost more than both types of water reactors for which we already can't find investors.
      - llsf 4y ago
        Because all the cost must be paid upfront, and takes 10+ years before the first GWh gets out. So, it does not fit well with private investors. The cost of the electricity exiting a nuclear reactor is directly related to the cost of money (interest) to build the reactor. The reason is because it is cheap to run the reactor once built. So, the cheaper the money is the cheaper the electricity is. That is why it is not interesting for private investors. It has to be financed by state to minimize the final cost if electricity at the end.

aidenn0 4y ago

My understanding is that breeder reactors are politically problematic because of proliferation concerns.

Manuel_D 4y ago

Reprocessing increases net efficiency considerably [1]. Few people do it since uranium is very cheap relative to the amount of energy extracted from it, even without reprocessing. But if fuel ever becomes constrained, reprocessing would become competitive. Nuclear weapons proliferation isn't a risk among most countries that have nuclear generation programs. Heck, most of them already have nuclear weapons. The rest can contract out reprocessing to nuclear-armed countries. 1. https://en.wikipedia.org/wiki/Nuclear_reprocessing https://en.wikipedia.org/wiki/Nuclear_reprocessing

jhallenworld 4y ago
Also there are "near-breeder" CANDU heavy water moderated reactors: they are a proven technology that exists today and can use non-enriched uranium. They also in theory can use a plutonium/thorium mixture, so can burn thorium. They are cheaper as far as fuel, but it turns out that fuel didn't become as expensive as anticipated in the 1970s (when it was thought that there would be 1000s of reactors). They are physically larger, so have a higher construction cost that put them at a disadvantage compared to conventional LWRs. The tritium needed for fusion reactors comes from these CANDU reactors (some of the deuterium from the heavy water is converted to tritium, it is collected).

vlovich123 4y ago

Peak uranium isn’t a thing even using today’s inefficient reactors. The key insight is that if you’re using fission to power DAC, then you don’t even need to worry about proliferation. Countries can continue to use coal and oil while nuclear fission is used for DAC. An international agreement that they pay a tax to the countries that do have the capability to do DAC powered by fission. China and USA make up the vast majority of emissions, make up a good chunk of global GDP and both have nuclear power plant capabilities & they're not the only two countries who have that. Yes, there’s an imbalance there to think through but it can be remediated a bit (and mostly it’ll be Brazil and India that we would need to worry about assuming we can get China on board). Certainly better than doing nothing for decades or even a century.

7speter 4y ago
I'm asking because I'm definitely not an expert on this, but if we can't use uranium efficiently, wouldn't that mean the plants would be creating lots of waste they wouldn't if they were more efficient? Would plants that would already be built be upgradable in the case more efficient methods of using uranium come online?
- vlovich123 4y ago
  You can reprocess “waste” in a breeder reactor. Not sure if plants can be retrofitted with a new generation of reactor, but even if you need a new plant that’s not that big a deal because the waste is still usable fuel (it’s not a use once thing)
  - Maursault 4y ago
    Trouble is, breeder reactors cost more than both types of water reactors for which we already can't find investors.
    - llsf 4y ago
      Because all the cost must be paid upfront, and takes 10+ years before the first GWh gets out. So, it does not fit well with private investors. The cost of the electricity exiting a nuclear reactor is directly related to the cost of money (interest) to build the reactor. The reason is because it is cheap to run the reactor once built. So, the cheaper the money is the cheaper the electricity is. That is why it is not interesting for private investors. It has to be financed by state to minimize the final cost if electricity at the end.