3 ms·

Safe? Probably. It has negative temperature coefficient without need for control mechanism, water or any other medium supply. When everything around fails it j

Safe? Probably. It has negative temperature coefficient without need for control mechanism, water or any other medium supply. When everything around fails it just sits there at its nominal temperature which means it is inherently safe. That is as good as it gets. Economical and safe? I am not 100% convinced. On the economical part, this is using air as a medium to remove energy. Air is pretty poor way to transform large amounts of energy. Compared to water it is tens of thousands times less efficient. Not only it is a lot less dense, it has less heat capacity, but it is also not possible to use state change as with water turning to steam. You would need to produce a huge reactor to move useful amounts of energy which would mean you would need to build a lot of reactors or huge reactor farms with a lot of actual nuclear material involved. You could try to build larger reactor, but you can't scale it easily because the pebbles cannot be subjected to too much forces.

credit_guy 5y ago
> this is using air as a medium to remove energy. No, it is using gas. I didn't find a precise quote, but it's very likely the gas is helium [1]. Air contains oxygen, and when it's very hot, oxygen is extremely corrosive. Helium is inert, it doesn't corrode, and it also does not become radioactive when exposed to free neutrons. So you don't need a primary and secondary coolant system, like for the water-cooled reactors. Separately, gas does not necessarily mean less energy dense than water. See for example [2] where they explain that supercritical CO2 has more energy density than supercritical steam. Finally, the root cause of why nuclear power plants are so damn expensive is the lack of experience of their construction crews. Virtually every new nuclear power plant is a one-of-a-kind new construction. Most of the workers don't have any prior experience with the same type of project. So the adage "measure twice and cut once" becomes "measure 100 times and cut once", and even then errors happen, with inevitable delays, because everyone is so terrified of a screw-up. This reactor is supposed to be followed by 18 more of the same design, on the same site. Workers will acquire a tremendous amount of experience. Lots of workers who then can go on different sites and train new trainees. With all this experience under their belt, more and more reactors could be build, for less and less money. The classical learning curve at work. [1] https://en.wikipedia.org/wiki/High-temperature_gas_reactor#Coolant https://en.wikipedia.org/wiki/High-temperature_gas_reactor#C... [2]https://www.powermag.com/what-are-supercritical-co2-power-cycles/ https://www.powermag.com/what-are-supercritical-co2-power-cy...
- lmilcin 5y ago
  > No, it is using gas. I didn't find a precise quote, but it's very likely the gas is helium [1] You are right, but that doesn't make my other arguments invalid. All gasses are poor at transporting energy because they have very low density, specific heat and because you can't use state change. > Finally, the root cause of why nuclear power plants are so damn expensive is the lack of experience of their construction crews. Virtually every new nuclear power plant is a one-of-a-kind new construction. (...) This reactor is supposed to be followed by 18 more of the same design, on the same site. It doesn't have to be and the pebble-bed doesn't change anything in that regard. You can take any reactor design and replicate multiple times. Actually, a lot of reactors are made this way. Both Chernobyl and Fukushima actually had multiple reactors made from the same blueprint. The issue with pebble-bed reactor is that you must create a lot of them because of how much less dense they are in energy production. You produce much less energy from one so you must get so much better at producing a lot of them (in this case whooping 18 of them -- and that is only a start). All this will cause a lot of reactors and a lot of nuclear material. So even if the individual reactor design is safer, you get many more of them and this might offset any safety improvements. There is after all a lot of factors that we just do not control like terrorism.
  - credit_guy 5y ago
    > You produce much less energy from one so you must get so much better at producing a lot of them (in this case whooping 18 of them -- and that is only a start) These reactors are not tiny. Each will produce 260 MW.
    - lmilcin 5y ago
      This is tiny. A typical power plant produces 1GW. Chernobyl produced 1000MW per reactor. Fukushima produced 1100MW per reactor. So you still holds true that you need many times more of these reactors -- in this case about 4 times.

credit_guy 5y ago

> this is using air as a medium to remove energy. No, it is using gas. I didn't find a precise quote, but it's very likely the gas is helium [1]. Air contains oxygen, and when it's very hot, oxygen is extremely corrosive. Helium is inert, it doesn't corrode, and it also does not become radioactive when exposed to free neutrons. So you don't need a primary and secondary coolant system, like for the water-cooled reactors. Separately, gas does not necessarily mean less energy dense than water. See for example [2] where they explain that supercritical CO2 has more energy density than supercritical steam. Finally, the root cause of why nuclear power plants are so damn expensive is the lack of experience of their construction crews. Virtually every new nuclear power plant is a one-of-a-kind new construction. Most of the workers don't have any prior experience with the same type of project. So the adage "measure twice and cut once" becomes "measure 100 times and cut once", and even then errors happen, with inevitable delays, because everyone is so terrified of a screw-up. This reactor is supposed to be followed by 18 more of the same design, on the same site. Workers will acquire a tremendous amount of experience. Lots of workers who then can go on different sites and train new trainees. With all this experience under their belt, more and more reactors could be build, for less and less money. The classical learning curve at work. [1] https://en.wikipedia.org/wiki/High-temperature_gas_reactor#Coolant https://en.wikipedia.org/wiki/High-temperature_gas_reactor#C... [2]https://www.powermag.com/what-are-supercritical-co2-power-cycles/ https://www.powermag.com/what-are-supercritical-co2-power-cy...

lmilcin 5y ago
> No, it is using gas. I didn't find a precise quote, but it's very likely the gas is helium [1] You are right, but that doesn't make my other arguments invalid. All gasses are poor at transporting energy because they have very low density, specific heat and because you can't use state change. > Finally, the root cause of why nuclear power plants are so damn expensive is the lack of experience of their construction crews. Virtually every new nuclear power plant is a one-of-a-kind new construction. (...) This reactor is supposed to be followed by 18 more of the same design, on the same site. It doesn't have to be and the pebble-bed doesn't change anything in that regard. You can take any reactor design and replicate multiple times. Actually, a lot of reactors are made this way. Both Chernobyl and Fukushima actually had multiple reactors made from the same blueprint. The issue with pebble-bed reactor is that you must create a lot of them because of how much less dense they are in energy production. You produce much less energy from one so you must get so much better at producing a lot of them (in this case whooping 18 of them -- and that is only a start). All this will cause a lot of reactors and a lot of nuclear material. So even if the individual reactor design is safer, you get many more of them and this might offset any safety improvements. There is after all a lot of factors that we just do not control like terrorism.
- credit_guy 5y ago
  > You produce much less energy from one so you must get so much better at producing a lot of them (in this case whooping 18 of them -- and that is only a start) These reactors are not tiny. Each will produce 260 MW.
  - lmilcin 5y ago
    This is tiny. A typical power plant produces 1GW. Chernobyl produced 1000MW per reactor. Fukushima produced 1100MW per reactor. So you still holds true that you need many times more of these reactors -- in this case about 4 times.