8 ms·

> All honor to Kairos if they can deliver, but history is against them. History is not really against them. Our current reactors (mainly pressurized water reac

> All honor to Kairos if they can deliver, but history is against them. History is not really against them. Our current reactors (mainly pressurized water reactors) are the way they are because Admiral Rickover determined that PWRs are the best option for submarines. He was not wrong, but civilian power reactors are not the same as the reactors powering submarines. PWRs are expensive mainly because of the huge pressure inside the reactor core, about 150 times higher than the atmospheric pressure. For comparison, a pressure cooker has an internal pressure about 5 times higher than the atmospheric pressure, and such a cooker can explode with a pretty loud bang. The Kairos Hermes reactor design is based on a design that was tested in the '60s, the Molten-Salt Reactor Experiment [1]. While such a reactor can be used to burn thorium, Kairos decided to go with the far more conventional approach of burning U-235. The reactor operates at approximately regular atmospheric pressure. This should reduce considerably the construction costs. Of course, there are unknowns. While the world has built thousands of pressurized water reactors, it has built maybe 10 molten salt reactors. For example one quite unexpected effect in the MSRE was the enbrittlement of the reactor vessel caused by tellurium, which shows up as a fission product when U-235 burns. The Nuclear Regulatory Commission is a very conservative organization, and they don't have much experience with molten salt reactors because nobody has. It took them 6 years to give NuScale an approval for a pressurized water reactor, design that they knew in and out. My guess is that they will not give Kairos an approval without at least 15 years of testing. But Google's agreement with Kairos is quite crucial to keep this testing going. [1] https://en.wikipedia.org/wiki/Molten-Salt_Reactor_Experiment https://en.wikipedia.org/wiki/Molten-Salt_Reactor_Experiment

cyberax 2y ago
> The Kairos Hermes reactor design is based on a design that was tested in the '60s, the Molten-Salt Reactor Experiment MSRs are a costly distraction. They are not viable without literally hundreds of billions in research and development money. That's why all the MSRs startups are failing long before they even start the licensing process. > For example one quite unexpected effect in the MSRE was the enbrittlement of the reactor vessel caused by tellurium, which shows up as a fission product when U-235 burns. It was not unexpected. The _main_ issue with MSRs is that they have to contain fluoride salts that release elemental fluorine radicals as a result of radiolysis. So the reactor vessel walls will be eaten up by them, rather rapidly. Especially when reactors are scaled up to a level that makes them practical. And then you have all the fission byproducts that literally include almost all the Periodic Table.
- pfdietz 2y ago
  The Kairos design does not dissolve the fuel in the salt.
  - cyberax 2y ago
    OK, that's interesting. And it's far better than MSRs, but it still exposes fluoride salts to radiation. It also is a pebble bed reactor, so it'll have all the problems of pebble beds: cracking pellets, difficulty in fuel reprocessing, more nuclear waste, etc. But yes, this design might be actually feasible for small reactors. But I bet that it won't be cheaper and it'll be impossible to scale to levels approaching PWRs.
    - conradev 2y ago
      The theory, at least, is that making SMRs in a factory allows for a steeper and more sustainable learning curve > Both Hermes and ETU 3.0 will be built using modular construction techniques, with reactor modules fabricated in Kairos Power's facility in Albuquerque, New Mexico, which will be shipped to Oak Ridge for assembly. https://www.world-nuclear-news.org/articles/work-begins-on-first-us-gen-iv-reactor https://www.world-nuclear-news.org/articles/work-begins-on-f...
    - pfdietz 2y ago
      Fluoride salts by themselves are very radiation resistant, chemically more so than water. The biggest concern would be liberation of elemental fluorine, but if the salt is kept slightly reducing (which one can do in a sterile salt without dissolved uranium) the fluorine instantly reacts back to fluoride. The slightly reduced salt is also preferred to limit corrosion, allowing the vessel and pipes to be made of stainless steel (FLiBe with dissolved uranium needs special more expensive alloys because chromium would dissolve.) Activation is also low. The two concerns would be traces of tritium from the two-step activation of beryllium (formation of 6He by (n,alpha) reaction, decay of 6He to 6Li, then (n,t) on 6Li), and also formation of 10Be (half life, 1.4 million years, but the thermal neutron capture cross section of 9Be is only 8.5 mb). The chemical toxicity of beryllium would considerably exceed its radiotoxicity, I imagine.
alwayslikethis 2y ago
> pressure cooker has an internal pressure about 5 times higher than the atmospheric pressure This isn't really accurate. The majority of pressure cookers you can buy operates at an absolute pressure of only about twice the atmospheric pressure.
- credit_guy 2y ago
  Ok. And they are still dangerous if they explode. Imagine what happens if something at 150 atm explodes.
  - jonkoops 2y ago
    You don't have to imagine, it happened several times.
    - DennisP 2y ago
      Once, if you're just talking about nuclear reactors. The reactor vessel didn't explode at Fukushima, just the outer building due to accumulated hydrogen. TMI didn't explode at all, the fuel melted but didn't breach containment.
bewaretheirs 2y ago
According to their web site at https://kairospower.com/technology/ https://kairospower.com/technology/ it uses a molten fluoride salt based coolant but unlike the MSR/LFTR designs the fissionable fuel is not dissolved into the coolant; instead, the Kairos reactor design puts the fissionables in pellets that are intended to remain solid while in operation; it looks more like a pebble-bed reactor than a MSR/LFTR.
- credit_guy 2y ago
  Yes, you are right, I was wrong. The Hermes design is even more conservative than the MSRE design. It is basically the same design as the helium-cooled reactor HTR-PM that China started operating two years ago, only that the helium cooling is replaced with FLiBe cooling; this achieves a higher power density plus a higher rate of passive cooling in case anything goes wrong. This IAEA report [1] has more details about this design, and the dozens if not hundreds of other types of molten salt reactor designs. The relevant section for the Kairos Hermes design is 4.5 (pages 41-44). [1] https://www-pub.iaea.org/MTCD/Publications/PDF/STI-DOC-010-489_web.pdf https://www-pub.iaea.org/MTCD/Publications/PDF/STI-DOC-010-4...
mattmaroon 2y ago
Not super relevant but pressure cookers only go up to about 1 bar. They definitely would blow before 5.
- earthnail 2y ago
  1 bar is atmospheric pressure. I.e., as far as you in your kitchen are concerned, no pressure at all.
  - roelschroeven 2y ago
    Pressure is very often stated as gauge pressure, i.e. zero-referenced against ambient air pressure. 1 bar gauge pressure is roughly equal to 2 bar absolute pressure.
rob74 2y ago
> The Nuclear Regulatory Commission is a very conservative organization I'm glad they are, actually! Personally, I'm not really convinced by the "small modular reactor" concept. Ok, so building a big nuclear power plant is expensive. But is it really cheaper to build 10 smaller nuclear power plants (which all need to conform to the same safety regulations, need maintenance, personnel etc.) instead?
- rkangel 2y ago
  I firmly believe that iteration is the key to good engineering. SpaceX has got where they are (partly) due to running flight after flight with incremental improvements each time. The problem with the massive reactors is that you get to build only a couple of them, so you never get to take advantage of learnings to make the next one better/cheaper/quicker.
  - rob74 2y ago
    So basically it's one economy of scale (making something bigger means the costs for safety, maintenance, personnel etc. are proportionally lower) vs. another economy of scale (making more of one thing decreases the costs per "unit"). Place your bets... About your comparison to SpaceX: the approach of building a rocket, launching it, letting it explode and then using the gathered data to make the next one explode later (or not at all) is fine for rockets, but I wouldn't want to see it applied to nuclear reactors.
    - rkangel 2y ago
      I do agree on not letting nuclear reactors explode, but I did use the SpaceX example on purpose. Before SpaceX started to do it, the concept of iterating to that degree on rockets was unthinkable. There was a self reinforcing loop of "rocket launches are expensive, so we must plan for every contingency, so the launch cycle is long and expensive". SpaceX proved that wrong. I think small modular reactors are the way out of the similar cycle we've got for nuclear reactors. And I think that building a small number of large ones is going to be a lot better if we're also building a large number of small ones and learning. It's like not building a y houses for 30 years and then building a massive skyscraper. If that's all we do then we'll only ever have one way of building a skyscraper because there's no room to experiment on other construction materials and techniques.
AtlasBarfed 2y ago
Using solid fuel in a msr is certainly a choice. Hopefully it is just a stepping stone.

cyberax 2y ago

> The Kairos Hermes reactor design is based on a design that was tested in the '60s, the Molten-Salt Reactor Experiment MSRs are a costly distraction. They are not viable without literally hundreds of billions in research and development money. That's why all the MSRs startups are failing long before they even start the licensing process. > For example one quite unexpected effect in the MSRE was the enbrittlement of the reactor vessel caused by tellurium, which shows up as a fission product when U-235 burns. It was not unexpected. The _main_ issue with MSRs is that they have to contain fluoride salts that release elemental fluorine radicals as a result of radiolysis. So the reactor vessel walls will be eaten up by them, rather rapidly. Especially when reactors are scaled up to a level that makes them practical. And then you have all the fission byproducts that literally include almost all the Periodic Table.

pfdietz 2y ago
The Kairos design does not dissolve the fuel in the salt.
- cyberax 2y ago
  OK, that's interesting. And it's far better than MSRs, but it still exposes fluoride salts to radiation. It also is a pebble bed reactor, so it'll have all the problems of pebble beds: cracking pellets, difficulty in fuel reprocessing, more nuclear waste, etc. But yes, this design might be actually feasible for small reactors. But I bet that it won't be cheaper and it'll be impossible to scale to levels approaching PWRs.
  - conradev 2y ago
    The theory, at least, is that making SMRs in a factory allows for a steeper and more sustainable learning curve > Both Hermes and ETU 3.0 will be built using modular construction techniques, with reactor modules fabricated in Kairos Power's facility in Albuquerque, New Mexico, which will be shipped to Oak Ridge for assembly. https://www.world-nuclear-news.org/articles/work-begins-on-first-us-gen-iv-reactor https://www.world-nuclear-news.org/articles/work-begins-on-f...
  - pfdietz 2y ago
    Fluoride salts by themselves are very radiation resistant, chemically more so than water. The biggest concern would be liberation of elemental fluorine, but if the salt is kept slightly reducing (which one can do in a sterile salt without dissolved uranium) the fluorine instantly reacts back to fluoride. The slightly reduced salt is also preferred to limit corrosion, allowing the vessel and pipes to be made of stainless steel (FLiBe with dissolved uranium needs special more expensive alloys because chromium would dissolve.) Activation is also low. The two concerns would be traces of tritium from the two-step activation of beryllium (formation of 6He by (n,alpha) reaction, decay of 6He to 6Li, then (n,t) on 6Li), and also formation of 10Be (half life, 1.4 million years, but the thermal neutron capture cross section of 9Be is only 8.5 mb). The chemical toxicity of beryllium would considerably exceed its radiotoxicity, I imagine.

alwayslikethis 2y ago

> pressure cooker has an internal pressure about 5 times higher than the atmospheric pressure This isn't really accurate. The majority of pressure cookers you can buy operates at an absolute pressure of only about twice the atmospheric pressure.

credit_guy 2y ago
Ok. And they are still dangerous if they explode. Imagine what happens if something at 150 atm explodes.
- jonkoops 2y ago
  You don't have to imagine, it happened several times.
  - DennisP 2y ago
    Once, if you're just talking about nuclear reactors. The reactor vessel didn't explode at Fukushima, just the outer building due to accumulated hydrogen. TMI didn't explode at all, the fuel melted but didn't breach containment.

bewaretheirs 2y ago

According to their web site at https://kairospower.com/technology/ https://kairospower.com/technology/ it uses a molten fluoride salt based coolant but unlike the MSR/LFTR designs the fissionable fuel is not dissolved into the coolant; instead, the Kairos reactor design puts the fissionables in pellets that are intended to remain solid while in operation; it looks more like a pebble-bed reactor than a MSR/LFTR.

credit_guy 2y ago
Yes, you are right, I was wrong. The Hermes design is even more conservative than the MSRE design. It is basically the same design as the helium-cooled reactor HTR-PM that China started operating two years ago, only that the helium cooling is replaced with FLiBe cooling; this achieves a higher power density plus a higher rate of passive cooling in case anything goes wrong. This IAEA report [1] has more details about this design, and the dozens if not hundreds of other types of molten salt reactor designs. The relevant section for the Kairos Hermes design is 4.5 (pages 41-44). [1] https://www-pub.iaea.org/MTCD/Publications/PDF/STI-DOC-010-489_web.pdf https://www-pub.iaea.org/MTCD/Publications/PDF/STI-DOC-010-4...

mattmaroon 2y ago

Not super relevant but pressure cookers only go up to about 1 bar. They definitely would blow before 5.

earthnail 2y ago
1 bar is atmospheric pressure. I.e., as far as you in your kitchen are concerned, no pressure at all.
- roelschroeven 2y ago
  Pressure is very often stated as gauge pressure, i.e. zero-referenced against ambient air pressure. 1 bar gauge pressure is roughly equal to 2 bar absolute pressure.

rob74 2y ago

> The Nuclear Regulatory Commission is a very conservative organization I'm glad they are, actually! Personally, I'm not really convinced by the "small modular reactor" concept. Ok, so building a big nuclear power plant is expensive. But is it really cheaper to build 10 smaller nuclear power plants (which all need to conform to the same safety regulations, need maintenance, personnel etc.) instead?

rkangel 2y ago
I firmly believe that iteration is the key to good engineering. SpaceX has got where they are (partly) due to running flight after flight with incremental improvements each time. The problem with the massive reactors is that you get to build only a couple of them, so you never get to take advantage of learnings to make the next one better/cheaper/quicker.
- rob74 2y ago
  So basically it's one economy of scale (making something bigger means the costs for safety, maintenance, personnel etc. are proportionally lower) vs. another economy of scale (making more of one thing decreases the costs per "unit"). Place your bets... About your comparison to SpaceX: the approach of building a rocket, launching it, letting it explode and then using the gathered data to make the next one explode later (or not at all) is fine for rockets, but I wouldn't want to see it applied to nuclear reactors.
  - rkangel 2y ago
    I do agree on not letting nuclear reactors explode, but I did use the SpaceX example on purpose. Before SpaceX started to do it, the concept of iterating to that degree on rockets was unthinkable. There was a self reinforcing loop of "rocket launches are expensive, so we must plan for every contingency, so the launch cycle is long and expensive". SpaceX proved that wrong. I think small modular reactors are the way out of the similar cycle we've got for nuclear reactors. And I think that building a small number of large ones is going to be a lot better if we're also building a large number of small ones and learning. It's like not building a y houses for 30 years and then building a massive skyscraper. If that's all we do then we'll only ever have one way of building a skyscraper because there's no room to experiment on other construction materials and techniques.

AtlasBarfed 2y ago

Using solid fuel in a msr is certainly a choice. Hopefully it is just a stepping stone.