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One thing not addressed is physical security. As pointed out by @adrianmonk it would take many of these tiny reactors to generate the same amount as a typical

One thing not addressed is physical security. As pointed out by @adrianmonk it would take many of these tiny reactors to generate the same amount as a typical older reactor. Older reactors are designed like fortresses, supposedly able to take a direct hit by a commercial jet and survive. They have armed guards, etc. It would be interesting to see how they would try to protect these. Typical electrical substations are protected by a chain-link fence and a padlock.

jabl 6y ago
The idea is to put multiple reactors at the same site, not to spread out mini reactors all over the landscape. So the end result would be a powerplant that produces about as much power as a "normal" nuclear power plant, just that it contains many small reactors instead of a few big ones.
- jessaustin 6y ago
  This undermines some of the claimed benefits. A bunch of little Fukushima Daiichi reactors in the same location wouldn't have fared any better than the actual Fukushima Daiichi reactor.
  - jabl 6y ago
    In this particular case, a power plant with these nuscale reactors would probably have survived a Fukushima type accident. One effect of being small is that the reactors are designed to be passively cooled after shutdown, using convection instead of pumped flow. So there is no need for emergency diesel generators to keep the coolant pumps running.
    - jessaustin 6y ago
      Sure, it's safer for reactors to tolerate flooding, if indeed these reactors actually do tolerate flooding. Definitely that would be a better design in flood/tsunami-prone areas. No design (from history, especially no reactor design) is perfect. A set of smaller reactors that were not co-located would be more tolerant of site-specific vulnerabilities in their design.
      - MurMan 6y ago
        > ... if indeed these reactors actually do tolerate flooding The reactor modules are partially immersed in a pond, the ultimate heat sink. Cooling is passive, i.e., no cooling pumps, and does not require electrical power.
      - hinkley 6y ago
        I think you're screwed either way. The odds that a concentrated site has an event are much higher with colocation. But the changes of having an event at multiple locations are higher if they're spread out. Some things that I believe would matter for colocation would be: - chance of cascading failures - economies of scale/safety in numbers (1 large team vs many small) - plant-to-home efficiency (n fewer reactors due to smaller transmission losses)
      - s1artibartfast 6y ago
        >A set of smaller reactors that were not co-located would be more tolerant of site-specific vulnerabilities in their design That depends on what risks you are trying to mitigate. IF you are talking about site specific natural disasters and freak occurrences damaging a site. Then spreading them out increases risk of failure. If you are worried about power loss after a site destroys a site, then colocation is worse. Of the two, damage to a site is the more pressing concern.
    - hinkley 6y ago
      What's the radius around a reactor where a critical core can trigger fission in the next reactor over?
      - jabl 6y ago
        You'd have to place both cores within the same reactor pressure vessel, which isn't possible.
        hinkley 6y ago
        So as long as the reactor vessel is intact it absorbs 100% of the neutrons? Going out as well as coming in? Because in a failure you’ll have only one pressure vessel between the two cores. If everything else goes right.
        jabl 6y ago
        > So as long as the reactor vessel is intact it absorbs 100% of the neutrons? Going out as well as coming in? Neutron diffusion is a statistical process, so yeah, a small amount of neutrons will escape through the reactor wall. But not enough that the neutron flux from one reactor would influence the next one in any measurable way. > Because in a failure you’ll have only one pressure vessel between the two cores. If everything else goes right. Yes, also in this case.
      - rmtech 6y ago
        In practice, 0.
  - garmaine 6y ago
    Uh, there are a bunch of reactors at Fukushima. It’s in the name: “daiichi” means “complex-1”, there is also a “daini”, etc.

jabl 6y ago

The idea is to put multiple reactors at the same site, not to spread out mini reactors all over the landscape. So the end result would be a powerplant that produces about as much power as a "normal" nuclear power plant, just that it contains many small reactors instead of a few big ones.

jessaustin 6y ago
This undermines some of the claimed benefits. A bunch of little Fukushima Daiichi reactors in the same location wouldn't have fared any better than the actual Fukushima Daiichi reactor.
- jabl 6y ago
  In this particular case, a power plant with these nuscale reactors would probably have survived a Fukushima type accident. One effect of being small is that the reactors are designed to be passively cooled after shutdown, using convection instead of pumped flow. So there is no need for emergency diesel generators to keep the coolant pumps running.
  - jessaustin 6y ago
    Sure, it's safer for reactors to tolerate flooding, if indeed these reactors actually do tolerate flooding. Definitely that would be a better design in flood/tsunami-prone areas. No design (from history, especially no reactor design) is perfect. A set of smaller reactors that were not co-located would be more tolerant of site-specific vulnerabilities in their design.
    - MurMan 6y ago
      > ... if indeed these reactors actually do tolerate flooding The reactor modules are partially immersed in a pond, the ultimate heat sink. Cooling is passive, i.e., no cooling pumps, and does not require electrical power.
    - hinkley 6y ago
      I think you're screwed either way. The odds that a concentrated site has an event are much higher with colocation. But the changes of having an event at multiple locations are higher if they're spread out. Some things that I believe would matter for colocation would be: - chance of cascading failures - economies of scale/safety in numbers (1 large team vs many small) - plant-to-home efficiency (n fewer reactors due to smaller transmission losses)
    - s1artibartfast 6y ago
      >A set of smaller reactors that were not co-located would be more tolerant of site-specific vulnerabilities in their design That depends on what risks you are trying to mitigate. IF you are talking about site specific natural disasters and freak occurrences damaging a site. Then spreading them out increases risk of failure. If you are worried about power loss after a site destroys a site, then colocation is worse. Of the two, damage to a site is the more pressing concern.
  - hinkley 6y ago
    What's the radius around a reactor where a critical core can trigger fission in the next reactor over?
    - jabl 6y ago
      You'd have to place both cores within the same reactor pressure vessel, which isn't possible.
      - hinkley 6y ago
        So as long as the reactor vessel is intact it absorbs 100% of the neutrons? Going out as well as coming in? Because in a failure you’ll have only one pressure vessel between the two cores. If everything else goes right.
        jabl 6y ago
        > So as long as the reactor vessel is intact it absorbs 100% of the neutrons? Going out as well as coming in? Neutron diffusion is a statistical process, so yeah, a small amount of neutrons will escape through the reactor wall. But not enough that the neutron flux from one reactor would influence the next one in any measurable way. > Because in a failure you’ll have only one pressure vessel between the two cores. If everything else goes right. Yes, also in this case.
    - rmtech 6y ago
      In practice, 0.
- garmaine 6y ago
  Uh, there are a bunch of reactors at Fukushima. It’s in the name: “daiichi” means “complex-1”, there is also a “daini”, etc.