5 ms·

Nuclear engineer here. I've read through a good portion of the regulatory submission to the NRC and have a few takeaways that oppose some of the less-well-info

Nuclear engineer here. I've read through a good portion of the regulatory submission to the NRC and have a few takeaways that oppose some of the less-well-informed takes in this thread: - The reactor differs substantially from existing PWRs by encasing the primary in double containment, using natural circulation flow for both normal operation and emergency cooling. There are no pumps needed (or installed) to move coolant through the reactor. - During normal operation, the primary is entirely contained within the primary containment, and circulates naturally, using the differential temperature and gravity. The steam system can is used to remove heat. - During an emergency, valves open to admit the reactor coolant into the backup containment. These valves are normally held shut by hydraulics with positive control from electronics-- their failure mode is to open with no other operator action in case of a loss of power. No additional operator action is needed to initiate the emergency cooling flow, which is also a natural circulation loop to the backup containment shell, which then conducts heat to the pool. - The backup containment shell is designed to withstand hydrogen explosions such as those that occurred at Fukushima, and which was possibly prevented at Three Mile Island by venting (whether there was a hydrogen explosion at TMI-2 is not fully understood). - There is no mechanism for positive reactivity addition via graphite moderator rod such as in the Chernobyl design. The specific failure mode at Chernobyl is not possible with this reactor. - The pool is specified as a stainless-steel-lined reinforced concrete and designed to withstand earthquakes. The safety systems are such that no reactor electricity supply is needed to remove heat-- the pool could be filled e.g. from a fire truck, and the immediate decay heat from shutdown does not require any additional heat removal or water addition. So the failure mode we saw at Fukushima (inability to remove decay heat due to loss of electricity) and hydrogen explosion breaching containment does not apply to this design.

candiodari 6y ago
> During normal operation, the primary is entirely contained within the primary containment, and circulates naturally, using the differential temperature and gravity. The steam system can is used to remove heat. If it's using gravity, what happens if this whole reactor gets tilted? What happens at 10 degrees? 45? 90? 180? Are there any critical angles where it would melt down? I'm curious how you would make such a design that would be both using gravity yet tolerate being moved around.
- nix23 6y ago
  >what happens if this whole reactor gets tilted? What happens at 10 degrees? 45? 90? 180? Are there any critical angles where it would melt down? Ahh i see, a flat earth believer ;)
  - wukerplank 6y ago
    I suppose earthquakes and other disasters happen (and possibly tilt the reactor) however Earth is shaped?
    - nix23 6y ago
      Sure, you are right but i see HN needs the ⸮ ....
- TheOtherHobbes 6y ago
  I'd be more concerned about possible coolant loss and/or valve failures because of corrosion. https://www.sciencedirect.com/science/article/pii/B9781845697655500159 https://www.sciencedirect.com/science/article/pii/B978184569...
tlear 6y ago
This is very interesting, can reactor like that be used on a ship or submarine(probably stupid question but I am curious). I remember reading some Tom Clancy novel that had a reactor with cooling that used no pumps as a major technical story point.
- HPsquared 6y ago
  On submarines that might be a liquid metal coolant, as used on a few soviet submarine reactors. Lead-bismuth eutectic is most likely, it would be sensible to avoid sodium/potassium coolant on a submarine.
SiempreViernes 6y ago
What is the maximum external temperature the design can operate in? Can you build it in hot places to power air conditioning and things like that during the worst days?
- evgen 6y ago
  I think that the only impact the outside temp has on this is how it relates to the cooling efficiency of the steam loop. External temp will have almost no effect at all on the reactor itself or its operation.
- yohannparis 6y ago
  Those reactors are small compare to usual one, but they still operate in a power plant like a gas or coal one. It's not a home or neighbourhood nuclear reactor.
sandworm101 6y ago
So it requires gravity. It may seem trivial, but how would this thing react if suddenly not mounted vertically, say if it got knocked onto its side while running? Would coolant still flow as planned?
- crowbahr 6y ago
  Anything that knocks a fully functional multiple thousands of tonnes of concrete, steel, water and fissile material onto it's side was already going to fuck up your day. As far as I'm aware we've never had a nuclear reactor go sideways, and it's kinda ludicrous to even ask. It's one of the most massive structures, built on bedrock because it's too heavy to be built on anything else, and even these "small" reactors will be incredibly heavy.
  - sandworm101 6y ago
    They are vertical cylinders to be suspended vertically in a pool of water, not massive squat objects sitting on bedrock. They are thin and relatively top-heavy. It is not ludicrous to ask what could happen should they not remain as vertical as designed. From a planning perspective, if verticality is a requirement then that verticality has to be protected as strongly as any other aspect. Any attachment or mounting points that maintain verticality must therefore be earthquake proof. If, as in the pictures, these reactors are held in place from the top, horizontal shaking from even a small earthquake would put massive strain on that joint. It isn't just the long/thin/heavy reactor but all the water sloshing around too. A super-strong joint and maybe something important bends/breaks under load? A flexible joint to allow the reactor to sway? Sway how much? What happens at the travel limit of the joint? Can we risk the reactor contracting its neighbours? These are not trivial engineering questions.
    - swader999 6y ago
      I was assuming they'd bury these.
    - torpfactory 6y ago
      I think they are not trivial but relatively easy parts of the design. I’m sure they can design support structure to withstand whatever arbitrarily large earthquake you throw at it. The structure doesn’t need to be particularly light or compact so there shouldn’t be any design constraints getting in the way of strength. The heat transfer problem is much much harder and they’ve already solved that apparently.
jhallenworld 6y ago
I'm amazed that convection alone provides enough flow. I mean this is compared to the massive pumps that previous reactors needed. An innovation of the AP1000 was that the massive pump was fully inside the containment (actually attached to the steam generator) and they had to show that it would work without service forever. https://www.neimagazine.com/features/featurethe-world-s-largest-canned-motor-pump https://www.neimagazine.com/features/featurethe-world-s-larg... Anyway, what if the valves to the backup containment open while it's running at full power? I mean the electronics fail so the valves open. I suppose the steam generator is still running, but even so lots of heat would be dumped into the pool. Maybe there is an interlock so that the reactor scrams in this case.
shadowprofile77 6y ago
Layman's question: I don't see how this small reactor is so unique or why it took so long to be developed for regulatory approval. The article claims it produces about 50MW of power with a planned 60MW version. Well, there are already very compact reactors in use on today's aircraft carriers (the A1B and A4W) that produce a much larger 500 to 700MW per module and are also relatively small (after all they fit on individual ships). And obviously deemed quite safe for the exact same reason -they're on ships that travel to all major ports and contain thousands of crew members right inside the same metal hull that the reactor is in. Even more compact and fit into an even smaller vessel quite safely for the crew: submarine reactors like the S8G, which produces over 220MW and measures only 42 x 55 feet in size, with a weight that's not unreasonably greater than that of the NuScale Basically: What's so dramatically difficult about doing the same for a terrestrial compact reactor to make something like the NuScale take so long to get approval?
- njarboe 6y ago
  The $1/2 billion they had to spend due to paperwork related to certification of the design. From an earlier comment[1] from a different thread about this approval quoting NuScale's press release: "NuScale spent over $500 million, with the backing of Fluor, and over 2 million labor hours to develop the information needed to prepare its DCA application" Military reactors don't have to go through this process and those designs (modified to work on land, etc) would. [1]https://news.ycombinator.com/item?id=24346808 https://news.ycombinator.com/item?id=24346808
  - shadowprofile77 6y ago
    In other words, the "impracticality" of compact, safe terrestrial reactor designs is almost entirely created by an immense mountain of bureaucratic hurdle that the military is excepted from? I can see the need for safety and careful documentation of contingencies but the scale of what you describe is simply dismaying. Thank you for that answer and link. checking further now.
  - shadowprofile77 6y ago
    Also, I can't even begin to imagine how much paperwork would be necessary (in literal visual, procedural terms) for the cost of fulfilling it to reach half a billion fucking dollars and 2 million man hours to fulfill. What would this even contain? Multiple 200+ page technical laboratory test breakdowns for every single nut and bolt and washer in the reactor set-up?

candiodari 6y ago

> During normal operation, the primary is entirely contained within the primary containment, and circulates naturally, using the differential temperature and gravity. The steam system can is used to remove heat. If it's using gravity, what happens if this whole reactor gets tilted? What happens at 10 degrees? 45? 90? 180? Are there any critical angles where it would melt down? I'm curious how you would make such a design that would be both using gravity yet tolerate being moved around.

nix23 6y ago
>what happens if this whole reactor gets tilted? What happens at 10 degrees? 45? 90? 180? Are there any critical angles where it would melt down? Ahh i see, a flat earth believer ;)
- wukerplank 6y ago
  I suppose earthquakes and other disasters happen (and possibly tilt the reactor) however Earth is shaped?
  - nix23 6y ago
    Sure, you are right but i see HN needs the ⸮ ....
TheOtherHobbes 6y ago
I'd be more concerned about possible coolant loss and/or valve failures because of corrosion. https://www.sciencedirect.com/science/article/pii/B9781845697655500159 https://www.sciencedirect.com/science/article/pii/B978184569...

tlear 6y ago

This is very interesting, can reactor like that be used on a ship or submarine(probably stupid question but I am curious). I remember reading some Tom Clancy novel that had a reactor with cooling that used no pumps as a major technical story point.

HPsquared 6y ago
On submarines that might be a liquid metal coolant, as used on a few soviet submarine reactors. Lead-bismuth eutectic is most likely, it would be sensible to avoid sodium/potassium coolant on a submarine.

SiempreViernes 6y ago

What is the maximum external temperature the design can operate in? Can you build it in hot places to power air conditioning and things like that during the worst days?

evgen 6y ago
I think that the only impact the outside temp has on this is how it relates to the cooling efficiency of the steam loop. External temp will have almost no effect at all on the reactor itself or its operation.
yohannparis 6y ago
Those reactors are small compare to usual one, but they still operate in a power plant like a gas or coal one. It's not a home or neighbourhood nuclear reactor.

sandworm101 6y ago

So it requires gravity. It may seem trivial, but how would this thing react if suddenly not mounted vertically, say if it got knocked onto its side while running? Would coolant still flow as planned?

crowbahr 6y ago
Anything that knocks a fully functional multiple thousands of tonnes of concrete, steel, water and fissile material onto it's side was already going to fuck up your day. As far as I'm aware we've never had a nuclear reactor go sideways, and it's kinda ludicrous to even ask. It's one of the most massive structures, built on bedrock because it's too heavy to be built on anything else, and even these "small" reactors will be incredibly heavy.
- sandworm101 6y ago
  They are vertical cylinders to be suspended vertically in a pool of water, not massive squat objects sitting on bedrock. They are thin and relatively top-heavy. It is not ludicrous to ask what could happen should they not remain as vertical as designed. From a planning perspective, if verticality is a requirement then that verticality has to be protected as strongly as any other aspect. Any attachment or mounting points that maintain verticality must therefore be earthquake proof. If, as in the pictures, these reactors are held in place from the top, horizontal shaking from even a small earthquake would put massive strain on that joint. It isn't just the long/thin/heavy reactor but all the water sloshing around too. A super-strong joint and maybe something important bends/breaks under load? A flexible joint to allow the reactor to sway? Sway how much? What happens at the travel limit of the joint? Can we risk the reactor contracting its neighbours? These are not trivial engineering questions.
  - swader999 6y ago
    I was assuming they'd bury these.
  - torpfactory 6y ago
    I think they are not trivial but relatively easy parts of the design. I’m sure they can design support structure to withstand whatever arbitrarily large earthquake you throw at it. The structure doesn’t need to be particularly light or compact so there shouldn’t be any design constraints getting in the way of strength. The heat transfer problem is much much harder and they’ve already solved that apparently.

jhallenworld 6y ago

I'm amazed that convection alone provides enough flow. I mean this is compared to the massive pumps that previous reactors needed. An innovation of the AP1000 was that the massive pump was fully inside the containment (actually attached to the steam generator) and they had to show that it would work without service forever. https://www.neimagazine.com/features/featurethe-world-s-largest-canned-motor-pump https://www.neimagazine.com/features/featurethe-world-s-larg... Anyway, what if the valves to the backup containment open while it's running at full power? I mean the electronics fail so the valves open. I suppose the steam generator is still running, but even so lots of heat would be dumped into the pool. Maybe there is an interlock so that the reactor scrams in this case.

shadowprofile77 6y ago

Layman's question: I don't see how this small reactor is so unique or why it took so long to be developed for regulatory approval. The article claims it produces about 50MW of power with a planned 60MW version. Well, there are already very compact reactors in use on today's aircraft carriers (the A1B and A4W) that produce a much larger 500 to 700MW per module and are also relatively small (after all they fit on individual ships). And obviously deemed quite safe for the exact same reason -they're on ships that travel to all major ports and contain thousands of crew members right inside the same metal hull that the reactor is in. Even more compact and fit into an even smaller vessel quite safely for the crew: submarine reactors like the S8G, which produces over 220MW and measures only 42 x 55 feet in size, with a weight that's not unreasonably greater than that of the NuScale Basically: What's so dramatically difficult about doing the same for a terrestrial compact reactor to make something like the NuScale take so long to get approval?

njarboe 6y ago
The $1/2 billion they had to spend due to paperwork related to certification of the design. From an earlier comment[1] from a different thread about this approval quoting NuScale's press release: "NuScale spent over $500 million, with the backing of Fluor, and over 2 million labor hours to develop the information needed to prepare its DCA application" Military reactors don't have to go through this process and those designs (modified to work on land, etc) would. [1]https://news.ycombinator.com/item?id=24346808 https://news.ycombinator.com/item?id=24346808
- shadowprofile77 6y ago
  In other words, the "impracticality" of compact, safe terrestrial reactor designs is almost entirely created by an immense mountain of bureaucratic hurdle that the military is excepted from? I can see the need for safety and careful documentation of contingencies but the scale of what you describe is simply dismaying. Thank you for that answer and link. checking further now.
- shadowprofile77 6y ago
  Also, I can't even begin to imagine how much paperwork would be necessary (in literal visual, procedural terms) for the cost of fulfilling it to reach half a billion fucking dollars and 2 million man hours to fulfill. What would this even contain? Multiple 200+ page technical laboratory test breakdowns for every single nut and bolt and washer in the reactor set-up?