4 ms·

These were among the only Lead-bismith cooled nuclear reactors ever operated. Sodium-potassium eutectic or pure sodium coolant is a better heat transfer fluid b

These were among the only Lead-bismith cooled nuclear reactors ever operated. Sodium-potassium eutectic or pure sodium coolant is a better heat transfer fluid but in a water environment it's just a little crazy due to sodium-water chemistry. The US Navy tried sodium coolant in the USS Seawolf [1] and it was smaller, quieter, and more powerful, but they had problems with the steam generators. Not an unsolvable problem but definitely a challenge. The success of the water cooled competitor eventually led to the predominance of water cooled reactors in the commercial fleet. Passively safe Lead-cooled commercial reactors are still thought about today. Challenges include high pumping power required due to high density, erosion issues at high coolant velocity, and corrosion issues without very stringent oxygen control. [1] https://en.wikipedia.org/wiki/USS_Seawolf_(SSN-575) https://en.wikipedia.org/wiki/USS_Seawolf_(SSN-575)

dragonwriter 9y ago
> The success of the water cooled competitor eventually led to the predominance of water cooled reactors in the commercial fleet. By commercial you mean operational (as in non-experimental Navy vessels.) There's precious few commercial nuclear vessels in history (four, each from a different country and I don't think they were ever operational all at the same time), so talking about the dominance of a particular nuclear technology being dominant in a “commercial fleet” seems misplaced.
- acidburnNSA 9y ago
  I meant to refer to the commercial fleet of commercial nuclear power plants making electricity on land, almost all of which have designs directly descended from naval designs. I guess "fleet" isn't a great word to use in the context of naval vessels. Whoops!
  - brandmeyer 9y ago
    Its not commonly known, but the initial generation of commercial power reactors in the US is basically the result of technology transfer from the Naval Nuclear Propulsion program.
jabl 9y ago
I wonder if we'll see non-pwr naval reactors anytime soon. A high temp reactor would allow using a supercritical CO2 Brayton cycle which would take up much less space. On another note, what would happen if a MSR powered ship would sink and the fuel salt would come into contact with sea water? Would the salts dissolve into the water? Much as I like MSR's as a concept, if so this would make them a quite bad idea on a ship...
- leeter 9y ago
  Not in the US Navy. Part of the reason the US Navy standardized on PWR is that while it's not the most efficient it is something you can restart at depth if necessary. The lesson of how much that matters was driven home by the loss of the USS Thresher.
  - acidburnNSA 9y ago
    It should be technically feasible to restart a liquid-metal cooled reactor at depth just as easily as a PWR, especially a Na- or NaK-cooled one. Certainly keeping the coolant liquid after shutdown can be a challenge but as long as the plant has operated for a while there should be significant decay heat to keep it warm, and trace heating in the pipes could be powered by auxiliary power if necessary.
  - cocoablazing 9y ago
    This had more to do with safety system failres and procedures regarding operation of critical valves than poison kinetics. LM designs were abandoned prior to this accident due to availability and maintainability issues.
  - brandmeyer 9y ago
    The kind of emergency restart procedure employed today would work just fine on a MSR design. We're talking restarts on the order 1-10 minutes after an emergency shutdown. That's not nearly enough time to solidify the core, even when you are drawing some steam for emergency propulsion needs while the reactor is shutdown.
- acidburnNSA 9y ago

dragonwriter 9y ago

> The success of the water cooled competitor eventually led to the predominance of water cooled reactors in the commercial fleet. By commercial you mean operational (as in non-experimental Navy vessels.) There's precious few commercial nuclear vessels in history (four, each from a different country and I don't think they were ever operational all at the same time), so talking about the dominance of a particular nuclear technology being dominant in a “commercial fleet” seems misplaced.

acidburnNSA 9y ago
I meant to refer to the commercial fleet of commercial nuclear power plants making electricity on land, almost all of which have designs directly descended from naval designs. I guess "fleet" isn't a great word to use in the context of naval vessels. Whoops!
- brandmeyer 9y ago
  Its not commonly known, but the initial generation of commercial power reactors in the US is basically the result of technology transfer from the Naval Nuclear Propulsion program.

jabl 9y ago

I wonder if we'll see non-pwr naval reactors anytime soon. A high temp reactor would allow using a supercritical CO2 Brayton cycle which would take up much less space. On another note, what would happen if a MSR powered ship would sink and the fuel salt would come into contact with sea water? Would the salts dissolve into the water? Much as I like MSR's as a concept, if so this would make them a quite bad idea on a ship...

leeter 9y ago
Not in the US Navy. Part of the reason the US Navy standardized on PWR is that while it's not the most efficient it is something you can restart at depth if necessary. The lesson of how much that matters was driven home by the loss of the USS Thresher.
- acidburnNSA 9y ago
  It should be technically feasible to restart a liquid-metal cooled reactor at depth just as easily as a PWR, especially a Na- or NaK-cooled one. Certainly keeping the coolant liquid after shutdown can be a challenge but as long as the plant has operated for a while there should be significant decay heat to keep it warm, and trace heating in the pipes could be powered by auxiliary power if necessary.
- cocoablazing 9y ago
  This had more to do with safety system failres and procedures regarding operation of critical valves than poison kinetics. LM designs were abandoned prior to this accident due to availability and maintainability issues.
- brandmeyer 9y ago
  The kind of emergency restart procedure employed today would work just fine on a MSR design. We're talking restarts on the order 1-10 minutes after an emergency shutdown. That's not nearly enough time to solidify the core, even when you are drawing some steam for emergency propulsion needs while the reactor is shutdown.
acidburnNSA 9y ago