3 ms·

Increasing temperatures increase steam pressure until a rupture occurs, and the water boils away. The steel reactor vessel and structural elements will then ine

by blake1 7y ago

Increasing temperatures increase steam pressure until a rupture occurs, and the water boils away. The steel reactor vessel and structural elements will then inevitably melt, and the reaction will continue until the molten fuel can spread out enough to lose criticality. This is called a meltdown.

exrook 7y ago
This is why many new reactor designs do not use water as coolant but instead molten salt[0] or inert gas[1], to avoid the risk of steam explosion. This alone does not make those reactors inherently safe but it can help keep radioactive material from being violently spread outside the reactor in the event of catastrophic failure. [0] https://en.wikipedia.org/wiki/Molten_salt_reactor https://en.wikipedia.org/wiki/Molten_salt_reactor [1] https://en.wikipedia.org/wiki/Gas-cooled_reactor https://en.wikipedia.org/wiki/Gas-cooled_reactor
hwillis 7y ago
> Increasing temperatures increase steam pressure until a rupture occurs, and the water boils away. Generally, no. Chernobyl is the biggest example of this happening, but it only happened because the reactor itself was basically exploding anyway. Steam pressure doesn't build up gradually, generally. Relief valves -even just burst points- are just too simple and robust. The much more common issue is that hot reactor fuel causes water to break down and release hydrogen which accumulates at the top of the reactor and eventually explodes, and then the water boils off.
- battery_cowboy 7y ago
  > Relief valves -even just burst points- are just too simple and robust I'm not sure you've heard about this[0] accident: "The accident began with failures in the non-nuclear secondary system, followed by a stuck-open pilot-operated relief valve in the primary system, which allowed large amounts of nuclear reactor coolant to escape." [0] https://en.wikipedia.org/wiki/Three_Mile_Island_accident https://en.wikipedia.org/wiki/Three_Mile_Island_accident
  - ohyes 7y ago
    The relief valve worked perfectly, as they said, there was no steam explosion. Unfortunately too much of the steam was released and the reactor melted.
    - battery_cowboy 7y ago
      Uhhh, the valve worked perfectly but released too much steam resulting in a meltdown? Think about this for just a wee bit more.
      - ohyes 7y ago
        okay not perfectly as it was stuck open, but it did release the pressure as was said.
chrisseaton 7y ago
But isn’t the water that is being cycled from the reactor to the turbine reducing the temperature? Isn’t cooling the reactor throwing energy away?
- satanspastaroll 7y ago
  Similarily to bikebreaks, it's often better to be safe than most efficient
- blake1 7y ago
  As one of the other sibling comments noted, a turbine can extract maybe 33% of the thermal energy if it’s operating at the theoretical maximum Carnot efficiency. The other 66% must be dumped somewhere to avoid accidents.
  - chrisseaton 7y ago
    So what is being cooled is really the backend of the turbine, not the reactor.

by blake1 7y ago

exrook 7y ago

This is why many new reactor designs do not use water as coolant but instead molten salt[0] or inert gas[1], to avoid the risk of steam explosion. This alone does not make those reactors inherently safe but it can help keep radioactive material from being violently spread outside the reactor in the event of catastrophic failure. [0] https://en.wikipedia.org/wiki/Molten_salt_reactor https://en.wikipedia.org/wiki/Molten_salt_reactor [1] https://en.wikipedia.org/wiki/Gas-cooled_reactor https://en.wikipedia.org/wiki/Gas-cooled_reactor

hwillis 7y ago

> Increasing temperatures increase steam pressure until a rupture occurs, and the water boils away. Generally, no. Chernobyl is the biggest example of this happening, but it only happened because the reactor itself was basically exploding anyway. Steam pressure doesn't build up gradually, generally. Relief valves -even just burst points- are just too simple and robust. The much more common issue is that hot reactor fuel causes water to break down and release hydrogen which accumulates at the top of the reactor and eventually explodes, and then the water boils off.

battery_cowboy 7y ago
> Relief valves -even just burst points- are just too simple and robust I'm not sure you've heard about this[0] accident: "The accident began with failures in the non-nuclear secondary system, followed by a stuck-open pilot-operated relief valve in the primary system, which allowed large amounts of nuclear reactor coolant to escape." [0] https://en.wikipedia.org/wiki/Three_Mile_Island_accident https://en.wikipedia.org/wiki/Three_Mile_Island_accident
- ohyes 7y ago
  The relief valve worked perfectly, as they said, there was no steam explosion. Unfortunately too much of the steam was released and the reactor melted.
  - battery_cowboy 7y ago
    Uhhh, the valve worked perfectly but released too much steam resulting in a meltdown? Think about this for just a wee bit more.
    - ohyes 7y ago
      okay not perfectly as it was stuck open, but it did release the pressure as was said.

chrisseaton 7y ago

But isn’t the water that is being cycled from the reactor to the turbine reducing the temperature? Isn’t cooling the reactor throwing energy away?

satanspastaroll 7y ago
Similarily to bikebreaks, it's often better to be safe than most efficient
blake1 7y ago
As one of the other sibling comments noted, a turbine can extract maybe 33% of the thermal energy if it’s operating at the theoretical maximum Carnot efficiency. The other 66% must be dumped somewhere to avoid accidents.
- chrisseaton 7y ago
  So what is being cooled is really the backend of the turbine, not the reactor.