5 ms·

And it's not cold enough to cool the reactor

by number6 2mo ago

masklinn 2mo ago
The reactor absolutely is not going to care, it’s the tertiary cooling circuit cooling for the steam turbines, it will have cooked off everything downstream long before it’s an issue. This is entirely an ecological and safety concern.
seszett 2mo ago
No that's never the problem, even 40°C intake is cool enough to cool a reactor, it's all just a question of returned water temperature that can be harmful to a river if too high (generally the limit in Europe is set to 30°C).
- masklinn 2mo ago
  It can vary by the river too (e.g. I remember Switzerland pulling back a reactor around 25 intake), and iirc there’s an absolute limit on the outflow (you don’t want to boil alive the stuff just off of the plant) and a relative one a bit downstream (you can’t heat the river to 20 when it’s freezing). These heatwaves reduce the margin from both directions, a hotter intake means you have less margin on the outflow, and the lower flow rate means there’s less water to dilute that outflow. And apparently for that specific plant there’s also the water level not even reaching the intake.
- Retric 2mo ago
  As long as it’s designed for those temperatures everything is fine, but efficiency still suffers.
shakow 2mo ago
Absolutely wrong. A difference of a couple degrees is not going to hamper cooling a reactor that is running at many hundred degrees. Just imagine what it would spell for your car otherwise.
- ZeroGravitas 2mo ago
  I think both nuclear steam and car engines are affected by high ambient temp, gas and coal engines too. That is after all why they bring in water or air to car radiators, to cool them. Probably only a single percent or so for a few degrees change though.
  - voakbasda 2mo ago
    Begs the question: coul reactors use radiative air cooling? Channel the water through a huge radiator and transfer the heat to the air
    - masklinn 2mo ago
      Not really, a large reactor is way too power dense. An EPR reactor has a thermal output of 4.6GW. And the tertiary is cooling steam turbines so it's below boiling, you'd need something like 10 sqkm worth of surface, per reactor, with an environment cool enough that this could actually radiate. Even using industrial air-cooling design you'd need on the order of a million sqm or two (for reference a good quality computer heatsink is about a third of a square meter worth of fins)
      - philipkglass 2mo ago
        The German THTR-300 reactor operated with air cooling: https://en.wikipedia.org/wiki/THTR-300 https://en.wikipedia.org/wiki/THTR-300 But it was admittedly a huge cooling system for a reactor that only produced 750 megawatts of thermal energy.
      - leonidasrup 2mo ago
        Mochovce nuclear power plant, with evaporative cooling towers, uses around 21.6 to 24.8 million m³ per year depending on operating units and seasonal weather demands. (About 0.7 m³ per second) https://www.seas.sk/wp-content/uploads/a3/b4/2023_SE_NPP_ENG.pdf https://www.seas.sk/wp-content/uploads/a3/b4/2023_SE_NPP_ENG...
    - 2mo ago
dredmorbius 2mo ago
The principle cooling mechanism is vapourisation. The heat of vapourisation for water, converting liquid to steam, is 40.66 kJ/mol, or 2257 J/g. It takes a lot of energy to boil off water.[1] That compares with the latent heat of liquid water, the energy required to heat one unit of water by one degree, which is 4.2 J/g*K (where K is the delta temperature in Kelvin). Raising the temperature of input by, say, 10 degrees, would only reduce the cooling factor by less than 2%. ________________________________ Notes: 1. Which is why live steam is so dangerous. Steam condensing will release a huge amount of thermal energy, making steam burns especially harmful.
- CobaltFire 2mo ago
  Backing this up, these high numbers are for typical cooling towers where they vent to atmosphere. Once you get into closed loop PWRs the numbers get crazy. Actual figures for Naval Nuclear plants are classified, but as a nice round number example if you pressurize the secondary loop to 250psi you end up with about 1,725 kJ/kilogram to boil it. Absolutely terrifying stuff.
  - dredmorbius 2mo ago
    One of us seems to have our numbers wrong. 1,725 kJ/kg is 1,725 J/g, which is less than the enthalpy of vapourisation I'd quoted. (Though yes, I understand your point: pressurisation raises boiling point, and so far as I'm aware, vapourisation energy.)
    - CobaltFire 2mo ago
      Probably me. I wrote that on the train...
VLM 2mo ago
OP is correct, the people making fun of OP don't have an engineering background. The pressure of a condenser at 90F (hot summer day) is about 1/20th of an atmosphere and ... pretty obviously the pressure of a condenser at 212F is about one atmosphere. You can't just arbitrarily decide to change the low pressure side of a turbine like that, its not going to turn out well. You could, in theory, design an entire thermal plant coolant loop to deal with the condenser running at 1 atm instead of 1/20th atm but most will not. There are also heat flow rate issues where the higher the delta V the higher the watts. Regardless of condenser pressure issue above, if a heat exchanger can pull 1 MW across a 150 degree delta-V then if you run the cold side much warmer at only 15 degrees delta V it can only "pull" 0.1 MW of heat. Its surface area doesn't magically get bigger LOL. Remember that for every watt of electricity you get to dump around three watts of thermal heat. If you lose 9 MW of cooling power you lose 3 MW of output electrical power. You have to move more heat than non-engineers expect, to generate electricity. Its a simplification, but for various reasons they like to design the hot side as hot as possible, so if you lose 100F of cooling you can't keep the same power output and simply run the hot side 100F hotter than normal and keep the same flow rate. Absolutely nothing good will come from overheating it like that. You could engineer a thermal plant (thermal as in coal, nuclear, burning recyclables and biowaste, anything to make steam) that runs at an ideal hot side of 212F and let the hot side literally boil water in a pool. However, they don't make plants like that IRL and trying to force it under those conditions would turn out very bad... The first thing that comes to mind is gunk buildup and higher corrosion rates. Steel (generically speaking) corrodes in water about twice as fast per every 20C increase, so turning a cold water plant into a water boiler would to first approximation cause about a year's worth extra corrosion per month. Could be designed around, but I would not want to cowboy a nuke and just try it. Some of those parts are very expensive; even if you can safely run the plant and replace the corroded parts at a substantially accelerated rate, the cost of power due to corroding the cold side parts might make the power too expensive even if its "safe enough", making it cheaper to just shut down. Moving large amounts of water (or air) is extremely expensive, both capex and opex, so an additional 10x higher once in awhile here and there could be a lot of money...
chermi 2mo ago
Lol no. Latent heat is basically all that matters

And it's not cold enough to cool the reactor

by number6 2mo ago

And it's not cold enough to cool the reactor

The reactor absolutely is not going to care, it’s the tertiary cooling circuit cooling for the steam turbines, it will have cooked off everything downstream long before it’s an issue. This is entirely an ecological and safety concern.

seszett 2mo ago

No that's never the problem, even 40°C intake is cool enough to cool a reactor, it's all just a question of returned water temperature that can be harmful to a river if too high (generally the limit in Europe is set to 30°C).

masklinn 2mo ago
It can vary by the river too (e.g. I remember Switzerland pulling back a reactor around 25 intake), and iirc there’s an absolute limit on the outflow (you don’t want to boil alive the stuff just off of the plant) and a relative one a bit downstream (you can’t heat the river to 20 when it’s freezing). These heatwaves reduce the margin from both directions, a hotter intake means you have less margin on the outflow, and the lower flow rate means there’s less water to dilute that outflow. And apparently for that specific plant there’s also the water level not even reaching the intake.
Retric 2mo ago
As long as it’s designed for those temperatures everything is fine, but efficiency still suffers.

shakow 2mo ago

Absolutely wrong. A difference of a couple degrees is not going to hamper cooling a reactor that is running at many hundred degrees. Just imagine what it would spell for your car otherwise.

ZeroGravitas 2mo ago
I think both nuclear steam and car engines are affected by high ambient temp, gas and coal engines too. That is after all why they bring in water or air to car radiators, to cool them. Probably only a single percent or so for a few degrees change though.
- voakbasda 2mo ago
  Begs the question: coul reactors use radiative air cooling? Channel the water through a huge radiator and transfer the heat to the air
  - masklinn 2mo ago
    Not really, a large reactor is way too power dense. An EPR reactor has a thermal output of 4.6GW. And the tertiary is cooling steam turbines so it's below boiling, you'd need something like 10 sqkm worth of surface, per reactor, with an environment cool enough that this could actually radiate. Even using industrial air-cooling design you'd need on the order of a million sqm or two (for reference a good quality computer heatsink is about a third of a square meter worth of fins)
    - philipkglass 2mo ago
      The German THTR-300 reactor operated with air cooling: https://en.wikipedia.org/wiki/THTR-300 https://en.wikipedia.org/wiki/THTR-300 But it was admittedly a huge cooling system for a reactor that only produced 750 megawatts of thermal energy.
    - leonidasrup 2mo ago
      Mochovce nuclear power plant, with evaporative cooling towers, uses around 21.6 to 24.8 million m³ per year depending on operating units and seasonal weather demands. (About 0.7 m³ per second) https://www.seas.sk/wp-content/uploads/a3/b4/2023_SE_NPP_ENG.pdf https://www.seas.sk/wp-content/uploads/a3/b4/2023_SE_NPP_ENG...
  - 2mo ago

dredmorbius 2mo ago

The principle cooling mechanism is vapourisation. The heat of vapourisation for water, converting liquid to steam, is 40.66 kJ/mol, or 2257 J/g. It takes a lot of energy to boil off water.[1] That compares with the latent heat of liquid water, the energy required to heat one unit of water by one degree, which is 4.2 J/g*K (where K is the delta temperature in Kelvin). Raising the temperature of input by, say, 10 degrees, would only reduce the cooling factor by less than 2%. ________________________________ Notes: 1. Which is why live steam is so dangerous. Steam condensing will release a huge amount of thermal energy, making steam burns especially harmful.

CobaltFire 2mo ago
Backing this up, these high numbers are for typical cooling towers where they vent to atmosphere. Once you get into closed loop PWRs the numbers get crazy. Actual figures for Naval Nuclear plants are classified, but as a nice round number example if you pressurize the secondary loop to 250psi you end up with about 1,725 kJ/kilogram to boil it. Absolutely terrifying stuff.
- dredmorbius 2mo ago
  One of us seems to have our numbers wrong. 1,725 kJ/kg is 1,725 J/g, which is less than the enthalpy of vapourisation I'd quoted. (Though yes, I understand your point: pressurisation raises boiling point, and so far as I'm aware, vapourisation energy.)
  - CobaltFire 2mo ago
    Probably me. I wrote that on the train...

VLM 2mo ago

OP is correct, the people making fun of OP don't have an engineering background. The pressure of a condenser at 90F (hot summer day) is about 1/20th of an atmosphere and ... pretty obviously the pressure of a condenser at 212F is about one atmosphere. You can't just arbitrarily decide to change the low pressure side of a turbine like that, its not going to turn out well. You could, in theory, design an entire thermal plant coolant loop to deal with the condenser running at 1 atm instead of 1/20th atm but most will not. There are also heat flow rate issues where the higher the delta V the higher the watts. Regardless of condenser pressure issue above, if a heat exchanger can pull 1 MW across a 150 degree delta-V then if you run the cold side much warmer at only 15 degrees delta V it can only "pull" 0.1 MW of heat. Its surface area doesn't magically get bigger LOL. Remember that for every watt of electricity you get to dump around three watts of thermal heat. If you lose 9 MW of cooling power you lose 3 MW of output electrical power. You have to move more heat than non-engineers expect, to generate electricity. Its a simplification, but for various reasons they like to design the hot side as hot as possible, so if you lose 100F of cooling you can't keep the same power output and simply run the hot side 100F hotter than normal and keep the same flow rate. Absolutely nothing good will come from overheating it like that. You could engineer a thermal plant (thermal as in coal, nuclear, burning recyclables and biowaste, anything to make steam) that runs at an ideal hot side of 212F and let the hot side literally boil water in a pool. However, they don't make plants like that IRL and trying to force it under those conditions would turn out very bad... The first thing that comes to mind is gunk buildup and higher corrosion rates. Steel (generically speaking) corrodes in water about twice as fast per every 20C increase, so turning a cold water plant into a water boiler would to first approximation cause about a year's worth extra corrosion per month. Could be designed around, but I would not want to cowboy a nuke and just try it. Some of those parts are very expensive; even if you can safely run the plant and replace the corroded parts at a substantially accelerated rate, the cost of power due to corroding the cold side parts might make the power too expensive even if its "safe enough", making it cheaper to just shut down. Moving large amounts of water (or air) is extremely expensive, both capex and opex, so an additional 10x higher once in awhile here and there could be a lot of money...

chermi 2mo ago

Lol no. Latent heat is basically all that matters