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Danube's record low levels force shutdown of Hungary's only nuclear plant

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Re: Danube's record low levels force shutdown of Hungary's only nuclear plant

#91

Post by dredmorbius »

noduerme wrote: post #42
wongarsu wrote: post #29

Earlier quoted context omitted.

Fully closed loop is probably not viable. But I suspect that's not the extreme GP might have meant. If for the sake or discussion we simplify cooling to four options: 1: just passing river water through a heat exchanger for cooling 2: ingesting river water, using it for cooling, then passing it through a cooling tower before returning it to the river 3: pass the water output from the cooling tower directly back in th…

How do these things, whose sole purpose is to turn heat into electricity, end up with so much extra heat that it takes more energy than they produce to disperse it? Can't the excess heat in a closed loop system be captured and used to power the cooling? Sorry, maybe this is a stupid question.

Thermodynamics, specifically the Carnot Cycle.

Heat engines do turn heat into mechanical energy (motion).

What they don't do is do this with infinite efficiency.

In practice, Carnot engines (heat engines) tend to operate at efficiencies between about 20 to 50%, with an average close to 30% percent. This means that most thermal electrical generation produces roughly three times as much heat as it does electricity. This applies across thermal mechanisms: diesel generators, gas turbines, coal-fired steam, and nuclear-powered steam plants.

There's some room for increased efficiencies, and multi-pass systems, or systems with incorporated thermal applications (district space heat, industrial heat, food preparation) can achieve higher net efficiencies, though I believe the peak is around 60%, and that is rarely achieved.

The other parts of the generating cycle are far more efficient. Generators typically operate well above 90% efficiency (mechanical energy in to electrical energy out), and distribution typically sees about 6% losses.

But that first thermal step costs a lot. There's no such thing as a free lunch.

https://en.wikipedia.org/wiki/Carnot_cycle>

Re: Danube's record low levels force shutdown of Hungary's only nuclear plant

#93

Post by Choco31415 »

petre wrote: post #57
comrade1234 wrote: post #8

Here in Switzerland during some heatwaves they have to shut down nuclear plants too because the river water is too warm and adding warm water to it would kill the fish.

Would a cooling pond with controlled discharge into the river maybe mitigate this problem? One could also cycle the water from the cooling pond through the plant's cooling loop. The worse that could happen is evaporate the water from the cooling pond which is gets replaced with new water (sans fish) from the river.

There's plenty of work happening with adapting non evaporative cooling loops for data centers. Maybe that can be applied here too, even if to mitigate some of the cooling needed?

Re: Danube's record low levels force shutdown of Hungary's only nuclear plant

#95

Post by philipkglass »

masklinn wrote: post #89
voakbasda wrote: post #88

Earlier quoted context omitted.

Begs the question: coul reactors use radiative air cooling? Channel the water through a huge radiator and transfer the heat to the air

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 comput…

The German THTR-300 reactor operated with air cooling:

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.

Re: Danube's record low levels force shutdown of Hungary's only nuclear plant

#96

Post by VLM »

I find it interesting the discussion here is entirely about water temperature whereas the shutdown is entirely about NPSH.

True there is a small different in NPSH pump limit of hot summer water vs cold winter water, but not as much as you'd think.

Its not that the intake pipes are hanging out in the breeze above water; most pumps are designed not to cavitate at a certain input pressure (often pretty low) and I was bored enough to look it up and when the river is 134 cm below reference at this site, the pumps will be very unhappy long term if you keep sucking water in. They'll keep running, at a reduced rate, but cavitation will cause serious issues. At some sites, perhaps not this site, filtration systems (grates and stuff) on the input are designed for a certain ideal pressure and ideal flow rate, so that can also be a problem.

Thermal limits are also very arbitrary and designed to a financial limit. Most plants worldwide are limited to a delta V, I suppose there could exist an environmental law that limits to an arbitrary fixed temp. Normally if 10 gallons/sec heats up 10 degrees, then 100 gallons/sec would only heat 1 degree. But it would cost 10x as much and only be needed a couple days/year in the driest summers, so a tradeoff point, well chosen or not, was selected. Most absolute limits are utterly ridiculous like 90F. The only long term way to maintain a river at or above 90F is an air dew point of 90F and most people will be dead by then. I find it improbable the water temp is too high, everyone without air conditioning would already be dead if the dew point were substantially over 90F. You could probably "cook" a small lake or dam area with a nuclear plant into something like a giant hot tub, but not a free flowing river.

Looking at the mass media coverage, its mostly pictures and discussion of low water levels (the true cause) followed by journalist and consumer discussion about water temps, there is no meeting of the minds between the engineers and the general public and AI and journalists.

If for whatever weird reason, river levels were low in the winter, low NPSH at the pumps would shut it down just as effectively at a water temperature of 1 C. Large industrial water pumps react extremely poorly to low input pressure.

Re: Danube's record low levels force shutdown of Hungary's only nuclear plant

#97

Post by throwway120385 »

noduerme wrote: post #42
wongarsu wrote: post #29

Earlier quoted context omitted.

Fully closed loop is probably not viable. But I suspect that's not the extreme GP might have meant. If for the sake or discussion we simplify cooling to four options: 1: just passing river water through a heat exchanger for cooling 2: ingesting river water, using it for cooling, then passing it through a cooling tower before returning it to the river 3: pass the water output from the cooling tower directly back in th…

How do these things, whose sole purpose is to turn heat into electricity, end up with so much extra heat that it takes more energy than they produce to disperse it? Can't the excess heat in a closed loop system be captured and used to power the cooling? Sorry, maybe this is a stupid question.

"Heat" is really entropy gain, and so in order to do useful work you have to increase the entropy of the system to higher and higher quantities. If you want to move entropy from one closed system to another(to cool one system down) then you must emplace even more entropy in the one system than you removed from the other because you must spend entropy(generate heat) in order to force a change in the state of the other system. It's a fundamental law of physics. You cannot reduce the entropy of the universe by any means.

This is true whether you use an engine, a river, or a solid-state fully electronic device. Even humans must obey this law, and indeed there has to be some air movement for us to cool down using our sweat, and interrupting or changing that air movement costs energy and therefore increases entropy somewhere.

Re: Danube's record low levels force shutdown of Hungary's only nuclear plant

#98

Post by HPsquared »

voakbasda wrote: post #88
ZeroGravitas wrote: post #73

Earlier quoted context omitted.

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.

Begs the question: coul reactors use radiative air cooling? Channel the water through a huge radiator and transfer the heat to the air

The temperatures aren't high enough to do that (or air cooling) efficiently enough. Some experimental designs for high temperature operation would have that as a possibility (e.g. molten salt reactor designs). I think a Chinese research project is looking into air cooling for nuclear power in dry regions.

Re: Danube's record low levels force shutdown of Hungary's only nuclear plant

#99

Post by sajithdilshan »

mertbio wrote: post #33
emsign wrote: post #18

This is what nuclear power enthusists like to ignore when they talk about nuclear power being a solution to energy and climate change.

They also constantly criticise Germany and its nuclear power plant closures, linking almost every negative news story about the country to this issue. It seems they’re completely unaware of the potential consequences of operating a nuclear power plant.

A lot of energy crisis in Germany is due to the closure of their power plants. Just like any other infrastructure, nuclear power plants needs to be modernised over the time and Hungary didn’t do that. It’s not the fault of nuclear technology, but lack of management in Hungary’s case

Re: Danube's record low levels force shutdown of Hungary's only nuclear plant

#100

Post by VLM »

number6 wrote: post #30
comrade1234 wrote: post #8

Here in Switzerland during some heatwaves they have to shut down nuclear plants too because the river water is too warm and adding warm water to it would kill the fish.

And it's not cold enough to cool the reactor

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...

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