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Comment by rawgabbit | Hacker News Reader

It said 41% of the water used in the US is for thermo electric cooling. Albeit, it didn't break this down into saltwater vs freshwater. It also said the vast majority of this water usage is due to older plants that did not recirculate the water. The newer plants that recirculate the water only used a tiny fraction of water in comparison.

So...if the US replaces all of its old nuclear power plants, we would free up almost 40% of water used today?

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Note that water use is not the same as water consumption. If 100 gallons of water passes through a heat exchanger and 99 gallons go back into the river, only then 100 gallons were used but only 1 gallon was consumed. Thermoelectric cooling makes up a lot of water use, but on 1-2% of water consumption because most of the used water is returned: https://watercalculator.org/footprint/water-use-withdrawal-c...

Furthermore, heat exchangers can use wastewater. This is done at the Palo Verde nuclear plant, for example.

Thanks. So the water of water consumed is by agriculture and “public use”.

More importantly, though, is that agricultural water is mostly consumption. That water is either evaporated or absorbed by plants.

By contrast, the overwhelming majority of water used by thermoelectric plants is not consumed. Electricity generation amounts to 1-2% of water consumption. There's hardly any water to be saved by changing power generation.

Thermoelectric cooling's 41% includes all thermal plants (coal, gas, nuclear), and most of this water is withdrawn but returned to source, not consumed - so modernizing would reduce withdrawals but not free up that water for other consumptive uses.

Thanks.

How did you go from "thermoelectric" to "nuclear"? The US has nearly as much coal power as nuclear power, and significantly more natural gas than nuclear.

I assumed only nuclear power plants need that much water for cooling. It is only an assumption. If I am wrong I am happy to be corrected.

I don't have numbers to quote at you, but I would assume not. Fundamentally coal, nuclear, and gas-boiler (but not gas-turbine) power plants work the same way - you heat up water until it boils, and run the steam through a turbine to turn that heat into mechanical energy. I.e. the "cooling" is also the electricity generation mechanism. As a result same amount of heat should result in the basically same amount of electricity for each process, and since the water is being used in the same way they should be pretty much equal in water (use or consumption)/electricity output efficiency assuming they were built with the same era of technology...

I was mentally referring to this article. It mentioned that natural gas plants only used one tenth that of coal. I assumed this is because natural gas plants are newer etc.

https://www.eia.gov/todayinenergy/detail.php?id=50698

      Natural gas-fired generation uses a more energy-efficient technology to produce electricity than coal and has a lower water withdrawal intensity than coal. Natural gas combined-cycle generation had an average water withdrawal intensity of 2,793 gal/MWh in 2020, compared with 21,406 gal/MWh for coal.

Yeah, that's the gas turbine thing. The first-stage (which generates the majority of the power) isn't boiling water, but extracting energy directly from pressure from burning the gas in a jet-engine like fashion.

The coal/nuclear like natural gas is what is labelled as "Steam Turbine" in the chart in this article: https://www.eia.gov/todayinenergy/detail.php?id=61444

Looks like it's already a small minority.

Coal and natural gas also emit some of their waste heat in the outgoing exhaust gases. Nuclear doesn't have exhaust gases (aside from evaporated cooling water) to carry away waste heat.

The big difference is the much lower thermal efficiency of LWR power plants.

Pretty much every power plant heats water to steam, then uses steam turbines to generate power. This is also how nuclear submarines and arcraft carriers work.

We never left the steampunk era.

We're leaving it now, the majority of new energy capacity is now solar, and not steam based (>70% in 2024). And a non-trivial chunk of the remainder is wind (also not steam based).

And in the US of the part that's still fossil based, new capacity is combustion turbine based, which at most gets a minority share of its power from a steam bottoming cycle.

> if the US replaces all of its old nuclear power plants, we would free up almost 40% of water used today?

FTFA: “thermoelectric power plants — plants that use heat to produce steam to drive a turbine.”

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