Posted Jan 11, 2021, 5:15 AM UTC
No, but like every other Nuclear plant, or any other type of power plant it needs some way to reject heat. It needs basically the same amount of water as any other nuclear plant.
We associate Nuclear power plants with large bodies of water, and with cooling towers, not because these are unique to Nuclear, but because Nuclear tends have very large Thermal Energy production. Every type of power plant needs heat rejection of about the same magnitude.
For example the [LeSalle Nuclear plant produces ~2.5GW electrical power] (https://en.wikipedia.org/wiki/LaSalle_County_Nuclear_Generating_Station). It is a traditional Boiling Water Reactor.
This 2.5GW of power is sent down the wires to customers. However the nuclear plant actually produces >7GW of thermal energy. This means that 4.5GW of thermal energy needs to be rejected to the environment. This goes into the massive cooling lakes.
Lets replace the Boiling Water Reactor of LaSalle with a Molten Salt Reactor.
What Changes?
Now rather than water heated by the Nuclear Pile and sent to the turbine, salt is heated by the fuel. This salt is then used to...
Boil water to send to a turbine.
No matter what nuclear tech you are using, unless it is super low powered ( <10KW ) it will always just be heating water to boil, super heating steam, then sending through a turbine.
The water usage of a BWR ( Boiling Water Reactor ), PWR ( Pressurized water Reactor ) or a molten salt reactor are basically identical, because the water used by the plant doesn't leave the plant!
Indeed the loop is basically identical between a PWR and a molten salt reactor, as in PWR the water that touches fuel never boils. It is used to heat other water, identical to the molten salt.
The improvements offered by the recompression closed Brayton cycle (RCBC) reportedly include "vastly reduce[d] water consumption" and "dry cooling" which makes RCBC "suitable for arid environments." Thoughts on it?
This was a question about molten salt reactors, not super critical CO2. Molten salt is not the working fluid of the actual thermal cycle, water steam is.
I am not familiar enough with "recompression closed Brayton cycle " to give an opinion.
But I'm considering MSR designs in which the molten salt flows through a primary heat exchanger which heats the sCO₂ that moves a turbine. Flibe Energy, for instance, is developing a LFTR with such a power conversion not only because it is more efficient, but also because the oxygen in CO₂ may capture any excess tritium to form tritiated water that can be removed: reference.
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Molten salt only transports the heat around from the reactor to the power cycle. You'd still require a heat sink for your power cycle. The nuclear reactor has the same heat output, the method of transportation is just different, i.e. you could also couple your power cycle directly to the nuclear reactor with (probably) water as your working fluid.
'More or less' water is a bit of an odd question. Usually you'd want your heat sink large enough that the heat you dump in has practically no or at least a negligible effect on the temperature of the heat sink. That's why nuclear reactors are frequently built near rivers or coast.
Modern (post-60s) reactors use a closed cycle for the coolant water, they never return the heated water back to the natural body of water. So it doesn't really matter how much water they operate with.
They are still built near bodies of water because they do have to replenish what they lose to evaporation.
Obviously modern power cycles are closed cycle due to water purity considerations, but they will still have heat exchangers to dump heat, which is what I'm referring to.
My point was that OP didn't raise the question of how much water is there overall in the system, but how much water the plant uses from the environment.
And the answer to that is "very little" in all cases.
A typical block comes with ~3 GW of thermal power, out of that 1 GW becomes electricity, the other 2 GW stay heat that needs to leave the power plant. You can heat 5 tonnes of water per second by 50 degree, or you can evaporate 1 tonne per second, but either way it's so much water that you need a large body of water nearby.
I would not call 1 tonne per second "very little".
OP specifically mentions "heat sink" in his first question which therefore includes the heat rejection requirement for the secondary heat exchanger.
The reason they built near these things is because they provide a large volume of cooling water for the main condenser and closed cooling water system.
This is generally called a circulating water system and is a once through system that is constantly operating at all times and heats the water near the outlet by a few dozen degrees, depending on load and other factors.
Make up in every plant ive worked in used the domestic water supply for replenishment, but ive only worked in plants near cities so i can see other sources being used for more remote location.
Youngest plant i worked on was built this century and still operates in this way.