A question about nuclear reactor design

[semipotentwalrus]

I've been Googling around but been unable to find an answer, so I figure I can ask here.

Do fast-neutron reactor designs utilizing molten lead, salt, or sodium reactor coolants need the same amount of water coolant for the steam driving the turbines or not?

From what I understand the coolant water that's not in a closed loop in a PWR design is the same as in a fast-neutron design, with the water in a PWR being in a closed system and thus not needing to be replaced anyway.

[Haighus]

Don't see why they wouldn't, the steam turbine is independent from the reactor right? Doesn't really matter what source of heat you use if you just let the steam out into cooling towers. I would think combustion or geothermal plants would be the same.

[pacific]

I work in the industry but am not an engineer, other than a high-level knowledge of AGR and PWR (the two types the UK uses) I don't know I'm afraid.

To my non-engineer mind, surely would the water input required for the steam turbines not be dependent on the energy/heat output of the reactor?

[semipotentwalrus]

From what I understand you usually have three separate systems working in conjunction:

One cools the reactor core. This is usually water, but designs with molten salt, lead, sodium or a bunch of other metals also exist. These lead heat from the core to the second system. They're always closed systems since they interact directly with the reactor core and become irradiated as a result.

The second system siphons heat from the first and converts water to steam, turning a turbine to generate power. As far as I understand this is usually a closed system as well since high-pressure steam is pretty nasty.

The third is a second set of water coolant that cools the steam in the second system after it's spun the turbines so that it can absorb heat from the first system again. This is the part that pumps water from a nearby source and returns the water to that source again after it's been cooled down using cooling towers, underground canals or similar.

As far as I've been able to tell the design of the core cooling, i.e what coolant the first system uses, shouldn't matter for the amount of cooling the third system needs to do for the steam in the second system; it just changes how efficiently the steam can be heated. Seeing as I am decidedly not an engineer though, I'm not sure if I'm missing something that would mean non-water core cooling would require less access to water sources. As far as I can see the only difference in water usage is the core coolant, which is a closed loop anyway since it's radioactive.