A nuclear reactor can range anywhere from 30-50% thermal efficiency, which is similar to a coal fired power plant, because Carnot engines and ain't thermodynamics a bitch. Coal and nuclear power plants also both need massive heatsinks and are normally situated by rivers. So while your comment implies that this is somehow worse than what we already have, it's not!

Also a nuclear power plant has a much smaller ecological footprint than many renewable sources of energy simply because it is relatively compact in terms of land use as compared to the amount of energy it produces. Solar requires converting acres of land into solar farms. Wind requires installing wind mills, and while they do kill a lot of birds and that's a shame, it is a little sensationalized imo, and this particular talking point against windmills is probably a scarecrow argument from fossil fuel companies. Instead, I'll focus again on land use. You can't really have land conservation for wildlife where solar and wind exist because they would disrupt most types of habitat.

Finally, hydro. You have to flood several square miles of perfectly good land to make a reservoir lake, destroying wildlife habitats.

But back to the main point. A 1 GWe nuclear power plant requires around 3 GWt of cooling, this is a rate of about 300 gallons (40 cubic feet) of water boiled per second (the true value used will be slightly higher due to inefficiencies, but this is ballpark correct), which sounds like a lot, and it is on a human scale, but for a typical river, this is a rounding error. If you go to the Wikipedia page for a list of US Rivers by discharge and scroll all of the way to the bottom, even the smallest rivers on this list, such as the St. John's River, which is described in its own page as "The drop in elevation from headwaters to mouth is less than 30 feet (9 m); like most Florida waterways, the St. Johns has a very slow flow speed of 0.3 mph (0.13 m/s), and is often described as 'lazy'," has a typical flow rate of 15,000 cu ft/s.

As an aside, we, of course, use river water for other things, and this use is considerably larger, for instance, irrigation uses, livestock uses, and so on. We essentially consume the entire Colorado river, which no longer flows to the sea. "Due to water diversions, flows at the mouth of the river have steadily declined since the early 1900s. Since 1960, the Colorado has typically dried up before reaching the sea, with the exception of a few wet years." There is no nuclear power plant on the Colorado river.