Nuclear Power Plants are city improvements in the Power category. They are very expensive, and used mainly by old nations with very large cities.
Nuclear Power Plants cost $500,000 and 100 Steel to build. Each turn they use 0.1 Uranium per 1,000 Infrastructure that they're powering and $875. This adds up to 1.2 Uranium per 1,000 Infrastructure and $10,500 a day.
Nuclear Power Plants add 0 points to your Pollution Index.
Nuclear Power Plants are great for old nations on any Continent. Many nations import the Uranium for their Nuclear Power Plants. They're very expensive to build, but save on Improvement Slots that would otherwise be taken up by multiple Coal or Oil Power Plants.
Each Nuclear Power Plant can only power up to 2,000 Infrastructure levels. Once a city reaches 2,000.01 or greater Infrastructure it requires at last 2 Nuclear Power Plants to stay powered.
To fuel a power plant, you must have the applicable resource available in your nation's inventory. For example, in a city with 1 Nuclear Power Plant and 2,000 Infrastructure, you'd need at least 0.2 Uranium on hand for your city to have power. Your power plants do not use the Uranium you produce every turn; instead they rely on what's available in your nation currently.