Wikipedia doesn't seem to have trouble showing their locations, and there are a hundred of them currently in operation, producing just shy of a fifth of our country's electrical power. Given those facts, it is a curious omission, to say the least.

Seriously. Nuclear plants make up 60% of the US' carbon free electricity and (as you say) 20% of its generated electricity. Very curious omission indeed.

FWIW on the Bloomberg Terminal all these types of infrastructure can be played with as interactive map layers. Nuclear, refineries, pipelines, etc., so the data is definitely available and not "secret" by any means.

Yeah, the Energy Information Agency publishes their locations:

http://www.eia.gov/state/maps.cfm

There's a layer there for Nuclear plants too, so it is easy to adjust the map to only show them.