To me it's the sheer volume of power you get from each reactor. Seabrook in NH is 1244 MW. Our subs measure the amount on uranium fuel used for a core's lifetime in grams. That's all the power used for propulsion, etc. for a period of years. Of course there's a lot more to it than that, but that's what gets me. Compared to 2 hydro dams near here that are 1.2MW or thereabouts a piece.
I loved it when I was in the Navy and all the protesters against Seabrook, and no one stopped to think that there were at least 4 mobile reactors at the shipyard across the river at any given time back then.