Yup, this is the headache with nuclear--your marginal costs of generating power are very small (and I wouldn't be surprised to learn they're negative as big mac

Yup, this is the headache with nuclear--your marginal costs of generating power are very small (and I wouldn't be surprised to learn they're negative as big machines prefer to run at constant settings--it wouldn't shock me one bit if throttling it up and down causes more maintenance cost than fuel savings) and thus it's only sensible in environments where 100% throttle is useful, or in environments where cost isn't an important driving factor (military vessels) or fueling is problematic (IIRC Russia had a nuclear-powered icebreaker.) Put your reactors on land, when the grid has too much power you direct it to something like this (or the hydrogen generator that showed up here a few days ago) and convert it to chemical energy.