For a vessel the size of a container ship, mounting an SMR (Small Modular Reactor) directly to power it would likely result in less energy loss.
In a perfect world however... endless cooling water unless they're in some shallow harbor. Would be the perfect application.
Still not, because all it takes is one thing going Seriously Fucking Wrong on another ship and boom, you got yourself a nuclear disaster. Just look at the Francis Scott Key Bridge and imagine that that ship hadn't hit a bridge support but a nuclear powered vessel.
Nuclear powered ships only make sense for ships operating in places where there is no other ship in sight for hundreds of miles (i.e. icebreakers) or for military ships that can and will shoot and sink anything with the potential of becoming a threat.
https://en.wikipedia.org/wiki/Russian_floating_nuclear_power...
Even navies are moving away from nuclear power due to how expensive it is.