Yea, micro reactors sound like a great idea for pollution control. But, given how many ships get seized every year trying to fake inspections and a dozen other things- the only way this works out is a modern version of Clipper ships (with less sinkings). Large premiums for getting your cargo across the ocean faster.

How much faster, is for somebody more knowledgeable than me to answer.

And now politics comes into play: these ships would have to not only have significant permanent armament, but given significant latitude to use lethal force.