“The cost of nuclear maintenance would be far too much for any shipping company.”
Possibly not so. The primary nuclear costs are one time, and yes with SOME higher operational costs, but with long periods before any “refueling”. If those costs are amortized over all the years oil would have had to be purchased - with the generally over time increasing cost of oil - the total costs may not be that much greater in the long run.
“some” higher operation costs? Most heavy labor on freighters is by 3rd world workers who make less than our minimum wage. They are treated like dogs because consequences outside the ship with diesel engines are minimal.
Reactors need far more qualified, far more expensive and far more rested personnel to be on duty at all times. The ancillary systems needed for a reactor have similar breakdown rates as diesel except the consequences of a breakdown are catastrophic That is why they must be constantly cleaned and worked on like white-glove boutique items. AND every system is multiplied for redundancy so it further multiplies the already expensive labor. You can’t get away with faulty work or temporary measures in a reactor like you can with diesel.
Just because you can’t build a fission device with the nuclear fuel, doesn’t mean you cant make a dirty bomb or force the reactor to meltdown once it is near a target. Not only do you need security for outside pirates but also intense watch for inside sobatuers. Plenty of medicated suicidal wackos out there are willing to kill as many people as they can. We dont even leave pilots alone in the cockpit these days and meltdown in a major port city would be many magnitudes worse.