The only real synthetic alternative is ammonia which brings it's own host of problems and potential for malicious use. while your arguments are valid, i think we can overcome most of the problems you mention with more research. at some point we'll need to make the hard decision to either give up on the environment or go nuclear and accept the extra cost of safeguarding it. It simply seems there's no other realistic alternative.

There are plenty of options that are more realistic than ship-based nuclear, such as sails and biofuels.

biofuels are not green and require huge land mass and come on dude, sails, really ?

Biofuels are carbon neutral. They require land, but a single engineered biofuel crop could grow on land that other crops couldn't. It's a promising use for the Canadian tundra that's melting.

Sails are very promising - a cargo ship would need enough fuel to maneuver in port and to generate electricity en route, but for most of the trip it could rely on (computer-controlled) sails.

Neither of these options are mature today, but they're a lot closer than nuclear-powered cargo ships.

> The only real synthetic alternative is ammonia

This is untrue.

Maersk launch a commercial 172-metre container ship running on run entirely on green methanol a bit over a year ago and has 25 more new green methanol ships in the build pipeline.

Australian companies have already contracted to supply green methanol sourced from solar farms after their build and trial of methanol shipping (tugboats) in Singapore.

> It simply seems there's no other realistic alternative.

You say that, the world disagrees.