OVERKILL
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Or, if there were some international regulation changes to allow entry. Sevmorput doesn't have this problem because it's only moving containers from one part of Russia to Siberia, but, IIRC, NS Savannah did have this issue, not being permitted into certain ports.Nuke would only be viable if a separate generator ship followed across ocean and did not follow into port. Then battery or other power source (generator) to enter any non developing countries ports.
But that's only one half of the problem, the other half is ensuring the security of the vessel. As was discussed in another thread, large shipping companies don't typically have armed security detail to deal with pirates for liability reasons and port entry issues. If you were to fit a vessel like the Triple-E with a nuclear power plant, even if it didn't run on HEU, you'd need a portion of the crew to be former navy nukes, and the vessel would have to have armed security (these could be the same folks). I still expect that to be cheaper than the fuel costs for a traditional vessel, but it's a significant set of obstacles to implementation.
I know there is discussion ongoing about this. I suspect if a test vessel is created, it will only run a specific route, with ports that are OK with this arrangement.