Please note that we've updated the Mount & Blade II: Bannerlord save file system which requires you to take certain steps in order for your save files to be compatible with e1.7.1 and any later updates. You can find the instructions here.
Oh, so a few nuclear cargo ships have actually been built. Didn't know that.
I guess the cost, maintenance and special nuclear engineer crew makes it a disadvantage.
Also sounds like a lot of nuclear waste would end up in the sea if they became widespread.