[klondike_]

The US tried this concept at one point with the nuclear powered NS Savannah, which was a cargo/passenger ship. Unfortunately it was already outdated by the time it was built, unable to accommodate the modular containers taking over the shipping industry. It was mostly a novelty at the time and was expensive to run.

Still though it seems nuclear would be a good fit for shipping. Most large ships use electric motors for their propellers anyways, and the US Navy has extensive experience deploying reactors in submarines. Theoretically you would only need to refuel such a ship every 10 years or so. Fears about terrorism or contamination will probably prevent such a ship from being made any time soon, not to mention the lack of infrastructure.

[nradov]

Large merchant ships don't use electric motors. The propeller is directly driven by a large diesel engine through a mechanical transmission because that is the cheapest and most efficient design.

[VBprogrammer]

They don't even use a transmission in most cases. The propeller is direct driven, the engine itself can be started in reverse to go astern.