I think the number one obstacle to this is it would be nowhere near viable from the costs perspective.

No one really wants to build cargo ships right now, shipping companies are barely staying afloat right now because there is a glut of cargo capacity.

This technology would need to be cheap enough that it would make sense to retrofit a ship with it... which would probably not be the case for a very long time.

I do think it's a very thought provoking idea however.

Norsepower provides modern sails: "a spinning cylinder that uses the Magnus effect to harness wind power to propel a ship."

"When the wind conditions are favourable, Norsepower Rotor Sails allow the main engines to be throttled back, saving fuel and reducing emissions while providing the power needed to maintain speed and voyage time. Rotor sails can be used with new vessels or they can be retrofitted to existing ships."

http://www.norsepower.com/

Unfortunately the energy density of batteries is really bad (in the bigger picture) and, besides, we're supposed to be using weight for cargo. Tankers also burn very nasty fuels that can't be used for anything else - so in practice they're very efficient.

There have been cracks at putting "sails" of one form or another on ships but they've always been heavy, relatively ineffective and basically just not worth the hassle.

The speed of a ship is actually quite easy to work out. You find the time/value curve for the cargo and the cost/time for the ship and see where they cross - essentially. The long and short of it is that the lighter and more valuable your cargo is, the faster the ship goes. This is why container ships are much faster than oil tankers.

I've heard that cargo ships are currently prevented from going much slower because of the human crew. Drone ships could help.

I wonder if they could use an underwater wing design, similar to this (https://www.youtube.com/watch?v=u5SHn0SdXjw). You keep swapping the angle of the wing so it's always pushing forward whether the vessel is moving up or down, but it would be powered by the waves moving the ship. It might be possible to get a slow base load speed for 'free' with a large enough wings

Container ships are already going slower:

https://www.theguardian.com/environment/2010/jul/25/slow-shi...

There are bigger problems with nuclear powered cargo ships than just waste disposal. They would need larger crews of highly trained (more expensive) experts to operate the reactor. Look at how much the US Navy spends to train competent technicians and engineers.

Every nuclear powered ship becomes a prime terrorist target, either to hijack it or destroy it in place and cause a radiological incident. So you also need constant armed security (also expensive).

A more practical way to have "nuclear powered" ships would be to use electric power from land based nuclear plants to manufacture synthetic hydrocarbon liquid fuels, then load that fuel on the ships. Nuclear plants on land are far more cost effective since they can be built much larger to achieve economies of scale on operations and security.

Shipping companies don't own the containers. Solar panels would get broken when they were transferred to shore. Panels and cabling would add more weight to the highest level of the cargo stacks: the worst place for ship stability. And even if you covered the entire top level with solar panels it still wouldn't provide enough propulsion power to be worth the expense.