Nuclear powered ocean going vessels have been around for decades. As well as the well known nuclear power submarines with their deadly payloads of nuclear weapons that can stay submerged for months at a time, there are also nuclear powered aircraft carriers and icebreakers out there. Nuclear power plants for shipping are expensive but have the advantage of large power outputs, less time spent refuelling and low carbon footprints.
The latter point on carbon footprints made me wonder: onshore nuclear power stations can offer low carbon electricity outputs, but are now massively expensive to build, get mired in politicial objections left, right and centre, and are often unpopular with the local residents around proposed sites. We need to find a way to deal with long lived nuclear waste from the legacy nuclear power stations. At the same time we need to find low carbon ways to ship bulk goods around. And it would be great if we could get cheap, renewable replacements for existing liquid fossil fuels so that we could keep more fossil fuels in the ground. What if we could find a way round all of those issues?
So, my quick brain fart for today: build very large, ocean going freight vessels that are nuclear powered.
By "very large" I mean bigger than the largest oil tankers available today by an order of magnitude - effectively floating metal islands that can plough across the oceans from continent to continent. Obviously they'd be too big for most ports to handle and many people may object to a nuclear powered vessel turning up in their local harbour (unless they're used to the military ones already). However what about if these giant vessels went just to the edge of territorial waters and unloaded onto smaller vessels? Those smaller vessel would be normal sized, conventionally power container ships and tankers.
If you build something big enough, you could effectively include a dock inside the huge ship for normal vessels to go into, protected from rough seas. The loading/unloading of the smaller ships could even be done enroute, which would mean that transshipment and handling time wouldn't be increased. Bringing boats inside a larger ship is already done: the US Navy have vessels that can take smaller boats inside for long distance transport, equipping and deployment. Or if you're into sci-fi its like the James Bond baddie with the oil tanker that could swallow submarines. Paging Elon Musk on that one!
Manufacture of this mega-freighter would have to be modular so that existing ship yards could build them sections at a time. Each completed section would be floated out of the dry dock and then joined up to other sections already held at sea. That's the bit I'm really not sure about: how easy would it be to join up sections at sea that are floating? That would obvious require calm weather to do, but could the modules be designed to interlock easily like some sort of giant floating Lego bricks? I don't know - I'm not a shipwright or naval architect. However large floating structures have been joined together in the past, so I don't think its insurmountable.
These floating freight islands would have to be powered by nuclear reactors that provide propulsion power, "hotel" power to keep the crew (and maybe passengers) supplied with heat, light & electricity and potentially enough "extra" power to use the various Fischer-Tropsch processes to combine sea water with air to produce liquid hydrocarbon fuels. We already know that works - the US military have tried it to produce jet fuel onboard their nuclear powered aircraft carriers. The synthetic hydrocarbon fuels could then be used to fuel the smaller servicing freighters and/or provide av-gas for helicopters or VTOL aircraft for the short hops to and from shore.
By using the nuclear reactors for the long haul ocean part of the freight journey we'd be reducing the carbon footprint of the goods. The reactors will effectively live out their lives at sea, many miles from the nearest land. If the reactors are designed using the proposed Gen-IV designs they'll be "walk away safe", and something so massive as this would also mean it would be unlikely to leak radioactive material into the sea (I assume the reactors would be in the heart of the floating metal island, so there could be a lot of steel and concrete between them and the water). Indeed this might be a great application for the various designs of modular reactors - don't build a ship with one 1GW pressurised water reactor but instead 10 modular 100MW molten salt reactors that can be swapped in and out for refuelling and replacement. That would help with the economies of scale that modular reactor designs really need if they are going to be constructed on a production line to bring costs down and safety up.
Tsunamis and earthquakes wouldn't be an issue for these reactors, and if they're making enough synthetic fuels as a by product of the reactor running they could even help provide low carbon fuels for import to the countries they visit. Indeed if they moor up at a fixed off shore point, they could be hooked up to the Grid in that country by a relatively short undersea HVDC power cable. It might transpire that some could even be nearly permanently moored like that as a safer place to put nuclear capacity for the Grid's low carbon base load supply.
I wonder what the limitations of build these would be? Cost is an obvious one: a nuclear submarine costs a couple of billion US dollars to make, and this would be something far larger. Yet Governments and companies are already handling projects that cost many tens of billions - things like new build on-shore nuclear power stations, failing Carbon Capture and Sequestration (CCS) projects, high speed rail lines, etc.
The anti-nuclear lobby would probably object to this as its another application of nuclear power, but if the Gen-IV design could make use of legacy high level nuclear wastes, it might be palatable as a way of cleaning up wastes from previous generations of nuclear reactors (which is after all one of the anti-nuclear groups' major concerns). Also there are already many nuclear reactors swimming around in the ocean and have been for decades.
I'm not sure what the legal position would be for nuclear reactors running on vessels in International waters that never actually enter territorial waters once launched. Would it be covered by the flag that the ship sails under? Could you pick a small country that doesn't have a huge amount of nuclear regulation red tape in order to make this viable?