On 223:

• Small reactors are bad for square-cube reasons.

• Shielding is just too heavy for road vehicles, even something like a main battle tank.

• Even trains have their load limits exceeded by reactor shielding - trains can carry a lot but it needs to be spread over many axles, whereas the reactor shields have to be concentrated in one place. Plus derailments are scary. The soviets studied this with the NS400 and gave up. Also if this was viable you probably just build catenaries powered by nuclear power stations and run electric locomotives.

• Having to rebuild your whole supply chain to allow for nuclear servicing is annoying, even though you don’t need to refuel.

• There is no demand for nuclear-powered aircraft because, again, the reactor is too heavy for commercial applications and the military applications are obsoleted by SLBMs, which can reach anywhere a nuclear bomber can reach, can loiter for much longer due to food stores, and are really really hard to detect.

• The nuclear navy did exist with all the nuclear cruisers etc in the 60s and 70s, but this took Rickover to make it happen.

• But the main reason it was retired, I think, was that the vessel either needs a super high price tag or a super long life to make the economics work. For a frigate with a 20 year lifespan, you end up spending 3-4 years in the middle with it in dry dock doing refuelling, and the upfront cost just doesn’t pencil out. Modern commercial freighters also have a lifespan around 20-25 yrs, don’t care about having to surface to run generators like subs, and don’t really care about going very fast for hours at a time like carriers.

• This is not so true anymore, but in the 20thC you needed highly trained personnel to operate the reactor who needed to be paid well. Navy nukes are famously selected for intelligence, half of Rickover’s job seems like it was producing this class of people.

• One problem with the NS Savannah (US nuclear freighter) was that there was constant conflict between the deck officers and the nuclear guys because the latter were paid a lot more.

• Other problems: Savannah was built to aura farm and not max out cargo economics, it was retired just before the oil crisis in the 70s, there has never been a commoditised supply chain for mobile reactors - again, Rickover was the only one who could make this work, and even he didn’t get unit costs low enough for the private sector to be really interested. Even if they were, there’s certification, national security…

• Nuclear icebreakers worked, but only for the Soviets.

• Savannah was, empirically, safe but still faced a lot of pushback e.g. countries like Japan not allowing it to dock because of public perception.

Edit: also, plowshare doesn’t work because ground bursts generate insane amounts of fallout, even with hypothetical ultra-clean warheads like Ripple: direct.mit.edu/jcws/art…

I looked into that last year because I was wondering if you could solve climate change by doing rock weathering with Ripple warheads, but even three to four nines of fusion still produces lethal amounts of fallout IIRC