In other words, where do “nuclear powered” vehicles get their power from?
I imagine it’s not from fusion or fission, nor can it involve getting water to turn to steam, an in many other types of power generation.
So how does it work?
EDIT: it seems that nuclear submarines actually do use fission, so I’m switching my question to only focus on space vehicle power generation.
In: 3
These are two different questions, really. The mechanism used in a submarine is different from what’s in a space probe.
The only thing they share in common is this: Nuclear effects make something hotter than the stuff around it. When there’s a hot thing and a cold thing near each other, you can convert that temperature difference into other forms of energy.
In the case of a submarine the nuclear effect going on is that there’s nuclear fission, which makes the uranium rods really hot. This heat is used to make a steam engine turn. In some designs this steam engine drives both a generator for the boat’s electricity AND the propeller shaft for the boat. In other designs it drives just the generator only and then a separate electric motor uses that electricity to drive the propeller shaft itself.
This is a bit different from in a space probe, where nuclear material is used in something called an RTG (Radioisotope Thermoelectric Generator). In this design, heat is still invovled, but this time its just the normal waste heat that comes from letting the nuclear material decay on its own at a natural pace. When an isotope material decays it does put out some amount of heat. An RTG uses that difference in heat between the hot isotope and the cold vastness of space to create a battery. If you make a “thermocouple” between two types of metal and make one hotter than the other, they generate electrical current flowing between them.
The big, big differences between the two approaches are:
1 – Moving parts: Submarine nuclear reactors have them (It’s a steam engine). Space Probe RTG’s do not (It’s just “this metal plate is hotter than that one so that makes a current”).
2 – Sprint vs Marathon: Nuclear reactors put out a LOT more power than an RTG but doing so causes the fuel to decay faster, so they have to return to port occasionally to swap fuel rods. Space Probe RTGs are much lower power by comparison, BUT they last and last and last because the decay happens at its natural rate.
3- Size: It’s hard to make a nuclear reactor that’s small. There’s a minimum size of ‘stuff’ needed to be to sustain the reaction. If you’re going to be driving a big giant boat with it, that’s fine. But if you’re going to be driving something smaller, it’s not fine. RTG’s can work on a very tiny scale, to power a small thing without costing a lot of mass to do it (and keeping mass low is everything when it comes to designing a space probe that has to be launched by rocket.)
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