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I am working on a story set on a world where cars (or in a broader sense road based vehicles) are the main transport mode (aircraft have never been invented here and most bodies of water are so small that water travel is mostly used for pleasure craft) and thus liked the idea that every even slightly conceivable way to fuel/power a car is in use here (no matter how inefficient it would be in real life) So off course I also arrived at nuclear powered cars. Now as part of this ''car dominated world'' I also wanted fuel stations to have as many fuel options as possible (I'm imagining huge fuel stations next to highways that offer fuel for every type of vehicle this world has.)

So I also want the nuclear cars to use those, but how would I go about doing that?

Any liquid type of fuel can be done the same way you would at a real life gas station, but nuclear?

If I want a nuclear car (imagine if something like a Ford Nucleon from the late 50's had really gone in production) that has to refuel from time to time like any other car, what would its owner do? Swap the (in this scenario portable sized and save to handle) core of the reactor/whole reactor, switch empty control rods for new ones, fill her up with liquid uranium, plutonium or thorium?

NOTE: The way to refuel this car only needs to be every so slightly ''theoretically possible''(slightly can be as loooong of a stretch as needed), it does not need to be doable by real world current tech standards, any way is good as long as it involves either swapping something something out or ''filling'' her up with some substance.

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    $\begingroup$ I have to ask why not just change out the reactor when is time to refuel. By default it has to be compact and it should only need refueling every few years so you just book an appointment at a local garage, they pop the hood, unbolt and hoist out the old module and reinstall/plug in a new one. The old module is then collected some time later and delivered to a service facility where it's opened up, serviced and refueled before being sent back out into the world to be reused. Meanwhile the spent fuel core and any irradiated components get recycled or disposed of properly. $\endgroup$
    – Mon
    Commented Apr 28 at 1:14
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    $\begingroup$ Its a similar idea BTW to what some companies are looking at for long range/heavy duty electric delivery trucks. They need large batteries at would normally take hours to recharge on the road so one idea being considered is that you don't. Instead the driver would stop at a charging station and have the modular batteries taken out and replaced on the spot with, new freshly charged ones. Meanwhile the old ones get re charged locally at the station. $\endgroup$
    – Mon
    Commented Apr 28 at 1:24
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    $\begingroup$ The question is fun as posed, but I think somebody ought to mention what a calamitously bad idea nuclear powered cars would be in real life. Even if we magic away all the technical problems and give everyone the best of intentions and the willingness to read the fissioning manual, every single car crash would be a serious hazmat event, and instead of recycling old cars for their steel, you have to bury them in the desert for a couple hundred years. And of course we live in a world where evil exists and nobody ever reads the manual. $\endgroup$
    – g s
    Commented Apr 28 at 9:41
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    $\begingroup$ I'm struggling to imagine how a car with a built-in reactor would be preferable to one with a battery that is charged from an electricity grid powered by full sized nuclear reactors. (Like we have now.) I also wonder whether railways have a place in this world, and whether larger vehicles like trains might be better suited for nuclear power? $\endgroup$
    – craq
    Commented Apr 29 at 4:22
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    $\begingroup$ Just avoid asking to Lybian terrorists for a plutonium refill ;) $\endgroup$
    – frarugi87
    Commented Apr 29 at 9:30

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Regular garden hose.

On the scale of a car it is much more efficient to just replace the whole car than to bother replacing the nuclear fuel.

A full tank of gasoline (about 30kg) has around 1000 MJ of stored energy.

If we have a plutonium or uranium fueled car with a 1kg fuel supply, it has around a hundred million MJ of energy in the "tank", or a hundred thousand full tanks of gas.

Let's give it 100x worse mileage than a gasoline engine because I feel like it - now it has about a thousand full tanks of gas worth of distance.

I fill up about once a week, and there are fifty weeks in a back-of-the-envelope year, so this fuel supply would last me for 20 years - the whole lifetime of an automobile.

Just add (lots of) water to both run the turbine and keep it from overheating.

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    $\begingroup$ Excellent answer! One thing worth noting: your "because I feel like it" estimate probably isn't far off. I doubt people would want to bother starting up a nuclear reactor every time they want to drive somewhere, so cars would probably "run" constantly. $\endgroup$ Commented Apr 27 at 18:09
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    $\begingroup$ @InHocSigno probably equal and opposite of modern electric vehicles... get home, plug your house into your car. $\endgroup$
    – g s
    Commented Apr 27 at 19:07
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    $\begingroup$ @g-s Now I want me a nuclear powered car... $\endgroup$
    – moonwalker
    Commented Apr 28 at 23:09
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    $\begingroup$ I guess it's similar to these nuclear-powered airplane carriers – they are only refueled once in the middle of their life time, by basically exchanging most of the reactor. $\endgroup$ Commented Apr 28 at 23:47
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    $\begingroup$ As an important note to your last sentence, as Ed Asner said: you can't put too much water in the reactor. onesnladay.com/2019/02/26/… english.stackexchange.com/questions/282388/… $\endgroup$ Commented Apr 29 at 14:19
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Whilst it is very tempting just to suggest pumping molten thorium salts, I'll restrain myself and suggest something slightly less daft: pebble bed reactors.

The fuel "pebbles" are approximately pool-ball sized spheres whose graphite casing acts as a moderator. They're also intended to be very tough and require very inconvenient machining operations to decapsulate the fuel inside, making them robust to accidental leakage through damage and against nuclear proliferation concerns (which might be less of a worry in the sort of world where nuclear vehicles actually exist). The system was designed to have the reaction slow as the fuel particles heat up, giving them a certain amount of intrinsic safety.

Fresh pebbles are relatively benign (you could probably load them by hand, rolling them down some shielded marble-run into the reactor core so it is slightly harder for any residual radiation to zap you), but used ones will have all sorts of unpleasant nuclear waste products in them, so its the removal that's the trickiest part of the operation, requiring well shielded mechanisms and probably underground water-filled cooling tanks or something to deal with residual decay heat. Having the pebbles fall out under gravity into a suitable shielded chute that fits to the underside of the vehicle seems like a starting point here.

Real-world pebble bed reactors ran into various technical issues, but there's no reason that in your world they're not a) resolved, or at least reduced, and b) everyone is a lot more relaxed about the way you can just buy fissionables and create your own nuclear waste just to go shopping.


That said, the Nucleon itself was imagined to have a sealed, replaceable reactor. There are some present day compact (ish) reactors designed to not be refuelled, but instead run for some time and are effectively decomissioned. This would be a slightly more sensible thing to do, as the whole assembly could be sealed and armored to a much higher level, making it much less likely for the radiation or fission products to get out, and removing some of the need for storing fuel rods and pellets (spent or otherwise). The power plant could be lifted out as a nice single chunk and shipped by itself, which probably also reduces logistics costs.

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    $\begingroup$ You read the question, you ready the answer in your head, scroll down- and there it is. Great one. $\endgroup$
    – Pica
    Commented Apr 27 at 17:42
  • $\begingroup$ [technical issues] And some very silly legal issues, at least in the US, where laws about what measures have to be taken to run a large-scale nuclear plant to protect against consequences of catastrophic failure were applied to small-scale nuclear plants physically incapable of catastrophic failure with those consequences, making them economically untenable even if all technical problems could be solved. $\endgroup$
    – g s
    Commented Apr 27 at 19:16
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    $\begingroup$ @Pica - that's my only real problem with Starfish. $\endgroup$
    – jdunlop
    Commented Apr 27 at 19:58
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Feels like you're using our modern definition of cars to artificially limit your nuclear cars.
"A car is something that needs periodic refuelling" which is not the case and bending your world to need this makes it all less plausible.

Consider a Nuclear-powered Surface Vessel or Submarine - At most they get exactly one "reactor swap" during a mid-life overhaul that lasts for a year and requires significant structural work, or they serve their complete term on one set of reactors and then get decommissioned.

Perhaps there's some other part of your vehicle that can be replaced often enough to serve the story and force a periodic stop:

  • Coolant - the liquid used as a coolant can be "used up" and needs topping off, or perhaps it somehow gets "worn out" and needs a drain-flush-recharge
  • Tyres - modern ones would last several years, but maybe your cars go faster and wear out the tread quicker ?

There's one constant, assuming no self-driving cars, and that's the driver/passengers also known as the "live load"
Everybody needs a bathroom break periodically, and to recharge with a stretch of the legs and a bite to eat/drink.

ANSWER: Refuel the people, not the car. Periodicity of about 2~6 hours.

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    $\begingroup$ I'd also expect nuclear cars to be MUCH heavier so even mor tire wear. $\endgroup$
    – Hobbamok
    Commented Apr 29 at 11:19
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If you compare with other nuclear powered vessels that exist, aircraft carriers and submarines, these are designed to run for 30-50 years without refueling. The reactors that are refueled every few years use lightly enriched (or natural uranium) but these designs are quite impractical for a mobile device owing to their size.

Even the highly enriched reactor designs of aircraft carriers are likely impractical for a car. The only real option is likely a RTG generator, like used on voyager (and some pace makers in the 1960s). This is always on, and both of these are still going. For this to work in a car, you would need a battery/supercapacitor that provides peak power that the RTG is constantly charging.

In the unlikely event that a reactor needs replacing (your car is going to be 50-70 years old), you simply replace the generator and dispose of the whole thing. No one wants to disassemble one of those

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    $\begingroup$ RTGs (at least those used in space probes) have less than ~5W/kg of electricity power output. You’d need a 3000kg RTG to provide 15kW of electricity which is what modern electric cars roughly consume on average. Assuming the power to weight ratio even scales up linearly. Since you need a lot of surface area to get rid of the heat it could even be worse. Sounds barely practical for a car. $\endgroup$
    – Michael
    Commented Apr 29 at 6:26
  • $\begingroup$ @Michael power output scales somewhat exponentially though, trading lower shelf life for higher output (unless moderated) $\endgroup$
    – Hobbamok
    Commented Apr 29 at 11:18
  • $\begingroup$ @Michael An electric car might use 15Kw when it is being driven, but is parked 90% the time, so is going to need more like 1.5Kw continuous charge to a hybrid battery - which is rather more reasonable. It's not like there is anything else that we have that has a prayer of being scaled to even 3000Kg anyway. Neutron absorbtion lengths simply don't permit other reactor designs to be scaled smaller than what they are. $\endgroup$
    – camelccc
    Commented Apr 30 at 14:03
  • $\begingroup$ @camelccc: If your car is (mainly) powered by the batteries you might as well use a proper nuclear reactor at home and don’t lug it around in your car. It’s the same reason why solar panels on cars don’t make sense (at least not for charging their >40kWh battery). $\endgroup$
    – Michael
    Commented Apr 30 at 14:49
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In the early 2000, while at University, I visited a nuclear power plant in Germany. One of the souvenir that could be purchased after the visit was the replica of a fuel pellet encased in a plexiglass cube, which could be used as key-ring. The pellet itself was a little cylinder not bigger than the nail of a pinky finger.

In the fuel rod these pellets were stacked one above the other and the rod would be immersed in the core.

Refueling a nuclear vehicle could use a similar principle: the fuel could be encased in a low melting point radiation protective casing and sold as is, then placed in a receptacle where first the casing would be smelted away and then the pellet would enter the core.

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    $\begingroup$ That will be soon quite a worthy souvenir... because meanwhile Germany has stopped all of their nuclear power plants. Your keyring is a piece of an once existed better world. $\endgroup$
    – Gray Sheep
    Commented Apr 27 at 20:05
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    $\begingroup$ There is no need for radiation protection when handling new fuel. All you need is some means to prevent it from contaminating anything. It's the spent fuel that will kill you if you stand anywhere near it without massive shielding between yourself and it. $\endgroup$ Commented Apr 28 at 0:29
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Nuclear reactors do not run out of fuel, instead the fuel they have decays over time, to the point that it needs to be replaced because it can´t generate enough heat to sustain production, but the fuel itself is still very active, hence the special care needed to dispose of it.

Nuclear plants are the size they are due to the immense energy they need to generate, there is no direct nuclear-to-electricity approach, the chain is more like nuclear/heat/mechanical/electric, but if all you need is to power a car, you can do with a smaller approach.

In Asia, there are companies like Gogoro, that offer swappable batteries for EV bikes, they are placed in a rack, and the driver just pulls up to it, and changes the one in use for a freshly charged one, you can take this approach and say that these contain the solid fuel for the reactor, or even better, the whole enclosure is the reactor, in essence, the car would be an EV, is just that the battery would be nuclear in nature, with the rack available at any store, gas stations included. You can even make it so that it uses very little fuel for safety, creating the need to replace them often. enter image description here

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  • $\begingroup$ In my mind to refuel, the reactor itself as a unit would be replaced like these battery stations. However, It'd be more like a car part, and could convey thermal energy to turn into electricity as well, depending on how sophisticated the car is built. Stretching the idea of nuclear powered cars though, RTG's seem like a possible technology or if there is a want to create direct-to-electricity, Betavoltaic cells could work but the energy density on those are puny, often used in small electronics. $\endgroup$
    – Harry Mu
    Commented Apr 28 at 3:43
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    $\begingroup$ @HarryMu I don't know how relevant it is to the story, but honestly, I'll treat it like a black box, you know it is nuclear and it produces electricity, there's really no need to elaborate further on how it works unless it is necessary for some reason. $\endgroup$
    – Inferry
    Commented Apr 28 at 4:55
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    $\begingroup$ IRL reactors are also this big because heat-electricity converters scale with size/heat. Which is also why small modular reactors have such a hard time $\endgroup$
    – Hobbamok
    Commented Apr 29 at 11:21
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Every answer so far assumes a fission-powered vehicle, which is logical since that is the only method we have.

Since the H-bomb, people have dreamed of controllable nuclear fusion. If your world had that, you could refuel with a few drops of water.

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    $\begingroup$ If you can do nuclear fusion in your car, the fuel would reach even longer than fission fuel. Though you might need to refill cooling water, like for a train's steam engine. $\endgroup$ Commented Apr 28 at 23:57
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Essence of the nuclear cars would be that they do not need refuel, or only very rarely. That is because the extremely high energy density of the nuclear fuel, obviously you do not need to tank a lot if a gram of fuel would substitute a train full of benzine.

A possibly reason is that you do not want too much fuel in the nuclear car. It can have two reasons:

  1. If you have only a milligram of fuel in the car, then yes, sometime you need refueling, thus providing them such cars give you regularly paying customers. (Note, these are also cheated customers, but that might be tolerated in your society. Keyword: Planned Obsolescence)

  2. If you have only a very little amount of fuel in the car, then in the case of a crash, only a very little nuclear contamination might go out, significantly reducing the related problems.

Car factories of the today would probably be motivated by (1), but they would communicate (2).

Now that we made clear, why would the car even need refueling, we can talk about the details.

Most importantly, nuclear reactions are not so nice as the burning chemical reactions. If you stop a nuclear reactor, a radioactive isotope named Xenon-135 is created, which stops the re-start of the reactor for some days (more read).

To have a nuclear chain reaction, you need at least some tens of kilograms of uranium. There is no known way to significantly decrease it, although using some higher isotopes, like Californum, had probably some chance. But not too much. I do not think that the usual neutron-induced fission could be possible with any isotope with lesser as some kilograms. That also means, that my previous paragraph about the tiny amount of fuel, can not be done with the today technology.

If you solved these all, what remains, that is... nothing unusual. To replace the fuel,

  • You need to stop the reactor
  • You need to open the reactor
  • You need to get out the spent fuel
  • You need to plug in the new fuel
  • You need to close the reactor
  • You need to start the reactor

These are the steps, none of them is simple, but all of them is well automatizable. The only reason, why not at least nuclear trains or nuclear transport vehicles exist, is economical and the general fear of the population from any nuclear.

They could exist, and maybe once, in a lesser fearful, more educated world, they will be. Until you live, there is hope.

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The single advantage of nuclear cars (against all the many many many disadvantages) is that you will basically never need to refuel it, or at least you'll have to only refuel it once every several years. So nuclear cars won't need any equivalents of a gas station. We change oil in our cars once in a while, as well as some parts which wear out over the years, but it is done rarely enough that there are no "oil changing stations" all along the highways, it's done as part of the regular service and maintenance.

If nuclear cars will need refueling at all, it will be done as part of the yearly checkup, whenever it's needed. If you forget it this year, the car will run another year, maybe with a barely perceptible loss of efficiency.

This means if you need the equivalent of modern gas stations, you'll need something else besides fuel which requires a fill-up or replacement every couple hundred miles. Maybe some sort of filters, or coolant, or whatever else?

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Do you really need to refuel the fuel?

In a small car the only reactor compact enough would be a FBR (maybe moderated with lead instead of sodium). Such a reactor could last ten years, then you could replace the entire core. But it doesn't mean that in those ten years the car won't need any service. The coolant of the second loop might need periodic refilling. Then there are the parts in common with the other cars, from the tires to the soapy water for the windshield. Instead of a fuel station you need a service station and your nuclear powered cars will have to pay periodic visits even if they don't need refuelling.

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