They could use radioisotope thermal generators like those that were used as energy generators for satellites in the past. The one that was used on the cassini spacecraft (picture in the link above) looks as if it might be transportable with a horse or at least with a cart drawn by one or two horses.

Three of those power sources combined (I first missed the part that the orbiter had 3 of them) provided around 880 watt at the beginning of its operational life (1997) and now still provides around 660 watt (2017). This isn't much but should be able to cover the direst needs.

In addition to the electrical output they generate a lot of heat (4400W each or 13200W for the trio) which could be used by the nomads. Thanks to WhatRoughBeast for pointing this out.

When camped foldable solar panels could be used to increase the power available.

No, nuclear power is just too complex (to get to on their own).

We, this modern world, got our nuclear toys due to the work of a lot of smart people. I think the Brits were the first with workable plans to create it. The Tizard Mission gave those to the USA.

But it took the USA's industrial base and manpower to build the first version. This we call the Manhattan Project. To give an impression of the size of the project, let me quote this:

The Manhattan Project began modestly in 1939, but grew to employ more than 130,000 people and cost nearly US $2 billion (about 27 billion in 2016 dollars). Over 90% of the cost was for building factories and to produce fissile material, with less than 10% for development and production of the weapons. Research and production took place at more than 30 sites across the United States, the United Kingdom, and Canada.

Once you know that a technology is possible it tends to be developed faster by other countries. Or just steal the tech.

The problems for your nomads to get to a Manhattan project will be at least two fold:

First is that they don't have the industrial base to make anything that big. You need to stay in place. Heavy industry is anything but mobile.

Second is the manpower. Nomad population density is very low compared to agriculture or cities. Tech innovation is way more likely to happen with more people that don't need to watch the herd.

Nuclear Weapons and Nuclear Power

There were some questions about the link between nuclear power and nuclear weapons. A large part of the production line is the same. ~95% I estimate. If you can do one part, you can do the other. Ask the Iranians about that one The second problem with nuclear weapons is with the bom delivery. Ask north Korea about that If you go for defence (and deterrence) you don't need rockets, you might just have them as mines.

Comparison of Tech,

The first steam engines, combustion engines, motorcycles and cars were built by a few people. One man alone or a small team < 5 people could make them.

Aircraft are a bit harder, you will need teams for that, ~10 people.

The above might be possible to build up in a nomad society, might. The next ones, you will see for yourself.

Rockets are the next (big) step up. Our modern rockets owe a lot from the V-2, which were developed by a state, at the cost of ~20.000 lives and many more people working on it.

Only now are we coming near nuclear tech. I reckon it is in the same order of difficulty (can't find good links) of computers and space ships like Soyuz and the Space Shuttle. It takes large states with a large industrial base and the will to invest to get there.

Unless

1) they are given the tech from outsiders. Our modern nuclear tech is not (mostly, see 1B) mobile and quite hard to learn to maintain.

1B) See Umbranus answer.

2) Some handwavium and the Mongol empire-like. Where they do the industrial revolution and as a state desire to develop nuclear tech. But I just don't see it happening. (Heavy) Industry is just not compatible to nomad live style.

Yes, but you're going to have to relax your requirements and expectations a lot to make it work.

China is currently developing nuclear reactors the size of a shipping container. These would be more than satisfactory for the needs of a nomadic people. But this is just the reactor, none of the infrastructure that goes into supporting it.

You've already moved away from the traditional image of the nomad by declaring they have access to satellite television, so it's just one more step for your culture to use vehicles in place of the horses and camels normally associated with nomadic cultures. There is precedent in reindeer herders -- who are nomadic to follow forage for the reindeer -- using vehicles. Still, a convoy of trucks rolling across the plain seems far from what you wanted.

But, you may have a solution already. You declared these are a nomadic people akin to the Mongols, and that might be the saving grace for this scenario.

Mongolian nomads move only twice a year, once in summer and once in winter. The winter home is usually in a valley. The nomadic people could have a cooperative relationship with another people who have built a permanent city in the valley and provide the nomads with the technology and infrastructure necessary for the high-tech society you want your nomads to have. You need some connection to a spacefaring society in order to support satellite television, after all.

So, yes, there is a way to make it work, but it's not realistic.

I see multiple problems with this that would make it extremely unlikely if not outright unviable.

Nomads in Mongolia type country that don't eat meat? What are they eating? Grass? Nomads don't grow crops, they don't have vegetable gardens, they herd. Herders eat meat and they utilise every part of their herd animals that is useful. If you only utilise part of the animal like milk then you have a huge problem, you have animal corpses to get rid of, and you need exponentially more animals to provide the protein you need to sustain yourselves and trade.

Everything you used to produce using animal bits (just about everything) you now need to trade for. Your only assets are animals, so you need much more of them, it's not a simple food equation. Your whole economy is unstable and extremely vulnerable. You need bigger herds so more people to herd/protect. And you have everyone subsisting on milk and substituting grass for what animal products are used for (almost everything).

If you can't use animal products like dung, you can't use sinews, skins... so you're making houses out of twisted grass etc,. sewing clothes and wounds together with grass.... what will you use for needles? Grass? You don't develop hunting skills or weapons, so you're sitting ducks for any belligerents. Basic Mongolian bows were made from horn, bone and sinew (not grass). Their armies were trained by hunting. You just took out THE major part of their economy. Everything from glue to eating utensils you now have to make from grass somehow. It's the major thing that made their way of life sustainable.

With the Nuclear bit, they're not going to find viable nuclear materials lying around easily accessible, we don't find them today like that. We also need to produce heavy water which in itself is a mission and is done on an industrial scale. (I have a very limited knowledge of nuclear physics and materials, but this is my understanding). In any case everything takes a lot of processing before it can be used and Nomads don't have labs and stuff like that. They don't mine metals, they don't have factories, they don't do a lot of necessary things. So the only way I think this could happen is if some third party was giving them these nuclear powered units. I can't see them ever producing them themselves.

So without some serious hand waving at multiple points in your story you can't do this.

As long as you are just using nuclear reactors and not making them yourself you should be good to go. Not only that you could use RTGs, you could use full fledged nuclear reactors.

NASA's SAFE reactor should provide you with 30 - 300 KWt (that fit a fridge size).

Students at MIT designed this 1MWt / 125 KWe reactor for their hypothetical mission to mars and it weights 2 tonnes.

Both reactors are high-temperature (meaning they can be cooled by radiation only), use heat-pipes which makes them less susceptible to damages due to movement and can fit into a (very) large fridge.

As bonus points you can use residual heat to do whatever you want including heating, melting softer metals, desalinating water, maybe even producing hydrogen from water...

Shielding is a problem. I am not sure how much gamma radiation do these reactor emit, but you might not need a lot of shielding. If you are traveling the steppes and deserts you don't really care if you are irradiating anything except your people. Just put reactor at the end of convoy and shield it in front. You will irradiate ground, air, everything to the sides of you and everything behind you, which is empty useless space anyway.

A nuclear reaction can occur WITHOUT technology if the world was the right age so the concentration of U235 in uranium ore is high enough that normal light water (as opposed to heavy water) provides enough neutron moderation to allow a chain reaction. This is exactly what happened in Gabon 1.7 billion years ago. See https://en.wikipedia.org/wiki/Natural_nuclear_fission_reactor. The estimates from the linked article show 100 kW of power generation - not too shabby!

But... it would not be portable. The nomads would have to be on top of a substantial amount of uranium bearing ore.

Nuclear powered oases perhaps?

The aforementioned thermoelectric nuclear reactors like the Topaz use heat emitted to make electricity These weigh 2 tons+ so are outside of your fridge weight limit.

I propose that chunks of isotope which are kicking out lots of decay heat be used to drive steam boilers, which generate electricity. That does not involve swanky space tech. A steam boiler can run on anything hot. The scheme requires:

1. Hot chunk of isotope. from http://newatlas.com/nasa-cancels-advanced-sterling-radioisotope-generator/29880/ Shown is the hot guts of one of those thermoelectric generators. Your nomads would find these glowing chunks as asteroids that fall to the ground. They would be identified by surrounding dead patch / snowmelt. Pick them up with tongs and put them into the lead-clad iron box. Quickly. This might be a job for the oldest and sickest among you. Then get the box into your boiler before the lead starts to melt. Don't let your boiler run dry.

2. Mini steam engine. From http://www.dangerouslaboratories.org/genset.html
   You could definitely tote this cute little rig behind a goat.

To do the Mars project there must be isotopes which kick out enough heat for long enough to make it practical. You would not want to get to Mars and find out your hot chunk of isotope had cooled off 6 months ago while you were en route.

A question I was not able to answer to my satisfaction is whether there exists any isotope which kicks out heat like this for many years. I think these hot wads of plutonium isotopes are synthesized & certainly concentrated, not mined up as glowing nuggets. If the nomads find a hot meteorite, what was it doing 100 years ago? 1000 years ago? Are these being produced in space by some natural process? Nearby supernova? That is the one dissatisfying aspect to this - the provenance of the high decay heat radioactive asteroids.

Re leukemia / cancer risk: do not ingest glowing isotope. Do not inhale glowing isotope. Use tongs and wear gloves and thick apron when handling glowing isotope. Put glowing isotope promptly into box.

When radiation causes cancer it is usually from prolonged direct contact to particle emitters (e.g. watch painters licking brushes with radium paint, Marie Curie carrying radium in her pockets), inhalation of airborne radioactive material (e.g. Chernobyl accident) or therapeutic radiation used to treat cancer. Chunks lying around are bad if you are a weed growing next to it, but these chunks would not produce a countrywide blight.

So some answers seem to think you're talking about actual Mongols rather than just using them as an example of nomads. But maybe like they were part of the modern world but then decided to live a different life.

There are loads of small(ish) nuclear reactors like the chinese one that fits in a cargo container or the ones in nuclear submarine (they could even be marine nomads).

If they can pick up diesel I guess you allow them picking up the nuclear fuel too.

I don't see a problem with it.

Sure. It's called a Radioisotope Thermoelectric Generator (RTG)

They can be small, last a really freaking long time, and require no maintenance as it has no moving parts. One the size of a portable gas generator (we're still talking 100 pounds here, but load it into a truck? Absolutely) can output enough power for a small home. One or two could easily supply a tribe of nomads with enough power for a stove and some lights.

Downside, they're not terribly efficient (about 7%; yuck) and their power output drops over time (about 0.8% per year) as the radioactive material decays.

I can't find the story now, but there was a report of two fellows who found this device that seemed to generate free energy. Perpetual motion sort of deal. They had no idea what it was and used it to power their house for around a decade. Later turned out to have been a Russian RTG that fell off the back of a truck.

Besides powering Russian lighthouses, they're frequently used in space probes due to the long lifespan and minimal maintenance. Voyagers 1 and 2, Galileo, Ulysses, and New Horizons all have one. Voyager 1's operational capacity was 470W at launch and by 2001 it would have dropped to 315W.

Both RTGs, and ny kind of reactor is not realistic by far.

RTGs, while light and not having many moving parts, are not radiologically safe to be around. Unless you understand "being around" as deploying it and having a no-go zone 200 meters wide around it, until it stops working by itself. While it is somewhat-useable on an unmanned space probe, or an automatic weather station in a polar area, its not feasible for any real use with people around.

Reactors are a step above that. They need heavy shielding around them (the pressure vessel alone will NOT cut it enough), they need support infrastructure (turbines, steam dehumidifiers, 2 or 3 (VERY) high pressure coolant loops (of which first one is deadly to be around just like that, due to radiological hazard, and they need large amounts of water (all nuclear plants, sans literally ONE, in the worlds, have either a river, lake, or similar water source nearby).

Furthermore, fuel. You cant just put a natural uranium ore or unenriched natural uranium into an RTG or reactor. Reactor grade fuel means 3-5% enrichment (you need an enrichment plant for that). This is the easy fuel. RTG's do not work on uranium - they use plutonium (highly purified, too! RTG plutonium fuel pellets relase realy obscene amounts of heat due to its high isotope purity and high activity), which is not found in nature unles you breed it (for which process, in turn, you need a specialised breeder reactor, and enrichment plant). All of which are high level of complexity, highly dangerous (radiation, chemicals used) heavy industries.

I'm not seeing a way to make this work well, as stated, for the following reasons:

1) I would think that large amounts of radioactive material lying close to the surface would be a massive, cancer causing blight in the area. Something much worse than the products of incomplete combustion. You are going to run the risk not only to the health of the adult population, but you might also get some nasty complications for children and such, reducing the number of surviving children, or children who don't survive long enough to reproduce due to leukemia and so on. The medical repercussions would be awful. Regardless of the material you could use, if it's close enough to the surface, you are going to be exposed to damaging radiation.

2) The specifics of HOW you use the radioactive material. An RTG is an option, but the fuel can be very harmful. It's not impossible to use, but very risky. Full on fission reactors would be almost impossible, even with small reactors as found in submarines and Chinese cargo containers. You have to move them, and they are very heavy. If you are doing traditional nomads with dray animals, you are stuck. You also need a means to process the radioactive material from ore into something useful.

Here is how you MIGHT make it work. Your world is a post apocalyptic wasteland. Load your reactor up in a mad max like heavy rig that is electrically powered. other vehicles are stolen from the Tesla factory and can recharge from the truck. Your people are raging, militant vegans. They move around and raid farms, stealing the produce and freeing all the animals. Every so often they return to the old nuke reactor for more fuel. Constant exposure to the radiation is going to weaken them over a number of generations, so you want to set it within a couple hundred years from the catastrophe.

I'm not totally sure of the science, but I think I could buy it from a layman's perspective.

yeah, but they're not going to do it well. It also depends on what you mean when you say nomads. Nomads just move around a lot, they live on the run. Doesn't mean they don't mine sometimes. You do also get to decide geography which is really useful and you don't require the nomads to have clean nuclear power. Your nomads could just get really really really lucky and find a mound of thorium and a place were you can get the right isotope of uranium. They could just drag furnaces around with them to burn this stuff. Hell they could even just put this shit in batteries. Just stop and charge up a capacitor and then have the capacitor dump its charge into a battery very slowly. This wouldn't be efficient enough to be practical by modern standards, but fuck it these nomads have nearly free nuclear energy. They should be able to waste as much energy as they want and still be fine, cause Thorium. I have no idea how they're planning on dealing with the waste though.

Thorium is pretty powerful stuff too. Thorium also meets all of your requirements. The hard part about using Thorium as nuclear fuel is getting the right isotope of uranium to start the nuclear reaction. If they can maintain this reaction then they shouldn't need too much of it.

This isn't the most unlikely scenario, but I'd call bullshit on it. But if they had lightsabers too.....

Why not? If we agree to

If necessary, the elements and isotopes involved can be different from those found in real life, such as having different half-lives, but the basic concepts involved with nuclear reactions should remain the same.

Looks like this plane will be known in future as Kirkasan from novel Starfog by Poul Anderson or one like it.

Let's say people arleady arrived and semi-crash-landed. Some time passed so they adapted to radiation level (ones who couldn't just died). They also regressed slightly (but not progressed back to space age yet or nomads decided they don't like core population and decided to go away). There are A LOT of heavy elements here, even including transuranium ones. So this nomad tribe just use radio-termal generators with natural (for them) isotopes.

If nomad tribe NEEDS SatTV (this includes somebody must be launching TV Sats and produce electronics for said SatTVs)...well, let's say they are splinters from core population and core population is arleady back in space age.

There is one small issue here - according to novel - they are no longer human per DNA analysis. They can't have children with regular humans.

I don't know how realistic it was, but the steampunk book Everfair featured airships powered by small nuclear reactors. I think it was partially handwavium combined with "indigenous priest knowledge", but it leveraged the naturally occuring uranium deposits in the Congo.