So I always wondered what is the issue that countries/companies do not look on manufacturing “mini” atomic generators?
I know that there exist small atomic generators maybe but they are like the size of a house or at least of a room.
Why not using e.g 10 grams or even 1 gram of uranium or any other suitable element to make really small generators that could fit e.g inside a bike or a small car?
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Making a nuclear reactor for controlled fission is already extremely difficult to do at scale. It would be virtually impossible to miniaturize.
Using the heat off of uncontrolled fission, like the Mars rovers do, is problematic because it relies on having some *really* radioactive material.
It would be a combination of all but impossible and very dangerous.
The power you generate depends on the geometry of the reactor elements. Each splitting Uranium atom fires off neutrons and you need those neutrons to fit other Uranium atoms for the reactor to keep running. The neutron direction can’t be controlled, because they have neutral charge, you have to have a Uranium atom that coincidentally happens to be in the right place. As a result, even for solid Uranium, you need a goodly amount – called a critical mass. That’s 52kg for U235 (the kind that’s hard to get). In a giant reactor, this isn’t a problem, but the atoms themselves don’t miniaturize.
You also need to consider that these reactors only generate heat, in a radioactive liquid. You’d need to extract that heat, hopefully without spilling any radioactive waste. That’s going to take pumps and pipes and “not going to fit on a bike” stuff.
Because it doesn’t matter how much of your 10 grams is U235, 10 grams of uranium will never go fissile. It takes about 100 lbs of it to even get critical mass. Plutonium is better, but it’s still about 23 lbs. It’s really not something that can be miniaturized any more than it already is.
And that’s before you put high radioactivity elements in the hands of people without the expertise necessary to handle it, in the case of the bike/car examples.
In all, 0/10, would not recommend
There are nuclear powered submarines with fairly small reactors.
There are also RTGs that are used in space probes. Slightly different technology to steam boiler type reactors. These don’t produce a lot of power, but last for a very long time.
But to answer your question on stuff for inside a bike/car. Economies of scale. You can shrink the uranium used to 1 gram, but you can’t shrink the pipes, pumps, valves, safety equipment, control systems, electronics etc. to the same amount. It is better to use a big power plant to create electricity first, and then transfer that power into an electric bike or car that has batteries.
Small, molten salt based nuclear reactors have existed, but their development has suffered due to more government interest in large fast breeder reactors. In technology as complex, risky and expensive as nuclear power there is not a lot of diversity possible and the larger reactors got the advantage in funding, as far back as the 1960s. But China and other countries are now developing the small reactors again and we might see them become popular, but AFAIK in the energy game there is more interest on renewables, and rightly so as they are far safer.
10 grams of pure uranium or plutonium is going to be 0.5mL (the volume of 10 drops of water) of metal that might feel slightly warm, but probably not enough to even notice. What are you going to power with that? The big power stations aren’t magic; they have tonnes and so can get hot enough to make steam to spin turbines. Nuclear fission just doesn’t scale down that far.
Of course it’s also both extremely poisonous chemically and an extremely dangerous source of radiation. Having millions of these in the world guarantees bad accidents whatever precautions are taken but a bigger issue is going to be people trying (and probably succeeding) in making things like dirty bombs.
Some mixed up answers here.
If you are talking about fission, there are minimum sizes to what you can use to generate power. It is not the same thing as the bare sphere critical masses that people are quoting; it can be smaller than that if you use moderators and reflectors. But to actually generate net power in a controlled way requires more than a minimum amount. It requires you to boil a substantial amount of water, and put that steam through a turbine, and then have a cycle for replacing the water in the reactor so it doesn’t overheat (and continuing the cycle). Even without safety equipment and shielding, this is still a lot bigger than “mini.” The smallest modular reactors that have been seriously proposed are about the size of a car. That’s pretty small, and it’s _just_ the reactor part — it outputs steam if you put water into it, but you still need a turbine, etc., to turn that steam into electricity.
Why are there minimum sizes? Because you need to create the conditions for the chain reaction. Again, it’s not as simple as there being a magic single size for that — it depends on a lot of factors — but there are minimums that are imposed by nature.
There are also radioactive elements which can be used in radioisotope thermoelectric generator (RTGs). These are not nuclear reactors; they take the heat of a very-radioactive element and convert it into electricity. This is not a great way to generate power if you are not in outer space. Or to put it another way, there are way better ways to generate power available to you if you are not in outer space. RTGs work great in some contexts (outer space) because they are self-sufficient and last a long time. But they don’t give you a lot of power output by itself. For anything not in outer space it is usually easier to just have a big battery and then recharge it based on power sources that give you a lot more electricity.
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