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Comment by reacweb | Hacker News Reader

I find it very hard to imagine that a 74 years old technology remains complex enough to be available only to governements.

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It's not. Nuclear fission reactors are built by large corporations like General Electric and Hitachi. If these companies wanted to they have the expertise to build a nuclear bomb but why would they unless their governments asked them to?

A huge number of 74 year old technologies are available for $0.75 direct from China.

The fact the nuclear reactor hasn't been miniaturized to the size of a coin and included in every $15 childrens toy to power lights is in large part because of public perception and government regulation rather than real safety/health concerns - there exist plenty of typical household materials that are more dangerous than the safest nuclear materials.

Nuclear technology scales horribly downwards so even in a world that fully-embraced the technology you won't have pocket reactors that do anything more than maybe a power some gimmick accessory. The true power potential of nuclear only comes into affect with full steam boiler-turbine infrastructure, which are large, heavy, and maintenance-intensive beasts; a good comparison would be an early-industrial coal steam boiler from the time before we really understood metallurgy. You'd have those boilers in factories, ships, and trains, and maybe even a small crappy one if you were rich for the home workshop, but nothing you'd carry around.

RTGs can be made small, but they also completely sacrifice the power density of nuclear due to their abysmal efficiency. Their main advantage is maintenance-free longevity more so than compactness or anything.

I think with investment nuclear technology could scale down - the full steam boiler design could maybe even be miniaturized via silicon micro machines type technology, but there might also be avenues for using the photoelectric effect for a more direct nuclear to electricity conversion.

Either way, I can totally imagine someone saying "punch cards and relays scale down horribly - you could never make a small computer".

> Nuclear technology scales horribly downwards

A small steam turbine is an apparatus with about the size and complexity of a car engine. But if it has to be licensed and inspected by the NRC then you can forget about it.

And you could make a little RTG that could power a phone for a decade. Even with the terrible efficiency of thermoelectric generators it would still be much smaller than a lithium battery that could store the same number of kWh, because it's ~10% of the efficiency multiplied by much more than 10 times the power density. The main limit you hit on size is practicality -- why make a tiny, tiny, tiny one that lasts for a month when you can make an only marginally larger one that lasts for ten years?

I'd accept a thick phone if it had a huge battery life. But then how do you perform waste disposal? People are, largely, irresponsible jackasses who would think nothing of throwing old RTGs into the ocean / landfill / other improper decomissioning methods.

Also the potential damage is a lot higher e.g. if you're in a car accident and the RTG gets punctured vs. just a Li-ion battery catching fire. In terms of cleanup and containment.

Using an RTG to power your phone isn't a real suggestion. Lithium batteries can last for a day (especially if you're willing to accept a thicker phone) and the inconvenience of having to charge it while you're asleep is minimal. A more realistic application might be something like military radios where you may want them to keep working for extended periods of time in areas where electricity is not available, and then you have an organizational structure that can take care of proper disposal.

The point is that it's not a scaling problem. It's practical to make an RTG that small as a technical matter.

>The fact the nuclear reactor hasn't been miniaturized to the size of a coin

But it has, or at least close to:

RTGs[1] weighting a couple dozen kilograms are used in space exploration and in rare cases in cold climates. Their main problem is low power density.

Nuclear pacemakers[2] of just a few centimeters across used to be a thing - long lasting and reliable. Also used thermoelectric generators. Replaced by cheaper lithium-based batteries due to high costs of making the nuclear capsule resilient against various possible sources of damage - like body cremation, car accidents, etc.

Nonetheless we have reached certain natural limit of nuclear fission, and only use of nuclear fusion[3] (or major scientific and engineering break-throughs) could change the status quo. The three main unsolved problems for wide scale commercial deployment of fission power:

1) radiation shielding - right now we only have passive shielding via use of structural materials, weights a lot

2) critical mass for active chain reaction (heavy and requires active management) vs passive generation via spontaneous fission (low power density)

3) operational safety and non-proliferation issues: a fission device requires radioactive material, and radioactive material is by its nature dangerous

Notably all three issues are either minimized or entirely absent for nuclear fusion.

Lastly, in typical nuclear power plant, the power generation facilities are usually of comparable size to, or even larger than, the nuclear reactor building itself - so miniaturizing the reactor would yield only diminishing results. High-temperature superconductors ought to be of some help here.

[1] https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_ge...

[2] https://www.medicaldesignandoutsourcing.com/medtech-memoirs-...

[3] "Typical fuel pellets are about the size of a pinhead and contain around 10 milligrams of fuel." - https://en.wikipedia.org/wiki/Inertial_confinement_fusion

> 2) Critical mass:

Can be dramatically reduced with a neutron reflector [1]. Bare Sphere's [2] can be as small as 6.9cm diameter, and use of a neutron reflector could perhaps reduce that by half or more. 3.5cm is pretty small. Research is still ongoing into reflecting neutrons, and it's possible that some clever arrangement of neutron 'lenses' might allow criticality with almost no mass.[3]

[1]: https://en.wikipedia.org/wiki/Neutron_reflector

[2]: https://en.wikipedia.org/wiki/Critical_mass#Critical_mass_of...

[3]: https://www.isis.stfc.ac.uk/Pages/neutron-reflectivity---int...

Has magnetic shielding been tried for fission? I guess it wouldn't work on neutrons, the same as fusion.

On the other hand, a child swallowing a tiny nuclear plant in the shape of a smiley would be an entirely new experience in the A&E department but that would never happens? would it?. I could see from here the lawyers salivating with a case like that.

Not to mention that those toys would end in a few days in the garbage, ready to be shipped by volume to be burnt ("recycled") in some other country.

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