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Comment by dheera | Hacker News Reader

By "nuclear", my understanding is that these used thermoelectric radioactive batteries, not nuclear fission reactors. Big difference. Much lower maintainence.

(Basically you get a hunk of radioactive material that heats up from its own radiation and harvest that heat for electricity.)

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It's still fission. Just natural decay without management to speed it up or slow it down. In reactors the fuel rods naturally decay slowly and can be sped up with neutrons. So they can be turned 'off' and adapt to changing electricity needs. But RTGS are very static. Principle is still the same though. Both decay, cause heat which is made into electricity.

Technically speaking, fission is defined as splitting a nucleus into large chunks, approximately half the size of the original atom.

These things use radioactive decay, which is either alpha or beta particles coming out at a constant rate. Alpha and beta decay are not considered fission. (Though you'd have a reasonable case with Beryllium-8 alpha decay to Helium-4!)

Spontaneous fission decay is a thing and does happen. But not enough to power any of these kinds of things.

So why can't we have this tech with radioactive waste in our home or cars? With a proper lead shield would it be dangerous or not?

RTGs don't provide enough energy to power a car. You're looking at 1kW electrical maximum. The one on mars lander Cruiosity provides about 100W electrical power nominal.

But the main reason is that people are stupid and some would inevitably pull theirs apart and contaminate their surroundings with pretty nasty radioactive material. There's no engineering or practical reason why we wouldn't have RTGs for a heap of civilian applications, the reason is that people suck.

NASA is currently working on a 'micro' scale fully self contained fission reactor for the next mission to meet the higher power demand of the craft.

https://en.wikipedia.org/wiki/Goi%C3%A2nia_accident

That's only about a factor of 10 from being useful. If you have a 10kW battery, or 10 1kW batteries, you can use that to charge a Lithium battery for a day which will get you 100 kW for 2.4 hours per day, which sounds pretty damn useful for typical urban commuter use.

I think it'd be much cheaper to use PV for this use case.

I was going to reply saying I don’t want tiny pieces of radioactive material all over my house/globe, but then realized I have a tiny explosive (battery) in my hand and littered all of my house.

Yeah but when your phone battery blows you just have fire. You don't have to abandon your house because it's contaminated :)

People freak out when they hear "nuclear" and "radiactive", but there are 3 types of radioactivity.

Alpha and low energy beta emitters such as those used in nuclear batteries are not dangerous at all if shielded properly. In fact they are MUCH easier to shield than shielding a Lithium battery from the possibility of fire.

It's gamma emitters that are much harder to shield properly.

> Alpha and low energy beta emitters such as those used in nuclear batteries are not dangerous at all if shielded properly.

Read: if there is no feasible route for them to be aspirated, ingested, or get into your eyes.

Making a new device that has this property seems to be a pretty straightforward problem that we know how to do. The problem comes when an old device has been damaged or destroyed kinetically or via pyrotechnics.

It's more complex than that in case of a failure, because ingesting an alpha or beta emitter - directly, or through the food chain - is going to be dangerous to health. Can't exactly line your intestines with lead.

And while giving RTGs to general population isn't the brightest idea, it's stupid to consider these issues as a wholesale dealbreaker for nuclear technologies.

Good question. Pity people on HN are downvoting such well-intentioned curiosity. I think people are working on that ...

https://www.energylivenews.com/2020/09/02/us-startup-unveils...

I'm not an expert on that tech though.

The danger depends somewhat on the type of radioactive material used and how much of its radiation is alpha, beta or gamma, it's toxicity (independent of its radioactivity, plutonium is one of the most toxic substances in existence), half-life etc. But really, the main problem with proliferation of RTGs is dirty bombs. If you used them in cars or homes you can imagine the kinds of issues you might have with a serious collision or wildfires.

In any case, people actually once proposed cars like that! https://en.wikipedia.org/wiki/Ford_Nucleon

Having lots of them around, means still lots of radioactive accidents, because of normal accidents.

And to actually power your car, I believe they have too little power output, so they would only make for a expensive and dangerous car batterie, but one you do not have to charge.

(also, terrorists, dirty bombs, ...)

Yes and their output is static. What do you do with all that heat when you're not driving?

Use the nuclear battery to charge a secondary lithium battery, and that is the battery that the car actually uses to drive.

Considering cars are typically used for <10% of the day, the battery's static output wattage only needs to be about 1/10 of a car's operational wattage.

Basically when you get home and park your car, it just starts charging on its own from its nuclear battery. Optimize the nuclear battery size to minimize excess. If that battery gets full, release the excess as heat to the ground or sky, and also use some of it to maintain the lithium battery at optimal temperature. It will be only 1/10 of the driving wattage, so it will be much easier to do something with it.

Or plug in the car when you get home and it can power a good fraction of your home.

Right now, I would say, I would not have to worry about getting into a cold and icy car. But in the summer ...

Mine bitcoins, help solve complex puzzles etc, charge batteries or the grid..

It does not generate a lot of power.

RTGs are also used on a lot of US and Russian deep space missions...

The most convenient decay source is Plutonium-238 because it does not produce any gammas during the decay which would require lots and lots of shielding to protect people. It has long half life of 87 years so a reduction in power of roughly 1% per year. However, it's weapons material - not okay for wide use. This cannot be overstated. Making nuclear weapons today is very easy when you have the requisite materials (Ted Taylor of Los Alamos used to say it would take 3 guys a few months starting from scratch). With today's off the shelf timing systems, explosives, and manufacturing, it could be even faster.

Next up is Strontium, but that is quite dangerous due to human uptake in the bones. And there's polonium - very poisonous and too short a half life to be used.

I have heard from a friend in the business of a new concept that generates desirable isotopes specifically for decay heat sources in a reactor in an encapsulated form which gets rid of any weapons material or processing of radioactive material.

https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_ge...

The Saturn mission Cassini had 72 pounds of plutonium on it. The Pluto mission New Horizons has 24 pounds of plutonium to power itself.

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