eli5 If nuclear waste is radioactive, can’t we generate electricity from it emitting radioactive particles?
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Waste is not super radioactive like the fuel is. It’s not hot enough to power a steam turbine like in a reactor, but it is hot enough to poison you.
There just isn’t enough energy density, and that’s why it is waste.
We could, I suppose, but it’s super toxic and dangerous. It could be packed into a radioisotope thermoelectric generator (RTG), and a small amount (2KW) of electricity produced. But it would have to be in a super secure facility, and powering the lights to keep evildoers from stealing it at night might take more electricity that the facility produces.
Its not super radioactive. When something has a super long half life it means it will put out less energy in the same time frame as something with a shorter half life. Nuclear waste is like the embers after a fire. Its still there and doing something, but not enough to do anything interesting,
Nuclear waste is radioactive, but we can’t tell it when to give off energy. It just does. We can’t decide when we want power, we just get a steady stream, and usually not near as much.
Technically? Yes
Usefully? No
[Betavoltaics](https://en.wikipedia.org/wiki/Betavoltaic_device) are a thing where you put a strong beta emitter inside the right materials and capture the electrons(Beta particles) that it throws off and use that to generate power. They’re not good for anything but tiny tiny power sources. There are some that exist for pacemakers but a “high powered” beta voltaic source will generate 100 uW
Gammavoltaic cells have been considered but not built. Gamma rays are really hard to collect, they just ignore most things
One of the big components of spent nuclear fuel is Caesium-137 which has a half life of 30 years making it quite radioactive. When it decays it gives off a Beta particle with about 0.5 MeV of energy and a Gamma ray with 0.66 MeV for a total of 1.1 MeV of energy which isn’t zero but isn’t a ton.
When you fission a single atom of Pu-239 you get 207 MeV of energy, so one atom of Plutonium splitting gives off as much energy as 200 of its longer lived decay products decaying.
To get a lot of power from the decay products you start needing a large amount of them because they’re not energy dense and that large amount of them results in lots of gamma rays and handling challenges. Its far far easier to just put them in the ground and add in fresh U-238 that’ll turn into Pu-239 and give off the big chunk of energy.
It’s radioactive, but nuclear reactors don’t work off of the natural decay of the materials in them (which are, in fact, a lot *less* radioactive than the produces in waste).
Nuclear reactors work by using a nuclear chain reaction to make atoms decay millions of times faster than they normally would. And it turns out that only a very few specific isotopes can sustain such a chain reaction. Once the chain reaction shuts down, you’re left with the normal decay rate of the material, which is high enough to be dangerous to life but not high enough to be useful for power generation.
To put some scale on this, a short-term radiation exposure of about 10 Sv is nearly always fatal to a human being. 1 Sv is, with some weighting, about 1 J of energy per kg of body tissue, meaning that for a 75 kg human, a 10 Sv exposure is only about 750 J of energy. That’s enough to power a lightbulb for a matter of seconds or, if you prefer, about as much energy as being hit by a heavy object at human-typical speeds. So even when it’s not emitting very much overall power, nuclear waste can still be incredibly dangerous to human life.
To add to what others have already said:
In nuclear power plants we don’t use the radioactivity directly to generate energy. We use the fact that we can control the rate of radioactive decay in some elements.
While decaying the material gets hot and heats water. The steam of the boiling water is used to turn turbines.
Even “nuclear batteries” like the radioisotopeic thermal generators (RTGs) used in some spacecraft like Couriosity and Perseverance don’t use the radioactivity directly.
They use the heat of the decaying material. The temperature difference between inside and outside the battery creates electricity.
While the financial aspect of the first methode is debatable, the second method is just too inefficient to use on earth.
We can, but it’s not nearly enough energy to be economical with the amount of nuclear waste you would need to use and have people working around. I believe Voyager uses decaying plutonium to keep it running since it’s too far for solar panels to be effective and that battery has since outlived its intended mission life, but it’s really the first time we’ve done something like this
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