If radioactive waste emits heat, why can’t we use it to produce energy?
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The technology that you’re talking about is called a radioisotope thermoelectric generator.
You can read more about it on the Wikipedia page here: https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator
>If radioactive waste emits heat, why can’t we use it to produce energy?
Nuclear power plants generate electricity by converting the heat from controlled nuclear fission into mechanical and eventually into electric energy *in the first place*.
The very fact that the final fuel state is called “waste” gives you a hint to the answer of your question: It can no longer emit **enough** heat to be a viable fuel.
Theoretically we can. In practice, it would be too expensive.
Also, for political and economical reasons, nobody wants to invest into research, that would make that a feasible source on industrial scale.
We aren’t very good at converting heat into electrical energy. That’s why we have to make systems that get rid of it. Machinery, electronics, cars, and even buildings all have cooling systems to get rid of heat because we don’t yet have the technology to turn it back into electrical energy. If we could solve that we would be in a much better position.
The Voyager space probes used this! Several other probes and some lunar missions as well.
https://en.m.wikipedia.org/wiki/MHW-RTG
We can and we do. But in commercial use they heatoutput isn’t enough to justify extraction of passive heat for use. There is lot of potential energy but released slowly.
In short, we can’t just produce energy from “heat”, we produce energy from a *difference* in EDIT – “Temperature”. Energy always flows from hot to cold, just like a waterfall drops water from high to low. You can’t just absorb energy from a river on the top of a mountain (it’s higher, right?) you need the water to be *falling* to capture the energy.
Radioactive waste *does* produce heat, but let’s make it up, if room temperature is 68 F, then the waste is at 78F. Compare this to a car engine where the temperature is around 3,000F. To make a car drive you use that heat differential of 3,000F to 78F to get useful energy. Or alternatively imagine a waterfall that’s just 2 inches, you can’t get a useful waterwheel that small to say, run a factory, off a 2 inch waterfall. That’s our problem.
The places where something like this *are* useful are applications that are both A. exposed to are really low outside temperature and B. require very, very little power. So essentially, space and the poles and we do use them for this in something called a “radioisotope thermoelectric generator”.
Not all radioactive waste emits heat. Most “nuclear waste” is “low-level”, meaning it was things like protective clothing, hand tools, or other things that might have some radioactive material clinging to them. It’s garbage that is contaminated, but usually not highly radioactive.
“High-level” nuclear waste does generate heat. It’s stuff like spent fuel or parts of the core. We could use them to generate power, but we often don’t. Much of the world, particularly the US, kind of stopped nuclear reactor development in the 1980’s. Older reactor designs didn’t really have a way to get further use out of “spent” fuel. Such designs do exist today, but since we’re not really building new nuclear plants, we’ve really got no good way to fully use the resource.
You may remember being taught that you can’t create or destroy energy. There’s always the same amount of it. It just changes form (eg from chemical energy to heat when you burn coal) or moves around.
So “producing energy” is easy. The heat is energy. What I think you mean is converting that energy into something useful; for example electricity.
Here there is a problem. The laws of thermodynamics say that what matters if you want to get useful work out of heat is the *difference* in temperatures. The bigger the drop in temperatures, the more you can do.
Note: this is not really a question of “we just don’t have the technology”. It is a pretty basic problem.
So, the problem with radioactive waste is that, generally, you can’t use it to make enough heat to maintain a decent sized temperature difference to make a significant amount of electricity to make it worthwhile for use in power stations.
But you absolutely can use it to generate electricity if your needs are more modest (for example in a space probe).
There are other things – for example radioactive waste is not very nice stuff so it isn’t just a useful source of heat. If you wanted to use it, you’d have quite a bit of extra work to do if you wanted to do it safely. That means that you don’t use it for just random bits of domestic power generation (most of the time). Safety is a factor too.
NB: I never like being untruthful, even in an ELI5. When I said earlier that “you can’t create or destroy energy”, that is fine for what we are talking about (practical power generation) but there are quite a lot of very deep subtleties that might come up in your next ELI5.
We *can* use it to produce energy, and on rare occasions we do, for stuff like powering space probes. But there aren’t many other good opportunities to use it – it’s hard to use because it’s, ya know, radioactive. Extremely radioactive.
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