If radioactive waste emits heat, why can’t we use it to produce energy?

Question

If radioactive waste emits heat, why can’t we use it to produce energy?

In: 132

Answer 1

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.