Isn’t nuclear waste hot and releasing neutrons or electrons or whatever? Why can’t we just throw nuclear waste in a chamber surrounded by water to heat it up and generate power?


Isn’t nuclear waste hot and releasing neutrons or electrons or whatever? Why can’t we just throw nuclear waste in a chamber surrounded by water to heat it up and generate power?

In: Engineering

There’s a large gap between “radioactive enough to generate power” and “radioactive enough to give you cancer”. Most nuclear waste is stuff like containers that nuclear material was stored in, or gloves and suits used by people handling nuclear material. That stuff is in the “radioactive enough to give you cancer” range.

We do throw nuclear waste in a pool of water, but the last thing you want is for it to boil. The steam would carry radioactive matter with it. Remember the Fukushima disaster in Japan. Yeah, the pools themselves became a potential problem. If you can’t maintain cooling of the pools, you’ve got yourself a big problem.

How efficient a power plant is depends largely on the difference of temperature between the steam you create and what comes out, cooled and expanded in the end. The larger that difference, the better. If radioactive waste could create enough heat to make a reasonable steam cycle, it wouldn’t be waste, it would be fuel. We throw it out because it doesn’t create enough heat any more.

Nuclear reactors run on *very* thin margins, money-wise, because of all the safety features they need and because they’re heinously expensive and slow to build. If you built a reactor to run on burned-down fuel you’d have all the expenses of a normal reactor but your electrical output and revenue would be sub-par.

Secondary reason – if you had some fuel bundles from Reactor A and some other ones from reactors C and G, their isotope contents are going to be different and that will make your reactor run weird. You could get hot spots, cold spots, spots that react faster or slower to control rod changes, spots that burn off xenon faster or slower. That might all be manageable, but it makes the system less safe. Compared to all those hassles, fresh fissile material isn’t all that expensive.

Bill Gates funded research for new types of reactors and they engineered a reactor that does not go into meltdown in all case power is off and there’s no generator (so incredibly safe) and can run on nuclear waste. They were suppose to open the first one as a trial in China, had an agreement and then Trump vetoed it. Of course without options to do it in US. So the technology is there, we just let it rot.
The ‘no nuclear power, let’s use wind’ folks are not helping, as all they do is stop the progress of better technology. Renewable energy is great, but we’re just not there yet, like not even remotely, except with countries that are geographically blessed (Like Norway). Nuclear energy can be sustainable and safe IF you allow the funding of new models, instead of making everyone use the outdated engineering, like Fukushima was.

The heat output in my plant’s spent fuel pool which has 6 cores of spent fuel would only produce 2-3 MW of electric power at most with a near perfect thermal electric conversion cycle.

There isn’t enough heat to justify it from the radioactive waste. You would need to spent a ridiculous money on a second power plant that has a vessel 6 times the size of the reactor that already was 400% over budget to build all to produce something that will never pay itself back.

So, yes there is heat there, but no it’s not enough to be meaningful.

When you turn off a nuclear reactor, 1 second after the reaction stops the fuel drops to about 7% of the heat it was while in the reactor. After 5 hours, it’s down to 1% of that heat, and slowly drops over time.

<1% of the heat of a fully-running nuclear reactor is hot enough to boil water, so you need to keep the fuel in cool water for several years to avoid it being a problem. But it’s not hot enough to generate much power.

For a truly ELI5 analogy, it’s the difference between a wildfire and a match. Yes, you can still burn yourself on a match. But it’s nothing like the wildfire.