The term "nuclear waste" conjures up images of rusty steel drums leaking their glowing green radioactive contents into rivers and soil, resulting in cancers and sickness in nearby communities – or maybe mutated creatures that run amok decimating those nearby communities. But as the world looks to wean itself off fossil fuels, nuclear power is set to play a bigger role in the global energy mix, so it's worth going beyond popular imagery and start looking at what exactly nuclear waste is, just what kind of risks it actually poses, and how do we get rid of it?

What is nuclear waste?

Simply stated, nuclear or radioactive waste is the byproduct of nuclear reactors, fuel processing and reprocessing, weapon production, medical facilities, and research laboratories. However, the term covers a lot of different kinds of waste. Plus, nuclear waste is unusual in that it changes its properties drastically over time, going from one form of waste to another.

So the answer is not straightforward, but perhaps the best place to start is with the most familiar and serious form of nuclear waste – high-level waste produced by civilian nuclear reactors.

How is nuclear waste produced?

In conventional nuclear reactors, the fuel is in the form of ceramic plugs about the size of a thimble. These contain enriched uranium, which is high in the fissionable isotope uranium-235. These pellets are placed inside metal alloy tubes to form rods and the rods are gathered into rectangular bundles.

When these bundles are placed together in the reactor, they are immersed in water that serves as a moderator and coolant. As the uranium atoms split naturally, they give off two neutrons each. The moderator slows these neutrons, so they have a better chance of being absorbed by another uranium-235 atom. If this happens, the second atom splits, giving off two neutrons, which can be absorbed by more atoms. If there's a great enough concentration of fuel, the result is a self-sustaining nuclear reaction.