My uninitiated mind would think that it would be the other way around.
I was watching a video about nuclear power. The guy being interviewed was wearing safety glasses and nitrile gloves while holding a uranium fuel pellet. Then the camera pans to a screen showing the robot handling spent fuel in the bottom of a 40-foot deep pool of heavy water. The pool is in a room behind a big red door with every “do not enter” warning imaginable. I would think the fuel would be less radioactive coming out than going in.
In: Chemistry
2 things. First, fresh uranium decays very slowly, so it’s less dangerous over short periods of time. Second, uranium decays via alpha decay, which means it emits alpha particles (aka helium nuclei). These are big and slow and get blocked by just about anything. So a thin latex glove is enough to block the alpha particles from getting to your skin.
As that fuel is in the reactor undergoing fission, those uranium atoms are being turned into atoms of other radioactive isotopes, which are removed from the reactor as spent fuel. These isotopes in the spent fuel are much more radioactive than uranium, and also emit different kinds of radiation that can pass straight through many materials, and can only be blocked by thick layers of stuff like concrete, steel, or water. So if you were handing spent fuel, you’d be handling material that’s giving you a lot more radiation and a different type of radiation that’s more dangerous to you.
Think of it like this: Before you put something in the oven it is safe to handle, after it spent a bunch of time in a hot oven you can’t pick it up with your bare hands for some time*
*YMMV
It sounds like you expect the uranium to be more dangerous because it has more potential energy that can be used, while the by-products should have less energy. And that is largely correct, uranium does have more stored energy which can be released as it naturally decays into elements with less energy available, until you reach iron and it won’t decay any further.
The difference is that uranium is stable on its own, and only very rarely or slowly breaks down into the next step in the decay chain. That is why it is found in nature- because it is stable and sits around. Once it is put in a reactor the decay happens at a massively faster rate, creating elements that are lower in energy but also less stable.
These unstable by-products then continue to break down on their own after they have been taken out of the reactor. This decay releases energy, which causes harm to the body, and makes them dangerous.
A loose analogy is flowing water. Uranium is like a mountain lake, high in energy but stable, there is little flow of the water. If you are in a boat and paddle out of the lake into a river it is then flowing much more rapidly down the hill, and the rate at which it drops down the mountain in rapids or a waterfall makes it dangerous.
So, to ELI5
In order for a nuclear reactor to pull power out of it’s fuel. The very atom the fuel is made from breaks down. Not the _chemical bonds_ between atomes (like splitting The 2 Hs from H²O) but the actual atom itself splitting. So the Uranium is no longer uranium. And other elements can have totally different levels of radiation.
[ HERE ](https://www.env.go.jp/en/chemi/rhm/basic-info/1st/02-02-03.html) is a link to the process. In a fairly easy to understand way.
(I’m simplifying a bit here) But ‘spent’ uranium fuel isn’t even uranium anymore.
It’s also worth noting that there are different kinds of radioactive. Some are more useful than other.
(I’m not an expert on nuclear reactors, but I’m going to go out on a limb here and say that _none_ of them are particularly useful in a uranium reactor. It’s free neutrons and massive deficits that produce the actual energy to heat the water and drive the turbines)
To ELI5 this part. You start your reaction with [Uranium + Neutron] that has _X_ mass. You end the reaction with all your [bi-products + 2 neutrons] which has a mass < _X_.
Then you can **E=mc²** on that missing bit of mass, and *that* is where the energy to heat the water came from.
Latest Answers