Eli5: How and why is uranium bad / deadly for the human body?
The uranium itself is not *that* radioactive, at least not the naturally occurring uranium (it has to be processed to be viable as nuclear fuel or weapons, the process is called *enrichment* because it enriches the proportion of radioactive isotope in your mix, with *isotope* being the version of atom you have, all uranium atoms have the same number of protons, but they can have different numbers of neutrons, and depending on how many neutrons they have, they are either stable or not, and non-stable isotopes split into smaller atoms, this is called radioactive decay). Anyway, your body does a lot of chemical reactions, and to those reactions an atom of Uranium actually looks a lot like some other atoms (I think it would be a lot like calcium but don’t quote me on that), so your body *could* accidentally use an atom of Uranium in chemical reaction, where it doesn’t belong, and it *could* work but down the line the product would not have chemical properties it should have. This is how most of heavy metal poisoning work on chemical level, when exposed directly to cells. But human body (and animal bodies in general) have evolved complex systems to filter out heavy metals from bloodstream, so most of uranium never reaches *most* of your cells, instead your kidneys filter it out of your bloodstream… Which means that for a time all of that uranium is concentrated in your kidneys, it gets into kidney cells and there it ends up in chemical reactions where it has no business being in.
Uranium is dangerous mostly because it’s very toxic if inhaled or eaten, similar to toxicity from other heavy metals. Uranium is often in powder form which can end up in your lungs, which is why workers wear protective equipment when working with uranium.
Refined uranium (uranium-235) is slightly radioactive, but U-235 atoms decay very slowly which means they emit very little radiation and hence toxicity generally still remains the most dangerous part of it.
Uranium is hazardous in two ways: as a source of radiation, and as a toxin.
Most uranium is not terribly radioactive unless it’s been refined to specifically the more radioactive kinds used in nuclear reactors and to make weapons.
It is, however toxic if it gets into your body, like other heavy metals. It gets wedged in enzymes and proteins on the surfaces of cells, screwing up the chemistry of the cells and their operation. It causes certain types of cells to die off by screwing up chemistry in the mitochondria (part of the cell that generates chemical energy to operate the cell), causes inflammation, and it can interfere with enzymes that do DNA repair in your body — which increases the risk of cancer as well as killing cells.
You can take uranium into your body by breathing in dust that contains it, or by eating / drinking things that have it mixed in. It’s a big concern for soldiers that may have fought in areas where “depleted” (not radioactive) uranium was used for artillery or as armor on tanks. When those things smash into stuff, microscopic bits of it are released into the air and become toxic dust.
You can think of it like having millions of tiny holes stab into you, doesn’t sounds fun for anything involved
Because it emits radiation, which damages the cells in your body, which increases the chance of (bad) mutations when new cells are made. Essentially being exposed to uranium increase the chance of your body being damaged in some way.