Eli5, what does ‘enriched’ mean in the context of, for example, ‘enriched uranium’?
In: Physics
In the context of chemistry, enriching basically means to increase the proportion of something.
Uranium naturally occurs in two main isotopes: U-238 and U-235. U-238 is very stable, not very radioactive, and not really usable as fuel. U-235 on the other hand is “fissile,” meaning it can sustain a nuclear chain reaction which might power a reactor or a bomb.
Problem is that uranium out of the ground is almost entirely U-238, usually less than 1% is U-235. Uranium enrichment is basically the process of separating out as much U-238 as possible, so that the material left over has a higher proportion of U-238. Usually it’s an iterative process; you take all your uranium and put it through a centrifuge or some other device, then take the enriched result and enrich it again. Repeat until the material left has the desired proportion of U-235; all the uranium-238 left over is called “depleted” uranium.
Uranium fuel used in nuclear reactors is enriched to less than 20% U-235, but usually closer to 5%. Weapons-grade uranium on the other hand must be enriched to 85 or 90% or higher.
Again, this is really all about separating out the U-238, not making more U-235. If you have 100kg of natural uranium, 1% of which is U-235, if you enrich it to 20% you’ll only have 5kg of enriched uranium by the end, plus 95kg of depleted uranium.
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