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.
Natural Uranium is mostly U-238 isotopes (99%) that isn’t useful for Nuclear Reactors or Weapons. The Enrichment process helps separate the U-235 isotopes from U-238 to create higher concentration of U-235.
Low Enriched Uranium (LEU) has concentrations below 20%. Nuclear Reactors use LEU generally.
Highly Enriched Uranium has concentrations l 20% and above. Weapons use HEU, with typical weapons using 85-90% in their primary.
[Wiki: Enriched Uranium](https://en.wikipedia.org/wiki/Enriched_uranium)
The Isotope Separation can be done using a [Gaseous diffusion](https://en.wikipedia.org/wiki/Gaseous_diffusion)
or [Gas Centrifuge](https://en.wikipedia.org/wiki/Gas_centrifuge) method. The latter becoming more economical and beneficial with improvements over time.
Uranium has 2 main isotopes U-235 and U-238 but only the U-235 is useful in nuclear reactions. The process of separating the two isotopes is known as enriching. The part with a higher percentage of U-235 is the “enriched uranium” the leftovers are “depleted uranium”
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It’s been processed to increase the level of things that aren’t normally in it. Natural sources of uranium has very little U-235, the most useful type of uranium. The enrichment process increases the percentage of U-235 in the sample to much higher than it would be in nature, making it more useful.
Enriched foods have added vitamins and minerals. Enriched soils have had various things added to it which make it better for growing. An enriched person has more money.
This is when the percentage of U^235 has been increased through separation of the isotopes.
There are a number of ways this can be done and it’s often very costly and time consuming.
https://en.wikipedia.org/wiki/Enriched_uranium
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