What Is Enriched Uranium?

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Uranium is found naturally in three different forms, all of which are radioactive. Find out about enriched uranium, which has a higher percentage of uranium 235 than natural uranium, with help from a science teacher in this free video on physical science.

Part of the Video Series: Physical & Life Science
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Video Transcript

Hi, I'm Steve Jones and I'm going to explain briefly what enriched uranium is. Uranium is found naturally in three different forms. All are radioactive so don't think that there's a stable form, there is no stable form with uranium. All are radioactive, uranium 238, uranium 235 and uranium 233. Now the most common one is uranium 238. 99.3% of uranium is uranium 238. It contains 92 protons and 146 neutrons and of course 92 electrons if it's in a neutral state. So uranium 235 is slightly different, it still contains the 92 protons of course, that's what tells us it's uranium, but only 143 neutrons and uranium 233 with 141 neutrons. We can forget uranium 233, it's like uranium 235 but there's so little of it that it will never be of any use for practical purposes. Uranium 235 is different from uranium 238 in the way it behaves when it is hit by a neutron. Here a neutron hitting uranium 235 atom can produce what we call fission. And fission is basically, it's a term that comes from biology when a cell divides, a cell divides into two equal parts, well fission means it's got two big lumps so the uranium 235 doesn't just spit out another particle, it actually falls to bits into two pretty hefty lumps and chucks out a pile of neutrons. Well maybe each neutron coming in, maybe three neutrons coming out. Most of these neutrons disappear into the air and don't cause a problem. But what you can do with this reaction is you can produce a chain reaction and the chain reaction is where these neutrons coming out hit other uranium 235 atoms and therefore produce further fission reactions. Considering this reaction takes 10 to the minus 9 seconds, that's one hundred millionths of a second, you can imagine these reactions taking place one after the other produce a huge amount of energy. This in itself produces a massive amount of energy, much more energy if you get a lot of reactions very, very quickly in a very short space of time. The chain reaction therefore will produce a huge bang and hence you've got your atomic bomb. But the problem is that uranium is not uranium 235, less than one percent of it is this. So actually less than one percent of these neutrons will produce other fissions reactions and therefore it will fizzle out, nothing will happen because most of these neutrons go on this reactions where they're absorbed by uranium 238 and produce plutonium 239 which does undergo fission but under different circumstances and basically this causes the whole thing to fizzle out. So what is enriched uranium? Well the answer is pretty simple. You have to make sure that the amount of uranium 235 is much higher in proportion in percentage than the .7 percent it is at present. It doesn't have to be approaching 100%, but it must be much higher, maybe 30, 40% at least. Once it is at that kind of level, you can get enough of these neutrons to produce reactions to produce this chain reaction and there are other things you can do to the components of what is a bomb to produce this reaction. Now the chain reaction can be controlled by absorbing neutrons. You know, if you absorb them, it'll stop the reaction and therefore you can get the chain reaction but control it and that's what we do in a nuclear reactor. We have a fission reactor, a fission process but we have something which controls the neutrons so that we can very finely tune it so it just produces enough reactions to produce a very hot body and the hotter it gets, the less reactive it becomes. So you can produce a chain reaction and control it but you still need enriched uranium that is uranium with a higher percentage of uranium 235. So there is the answer to your question, what is enriched uranium, it is uranium which has a higher percentage of uranium 235 than natural uranium.


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