Hi, Dr. Zoomie! So I’m wondering…Russia is saying that sending depleted uranium weapons to Ukraine is like sending them nuclear weapons. I know that nuclear weapons can be made with uranium – how is this different?
So here’s a question for you – what do these two things have in common?
In case you’re wondering, the first is a bucket of sand with a few drops of gasoline mixed in and the other is a type of weapon that sprays an aerosol of fuel into the air and sets it off in a massive explosion. Both contain gasoline…so why is the one a powerful explosive and the other is a bit of a dud? It comes down the amount of fuel that’s present – with uranium, the term that’s used is “uranium enrichment.” And the logical next question is “what’s that”? Which brings us to the photo of my favorite radioactive mineral!
Here’s a photo of a uranium mineral called torbernite – I bought it at a rock and mineral show nearly 30 years ago, and I don’t worry that it’s going to suddenly explode and destroy my home:
Uranium comes in two “flavors” – all uranium atoms have 92 protons; it’s the number of protons that makes it an atom of uranium instead of, say, tin. About 99.2% of the uranium atoms in my rock have 146 neutrons giving them a total mass of 238 atomic mass units (which we call U-238) while 0.72% will have 143 neutrons and a mass of 235 amu. And here’s the thing – U-235 fissions wonderfully while U-238…not so much.
The uranium in my rock has too little U-235 to sustain a chain reaction and way too little to explode. In order to become reactor fuel I’d have to concentrate the U-235 atoms to the point where they’d sustain a chain reaction – for most reactor designs you need to have U-235 comprise at least 2-3% of your uranium atoms…it would have to be enriched to at least 2-3% in the parlance of nuclear engineering. Making a nuclear weapon requires far more – the Hiroshima bomb was enriched to about 80% U-235 and modern weapons run at over 90% U-235. I should also note that if you take a bunch of uranium and enrich it, you’re going to be left with a lot more depleted uranium than the amount you’re able to enrich – for every 1 kg of reactor fuel you produce 8-10 kg of depleted uranium.
A better analogy comes to mind, though when I think about the difference between depleted and enriched uranium with regards to making a nuclear weapon…let’s think about a big bucket of gasoline and an even larger bucket of sand.
We know that gasoline burns very well – but how well is it going to burn if you put a single drop of gasoline in a bucket of sand and mix it well? A lot of nothing – because there’s way too little gasoline and way too much sand. To get a fire going, you’ll have to add more gas until the concentration is high enough to keep a fire burning. Similarly, depleted uranium will no more sustain fission than a bucket of sand with a few drops of gasoline will sustain a fire. Or, put another way, depleted uranium (abbreviated DU) is about as far from being a nuclear weapon as a few drops of gasoline in a bucket of sand is far from a thermobaric explosive such as the “Mother of All Bombs.”
SO…depleted uranium won’t fission and can’t go “boom,” but it does have its uses.
One use is as a radiation shield – depleted uranium is so weakly radioactive and so dense that it absorbs more radiation than it emits, making it a very effective radiation shield; I’ve seen it used to help shield potentially dangerous sources as well as to reduce radiation exposure from radiopharmaceuticals – which is what’s shown in this photo:
Because it’s dense and tough, DU also makes great armor, which is why it’s included in many newer tanks:
Now only that, but DU is also great at punching holes in armor, making it a wonderful weapon to use to kill tanks. And that’s why Ukraine has been receiving depleted uranium weapons – to help them kill Russian tanks more effectively. And the reason that Russia isn’t happy with this has nothing to do with nuclear weapons – it’s because they’re doing so poorly in this war, because they’ve lost so many tanks already, and because, with DU weapons in Ukrainian arsenals, they’re going to lose more tanks more quickly.