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Physics/Japan nuclear capabilities

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Question
I read news that said that Japan possesses 1.2 tons of weapons grade uranium enough for 5000 nuclear bombs. So what would be the yield of these bombs if the uranium was split evenly?
And for future reference, how many kilotons could we get optimally from (by optimally I mean have the largest % fissioned of the total mass):
a) 10kg of uranium
b) 10kg of plutonium?

Answer
Well, your numbers for Japan are way too high.  They're also downblending and converting all of that to Low-Enriched Uranium or in the final stages of handing it over to the US.  Also, don't you think that (1200/5000=0.24kg) under a quarter kilo of uranium sounds a tiny bit low for a weapon?  I mean, I suspect that the mass is probably highly classified, but I'm sure you can google "minimum critical mass of uranium" and come up with 52 kilograms...meaning that you're already off by a factor of over 200 in whatever you read.  So they're just flat-out wrong on both counts.  So you're already down to minimal-sized bombs, and only 23 of them...assuming perfect splitting of the material.  And no industrial process is perfect.  So the answer to your second question is...a) no detonation.  b) the energy would probably be close-ish (google it) to the yield of one Hiroshima-sized weapon.

Nuclear weapons are also not perfect. When you consider ( http://www.ctbto.org/nuclear-testing/types-of-nuclear-weapons/ ) that only 1.4% of the Hiroshima bomb actually fissioned, you have to factor that in.  Say you're being optimistic and you think you can get 2% to fission.  Comparing to Hiroshima, you might be able to maximize that at 30 kT.  Similar to, but with assumed engineering enhancements, the weapons dropped on Japan.  Not exactly a global threat, there.  The yield of a thermonuclear design is far, far higher...however, as every junior physics or nuclear engineering major knows, it requires a full critical fission mass at its core to drive it.  You can google that, too, or look it up in your standard nuclear physics/engineering texts.  

So no, Japan's not some looming nuclear threat, and you should be more careful about how much you trust that "news" source that had such bad information.

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Dr. Stephen O. Nelson

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I can answer most basic physics questions, physics questions about science fiction and everyday observations of physics, etc. I'm also usually good for science fair advice (I'm the regional science fair director). I do not answer homework problems. I will occasionally point out where a homework solution went wrong, though. I'm usually good at explaining odd observations that seem counterintuitive, energy science, nuclear physics, nuclear astrophysics, and alternative theories of physics are my specialties.

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I was a physics professor at the University of Texas of the Permian Basin, research in nuclear technology and nuclear astrophysics. My travelling science show saw over 20,000 students of all ages. I taught physics, nuclear chemistry, radiation safety, vacuum technology, and answer tons of questions as I tour schools encouraging students to consider careers in science. I moved on to a non-academic job with more research just recently.

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Ph. D. from Duke University in physics, research in nuclear astrophysics reactions, gamma-ray astronomy technology, and advanced nuclear reactors.

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