This is something that has just recently occured to me. How limited is the sources of uranium/plutonium, etc that could be used to make nuclear weapons? How long would it take for all the weapon-grade isotopes to degrade?
Is there anyway to produce more weapon-grade uranium once it has all decays? If not, then it would seem that if we can wait and survive long enough, the threat of nuclear war will eventually become impossible.
The numbers I’ve seen vary a bit, but they all say that Uranium-235 (the weapons-grade stuff) has a half-life between 710 and 760 million years. That’s a long time to wait. And if you have uranium, you can make plutonium.
Yikes…I had no idea that it had such a long half-life. So much for my hope for a nuclear free world.
It was here when the Earth was created, and hasn’t been produced since. If it didn’t have a looong half-live, it wouldn’t be here now.
U-235 (half life 700 million years) occurs naturally in only small amounts (less than 1% of naturally occuring uranium). It is rather difficult to concentrate enough to make bombs with though. The bomb dropped on Hiroshima was a U-235 bomb.
In addition you can make fissionable Pu-239 (half life 24,000 years) from the much more common U-238 (more than 99% of naturally occuring uranium) in a breeder reactor. The bomb dropped on Nagasaki and the one tested earlier in New Mexico were a Pu-239 bombs.
You can also make fissionable U-233 (half life 160,000 years) in a breeder reactor from Thorium-232 (half life 14 billion years). Th-232 accounts for virtually 100% of naturally occuring thorium, and it’s about as common as lead in the earth’s crust. The U.S. tested some U-233 bombs in the 1950s.
U-233 and Pu-239 are virtually non-existant in the earth’s crust. Like U-235 they can be used either to make weapons or to fuel nuclear power plants.
U-235 (fissile) can be used as both reactor fuel and weapons.
U-238 (depleted) is a by-product of U235 reactors, and also occurs naturally. Weaponry applications of U-238 include armor and shell casings.
Plutonium is also a by-product of U-235 reactors, which can re re-consumed as fuel (breeder reactors) or refined for fission weapons applications.
The by-products of a plutonium (breeder) reactor, or by-products from U-235 reactors can be refined or used as is in non-fissile radiological weapons (“dirty bombs”).
The half lives of these isotopes, as indicated above, are huge. In short, there’s no gitting rid of them.
Have a nice day.
-FK
So when will we run out of sources of uranium to mine? As mentioned on the Hydrogen energy thread, Uranium (235 and 238) is a finite resource in the earth’s crust, and might become hard to find in the foreseeable future…
is this a real problem, and if so, can we get round it by using plutonium (breeder) reactors?
I am not a great fan of fission energy, but if it gets us out of an energy hole long enough to fully develop renweable energy, then we must adopt it.
I’m sure we will find nice and easy ways to fuse hydrogen without the fission trigger long before the Uranium runs dry.
To answer eburacum’s question: I attended a lecture at a one of our national laboratories run by the Dept. of Energy. The scientist giving the lecture pointed out that we have a limited supply of Uranium, using conventional fission reactors (about 50 years at current rates) The problem of course, is that the radioactive waste (mixtures of different isotopes of Uranium and plutonium) not only have a ridiculously long half-life, but they can be used to make nuclear weapons when separated and processed.
This problem could be solved by recycling the unseparated waste in a new type of reactor (Fast) to get more energy out of it, instead of the “once-through” cycle most reactors now employ. If I understand it correctly, the waste products, provide more energy by a large factor (100x) than the original uranium. An additional benefit is that the half life of the final waste product is numbered in hundreds instead of millions of years, and is less radioactive than the original uranium you started with. You wouldn’t need to truck stuff to Yucca mountain.
It’s explained here:
http://www.era.anl.gov/presentations/frontier2002article.pdf
The scientist expressed doubt that this type of program would ever be developed in a timely matter. He said that in order for such reactors to come online by 2030, they’d have to begin now, and the political climate is extremely hostile to anything with the word “nuclear” in it. People just don’t trust it anymore. He predicted an energy bottleneck, sometime in the near future. It sounds like a great solution, if all is as they say. The only drawback mentioned is that it generates some radioactive gasses that they still have to figure out how to store. (it’s harder to sequester a gas than a solid)
Though I can’t find a cite for it at the moment, filtering the uranium that’s dissolved in seawater would provide enough fuel to power the entire world at the current US level for several thousand years. That’s enough time for just about any development, though after several thousand years we could still be 20-30 years from a working fusion reactor (like we have been since 1960 or so…).
:hijack:
Anyone care to speculate on how long it would take to deplete our Uranium resources if we switched all of Earth’s energy production methods to Fission?
:hijack: