The Fermi Chronicles - Part 11: Worldwide Uranium Availability

As I mentioned in prior posts, there is no naturally occurring elements with an atomic number greater than 92, which is uranium. Recall also that U-238 is more than 99% of available uranium. It is fissionable, but not fissile. It's isotope, U-235, however, is fissile but is only 0.72% of all uranium dug up out of the ground. Depending on the application then, uranium has to be enriched. Enriched means that the U-235 percentage is made to go above the naturally-occurring 0.72%. This is done several ways, but most people have heard of centrifuges in the news as it relates to what Iran and North Korea are doing. Depending on the nuclear reactor core design, the enrichment of uranium can range from nothing (0.72% U-235) to over 80% in nuclear powered naval ships. It is very expensive to enrich uranium. Weapons-grade uranium requires a minimum enrichment of 90% or more for not only a self-sustained nuclear fission, but for an uncontrollable explosion of all nuclear material once critical mass is achieved. Thus, nuclear reactors in civilian use have exactly zero chance of exploding in a mushroom cloud. The uranium is nowhere near enriched enough. Any uranium with a U-235 content below 0.72% is termed depleted.

Now, uranium is spread all over the Earth is mall concentrations. Large swaths of dirt must be dug up and processed to capture enough raw uranium ore that is termed "yellow cake" for its color and texture, do do something useful with. There are parts of the world where uranium is found in larger quantity. Here's the map:

So the Aussies are sitting on a gold mine so to speak in terms of uranium. Canada isn't in too bad a shape either. Here's a U.S. map with proven uranium reserves and their general locations:

So lots of 'red states.' This is the reason countries like Japan and Spain are pursuing breeder technology. They have basically no indigenous uranium so they have to import it all from other countries (the stuff is highly expensive). Thus, it makes sense for them to breed plutonium-239 from the fissionable U-238 and keep the train going for as long as possible.

Speaking of other countries, there is one that I want to mention in particular that used to have an active natural fission reaction occurring continuously for many years. That place on the map would be the Oklo region in Gabon, Africa - what is known as the Oklo natural nuclear reactor. Sounds pretty weird, no? Wikepedia (no, you can't trust them for everything) has this to say about the Oslo site:

A natural nuclear fission reactor is a uranium deposit where analysis of isotope ratios has shown that self-sustaining nuclear chain reactions have occurred. The existence of this phenomenon was discovered in 1972 by French physicist Francis Perrin. The conditions under which a natural nuclear reactor could exist were predicted in 1956 by P. Kuroda. The conditions found at Oklo were very similar to what was predicted.
At the only known location, three ore deposits at Oklo in Gabon, sixteen sites have been discovered at which self-sustaining nuclear fission reactions took place approximately 2 billion years ago, and ran for a few hundred thousand years, averaging 100 kW of power output during that time.
In May 1972 at the Pierrelatte uranium enrichment facility in France, routine mass spectrometry comparing UF6 samples from the Oklo Mine, located in Gabon, Central Africa, showed a discrepancy in the amount of the 235U isotope. Normally the concentration is 0.7202%; these samples had only 0.7171% – a significant difference. This discrepancy required explanation, as all uranium handling facilities must meticulously account for all fissionable isotopes to assure that none are diverted for weapons purposes. Thus the French Commissariat à l'énergie atomique (CEA) began an investigation. A series of measurements of the relative abundances of the two most significant isotopes of the uranium mined at Oklo showed anomalous results compared to those obtained for uranium from other mines. Further investigations into this uranium deposit discovered uranium ore with a 235U to 238U ratio as low as 0.440%. Subsequent examination of other isotopes showed similar anomalies, such as Nd and Ru as described in more detail below.
This loss in 235U is exactly what happens in a nuclear reactor. A possible explanation therefore was that the uranium ore had operated as a natural fission reactor. Other observations led to the same conclusion, and on September 25, 1972, the CEA announced their finding that self-sustaining nuclear chain reactions had occurred on Earth about 2 billion years ago. Later, other natural nuclear fission reactors were discovered in the region.

Now that is pretty cool! Actually, that was pretty hot some time ago! Kept the place warm, not that Gabon, Africa needed that. I'll save whatever debate there is on estimating the age of the deposits for another time.

Previously:
The Fermi Chronicles - Part 10: Utilizing Nuclear Reactions To "Breed" More Fuel
The Fermi Chronicles - Part 9: Nuclear Fission
The Fermi Chronicles - Part 8: Neutron Interaction
The Fermi Chronicles - Part 7: Radioactive Decay and Half-Life
The Fermi Chronicles - Part 6: Atomic Structures
The Fermi Chronicles - Part 5: Nuclear Waste Storage
The Fermi Chronicles - Part 4: Radiation Types and Radiation "Dose"
The Fermi Chronicles - Part 3: Radiation Types
The Fermi Chronicles - Part 2: A week of training
The Fermi Chronicles - Part 1: The alpha post