As the ongoing debate over nuclear continues to delay our efforts to create a sustainable global society, it is important to understand everything we can about this oft-criticized energy source in order to demystify such a powerful energy source.
For a future wrought with concerns about how we consume and conserve resources, nuclear energy has the potential to solve many problems, but we must approach it correctly. Knowing how it all works is the first step in creating safe and efficient technology.
The process involved in nuclear reactions is much simpler than many believe. Nuclear fission, the go-to for energy creation, works by bombarding an isotope (Uranium 235, or U-235) with a neutron. The collision splits the isotope into two pieces, each holding half of the neutrons and protons of the original atom. This occurs multiple times, with each collision producing two more neutrons. The act of exponentially producing more energy through a chain reaction-like event will continue until there are no more U-235 isotopes available.
In nearly every case, uranium extracted from the ground is comprised of three isotopes (U-234, U-235, U-238). This requires uranium enrichment as a way to create the proper proportions of the highly efficient U-235, and therefore, nuclear fission.
But what is truly fascinating about this seemingly complicated process is that it has been found to be naturally occurring.
How does the natural world forgo man-made enrichment? The answer can be found in uranium half-life. With U-235 having a significantly contracted half-life as compared to its U-238 brethren, it was likely in much greater supply in the distant past than today. Scientist Paul K. Kuroda made this observation in 1956 and asserted that, under the right conditions, natural nuclear reactors could be formed to support nuclear fission and chain reactions.
The visionary scientist was in fact correct, when in 1972, French researchers in Gabon, West Africa examined ore from a mine and discovered that a natural nuclear reactor had spontaneously manifested in that region during earth’s primordial past (about 1.7 Billion years ago), creating what was estimated to be 100 Kw worth of energy for a few hundred thousand years. This mine is referred to as the Oklo Fossil Fission Reactor.
Considering the difficulty of splitting atoms, it may seem impossible to think it could occur in nature without the need of smart humans, but there are two working theories about how this happened:
1. The uranium was covered with groundwater, moderating the neutrons and providing an environment that supported a chain reaction. The energy ended up heating the ground water to a boil, and it steamed away. With no groundwater, the reaction stopped. But eventually, water seeped back into the uranium cavern and the process repeated, until the concentrations were too low to support further reactions.
2. A less popular theory, the second assertion proposed that the burning reactor released particular rare earth elements (samarium, gadolinium, and dysprosium) which absorbed the neutrons and stopped the chain reaction, for a time, or in certain places, only to have it pop up again nearby.
Details of the first theory were reported in Space Daily in 2004:
This similarity (to a geyser) suggests that a half an hour after the onset of the chain reaction, unbounded water was converted to steam, decreasing the thermal neutron flux and making the reactor sub-critical.
It took at least two-and-a-half hours for the reactor to cool down until fission Xe (xenon) began to retain. Then the water returned to the reactor zone, providing neutron moderation and once again establishing a self-sustaining chain.
While the theories are still being worked out, the proof of natural fission came in the initial French investigation, when it was found that the concentration of U-235 from the site was much lower than typically observed in nature; in fact, the concentrations from the Oklo samples were similar to those found in spent nuclear fuel.
Subsequent studies from Washington University gave credence to what the original researchers suggested.
The most amazing observation gleaned from this natural reactor was that, unlike our fission technology, nature itself was able to safely dispose of the waste. According to Washington University researchers, the natural reactor safely trapped its toxic waste (Xe and Kr-85) in the chemical compound aluminophosphate.
The scientist noted, likely with glee, “It is fascinating to think that a natural nuclear can reach critical conditions, and that it is also capable of storing its own waste.”
Now that we can see that this took place, the important thing is to take what we have learned and apply it to the creation of safe, smart, nuclear technology.