The Atomic Age began more than 70 years ago, and since then, the use of nuclear power has both terrified and fascinated the world. Its use as a weapon was limited to only two tragic events, but there have been plenty of threats and crises over the years. More importantly, at least for the purpose of this article, is the other hotly debated topic related to nuclear elements – their use as a power source.
Given that nuclear power plants are far more efficient and powerful than traditional fuel methods, the second half of the 20th century saw an overwhelming increase of nuclear power use, and there are presently about 450 nuclear power plants in operation around the world. However, there are many concerns with the use of nuclear power, including the risk of nuclear reactor accidents, the use of nuclear fuel/waste for malicious intent, and the depletion of uranium reserves around the world. Most notably, of course, is the huge amount of nuclear waste that is produced in the production process of nuclear energy. The question is…. is there a better use for it?
Short Answer: There are a few different options, but each comes with their own obstacles. Also, a bit of background on nuclear energy and waste is important before going too deeply into the alternative uses….
The Science of Nuclear Waste
This nuclear waste produced as a byproduct of nuclear energy generation is highly radioactive, meaning that it is extremely dangerous for the environment and human populations. Therefore, this waste must be stored and disposed of in expensive and energy-intensive ways. Even then, the risk of spillage or leakage over time is a real concern, and some forms of nuclear waste (such as transuranic elements) will not be neutralized for more than 10,000 years.
Without going into too much scientific detail, let’s unpack the problem of nuclear waste. The vast majority of nuclear power plants have thermal reactors powering them, which smash neutrons into fissionable atoms (typically Uranium 235 and 238) at relatively low speeds in the reactor core. When the nuclei of these atoms are “cleaved”, they release a huge amount of heat and energy (electricity), which makes them such a powerful source of energy.
Along with this energy are other nuclei, which then bounce off to cleave other atoms, creating the “chain reaction” that is sought after in a nuclear core. However, Uranium-238 is slightly different than 235, and does not always split when struck by a neutron; in this case, the element is changed to Plutonium 239, which can also sustain chain reactions in a nuclear reactor. After about 3 years in service, only about 5% of the Uranium 235/238 and Plutonium 239’s inherent energy has been depleted. Once the fuel has technically been “used”, the remains are considered waste, despite the fact that it has the capacity to fuel reactors for much longer.
Of these “tailings”, as the “spent” fuel is called, about 5% are lighter elements caused by the splitting of the atoms that are highly irradiated, and require about 300 years of half-life diminishing to be harmless. These are the only “true” wastes of this process – meaning that they can’t be used for another purpose. More than 90% of the waste is unfissioned uranium (238, which cannot be fissioned by a slow, low-energy neutron), which has had its Uranium-235 depleted (235 can be fissioned by a slow, low-energy neutron. The remaining 1% of the waste is composed of transuranic elements, those heavier than uranium, such as plutonium isotopes. The half-life of these elements exceeds 10,000 years, and therefore poses the biggest concern for nuclear waste disposal.
What a Waste!
What many people don’t realize is that the “spent” fuel can be repurposed as nuclear fuel, but not in the present infrastructure of light-water reactors (where slow-moving neutrons are responsible for fission). If the plutonium isotopes and uranium-238 waste products were used in fast-neutron reactors, which reduces the amount of neutrons lost to non-fission reactions, this “waste” could be effectively used for more energy production. These fast-neutron reactors are able to pull more energy from that 95% of unused atoms in the waste, reducing our dependence on fresh uranium. However, since plutonium (the element relied on for a great deal of energy production in this fast-neutron method) is a key ingredient in the creation of nuclear weapons, this sort of closed-cycle nuclear strategy was banned by the United States at the height of the Cold War.
Many other nations in the world have pursued this type of recycling, but without some of the world’s largest nuclear nations signing on, the problem of waste won’t be solved. The technical details of fast-reactor technology are beyond the scope of this article, but you can learn more about it here. (Source)
A particularly clever means of handling the waste has also been developed by researchers at the University of Bristol Cabot Institute. As we mentioned above, the nuclear waste from uranium fission can be very toxic and difficult to dispose of, but where does it go? In most nuclear reactors, the waste is collected by depositing itself on a graphite core in the reactor. After three years or so, that core is removed, and the radioactive graphite must be disposed of. With a half-life of over 5,700 years, this presents a major problem.
However, in this new approach, the graphite core is heated up to release its radioactivity in a gaseous form. At this point, by subjecting that gas to extreme pressure and low temperatures, the gas can be pressed into a radioactive diamond – extremely dense and packed with energy. When this radioactive diamond is placed near a radioactive field, electricity is generated.
By encasing the radioactive diamond in a non-radioactive diamond, all of the harmful radioactive emissions are absorbed, acting as a feedback loop to provide even more electricity, essentially making the battery 100% efficient. A single nuclear battery of this form will produce electric current for more than 5,000 years, and will require no maintenance, while also being completely safe for use.
Pour Some Salt On It
Somewhat in line with the advanced, fast-neutron reactors is the concept of a molten salt reactor, which mixes molten salt in with the nuclear fuel, rather than water, as is normally done in a reactor. The concept is that as the chain reaction increases speed and power, the core needs to be cooled in order to prevent a meltdown. This is largely why uranium is considered “spent” so quickly, as the more enriched elements, along with plutonium, are more likely to result in uncontrollable chain reactions, leading to dangerous compromises in safety.
With salt as the component agent to the fuel, it does this naturally. As the fission reactions increase, the temperature goes up and the salt will naturally expand, thus slowing the fission reactions and maintaining a balanced level in the core. This will allow for the much longer use of these “waste” fuels. While the amount of energy produced by this type of reactor is only 50% of what is gained from a light-water reactor, the projected efficiency of such a reactor could be as high as 98%, rather than the pathetic 5% we typically get now.
Clearly, there are other options out there when it comes to nuclear waste; instead of burying it in the mountains of the American Southwest for the next 10,000 years, perhaps we could do something a bit more sustainable, smarter and safer.
- Scientific American
- Fast Breeder Reactor Programs: History and Status – Fissile Materials Working Group
- Radioactive Diamond Batteries: Making Good Use Of Nuclear Waste – Forbes.com
- Molten Salt Nuclear Reactor – Google Books