Nuclear waste is scary. What do you do with something that can give you cancer or potentially kill you even when it’s in the next room? For a long while, the status quo has been to advocate putting all our radioactive waste in a pit where it can’t hurt anybody for the next 10,000 years.
Considering firstly that even the longest-lived civilization ever to grace the earth only lasted 1,500 years (and that’s being generous), and secondly that 10,000 years isn’t nearly long enough of a storage period to make nuclear waste safe, if we are to keep using nuclear energy as a means to curb climate change, we very clearly need new solutions for tackling nuclear waste.
In today’s issue of Science, a new technique takes a small step towards sustainable nuclear waste management, but to understand it requires some background.
Radioactivity is basically a spray of energetic particles that can damage human DNA. It generally comes from unstable atoms falling apart to form more stable atoms. Unstable atoms (such as uranium) occur in nature because they are produced when stars explode. One such explosion is thought to have triggered the formation of the solar system, which is why we find uranium here on Earth.
When uranium falls apart it releases heat. A nuclear reactor is essentially an environment that encourages uranium atoms to fall apart in a controlled manner. When used with a steam engine, this produces electricity.
Since uranium falls apart in an effort to become more stable, it may seem strange that the radioactive waste it produces is more radioactive than the original uranium. There are two ways that nuclear reactors produce additional radioactivity. The first is a side effect of splitting atoms. Sometimes the atoms that uranium splits into aren’t quite stable yet, so they’re still radioactive en route to becoming stable. The atoms that cause the most concern here are Strontium-90 and Cesium-137. Such atoms are most responsible for the heat and acutely intense radioactivity within nuclear waste.
The second route comes from the fact that there’s no way to set up a nuclear power plant without unintentionally making a few uranium atoms heavier rather than splitting them apart. This produces atoms that are said to be “transuranic” meaning they’re “beyond uranium.” The atoms that cause concern here include Plutonium-239 and Americium-243. These atoms are most responsible for the chronic, long-term radioactivity within nuclear waste.
To make nuclear waste safe, the first step is to separate it. When separated, these two groups of atoms can be individually dealt within a time frame far shorter than thousands of years. The first “high-heat” group need only be stored for around 350 years to decrease to safe levels of radioactivity. The second “chronically-radioactive” group can be encouraged to decay into safer elements using certain “transmutation reactors” specially designed to decrease radioactivity. The only thing is these special reactors require the removal of impurities called lanthanides. That’s what the paper in today’s issue of Science is about.
A mixture of lanthanides and Americium-243 can already be easily recovered from nuclear waste. To purify the Americium-243, scientists developed a technique called “Electrochemical Oxidation in Nitric Acid by a Terpyridyl-Derivatized Electrode.” Basically, batteries and special chemicals can be used to separate out the Americium-243.
With continued development of separation methods and transmutation reactors, we might find ourselves in a future where nuclear waste is no longer a persistent danger. Since nuclear power is one of few carbon-neutral methods of energy generation that doesn’t place us at the mercy of nature’s schedule of sun and wind, it’s likely it will have a role to play in our carbon-neutral future.