|Fig. 1: Picture of a facility that stores vessels filled with radioactive waste. (Source: Wikimedia Commons)|
While nuclear energy is generally much cleaner than coal and natural gas, the production of nuclear energy creates a dangerous byproduct called nuclear waste. Nuclear waste, also referred to as "spent fuel," is dangerously radioactive even in small doses. To understand nuclear waste, it is important to understand the nuclear power generation process that occurs in nuclear power reactors. The process begins with fuel (in the encasement of metal rods) that is made mostly of uranium, thorium, oxygen and steel.  Passing the starting fuel through a reactor sets off a series of nuclear reactions. After this process has taken place, the uranium atoms have split, resulting in various isotopes that constitute what we refer to as "nuclear waste." Although the composition of the nuclear waste is a fuel that highly resembles the fuel used to create the electricity, it has a much different nuclear composition, resulting in its related hazards. These isotopes are typically transition metals, resulting in a material that is both thermally hot and highly radioactive.
In short, it is very dangerous. If you were to stand a few meters away from the fuel when it first came out of the reactor you would receive a deadly dose of radioactivity within a couple of seconds.  Consider this: the fatal radiation dosage for a human body is 500 rem (received at one time). Generally, nuclear waste that is ten years removed from the nuclear reactor can generate a surface dose rate of 10,000 rem/hour.  What's more, if this nuclear waste enters ground waters and rivers, the possibility of a larger population being exposed to the radiation (albeit in a smaller dosage because of its indirect source) through our food is extremely troublesome.
The basic fuel inside of metal rods that is put into the nuclear reactor is comprised of U-235. At this point, the fuel rods are only slightly radioactive and therefore can be handled without shielding (the term used to describe methods to avoid radioactive content). However, the nuclear fission that occurs inside the reactor produces radioactivity that lasts long after the process is completed. Overtime, the radioactive isotopes will overtime decay to a point of stability. Different types of isotopes take different amount of times to disintegrate to harmless materials. For example, Cs-137, one of the possible isotopes that emerge from the nuclear reactor, has a half-life of 30 years (half of the radioactivity of a given quantity will decay after 30 years), while other isotopes can take hundreds of thousands of years to fully decay.  The issue is that while the isotopes are decaying, they continue to emit radiation that is extremely harmful to humans and the environment.
Nuclear waste is currently stored underwater in large water-filled pools and in dry storage casks at the nuclear reactor sites seen in Fig. 1. The Department of Energy is the government agency responsible for overseeing the construction of new depositories of nuclear waste. For the last decade, the DOE was in the process of authorizing nuclear waste storage at the Yucca Mountain site, an area in Nevada where geological deep underground storage of nuclear waste is possible, until the Obama administration pulled the plug on the project in 2010. 
Other options currently being researched involve recycling more nuclear waste (nuclear waste is largely uranium, which can be used again in advanced fast reactors as a source of more energy) and slightly changing the chemical makeup of the original fuel source to achieve more efficiency and less waste during the process.
As nuclear energy becomes an increasingly attractive source of energy, the storage of nuclear waste becomes an increasingly daunting task. Thankfully, the grave danger that radioactive material poses to the human population and the environment are recognized. Scientists and government officials remain committed to developing ways to produce the same amount of energy with less nuclear waste, to finding new technology to store the nuclear waste, and to overseeing new nuclear waste disposal sites. Even now, a method of disposal called deep borehole disposal is being developed, where nuclear waste is stored in holes so deep in the Earth's crust that the structure of the Earth above ground, the climate, and the human activities there would not matter.  Although the task ahead is daunting, the future success of handling the large-scale storage of nuclear waste is promising.
© Lucy Dikeou. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
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