Nuclear waste. We've all heard about it, but what is it? Is it a problem without a solution? How big is the problem? And what exactly is this waste and why is it so important? New Atlas takes a look at the basics. The term "nuclear waste" conjures up images of rusty steel drums leaking their glowing green radioactive contents into rivers and soil, resulting in cancers and sickness in nearby communities – or maybe mutated creatures that run amok decimating those nearby communities. But as the world looks to wean itself off fossil fuels, nuclear power is set to play a bigger role in the global energy mix, so it's worth going beyond popular imagery and start looking at what exactly nuclear waste is, just what kind of risks it actually poses, and how do we get rid of it? Simply stated, nuclear or radioactive waste is the byproduct of nuclear reactors, fuel processing and reprocessing, weapon production, medical facilities, and research laboratories. However, the term covers a lot of different kinds of waste. Plus, nuclear waste is unusual in that it changes its properties drastically over time, going from one form of waste to another. So the answer is not straightforward, but perhaps the best place to start is with the most familiar and serious form of nuclear waste – high-level waste produced by civilian nuclear reactors. In conventional , the fuel is in the form of ceramic plugs about the size of a thimble. These contain enriched uranium, which is high in the fissionable isotope uranium-235. These pellets are placed inside metal alloy tubes to form rods and the rods are gathered into rectangular bundles. When these bundles are placed together in the reactor, they are immersed in water that serves as a moderator and coolant. As the uranium atoms split naturally, they give off two neutrons each. The moderator slows these neutrons, so they have a better chance of being absorbed by another uranium-235 atom. If this happens, the second atom splits, giving off two neutrons, which can be absorbed by more atoms. If there's a great enough concentration of fuel, the result is a self-sustaining nuclear reaction. As these uranium atoms split, they give off an incredible amount of energy, but they also become two smaller atoms, like cesium-137 and strontium-90. These radioactive isotopes can then break down to produce new elements. Meanwhile, some atoms of uranium-238 can absorb neutrons and become plutonium and other transuranic elements. When enough of the uranium-235 has been consumed, the fuel is regarded as spent and is now, essentially, waste. The reason why nuclear energy is so attractive is that the fuel is remarkably dense in terms of the energy it puts out. A single gram of uranium releases the equivalent energy of three tonnes of coal. This means that in a large gigawatt reactor, less than 30 tonnes of used fuel is produced per year. If you divide up that spent fuel by the number of people the reactor serves, it works out to a volume of waste the size of a brick each, which includes only 5 grams of high-level waste after recycling. The most obvious threat posed by nuclear waste is radiation. Something that can kill you just by being next to you is about as far from the definition of "safe" as it's possible to get. So what is the nature of the radiation threat and how long does it last? High-level waste makes up 3% of the spent fuel by volume, but it produces 95% of the radioactivity. It's not only highly radioactive, but it's thermally hot, so it has to be carefully shielded and can only be handled by remote manipulators. To give an idea of how radioactive this waste is when it comes out of the reactor, it gives off 10,000 rem/hour of radiation for the next 10 years. Just 500 rem/hour is enough to kill a human being. Unlike many non-nuclear waste products like arsenic or asbestos, nuclear waste changes over time as the atoms undergo radioactive decay and the waste products change from one element to another. The rate at which this decay occurs is called the half-life. That is, the half-life of a radioactive element is how long it takes for half of the given quantity to break apart. For example, the isotope iodine-131 has a half-life of about eight days, while plutonium-239 has a half-life of 24,000 years. At first glance, it seems as if the iodine is safer than the plutonium because the iodine goes away very quickly while the plutonium lingers for ages. In fact, it's exactly the opposite. The iodine-131 is extremely dangerous because its short half-life means it's blasting out radiation, while the plutonium is only mildly radioactive. The only way that plutonium can become dangerous is if it is ingested and particles embed in soft inner tissue, where it can cause cell damage. This is why spent fuel is stored at the reactor site when the rods are removed from the reactor. The fuel is kept under water in storage pools for several years while the dangerous isotopes decay. Within 40 years the radioactivity is reduced to one-thousandth of when the fuel was unloaded, and within 1,000 to 10,000 years the fuel is only as radioactive as the original ore it was made from. The long-term radioactivity is due to the spent fuel changing into transuranic elements, making it go from high-level waste, which is highly radioactive, to intermediate-level waste, which is mildly radioactive. For this reason, high-level waste disposal also means intermediate-level disposal. But how is this high-level waste disposed of and what are the alternatives? There are a number of different methods of disposal, some of which are much easier than the one currently favored. For example, waste could be sealed in steel canisters and left in a stable region of the Antarctic ice cap, where it would melt down and bury itself under a couple of miles of ice for the next 100,000 years. Or waste could also be deposited in deep shafts where two tectonic plates meet and the waste could be left to slide down into the Earth's molten mantle. Perhaps the simplest way would be to put the canisters inside darts with pointed lead-filled nose cones and drop them in the deep ocean, where they would hit the seabed at high speed and bury themselves deep in the silt. It's a method that was inadvertently used for the reactors of the US nuclear submarines Scorpion and Thresher, which broke up underwater in the 1960s in two separate accidents. The US Navy never bothered to recover the reactors because it wasn't possible to find them, much less dig them out. There are several reasons why these and other methods aren't used. Some were rejected for technical reasons, others because of international treaties. But most of them had one shortcoming in common. The waste couldn't be retrieved after disposal. Though it isn't discussed much, high-level nuclear waste is incredibly valuable. Not only can such waste be reprocessed to create new fuel, it also contains a smorgasbord of nuclear isotopes that are in high demand by medicine and industry, so being able to retrieve this waste in the future is highly desirable. After the fuel rods have cooled in the containment pools, they are moved into dry cask storage for about 10 years. The cooled rods are put into 17-ft-tall (5-m) steel and concrete cylinders with multiple inner layers, concentric seals, and shock absorbers. Filled with an inert gas, they are made to withstand tornadoes, earthquakes, terrorist attacks, or unauthorized entry. Not only do they shield the outside from radiation, but they also passively release the lessening heat from the rods. The next step is either to send the fuel for reprocessing to turn it into more fuel or for long-term storage in a deep underground facility. For storage, the spent fuel is stripped out of the rods, the high-level wastes are extracted and then turned into a dried powder, which is mixed in with molten glass. This is then poured into stainless steel containers about 3 feet (1 m) tall and allowed to cool. The end product is almost chemically inert and the radioactive material is dispersed throughout the glass, reducing the amount of radiation emitted. Once processed, the waste casks are then moved to the storage facility, which is built into a geologically stable area isolated from the environment. Though the waste can be retrieved, the assumption is that, at some point in the future, the facility will be backfilled and sealed. How effective such storage can be is illustrated by a natural nuclear reactor in Gabon, which formed two billion years ago when nuclear ores became unusually concentrated. Despite rains and groundwater seepage, the nuclear materials from that reactor only migrated 33 ft (10 m) through the rock over millions of years. Such geological storage facilities have been approved in many countries and the United States is already operating one to handle waste from nuclear weapons production. Finland is also expected to open a civilian storage facility in the near future. From a technological point of view, the problems of nuclear waste disposal have been largely solved. Low level wastes are routinely handled and high-level waste disposal methods have already been implemented or await approval. Aside from storage of high-level wastes, there are other ways to get rid of them, including new fast reactors and advanced reprocessing. However, this is not to say that everything is lovely in the garden. Nuclear waste is a very dangerous thing and not to be trifled with, so handling it to make sure none of it enters the biosphere is a very serious business. The nuclear waste problem remains one of the biggest hurdles for the nuclear industry, but the trouble isn't technological. Nor is it economic. The nuclear industry is unusual in that it has to factor waste disposal into the cost of a plant's operating lifetime, but experience has shown that dealing with the waste only makes up 10% of the total cost of nuclear electricity generation. The problem is mainly political. It doesn't do any good to have a successful waste storage design if no one wants it built in their backyard. The reasons for this are many. For some people, it's out of genuine and specific environmental concerns sparked by events like Chernobyl. Others see nuclear power as an obstacle to an economy based on renewables and deliberately limited energy consumption, while many react to anything nuclear with memories of the Cold War and fears of nuclear weapons. Whether the nuclear waste issue will continue to hinder the nuclear industry remains to be seen. What is certain is that, whatever one's views on nuclear waste, it is not a theoretical matter that can be used to dismiss an entire energy sector on first principles. It is a problem that needs to be solved. There is over 80 years worth of it all over the world, and we have to do something with it. The question is, what?
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