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What Is Uranium?

You know, just in case the question comes up.

There might come a time in a person's life when they're standing in front of a room full of reporters and they get asked about their responsibility as the leader of a world nuclear power. This can be a tough and awkward question, particularly if you don't know much about one of the critical components of many nuclear weapons: enriched uranium. To help you navigate this pivotal moment in your life, we've compiled this helpful beginner's guide to the world's favorite heavy metal.

What is uranium?

Uranium is a radioactive element discovered by the German chemist Martin Klaproth in 1789, which he decided to name after Uranus for some reason. Uranium has an atomic number of 92, which means that it has 92 protons in its nucleus. It is surprisingly common in nature, with the World Nuclear Association reporting that it is "found in most rocks" in small quantities (about 2 to 4 parts per million). This makes it about as common as tin in the Earth's crust, and about 40 times more common than silver. It also occurs in seawater and can be extracted for use. Originally, uranium was formed by supernovas and its slow radioactive decay (Uranium-238, the most common uranium isotope, has a half-life of 4.5 billion years) is the main source of heat in Earth's core.

What's so special about uranium?

In 1938, physicists Otto Hahn and Fritz Strassman discovered something unique about uranium: when uranium was bombarded with neutrons, it would split into two nearly equal parts—a process called nuclear fission. Soon after, it was discovered that nuclear fission can produce a cascading effect: firing a neutron into the nucleus of a uranium isotope splits the nucleus of the uranium isotope in two, which releases heat but also knocks a couple of neutrons loose. If those neutrons go on to split other uranium atoms, this creates a "fission chain reaction" and when this happens millions of times, it can create a lot of heat from relatively small amounts of uranium.

How is Uranium used?

When most people hear uranium, they think nuclear weapons. Indeed, uranium was the critical component the two nuclear bombs dropped on Japan during World War II, but the type of uranium used for these bombs was highly enriched. In nature, uranium ore consists of about 99.3 percent uranium-238 isotopes and .7 percent uranium-235 isotopes, and the difference between the two uranium isotopes consists of the number of neutrons in the nucleus: 146 neutrons and 143 neutrons, respectively. While this might sound inconsequential, it means that U-238 cannot sustain nuclear fission reactions, but U-235 can. Yet because U-235 is found in such small amounts in naturally occurring Uranium ore, its percentage needs to be increased so that it can be used to power nuclear reactors and create nuclear weapons.

To power a nuclear reactor for energy, U-235 needs to be enriched to about 3 to 5 percent. When this uranium undergoes a fission chain reaction, it boils water to generate steam, which spins a turbine to power a generator and produce electricity. The uranium-235 used for bombs, on the other hand, needs to be enriched to about 90 percent—when uranium is this enriched, it only takes a very small amount to produce a huge result. The bomb that leveled Hiroshima contained about 140 pounds of enriched uranium, but only two percent of it underwent fission (just under three pounds)–still, it produced a blast equivalent to 15 kilotons of TNT.  

Uranium and Politics

Even though uranium is abundant on Earth, who gets to enrich the stuff is the subject of intense political debate. This is currently at the center of the United States beef with Iran, which was enriching uranium to about 20 percent, not enough for a bomb, but more than enough for a nuclear reactor. The 2015 nuclear deal with Iran calls for the country to decrease its stockpile of low-enriched uranium by 98 percent, not produce uranium-235 enriched above 3.7 percent, and repurpose the facility it was building to create weapons grade Plutonium from naturally occurring uranium.

The production of uranium was also at the center of an agreement struck between the Russian atomic energy agency and a Canadian company called Uranium One in 2013. The agreement gave the Russian agency a majority stake in the company, whose mining operations in Utah and Wyoming accounted for 20 percent of the uranium production capacity in the United States (which is not the same thing as owning 20 percent of the existing uranium in the United States). There was concern that Hillary Clinton had conflicts of interest when signing off on the deal as Secretary of State.

Uranium also has significant environmental implications. According to the Argonne National Laboratory, nuclear energy plants powered by uranium reactions accounted for "90 percent of all carbon emissions averted between 1981 and 1994." On the other hand, this energy supply also produces small amounts of highly-radioactive nuclear waste, which needs to be totally isolated in storage to avoid severe health and environmental problems.

This information probably isn't crucial to 99 percent of the population's day-to-day existence. But for those select few who should be thinking about responsible uses of nuclear power on the reg, there's no more excuses for not knowing about one of the world's most abundant elements.

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Correction: This article previously stated that the bomb that leveled Hiroshima produced a blast equivalent to 150 kilotons of TNT. The bomb produced a blast equivalent to 15 kilotons of TNT. Motherboard regrets the error.