Uranium

• 1. Introduction

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  Uranium sits at atomic number 92, the heaviest element that forms naturally on Earth in significant quantities. On the 6th of August 1945, a device called Little Boy detonated above Hiroshima, Japan, with a yield equivalent to 12,500 tonnes of TNT. It destroyed nearly 50,000 buildings and killed about 75,000 people. That bomb ran on uranium. Yet the same element also quietly powers commercial electricity grids, and traces of it color the yellow glaze on ancient Roman ceramics found at Cape Posillipo in the Gulf of Naples. How does one substance span Roman kitchenware, Cold War arsenals, and the heat engine of the Earth itself? That is what this documentary will work through.

• 2. What Uranium Actually Is

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  Uranium is a silvery-white metal with a density of 19.1 grams per cubic centimeter, denser than lead, which sits at 11.3 grams per cubic centimeter, and only slightly less dense than gold or tungsten at 19.3. Its Mohs hardness of 6 is roughly equal to that of titanium and manganese, hard enough to scratch glass. Uranium is malleable, ductile, and a poor electrical conductor. Left in air, its surface darkens under a layer of uranium dioxide.

  Natural uranium is not a single substance but a mixture of isotopes. Uranium-238 makes up 99.28% of all natural uranium, while uranium-235 accounts for just 0.71%. That tiny fraction of uranium-235 turns out to be the one that matters most for both nuclear power and nuclear weapons, because it is the only naturally occurring isotope present in meaningful amounts that will split when struck by a slow neutron. Uranium-238 can absorb neutrons too, but it requires fast neutrons to fission and yields plutonium-239 when it does so inside a reactor.

  The half-life of uranium-238 is roughly 4.47 billion years, approximately the age of the Earth itself. Uranium-235 has a half-life of about 7.04 billion years. These extraordinarily long half-lives explain why both isotopes are still present on Earth at all. They are primordial radionuclides, survivors of stellar nucleosynthesis that predates the Solar System. Like all elements heavier than iron, uranium was forged by rapid neutron capture in supernovae and neutron star mergers.

• 3. Discovery and Early Science

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  Martin Heinrich Klaproth, working in his experimental laboratory in Berlin in 1789, dissolved pitchblende in nitric acid, neutralized it with sodium hydroxide, and precipitated a yellow compound. He heated that compound with charcoal and obtained a black powder he believed was a new metal. He was mistaken: the powder was a uranium oxide. Still, Klaproth correctly identified an unknown element and named it after Uranus, the planet William Herschel had discovered eight years earlier.

  The actual metal had to wait until 1841, when Eugène-Melchior Péligot, Professor of Analytical Chemistry at the Conservatoire National des Arts et Métiers in Paris, isolated the first true uranium sample by heating uranium tetrachloride with potassium.

  The element's most consequential property arrived in 1896. Henri Becquerel, working in Paris, placed a sample of potassium uranyl sulfate on an unexposed photographic plate inside a drawer. When he retrieved the plate it had fogged. Becquerel deduced that uranium emitted invisible rays capable of exposing the plate without any light source. That observation opened the science of radioactivity. Marie Curie's subsequent work isolating radium from pitchblende created an unexpected side effect for uranium itself: it took three tonnes of uranium ore to extract a single gram of radium, leaving vast quantities of uranium as a waste product. That surplus was diverted to the glazing industry, making uranium-based ceramic glazes abundant and cheap throughout the early twentieth century.

  During World War I, when the Central Powers ran short of molybdenum for artillery barrels and high-speed tool steels, they substituted ferrouranium alloy, which shares many of the same physical properties. When this practice became known in 1916, the US government asked several universities to research uranium's uses in manufacturing and metalwork. Those tools remained in service for decades, until nuclear fission research drove demand in an entirely different direction.

• 4. The Road to Fission

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  In 1934, a team led by Enrico Fermi bombarded uranium with neutrons and produced beta rays. The products were mistaken for new elements with atomic numbers 93 and 94, which Orso Mario Corbino, Dean of the Sapienza University of Rome, named ausenium and hesperium. The real explanation came years later, when Otto Hahn and Fritz Strassmann, working in Hahn's laboratory in Berlin in 1938, found that bombarding uranium-235 with neutrons produced barium, a much lighter element. Lise Meitner and her nephew Otto Robert Frisch published the physical theory of nuclear fission in February 1939, naming the process for the first time.

  Fermi then hypothesized that each fission event might release enough neutrons to sustain a chain reaction. Confirmation arrived in 1939, and further work established that each fission of uranium-235 releases on average about 2.5 neutrons. Fermi urged Alfred O. C. Nier to separate the isotopes, and on the 29th of February 1940, Nier used an instrument he had built at the University of Minnesota to separate the world's first uranium-235 sample in the Tate Laboratory. John Dunning confirmed it the following day using Columbia University's cyclotron.

  On the 2nd of December 1942, another team led by Fermi achieved the first artificial self-sustained nuclear chain reaction, known as Chicago Pile-1. The team worked in a lab below the stands of Stagg Field at the University of Chicago, stacking 360 tonnes of graphite, 53 tonnes of uranium oxide, and 5.5 tonnes of uranium metal. Most of the uranium was supplied by Westinghouse Lamp Plant through a makeshift production process. Germany's parallel effort, the Uranverein, was hampered by scarce resources, infighting, and a critical error: impurities in available graphite samples made the material appear less suitable as a neutron moderator than it actually is. Germany's natural uranium and heavy water reactor had not approached criticality by the time Allied forces reached Haigerloch, the site of its last wartime reactor experiment.

• 5. Nuclear Weapons

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  Little Boy, the uranium device dropped on Hiroshima on the 6th of August 1945, required highly enriched uranium-235 as its fissile core. As little as 15 pounds of uranium-235 can be used to make an atomic bomb. The plutonium bomb called Fat Man, detonated over Nagasaki, and the Trinity test device called the Gadget both used plutonium derived from uranium-238, not uranium-235 directly.

  In 1943, the Manhattan Project contracted Union Carbide and Chevron to survey uranium deposits around the world. Two geology professors who studied the results pointed to uranium associated with gold mines in the Rand area of South Africa as a promising new source. Initially the project planners believed uranium was rare enough that proliferation could be controlled simply by purchasing all known stocks. Within a decade, large deposits turned up across the globe, making that strategy unworkable.

  During the Cold War the United States and the Soviet Union assembled tens of thousands of nuclear weapons using enriched uranium and plutonium derived from uranium-238. After the Soviet Union broke apart in 1991, an estimated 600 short tons, or 540 metric tons, of highly enriched weapons-grade uranium enough to build 40,000 warheads had been stored in often inadequately guarded facilities across Russia and several other former Soviet states. Between 1993 and 2005, police in Asia, Europe, and South America intercepted smuggled bomb-grade uranium or plutonium on at least 16 separate occasions, most of it from ex-Soviet sources. The US-operated Material Protection, Control, and Accounting Program spent about $550 million over those same years to help secure stockpiles in Russia. Russia's own federal nuclear and radiation safety program, approved in November 2015, allocated 562 billion rubles, roughly $8 billion, for the period 2016 to 2030, with about 73% of that earmarked for decommissioning aged and obsolete nuclear reactors and facilities.

• 6. Power and the Peaceful Atom

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  One kilogram of uranium-235, assuming complete fission, can theoretically yield about 20 terajoules of energy, as much as 1,500 tonnes of coal. Commercial nuclear power plants typically use fuel enriched to around 3% uranium-235. The CANDU and Magnox reactor designs are the only commercial types capable of running on unenriched uranium fuel. Fuel for United States Navy reactors is highly enriched in uranium-235, though the exact figures remain classified.

  Argonne National Laboratory's Experimental Breeder Reactor I, at the Atomic Energy Commission's National Reactor Testing Station near Arco, Idaho, became the first reactor to generate electricity on the 20th of December 1951. The initial output lit four 150-watt light bulbs. Later, the town of Arco became the first in the world to receive all its electricity from nuclear power, generated by another Argonne design, BORAX-III. The world's first commercial-scale nuclear power station, Obninsk in the Soviet Union, began generating with its reactor AM-1 on the 27th of June 1954. Calder Hall in England followed on the 17th of October 1956, and the Shippingport Atomic Power Station in Pennsylvania began on the 26th of May 1958.

  Nuclear power also moved underwater. The submarine USS Nautilus used nuclear propulsion for the first time in 1954. Worldwide uranium production reached 60,213 tonnes in 2024, with Kazakhstan alone accounting for 23,270 tonnes, or 39% of total output.

• 7. Natural Reactors and Deep Time

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  In 1972, French physicist Francis Perrin discovered that nature had already built and run nuclear fission reactors long before humanity. Fifteen ancient and now inactive natural reactors were found across three separate ore deposits at the Oklo mine in Gabon, Africa. The ore deposit is 1.7 billion years old. At that time, uranium-235 constituted about 3% of all uranium on Earth, high enough to support a sustained chain reaction given the right surrounding conditions.

  The evidence that identified these reactors was subtle: during uranium enrichment work in France, analysts noticed that the Oklo ore contained slightly less uranium-235 than the expected natural ratio. Subsequent investigation ruled out human interference and confirmed that the deficit matched the isotope ratios of known fission products and their stable daughter nuclides. The US federal government has cited the capacity of the Oklo sediments to contain radioactive waste products over geological timescales as supporting evidence for the feasibility of storing spent nuclear fuel at the Yucca Mountain repository.

  Uranium's role in geological timekeeping stretches even further. The decay of uranium-238 produces a series of 18 daughter nuclides before arriving at stable lead-206. The constant rates of this decay chain underpin uranium-lead radiometric dating, which allows scientists to estimate the ages of the oldest igneous rocks on Earth. Uranium also contributes to the planet's internal heat: the decay of uranium, thorium, and potassium-40 in Earth's mantle is thought to be a primary source of the heat that keeps the outer core liquid and drives mantle convection, which in turn drives plate tectonics.

• 8. Living with Uranium

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  Uranium occurs in all rock, soil, and water at low concentrations. Its abundance in the Earth's crust is 2 to 4 parts per million, about 40 times as plentiful as silver. In 2024, the largest single uranium deposit in the world was located at the Olympic Dam Mine in South Australia, which sits in a country holding 28% of all known uranium ore reserves.

  Exposure risks to the general population are mostly chemical rather than radiological. Alpha particles from uranium cannot penetrate skin, and most ingested uranium passes through the body without being absorbed; only about 0.5% of insoluble uranium forms enters the bloodstream. Soluble uranyl compounds can be absorbed at up to 5%, and once in the bloodstream, uranium accumulates in bone tissue, liver, kidneys, and reproductive tissues because of its affinity for phosphates. The Occupational Safety and Health Administration has set the permissible workplace exposure limit at 0.25 milligrams per cubic meter over an eight-hour workday. At concentrations of 10 milligrams per cubic meter, uranium is immediately dangerous to life and health.

  Navajo uranium miners have been documented as having an excess risk of lung cancer linked directly to their occupation. The Radiation Exposure Compensation Act, a US law enacted in 1990, required $100,000 in payments to uranium miners diagnosed with cancer or other respiratory ailments. In nuclear weapons-era Russia, a 1993 peak of 29 nuclear incidents ranked above level 1 on the International Nuclear Event Scale had dropped to fewer than four per year by the period 1995-2003, reflecting significant safety improvements at storage and research facilities since the political and economic turbulence of the early 1990s.