Radioactive waste is made of a wide range of materials, from used nuclear fuel rods containing uranium and plutonium to everyday items like gloves, mops, and syringes that have been contaminated with radioactive elements. What’s inside the waste depends entirely on where it came from. A nuclear power plant produces spent fuel packed with dozens of radioactive isotopes. A hospital produces bags of used syringes carrying trace amounts of short-lived medical isotopes. An oil drilling operation brings up rock and water laced with naturally occurring radium and thorium.
What’s Inside Spent Nuclear Fuel
The most intensely radioactive waste comes from nuclear power plants in the form of spent fuel. These are fuel assemblies that have been used in a reactor until they’re no longer efficient at producing electricity. Despite being “spent,” they still contain enormous amounts of radioactive material. A typical spent fuel assembly with moderate use consists of about 93.4% uranium, 5.2% fission products, 1.2% plutonium, and 0.2% other heavier-than-uranium elements like neptunium, americium, and curium.
The fission products are what make spent fuel so dangerous in the short term. When uranium atoms split inside a reactor, they break into lighter, highly radioactive elements. The two most significant are cesium-137 and strontium-90, both with half-lives of roughly 30 years. These isotopes generate most of the heat and penetrating radiation that make high-level waste so hazardous. For the first few decades after removal from a reactor, they dominate the radioactivity picture.
But spent fuel also contains isotopes that will remain radioactive for staggering lengths of time. Technetium-99 has a half-life of 210,000 years. Iodine-129 lasts 16 million years. After several hundred years, once the shorter-lived fission products have decayed, the radioactivity becomes dominated by long-lived heavy elements: plutonium-239 (half-life of 24,100 years), neptunium-237 (2.1 million years), and the original uranium-238 (4.5 billion years). This is why storing high-level waste is such a difficult engineering problem. The material needs to be isolated from the environment for timescales that dwarf all of recorded human history.
What Makes Up Low-Level Waste
Low-level waste is far less dramatic but much more common. It includes any item that has picked up radioactive contamination or become radioactive through exposure to neutron radiation. The physical objects themselves are ordinary: protective shoe covers, clothing, wiping rags, mops, filters, water treatment residues from reactor cooling systems, tools, and equipment. These items aren’t dangerous because of what they’re made of. They’re dangerous because radioactive atoms have settled on or been absorbed into them.
The radioactivity in low-level waste varies enormously. Some items are barely above the natural background radiation found everywhere in the environment. Others, like metal components removed from inside a reactor vessel, can be intensely radioactive. The category also includes waste from the decommissioning and dismantling of nuclear facilities, which can mean everything from contaminated concrete to piping that spent decades near an active reactor core.
Medical and Laboratory Waste
Hospitals and research labs generate their own stream of radioactive waste, mostly from diagnostic imaging and cancer treatment. The workhorse isotope in medical imaging is technetium-99m, a short-lived form of technetium used in millions of scans each year. Because it has a half-life of only six hours, waste contaminated with it (used syringes, gloves, disposable supplies) can typically be mixed with normal hospital waste after a 48-hour waiting period, by which point the radioactivity has dropped to negligible levels.
Iodine-131, used to treat thyroid conditions and certain cancers, creates a more complex waste stream. It has a half-life of about eight days, long enough that contaminated materials need careful handling. Hospitals collect solid waste from patient isolation wards in labeled bags and route liquid waste from toilets into delay tanks, where it’s held and diluted before release. Gallium-67, used in some specialized imaging, adds another isotope to the mix. Each of these gets sorted into separate containers because they decay at different rates and require different storage times.
Laboratory waste rounds out this category with items like animal carcasses and tissues from research involving radioactive tracers, as well as contaminated lab equipment and supplies.
Waste From Oil, Gas, and Mining
Radioactive waste doesn’t only come from the nuclear industry. Oil and gas drilling brings up material from deep underground where naturally occurring radioactive elements have been concentrated over geological time. This type of waste, known as NORM (naturally occurring radioactive material) or TENORM (technologically enhanced NORM), contains radium, radon, uranium, thorium, and potassium. Radium is particularly problematic because it dissolves readily in the briny water that comes up alongside oil and gas, meaning it can coat the insides of pipes, accumulate in storage tanks, and concentrate in filter sludge.
Mining operations, particularly those extracting uranium, rare earth elements, or phosphate, produce similar waste. The tailings and process water can contain elevated levels of thorium and radium that persist for thousands of years. Because these industries operate on a massive scale, the total volume of NORM waste worldwide is substantial, even though the radioactivity per unit of material is far lower than what you’d find in spent nuclear fuel.
Consumer Products and Industrial Sources
A small but noteworthy fraction of radioactive waste comes from consumer products and industrial equipment. The most familiar example is the ionization smoke detector, which contains a tiny amount of americium-241, a synthetic element heavier than uranium. A typical household smoke detector holds about 0.9 microcuries of americium-241, an almost unimaginably small quantity (one gram of americium dioxide is enough to manufacture 5,000 detectors). Americium-241 is also used in industrial gauging devices that measure material thickness or density, and in some medical diagnostic instruments.
When these products reach end of life, they become radioactive waste. The quantities per item are minuscule, but americium-241 has a half-life of 432 years, so it doesn’t simply fade away in a landfill. Industrial gauges containing stronger radioactive sources need proper disposal through licensed waste handlers.
Transuranic Waste From Weapons Production
A distinct category of radioactive waste comes from nuclear weapons manufacturing and the recycling of spent fuel. Transuranic waste, or TRU, is material contaminated with elements heavier than uranium on the periodic table: plutonium, neptunium, americium, and curium. These elements are almost entirely human-made, produced when uranium atoms inside a reactor absorb extra neutrons and transform into heavier elements.
Transuranic waste doesn’t generate as much heat or penetrating radiation as the fission products in spent fuel, but it remains hazardous for far longer. Plutonium-239, the most well-known transuranic element, has a half-life of 24,100 years. After about 1,000 years, when cesium-137 and strontium-90 have largely decayed away, transuranic elements account for most of the remaining radioactive hazard in high-level waste. In the United States, transuranic waste from defense activities is disposed of in a deep geological repository in New Mexico, isolated in salt formations 2,000 feet underground.