The world’s roughly 440 commercial nuclear reactors produce about 12,000 metric tons of spent fuel each year. In the United States alone, commercial reactors discharged approximately 80,000 metric tons of spent fuel between 1968 and 2017, averaging around 2,000 metric tons per year during peak operating decades. That sounds like a lot, but nuclear waste is remarkably compact compared to waste from fossil fuels. All the spent fuel ever produced by U.S. commercial reactors would fit on a single football field stacked less than 10 yards high.
How Much the U.S. Produces
U.S. commercial nuclear power plants have generated a cumulative total of roughly 80,000 metric tons of heavy metal in spent fuel since the industry began in the late 1960s. That figure covers about 277,000 individual fuel assemblies discharged through 2017, according to the U.S. Energy Information Administration. Annual output has fluctuated with the number of operating reactors and how frequently they swap out fuel rods, but a typical year in recent decades adds around 2,000 metric tons to the national inventory.
Nearly all of this spent fuel sits in storage at the reactor sites where it was used. After removal from a reactor, fuel assemblies spend several years cooling in water-filled pools, then many are transferred to dry cask storage: thick steel and concrete containers that sit on concrete pads outdoors. The U.S. has no permanent deep geological repository in operation, so this on-site storage continues to accumulate.
Types of Radioactive Waste
Not all radioactive waste is the same, and the distinctions matter because they determine how dangerous the material is and how long it needs to be isolated.
- High-level waste (HLW): Spent nuclear fuel and the byproducts of reprocessing it. This is the most radioactive category, generating intense heat and requiring isolation for thousands of years. It represents only about 3% of the total volume of radioactive waste worldwide but contains roughly 95% of the radioactivity.
- Intermediate-level waste (ILW): Reactor components, chemical sludges, and contaminated materials from fuel reprocessing. These need shielding during handling and storage but produce far less heat than spent fuel.
- Low-level waste (LLW): Contaminated clothing, tools, filters, and other items from reactor operations, hospitals, and research labs. This makes up the vast majority of radioactive waste by volume but contains only a small fraction of total radioactivity. Most of it decays to safe levels within a few hundred years or less.
Waste From Medical and Industrial Sources
Nuclear power plants get the most attention, but hospitals, research labs, and industrial facilities also produce radioactive waste. Nuclear medicine departments use radioactive isotopes for imaging and cancer treatment, generating contaminated syringes, vials, gloves, and patient waste daily. The most commonly used isotope in diagnostic imaging, technetium-99m, accounts for the bulk of medical radioactive waste by activity level. One nuclear medicine department’s waste audit found technetium-based waste accounted for over 1,100 millicuries of activity, far exceeding contributions from therapeutic isotopes like iodine-131 and lutetium-177.
The good news is that most medical isotopes have very short half-lives, often measured in hours or days. Technetium-99m’s half-life is just six hours, meaning its waste loses nearly all radioactivity within a few days. Hospitals typically store this waste on-site in shielded rooms until it decays to background levels, then dispose of it as ordinary trash. The total volume of medical radioactive waste is significant in number of containers handled, but its radiological impact is negligible compared to spent nuclear fuel.
Industrial sources, including equipment used for inspecting welds, sterilizing food, and measuring material density, also contribute low-level waste. Research reactors at universities add a small amount as well.
What Happens When a Reactor Shuts Down
Decommissioning a nuclear power plant creates a one-time surge of radioactive waste on top of the spent fuel it already produced during operation. A single standard reactor unit generates roughly 12,000 cubic meters of decommissioning waste, which includes contaminated concrete, metal piping, reactor vessel internals, and other structural materials. That volume is roughly equivalent to filling five Olympic swimming pools.
Most decommissioning waste falls into the low-level or intermediate-level categories. The reactor vessel itself and components closest to the core are the most radioactive, but the bulk of the material is lightly contaminated steel and concrete that can be disposed of in near-surface repositories. The decommissioning process typically takes 10 to 20 years from shutdown to complete site clearance, though some operators choose a longer timeline to let radioactivity decay before dismantling begins.
How Nuclear Waste Compares to Other Energy Sources
One reason nuclear waste draws so much public concern is that it’s concentrated and clearly identified. A 1,000-megawatt nuclear plant produces about 20 to 30 metric tons of spent fuel per year. A coal plant of the same capacity produces roughly 300,000 metric tons of ash annually, some of which contains naturally occurring radioactive materials like uranium and thorium. Coal ash is typically stored in open ponds or landfills with far less regulatory oversight than nuclear waste receives.
Natural gas plants produce no solid waste comparable to spent fuel, but their carbon dioxide emissions dwarf nuclear’s. Solar panels and wind turbines create non-radioactive but still problematic waste streams at end of life, including fiberglass blades and panels containing heavy metals. Every energy source has a waste problem. Nuclear’s is uniquely small in volume but uniquely long-lived in hazard.
Where It All Goes
Finland is building the world’s first permanent deep geological repository for spent nuclear fuel, called Onkalo, designed to store waste in bedrock 400 meters underground. Sweden has approved a similar facility. Most other countries, including the United States, are still debating or developing long-term storage plans. The U.S. designated Yucca Mountain in Nevada as its repository site decades ago, but political opposition has stalled the project indefinitely.
In the meantime, spent fuel remains at reactor sites in pools and dry casks. These storage methods are engineered to be safe for decades, but they were never intended as permanent solutions. Low-level waste from reactors, hospitals, and industry is disposed of at licensed shallow burial facilities, with four active sites in the United States handling the bulk of commercial low-level waste.
Reprocessing offers another path. France and a few other countries chemically separate reusable uranium and plutonium from spent fuel, recycling about 96% of the material and reducing the volume of high-level waste that needs permanent storage. The U.S. does not currently reprocess commercial spent fuel, largely due to concerns about nuclear weapons proliferation and cost.