Radioactive waste is disposed of through a combination of methods matched to how dangerous the material is and how long it stays radioactive. The most hazardous waste, which makes up only 3% of total volume but carries 95% of all radioactivity, requires isolation deep underground for tens of thousands of years. Less dangerous waste can be buried in shallow facilities closer to the surface. No single method handles everything, so the global approach relies on classifying waste by risk and applying the right disposal technique to each category.
How Radioactive Waste Is Classified
Not all radioactive waste is equally dangerous, and the disposal method depends entirely on what category the waste falls into. In the United States, the Nuclear Regulatory Commission divides low-level waste into Class A, Class B, Class C, and Greater-Than-Class-C. Classes A through C can be buried in shallow land facilities, while Greater-Than-Class-C waste generally needs deeper, more engineered solutions. High-level waste, which includes spent fuel rods from nuclear reactors and liquid byproducts from weapons production, is in a category of its own. It remains intensely radioactive for tens of thousands of years and demands the most robust containment strategies available.
The International Atomic Energy Agency uses a broader framework with categories ranging from very low-level waste up through high-level waste, but it deliberately avoids setting universal numerical thresholds between classes. The boundaries depend on site-specific factors, like how well a particular disposal facility can protect people from accidental exposure. The one exception is transuranic waste (elements heavier than uranium), which has a firm quantitative cutoff at 100 nanocuries per gram.
Interim Storage: Buying Time
Most countries don’t yet have a permanent home for their most dangerous waste, so interim storage fills the gap. Spent nuclear fuel is initially kept in cooling pools at reactor sites, where water absorbs both heat and radiation. After several years of cooling, the fuel can be transferred to dry cask storage: steel cylinders that are welded or bolted shut, then surrounded by additional layers of steel, concrete, or other shielding material.
These casks are licensed for up to 40 years, with possible renewals of another 40. The U.S. Nuclear Regulatory Commission has expressed confidence that spent fuel can be stored safely in pools or casks for at least 60 years beyond the licensed life of any reactor without significant environmental effects. That’s reassuring, but interim storage was never meant to be the answer. It’s a holding pattern while permanent disposal catches up.
Shallow Burial for Low-Level Waste
Low-level radioactive waste, which includes things like contaminated protective clothing, tools, filters, and medical isotopes, is disposed of in near-surface facilities. These are engineered burial sites, typically within the top 30 meters of the ground, designed with layers of natural and manufactured barriers to keep radioactive material from reaching groundwater or the surface. Class A waste, the least hazardous, has the simplest requirements. Class B and C waste must meet stricter standards for structural stability, and Class C waste requires additional protections like engineered barriers or deeper burial to prevent someone from accidentally digging into it in the future.
Vitrification: Locking Waste in Glass
Liquid high-level waste, particularly from nuclear weapons production, can’t simply be buried. It first has to be converted into a solid form stable enough to last thousands of years. The primary method is vitrification, a process that fuses the waste into borosilicate glass. The typical glass composition is 33 to 65% silica, 3 to 20% boron oxide, 4 to 22% sodium oxide, 3 to 20% aluminum oxide, and varying amounts of other metal oxides. This glass is poured into stainless steel canisters, where it hardens into a form that resists leaching from water and remains structurally stable over geological timescales.
U.S. federal law requires that certain high-level mixed waste be vitrified before disposal in a deep geological repository. The Department of Energy plans to vitrify a portion of low-activity waste at its Hanford Site in Washington State, though the treatment facility has faced persistent challenges in starting operations.
Deep Geological Repositories
The international consensus for permanently disposing of high-level waste is to bury it hundreds of meters underground in stable geological formations. The idea is straightforward: place the waste deep inside rock that hasn’t moved significantly in millions of years, seal the tunnels, and let geology do the containment work that no human institution can guarantee over tens of thousands of years.
The United States currently operates one deep geological repository, the Waste Isolation Pilot Plant near Carlsbad, New Mexico, but it only accepts defense-related transuranic waste, not commercial spent fuel. Under the Nuclear Waste Policy Act, the Department of Energy is responsible for siting, building, and operating a repository for high-level waste and spent fuel, with the EPA setting environmental protection standards and the NRC licensing the facility. Progress has been slow. The proposed Yucca Mountain site in Nevada has been politically stalled for decades.
Finland is ahead of everyone else. Its Onkalo repository, under construction in the municipality of Eurajoki, is set to become the world’s first operating deep geological repository for spent nuclear fuel. Construction began in 2015, and the operating license application was submitted in December 2021. Disposal activities could begin as soon as the license is granted, potentially by the end of 2025. Sweden has received approval to construct its own repository. France plans to begin construction around 2027, with disposal starting between 2040 and 2050. Switzerland and Canada have selected sites and expect to begin disposal around 2050 and the early 2040s, respectively.
Deep Borehole Disposal
An alternative to mined repositories is drilling narrow boreholes 5 kilometers (about 3 miles) deep into crystalline basement rock. In the U.S. concept, the bottom 3 kilometers would be drilled into the basement, and waste would be placed in the lower 2 kilometers, with the space above sealed and plugged. The appeal is that at these depths, groundwater is extremely old, dense, and essentially stagnant, meaning there’s very little chance of radioactive material migrating to the surface.
The engineering challenges are substantial, though. Drilling projects at these depths have struggled with equipment failures, borehole instability, and the difficulty of characterizing rock and water conditions far underground. Packers designed to seal test sections have leaked because the boreholes were misshapen from pressure-induced breakouts. Core samples brought to the surface crack from stress relief, and fluid samples change as pressure and temperature drop during retrieval. Deep borehole disposal remains a concept under study rather than an active disposal program.
Reprocessing Spent Fuel
Rather than treating all spent fuel as waste, some countries chemically separate the reusable uranium and plutonium from the truly unusable byproducts. This is reprocessing, and it reduces the volume of material that needs permanent disposal while recovering fuel that can be recycled into new reactor fuel.
The dominant industrial method dissolves spent fuel in nitric acid, then uses a chemical solvent to selectively pull out uranium and plutonium while leaving fission products and other waste behind in the acid solution. France actively reprocesses its spent fuel using this approach. The United States developed a modified version called UREX, which extracts uranium but intentionally blocks plutonium separation by adding a chemical that prevents plutonium from being pulled into the solvent. This was designed to reduce nuclear weapons proliferation risks, since separated plutonium is a weapons-usable material. France has taken a different approach with its COEX process, which extracts uranium and plutonium together as a mixed product rather than producing pure plutonium.
Reprocessing doesn’t eliminate the need for geological disposal. It reduces waste volume and recovers energy, but the leftover fission products and minor actinides are still highly radioactive and still need to be vitrified and buried.
Transmutation: Shortening the Clock
The most ambitious approach to radioactive waste aims to transform the longest-lived components into isotopes that decay much faster, or into stable elements that aren’t radioactive at all. This is transmutation, and it works by bombarding problematic isotopes with neutrons. When certain long-lived actinides absorb a neutron, they can be split apart through fission, converting into shorter-lived or stable products. Long-lived fission products don’t undergo fission but can still be transformed through neutron capture into less problematic isotopes.
The leading technology for this is the accelerator-driven system, which couples a particle accelerator with a subcritical nuclear reactor. The accelerator fires high-energy protons at a lead target, which releases a shower of neutrons through a process called spallation. Those neutrons enter the reactor core, where they sustain nuclear reactions and irradiate the waste mixed into the fuel. Because the reactor is subcritical, it can’t sustain a chain reaction on its own, making it inherently safer for handling the exotic fuel mixtures involved. MYRRHA, currently being built in Belgium, will be the first subcritical fast reactor designed to test high-level waste transmutation. If the technology proves out at scale, it could significantly reduce both the radioactivity and the required isolation time for the most dangerous waste streams.
What’s No Longer Allowed
For decades, countries disposed of radioactive waste by dumping it into the ocean. The Soviet Union, the United Kingdom, the United States, and several European nations dropped sealed containers of low-level waste into deep water, assuming dilution would solve the problem. Amendments to the London Convention, adopted in 1993 and entering into force in 1994, banned the dumping of all radioactive waste at sea. That practice is now universally prohibited under international law, and every country with a nuclear program is expected to manage its waste on land.