What happens to nuclear waste?

Nuclear fuel is very energy dense, so relatively small amounts are needed to produce immense amounts of electricity, compared to other energy sources. As a result, a correspondingly small amount of waste is produced.

A 1000 MWe nuclear power station can supply electricity to millions of homes, yet it produces only about three cubic metres of solid high‑level waste each year when the fuel is reprocessed. By contrast, a coal‑fired power station of the same size produces around 300,000 tonnes of ash and more than six million tonnes of carbon dioxide every year.

Fission Fact: About 450,000 tonnes of used nuclear fuel has been produced since the first nuclear power reactor commenced operation in the 1950s. By contrast, over 60 million tonnes of electronic waste is produced worldwide annually.

We are surrounded by naturally occurring radiation, from the cosmic rays, rocks and building materials where we live, the food we eat, as well as the human body. Radiation is an unavoidable part of life on our planet, and life evolved and is thriving in this radioactive environment. What matters for health is not whether something is radioactive, but the type and amount of radiation people may be exposed to.

Since the start of the civil nuclear power industry, nuclear waste has never caused harm to people. A common misconception is that if some nuclear waste remains radioactive for a very long time, it must remain dangerous for just as long. In fact, the radioactivity that poses the greatest health risk falls sharply over time, making nuclear waste progressively safer to manage.

Fission Fact: After 40 years, the radioactivity of used fuel has fallen to one-thousandth of its initial level.

When used nuclear fuel is taken out of a reactor, it is very hot and highly radioactive, so it must first be stored safely under water to cool down. Later, it can stay in water ('wet storage') or be transferred into sealed containers ('dry storage'). Letting the fuel cool and lose some radioactivity makes future recycling or disposal easier.

These storage methods are only temporary. Countries choose one of two main long‑term approaches: recycling used fuel or direct disposal. The choice depends on each country’s political, economic, and technological priorities. 

Fission Fact: On average, the waste from a reactor supplying a person’s electricity needs for a year would be about the size of a brick. Only 5 grams of this is high-level waste – about the same weight as a sheet of paper. 

Although some countries treat used nuclear fuel as waste, most of the material in used fuel can be recycled. Approximately 97% – the vast majority (~94%) being uranium – of it could be made into new fuel.

Recycling typically involves separating out uranium and plutonium, which can then be mixed with fresh uranium and turned into new fuel. Countries such as France, Japan, Belgium and Russia have been using this approach, which also reduces the amount of long‑lived radioactive waste.

Only a small fraction of the material – about 4% – cannot be recycled. This remaining waste is mixed with glass, a process known as vitrification, before it is placed in a disposal facility.

Fission Fact: Orano Group have found that thanks to recycling, the volume of the most radioactive waste is reduced by 5 and its radiotoxicity by 10. In France, nearly 1 in 10 light bulbs run on recycled nuclear materials.

Direct disposal is the eventual resting place for nuclear waste. Vitrified waste from reprocessing – isolating the so-called fission products – and used fuel that has been designated as waste will be disposed of in an underground repository. Waste is placed in canisters which, in turn, are placed in tunnels and subsequently sealed with rocks and clay.

Fission Fact: The first repositories for high-level radioactive waste are under construction or at the planning stage. In Finland, the world's first geological disposal facility (GDF) for spent nuclear fuel is expected to reach completion in 2026.