Let us first take a high-level perspective on the waste produced through human activities.
In 2022, global CO2 emissions from energy combustion and industrial applications reached an all-time high of 36.9 billion tons. [38] At least 20% of it will stay in the atmosphere for thousands of years. [39]
Globally, we produce 7 to 10 billion tons of solid waste each year. This includes 300 to 500 million tons of hazardous waste that pose a significant threat to human health, safety, and the environment. [40]
Some of these compounds, such as mercury, lead, and other heavy metals, remain hazardous forever. Others will take millennia to degrade to a non-toxic state. An example that recently attracted public attention is PFAS. Due to their unique properties, they have been integrated in a wide range of products, from non-stick pans to semiconductors. However, they also happen to be both toxic and indestructible in nature—which lead to their nickname of “forever chemicals”. A study led by a group of media recently revealed an estimated 17,000 sites across Europe with contamination levels that require the attention of public authorities, and at least 2,100 clusters with contamination levels considered as dangerous. [41]
These are staggering numbers that highlight the magnitude of the negative impact of human activities. There is substantial room for improvement, and opportunities to deploy regenerative strategies such as circular economy. We have to prevent, reuse, recycle, recover, and only as a last resort should we dispose of waste.
A great awareness-raising campaign highlighting how little waste nuclear energy produces. Hats off to Isabelle Boemeke and her team for their creativity.
In light of this new perspective, what about radioactive waste? While it has long been considered as a major weakness of nuclear energy, it is now increasingly perceived as one of its chief selling points. Waste can be effectively isolated, there is a small amount of it, its safety improves over time, and it might actually not be waste at all.
First, it is important to understand the nature of the hazard. Radiation is a natural process, which constitutes an inherent aspect of life on Earth. Since its discovery in 1896 by French physicist Henri Becquerel, we have considerably progressed in our understanding of this phenomenon. The United Nations Environment Programme goes as far as stating that “we know more about the sources and effects of exposure to radiation than to almost any other hazardous agent, and the scientific community is constantly updating and analysing its knowledge”. [42]
Our senses are blind to radiation. However, it can easily and accurately be measured with cheap and accessible equipment, while other hazardous materials would require costly and time-consuming laboratory analysis. Radioactivity is expressed in terms of becquerels, which are the number of disintegrations per second. Bananas have a radioactivity of around 15 becquerels each, due to their high concentration of potassium, which contains a fraction of the naturally occurring radioactive isotope potassium-40. A kilogram of coffee has a radioactivity of 1,000 becquerels—same for granite. An adult human has a radioactivity of around 7,500 becquerels, mostly from Potassium-40 and Carbon-14. [43]
Radioactive waste is classified in terms of its level of radioactivity. The vast majority, roughly 90% of the total volume, is low-level waste, below 1 million becquerels per gram. [44] You can thus infer that 1 gram of low-level waste has roughly the same radioactivity as 1 ton of coffee, or 130 people. In other words: the amount of radioactivity you receive from standing next to 1 gram of low-level waste is the same you would receive from sitting in a relatively small movie theatre–which you probably never considered as a radioactive threat. Low-level waste consists of lightly-contaminated items such as laboratory equipment and work clothes. This fraction is not only generated by the nuclear energy sector, but also by hospitals and industrial activities.
Another 7% is intermediate-level waste such as used filters or steel components from within the reactor. A mere 3% is high-level waste, the actual spent fuel, with a radioactivity in excess of 1 billion per gram. In France, where spent fuel is reprocessed, this fraction falls down to less than 0.25%. [45] Only around 400,000 tons of used nuclear fuel has been discharged from reactors worldwide since the beginning of civil nuclear. [46] While it is a staggering number in itself, it only represents 0.1% of the amount of hazardous waste generated by human activities each year.
In addition to its classification in terms of radiotoxicity, all radioactive waste is thus also classified in terms of short-lived or long-lived. The metric used is the half-life, which is the time after which the initial activity is halved. Short-lived waste mainly contains radionuclides with a half-life under 31 years. The initial activity will be reduced a thousand-fold after 10 periods, hence roughly 300 years. By comparison, part of the long-lived waste will take 1,000 to 100,000 years to reach the same radioactivity as the natural uranium ore required to produce it. However, it decays exponentially—which means it reaches safe levels much earlier. After about 40 years, the heat and radioactivity of spent fuels will have fallen by over 99%. After about 200 years, standing 30 cm away from unshielded high-level nuclear waste for one hour would expose you to the same dose as four whole body CT scans. After about 500 years, it would only cause significant harm if inhaled or ingested—you can safely hold it in your hands. At this point, most of the remaining activity is alpha radiation, which is blocked by the thin layer of dead epiderm on human skin.
Since the dawn of the civil nuclear power industry, spent nuclear fuel has never caused harm. Protection is relatively straightforward: shields of lead, concrete, or water will typically provide enough protection even from the most hazardous kind of radiation.
The core principle of radioactive waste management is to store it in order to avoid radiation exposure to people or the environment. Waste management strategies differ from one country to another, albeit always with a similar philosophy. Low-level radioactive waste is typically packaged for long-term management and then stored on or near the surface, in concrete bunkers. It is actually so safe that the Central Organisation For Radioactive Waste in the Netherlands uses its storage building for low-level and intermediate-level waste as a depot for regional museums. Artworks are displayed between the radioactive waste containers—an inspiring sight.
High-level waste is first stored, often in pools, to allow decay of radioactivity and heat. It is then shipped to final disposal facilities such as deep geological repositories. The public perception of these facilities is often misled to believe that they will require constant management during millenia. On the contrary, once filled, these repositories are meant to become entirely passive. Experts from the Joint Research Centre, the in-house science and knowledge service of the European Commission, wrote a technical report on the ‘do no significant harm’ aspects of nuclear energy. They concluded that "there is broad scientific and technical consensus that disposal of high-level, long-lived radioactive waste in deep geologic formations is, at the state of today’s knowledge, considered as an appropriate and safe means of isolating it from the biosphere for very long time scales." [47]
There is, however, a reasonable argument against deep geological disposal of highly active radioactive waste: it’s not waste. Most current nuclear reactor technologies utilise less than 1% of the fuel’s energy potential. Fast reactors can burn plutonium and other elements heavier than uranium which are typically part of the long-lived waste. Even better: spent fuel can be upcycled in breeder reactors, which produce up to 30% more nuclear fuel than they consume. The potential is enormous: Europe’s existing inventories of nuclear materials could fulfil all its electric power needs for 600 to 1,000 years, without requiring any additional uranium mining. [48] This would also drastically reduce the amount of long-lived waste, thus significantly scaling down the need for deep geological disposals.
This technology is not science-fiction: the first electricity-generating nuclear reactor, in 1951, was actually a breeder reactor, which was used to power four light bulbs. While this perspective to close the fuel cycle has not been a key priority for the Western world in the past decades, it clearly is coming back on top of the agenda. Several skilled teams are actively working on it, and we should be able to witness the fruits of their efforts in the coming years.
While we’re at it, let’s note that nuclear power is the only power generation sector that takes full responsibility for its waste. All nuclear waste is regulated, and none is allowed to cause pollution. The cost of managing and disposing of nuclear waste is internalised in the cost of electricity.