[LUM#19] Sustainable Waste
What should be done with the radioactive waste produced by nuclear power? This is a major challenge, given that some of it will continue to emit radiation for hundreds of thousands of years. The solution? Isolate and store it to avoid exposure. Xavier Deschanels, a researcher at the Marcoule Institute of Separative Chemistry*, explains how we manage these special materials.
Although nuclear power accounts for only 10% of global electricity generation, it is by far the leading source of electricity in France, with 70% of the country’s electricity coming from the 18 nuclear power plants located throughout the country.
A production method that emits few greenhouse gases but leaves behind a problematic byproduct: radioactive waste. How can this unique waste be managed safely? “It all depends on the type of waste in question, because in reality there are different categories of radioactive waste,” explains Xavier Deschanels, a researcher at the Marcoule Institute of Separative Chemistry (ICSM). It is classified according to two parameters: the intensity of its radioactivity and the half-life of the radionuclides, which determines how long it will remain radioactive. Regardless of the type of waste, the principle is the same: isolate it as effectively as possible from the environment to minimize exposure to radioactivity. But isolation methods differ depending on the category of waste.
Packages in quarantine
“The vast majority of nuclear waste is short-lived waste. It accounts for more than 90% of the total volume of radioactive waste in France, but only 0.03% of the total radioactivity,” the researcher points out. For this waste, the chosen solution is surface storage. “It’s a highly organized process; it’s far from a simple landfill. This waste is first packaged into bundles, meaning it is enclosed in a steel or concrete container after undergoing various treatments such as incineration and compaction, ” explains the researcher.
These unique packages are then sealed underground in reinforced concrete storage structures. “These structures are then sealed with a permanent cover consisting of several layers of natural materials such as clay to protect them from the elements and ensure long-term storage safety, and are monitored for 300 years, after which they will no longer emit radioactivity, ” explains Xavier Deschanels.
Deep burial
300 years is a fraction of a second compared to the thousands of years during which so-called high-level radioactive waste will remain radioactive. While its radioactivity accounts for more than 95% of the total radioactivity of nuclear waste, its total volume represents only about 0.2% of the total volume of that waste. “That’s the equivalent of an Olympic-sized swimming pool since the start of nuclear power in France, ” the researcher explains.
And for this category of waste, considered the most dangerous, surface storage is out of the question. The solution? Deep geological disposal. This waste isn’t buried as-is but undergoes complex technological processes. “Initially, it is in the form of a highly radioactive liquid that we evaporate to obtain what is called a calcined residue—a true concentrate of radioactivity—which is then mixed with glass powder to stabilize the inorganic materials.”
The end result is glass packages weighing about 400 kilograms each, with such high levels of radioactivity that their temperature reaches around 350°C—a heat that will take about sixty years to dissipate through radioactive decay. “For now, they are kept in continuously cooled pools and then stored in concrete shafts at the La Hague processing plant, awaiting the upcoming opening of the Cigeo geological storage facility in Bure, where they will be buried 500 meters underground at a site selected for its geological characteristics to ensure no radioactive leakage to the surface, ” explains Xavier Deschanels.
Transmutation
What other approaches are being considered for managing nuclear waste? “At ISCM, we are working to develop solutions such as transmutation, which involves extracting certain radionuclides known as minor actinides and then transforming them, through a series of nuclear reactions, into fission products similar to those produced by uranium fission, which have lower radiotoxicity, ” adds the researcher. A process that would require new nuclear facilities, which themselves produce waste that would also need to be stored deep underground.
Another approach being explored by researchers is “the use of mesoporous materials, which have the unique ability to encapsulate radioactive elements. In practice, the radioactive liquid passes through a selective membrane that retains the radionuclides; the radioactivity then breaks down the material’s porosity, trapping them.” These innovations will not replace the current approach for the time being: “Isolating and storing nuclear waste remains the universal solution,” concludes Xavier Deschanels.
*ICSM (CNRS, CEA, UM, ENSCM)
UM podcasts are now available on your favorite platform (Spotify, Deezer, Apple Podcasts, Amazon Music, etc.).