Geological disposal: a protection commensurate with the risks and the timescales of High-Level waste
The Cigeo deep geological disposal project protects humans and the environment from radioactive waste for as long as it remains dangerous by placing it in drifts constructed 500 meters below the ground within a clay layer that has remained stable for 160 million years. It responds to the ethical imperative of removing the burden of managing this waste from future generations, geological disposal is the result of 25 years of research, a lengthy democratic process and is the solution for which there is international consensus.
Waste repository concept
Protection of humans and the environment
The high hazard posed by high-level waste and intermediate-level long-lived (HA and MA-VL) waste as well as its half-life – up to several thousand years – require long-term protection to be provided to humans and the environment without the need for actions or monitoring by society which could not be guaranteed over such timescales.
Deep geological disposal, by virtue of its depth, its design and its location in an impermeable claystone and in a stable geological formation make it possible to protect the waste from human activities and natural phenomena (such as erosion) and to isolate HLW and ILW-LL from humans over very long timescales.
The principle is to dispose of this waste in drifts (called disposal cells) at a depth of 500 meters below ground, with a rock chosen for its containment properties, then to close the repository once all the waste has been placed. Over time, the waste packages will gradually deteriorate and release radioactive elements. That is when the geological formation will take over, trapping the majority of these elements in the rock and slowing the movement of the most mobile elements. At the same time, the radioactive waste becomes less hazardous through a natural process called radioactive decay. The majority of radioactive elements will therefore never reach the surface or will reach it after thousands of years and in very small quantities, well below the natural radioactivity level in such a way that it presents no danger to humans and the environment.
Geological layer
The site on which the Cigeo facility will be built is located in the East part of the Paris Bassin, a highly stable geological environment characterized by low seismicity. The clay formation studied by Andra Meuse/Haute-Marne, in particular by its Underground Laboratory, was deposited around 160 million years ago. This formation, called the Callovo-Oxfordian, is homogeneous across a wide surface area and very thick (more than 130 meters). No faults affecting this layer have been identified in the studied zone. The only known faults are located outside this zone (the Marne fault, the Poissons/Roche-Betaincourt fault and the Gondrecourt graben).
Sample analyses from a 2,000-metre deep borehole have confirmed that there are no notable natural resources directly above the zone surveyed for deep geological disposal In its Report No.°4 of June 2010, the French National Assessment Board reached the same conclusions: "Under the current technological and economic conditions, the Triassic layer in the Bure area has no attractive potential as a geothermal resource."
Finally, this claystone has properties that enable radionuclides contained in the waste to be confined over very long periods.
The Callovo-Oxfordian formation selected for the siting of the Cigeo deep geological repository therefore exhibits highly favorable properties with regard to the site selection criteria defined in the ASN's safety guide.
Avoiding the dispersion of radioactive elements in the environment
First the radioactive waste packaging then the claystone confine the radioactive elements in the waste so as to limit and slow the migration of these elements up to the surface.
Initially, the radioactivity will be contained by the materials used to package the waste (e.g., high-level waste is embedded in glass which dissolves very slowly).
Over time, the packages of waste will gradually deteriorate and it is the properties of the rock which will greatly limit the movement of the radioactive elements contained in the waste: the geological formation can contain the radionuclides over very long periods of time.
The properties of the great majority of radioactive elements are such that they will travel only very little within the geological formation, a few meters at most: they will be trapped within the repository or within the Callovo-Oxfordian formation and will therefore not rise to the surface.
Only a few radioactive elements such as chlorine-36 and iodine-129 will be able to migrate and escape from the repository through the geological formation. But these movements will be very slow and so they will be released very gradually, in very small amounts, spread over the course of a million years.
The principle of waste disposal in Cigeo
An ethical responsibility
The high-level and intermediate-level long-lived waste exists: currently, approximately half the waste to be disposed of at Cigeo has already been produced.
Over and above the political, economic, scientific, technical and technological aspects, a failure to deal with this waste here and now would pass on the responsibility for this task to future generations when all the technical and technological expertise as well as the financial possibilities are already available setting up Cigeo.
Because it offers a safe management method in the very long term, deep disposal meets the ethical objective of not passing on to future generations responsibility for waste produced by activities from which we benefit every day.
A democratic choice
The Cigeo project is the outcome of a lengthy democratic process involving the passing of three laws (in 1991, 2006 and 2016) and the holding of two national public debates, with the result that solutions have been found collectively for managing the most hazardous radioactive waste.
In 2005, after fifteen years of research, a first national public debate was held. In 2006, on the basis of this debate and the assessments carried out, in 2006 the French parliament opted for deep geological disposal but laid down a requirement of reversibility for at least 100 years.
In 2013 a second national public debate was held on the Cigeo project. As part of the follow-up to the public debate, in response to the opinions and expectations expressed, Andra decided to make changes to the Cigeo project, particularly by including an industrial pilot phase at the start-up of the facility and fostering greater engagement with the public.
In 2016 the French parliament passed a third law (the Act of 25 July 2016) on the terms of construction of Cigeo and its reversibility.
An international consensus
The countries that use nuclear energy have chosen deep geological disposal as a safe, permanent means of managing their most highly radioactive waste in the very long term.
Together with France, Finland and Sweden are the countries that have made the most progress in this area. Geological disposal is planned to start during the next decade:
- Finland: with a modest nuclear electric fleet (3, shortly 4 reactors), Finland has initiated its repository project by directly excavating the facilities in a hard, crystalline rock under the Olkiluoto site. It has obtained the initial permits for constructing the disposal facilities at that location following an underground testing phase and the examination of a safety report by the competent authorities. Spent fuel emplacement in the repository should begin after 2023.
- Sweden: the licensing process has been initiated and the repository is expected to enter into operation during the second half of the next decade. Sweden plans to dispose of spent fuel in a granite environment.
Other countries have started a process to find suitable disposal sites, with a view to emplacement of waste after 2040:
- Canada : Canada has non-enriched uranium based fuel which will be directly placed in deep disposal. Eight sites are currently under investigation, of the 23 that volunteered following an information campaign and calls for applications.
- Switzerland: the studies have focused on 2 sectors in clay formations, as in France. Switzerland has vitrified waste and spent fuel.
- The United Kingdom: a new consultation process is ending before undertaking a new call for applications for a disposal site. The United Kingdom has a wide range and a large volume of waste to dispose of.
- Germany: a new volunteer-based process to find a site has been set up. The first decisions on the choice of site are expected after 2030, for disposal approximately twenty years after that.
- Belgium: Belgium is also envisaging disposal in clay formations but must also check the feasibility of alternative media.