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Geological disposal in clay

Storing radioactive waste in a subsoil of clay

SCK CEN is a pioneer in research into storing nuclear waste in deep clay layers. Today, together with ONDRAF/NIRAS and other Belgian partners, it is examining the various options.

SCK CEN - Infrastructuur HADES (2019)

Geological disposal in clay: a safe option

At the underground laboratory HADES, experts are developing and testing industrial technologies for building, operating and sealing a repository in deep clay. There, scientists are conducting experiments in a deep clay layer, on a large scale and over a long period of time to evaluate the safety and feasibility of geological disposal in poorly indurated clay.

40 years of research shows that such a repository can be industrially excavated and that long-term safety can be assured. The radioactivity that would be released from the clay layer in highly diluted concentrations after thousands of years would have no impact on people or the environment.

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Dive 225 metres underground and read more here.

Frequently asked questions about geological disposal

  • Experiments at the underground laboratory HADES show that clay has good properties for containing radioactive waste. To begin with, clay barely lets water through. No water currents are possible that would quickly move the radioactive materials. Moreover, clay is plastic. This means that the cracks that form in the clay during the excavation of tunnels will close on their own after the concrete wall is in place. Finally, the clay minerals, the smallest particles in the clay, have the ability to bind much of the radioactive substances to themselves. This keeps them trapped in the clay layer when they are released from the waste packaging in the long term. These three properties together make clay suitable for geological disposal.

  • In geological disposal, both natural and artificial barriers ensure that the radioactive waste does not pose a danger to people and the environment for hundreds of thousands of years. Clay is an important natural barrier. It has the property of not letting water through and retaining radioactive particles, allowing them to disperse only very slowly. Due to its plasticity, the clay automatically closes all possible cracks and fissures that may appear. This way, the barrier remains closed.

    In addition, the highly radioactive waste is packed in specially designed disposal containers: a supercontainer. The supercontainer consists of several concrete and steel barriers that contain the waste.

  • Transmutation literally means 'to convert', in this case converting specific long-lived radioactive elements into other, shorter-lived radioactive elements. Current research on transmutation may lead to future reductions in the volume of certain types of radioactive waste. For current waste already processed, however, nothing will change. There remains a large volume of long-lived waste that must be shielded from humans and the environment over the long term. For that, geological disposal is the safest solution. Thus, transmutation is not an alternative to geological disposal. It may add value in the future and lead to an optimisation of the disposal system.

    More generally, we do not think it is responsible to wait for a new technology that may not be found. After all, in this way we postpone the problem and ensure that our children and grandchildren will have to pay for it and take care of the waste, while funding could become uncertain. The construction of a repository takes decades. Should other and better solutions present themselves in the meantime, they will certainly be taken into account.

  • In fact, climate change is an important argument for choosing geological disposal.

    Today we mostly talk about global warming. If, in the long run, all the ice on Earth were to melt, the sea level would rise several tens of metres. Part of Belgium could then be flooded. This makes storage in buildings a vulnerable situation. In the deep underground, waste remains contained and isolated from these changes.

    In the really long term, and by that we mean the next hundreds of thousands of years, researchers are mainly looking at the influence of ice ages. Ice ages and warmer intervals like the one we are living in now alternate about every hundred thousand years. In our regions, an ice age mainly means colder temperatures, the occurrence of permafrost and possibly the incision of rivers. That is also why a repository will be built several hundred metres deep. In this way, these disruptions do not affect the safety of a repository.

  • No. In fact, this is one of the safety requirements for geological disposal.

    The radioactivity of the waste decreases with time, although for some radioactive substances this is a very slow process. By enclosing the waste for tens of thousands of years in a special waste container such as a monolithic block or a supercontainer, the radioactivity has already diminished by the time the radioactive substances enter the clay. Its movement is then greatly inhibited by the clay minerals, which are the smallest particles in the clay layer and bind a significant portion of the radioactive substances to themselves. In addition to this slow movement, the concentration of radioactive substances is greatly diluted. Based on the experiments in HADES, we have a good understanding of these processes and can accurately determine how radioactive materials move in the subsurface over the long term. The amount of radioactivity that will get into the groundwater is negligible and will not pose a danger to people who use this water in the future.

    In other words, disposal will in no way make the groundwater unfit for consumption.

  • After decades of research, scientists at home and abroad agree that geological disposal is the only safe final destination for highly active and/or long-lived waste. All over the world, alternatives to geological disposal have been evaluated, weighed and finally rejected. They go against international agreements or involve too great risks. Disposal at sea (seabed), in an ice cap or in space, for example, is not possible. So although there are no alternatives to geological disposal today, ONDRAF/NIRAS continues to monitor all scientific developments with an open mind.

  • Currently, nothing has been decided on the location of a future repository. Where such a repository can be built will depend on the characteristics of the subsurface and the safety requirements determined by the Federal Agency for Nuclear Control. In the northern part of Belgium, mainly poorly indurated clay layers qualify, whereas in the southern part harder varieties such as slate are being considered. Where the repository might be built will be the result of community consultation in addition to safety requirements. To that end, ONDRAF/NIRAS will look for a region willing to become a partner in the development of such a project. Ultimately, FANC will assess whether the concrete proposal at a specific site meets all safety requirements for a geological repository.

  • An earthquake occurs when two rock blocks in the subsurface suddenly move relative to each other along a fault plane. This causes a vibration or quake that propagates into the subsurface. The greatest damage occurs at the Earth's surface, where additional vibrations are generated at the contact between the solid ground and the air. In such case, the waste is therefore better off deep underground, hermetically sealed in a repository.

    The earthquakes that occur in Belgium are usually of low intensity. They often occur in existing and known fault zones, such as those found in northeastern Belgium. A repository will be built at a safe distance from these known fault zones. This keeps the potential impact of an earthquake on an underground repository to the absolute minimum.

  • The construction and operation of the repository will take several decades. During that time, the facility will be accessible. The design of the repository and the supercontainer allows for the waste to be taken back out during a limited period of time. Exactly how long this period is will have to be determined in consultation with citizens and stakeholders. We are talking about an order of magnitude of 100 years. The intention is to close the repository at some point to ensure safety for future generations without them having to do anything. We call this passive safety.

    So yes, we will be able to retrieve the waste during a certain period of time.

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