Deep storage is an increasingly important topic for our modern society, which is facing the increasing production of radioactive waste.

Deep storage involves burying radioactive waste at considerable depths, often Several kilometers under the ground, to isolate them from the environment and protect them from future natural phenomena such as earthquakes, floods and volcanic eruptions.

This storage technique has been widely used around the world and is considered to be one of the most viable solutions for managing radioactive waste in the long term. These materials can be of low, medium or high activity, with a long or short lifespan.

So what is the principle of deep storage? How are the locations for the installations selected?

The principle of deep storage

Deep storage is considered to be a long term solution to manage radioactive waste, as it can release radioactivity for thousands of years. So the purpose of deep storage is to protect the environment And the people the harmful effects of radioactivity during this period.

The deep storage process involves several key steps. First, radioactive waste is carefully packed and stored in sturdy containers. These containers are then transported to the deep storage site and deposited at considerable depths in underground cavities specially designed to accommodate them.

Subterranean cavities are often dug into rocks that are very hard and stable, such as granite, to minimize the risks of leaks and environmental contamination. Once the radioactive waste is in place, layers of rock are added on top of it to protect and insulate it from the surface.

Deep geological disposal does not concern all radioactive waste. In addition, the place to bury them must be built so that safety is ensured over a long period of time in a passive manner. This means that he should not require human supervision no institutional control. Added to this is The principle of reversibility waste storage.

Radioactive waste to be buried underground

Deep geological storage is designed to receive the ultimate radioactive materials and wastes. They are radioactive substances which can no longer be processed under the processing conditions at the time. This is generally:

• Of high activity mass wastes which contain large quantities of radionuclides of long lasting. They come from the transformation of spent fuel and release heat.
• Of wastes that have an average mass activity and contain a lot of long-lived radionuclides.
• Of spent fuels which will no longer be treated.

For reasons of safety and radiation protection, these radioactive materials cannot be stored on the surface. Nor can they remain in a long-lived low-activity radioactive waste facility. Radiation protection is the set of measures taken to protect humans and their environment the harmful effects of waste.

Deep storage, a reversible installation

The reversibility of deep storage is raised in the Environmental Code in article L542-1-1. To respect this principle, the installation site is designed progressively according to the arrival of the waste packages. Which means thatIt is not permanently closed. However, measures are taken to ensure that it remains safe and without consequences for humans and the environment.

When the storage is full or contains sufficient radioactive waste, it is closed with a soft and durable material such as clay. This will allow future generations to act on the decisions made today on the long-term management of waste. They may choose to continue with deep storage or adopt other secure management methods.

A site chosen according to numerous technical criteria

Before building deep storage on a site, many analyzes are carried out. They relate to:

• the stability of the site,
• the depth,
• hydrogeology,
• the absence of exploitable underground resources.

These investigations follow rigorous protocols and make it possible to know if the geological environment can accommodate this type of installation.

The stability of the geological environment

The site must be highly stable and able to withstand possible changes in the initial conditions. During the verification, it is therefore necessary to take into account the impact that natural phenomena such as earthquakes, glaciation could have... Deep storage is built to receiving radioactive waste over hundreds of years. It is therefore necessary to ensure that the stability of the soil will remain the same for at least 10,000 years.

The depth of the site

It is important to have a very good depth, as it contributes to safety and radiation protection. If radioactive materials are buried far into the ground, they will not be affected by natural phenomena. In addition, they will be sufficiently far from the environment and humans, which will prevent any risk of exposure.

Hydrogeology

To know the hydrogeology of the soil, experts check its permeability level as well as that of the hydraulic load gradient. Hydraulic gradient is the loss of hydraulic pressure or the loss of pressure along a flow line. These two technical elements must be weak for deep storage to be installed in a geological environment. The scope delimited for this type of analysis is broad, since it is necessary to provide underground tunnels for the transport of waste.

It is also necessary to identify and take into account the impacts that nature and geometry (water-conducting elements) can have on the host rock.

The absence of exploitable underground resources

The ecological environment chosen should not be close to an area rich in extractable underground resources. The use of this mineral wealth would become impossible at the risk of putting the environment in danger. Apart from these criteria, the rock must be compatible with closure and reversibility goals storage.

Perfect knowledge of waste packages for an adequate installation

Waste must be studied carefully in order to design installations compatible with its characteristics. This will make it possible to take the necessary measures to ensure a good storage safety. These evaluations must be done by package family. It will be about:

• determine the activity of volatile radionuclides and that of long-lived radionuclides,
• know the nature and quantities of gases that will emanate from packages when they are subjected to corrosion, radiolysis, microbes...,
• know the chemical content of radioactive waste,
• evaluate the density, the filling rate of the packages, their mechanical characteristics...,
• determine the containment capacities of packages and their evolution under the various storage conditions.

Apart from the characteristics, long-term behavior studies are also carried out on packages. They make it possible to know if they will be affected by the rock, by the materials of the worked components...

A deep storage experiment to bury nuclear waste in France

A deep storage facility is in progress at Bure In the Meuse, this is the project Cigéo. The objective is to bury all of France's nuclear waste on this site by 2030. To do this, the National Agency for Radioactive Waste Management (ANDRA) has already started the first installations.

The rock was dug 500 meters away deep and nearly 300 kilometers of tunnels have been built. This project raises some questions, most of which are linked to the definitive end of nuclear reactors, to their dismantling...

Cigéo storage project — Source: Ouest France

Checks to do before closing deep storage

Prior to the closure of the site, arrangements are made to limit the damage to the rock and restore its containment capacity. They are called engineered components and participate in safety functions. They consist in reducing the voids present in the galleries and cells built to transport waste packages. This allows:

• to avoid the circulation of water in the installation,
• to confine the storage system and to delay the migration of radionuclides,
• to prevent water intrusions other than that found in the host rock.

The components are made according to numerous calculations and under rigorous conditions. For example, account must be taken of the force caused by technical constraints, the evacuation of heat and gases from the packages...

Deep storage is considered to be the future of radioactive waste management. It offers a sustainable solution to protect the environment and future generations from the potential dangers of radioactivity.

However, it is important to continue to develop safe and reliable storage methods to ensure long-term safety. Governments and manufacturers need to work together to invest in the research and development of advanced storage technologies.

To go further, do not hesitate to read our article: What are the differences between an EPR and an SMR?