1. Introduction

2. Short Presentation of Cigéo, the French Deep Geological Disposal Project

Cigéo is a deep geological disposal facility designed to manage the French high-level radioactive waste (HLW) and intermediate level radioactive waste long-lived (ILWLL). It is located in Eastern France, next to Andra’s underground research laboratory (URL) in Bure (around 250 km from Paris).

Cigéo is composed of surface facilities and underground infrastructures (Fig. 1). The surface facilities’ main functions are 1) to control the waste packages and to prepare them prior disposal 2) to support disposal activities and construction works for the progressive extension of Cigéo. Cigéo’s surface infrastructures include a rail connection and a road link connecting the two main surface zones. The waste is shipped to Cigéo by train. The waste packages are conditioned at their production sites.

Fig. 1

Illustrative scheme of Cigéo.

The underground facilities include disposal areas, support areas and the links connecting these to the surface (5 shafts and 2 ramps). HLW and ILW-LL are disposed of in separated zones implanted at a depth of around 500 m. The host rock is the 160 million-years old Callovo-Oxfordian clay layer.

Cigéo is dimensioned to accommodate the entire projected inventory of all the HLW and ILW-LL produced by the operations and dismantling activities of French present, past and foreseen nuclear facilities (inventory fixed at the end of 2018). Its overall capacity is around 83,000 m³ (10,000 m³ HLW and 73,000 m³ ILW-LL). HLW are disposed of in horizontal micro-tunnels of about 0,8 m diameter equipped with a steel liner. ILW-LL are disposed of in concrete tunnels of about 10 m of diameter. Underground nuclear operations are fully automated.

France is reprocessing spent fuel to recover the valuable substances it contains, namely Uranium and Plutonium. These materials are recycled to produce more electricity. As a result, French HLW is mostly vitrified fission products and ILW-LL is mostly by-products of the reprocessing process or used equipment of this process (Fig. 2).

Fig. 2

Examples of mock-up packages of vitrified HLW (left) and compacted ILW-LL (right) produced in Orano’s fuel reprocessing plant in La Hague.

Cigéo is intended to be operated from around 2040 to until around 2150 [3]. During this long operational period, the characteristics and nature of the waste may change, for example as a result of modifications in the National nuclear policy. Cigéo is so designed that it may be adapted to accommodate these changes. In order to demonstrate its ability to adapt Cigéo during its operational period, Andra studied a variety of potential design evolutions. The potential introduction of these design modifications would enable to dispose of larger quantities of waste and to accept other kind of wastes in Cigéo, including spent fuel.

The disposal vaults and connecting galleries will be gradually constructed (Fig. 3). Gradual extension implies successive investment decisions and authorizations. The investments will be programmed by Andra according to the industrial needs. The works will be conducted under the regulatory conditions set by the authorizations. Upgrades of the design may be proposed in the future. The gradual development of the facility is a strong tool enabling to integrate potential modifications in due time (design improvements, introduction of new techniques, optimizations, evolution of needs, change in waste characteristics…).

Fig. 3

Illustration of the principle of gradual extension of the underground facility.

The industrial full-scale disposal of HLW will only be started around 2080 (since they are shipped to Cigéo, the HLW will be kept in surface interim storage facilities at their production sites). To prepare for this important milestone, a small pilot HLW disposal area of around 20 disposal cells will be constructed and operated from the beginning (the pilot HLW disposal area receives lower thermal emission HLW packages, but has similar thermal requirements as the full-scale HLW disposal area). It will enable to gather operational feedback for around 40 years before the industrial HLW disposal area is build and authorized. The results gathered in the HLW pilot disposal area will support potential design optimization studies and will further substantiate the safety demonstration.

In January 2023, Andra submitted the license application file of Cigéo to the French government. In June 2023, the nuclear safety authority declared that the receivability checks of the file had been completed and that its technical assessment was launched [4]. The entire authorization process of Cigéo is defined by law and inscribed in the environmental code [5] (Fig. 4). It includes thorough technical reviews led by the nuclear safety authority and its technical support organization, opinions from territorial communities and reports from the National evaluation commission [6], from the environmental authority and from the Parliamentary office for science and technology. It also includes a public inquiry and various legal steps for the preparation of the authorization decree. Provided the outcome of this process is positive, the initial construction of Cigéo may be authorized around 2027. Andra is the owner of the Cigéo project and is responsible for the implementation and operations of the DGR.

Fig. 4

Schematic steps of Cigéo’s authorization process (hypothesis of a positive outcome).

The potential decree authorizing the construction of Cigéo is only the first of the progressive authorization steps facing the project. The start of the disposal operations pends on a future authorization by the nuclear safety authority. Moreover, a law is expected to be voted after a few years of operations in order to determine the conditions for the continuation of the disposal operations. The period starting from the decree authorizing Cigéo’s initial construction and ending after a few years of disposal operations is named the “Industrial pilot phase” (IPP) [7]. This IPP could last around two decades. It will provide extensive information and operational feedback. The characteristics and conditions of the operations that will be carried out after the IPP will be validated by the French Parliament. On the basis of the information and teachings gained during the construction and during the first years of operations, the Parliament may confirm the disposal of HLW and ILW-LL, but it may also complement, modify or redirect the program.

3. The Progressive Siting Process of the Facility

The French HLW management program is steadily going forward and can be considered to be on good tracks. However, this has not always been the case. The first studies in support of the HLW management program started in the late 70’s. From 1982, collaborations were gradually launched with European partners that were studying the properties of various rock formations with the objectives of implementing geological disposal: Clay was studied by Belgium in the URL in Mol, Granite was studied by Switzerland in the URL in Grimsel and Salt was studied by Germany in the Asse mine. In 1987, with the scientific support of the National Bureau of Geological and Mining Research (BRGM), four sites, representative of four different rock types, were selected in order to study their suitability for HLW disposal [8]. This selection was carried out solely on geological criteria without prior consultations with the public and local stakeholders. The geological investigations started immediately after the sites were made public (geophysical campaigns and exploratory drillings). Unfortunately, growing on-site protests led the Prime minister to decide to stop the geological surveys and to declare a moratorium on the program in February 1990.

In December 1991, the Parliament voted to establish a completely new legal frame for the management of highlevel waste [1]. By law, it became mandatory to organize consultations with local elected representatives and with the public prior the beginning of any work linked with a URL project. A transparent financial support scheme was created to support the communities of the territory hosting the URL. The National evaluation commission reporting to the Parliament was formed [6]. Andra, the public body in charge of the management of French radioactive waste, was made independent from the radioactive waste producers. Most importantly, a comprehensive 15 years research program was launched that included the publication of periodic reports documenting the advances. At the end of this program, a Parliamentary vote was made necessary to advance toward the creation of the DGR. In fact, the law voted in 1991 created a progressive and open technical and democratic process, where all important choices were put under the scrutiny of the Parliament.

After the 1991 law was voted, the Parliament actively engaged in the resolution of the conflicts. A Parliamentary mission started exchanges and discussions with local communities. The mission managed to gather around 30 candidates to host the URL. After the first technical screenings, four sites were selected for more detailed geological and environmental assessment (Fig. 5): one in Granite (“département de la Vienne”), one in Silty-Shale (“département du Gard”), two in the Callovo-Oxfordian Clay (neighboring “départements de la Meuse et de la Haute-Marne”).

Fig. 5

Map presenting the approximate locations of the four main candidate sites identified in 1998 to host the French URL and the approximate final location chosen for the URL in Bure.

In 1998, after a thorough geological review by the safety authority and by the National Evaluation Commission and on the basis of public enquiries led in all candidate departments, the sites in Granite and in Silty-Shale were rejected [9]. The quality of the granitic site was impaired by the presence of local fractures, by the complexity of its hydrogeology and by its significance in terms of local water resources [10]. The Silty-Shale site was rejected because of the uncertainties caused by the local seismicity and by the long-term instability of the geological context. Some specific local environmental impact issues were also raised.

On the contrary, the two sites in the Callovo-Oxfordian clay were seen as very promising for the development of a disposal facility. The geological structure is simple and continuous. It is stable and distant to the greater tectonic movement. The regional seismicity is very low and the local hydrogeology is favorable. The Callovo-Oxfordian layer is thick (around 120 m thickness at least), watertight and has strong retention properties. At a depth of around 500 m, it is well positioned to isolate the radioactive waste from the environment and to limit the risks of intrusion.

After the review, the neighboring candidate “départments” of Meuse and Haute-Marne confirmed their intentions to host the URL in view of the development of a future DGR and merged their candidacy. As a result, the French Government decided that the French URL would be located in Bure, a village placed near the border between the two departments. Ever since 1998, the two candidate departments have periodically reaffirmed their will to host the deep geological repository [11].

4. Andra’s Underground Research Facility (URL) in Bure

Andra received the authorization to build the URL in Bure in August 1999 and started the construction in 2000. The work started with the digging of the two shafts and with the construction of a small experimental gallery (named the “niche”) in the upper part of the Callovo-Oxfordian layer (approximate depth of 440 m). When the middle of the clay layer was reached (approximate depth of 490 m), the network of galleries was progressively expanded. In its current state, the URL comprises around 2 km of galleries where experiments and technological tests are carried out (Fig. 6). Around 1,000 boreholes enable samplings or implantation of various sensors and surveillance devices. In the URL, Andra collects more than a million data every day from around 18,400 measurement points.

Fig. 6

Schematic layout of the URL in Bure showing its current main architectural structures (shafts and galleries in grey) and experimental or testing boreholes (in various colors).

The operations carried out in the URL are supported by surface activities (administrative buildings, workshops, laboratories and communication facilities) (Fig. 7).

Fig. 7

Picture of some of the surface facilities in Bure (namely the heads of the shafts).

5. The Crucial Contribution of Andra’s URL to the Development of a Sound Scientific and Technological Program Supporting Cigéo

Since the very first start of its construction, the URL has been a great tool to gather scientific and technological knowledge and to characterize the geology of the site, in particular the clay host-rock. Right from the start of the digging of the vertical shafts by blasting and during the construction of all horizontal galleries, data were collected to characterize the geological context, to confirm or modify the design of the structures and to improve the efficiency of the underground work.

Indeed, the construction of underground structures may be regarded as specific opportunities to acquire data and may be organized for this purpose. In the URL, different excavation techniques were tested and used, associated with different support coatings. The follow-up monitoring of these works enables to comprehend the interactions between the supports and the rock and the nature and development of the excavation damages. Some specific underground structures are being followed through a reinforced monitoring program aiming at acquiring the most sensitive data (for example those needed for future optimizations).

The scientific and technological program unfolded in three major successive phases during which the underground facility was regularly expanded (Fig. 8).

Fig. 8

Schematic illustration of the development of the URL with time.

The first years (2000–2005) were devoted to the characterization of the intrinsic properties of the Callovo-Oxfordian clay and to the confirmation of the feasibility of the disposal in this rock formation. The physico-chemical properties of the clay were accurately measured (pore water chemistry, permeability, diffusion/retention, geo-mechanical behavior…) and the primary effects of the construction work on the clay were studied (EDZ, chemical perturbation of the clay due to ventilation, interaction with construction materials like concrete, steel…).

The second phase (2006–2010) was devoted to the confirmation of the disposal concepts and to the study of the perturbation generated by a potential disposal in clay. The potential disturbances caused by heat and chemical interactions were studied, as well as the thermo-hydro-mechanical coupled processes. Experiments were launched to characterize the behavior of gas and the complex long-term interactions between the materials present in the disposal (clay/cement/iron/glass…). Technological developments were oriented towards the improvement of gallery design and construction techniques. Different kinds of galleries were built (from horse shoe shape to cylindrical) with various kind of supports and bolds. The first “demonstrators” or “mock-up” of HLW cells were constructed, tested and monitored. Sealing plugs experiments were constructed and studied [12, 13].

The third phase (2011–present) particularly focuses on the long-term interactions between clay and underground structures or materials (robustness/alteration) and on the optimization of the design and construction techniques. Strong attention is given to the study of in-situ gas generation processes and on thermo-hydro-mechanic couplings. A tunnel boring machine was tested and gallery support were optimized. Large galleries (up to the side of around 9 m) were build, as well as different kind of gallery crossings. The aim is to gradually get closer and closer to the actual DGR design (Fig. 9).

Fig. 9

Example of a gallery and scientist controlling an experiment in Andra’s URL in Bure.

The geological studies in the URL are complementary to those carried out from surface (2D and 3D seismic imaging campaigns, drillings, samplings…). They led to more than a hundred PhD theses. The quantity and the quality of the data obtained by Andra in the last 30 years from surface and in-situ studies, probably make the area of Bure the best-known geological site in France and in the world.

Through all these years of research and developments in the URL, Andra also carried out complementary scientific and technological developments in surface facilities and in collaboration with its international partners. The URL allowed to test and assess the performances of the technologies in underground conditions.

The data, knowledge and operational feedback gained in the URL were used by Andra to continuously feed the design and safety studies of Cigéo. Their quality and representativity permitted to optimize the design, to reduce the uncertainties and to make sound technical choices for the DGR as presented in the license application.

6. The Crucial Contribution of Andra’s URL to the Safety Demonstration and to the Security of Cigéo

A deep geological disposal facility is designed to provide safety during its unusually long period of operation (typically around a century) and then, after its closure, during the very long period of time during which the HLW still constitute a danger to the environment and to human health (typically a few hundreds of thousand years). Safety is the fundamental goal and the number one priority of radioactive waste management programs.

The safety demonstration of a deep geological disposal facility (during operations and after closure) should be progressively established and deepened by carrying out safety assessments at the early siting, design and construction stages and by regularly updating the demonstration during the operational and closure phases. At the different stages, renewed comprehensive safety analysis are carried out to assess the robustness of the disposal concepts and design, using up-to-date data and knowledge. After the assessment, modifications or optimizations may be introduced in the disposal concepts or in the facility design and complementary research programs may be launched to further increase the quality of the data and knowledge to be used in the future assessments (Fig. 10).

Fig. 10

Simplified scheme of the Safety/Design/Knowledge iteration process.

In the case of the Cigéo project, three major assessments reviews were carried out by the Safety authority in 2005, 2009 and 2016 [14]. The first one concluded in the feasibility of the disposal. The second one focused on the improvement of the operational and long-term safety analysis and on the potential reversibility of the disposal. The third one reviewed the safety options of the disposal defined on the base of the basic design studies of Cigéo. The findings of this third review were introduced in the most recent version of the safety case that was submitted this year by Andra to the Government for the license application of the disposal facility Cigéo.

Most importantly, all the iterative safety assessments of Cigéo benefited from the results of the HLW management R&D program. These results provided a solid base for the studies and analysis that were submitted to the safety authority. They were key to reduce the uncertainties and to provide a firm ground for the review conclusions and follow-up decisions that led to go forward with the HLW program. Every iterative review provided new inputs for the R&D program and to the DGR design studies as new issues emerged and updated requirements and specifications were enacted.

Aside the scientific and technological teachings, there is another very practical contribution of the URL to the future safety and security of the DGR. Every day, the construction work and the operations of the URL provide feedback in terms of underground working and intervention conditions (Fig. 11). Rescue teams are trained in the URL, intervention material is adapted to underground conditions and security procedures may be improved. As a matter of fact, Andra has become an important partner of the University of Nancy in its academic efforts to improve underground know-hows. A URL is a good tool to develop the skills of the workforce and to prepare for secure work conditions in the future DGR.

Fig. 11

Intervention control room of Andra’s URL in Bure.

7. The Crucial Contribution of Andra’s URL for the Assessment of the Environmental Impact of Cigéo

The objective of a deep geological repository (DGR) is to protect the environment and the human health. As a consequence, its first objective should be to keep its environmental impact as low as possible. Moreover, considering the growing sensitivity of the public to the degradation of the environment, a HLW management program may wisely seek high environmental standards thus preventing to fuel oppositions with valid reasons for concerns.

An underground research laboratory (URL) bears many features that resemble those of the future DGR. For example, they both require shafts, galleries, ventilation and excavated material handling operations. For the operator, the way the environmental impacts of the URL are managed (avoided, reduced or compensated) can be seen as a good practice and preparation for the future DGR. For the public, it will be an indication on how serious and trustful the HLW program may be considered.

In the case of the French URL in Bure, valuable feedback was gained, especially from the management of digging construction activities and stockpiles, from the surveillance of water local resources and from the treatment and discharge of collected ground water and effluents. The lessons learnt were used for the environmental design of Cigéo. They helped to define practical and efficient requirements guaranteeing low to moderate impacts at all stages [15].

Effective impact reduction provisions can only be designed and enforced if the surrounding environment is carefully characterized and understood. The specific sensitivity of the territory may be apprehended by dedicated surveys. As the Cigéo facility is envisaged in the close vicinity of the Bure URL, the environmental impact assessment of the future DGR benefited from all the surveys and knowledge gained starting from the first on-site work in the 90’s. These surveys were periodically up-dated and extended to cover all topics. In Cigéo’s case, the potential presence or habitats of protected species on site (fauna and flora), the local usages (forestry, agriculture…) and the complexity and sensitivity of the local hydrogeology were amongst the most sensitive factors.

To reinforce its knowledge of the surrounding environment, Andra launched in 2007 the scientific project of a perennial observatory of the environment (OPE). The OPE measures and monitors environmental parameters in a large perimeter around the URL and Cigéo. Not only does it help to continuously gather the best possible knowledge of the local environment, but it will also help to discriminate the cause of the potential changes (climatic, industrial, socioeconomic…). Andra also organized a geological core sample library in 2012 and an environmental specimen bank in 2014 (Fig. 12). The careful conservation of environmental and material sample will be a strong asset to fully assess the impact of the DGR in the long run.

Fig. 12

Example of environmental sample preservation in Andra’s perennial observatory of the environment (OPE).

8. The Crucial Contribution of the URL to Public Information and Participation and to Building Confidence in the Cigéo Project

The HLW management program defined by law in 1991 puts the exchanges with the public and the involvement of the stakeholders at the very heart of the project. Two more laws were voted in 2006 [16] and 2016 [17] to progressively define the conditions of authorization and of continuation of the Cigéo project. These laws were voted after two National public debates (2005 and 2013) that gathered hundreds of public interventions and written contributions. The latest public debate on the National plan for the management of radioactive material and waste organized in 2019–2020 was again the occasion for exchanges on the Cigéo project at the National level.

The development of the project on-site was accompanied by several public enquiries. The first one was held in 1997 prior to the confirmation of the site. A second one was held in 2011 for the renewal of the license of the URL. The latest was held in 2021–2022 after which the government declared the Cigéo project of National public interest.

On a practical basis and within the limits of its own responsibilities and regulatory duties, Andra conducts exchanges with the public and stakeholders prior to every decision and major orientations of the project (for example prior decisions on the location of Cigéo’s underground and surface infrastructure or on the preferential transport routes to the facility). These exchanges may cover various forms: from basic information meetings, events or distribution of publications, up to surveys, questionnaires and participative work-gatherings on specific subjects. In 2021, a citizen’s conference was organized before Andra produced its propositions in terms of governance of Cigéo. As much as possible, the concerns and recommendations of the public and stakeholders are introduced in the project. Andra always publicly explains why it may not follow some recommendations originating from the public.

Andra also communicates regularly with the local information commission (CLIS) and answers every question asked. To illustrate its transparency, Andra organizes visits of the URL for all stakeholders and “open-door week-ends” where the public may visit its installations and get a better knowledge on the URL, the Cigéo project and the management of HLW. In 2022 the URL received around 7,000 visitors.

The years of exchanges at the national and local levels, the broad information provided and the transparency and openness promoted by Andra for the URL have contributed to build understanding and confidence in the HLW waste management project. They were crucial to preserve, comfort and expand the socio-political support to the DGR project Cigéo.

9. Conclusion

Since 1991, the French program for the safe management of the high-level waste (HLW) and intermediate level waste (ILW-LL) has been going forward under the scrutiny of the Parliament. A comprehensive gradual R&D program, phased and organized in coherence with the regulatory and design processes, was run by Andra in the URL and in surface laboratories, in collaboration with National and International partners. This program provided the scientific and technological base for the decisions to go forward with the program.

After more than 30 years of research and development, Andra completed the license application for the construction of the deep geological facility Cigéo and submitted it to the government in January 2023. The authorization to initiate the construction of the nuclear facility could be granted by 2027. From the French experience, the main drivers for the development of a deep geological facility are: the gathering of sound science and technical knowledge, the priority given to safety and security at all stages of the project, the protection of the environment and the definition of a transparent and open democratic decision process.