1. Introduction

Due to their radioactivity and content of hazardous substances, high-level radioactive waste (HLW) and spent nuclear fuel (SNF) generate very long-lasting risks for human health and the environment. Deep geological disposal is internationally advocated as the reference solution for the safe long-term management of HLW and SNF [1, 2]. According to the Nuclear Energy Agency (NEA), “deep geologic disposal is the most appropriate” of the various options considered [3]. For European countries, a Directive provides a common framework to establish and maintain National programs for the safe management of HLW and SNF including interim storage and disposal facilities [4]. According to the Directive, “spent fuel can be regarded either as a valuable resource that may be reprocessed or as radioactive waste that is destined for direct disposal. Whatever option is chosen, the disposal of high-level waste, separated at reprocessing, or of spent fuel regarded as waste should be considered”.

Research and studies into the geological disposal of HLW and SNF has been under way for several decades around the world. Many countries have constructed and operated underground research laboratories (URL) to characterize potential host-rocks and to establish the feasibility of disposal [5, 6].

However, practical experience of underground disposal has remained limited to the sub-surface disposal of low and intermediate short-lived radioactive waste (L-ILW) and to deep disposal of intermediate level transuranic radioactive waste (TRU). Low and intermediate level radioactive waste (LILW) is commonly disposed of in Granite sub-surface caverns and silos, for example in Finland (VLJ cave, Olkiluoto and Loviisa), Sweden (SFR, Forsmark) and Korea (Underground Silos, Gyeongju-si).

As a matter of fact, the successful development of a deep geological repository (DGR) is highly dependent on the process of choosing the appropriate location for such a facility. The site selection process is the essential step without which the technical development of a long-term management solution for HLW and SNF remains limited to generic and conceptual studies.

Four European countries (Finland, Sweden, France and Switzerland) have successfully passed this important milestone and are making progress in the pursuit and finalization of their respective National HLW and SNF management programs. Recently, Canada also chose a site for its deep geological repository (Wabigoon Lake Ojibway Nation was chosen the 28th of November 2024). Other countries, for example Germany or England, have started geological surveys and preliminary sitting process for their DGR projects.

The present article aims at presenting synthetically the respective national nuclear industrial contexts, main features, status and development process of the HLW management programs run by Finland, Sweden, France and Switzerland, as well as the global methodology used for selecting a site for the repository. It shows that a variety of technical solutions and organization, respectful of each country practice and choices, may contribute to the common goal of securing HLW over the long term, for the benefit of human health and the environment [7].

For the development of their respective DGR projects, Posiva, SKB, Andra and Nagra launched and finalized extensive R&D programs. Studies and collaborations were carried out with multiple universities and research centers, for example on fuel waste types, bentonite, seismology, geosphere and biosphere evolutions, transport and accumulation… These programs cannot be detailled in the present article.

2. Finland

2.1 Finnish National Context and Program Organization

Finland operates 5 nuclear reactors on two nuclear power plant (NPP) sites (Olkiluoto and Loviisa host the Finnish nuclear electricity generating reactors). The Finnish reactor fleet includes Olkiluoto-3, Europe’s most powerful reactor by production capacity (1.6 Gigawatt EPR type reactor). Except for some uranium mining, Finland has no other industrial nuclear capacities (the national contexts reported in the present article do not address research facilities or nuclear reactor prototypes, but only energy generating reactors and fuel cycle facilities). All nuclear fuel is imported [8].

Finland’s energy policy may be considered as nuclear oriented [9]. Finnish nuclear electricity producers currently investigate the possibility of further extending the operating lifespan of their existing reactors and examine the conditions for the construction of new nuclear power plants (in 2023, Loviisa NPP was granted an extension of the operating license until 2050).

Since 1994, the Nuclear Energy Act establishes that “Nuclear waste generated in connection with or as a result of use of nuclear energy in Finland shall be handled, stored and permanently disposed of in Finland”. In 2000, the Finnish Government made a “Decision in Principle” according to which geological disposal “was the most realistic possibility” to isolate high-level waste from the biosphere and human habitat [10]. That decision was ratified by the Parliament in 2001 [11].

In 1995, following the Nuclear Energy Act, the two nuclear electricity producers Teollisuuden Voima Oyj (TVO) and Fortum Power and Heat Oy (Fortum) created Posiva as a joint venture. As a private company, Posiva holds the mission to develop disposal solutions for the spent nuclear fuel produced by its owners (the other types of radioactive waste, are managed directly on site by each operator).

Posiva is the operator in charge of implementing the Finnish DGR program. Posiva is based in Eurajoki and has around 90 employees. Posiva does not yet operate a nuclear facility.

2.2 Location and Main Technical Features of the Finnish DGR Project

Posiva’s spent nuclear fuel management program includes an encapsulation plant, where the SNF is introduced in a canister prior to its disposal, and the DGR facility Onkalo. Both facilities are located on Olkiluoto, a small island located around 250 km from Helsinki, in the South-West of Finland, in the Gulf of Botnia.

Olkiluoto’s island also accommodates an existing nuclear site operated by TVO with three electricity generating reactors. This nuclear site already holds some essential management tools for the management of radioactive waste (a low and intermediate disposal facility and interim storage facilities for TVO’s SNF).

In the encapsulation plant, the SNF assemblies are placed in the cast iron inner structure of the canister which is filled with Argon and sealed with an iron lid. The inner structure is covered with a 5 cm thick copper shell designed to provide long-lasting corrosion protection (see Fig. 1). SNF stored in Olkiluoto will be transferred to the encapsulation plant in a standard cask on a trailer (2 km). SNF stored in Loviisa will be transported either by road or sea (300 km).

After the top copper lid has been friction stir welded to the body of the canister, the sealed canister is transferred down to the disposal level with a lift. The encapsulation plant is located above the DGR and directly connected to its canister shaft.

Onkalo’s underground infrastructures consist of a spiral-shaped access ramp, four vertical shafts (one for personnel, one for the canisters, two for ventilation) and horizontal galleries leading to vertical deposition holes (see Fig. 2). The disposal level is constructed at a depth of about 400 m.

Onkalo is constructed in crystalline bedrock, which constitutes the majority of the Finnish bedrock, one of the oldest in the world [12]. All shafts were constructed by raised boring techniques, while galleries were excavated by drill and blast techniques and the deposition holes by drilling.

The Finnish disposal concept is based on the KBS-3V developed together with the Swedish company SKB. A single disposal canister (1.05 m of diameter) is placed in a vertical deposition hole (around 8 m deep and 1.75 m of diameter) by an autonomous vehicle. The “canister transfer and installation vehicle” transports the canister in the galleries (around 4 m high and around 3.5 m wide) and places them in the vertical deposition holes by lowering them in the center of the pre-installed buffer blocks.

Buffer blocks containing bentonite are positioned around the canisters and the remaining empty spaces are filled with fine-grained bentonite to seal the buffer. Then the deposition holes are filled, and the disposal tunnel is backfilled with a granule mixture of bentonite containing pellets (see Fig. 3).

Posiva has designed Onkalo for about 6,500 tons of SNF (about 3,250 canisters) [13]. As final disposal progresses, the repository will be expanded by excavating more galleries and deposition tunnels. Disposal operations are estimated to be carried out until around 2120.

2.3 Status of the Finnish DGR Program

Finland has, without any possible contest, the most advanced DGR project in the world.

The national site selection program was launched in 1983. The site of Olkiluoto was selected by Posiva in 1999 and confirmed by the local municipality in 2000.

Posiva applied for the construction license of Onkalo in 2012 and was granted this authorization in 2015. Posiva submitted the operating license application of the DGR in December 2021 (see Fig. 4).

The Finnish DGR’s construction is almost finished and it’s commissioning is considered to be more than 80% completed.

Posiva is getting ready to launch the trial run. Nominal industrial disposal of SNF may then be authorized by be Finnish Safety Authority in 2025. Onkalo would be the world’s first deep geological disposal facility for high-level waste to start operation.

2.4 Development of the Finnish DGR Program

Interestingly, Posiva could not count on a national URL to develop its facility. Finland first developed its disposal concepts while collaborating with international partners and contributing to international studies, for example in the Swedish URL in Aspö and the Swiss URL in Grimsel.

Finland then confirmed the suitability of the Olkiluoto bedrock and finalized the design of the DGR on site, during the initial phase of the construction program of the DGR (Onkalo’s construction started in June 2004). As a matter of fact, Onkalo was primarily an underground research and development facility in its initial construction phase. From the beginning, it had strategically been designed in such a way that it may be upgraded into a nuclear disposal facility provided its results were to be found positive. Hence, it was gradually developed by Posiva to carry out characterizations, full-scale experiments, final technological qualifications and nuclear operations. This approach of on-going upgrade and optimization surely played an important role in the successful development of Onkalo and contributed to Finland’s leading position in the field of DGR programs.

3. Sweden

3.1 Swedish National Context and Program Organization

Sweden operates 6 electricity generating nuclear reactors on three different sites (Forsmark, Oskarshamn and Ringhals host the Swedish electricity generating nuclear reactors). Sweden has no uranium mine, but has the capacity to produce nuclear fuel from uranium enriched in foreign countries (Westinghouse operates a fuel fabrication facility at Vasteras for 400 tons of BWR and PWR fuel per year).

Sweden once had an ambivalent relation toward nuclear energy [14]. In 1980, the Swedish government decided to phase out nuclear power, but this decision was repealed by the parliament in 2010. In June 2023 Sweden’s parliament voted to change the country’s electricity production target by 2040 from “100% renewable” to “100% fossil-free”, thus creating the conditions for the future use of nuclear power in the electricity mix. In November 2023, the Swedish government announced a roadmap to build the equivalent of two new reactors by 2035 and studies the possibility to implant further capacities by 2045.

Sweden has a long-established legal framework for the management of radioactive waste. In 1977, the “Waste legislation” requested the nuclear operators to develop a comprehensive concept for the management of their radioactive waste.

In 1977, following that act, Swedish nuclear electricity producers created Svensk Kärnbränslehantering AB (SKB) as a joint venture. SKB is currently owned by Vattenfall, Forsmarks Kraftgrupp AB, OKG Aktiebolag and Sydkraft Nuclear Power AB. As a private company, SKB holds the mission to develop disposal solutions for all the radioactive waste produced by its owners.

SKB has around 550 employees. It has offices in three locations: 1) Solna, in the northern suburb of Stockholm, where the headquarters are based, 2) Forsmark, in the municipality of Östhammar around 120 km north from Stockholm, on the coast of the Gulf of Botnia, where SKB operates SFR a disposal facility for LILW, and 3) Oskarshamn, in the south east of Sweden, around 250 km South from Stockholm, on the coast of the Baltic sea, where SKB operates the interim storage facility CLAB and its URL.

SKB is the operator in charge of implementing the Swedish DGR program. SKB already has experience managing SNF as it operates the underground interim storage facility CLAB (see Fig. 5) and a ship to transport the SNF from power plants to CLAB (M/S Sigrid) (see Fig. 6).

3.2 Location and Main Technical Features of the Swedish DGR Project

The Swedish HLW management program includes an encapsulation plant and the DGR for SNF.

The encapsulation plant will be located in Oskarshamn. The encapsulation plant will be located directly above and connected to the existing SNF interim storage facility CLAB.

The DGR is to be built on the site of Söderviken, neighboring the existing nuclear plant of Forsmark. The encapsulated SNF will be transported to the DGR by boat.

The Swedish disposal concept is similar to the Finnish one, as it was jointly developed by both countries (KBS- 3 system). The operations carried out in the encapsulation plant and DGR are of similar nature (see Figs. 1 and 3).

The planned SNF repository’s underground infrastructures consist of a spiral-shaped access ramp, three vertical shafts and horizontal galleries leading to vertical deposition holes. The disposal level is constructed at a depth of about 500 m. The disposal container will be transported to the underground disposal level on a special truck driving down the ramp (see Fig. 7).

The Swedish DGR is constructed in Granite, which constitutes the majority of the Swedish bedrock. It is designed by SKB to dispose of around 12,000 tons of SNF (6,000 canisters). Disposal operations are estimated to be carried out during a period of about 50 years.

3.3 Status of the Swedish DGR Program

The Swedish national site selection program was launched in 1995. The site of Söderviken was selected by SKB in 2009.

SKB applied for the construction license of the encapsulation plant and the DGR in 2011 [15] and received this authorization in 2022 (see Fig. 8) [16].

The 26^th of October 2024, SKB received an environmental permit to build and operate the DGR for spent nuclear fuel in Forsmark and the encapsulation plant in Oskarshamn. The judgement was issued by the Land and Environmental Court, which is also granting SKB an enforcement order to enable initial work on the Forsmark area to begin in 2025 (initial work involve tree felling, excavation for the operational area, construction of rock-storing areas, construction of a bridge, backfilling of the operational area and construction of environmental nitrogen purification facilities).

SKB expects the construction of these facilities to start around the middle of the 20’s and to last around 10 years. The Swedish repository for high-level waste, is expected to be operational around 2035.

3.4 Development of the Swedish DGR Program

For the development of its DGR project, SKB carried out large amount of R&D, amongst which specific programs were performed in the hard rock URL in Äspö (Sweden) and in the surface canister laboratory in Oskarshamn (Sweden). Äspö is located north of Oskarshamn, in the Misterhult Archipelago close to the Oskarshamn nuclear power plant.

The URL in Äspö was authorized in 1990 and commissioned in 1995. It is owned and operated by SKB. It’s implanted at almost 500 m depth in Granite. It hosted most of the Swedish and Finnish underground research programs supporting their DGR developments.

Äspö also has surface test facilities devoted to technological trials of buffer and backfill material installation. After 30 years of research, SKB intends to close the Äspö facility in 2025.

SKB’s canister laboratory is mainly used for the development of the encapsulation technology, for example the fine tuning of the copper welding technology has been developed there.

Although it is far advanced into the development of its encapsulation plant and DGR program, SKB still has an extensive R&D program in order to enable optimization. The program is updated and published on SKB’s website every third year (https://skb.se/publikation/2506485).

4. France

4.1 French National Context and Program Organization

France has one of the most developed nuclear industry in the world [17]. Nuclear energy amounts for around 75% of French electricity production. France operates fifty-six electricity generating nuclear reactors on eight-teen different sites (the site of Belleville, Bugey, Cattenom, Chinon, Chooz, Civeaux, Cruas, Dampierre, Flamanville, Golfech, Gravelines, Le Blayais, Nogent-sur-Seine, Paluel, Penly, Saint-Alban, Saint-Laurent des Eaux, Tricastin host the French electricity generating nuclear reactors). France’s fifty- seventh reactor (EPR type reactor) in Flamanville started operations on the 21st of December 2024.

France also has uranium enrichment and fuel fabrication capacities. It reprocesses spent nuclear fuel in the Orano La Hague Plant and produces Mixed Oxide fuel (MOX) from the plutonium recovered in the Orano MELOX plant in Marcoule. It has several major nuclear civil R&D centers, for example Cadarache, where the international fusion project ITER is developed, and also has military facilities (aside the eight-teen electricity producing sites, operated by EDF, twenty-three other major nuclear centers host the French civil and military nuclear activities).

The development of nuclear generated electricity is an essential part of the French energy policy. In 2023, the French government announced a road-map for the construction of six additional new reactors and for the studies of eight more [18] (in total, 14 new electricity generating reactors could potentially be built in France). In 2024, the French government confirmed that reprocessing of spent nuclear fuel would be further developed and announced an ambitious investment program for the La Hague reprocessing plant [19]. The national electricity producer EDF is pursuing studies to gradually extend the lifespan of its operating reactors (extensions from 40 to 50 years are gradually introduced. Studies are underway to evaluate the possibility to reach 60 years and more).

France legal framework for the management of HLW and intermediate-level long lived waste (IL-LLW) was set by the parliament in 1991 [20]. It was then gradually deepened and extended by to new laws in 2006 [21] and 2016 [22], that respectively defined the conditions for licensing and starting the operation of a future DGR, considered as the reference option for the long-term management of French HLW. The French legal framework imposes that disposal of HLW and of IL-LLW might be reversible for at least 100 years.

Andra, the national agency for the management of French radioactive waste was created by law in 1991. Andra is a public body, fully independent from radioactive waste producers. Andra’s missions are defined by law. They comprise the task of developing, designing, building and operating disposal facilities for all French radioactive waste.

Andra is based in Châtenay-Malabry, in the southern suburb of Paris, and has around 750 employees. Andra operates a land-filled disposal facility for very low-level radioactive waste (CIRES) and a surface disposal facility for low and intermediate level short-lived radioactive waste (CSA). Both are located in the Aube department, around 175 km east from Paris. Andra is also responsible for operating and monitoring the surface disposal facility neighboring the La Hague plant (CSM).

CSM is not receiving radioactive waste anymore. It closed and is currently in the gradual process of entering its surveillance phase.

4.2 Location and Main Technical Features of the French DGR Project Cigéo

The French DGR project is named Cigéo. It is located in Bure and Saudron, two small communities located around 200 km east from Paris. Its environment is very rural, with no pre-existing nuclear, nor major industrial activities.

Cigéo is designed to dispose of both HLW and intermediate- level long lived waste (IL-LLW) (see Fig. 9). As France has a national policy of reprocessing its SNF, French HLW comes in the form of vitrified waste. Due to its large nuclear industry, French IL-LLW comes in various nature and type of container (cemented, compacted, bituminized…). All HLW and IL-LLW are conditioned in the form of solid waste packages at their initial production sites prior to their shipment to Cigéo.

The waste packages will be shipped to Cigéo by train.

The French disposal center Cigéo consists of surface facilities and underground infrastructures (Fig. 10).

The surface facilities are regrouped on two main surface zones. Their main functions are respectively: 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.

If necessary, preparation for disposal of the waste packages may include the addition of an overpack. The vitrified HLW packages will be introduced into a welded carbon steel disposal overpack. The IL-LLW may be placed into a concrete disposal overpack or in a steel handling basket. These overpacking operations will be carried out by Andra in Cigéo’s surface facilities.

Cigéo’s surface infrastructures also include a private rail track connecting Cigéo to the public rail network and a private road linking the two main surface zones.

To enable Cigéo’s construction and operation, an additional program of site preparation works will be carried out by the relevant operators (water and electricity supplies, public road and public rail network modifications).

Cigéo’s underground infrastructures consist of two linear access ramps, five vertical shafts and horizontal galleries leading to horizontal disposal tunnels [23].

From the surface, the waste containers are transported to the disposal level with a funicular operating in one of the two ramps. They are brought to their disposal positions by automated vehicles and handling tools on rails.

For their disposal (see Fig. 11), HLW disposal containers are introduced in steel coated horizontal micro-tunnels (from 80 to 150 m long, around 0.8 m of diameter), when ILW-LL packages are introduced in concrete tunnels (up to 500 m long, around 10 m of diameter).

HLW and ILW-LL disposal tunnels (also called disposal vaults) are regrouped in distinct separated disposal zones.

The disposal level is constructed at a depth of about 500 m in Callovo-Oxfordian Clay. The thickness of the clay layer is of at least 120 m on site. This rock’s main feature is the ability to confine radionuclides through sorption phenomena and through very slow transport by diffusion processes.

Cigéo is designed to dispose of 10,000 m³ of HLW and of 73,000 m³ of ILW-LL. As final disposal progresses, the repository will be expanded by excavating more galleries and deposition tunnels. Disposal operations are estimated to be carried out until around 2150.

4.3 Status of the French DGR Program

The French national program for the management of HLW was launched in 1991. The site of Bure was gradually selected for implanting a URL (1998), for determining a transposition area around the URL (2005) and for carrying out detailed geological investigation in view of a DGR (2009) (in 2009, an underground rock volume, deemed of suitable size and properties for hosting a DGR, was selected for detailed characterization).

The underground and surface sites were confirmed after a public debate on the Cigéo project in 2014 (see Fig. 12). In 2022, on the basis of an assessment process that included a public enquiry, the French government announced that Cigéo was to be considered a project of national interest and signed a Decree declaring its “Public convenience and necessity”. Andra applied for the construction license of Cigéo in 2023.

Andra is currently in the process of obtaining the construction authorization for Cigéo. The project is being reviewed by the French safety authority and other stakeholders according to a process defined by law.

Andra expects the construction of the nuclear facility to start after its authorization is granted around 2027−2028. Cigéo is expected to be operational around 2040.

Interestingly, Cigéo’s operations will start with an industrial pilot phase. On the basis of the feedbacks and lessons learned during construction and during a few years of HLW disposal operations, the parliament will decide on the conditions for the potential continuation of disposal.

4.4 Development Process of the French DGR Program

France has a diverse geology were many different natures of rocks can be found. France chose to build Cigéo in Callovo-Oxfordian Clay after carrying out a national siting and development process designed by law. This legal process included the mandatory construction and the operation of a URL for the characterization of the DGR’s host-rock [24].

Andra has carried out its main R&D programs for Cigéo in the URL of Bure (France). This URL was authorized in 1999. Its construction started in 2000 and it was commissioned in 2004. It is owned and operated by Andra. It is located at around 500 m in Callovo-Oxfordian Clay.

The URL of Bure currently comprises around 2 km of galleries where experiments and technological tests are carried out. Around 1,000 boreholes enable samplings or implantation of various sensors and surveillance devices.

Andra also carried out research and technological developments in surface facilities, for example it tested a fullsize mock-up of the funicular near Bure [25].

5. Switzerland

5.1 Swiss National Context and Program Organization

Switzerland is the latest European country to have decided on the location of its future facilities for its national HLW management program, including its future DGR.

Switzerland operates four reactors on three nuclear sites (Gösgen, Leibstadt and Beznau host the Swiss electricity generating nuclear reactors). Swiss has no active uranium mine or other nuclear industrial activities (CERN and PSI are research facilities). All nuclear fuel is imported [26].

Switzerland is gradually phasing out nuclear power and has not been recently inclined to change this energy policy. In 2011, the government and the parliament resolved that the Swiss nuclear reactors would not be replaced. This decision was confirmed by referendum in 2017. The existing reactors may remain in operation as long as the Swiss safety authority considers them safe.

The Swiss nuclear energy act stipulates that “any person who operates a nuclear installation is obliged to safely manage all radioactive waste arising from that installation” [27]. In 1972, all Swiss radioactive waste producers founded Nagra (“Nationale Genossenschaft für die Lagerung radioaktiver Abfälle” in German).

Nagra is founded mostly by nuclear plants operators and, for a few percent of its budget, by the Swiss federal government who is responsible for the research, technical and medical radioactive waste. As a cooperative company, Nagra is responsible for the development of disposal solutions for all Swiss radioactive waste.

Nagra is based in Wettingen (Canton of Aargau) near Zürich, and has around 130 staff. Nagra does not yet operate a nuclear facility.

5.2 Location and Main Technical Features of the Swiss DGR Project

The Swiss DGR project is designed to dispose of all Swiss waste, including low and intermediate level waste (LILW) and HLW. Swiss HLW inventory holds both SNF and vitrified waste, as Switzerland had its SNF partly reprocessed abroad through commercial contracts.

The Swiss HLW management program includes an encapsulation plant and a DGR. Nagra is currently carrying out the conceptual design studies of these two facilities.

At the encapsulation plant, the waste will be conditioned and prepared for transport and disposal. No decision has yet been taken by Nagra concerning the definitive design of the disposal containers. The encapsulation plant for the Swiss waste is to be constructed in Würenlingen, around 30 km North-West from Zürich, at the site of the Swiss interim storage facility ZWILAG. This site already hosts the competence center for the conditioning and packaging of radioactive waste and a conditioning facility for LILW.

The Swiss DGR will be located in the region of Nördlich Lägern in the community of Stadel, in the Haberstal area, around 20 km north from Zürich. The Swiss DGR consists of surface facilities and underground infrastructures (see Fig. 13).

The surface infrastructures are composed of a main surface facility that serves as main gateway to the DGR and of an auxiliary access to the underground disposal level. Surface facilities will also comprise various site development infrastructures and landfills for the materials arising from the excavation process.

The underground facility is composed of vertical shafts for construction, waste transfer, personal access and ventilation and of two separated zones for the disposal of HLW and LILW.

The disposal concept envisaged by Nagra is to emplace the canisters containing the SNF and the HLW in horizontal underground tunnels which are subsequently backfilled with bentonite clay (see Fig. 14).

The Swiss DGR will be constructed in Opalinus Clay, an over consolidated shale sediment with properties equivalent to those of the French Callovo-Oxfordian Clay in terms of radionuclide confinement. A very important feature of the Nördlich Lägern site is the thickness of its Opalinus Clay formation of around 110 m at the potential disposal depth of around 900–1,000 m below ground level.

The Swiss DGR is designed to host around 82,000 m³ of conditioned waste (around 10% HLW, around 90% LILW) [28]. Nagra estimates that the Swiss DGR will be operated until around 2125.

5.3 Status of the Swiss DGR Program

The Swiss national program for the siting of the Swiss DGR was launched in 2004 and started in 2008 [29]. The site of Nördlich Lägern was proposed by Nagra in 2022 after a gradual selection program that first narrowed down the number of potential sites from all of Switzerland, to six and then to three sites (the three selected sites that were compared in the final selection process were the region of Jura Ost, Zürich Nordost and Nördlich Lägern). A DGR would have been feasible in all of these three particular sites, but Nördlich Lägern was chosen because its geology offers better confinement, stability and flexibility for the layout of the underground repository.

Nagra is currently in the process of producing the two general license applications with all supporting documents to obtain the general authorization for the location of the DGR and of the encapsulation plant (see Fig. 15). In June 2024, Nagra founded two dedicated subsidiaries to conduct the construction and operation respectively of the deep geological repository (Nagra gTL AG) and of the encapsulation plant (Nagra BEVA AG).

The 19^th of November 2024, Nagra submitted the general license application for the DGR and for the encapsulation plant. The approval decision will be made by the federal council and the federal parliament. A referendum is not a legal obligation to authorize the DGR and the encapsulation plant, however there is a possibility that one may be called and would become legally binding.

According to the current planning, the federal council will decide on the DGR application in 2029 and parliament in 2030. If a national referendum takes place, it could be in 2031. Nagra expects the first initial construction work to start a few years later (geological investigations). The first disposal operation of ILW should start around 2050 and those of HLW around 2060.

5.4 Development Process of the Swiss DGR Program

In general, Switzerland has a very diverse and complex geology (in opposition, the region of Nördlich Lägern proposed by Nagra, has a relatively simpler geology). Its main feature is the geo-mechanical perturbations and folding linked with the surrection and uprise of the Alps that began forming only 10 million years ago.

To carry out its R&D programs, Nagra could count on two main URL: the Grimsel Test Site and the Mont-Terri Project.

The Grimsel Test Site was established in 1984 [30]. It is located in the granitic formations of the Aar Massif at a depth of around 450 metres, in the community of Guttannen. It is operated by Nagra. The laboratory itself is around one kilometer long. It is a derivation from the access tunnel of the Oberhasli AG hydropower plant (KWO). One of its remarkable features is that it may be used to directly study the transport mechanisms of radioactive substances through the rock.

The laboratory in the Mont-Terri tunnel was established in 1996 [31]. It is located in the Opalinus Clay formation of the “Falten Jura”, at a depth of around 300 m, in the community of St-Ursanne. It is operated by Swisstopo. The laboratory is around 1.2 km long. It is a derivation from a safety gallery of motorway tunnel.

6. An Essential Technical and Practical Issue for All High-Level Waste Management Programs: The Selection and Confirmation of a Suitable Site for the Deep Geological Repository

6.1 Importance and Role of the Host-Rock for a DGR

Geological disposal’s fundamental objective is to protect human health and the environment from the very longlasting hazards generated by high-level radioactive waste. It involves containing and isolating radioactive waste from the biosphere for very long period of times (exceeding several tens of thousands of years).

For the purpose of containment of the radionuclides present in the radioactive waste, the safety of the DGR is based on the concept of intersecting a series of barriers between the harmful radionuclides and the biosphere (i.e. the waste form itself; the waste packaging and containers; the engineered barriers such as backfill material and civil engineered structures; the host geology) [32]. Each barrier plays its particular role and participates in the safety functions of the facility. They may be effective over different timescales. The barriers are independent and complementary so that the potential failure of one of them does not jeopardize the safety of the entire facility [1]. The host-rock participates to the containment by providing a geothermal, chemical, mechanical and hydrological environment that favors package and engineered barriers integrity and performance over tens of thousands of years. Over a very longtime period, the man-made waste package and engineered barrier will eventually degrade and radionuclides may be released deep in the geosphere. At this point in the future, the host-rock hydrogeologic properties will still participate in the containment of radionuclides. It may provide an environment that limits their solubility and that minimizes their mobility through pores and fractures by reducing the inflow of groundwater at the contact of the waste and out of the disposal system (e.g. low permeability formations, low hydraulic gradients, dispersion, retardation, precipitation properties).

The long-term isolation of the high-level radioactive waste relies on the characteristics of the host-rock. Its depth ensures that the waste is distant enough from the biosphere so that humans and living entities are not at risk to be exposed to dangerous level of radiations in normal or accidental situations. It also ensures that the disposal system itself cannot be altered by external events happening at surface (glaciations, drought, tornados, flooding, wars or social unrests). Isolation is also provided by the capacity of the host-rock to ensure that, when released, the radionuclides originating from the waste remain either trapped within the geosphere, or migrate and reach the biosphere in concentrations low enough to remain harmless to human health and the environment (concentrations of radionuclides in groundwater naturally decrease with the radioactive decay associated with slow transfers and with the dilution and spread linked with the long transport distances).

As the consequence of these essential roles played by the host-rock in the long-term safety of the DGR, the identification of a suitable and adapted geological site is one of the most important choices faced by any high-level waste management program.

6.2 The Site Selection Criteria

The process of site selection aims at progressively winnowing down the number of potential locations to identify, evaluate and finally choose a site for the DGR that may be both technically suitable and socially acceptable.

The site selection process usually comprises screening analyses of the entire national territory through a set of technical criteria reflecting the favorable characteristics and long-term stability properties of the geological environment sought for the place of implantation of a safe DGR. These criteria may be stipulated by national authorities and be validated by regulators, i.e. in the form of guidelines. They should aim at identifying a volume of rock that notably:

Consistently with internationally accepted strategies, approach to ensure an informed and willing host territory (municipality, district or region) should be implemented in parallel to the scientific and technological programs. One of the most essential criteria for the siting of the DGR may be to identify a community that steadily accepts to host the project (e.g. a community that participated in an open candidacy process). Addressing the needs and constraints of these local community at each step of the DGR development process is essential to improve the program and secure its advances [33]. In this respect, different countries may pursue different paths an use different tools for the consultations of the public, for example ratification votes by collectivities, national debates or public enquiries.

6.3 The Site Selection Process

The site selection procedure is typically designed to be phased and iterative. It comprises several steps of early comprehensive literature surveys, after which several other steps of preliminary investigations and then detailed investigations may be launched. It is carried out in parallel to the development of the disposal concepts and technologies necessary for the disposal (containers, engineered barriers, handling and disposal machinery, seals for closure, global architectures, boring and monitoring devices, underground construction techniques…) and to the progressive consolidation of the disposal safety demonstration (operational safety, long-term safety, risk analysis, evaluation of scenarios, production of the safety case documentation…).

For Finland, Sweden, France, and Switzerland, the research and development programs run in underground research laboratories (URLs) have been essential to the characterization of the chosen host-rocks and for the development of disposal technologies. As seen in Finland during the construction of Onkalo, a dedicated program of detailed rock characterization during the construction of the facility may confirm the data used for the safety demonstration and provide opportunities for optimizations in the design.

In order to progressively feed the DGR design and safety studies, an appropriate and increasing level of knowledge of the geological setting and of its should be acquired and assembled. This comprehensive set of technical and geological data includes notably local and regional structural and stratigraphic data of the rocks, sediments and soils and the understanding of their chemical, physical, mechanical, thermal and hydraulic properties and evolutions. These will be by obtained by a an increasingly thorough program of paper work, laboratory analysis of samples, and field investigation campaigns. The latter notably comprise 2D seismic and then high-resolution 3D seismic survey (see Fig. 16) as well as drilling and geophysical borehole measurements [34, 35]. The production of 3D numerical models for the simulation of solute, gas and heat transport from the nearfield to the far-field allows for the safety assessment of the facility using quantitative performance indices [36]. Comprehensive pluri-annual field surveys may substantiate the environmental impact studies and provide decisive information for the design and positioning of the surface facilities, as well as for the preparation and monitoring of the environmental protection provisions.

The site selection process moves forward from one step to the next, after global technical evaluations, safety assessment by the regulators and socio-political decisions by the Authorities involving stakeholders’ consultations. At each stage of the process, the technical and socio-economical site selection criteria are used to confirm the appropriateness of the future site. The outcomes of each stage feed and determine the program of the next phase. For Finland, Sweden, France, and Switzerland, the national laws and regulations structure the siting process notably by identifying the progressive decision points and the process for moving from one stage to the next.

6.4 The Long Duration of the Site Selection and Confirmation Process

Not surprisingly, the activity of choosing a site for a DGR is a demanding and challenging activity for any HLW management program. As stated by a report to the American congress in 2015, selecting a site for a DGR “is an archetypical example of what social scientists call a messy problem” [37]. The complexity comes notably from the technical and societal uncertainties associated with the length of time needed to develop, operate and close such facilities (around a century and more), from the debates and conflicts that may arise over the justification of projects designed to reach their objectives in a far future, from the numerous interested parties at the national and local levels. Additionally, the sociopolitical decisions for siting and developing a DGR are generally governed by an imbricated set of laws and regulatory requirements yielding unusually complicated administrative procedures (environmental protection, land use including underground, nuclear safety, planning and construction permitting, accessibility of administrative documents, participation of stakeholders…).

As stated in the preceding chapters, Finland, Sweden, France, and Switzerland took decades to choose the right geological settings for their DGR [38] (they actively started their HLW management programs in the 80’s or 90’s, but some of the first geological surveys had already been launched in the 70’s). Regardless to their different national natural environments, cultural backgrounds and regulatory systems, the main common reasons for the success of their programs are 1) the cautious and very detailed technical investigations and studies that were carried out to first identify, select and then fully characterize a suitable site for their repository and 2) the scrupulous respect of the progressive decision-making process defined by their respective legal frameworks, including iterative assessment of the program results and the engagement of communities and stakeholders.

7. Conclusion

Finland, Sweden, France, and Switzerland share the same fundamental objectives of short and long-term protection of human health and the environment. Regardless to the differences in their respective waste management policies, inventories and national energy context, they are steadily pushing forward their respective long-term management programs to secure their HLW and SNF.

Differences can be observed in the type of rocks that these countries have chosen for their respective DGR, in the technical features or their facilities and in the development processes that they follow. These differences show that several development paths, technological solutions and organizational strategies are possible for HLW and SNF management projects.

The Finnish, Swedish, French, and Swiss projects have different state of development. These are the result of each country’s waste inventory, geology, legal framework, social environment and industrial development practice. In this respect, on a technical point of view, every DGR may remain a “one-of-a-kind” industrial project.

However, the Finnish, Swedish, French, and Swiss DGR projects also share common features that contribute to the success of these multi-decade long endeavors:

These common key-features may be inspirational for any country engaging in the development of its own national HLW management solution.