CNSC research on geological repositories

As the Canadian nuclear regulator, the Canadian Nuclear Safety Commission (CNSC) is responsible for licensing geologic repositories intended to provide for the long-term management of radioactive waste.

• Background on geological repositories
• CNSC regulatory research
• Research results
• Research in other countries New
• Participation in international projects
• Published regulatory research on geological disposal of radioactive waste

Schematic of the OPG DGR project

CNSC regulatory research

Since 1978, the CNSC has been involved in independent and internationally collaborative research focusing on long-term safety issues related to the disposal of radioactive waste and used nuclear fuel in both crystalline and sedimentary rock formations. Geological repositories rely on multiple barriers (for example, the waste form, container, engineered seals, and host rock) for the long-term containment and isolation of radioactive waste. Therefore, the CNSC’s research program looks at the long-term performance of those barriers.

In Canada, used nuclear fuel is currently safely stored in interim storage facilities.

This research program consists of independent scientific research conducted by CNSC staff in collaboration with national and international institutions, such as Canadian universities, the BGR (German Geological Survey), IRSN (Institut de Radioprotection et Sûreté Nucléaire, France) and CANMET (Canada Centre for Mineral and Energy Technology). This collaboration has provided CNSC staff with invaluable experimental data obtained from laboratory and field tests that are used in the development and validation of mathematical models.

It also includes the monitoring and critical review of state-of-the-art scientific advancements and staff participation in international forums to exchange information about geological repositories.

The program helps in the development and update of regulatory documents that form the basis for CNSC staff recommendations to the Commission on geological repositories for radioactive waste.

The CNSC’s research is not meant to duplicate research done by the project applicant, but rather to identify gaps in information, and to verify key safety aspects related to geological repositories.

Technical reports resulting from the Nuclear Waste Management Organization’s research activities are available on their website. Research from other countries, which focus either on sedimentary rocks (France) or crystalline rocks (Finland, Sweden), are also described on their respective websites.

Core sample room

Research results

View the CNSC timeline: “The science behind safe nuclear waste disposal: decades of research” New Printable version

Research activities from 1978 to 1996 focused on the suitability of granitic Canadian Shield rocks to host this type of repository.

Research activities from 1996 to 2008 continued on granitic rock, with the addition of projects on the long-term performance of engineered seals.

Research activities from 2009 to the present expanded to include an understanding of the potential for a geological repository within sedimentary rock, so that CNSC staff are prepared to assess any future proposal involving geological repositories in either rock type. The current research projects also look at waste characteristics and engineered barriers (in particular the sealing materials). Natural analogues are natural examples of materials found in or processes caused by geological repositories. High-grade uranium deposits such as Cigar Lake are examples of natural analogues; they prove that radionuclides can be contained within favourable geological formations for up to billions of years. CNSC staff are also currently performing research on natural analogues.

The results of CNSC’s regulatory research program have been published in peer-reviewed journal papers, reports, conference abstracts and papers, and workshops.

Future research projects will focus on waste characteristics, engineered barriers (in particular the sealing material), and geosphere issues.

The CNSC will continue to collaborate with the BGR, the IRSN, CANMET, and Canadian universities carrying out experimental and theoretical research on the performance of engineered and natural barriers.

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Grimsel Test Site, underground research and development URL, Switzerland

Research in other countries

France

In 1991, the Government of France conferred to the French national radioactive waste management agency (ANDRA) the mission to assess the feasibility of deep geological disposal of high-level, long-lived radioactive wastes. ANDRA performed feasibility studies in both crystalline and sedimentary rock formations, with major effort spent on the latter. Since 1994, ANDRA has characterized the Meuse-Haute Marne sedimentary formations by completing deep boreholes and creating an underground research laboratory in these formations. In addition to in situ and laboratory experiments, hundreds of kilometres of seismic survey lines were also performed.

These research activities have provided ANDRA with enough information to submit the “Dossier Argile 2005”, a safety case that provides evidence on the feasibility of disposal of high-level and long-lived radioactive waste in argillaceous sedimentary rocks at the Meuse-Haute Marne site. The ”Dossier Argile 2005” was  assessed by the Autorité de Sûreté Nucléaire and the National Review Board, and reviewed by international experts.The Institut de Radioprotection et de Sûreté Nucléaire also performed the technical review of the safety case. In preparation for this review, the IRSN has maintained very close oversight of ANDRA’s publications and reports throughout the years, as well as conducted independent geoscientific research at its own URL at the Tournemire site.

Sweden

In 2011, the Swedish Nuclear Fuel and Waste Management Company (SKB) submitted an application to the Swedish government for the construction of a DGR and an encapsulation plant at the Forsmark site in Oskarshamn. Through this project, the SKB would manage the final disposal of Sweden’s used nuclear fuel in crystalline rocks. The application material contains an environmental impact statement and a long-term safety case. The application is supported by more than three decades of research performed by SKB on scientific, technological and social aspects. All relevant information resulting from that research is summarized or provided as reference material in the application. SKB’s ongoing scientific and technological research is conducted at three laboratories: the Äspö Hard Rock Laboratory, the Bentonite Laboratory and the Canister Laboratory.

Finland

In 2012, Posiva submitted a construction licence application for a DGR and surface encapsulation facility at Olkiluoto, Finland, to the Radiation and Nuclear Safety Authority (STUK) for the disposal of used nuclear fuel in crystalline rocks. The construction licence was granted in 2015. A safety case was submitted in support of the construction licence application. The safety case is a suite of documents that provides multiple lines of evidence on the safety of the DGR during operations and hundreds of thousands to millions of years after closure. Those lines of evidence are the outcomes of more than forty years of research performed by Posiva on the host rock, bentonite seals and copper canisters.

Participation in international projects

Participation in international projects allows staff to maintain their knowledge and competence by keeping up to date with international state-of-the-art science, practices and regulations.

It increases the CNSC’s visibility, since CNSC staff contribute actively to those projects by sharing their knowledge, acting as team leaders, and by contributing to the writing and/or peer review of project documents.

Below are brief descriptions of international projects in which CNSC staff have participated.

IGSC (Integration Group for the Safety Case)
The IGSC is the main technical advisory body to the Nuclear Energy Agency (NEA) Radioactive Waste Management Committee on the deep geological disposal of long-lived and high-level radioactive waste. The objective of the IGSC is to monitor scientific advancements related to developing a safety case. The IGSC organizes annual plenary and specialized workshops on specific subjects (e.g., gas generation and migration, monitoring for the performance of a repository). CNSC staff contribute actively by giving presentations and discussions on specific subjects.

SITEX (Sustainable network of independent technical expertise for radioactive waste disposal)
SITEX is a project within the Seventh Framework Program of the European Atomic Energy Community (Euratom). The objective of SITEX is to establish a sustainable network of technical support organizations and regulatory bodies with the goal of harmonizing European and international approaches to reviewing safety cases. The CNSC participates in working groups looking at the development of guidance documents, regulatory research and planning for the review of safety cases.

DECOVALEX
DECOVALEX, an international project that started in the early 1990s, compares modelling results for the performance of seals and host rocks using experimental data from underground research laboratories and other experimental facilities. The CNSC has been an active participant in DECOVALEX since its beginning.

GEOSAF – International Project on Demonstrating the Safety of Geological Disposal
The GEOSAF project was initiated in 2008 by the IAEA with the objective of harmonizing approaches for preparing a safety case with a special emphasis on the expectations of regulator authorities with respect to the development of the safety case. GEOSAF provides a forum to exchange ideas and experience in developing and reviewing the safety case. Through GEOSAF, the CNSC contributes to the development and finalization of IAEA guidance documents on radioactive waste safety.

Underground Research Facilities (URF) Network for Geological Disposal
This IAEA program provides an overview and general update of experimental programs in all URFs that are part of the network at annual network meetings. The CNSC contributes on regulatory guidance and receives access to expert information and training.

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HIDRA working group

HIDRA Project – IAEA Human Intrusion in the context of Disposal of Radioactive Waste
The CNSC participates in and contributes to the project to provide recommendations to clarify existing IAEA requirements and guidance relevant to the assessment of future human actions and human intrusion.

Published regulatory research on geological disposal of radioactive waste

1. Research activities from 1978 - 1996

In 1978, the governments of Canada and Ontario announced the Nuclear Fuel Waste Management Program. Under this program, Atomic Energy of Canada Ltd. (AECL) was directed to develop the concept of deep geological disposal of used nuclear fuel (UNF) at depths of hundreds of metres in a rock formation.

AECL focused on crystalline rock (rocks that are formed of crystallized minerals, for example granite) in the Canadian Shield, with the host rock as the major barrier to radionuclide movement from the emplaced used fuel.  The Atomic Energy Control Board (AECB) – the Canadian nuclear regulator at that time – began its own research to be able to confirm the feasibility of the disposal concept. The focus of the regulatory research was on the host rock and its long term performance^{Footnote 1 Footnote 2 Footnote 3 Footnote 4 Footnote 5 Footnote 6 Footnote 7 Footnote 8 Footnote 9 Footnote 10 Footnote 11 Footnote 12 Footnote 13 Footnote 14 Footnote 15 Footnote 16 Footnote 17 Footnote 18 Footnote 19 Footnote 20 Footnote 21 Footnote 22 Footnote 23}. The main findings from the regulatory research follow.

• Uranium ore bodies that formed billions of years ago and remain stable today, such as the high grade Cigar Lake deposit in northern Saskatchewan, owe part of their long term stability to the geochemical conditions of the groundwater which help to prevent the oxidation and mobilization of uranium . The above conditions are defined as reducing conditions. Other uranium ore deposits have remained stable even under relatively oxidizing (as opposed to reducing) groundwater conditions, where the extent of uranium remobilization was limited (as documented for the shallower Alligator River deposits in Australia) by uranium sorption onto secondary iron oxides within that aquifer^{Footnote 1}.
• The groundwater at depths of more than a few hundred of meters in crystalline rocks of the Canadian Shield are both very old^{Footnote 2} (at least 10,000 years old) and saline^{Footnote 3}.
• While the construction of a repository would be on the same scale as several mines, the mass of the used fuel that would be disposed of within a repository is very small in comparison with the mass of the material that would be involved in excavating the repository and establishing the engineered barriers. A used fuel repository would have a similar geochemical impact on the geosphere as a uranium ore deposit^{Footnote 5}.
• The radiotoxicity of the used nuclear fuel would be comparable to a low-grade (0.1%) uranium ore body after a few tens of thousands years^{Footnote 6 Footnote 7}.
• The main agent of radionuclide transport is groundwater. Mathematical modelling^{Footnote 8 Footnote 9} confirmed that with proper site selection and engineering design, the rate of groundwater flow in the vicinity of the repository would be very slow.
• Since the main barrier in the AECL’s concept was the host rock, a mathematical model was developed to assess the long term evolution of the host rock^{Footnote 11 Footnote 12 Footnote 13 Footnote 14 Footnote 15 Footnote 16 Footnote 17 Footnote 18 Footnote 19 Footnote 20 Footnote 21 Footnote 22}. The model takes into account the complex interaction between the heat generated from the used fuel, the mechanical response of the rock and the movement of the groundwater.
  • The model was extensively verified with analytical solutions and validated against experiments^{Footnote 11 Footnote 12 Footnote 13 Footnote 15 Footnote 17 Footnote 18 Footnote 19 Footnote 20 Footnote 39 Footnote 48}
  • It was used to assess the robustness of the host rock against earthquakes^{Footnote 22}, glaciation^{Footnote 21}and the effects of the heat generated from the used fuel^{Footnote 14 Footnote 16}. It was found that the host rock is a very efficient barrier against radionuclides migration when relatively unfractured. Used nuclear fuel should be emplaced in such type of rock at a minimum distance from a major fracture zone. That minimum distance depends on the specific characteristics of the rock. It was emphasized that in practice it could be difficult to verify that requirement; therefore there should be more reliance on the engineered barriers in order to provide additional and redundant safety features.

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How the regulatory research was used

Based on the independent regulatory research, assessment, and international collaboration, the AECB was able to conclude that although there were deficiencies in the way it was demonstrated the AECL’s concept was feasible and that Canada should move beyond the concept assessment stage and start to select a site. The AECB submitted its report^{Footnote 23} to the Seaborn Panel, the federal environmental assessment review panel established to review the AECL concept.

2. Research activities from 1996-2008

During this period, the AECB and its successor the Canadian Nuclear Safety Commission (CNSC) (from 2000) continued regulatory research in geological disposal in order to keep up-to-date with new technological and scientific developments. The research activities were conducted in collaboration with national and international organizations and consist of the following:

• Research on the geochemistry of Canadian Shield groundwater continued. The groundwater is distinctly zoned: salinity increases with depth and the groundwater composition evolves from relatively fresh in the shallower crust above ~300m, becoming increasingly brackish with depth. The increased salinity at depth indicates that the groundwater is very old and had not mixed with fresh water from the surface; this in turn suggests that the rate of groundwater movement at depth is very slow. These brines likely infiltrated the Shield 300 – 400 million years ago. Lithium isotopes were used to distinguish the origins of ancient brines derived from a variety of marine sources^{Footnote 24}. Geochemical and isotopic data were further used to investigate the ancient origin of Shield brines, from Paleozoic sedimentary rocks^{Footnote 25}.
• The AECB/CNSC participated in the DECOVALEX project^{Footnote 43}.  DECOVALEX is an international collaborative consortium. DECOVALEX gathered research teams from many countries, to interpret experimental data from Underground Research Laboratories (URL) through the development and validation of mathematical models.
• Research on the long term performance of crystalline rock (similar to Canadian Shield’s rock) continued. The potential damage to the rock, its extent and characteristics, were studied, using experimental data from small-scale experiments^{Footnote 34 Footnote 50}, but also from URL such as the Kamaishi Mine, in Japan^{Footnote 35}, the URL in Whiteshell, Canada ^{Footnote 28 Footnote 40 Footnote 41}, and the Grimsel URL^{Footnote 47 Footnote 49}, Switzerland. In general, it was shown that damage due to excavation and heat generated from the used fuel is confined in small zones around the excavated zones. However, the permeability in that damage zone can constitute faster pathways for radionuclide migration. The design and safety assessment of geological disposal repositories must take the damage zones into consideration.
• Research on the long term performance of bentonite seals was started. Bentonite is a clay that is added around the container as another barrier.
  • A model for determining the complex interaction between the heat generated from the used fuel, the flow of water and vapour in the seals, and the deformation and pressure in the seals due to the swelling potential of the bentonite were developed using experimental data from small-scale laboratory tests^{Footnote 26 Footnote 36 Footnote 37 Footnote 44 Footnote 46}.
  • The model was used to predict the behaviour of the seals and their interaction with the surrounding granite during heater experiments performed at the Kamaishi^{Footnote 31 Footnote 32 Footnote 33 Footnote 38 Footnote 45}and Grimsel^{Footnote 29 Footnote 30} URLs.
  • The model was used to assess implications on the safety features of a hypothetical repository for used fuel in the Canadian Shield ^{Footnote 27 Footnote 42}. It was found that swelling induced additional pressure on the container, and therefore its design must take this extra loading into account. Secondly, the heat from the used fuel would be transferred through the seal, into the rock. The higher temperature can increase the extent of the rock damage zone that was induced by excavation. The damage zone could constitute preferential pathways for radionuclide transport, and therefore must be taken into account in the design and safety assessment of the repository.

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3. Research activities from 2009-present

During this period, the CNSC:

• Published guidance document G-320^{Footnote 49} that introduces the concept of a safety case to demonstrate the long term safety of radioactive waste management.
• Performed research on sedimentary rock

Guidance document G-320^{Footnote 51} recommends that the safety of waste management facilities be demonstrated by a “safety case”, a documented set of arguments that provide reasonable assurance that human health and the environment would be protected. Central to the safety case is a systematic and quantitative analysis of the future impact of the facility on human health and the environment. That analysis is called a safety assessment, which must be supported by additional arguments such as natural analogues (examples in nature of materials or processes which are similar to the ones around or caused by a geological repository), robustness (the resilience to future perturbations such as earthquakes, etc.) and other multiple lines of reasoning and evidence.

The research on sedimentary rocks over this period is summarized as follows:

• Experimental^{Footnote 57 Footnote 60} and theoretical^{Footnote 52} research on the mechanical behaviour of sedimentary rocks was performed. That mechanical behaviour is time-dependent and is influenced by the layers that formed in that type of rock during the sediment deposition.
• Using the results of field tests performed at the Mont Terri URL, the extent and characteristics of the excavation damage zone (EDZ) around tunnels were predicted and compared to the field measurements. Although the extent of the EDZ is limited, it can constitute faster pathways for water and gas migration^{Footnote 53 Footnote 54}. The EDZ must then be considered in the design and safety assessment of a deep geological repository ^{Footnote 65}.
• Gas generated in a deep geological repository can potentially migrate and transport radionuclides to the surface. Mathematical models of gas migration in sedimentary rocks were developed using experimental data from surface laboratories and URLs ^{Footnote 53 Footnote 55 Footnote 61 Footnote 63 Footnote 64}. The models, validated with experimental data, show that if the gas pressure is smaller than the existing state of stress around a geological repository, gas migration would be confined in the host rock in the vicinity of the repository. This would be the case for the DGR proposed by the OPG^{Footnote 61}.
• Sedimentary rocks of the Michigan Basin have been submitted to nine glacial cycles during the past million years. The maximum thickness of the ice cap could attain 3-5 km, resulting in an enormous stress on the surface (30 to 50 MPa, equivalent to the pressure under a water depth of 3 to 5 km). Mathematical modelling of the effects of past and future glaciation^{Footnote 56 Footnote 58 Footnote 59 Footnote 62 Footnote 66 Footnote 67}, validated with field data indicates that:
  • Despite nine glacial cycles, the groundwater at more than 500 m depth at the Bruce site has remained stagnant. The chemistry of that groundwater shows irrefutable evidence that groundwater at that depth is millions of years old and had not mixed with shallower groundwater or surface water.
  • Damage of the rock due to the ice pressure is restricted to a few hundred of metres from the surface.
  • If a future glaciation cycle occurs on the site of a deep geological repository, modelling shows that radionuclides will be contained in the vicinity of the host rock. Only in the improbable case of severe failure of the shafts, would radionuclides reach the shallower groundwater.
• Natural analogues (e.g. ancient uranium ore bodies that formed billions of years ago, and have remained stable since that time) for nuclear waste disposal provide information over geological timescales and spatial scales. Natural analogues for nuclear waste were reviewed^{Footnote 68}, and are deemed necessary to complement experiments carried out over months or years, and to validate numerical safety assessment models.

Effect of glaciation on sedimentary rocks. Glaciation imposes an enormous load on the rock formation, generating very high pressures in the rock (red zones in a) approximately equivalent to a 3-km column of water. However, the rock at depths of more than 500 m is practically impermeable and would contain the movement of radionuclides to very small zones (red zones in b).

a) Pressure distribution

b) Tracer movement

The SEALEX experimental program at the Tournemire URL, France. The CNSC and France’s Institute for Radiation Protection and Nuclear Safety (IRSN) collaborate on experimental and theoretical studies on the long-term performance of bentonite seals.

a) Test setup
 

b) Precompacted bentonite seal blocks emplaced in horizontal borehole