AECL'S UNDERGROUND RESEARCH LABORATORY
DEMONSTRATION OF KEY ASPECTS
OF A USED-FUEL DISPOSAL PROJECT

M.M. Ohta; N.A. Chandler; G.W. Kuzyk and P.M. Thompson
AECL, Whiteshell Laboratories, Pinawa, MB, Canada

ABSTRACT

During the development of the Canadian Nuclear Fuel Waste Management Program in the 1970's, the need for an underground facility was recognized. AECL constructed an Underground Research Laboratory (URL) to conduct large-scale tests and in situ engineering and performance-assessment-related experiments on key aspects of deep geological disposal in a representative geological environment.

The URL is a unique geotechnical research and development facility because it was constructed in a previously undisturbed portion of a granitic pluton that was well characterized before construction began, and because most of the shaft and experimental areas are below the water table. Specific areas of research have included surface and underground characterization; groundwater and solute transport; excavation response and excavation disturbed zone behaviour, in situ rock stress conditions; and thermal and time-dependent deformation and failure characteristics of rock.

Current and future activities at the URL are summarized. Some topic areas of an infrastructure nature that have potential application to siting, design and construction, and operating phases of a used-fuel disposal project, have also been demonstrated and are described:

INTRODUCTION

Over the last 18 years under the Canadian Nuclear Fuel Waste Management Program, AECL has developed and assessed a concept for the safe disposal of nuclear fuel waste from Canada's CANDUÒ reactors in the plutonic rock of the Canadian Shield. A Canadian Environmental Assessment Agency (CEAA) review, to determine if the concept is safe and acceptable, has been completed. The Panel report to the government is expected in early 1998.

This paper describes some key aspects of the Used Fuel Disposal Project that have been demonstrated at the Underground Research Laboratory and which will continue to be important in gaining public, technical and regulatory confidence in the Canadian disposal project. Background information on the Canadian program is provided as well as some details on the future use of the Underground Research Laboratory.

ROLES AND RESPONSIBILITIES FOR RADIOACTIVE WASTE MANAGEMENT

In Canada, the Federal Government has legislative authority for the development and control of nuclear energy and regulates nuclear energy through the Atomic Energy Control Board (AECB) and is responsible for the development of the Policy for radioactive waste disposal. The AECB ensures that the use of nuclear energy does not pose undue risk to health, safety, security and the environment. They license nuclear facilities, including nuclear waste disposal sites and facilities. The waste producers and owners include utilities with nuclear power stations, Atomic Energy of Canada Limited (AECL), uranium mining and processing/fabrication companies and others. They are responsible for the funding and the management of their wastes.

In 1978, the governments of Canada and the Province of Ontario issued a joint statement regarding the research and development program for nuclear fuel waste management. The responsibilities were assigned as follows: AECL to develop the technology for immobilization and disposal and Ontario Hydro to continue work on storage and develop technology for transportation of used fuel.

The nuclear fuel waste management program in Canada is in transition. With the completion of the Environmental Impact Statement and the environmental review of the disposal concept, AECL's responsibilities as defined above are essentially complete. Ontario Hydro has the majority of the used fuel in Canada, about 90%. Towards the end of the concept development phase, in 1996, Ontario Hydro assumed responsibility for funding and direction of the Canadian program, pending the outcome of the environmental review. Major facilities, such as the URL, continue to be owned and managed by AECL and work is undertaken for Ontario Hydro and other customers under contract.

POLICY FRAMEWORK

Concurrently with the environmental review, Natural Resources Canada developed and issued a Policy framework for Radioactive Waste Disposal in Canada (Morrison et al. 1996). The elements of this framework consist of a set of principles governing the institutional and financial arrangements for disposal of radioactive wastes by waste producers and owners. These principles are:

  1. The Federal Government will ensure that radioactive waste disposal is carried out in a safe, environmentally sound, comprehensive, cost effective and integrated manner.
  2. The Federal Government has responsibility to develop policy, to regulate, and to oversee producers and owners to ensure that they comply with legal requirements and meet their funding and operational responsibilities in accordance with approved waste disposal plans.
  3. The waste producers and owners are responsible, in accordance with the principle of "polluter pays", for the funding, organisation, management and operation of disposal and other facilities required for their wastes, recognizing that arrangements may be different for nuclear fuel waste, low-level radioactive waste, and uranium mine and mill tailings.

The Policy Framework is an important milestone towards the goal of ensuring comprehensive, environmentally sound, integrated, and cost effective approach to the disposal of radioactive waste in Canada. It lays the ground rules and defines the role of government and waste producers. With the Policy Framework in place the context is set for further development of the financial and institutional structures that will govern waste disposal.

THE CANADIAN CONCEPT AND THE ROLE OF THE
UNDERGROUND RESEARCH LABORATORY

The long term management of nuclear fuel waste has been an issue in Canada for many years and it has been raised in a number of reviews of nuclear energy. Today, used fuel from Canadian nuclear generating stations is safely stored at the station sites. Many years of experience have been accumulated with both pool storage and dry storage systems and supporting R&D indicates that these practices can be safely continued for many decades to come. However, because the used fuel remains hazardous for thousands of years, it has long been recognized that such storage systems are not a permanent solution, and that a passively-safe method of management that does not rely on institutional controls needs to be developed.

Canada, like other countries, is basing its plans for disposal of nuclear fuel waste on deep geological disposal, in the Canadian case in stable plutonic rock of the Canadian Shield. In common with the approach adopted in other countries, the Canadian concept for deep geological disposal, as developed by AECL, entails isolating the waste from the biosphere by a series of engineered and natural barriers. These barriers include: the form of the waste itself; long-lived containers in which the waste is sealed; buffer materials to separate the containers from the surrounding rock and to control the movement of water to, and corrosion products away from, the container; the use of seals and backfill materials to close the various openings, tunnels, shafts and boreholes; and the rock mass in which disposal vault is located, the geosphere. There is international consensus that this approach can best achieve the goal of safely managing nuclear fuel waste in the long-term. The biosphere, although not a barrier per se, is an important part of the overall system. Because it contains the pathways through which direct exposure of humans and non-human biota to contaminants could occur, its study must be part of any waste management program.

In the Canadian concept, as in most countries, waste will be emplaced in a vault excavated below the water table. Hence, the principal concern from the point of view of long-term safety is the possibility that groundwater will eventually become contaminated with radioactive or other hazardous materials from the waste and that this contaminated groundwater will eventually make its way to the surface where it would pose an unacceptable risk to human health or the environment. The multibarrier systems under development will prevent this because of the combined effects of radioactive decay and the containment, retardation, dispersion and dilution caused by the many barriers of the disposal system (the waste form, the container, buffer, backfill and the geosphere). Thus, human health and the environment will be protected.

Considerable efforts have been made internationally to evaluate the behaviour of deep geological repositories with time and their long-term safety. There is an international consensus among waste management experts that appropriate use of safety assessment methods, coupled with sufficient information from proposed disposal sites, can provide the technical basis to decide whether specific disposal systems would offer to society a satisfactory level of safety for both current and future generations.

Several countries, including Canada have carried out quantitative assessments of the risk associated with disposal and these analyses show that the flux of contaminants from a disposal facility to the surface would be very small and that the radiological impact would be many orders of magnitude less than that from naturally occurring radioactivity in the surface environment.

Early in the Canadian program it was recognized that an underground research laboratory was a key program element to develop the technology to engineer the safe and permanent disposal of Canada's nuclear fuel wastes and to provide an underground environment for geoscientific investigations. The laboratory was developed to carry out in situ tests in a granite rock mass relating to site selection, design, construction and safety and environmental assessment of a nuclear fuel waste disposal vault (Allan et al. 1997).

Selecting a safe disposal site requires a comprehensive understanding of a large number of properties and processes including rock properties, evolution of groundwater chemistry with time, geochemical interactions between groundwater and engineered barriers, used fuel and used fuel containers, transport of groundwater through sparsely, moderately and highly fractured rock, geochemical and transport behaviour of dissolved and colloidal radioisotopes in geological environments and diffusion into the interconnected pore space of the rock matrix and the excavation damaged zone. The design and performance assessment of a disposal vault requires an in-depth understanding of in situ the geological environment, the temperature and time-dependent deformation characteristics and failure behaviour of the host rock, techniques to minimize the excavation damage, minimize the costs and ensure safe working conditions during construction, and the adsorption properties of the rock fracture and fracture in-filling materials around the vault. With access to a very well characterized and understood rock mass, AECL's URL has been and continues to be a key tool in supporting work to develop and maintain this understanding.

GEOLOGICAL SETTING AND DESIGN

AECL's URL is constructed within the Lac du Bonnet batholith and consists of a vertical shaft to a depth of 443 m, with shaft stations at 130-m and 300-m depths and major experimental levels at 240-m and 420-m depths as shown in Figure 1. The batholith lies within the Superior Province at the western edge of the Canadian Shield, approximately 100 km northeast of Winnipeg, Manitoba. It was intruded approximately 2,670,000,000 years ago, near the close of the regional deformation that affected the surrounding metavolcanics, metasediments and gneisses. The fracture pattern at the URL is dominated by low dipping thrust faults and splays (fracture zones) as shown in Figure 1. They are less frequent, less continuous, and simpler in pattern with increasing depth. Complex local and regional scale patterns of permeability and hydrogeochemistry may be correlated with the structure of the fracture zones (Everitt et al. 1990).

Above Fracture Zone 2, the rock mass around the excavations on the 240 Level responds essentially as an elastic material. Below this zone, on the 420 Level, the in situ stress levels are sufficiently high that failure occurs in some excavations in regions of high stress concentrations. The design of the URL layout allows easy access to these fractures and to the two distinct stress domains.

PAST AND CURRENT PROGRAMS AT THE URL

Twenty-one-year leases from the Government of the Province of Manitoba for the surface and underground land use, granted in 1980 (and later extended to 2011) allows drilling, excavation, and testing for research purposes but excludes the use of radioactive wastes. Detailed surface characterization of the URL lease was carried out in stage during 1980-1983. The objective of this work was to develop an approach to characterization that would provide the necessary information for designing and constructing a disposal vault in granitic rock, as well as providing site specific information for the design, construction and safe operation of the URL facility and for the design of its experiments and interpretation of the results. The location of the shaft was specified in a region of moderate fracture zone permeability to allow easy access to proposed areas of future underground experiments. The major milestones related to the construction phase are summarized below:

1984

Surface facilities constructed

1985

Rectangular shaft excavated to 255 m depth

1987

Initial development of the 240 Level tunnels and excavation of the upper ventilation raise

1988

Circular shaft excavated to 443 m depth and completion of 240 Level access tunnels

1989

Excavation of 420 Level access tunnels

1990

Ventilation raise between the 420 and 240 Levels completed

During the construction phase, valuable scientific knowledge was gained related to performance assessment and implementation of the disposal vault (Ohta and Chandler 1996).

In 1990 the Program of Operating Phase Experiments was initiated. The following is a listing of the specific experiments which have been completed or are in progress (shown in bold). Their location is shown on Figure 2.

Characterization Development

Solute Transport in

Thermal-Mechanical-Hydraulic Investigations

Vault Sealing Investigations

As described above, the URL has been an integral part of the Canadian Program, providing a sound foundation for the concept development work. Details of the past work have been published and presented. The on going work will be documented under contract and papers and journal articles will be published.

APPLICATION OF KNOWLEDGE AND EXPERIENCE

There have been many lessons learned during the implementation of the URL Project which can be applied to the execution of the siting phase of a Used Fuel Disposal Project. The development of site characterization strategies, tools and procedures, the application of data on in situ stress and excavation design; the knowledge of in situ performance of buffer materials, and many other areas of study have been documented in the EIS document and its primary references (AECL 1994, Greber et al. 1994, Davison et al. 1994a, Johnson et al. 1994a, Simmons and Baumgartner 1994, Grondin et al. 1994, Goodwin et al. 1994, Johnson et al. 1994b, Davison et al. 1994b, and Davis et al. 1993). A few of the technical program highlights from the list of experiments in the previous section are described below.

Groundwater Flow and Site Characterization

Our program has provided us with an understanding of the processess governing groundwater flow in the Canadian shield and with a demonstrated technology for site characterization. The characterization program has been under way since 1980 and aims to develop an approach that would provide the necessary information for siting, designing, constructing and operating a disposal vault in granitic rock as well as specific site information for the design and construction of the URL. Characterization includes; general geology, fracture framework, hydrogeology, groundwater chemistry, microbiology, mechanical properties of the rock mass, in situ stresses and numerical modelling. Equipment and procedure developments are almost complete, existing databases are being maintained, and long-term monitoring is continuing. The tools and methods developed for characterization of the URL will be used to define the requirements for, and the overall plan for characterization of potential repository sites. The measurement of in situ stress, for example, has been demonstrated at the URL to depths greater than 900 m, using a technique developed at the URL, where conventional stress measurement methods failed as a consequence of the high in situ stresses. The results of the characterization during siting and construction of the URL were incorporated into the geosphere model of one of the case studies to illustrate the performance disposal concept for the EIS. This work also provides site-specific information for the design, construction and safe operation of the URL facility, and for the design of its experiments and interpretation of results.

The ability of the rock mass to act as an effective barrier to inhibit transport of radionuclides to the surface will depend largely upon the degree of fracturing in the rock, distance between tunnels and major conductive pathways, and the extent of excavation induced fracturing adjacent to the tunnels. The solute transport experiments in highly fractured rock at the URL provides estimates of the physical solute transport properties in fractures zones at local and regional scales for the development of groundwater flow and solute transport models. Seven groundwater tests ranging in scale from about 20 to 200 m were conducted in Fracture Zone 2, and allowed development of numerical models to simulate tracer transport for each test (Frost et al. 1995a, b). A series of six small-scale tracer tests examined the effects of flow direction and rate, and compared the transport behaviour of different tracers (anionic, colloid and redox-controlled chemical tracers). Larger-scale tests were performed to help establish whether the solute transport properties within zones of intensely fractured rock are scale- or direction-dependent and to develop methods for extrapolating the test results to larger scales by combining tracer tests with crosshole hydraulic response tests. These types of experiments have helped us with an understanding of the processes governing groundwater flow in the Canadian shield.

Vault Sealing Investigations

The buffer and backfill between the container and rock provide a low permeability barrier around the container. For the past 15 years, AECL has been investigating the technologies required to design and construct repository seals in granite (Chandler et al. 1996). The Buffer/Container Experiment was a full-scale simulation of a single emplacement hole in the in-floor borehole emplacement design for waste disposal (Kjartanson et al. 1996). This experiment studied the thermal-hydraulic processes around an emplacement hole and within the buffer material. The fuel waste container was simulated by a 2-m-high and 0.6-m-diameter electric heater. The heater was placed within a 1.24-m-diameter by 5-m-deep borehole in granite and completely surrounded by sand-bentonite buffer material compacted in situ. The heater was operated at a constant-power setting which maintained the temperature of the heater surface at approximately 85oC. After two and a half years of operation, the heater was turned off and the heater and buffer material were removed from the experiment.

An important element of this work included the development of techniques for mixing, storage and placement/ compaction of the buffer material. Also, much insight was gained from this experiment in the thermal-hydraulic coupled processes affecting the movement of water through rock and buffer, and this insight was applied to further develop numerical models for predicting the performance of seals. The buffer material in the experiment performed essentially as expected (Graham et al. 1996). Over the course of the experiment, the buffer absorbed some moisture from the rock; however, most of the moisture content changes were attributed to moisture redistributed within the buffer itself. The annulus of buffer material between the heater and the rock was 26 cm in thickness and the temperature drop across this annulus was 30oC. At the end of the experiment the buffer material adjacent to the rock boundary was saturated while considerable drying of the buffer had occurred next to the heater. Upon removal of the buffer at the end of the experiment, drying shrinkage was visibly evident by the presence of cracks extending radially away from the heater. These cracks extended a maximum of about 10 cm within the 26-cm-thick annulus of buffer surrounding the heater cavity, beyond which there was no evidence of cracking. Samples of the desiccated and cracked buffer adjacent to the heater were removed at the end of the experiment. Upon resaturation, this material regained the low hydraulic conductivity of buffer which had never experienced thermal drying, illustrating the self-healing properties of the material.

Thermal-Mechanical Investigations

Several studies have been carried out to investigate design and performance assessment issues related to the development of the excavation damaged zone around underground openings. The Mine-by, Heated Failure and Excavation Stability Studies were large scale experiments which provided valuable information.

The Mine-by Experiment was conducted in situ at the 420 Level of the URL to study progressive failure and the development of excavation damage around a 3.5-m-diameter circular tunnel. The test tunnel for the experiment was aligned subparallel to the intermediate principal stress direction to maximize the potential for progressive failure and damage around the tunnel. The in situ stress ratio in the plane perpendicular to the Mine-by tunnel exceeds 5-to-1. In comparison to other stable tunnels at the 420 Level, the test tunnel represents a worst-case scenario in terms of shape and orientation, for damage development on this level of the URL (Read and Martin 1996).

The progressive brittle failure of the rock in the high-compressive-stress regions around the tunnel resulted in the development of V-shaped notches, similar to those observed in borehole breakouts. Observation slots cut into the roof and floor of the tunnel generally showed that the depth of intense fracturing at the notch tip was less than 30 cm. Fracturing beyond the stable tunnel perimeter was essentially non-existent at a lateral distance of 50 cm to either side of the notch tip. From observations of damage and from AE/MS results, the highly crushed rock (also referred to as a "process zone") at the notch tip and the fractures forming the thin slabs along the flanks of the V-shaped notch would be the locations with the greatest potential to contribute to contaminant transport. The hydraulic connectivity and the physical transport properties of the excavation damaged zone was also studied.

The Heated Failure Tests examined the effect of thermal loads on the extension of the excavation damaged area in highly-stressed rock (Read and Martino 1996). This experiment was conducted in four stages. The tests were conducted around half scale or 600 mm. diameter boreholes in the floor of the Mine-by experiment room. Tubular electric heaters were installed in boreholes were used to heat the walls of the 600 mm. boreholes to 85° C. The various stages were designed to assess the effects of drilling/heating sequence, borehole interaction and confining pressure on the progressive failure in the walls. The findings from these tests indicate that the extent of the excavation damaged zone is dependent mainly on the magnitude of the radial and tangential boundary stresses, but can also be influenced by thermal-mechanical loading sequence. In cases where a damaged zone occurs, these tests indicate that the damage is limited to a small region close to the opening, even when multiple openings are spaced close enough to interact. The confining pressure tests suggest that swelling sealing material which applies confining pressure on the rock mass will reduce the likelihood of instability and inhibit excavation damage zone development.

The excavation stability study evaluated the stability and extent of damage in tunnels as a function of tunnel geometry and orientation, geology, and excavation method (Read and Chandler 1997). Tunnel segments of different ovaloid and circular cross sections were excavated in three tunnels in granite and granodiorite. They were designed to achieve specific boundary stress levels. Full-face careful drill and blast excavation method was utilized. This work demonstrated that practical, stable tunnels can be excavated in the most adverse stress conditions at the URL. The tunnel stability and the extent of excavation damage are affected by tunnel geometry and orientation relative to the in situ stress direction, and geological variability. Some minor differences between the mechanical and drill and blast techniques was observed. With drill and blast, some tensile cracks developed in the side walls of the tunnels.

The preceding paragraphs summarize a substantial program aimed at defining the requirements for the design of stable repository excavations. It has been demonstrated that stable excavations, with a minimal volume of damaged rock adjacent to the excavation, can be constructed under severe in situ stress conditions. Research to date suggests that an effective design of the excavation and backfill system will allow these tunnels to remain stable under the thermally-induced stresses following closure of the repository tunnels.

PROJECT IMPLEMENTATION PROCESSES

The implementation of the URL Project has also developed project implementation processes which can be applied during the siting phase of a Used Fuel Disposal Project. They are, we believe, essential ingredients for a successful project. These are ingredients for building confidence in the technical program results within the project team and external reviewers, regulators and the public. A few of the lessons learned are described below.

Lesson No. 1 - Integration of a Multidisciplinary Team

Perhaps the single most important lesson learned is the benefit obtained from integrating construction and experimental activities and for adopting a multidisciplinary team approach to projects. It is the key to producing quality work in a safe and cost effective manner for underground projects. As the skills of a scientist or engineer grow with experience, so do the capabilities and knowledge base of a team of professionals. With each new project the team learns to work together. As the projects become more complex, the team members develop their own skills, while learning to rely on the strengths and abilities of others. In so doing, multidisciplinary projects can be accomplished with increasing efficiency, without duplication of effort, and without tasks falling through gaps in responsibility.

A list of URL experiments is provided in the above section, "Past and Current Programs at the URL". Skills in instrumentation and characterizing the rock mass using geophysical and hydrogeological techniques were first honed in the URL Characterization Program. These skills were then applied to highly specialized areas such as solute transport studies in fractured rock and the development of methods for characterizing rock damage due to excavation (Mine-by Experiment, Connected Permeability Test). The Buffer/Container Experiment represents an early example of the integration of a variety of disciplines. In this experiment construction optimization became important to minimize the damage in the floor due to excavation and to drill a large-diameter borehole using high pressure water. Characterization of the volume of intact rock around the emplacement borehole involved the expertise of geophysicists, rock mechanics engineers, and hydrogeologists. The specifications for the engineered materials (buffer, backfill and sand), the characterization of their properties and development of placement methods were required by geotechnical engineers. Civil and electrical design engineers were required to design and construct a restraint system to resist the swelling of the bentonite, and an electrical heater, with both designs meeting the needs of the experiment.

Virtually all the same people worked together in a variety of other multidisciplinary activities culminating, recently, in the Tunnel Sealing Experiment. The experiment involves design and excavation of a tunnel in highly stressed rock with little damage due to excavation; characterization of the excavation damage and development of excavation techniques for interrupting the zone of damaged rock. The experiment requires development of methods for construction of the bulkheads; selection, modification and testing of instruments and data management systems; measurement of the flow through bulkheads and the changes in hydraulic gradients in the rock around the bulkheads; and the design and construction of large steel and concrete structures and high-pressure water supply systems. In addition, the project has four different customers, PNC, ANDRA, USDOE (WIPP) and AECL, each having specific technical objectives for their involvement. On this project, open communication lines are of paramount importance. It was also important that all the technical experts on the project and all the customers define the experiment requirements, and assignment of responsibilities early in the project. It is essential that representatives of all disciplines meet regularly and are available to address issues with other team members between the regularly scheduled meetings. A QA plan which specifically defines responsibilities and ensures communication links between disciplines, is necessary for success of large multidisciplinary projects. The QA plan must also address the needs of the customers, in that a mechanism for obtaining consensus on technical direction is in place, and that the final reports are well defined early in the program. The plan for regular reporting must also provide the overall program managers with a comfort level that minimizes the requirement for managerial direction.

This system works well in the environment which exists at the URL. All the people involved in the experimental program, from managers to technicians, are permanently stationed at, or near, the underground facility. This makes for a cohesive team working together on a daily basis; establishing both confidence in, and respect for the work of other team members.

Lesson No. 2 - Use of the Observational Method

Given the variability of properties in natural materials, an iterative engineering design approach is required. The engineering approach evolved at the URL. The excavation design and implementation is an example of the use of this approach. It was recognized in the planning of the excavations (e.g., shaft, tunnels and test rooms) for the URL that a drilling and blasting method of excavation would be more versatile and cost effective than mechanical boring methods. However, standard drilling and blasting methods normally used in mining would not be acceptable, as they may cause excessive damage to the rock mass surrounding the excavations. This would increase the need for ground support and leave a poor impression on experts, who would carry out peer reviews of the R&D programs, as well as any general public visitors to the URL. It is postulated that the rock mass surrounding the disposal rooms in a used fuel disposal facility could become potential pathways for the escape of radionuclides if unduly fractured by bad excavation practices. As a result, it was important to demonstrate that damage to the rock mass surrounding excavations at the URL could be minimized.

Improvements to drilling and blasting techniques evolved during the construction of the URL (Figure 3). Attempts at controlled drilling and blasting during the initial shaft sinking project were only moderately acceptable. The rectangular configuration of the shaft and benching method of excavation used by the shaft sinking contractors did not lend to controlled drilling and blasting principles. Subsequently, the "observational method" (Peck 1969) was introduced during the excavation of the tunnels and experiment rooms on the 240 Level to improve upon the drilling and blasting quality. This is an iterative process that provides a continuous cycle of design, assessment and adjustment. The process is commonly used in underground civil projects, such as rail and highway tunnels, power stations, storage chambers, subways, etc., to accommodate design changes needed to accommodate unexpected changes in geological conditions.

Quality control inspectors were placed on each shift to work with the contractor's crews. They kept accurate records of the work done and the results achieved. It was necessary for the contractor to have a bonus system to attract suitably qualified mining crews. To encourage cooperation and acceptance of new techniques by the crews, a quality-based incentive system was devised. With reliable records and assurance that the crews were precisely following the intended designs, the blast design engineer was able to progressively refine the designs to achieve better results (Kuzyk et al. 1986). The observational method was initially used to develop a pilot-and-slash technique, which significantly reduced damage to the rock mass surrounding excavations and the need for ground support (Kuzyk et al. 1986). Next, a full-faced technique was developed, which maintained this desired level of quality and improved productivity (Favreau et al. 1987).

The observational method was further applied to the shaft extension project during which URL shaft was deepened from 255 m to 443 m. A Galloway Stage was designed to integrate geotechnical and excavation/construction activities (Kuzyk and Versluis 1989, Kuzyk et al. 1986, Everitt et al. 1994). The shaft configuration was changed to circular and a full-faced blasting technique employing a burn-cut was introduced (Hagan et al. 1989). The full-face method allowed for variable length blast rounds, a simpler shaft profile and a relatively flat face at shaft bottom, which were beneficial to the geotechnical characterization program. The controlled drilling and blasting results were superior to the benching method used previously.

As in other underground civil projects, expertise in the implementation of the observational method and a similar iterative process of quality improvement will be needed during the planning, siting, excavation and construction of a used-fuel disposal vault.

Lesson No. 3 - Quality Assurance

An effective and appropriate quality assurance program will be required for the Used Fuel Disposal Project. A potential outline of such a program was envisaged to respond to a comment during the environmental impact assessment of the Canadian disposal concept (Cooper and Abel 1996). To accommodate the uncertain rock conditions that would be encountered in engineering the disposal vault, the observational method (Peck 1969) which is used widely to optimize underground designs and mining methods is a key feature. Many elements of such a program have been developed and tested at the URL. During the site evaluation and construction stage, many new methods and techniques had to be developed and demonstrated. Appropriate but flexible quality control and inspection procedures were instituted. The goals were to:

As construction was completed and the URL entered into the operating phase, these quality control and inspection procedures were formalized into a QA plan for activities deemed important for the Canadian Nuclear Fuel Waste Disposal Program and the operation of the Underground Research Laboratory. The QA program, formalized in 1990 June, consists of three tiers. Tier I is a manual that describes policies, responsibilities and overall organization of the QA program. Tier II documentation comprises administrative procedures that describe the application of each of the program elements. Tier III documentation comprises project and experiment plans, design documents and working procedures to guide activities at the working level to meet the requirements of the QA program. The QA program documents are updated on a continuing basis and audited periodically. Some examples of QA administrative and working procedures are shown in Tables I and II respectively.

With the reorganization of AECL and the evolution from a concept development stage to the pre-project planning phase of a Used Fuel Disposal Project under the direction of Ontario Hydro, the QA needs of the Canadian program are being reviewed. A program will be prepared to suit new requirements. The development, testing, and continuous quality improvement process of key elements of a QA program that may be applied to a used fuel disposal project has been demonstrated at the URL. The URL experience will be valuable in developing an appropriate QA program for the siting phase.

Lesson No. 4 - Occupational Safety Program

The proactive implementation of an effective occupational safety program is the foundation for a cost effective and high quality program at the URL. Safety of people and the environment is the number one priority. Occupational safety, environmental protection and quality are interrelated and inseparable. One cannot exist with the other. The nature of the underground and surface construction, operations and experimental work, and the integration of R&D activities make it necessary for technical personnel to work in an underground and outdoor environment where the risk of potentially serious accidents is high. A serious accident or fatality and a poor safety record are undesirable and can have a detrimental effect on the progress of work and public support for nuclear fuel disposal.

As of 1996 December the total time worked at the URL over the last 13 years (including both AECL and underground service contractors' personnel) is 2,085,116 persons-hours with 13 lost time accidents, or a frequency of 1.25 accidents per 200,000 person hours. This is well below the average for underground operators and drilling and mining contractors in the Province of Manitoba, which is 5 (MAPAM 1996). While these statistics are impressive, the key measure of a successful program is the vibrancy of the safety culture. Several safety activities are described.

Safety and Health Committee meetings, held on a regular monthly basis, constitute an important part of the URL safety program. The Committee, comprised of representatives from management and unionized employees, organizes and runs the meetings which lasts about an hour. All personnel working at the URL, including contractors and attached staff, are encouraged to attend or send representatives. Incident reports are reviewed, issues are raised and corrective actions assigned. Presentations on safety and health topics of interest or concern related to prevention, protection, mitigation of consequences and recovery aspects for the workplace and at home. Thus, the importance of the safety program is reinforced on a regular basis.

All personnel working at the URL, underground and surface, are required to complete an orientation, which is basically a review of the appropriate safety and operational procedures, requirements and facilities, including emergency response and underground travel; personnel protective equipment; and location of telephones, refuge stations, eye wash stations, fire alarms, environmental protection, etc. Specific job training is instituted where required.

Other important safety programs include: Workplace Hazardous Materials Information System (WHMIS), Mine Rescue, First Aid and CPR, safety reviews and audits of designs prior to construction and operation field work, and emergency response and business resumption planning.

Our safety program is very vibrant and has been enduring with changing staff and changing budgets. The key is a safety culture that ensures a strong commitment by staff and management to a willingness to continuously seek ways to improve safety.

Lesson No. 5 - Environmental and Public Interaction Program

A detailed environmental screening (Pollock and Barrodos 1983) conducted prior to the initial shaft sinking project and prior to the shaft extension project (Lemire 1987) led to the conclusion that the activities at the URL were highly unlikely to create any significant adverse environmental effects for most potential areas of impact. Mitigative actions were identified and implemented to minimize the impacts:

As follow-up to the environmental screenings, AECL committed to these actions and implemented effective procedures to ensure that any adverse environmental effects were identified and mitigated. A formal environmental monitoring program was established to monitor the actual impacts of the URL project. The results of this program are summarized and recorded each year in an annual environmental monitoring report.

The URL has proven to be a very powerful tool in communicating the notion of a multiple barrier concept and the openness of our program to the public. Although not required explicitly by the environmental regulations, AECL consulted with Lac du Bonnet, Pinawa and Lee River Cottage communities; municipal offices; and appropriate provincial and federal government departments (e.g., Manitoba Department of the Environment and Environment Canada) during the initial site approval and leasing phase. A concerted effort was made to address public concerns. We developed and maintain good relationships with residents in the surrounding areas. AECL hires and encourages the contractors working at the URL to hire local people where ever possible. During tours, the public can witness first-hand the stable nature of a geologic formation in the Canadian Shield, discuss the concept of disposal in situ, and view the quality of work and a vibrant safety culture. By interacting with the scientists and engineers who work at the facility, they can question and debate any concerns that they may have. This has also been of great benefit to the scientists and engineers. Hearing the public concerns directly allows them to address their information needs and to become more sensitive to the public points of view.

Lesson No. 6 - Instrumentation Development

The culmination of an experiment or study is a report which has summarized the results and their analyses. About 27 Gigabytes of information has been collected at the URL to date. The quality and reliability of the experimental data begins with the performance of the field instrumentation. The performance requirements of instruments (sensors, amplifiers, cables, data acquisition systems, bearings/ seals etc.) used at the URL are very demanding. In many cases, the behaviour of the rock mass must be monitored over a long time frame and hence instruments must have a life of many years without any degradation or failure. Because the granite is a massive and stiff rock type, dimensional changes to openings are in the order of microns, well beyond the measurement capabilities of standard rock mechanics instruments. In many instances, the instruments must be rugged enough to withstand severe shock and vibration from drilling and blasting operations less than 0.5 metres from the measurement borehole collar. Because the granite rock mass is below the water table, it is fully saturated, and the instruments used in ambient temperature measurements must operate in damp and humid conditions. Other environmental conditions include both high temperature conditions (Buffer/Container Experiment, Heated Failure Test, Thermal-Hydraulic Experiment and the proposed second stage of the Tunnel Sealing Experiment), and high water pressures (deep packer systems, the Tunnel Sealing Experiment, and deep overcoring in situ stress determinations). Also, since the site is a high local elevation, facilities are designed to mitigate the consequences of lightning strikes.

The unusually severe performance requirement for field instrumentation at the URL has resulted in the development of modified or new instrument types that also have applications in other areas of geotechnics. Such instruments include:

Experience at the URL indicated the majority of the instrumentation (about 80-90%) as purchased commercially will not meet our performance requirements. We have developed, by necessity, the capability to assure very high probability of successful measurement. Each individual instrument must be calibrated, modified and tested under simulated conditions. Special testing and development, calibration, and installation procedures and equipment are used. In many cases, measurement redundancy and the use of different instrument types are used to increase confidence in the measured values.

FUTURE URL PROGRAM

With the completion of the initial mandate of AECL to develop the concept and to seek approval for it through the environmental review, Ontario Hydro assumed leadership for the Canadian program, contingent on the recommendations from the Panel on the implementation organization and the Government response to the recommendations. Their reference strategy and plan (Ontario Hydro 1995) was approved by their Board of Directors and states that they will:

In 1996 Ontario Hydro initiated pre-project planning for the Used Fuel Disposal Project to provide a transition between the concept development and siting phases. Their objectives are to ensure judicious and cautious use of the provisions which they have collected from electrical power rate payers for nuclear fuel waste management and to minimize the risks during the implementation of the project. The planning work involves the development of detailed siting, engineering, safety assessment, licensing and project management subplans and integrating them into a cohesive plan with clear objectives. The plan is a result of AECL and Ontario Hydro staff and management working together utilizing Canadian and international knowledge.

Although, the Used Fuel Disposal Project implementation plan has not been completed, Ontario Hydro has concluded that the URL is an integral component of a forward moving Canadian program. The broad objectives of the Underground Research Laboratory have been defined to address technical and public issues and are as follows:

The Used Fuel Disposal Project will address specific technical concerns or issues and concerns arising from the Environmental Review and those required by the above project sub plans. Current experiments and studies are noted in the Section titled Past and Current Programs at the URL and these new programs will be carefully planned and implemented.

International participation and collaboration will continue to be an important feature of future Canadian plans. The expertise which has been developed at the URL is being applied to assist in the development and implementation of national waste management programs in several countries. International teams from Canada, France, Japan, Sweden, and USA are involved in many activities at the URL. The Quarried Block Radionuclide Migration, Tunnel Sealing and Isothermal Buffer/Rock/Concrete Plug Interaction Experiments are examples. In addition guidance is being provided to assist in the definition and implementation of URL programs in France, Hungary, Japan and USA.

CONCLUSION

Work at AECL's Underground Research Laboratory during its siting, construction and operation phases has provided valuable knowledge and experience in support of the Canadian Nuclear Fuel Waste Management Program and has been documented in various papers, reports and journal articles. It will continue to be a fully operational laboratory within the Canadian program and provide access to a variety of conditions with a quality assured infrastructure to carry out a wide variety of multi-disciplinary studies and experiments. Key aspects of the implementation of a Used Fuel Disposal Project have been demonstrated. These aspects have been very important in communicating to the public the concept of disposal and to allow the engineering and scientific community to gain an insight into the issues and requirements of an actual project.

FOOTNOTE

*CANDUÒ is a registered trademark of Atomic Energy of Canada Limited.

REFERENCES

  1. R.W. MORRISON, P.A. BROWN and G.A. UNDERDOWN. "Policy Framework for Radioactive Waste Disposal in Canada." In Proceedings of the International Conference on Deep Geological Disposal of Radioactive Waste, Canadian Nuclear Society, Winnipeg, Manitoba (1996).
  2. C.J. ALLAN, P. BAUMGARTNER, M.M. OHTA, G.R. SIMMONS and S.H. WHITAKER, "Issues Related to the Construction and Operation of a Geological Disposal Facility for Nuclear Fuel Waste in Crystalling Rock - The Canadian Experience." Paper presented at International Symposium on the Concept Development of the High Level Waste Disposal System, 1997 October 10-11, Taejon, Korea. To be published as an AECL Report (1997).
  3. R.A. EVERITT, A. BROWN, C.C. DAVISON, M. GASCOYNE and C.D. MARTIN, "Regional and Local Setting of the Underground Research Laboratory." In Proceedings of the International Symposium on Unique Underground Structures, Denver, CO, pp. 64-1 to 64-23 (1990).
  4. M.M. OHTA and N.A. CHANDLER, "AECL's Underground Research Laboratory: Technical Achievements and Lessons Learned." Atomic Energy of Canada Limited Report, AECL-11760 (1996).
  5. AECL, "Environmental Impact Statement on the Concept for the Disposal of Canada's Nuclear Fuel Waste." Atomic Energy of Canada Limited Report, AECL-10711, COG-93-1 (1994).
  6. M.A. GREBER, E.R. FRECH and J.A.R. HILLIER, "The Disposal of Canada's Nuclear Fuel Waste: Public Involvement and Social Aspects." Atomic Energy of Canada Limited Report, AECL-10712, COG-93-2 (1994).
  7. C.C. DAVISON, A. BROWN, R.A. EVERITT, M. GASCOYNE, E.T. KOZAK, G.S. LODHA, C.D. MARTIN, N.M. SOONAWALA, D.R. STEVENSON, G.A. THORNE and S.H. WHITAKER, "The Disposal of Canada's Nuclear Fuel Waste: Site Screening and Site Evaluation Technology." Atomic Energy of Canada Limited Report, AECL-10713, COG-93-3 (1994a).
  8. L.H. JOHNSON, J.C. TAIT, D.W. SHOESMITH, J.L. CROSTHWAITE and M.N. GRAY, "The Disposal of Canada's Nuclear Fuel Waste: Engineered Barriers Alternatives." Atomic Energy of Canada Limited Report, AECL-10718, COG-93-8 (1994a).
  9. G.R. SIMMONS and P. BAUMGARTNER, "The Disposal of Canada's Nuclear Fuel Waste: Engineering for a Disposal Facility." Atomic Energy of Canada Limited Report, AECL-10715, COG-93-5 (1994).
  10. L. GRONDIN, K. JOHANSEN, W.C. CHENG, M. FEARN-DUFFY, C.R. FROST, T.F. KEMPE, J. LOCKHART-GRACE, M. PAEZ-VICTOR, H.E. REID, S.B. RUSSELL, C.H. ULSTER, J.E. VILLAGRAN and M. ZEYA, "The Disposal of Canada's Nuclear Fuel Waste: Preclosure Assessment of a Conceptual System." Ontario Hydro Report N-03784-940010 (UFMED), COG-93-6 (1994).
  11. G.W. GOODWIN, D.B. MCCONNELL, T.H. ANDRES, W.C. HAJAS, D.M LENEVEU, T.W. MELNYK, G.R. SHERMAN, M.E. STEPHENS, J.G. SZEKELY, P.C. BERA, C.M. COSGROVE, K.D. DOUGAN, S.B. KEELING, C.I. KITSON, B.C. KUMMEN, S.E. OLIVER, K. WITZKE, L. WOJCIECHOWSKI and A.G. WIKJORD, "The Disposal of Canada's Nuclear Fuel Waste: Postclosure Assessment of a Reference System." Atomic Energy of Canada Limited Report, AECL-10717, COG-93-7 (1994).
  12. L.H. JOHNSON, D.M. LENEVEU, D.W. SHOESMITH, D.W. OSCARSON, M.N. GRAY, R.J. LEMIRE and N.C. GARISTO, "The Disposal of Canada's Nuclear Fuel Waste: The Vault Model for Postclosure Assessment." Atomic Energy of Canada Limited Report, AECL-10714, COG-93-4 (1994b).
  13. C.C. DAVISON, T. CHAN, A. BROWN, M. GASCOYNE, D.C. KAMINENI, G.S. LODHA, T.W. MELNYK, B.W. NAKKA, P.A. O'CONNOR, D.U. OPHORI, N.W. SCHEIER, N.M. SOONAWALA, F.W.  STANCHELL, D.R. STEVENSON, G.A. THORNE, S.H. WHITAKER, T.T. VANDERGRAAF and P. VILKS, "The Disposal of Canada's Nuclear Fuel Waste: The Geosphere Model for Postclosure Assessment." Atomic Energy of Canada Limited Report, AECL-10719, COG-93-9 (1994b).
  14. P.A. DAVIS, R. ZACH, M.E. STEPHENS, B.D. AMIRO, G.A. BIRD, J.A.K. REID, M.I. SHEPPARD, S.C. SHEPPARD and M. STEPHENSON, "The Disposal of Canada's Nuclear Fuel Waste: The Biosphere Model, BIOTRAC, for Postclosure Assessment." Atomic Energy of Canada Limited Report, AECL-10720, COG-93-10 (1993).
  15. L.H. FROST, N.W. SCHEIER and C.C. DAVISON, "Transport in Highly Fractured Rock Experiment - Phase 1 Tracer Tests in Fracture Zone 2." Atomic Energy of Canada Limited Technical Record, TR-672, COG-95-85 (1995a).
  16. L.H. FROST, N.W. SCHEIER and C.C. DAVISON, "Transport in Highly Fractured Rock Experiment - Phase 2 Tracer Tests in Fracture Zone 2." Atomic Energy of Canada Limited Technical Record, TR-685, COG-95-198 (1995b).
  17. N.A. CHANDLER, R.S. READ and A.W.L. WAN, "Implications of the Results of URL Experiments on the Design Repository Seals in Granite." In Proceedings of the Canadian Nuclear Society International Conference on Deep Geological Disposal of Radioactive Waste, Winnipeg, MB, pp. 7-1 to 7-10 (1996).
  18. B.H. KJARTANSON, N.A. CHANDLER and A.W.L. WAN, "In Situ Performance of a Clay-Based Barrier." In Sealing of Boreholes and Underground Excavation in Rock, Chapman and Hall, London, pp. 96-125 (1996).
  19. J. GRAHAM, N.A. CHANDLER, D.A. DIXON, P.J. ROACH, T. TO and A.W.L. WAN, "The Buffer/Container Experiment: Results, Synthesis, Issues." Atomic Energy of Canada Limited Report, AECL-11746, COG-97-46-I (1996).
  20. R.S. READ and C.D. MARTIN, "Technical Summary of AECL's Mine-by Experiment, Phase 1: Excavation Response." Atomic Energy of Canada Limited Report, AECL-11311 (1996).
  21. R.S. READ and J.B. MARTINO, "Effect of Thermal Stresses on Progressive Rock Failure at AECL's Underground Research Laboratory." In Proceedings of the Canadian Nuclear Society International Conference on Deep Geological Disposal of Radioactive Waste, Winnipeg, MB, pp. 7-43 to 7-53 (1996).
  22. R.S. READ and N.A. CHANDLER, "Minimizing Excavation Damage Through Tunnel Design in Adverse Stress Conditions." Tunnels for People. Golser, Hinkel & Schubert (eds.), Balkema, Rotterdam, ISBN 90 5410 868 1, p. 23 (1997).
  23. R.B. PECK, "Advantages and Limitations of the Observational Method in Applied Soil Mechanics." Extract from Publication No. 116. Ninth Rankine Lecture. Geotechnique, June 1969, 19, pp. 171-187 (1969).
  24. G.W. KUZYK, P.A. LANG and D.A. PETERS, "Advances In Technology for the Construction of Deep-Underground Facilities." In Proceedings of Tunnelling and Underground Space Technology Association (1986).
  25. G.W. KUZYK, P.A. LANG and D.A. PETERS, "Blast Design and Quality Control on the Second Level of Atomic Energy of Canada's Underground Research Laboratory." In Proceedings of the International Symposium on Engineering Geology and Underground Construction. International Association of Engineering Geology (1986).
  26. R.F. FAVREAU, G.W. KUZYK, P.J. BABULIC, R.A. MORIN and M.J. TIENKAMP, "The Use of Computer Blast Simulations to Improve Blast Quality." In Proceedings of the Second International Symposium on Rock Fragmentation by Blasting, Society for Experimental Mechanics, Keystone, CO, USA (1987).
  27. G.W. KUZYK and W.S. VERSLUIS, "Full-Face Shaft Sinking at AECL's Underground Research Laboratory." In Proceedings of the Society of Mining Engineers Annual Meeting, Las Vegas, Nevada (1989).
  28. G.W. KUZYK, P.A. LANG and D.A. PETERS, "Integration of Experimental and Construction Activities at the Underground Research Laboratory." In Proceedings of the 6th Annual Canadian Tunnelling Association Conference, Niagara Falls, Ontario, Canada (1986).
  29. R.A. EVERITT, C.D. MARTIN and P.M. THOMPSON, "An Approach To Underground Characterization of a Disposal Vault in Granite." Atomic Energy of Canada Limited Report, AECL-19560, COG-094-38 (1994).
  30. T.N. HAGAN, G.W. KUZYK, J.K. MERCER and J.L. GILBY, "Design, Implementation and Monitoring of Full-Face Blasts to Extend a Shaft at Atomic Energy of Canada Ltd.'s Underground Research Laboratory." In Proceedings of Shaft Engineering Conference, IMM, London, England, 1989 June 5-7 (1989).
  31. B. COOPER and R. ABEL, "An Approach to Applying Quality Assurance to Nuclear Fuel Waste Disposal." AECL Report AECL-11705 (1996).
  32. Mines Accident Prevention Association of Manitoba (MAPAM), "35th Annual Report for the Year 1996." (1996).
  33. R.W. POLLOCK and M. BARRODOS, "Environmental Screening for the Atomic Energy of Canada Limited Underground Research Laboratory near Lac du Bonnet and Pinawa, MB, Canada." Atomic Energy of Canada Limited Report, WNRE-523 (1983).
  34. A.E. LEMIRE, "Supplement to Environment Screening for the Atomic Energy of Canada Limited Underground Research Laboratory Near Lac du Bonnet and Pinawa, MB, Canada." Atomic Energy of Canada Limited Report, WNRE-523-1 (1987).
  35. P.M. THOMPSON, P.A. LANG, and G.R. SNIDER, "Recent Improvements to In Situ Stress Measurements Using the Overcoring Method." In Proceedings of the 39th Canadian Geotechnical Conference, Ottawa (1986).
  36. P.M. THOMPSON, E.T. KOZAK and C.D. MARTIN, "Rock Displacement Instrumentation and Coupled Hydraulic Pressure/Rock Displacement Instrumentation for Use in Stiff Crystalline Rock." In Proceedings OECD/NEA Workshop on Excavation Effects of an Underground Repository for Radioactive Waste, Winnipeg, 1988 April, OECD, Paris (1989).
  37. P.M. THOMPSON, "A Borehole Deformation Gauge for Stress Determinations in Deep Boreholes." In Proceedings of 31st US Rock Mechanics Symposium, Golden, 1990 June, ISRM (1990).
  38. P.M. THOMPSON and E.T KOZAK, "In Situ Measurement of Coupled Hydraulic Pressure/Fracture Dilation in Stiff Crystalline Rock." In Proceedings of the 3rd International Symposium on Field Measurements in Geomechanics, Oslo, 1991 September. pp. 23-32 (1991).
  39. P.M. THOMPSON, J.B. MARTINO and M.H. SPINNEY, "Detailed Measurements of Deformation in the Excavation Disturbed Zone." In Proceedings of 34th US Rock Mechanics Symposium, Madison, Wisconsin, 1992 June, ISRM (1993).
  40. P.M. THOMPSON, R. CORTHÉSY and M.H. LEITE, "Rock Stress Determinations at Great Depth Using the Modified Doorstopper Gauge." In Proceedings of the International Symposium on Rock Stress, Kumamoto, Japan, 1997 October, pp. 59 - 64, A.A. Balkema, Rotterdam (1997).
  41. Ontario Hydro, "Nuclear Waste Management and Decommissioning Report." Ontario Hydro Report, N-REP-03462-0124 (1995).

Table I. QA Tier II Procedures

Table II. QA Tier III Working Procedures

Fig. 1.

Fig. 2.

Fig. 3.

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