Abstract

Canada, along with other countries that are considering the permanent disposal of high-level radioactive wastes from nuclear power generation, is undertaking a program of research into deep geological disposal. This program, led by Atomic Energy of Canada Limited (AECL) with support from Energy, Mines and Resources Canada, other federal government departments, universities, and industrial consultants, has been in progress since early in 1973. Geoscience research, the subject of this symposium, complements research on fuel waste immobilization to provide the data and information essential to the design and assessment of a complete disposal concept involving both natural and engineered barriers to the migration of radioactive material from the waste vault.During the early phases of the program, prior to 1975, an evaluation of the potential of Canadian salt deposits for nuclear waste disposal, as well as a preliminary assessment of the suitability of other geological formations, was made. Because the Province of Ontario was, and remains, the principal region in Canada for nuclear power development and because resources available for geoscience research would not permit simultaneous, intensive research on a number of rock types, the decision was taken to direct the main thrust of the geoscience research toward plutonic igneous rocks of the Canadian Shield in Ontario (Scott 1979). Lesser studies of salt and other sedimentary formations, including seabed, are continuing within the Geological Survey of Canada.Because the rock mass surrounding the vault will provide the principal barrier to the migration of radionuclides, should these be released from the emplaced wastes, knowledge and understanding of potential pathways through the rock mass and of the mechanisms of radionuclide transport and retention within the rock mass over the functional lifetime of the vault are fundamental requirements.Accordingly, the objectives of the geoscience research program (Dormuth and Scott 1984) are the following:(1) Develop and apply techniques to define the physical and chemical properties of large rock masses and of fluids within these rock masses.(2) Use these techniques in selected field research areas to calibrate and evaluate models developed to calculate fluid flow and mass transport through a large rock mass containing a hypothetical underground nuclear fuel waste-disposal vault.(3) Establish procedures to evaluate quantitatively rock bodies for their potential as disposal sites and thereby acquire the capability to compare different rock bodies.(4) Determine the long-term stability of plutonic rock masses by assessing the potential disturbance by seismic activity, glaciation, meteorite impact, and other disruptive events and processes.To achieve these objectives it has been necessary to undertake simultaneously a large number of research tasks involving the disciplines of geology, geophysics, hydrogeology, geomechanics, geochemistry, and mathematics. Some of these tasks are concerned primarily with regional aspects of the Canadian Shield, such as stress distribution, glaciation, and tectonic history; others with details of the surface and subsurface geology and hydrogeology of specific field research areas; and still others with the development and application of exploration technology to detect and evaluate the structural characteristics of igneous rock masses of relatively high integrity and uniformity. Field and office studies are supported by laboratory investigations of the physical and chemical properties of plutonic rocks, with specific reference to origin, history, and ability to retard or transmit radionuclides.Deep exploratory drilling and detailed surface mapping are carried out at designated field research areas in the Canadian Shield. Geoscience work at research areas has the two-fold purpose of (i) testing new and existing exploration techniques for the evaluation of rock masses; and (ii) through application of these airborne, surface, and subsurface techniques, providing the field data necessary for the development of concepts and models that form the basis for establishing site-selection criteria and performing safety analyses.The latest research areas have been established at Atikokan, Ontario, an area underlain by granitic rocks, and at East Bull Lake north of Massey, Ontario, where gabbroic rocks are the dominant type. These research areas complement previously established research areas developed on granitic rocks at AECL properties at Chalk River, Ontario, and Pinawa, Manitoba, and at a research area, also on granitic terrane, near White Lake, Ontario, where work was done early in the program to test geophysical exploration and borehole-logging equipment.The ability to predict subsurface geological and hydrogeological conditions at future waste-disposal sites is one of the primary goals of geoscience research in the Canadian Nuclear Fuel Waste Management Program (CNFWMP). One of the most important program elements designed to test this predictive capability was the construction of the Underground Research Laboratory (URL) in the Lac du Bonnet Batholith near the site of the Whiteshell Nuclear Research Establishment. Airborne, surface, and borehole methods were used to develop a geological model on the site, and hydrogeological investigations were carried out to establish preconstruction groundwater characteristics. As the excavation of the URL facilities proceeded, the geological features encountered and the changes in the hydrogeological systems were carefully monitored. These data are being used to assess and improve the geological and hydrogeological models being developed for the rock mass surrounding the URL.The URL provides an excellent opportunity to (i) study the effect of excavation techniques, heat, and stress on a rock mass; (ii) simulate and study the complex systems that may exist in a disposal vault environment; and (iii) develop and test shaft- and drift-sealing techniques. Recently, a bilateral agreement between AECL and the United States Department of Energy was signed for co-operative research on nuclear fuel waste disposal. A substantial part of this co-operative effort will be directed toward extension of the URL shaft beyond its present depth of 240 m and conducting a variety of nonnuclear experiments within the shaft and excavated chambers of the URL.From the time of formalization of CNFWMP over 10 years ago, a concerted effort has been made by AECL and other program participants to ensure both peer review of and widespread accessibility to results of research arising from CNFWMP. This symposium is the third to be sponsored by the Geological Association of Canada (GAC)—the two previous symposiums were held at GAC annual meetings in Winnipeg in 1982 and Toronto in 1978. In addition to these major symposia, general information meetings sponsored by AECL have been held annually at various centres across Canada, and research elements of CNFWMP formed a significant part of the technical program for an international meeting held by the Canadian Nuclear Society in Winnipeg in September 1986.Since 1979 the CNFWMP review process has been further enhanced by the Technical Advisory Committee chaired by L. W. Shemilt, McMaster University. This committee, comprising members nominated by major Canadian scientific and technical societies including the Canadian Geoscience Council, has annually provided a publicly available report of constructive criticism and recommendations for improvement in the research content of CNFWMP.During the second half of 1988 it is expecte

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