Chemical, Physical and Engineering Characterization of Candidate Backfill Clays and Clay Admixtures for a Nuclear Waste
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CHEMICAL, PHYSICAL AND ENGINEERING CHARACTERIZATION OF CANDIDATE BACKFILL CLAYS AND CLAY ADMIXTURES FOR A NUCLEAR WASTE RESPOSITORY-PART I
DR. SUDESH K. SINGH Materials Research Laboratory Ltd.,
9B Caesar Avenue,
Nepean, Ontario,
Can.
ABSTRACT Fourteen Canadian clays and clay admixtures were subjectThe ed to simulated nuclear waste repository environments. present work is concerned with the montmorillonite-dominant materials only. The montmorillonite-dominant samples showed significant leaching on interaction with deionized water. 0 On heating the samples at 200 C for 500 hours, montmorillomites lost intermicellar water completely and acquired The loss of water cusp-like to cylindrical morphologies. and the morphological changes in montmorillonites significantly altered the engineering characteristics. Permeability, shrinkage limits, compactability and shear strength varied in response to the dominant exchange cation in the structure of montmorillonites and the presence of other The synthetic granite mineral components in the materials. water reacted with montmorillonites and led to changes in chemical and mineralogical compositions, crystalline state and engineering properties.
INTRODUCTION Many countries, including Canada, are investigating techniques of storing or The disposing of irradiated fuel or wastes from reprocessing irradiated fuel. Canadian program envisages multi-barrier disposal in vaults mined some 500 to 1000 meters below the surface in plutonic rocks of the Canadian Precambrian Shield. It is anticipated that the containers of nuclear waste, containing either vitrified high level radioactive waste or irradiated fuel, will be placed Buffering materials will in boreholes or channels cut into the vault floor. Backfill materials will fill the remainder of surround the waste containers. the mined cavity. The objectives of providing buffering and backfill material barriers are to (a) retain radionuclides or to retard their rate of migration after an accidental breach of the containers takes place, (b) provide a relatively stable and quite impermeable barrier to the flow of water, and (c) act as conductive media for the transfer of heat from the container to the host rock without undergoing thermal or chemical decomposition. The sorption materials must remain mechanically, thermally and chemically stable in the repository environment. In view of the above, it was decided to characterize potential Canadian materials for their chemical, physical and engineering behaviour under simulated repository environments. Some of the anticipated water-material interaction environments in a repository are described below: 1. The materials in the nuclear waste vault remain dry and reach temperatures 0 of up to 150 C. This or lower temperatures may prevail for several hundreds of years; 2. The containers are breached by a physical mechanism such as differential crushing and the nuclear wastes come in contact with the dry buffering materials. This event can take place due to diffe
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