Deep Borehole Placement of Radioactive Wastes a Feasibility Study
DEEP BOREHOLE PLACEMENT OF RADIOACTIVE WASTES A FEASIBILITY STUDY Bernt S. Aadnøy & Maurice B. Dusseault Executive Summary Deep Borehole Placement (DBP) of modest amounts of high-level radioactive wastes from a research reactor is a viable option for Norway. The proposed approach is an array of large- diameter (600-750 mm) boreholes drilled at a slight inclination, 10° from vertical and outward from a central surface working site, to space 400-600 mm diameter waste canisters far apart to avoid any interactions such as significant thermal impacts on the rock mass. We believe a depth of 1 km, with waste canisters limited to the bottom 200-300 m, will provide adequate security and isolation indefinitely, provided the site is fully qualified and meets a set of geological and social criteria that will be more clearly defined during planning. The DBP design is flexible and modular: holes can be deeper, more or less widely spaced, at lesser inclinations, and so on. This modularity and flexibility allow the principles of Adaptive Management to be used throughout the site selection, development, and isolation process to achieve the desired goals. A DBP repository will be in a highly competent, low-porosity and low-permeability rock mass such as a granitoid body (crystalline rock), a dense non-reactive shale (chloritic or illitic), or a tight sandstone. The rock matrix should be close to impermeable, and the natural fractures and bedding planes tight and widely spaced. For boreholes, we recommend avoiding any substance of questionable long-term geochemical stability; hence, we recommend that surface casings (to 200 m) be reinforced polymer rather than steel, and that the casing is sustained in the rock mass with an agent other than standard cement.
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