Deep borehole testing techniques developed for Canada's nuclear fuel waste management program

Abstract

Atomic Energy of Canada Limited's nuclear fuel waste management program is presently centred around the concept of deep burial of immobilized fuel waste within igneous plutons of the Archaean Canadian Shield. Contaminant transport within this host medium would be by movement through rock fractures. Consequently, as part of the overall concept assessment phase, hydrogeological research has been initiated to assess potential pathways for contaminant leaks to the biosphere. Determination of accurate rock mass and fracture hydraulic conductivities and travel times are essential to the deep burial concept. Five continuously cored, inclined boreholes have been drilled to equivalent vertical depths up to 1100 m into the Eye-Dashwa Lakes pluton of Northern Ontario. This granitic body is a massive, medium to coarse grained hornblende — biotite granite which is intrusive into a series of tonalitic gneisses. Detailed core logging and surface fracture mapping have provided fracture geometry data as vital input to the on-going hydrogeological research. Slim-hole, single - and double-packer assemblies including down-hole transducers and thermistors have been developed to measure transient and steady state pressures and temperatures. Down-hole measurements are multiplexed to surface recording equipment via a single conductor cable. Pressure and temperature responses can be observed as frequently as every four seconds. Essential test data are recorded on magnetic tape. The on-site, surface data acquisition system has the capability of plotting the pressure-temperature data as it is recorded, thus allowing immediate inspection and evaluation of test data. Preliminary analysis of hydraulic data indicate that at least three discrete flow regimes may exist within the pluton. Hydraulic conductivity values show a general decrease with depth, although zones of relatively high hydraulic conductivity do occur: values range from 10 −6 m/s near the surface to about 10 −13 m/s at 1000 m vertical depth, when porous medium analysis is used.