Creep Processes Involved in the Maturation of Clay-isolated Highly Radioactive Waste in Very Deep Holes

摘要

The basic idea of concepts for disposal of highly radioactive waste deep in rock isthat the heavy, saline, stagnant formational waters are unlikely to rise tocontaminate shallow groundwater. A recent concept involves placement of thewaste in the lower 2 km part of up to 4 km deep holes bored in granitic rock, andrelies on the sealing capacity of engineered barriers in the form of concrete andclay in the upper parts of the holes. The parts located in fracture-poor rock aresealed with dense expandable clay, while concrete is cast where pre-groutedfracture zones are intersected. The holes will converge by creep and eventuallyexert the seals to radial compression. Using a new rheological model based on theKelvin model in combination with a stochastic mechanical model, the predictedradial hole convergence causes a vanishingly small increase in pressure on theseals in the first 10,000 years. In a long time perspective they will be compressedand become less permeable. Parallel conversion of the clay minerals to becomeless expandable will, however, reduce this potential.