Rock Mechanical Analyses in Deep Underground Tunneling Projects for High Level Nuclear Waste Disposals

Since the consumption of energy can be expected to rise as population increases, the world has a constant increased demand of energy. Moreover, the need of a clean and powerful source of energy is even a bigger requirement due to the potential impact that the burning of fossil fuels has on the environment. Nowadays, many scientists consider atomic energy an alternative source of energy, both to supply essential energy as well as to be of low impact on the environment. However, major environmental problems are related to atomic energy. Some of these problems concern the storage of nuclear wastes. In fact the spent fuel from the nuclear fission is anyhow still radioactive, and therefore hazardous for the environment. There is a classification of nuclear wastes; low-level, intermediate-level and high level. The division is an imprecise one. The low-level and intermediate level wastes are relatively low radioactivity wastes, not requiring extraordinary disposal precautions. Volumetrically they account for 90% of radioactive wastes generated. High-level wasted are more dangerous and various more or less elaborate disposal schemes must be used. The basic disposal of high- level wastes is to isolate them from the biosphere with the confidence of providing any contact of them with the biosphere for many thousand of years. It is therefore necessary to depose this kind of radioactive wastes in a safety place, where contact from the biosphere, atmosphere and hydrosphere is avoided. Nowadays, many ideas have been raised on the disposal of high-level radioactive wastes. However, the proposal that has received the most serious attention is the deposition of the radioactive wastes underground, on which this report is about. Caverns hollowed out of low-permeability, not fractured igneous rocks such as basalt or granite are used in the high latitude countries, such as Canada and Scandinavia. Other disposals are constructed in salt formations, such as in Germany and USA, as well as in deep cemented sedimentary rocks. The principle is anyhow the same that is to depose the wastes in a safe and deep place, away as much as possible from the contact with the biosphere. There is general agreement among geologists that the ideal underground storage site for radioactive wastes should possess the following characteristics • The enclosing rock should have few fractures and low permeability • The enclosing rock should be effective at dissipating heat and chemicals absorbing any potential leaks • The enclosing rock should contain no mineral with present or future economic potential • Local groundwater flow should be as slow as possible and in a direction away from the biosphere • Only very long paths of groundwater flows should be directed toward places accessible to humans • The area should have low rainfall • The zone of aeration should be thick • The rate of erosion should be very low • The probability of earthquakes or volcanic activity should be very low • Future changes of climate in the region should be unlikely to affect groundwater conditions substantially The types of reservoir rock that are being investigated for long-based geologic isolation of high-level radioactive wastes are: