REGIONAL THERMOHYDROLOGICAL EFFECTS OF AN UNDERGROUND REPOSITORY FOR NUCLEAR WASTES IN HARD ROCK

The principal mechanism for underground migration of radionuclides is transport with groundwater. In the selection and assessment of suitable sites as potential repositories of nuclear wastes, it is important to predict the effects of heat generated by the wastes upon the water movement between the repository and the biosphere. With the absence of relevant engineering experience and the limitation on duration of in situ testing, simulation of global and long term thermal responses of the rock mass in hypothetical models is the main method for the understanding of the mechanism and the identification of the sensitive parameters controlling groundwater flow. This paper presents results of two sets of calculations: 1) Regional temperature effects are studied for different waste forms, repository dimensions and rock formations. The type of reprocessing treatment and the length of cooling period of the nuclear wastes before emplacement into the repository are found to be two of the more important factors. 2) Thermally induced fluid flow is calculated assuming a simple two-fracture system to make a “worst case” estimate of the transit time of water from repository to ground surface. Recharge capacity from the surrounding formation is found to be a controlling factor.