Formation selection methodology for deep geological repository in Lithuania

A special program and action plan have been developed in Lithuania for the purpose of implementing the European Council Directive 2011/70/Euratom of 19 July 2011, establishing the Community framework for the responsible and safe management of spent fuel and radioactive waste. An important part of this plan is related to geological investigations for the site selection, design and construction of deep geological repository (DGR) for spent nuclear fuel and high-level long-lived radioactive wastes. The main task of geological investigations is to select a suitable geological environment for DGR, which is closely related to that of the DGR site. There are several alternative geological formations potentially suitable for DGR in Lithuania. Selection of the most suitable DGR site should be made and the DGR concept should be developed applying clear methodology. The proposed methodology is based on the safety requirements established by International Atomic Energy Agency (IAEA), systematic approach and criteria that are widely used worldwide. The suitability evaluation criteria are divided into 4 groups according to the factors responsible for the stability and safety of the DGR system. The highest rank of significance is assigned to the group of criteria that are associated with the factors responsible for the loss of the long-term stability of the system. The criteria associated with the DGR system confinement are assigned to the second group and are ranked second in significance. The third group of evaluation criteria could be characterized as a data availability group. It consists of the evaluation criteria associated with the emergence of uncertainties. Features or processes responsible for the improvement of formation properties over time are assigned to the fourth group and have the lowest rank of significance. The application of this methodology allows calculating the suitability score of each potentially suitable geological formation depending on the level of data detail at any stage of the investigation.