This study demonstrates the selection process for the Horonobe URL based on surveys of existing information and geophysical surveys on a regional scale. In addition, preliminary requirements on the geological environment, safety (during construction of the underground facility) and social and environmental constraints were taken into consideration. The technical know-how utilised through the experiences for the site selection is described here. The proposed Horonobe URL site required the existence of argillaceous sedimentary formations and associated groundwater. Further fundamental requirements were appropriate rock mechanical properties and low gas content in the host rock to meet safe underground construction and operation regulations. This led to a stepwise narrowing down from several potential URL areas located completely within the Horonobe District to one candidate URL area and, finally, to a specific URL site. In the URL investigation area (ca. 3 km × 3 km) the main surface-based investigations were conducted as the first step to choosing the actual URL site. This was selected based on establishing fundamental factors related to the geological environment, safety and societal issues. This paper provides an outline of the process utilised in selecting the URL site by taking into consideration technical and social requirements. Thus stepwise approach and experience in selecting the URL site will be applicable when NUMO needs to select a site through literature surveys, and preliminary and detailed investigations in the future.

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