Three decades of underground research laboratories: what have we learned?

This paper provides firstly how four scientific and safety relevant issues have been addressed in special-purpose research laboratories focusing on the geological disposal of high level and long-lived radioactive waste. These are: (i) the effects of heat on the engineered barriers and the geological environment, (ii) the geochemical characterization of pore water in argillaceous rocks, (iii) the diffusion and retention of radionuclides, and (iv) the full-size sealing of a waste emplacement. They are illustrated by experiments conducted in five URLs, three of which are in clay formations (Mol in Belgium, Centre de Meuse–Haute-Marne in France, and Mont Terri in Switzerland) and two in granite (Äspö Hard Rock Laboratory in Sweden and Grimsel Test Site in Switzerland). Then the experiences gained from 3 decades of URL's experience have been outlined. The possible future activities in next 30 years in URLs and the roles of URLs are suggested.