[en] The Swiss Federal Nuclear Safety Inspectorate ENSI, acting as the regulatory body of the Swiss Confederation, assesses and monitors nuclear facilities in Switzerland. These include five nuclear power plants, the interim storage facilities based at each plant, the Central Interim Storage Facility (ZWILAG) at Wuerenlingen together with the nuclear facilities at the Paul Scherrer Institute (PSI) and the two universities of Basel and Lausanne. ENSI ensures that the facilities comply with regulations and operate according to the law. Its regulatory responsibilities also include the transport of radioactive materials to and from nuclear facilities and the preparations for a deep geologic repository for nuclear waste. It maintains its own emergency organisation, which is an integral part of a national emergency structure. Building on the legislative framework, ENSI also formulates and updates its own guidelines. It provides the public with information on particular events and findings in nuclear facilities. In 2011, all five nuclear power reactors in Switzerland (Beznau Units 1 and 2, Muehleberg, Goesgen and Leibstadt) were operated safely and ENSI concluded that they had complied with their approved operating conditions. There were 27 reportable events in the nuclear power plants in Switzerland: 7 at Beznau, 5 at Goesgen, 11 at Leibstadt und 4 at Muehleberg. On the international INES scale of 0 to 7, ENSI rated 26 events as Level 0. One event, at the Muehleberg nuclear power plant, was rated as INES Level 1. This related to a potential blockage of the emergency water intake system in the event of extreme flooding. The operator BKW shut down the Muehleberg plant ahead of the scheduled maintenance date and upgraded the system. ZWILAG consists of several interim storage halls, a conditioning plant and a plasma plant (incineration/melting plant). At the end of 2011, the cask storage hall contained 34 transport/storage casks with fuel assemblies and vitrified residue packages as well as 6 casks with decommissioned waste from the experimental nuclear power plant at Lucens. About 17 % of the capacity of the high-level radioactive waste store had been used and about 23 % of the low- and intermediate-level waste store. During the year, ZWILAG conducted two campaigns to incinerate and melt radioactive waste. ENSI recorded no reportable events at ZWILAG during 2011. ENSI is also responsible for the surveillance of the nuclear facilities at PSI: the research reactor PROTEUS, the hot laboratory, the collection point for radioactive waste from medicine, industry and research, and ZWILAG. From the radiological standpoint, decommissioning work at the two research reactors DIORIT and SAPHIR progressed correctly. There were no further irradiation experiments during 2011 at PROTEUS and operational activities were restricted to routine maintenance and checks. During 2011, there were three reportable events at PSI relevant to nuclear safety. All were rated as INES Level 0. ENSI recorded one reportable event at the research reactor at the Federal Institute of Technology in Lausanne and none at the University of Basel. ENSI concluded that the nuclear facilities at PSI and the research reactors at Lausanne and Basel had complied with their approved operating conditions during 2011. Last year the amount of radioactive material released into the environment via waste water and exhaust air from nuclear power plants, ZWILAG, the PSI and the nuclear facilities at Basel and Lausanne was considerably less than the limits specified in the operating licenses. They resulted in maximum calculated doses, including for those residents in the immediate vicinity of a plant, of less than 1 % of the annual exposure to natural radiation. During 2011, two consignments of compacted reprocessing waste were transported from La Hague in France to ZWILAG. The consignments of fuel assemblies and radioactive waste were transported in accordance with the limits specified in the regulations. As part of Stage 1 of the Sectoral Plan for the deep geologic repository, the National Cooperative for the Disposal of Radioactive Waste (NAGRA) proposed six possible locations for geologic disposal for ILW waste and three for HLW waste. ENSI reviewed the procedure used by NAGRA and found it to be both transparent and understandable. It approved the proposed locations. The main ENSI demand was for more information on the host rock. In addition, ENSI demanded a systematic description of the hydraulic flow paths for the various locations and in-depth studies of structural issues. During 2011, NAGRA continued its geologic research at the Rock Laboratories of Grimsel (crystalline rock) and Mont Terri (Opalinus clay). For its part, ENSI is conducting an experiment at Mont Terri to determine the geo-mechanical behaviour of the Opalinus clay. It is also participating in two other experiments: one to determine the drying out behaviour of the tunnel walls of Opalinus clay, another to evaluate a new method for measuring porosity