Research and experience report 2012. Developments in the technical and legal basis of nuclear oversight

The Swiss Federal Nuclear Safety Inspectorate (ENSI) acts upon the basis of the latest developments in science and technology. ENSI supports and coordinates safety research, the results of which influence directly its Guidelines, individual decisions and resources. Research projects also serve training purposes and maintain competence within ENSI and its experts. The research in fuels and materials covers the reactor core and the graded approach to barriers used for the confinement of radioactive materials. Based on test results from accidents involving a loss of coolant ENSI instructed the operators of Swiss nuclear power plants to review whether they were relevant to their own facilities. Ageing mechanisms affecting structural materials are crucial to the long-term operation of nuclear power plants. Specialised thematic databases are being created in order to facilitate a systematic analysis of relevant operating experience from numerous countries. In addition to damage that may result from events within nuclear power plants, the safety analyses also reflect external events. ENSI supports international projects conducting complex experiments and simulations of aircraft accidents and earthquakes. It is involved in some projects relating to flood risks. The effect of operator behaviour on accidents in nuclear power plants is the focus point of research into human factors which identifies and analyses certain operator errors influencing negatively the course of an accident. Proposals to improve accident procedures were developed. This research area also focuses on the influence of the control room layout on the performance of operating staff. System behaviour and accident sequences in nuclear power plants are analysed in conditions ranging from normal operations through to accidents resulting in core melt-down. The results are used for the quantitative evaluation of the plant risk in probabilistic safety analyses. Applied research in radiological protection ranges from the radiation measurement technology through to aero-radiometry and the development of new radionuclide analytical methods. The ENSI involvement in the development of international norms is contributing to cross-border harmonisation of radiological protection methods. The projects in decommissioning and disposal include research into the Opalinus Clay as a host rock and the design and monitoring of a deep geological repository. Research is focussed into the development of gases and the coupled thermal, hydraulic, mechanical and chemical processes. With regard to the potential erosion of future glaciers, the project on climate modelling has provided a better understanding of atmospheric circulation during an ice age. Incidents in nuclear facilities provide information on weaknesses and on potential for improvements in all aspects of design and operation. The current report provides information on a selection of particularly instructive events in facilities outside Switzerland. They have been analysed in order to determine their relevance to Swiss nuclear facilities. Switzerland had introduced measures to prevent errors during maintenance shutdowns. By cooperating with international organisations and regulatory bodies, ENSI ensures that Switzerland remains abreast of developments in the field of nuclear safety. It has bilateral agreements with neighbour countries. The accident at Fukushima Dai-ichi continued to affect international cooperation. ENSI introduced concrete proposals for more binding obligations and greater transparency and a strengthening of international safety requirements. In the field of the European Union Stress Test, ENSI took part in the international review process completed in April 2012; it is supporting improvements to and a harmonisation of safety standards. Switzerland meets its obligations on the disposal of radioactive waste. The assessment emphasized several positive features such as the Sectoral Plan on the deep geological repositories, the existence of a disposal programme, the periodic review of disposal costs and the regular review that ENSI conducts of its own activities. The existing regulatory framework of ENSI is being revised so that it complies with recent national nuclear energy legislation and is harmonised with international standards