Research and experience report 2011

In order to carry out its regulatory responsibilities for nuclear facilities, it is essential that the Swiss Federal Nuclear Safety Inspectorate (ENSI) remains informed of the latest developments in science and technology. Hence, it supports and coordinates research into regulatory safety. Some of the findings from this research feed directly into the guidelines. Research projects provide training and thereby ensure that ENSI and its experts possess the required expertise. ENSI also contributes to many international projects. The research into fuels and materials relates to the reactor core and the multiple barriers used for the containment of radioactive materials. It looks primarily at stresses on fuel rod cladding caused by mechanisms like ageing and the increasingly high burn-up rates. Within OECD, specialist databases are being created, e.g. on pipe damage, fire damage or common cause errors. ENSI has given considerable attention to external events; it has been conducting research into earthquakes, plane crashes and energy-rich surges in the high-voltage network. The research on operator behaviour in accidents in nuclear power plants (NPPs) is looking at the reliability of operators under difficult conditions but also on the influence of control room lay-out on the performance of operating staff. Analysis of system behaviour and accident sequences in conditions ranging from normal operations to accidents involving core melt-down is part of a research on computer models in order to provide a more comprehensive simulation of plant behaviour. Research in radiological protection ranges from the technology used to measure radiation to aero-radiometry and the development of new methodologies for radionuclide analyses. Work is continuing on the procedures specified in the Sectoral Plan for deep geologic repositories. In addition to the ongoing research at the Mont Terri Rock Laboratory into Opalinus Clay as a host rock, the research includes the design and monitoring of deep repositories, the properties of radioactive waste, the gases they develop and the possible influence of future glaciers. A project is looking at the long-term development of the landscape of the northern alpine foreland. Incidents in nuclear facilities outside Switzerland are analysed with a view to identifying any potential relevance to Swiss nuclear facilities. The accident at Fukushima was by far the most important event in 2011. The strongest earthquake ever recorded in Japan occurred on 11 March on the North-East coast of Japan. Although the NPPs withstood the immediate effects of the earthquake, the subsequent tsunami destroyed numerous auxiliary units, water-supply systems, piping, etc. at Fukushima Dai-ichi. The on-site power and coolant supply failed and despite emergency management measures, it was impossible to avoid serious damage to four of the six reactor units. The resultant release of radiation into the environment was significant and the accident was classified as level 7, the highest on the INES Scale. The area around the power station was largely evacuated. ENSI conducted an in-depth analysis of the accident in order to identify whether it could have implications for the safety of NPPs in Switzerland. The hazard profile assumed for each individual plant location must be reviewed regularly. If an accident does occur, emergency equipment and procedures capable of limiting its consequences must be available; in particular this must include emergency Diesel generators, systems to prevent hydrogen explosions, filtered containment venting and adequate technical decision-making tools for accident management purposes. The accident management must be designed to cover difficult external conditions. The required equipment must also be stored externally and capable of being transported to the accident location. Clear action must be taken to protect the public and evacuations from the vicinity of the power plant must be well planned. International cooperation in the nuclear field must be improved. ENSI required the participation of all Swiss nuclear power plants in the IAEA stress tests. Two incidents were noticed in French NPPs: the failure of an emergency Diesel generator, and the lack of the required siphon breaker orifices in the injection pipes for the cooling of the fuel storage ponds. The Swiss nuclear power plants reviewed the French findings for relevance and introduced some additional measures. ENSI was reviewed by a Mission from IAEA. Although the results were positive, the Mission also made constructive recommendations and suggestions for further improvements. The existing regulatory framework in surveillance principles is being revised so that it complies with recent nuclear energy legislation. ENSI revised its guideline and also approved three new guidelines: safety classification for existing NPPs, ageing management of nuclear facilities and the collection/recording of doses of persons exposed to radiation