The Swiss Federal Nuclear Safety Inspectorate ENSI has published its report on the assembly deviation on two of six emergency diesel generators at the Beznau nuclear power plant (KKB). ENSI concludes that KKB was safe and protected against earthquakes despite the assembly deviation.
As a consequence of Fukushima, ENSI increased the earthquake protection requirements for all Swiss nuclear power plants in 2012. At that time, KKB provided the necessary verifications with a positive result. In 2020, however, the assembly deviations on the emergency diesels were discovered. As a result, it only became clear in retrospect that the formal requirements had not been fully met in the event of an earthquake, which is to be expected only once every 10,000 years. This resulted in a formal deviation during two months (April and May 2012). With the commissioning of two retrofitted diesel generators in June 2012, the requirements were met again according to the authority.
Thanks to various retrofits and other measures, ENSI certifies that the KKB has a very high level of earthquake safety. Over the past decades, Axpo has invested around CHF 2.5 billion in the reliability and safety of the plant. During the months of April and May 2012, the level of earthquake protection was the same as in the months and years before.
In the meantime, KKB has analysed the reasons for the non-detection of the assembly deviation and various measures are being implemented. For example, additional checks are being carried out on ongoing projects to determine whether the components supplied correspond to the design. In addition, existing processes are being analysed and adjusted if necessary.