Precaution against earthquakes

ll German nuclear power plants should be able to withstand an earthquake. This design is based on an assumption as to what category of earthquake an individual power plant must be able to withstand; this is then termed the design basis earthquake.

Based on this assumption, the building and the technical equipment are constructed so as to allow the safe shutdown of the plant in the event of such an earthquake, while guaranteeing the essential on-going cooling of the fuel rods. In some cases plants undergone backfitting for improvement.

Design basis earthquake

During the nuclear power plant licensing procedure, the design basis earthquake is individually calculated for the site in question. According to the procedure specified in the nuclear regulatory framework, this equates to the strongest earthquake likely to occur within a radius of at least 200 kilometres from the nuclear site.

Systematic assessments of earthquake observations made in the relevant region since 800 A.D. formed the basis for this assumption. Geological findings concerning seismic shifts are also referred to. Since the assumptions required to calculate the design basis earthquake are naturally subject to uncertainty, a safety margin was included to prevent underestimation. The result was the specification of a design basis earthquake which, it may be assumed, will occur on average every 100,000 years.

Since earthquakes occurring in the Rhine rift valley, for instance, are likely to be stronger than those affecting the north German lowland plain, the nuclear power plants in the region also had to be able to withstand stronger earthquakes.