In Scandinavia seismic activity is generally low. Only a few incidents have been registered in historic time, which might have damaged an industrial plant of today. The risk of a nuclear accident in Sweden, caused by an earthquake, may thus be considered to be low.
The two latest reactors Forsmark 3 and Oskarshamn 3 have been analysed and designed to resist a specified earthquake. For the older reactors no corresponding analyses or designs have been made initially. Their general design is robust.and was considered to provide enough safety with regard to earthquakes of the magnitude reasonably to be taken into account.
In the last ten years period the demands on safety with respect to nuclear power has increased. This fact has necessitated studies of possible incidents with a lower and lower probability. In order to obtain a complete picture of the risk, it is therefore also necessary to evaluate the seismic safety for the older reactors and to apply this knowledge during operation and in connection with alterations of existing plant design.