On elastic lim it margins for earthquake design

In the Federal Republic of Germany KTA rule 2201 being the basis for the design of nuclear power plants against seismic events is now under discussion for revisions. One of the main demands to modify KTA rule 2201 consists in cancelling the existing design philosophy, i.e. design against an operating basis earthquake (AEB) as well as against a safe shutdown earthquake (SEB). The present KTA rule 2201 specifies with respect to class 1 systems and components elastic (or pseudo-elastic) limits to be regarded for AEB, while those limits may be exceeded for SEB on condition that functionability is guaranteed. When using the present rule the ‘lower’ earthquake (AEB) can become design-predominant, since for AEB and SEB different types of load cases are to be superimposed with different safety factors.