Principles of earthquake design for nuclear power plants in the FRG — A critical review and a realistic approach

Abstract

The principles of earthquake design for NPP in the FRG are recorded in the German nuclear safety standard KTA 2201.1 “Design of NPP's against Seismic Events, Part 1: Basic Principles”, prepared in 1971 and 1972 and issued in 1975. The regulations of KTA 2201.1 are based on the US regulation App. A CFR 100 “Seismic and Geologic Siting Criteria for NPP's”. The principles are therefore basically the same in the States as in the FRG. This results at least in an overestimation of the earthquake risk in Germany. One of the important reasons for unrealistic design procedures and therefore uneconomic soft- and hardware consequences is bound to the requirement for a double earthquake design, namely the design against the Safe Shutdown Earthquake (SSE) and the Operating Basis Earthquake (OBE). Because of the identical physical consequences of these two earthquakes, at least for most of the known plant sites, where fatigue due to the smaller but more frequent eartquake (OBE) has no technical relevance, there is no reason for an OBE. Therefore the present regulatory standpoint should be revised. On the basis of this knowledge a group of German experts has drafted a new proposal for KTA 2201.1, including the following basic modifications: • - calculations for the “Design Earthquake” will be deleted • - design for a single maximum earthquake, the “Safety Earthquake” • - definition of a smaller earthquake, with the requirement to inspect and if necessary to shut down the plant in the case that such a defined earthquake occurs. • - possibility of using site-specific seismic input data instead of standard response spectra. • - no need for any calculations in the case of site intensity I ⩽ 6.