Development of the in-structure response spectra of the VVER-440 Model 230 Kozloduy Plant

The Kozloduy NPP is located in the North-West part of Bulgaria on the Danube river. The plant consists of four units of 440 MW and two units of 1,000 MW. In the last 15 years there have been three strong, intermediate depth earthquakes in the Vrancea seismic zone (1977, 1986, 1990) which have affected the NPP site. The Vrancea zone is located approximately 300 km northeast of the plant. It is known for the generation of strong, long-period seismic motions. In 1990 an intensive work program for qualification of the plant according to the international standards (IAEA 1991; IAEA 1992) was initiated. The work started by a project for site confirmation. As a result, new design seismic characteristics were obtained. A Review Level Earthquake is defined by a maximum acceleration of 0.2 g; a response spectrum is shown. The generation of the in-structure response spectra for units 1 and 2 VVER-440 Model 230 is presented in this paper. The coauthors belong to an IAEA Advisory Team assisting the seismic upgrading project of the Kozloduy plant.