Seismic Re-Evaluation of the Armenian NPP Unit 2: Issues and Engineering Approach

As part of the overall effort of seismically upgrading the Armenian Nuclear Power Plant (ANPP) - Unit 2, the Armenian Nuclear Regulatory Authority (ANRA) with the technical support of the US NRC is performing a host of independent studies on key seismic issues associated with the nuclear facility. Specifically, by taking into account new information that has been generated by a number of sources on (a) the seismic hazards at the site, (b) the soil condition and layering, (c) the particularities of the reactor foundation design and its interface with the surrounding soil, and (d) structural details of the reactor and generator buildings, a comprehensive effort has been undertaken to independently establish floor response spectra that, in turn, better reflect the seismic reality at the plant. To accomplish the task of generating floor response spectra, that will be used in the seismic upgrade, detailed analyses focusing on (a) the site response using the capabilities of the SHAKE program, (b) the Soil-Structure-Interaction (SSI) aspect of the problem utilizing the SASSI and POROSLAM codes, and (c) the dynamic response of the reactor building through the use of the STARDYNE code were performed. The combined output of the various aspects of the analysis lead to a set of floor spectra at key locations on the structure so that the existing capacity of safety systems can be assessed as well as the need for upgrade to meet their revised seismic margins. While the current effort is work-in-progress, the paper presents preliminary results of this independent study and it attempts to make engineering comparisons with other on-going studies performed on behalf of the nuclear power utility in its effort to seismically upgrade the plant.