Author(s)

G. Dundulis & E. Uspuras

Abstract

The Ignalina NPP located in Lithuania, close to the borders of Belarus and Latvia. The Baltic region is considered as an aseismic or of very low seismic activity. However, the Ignalina NPP is in the area of the East-European platform, at the junction of two large structure elements: the Baltic sineclize and the Mazur-Belarus antiklize. Therefore, the crystal foundation and sediment case are separated by a series of tectonic breaks. From the evidence of the tectonic disintegration of this area, the probability of availability of tectonic disintegration zones near the Ignalina NPP is relatively larger compared to the neighbour regions. According this the seismic assessment of the Ignalina NPP is important. The seismic assessment of the downcomers pipes is presented in the paper. The analysis was carried out according to code ASME III, division I, subsection NC. The finite element method was used for the present analysis. The envelopes of floor response spectrum were used for seismic analysis. The stresses of the pipes were examined. The results of the seismic analysis confirmed that downcomers pipes fulfil the ASME requirements. Keywords: nuclear power plant, seismic analysis, finite element method, floor response spectra, stress analysis. 1 Introduction The Ignalina NPP operates a RBMK (Chanelized Large Power Reactor) type reactor. Disadvantage of this reactor is extremely complex design of the buildings and piping systems with respect to those built in Western countries. The graphite structure consists of 2488 channels, made up of columns of bricks each with an axial hole for the channel tube [2]. These channels are welded to the

Keywords

nuclear power plant, seismic analysis, finite element method, floor response spectra, stress analysis.