Seismic qualification of distribution board for Kozloduy NPP, units 5 and 6, by analytical method and by analogy

This abstract presents the basic approach for seismic qualification by analysis of a distribution board for fire dampers control at Kozloduy NPP WWER-1000 MW Reactor Buildings - Units 5 and 6. The distribution board is a steel cabinet with mounting plate inside it on which are mounted all the components. For this qualification are used results from preliminary tested on uniaxial seismic platform distribution board with smaller dimensions, but with the same components mounted in it. The smaller board passed successfully the seismic tests and stayed functional after the seismic excitation specified with the prescribed Required Response Spectra (RRS). The seismic qualification by analytical method of the distribution board begins with an overview of the input data used for the analysis, including the RRS and Test Response Spectra (TRS) of preliminary tested distribution board with smaller dimensions. Detailed 3D computer model of the preliminary tested board and comparison between the test results and the results derived by analytical methods are done. For getting more precise modelling, very detailed evaluation of the components (material, mass, location, way of fixture etc.) is made. The mesh of shell and frame elements is suitably selected to describe the behaviour of the board during the seismic tests. Way of fixing of the tested board to the seismic platform is evaluated and properly modelled. Calculated damping for registered by test resonance frequencies of the board is used for adjusting the modal damping in the model. The acceleration time history registered on the seismic platform for selected seismic level is used as an input excitation for the model of the tested board. Calibration of the modelled and the tested distribution board is done by comparison of the generated TRS for given direction of excitation, for selected points at height of the tested board for given damping from one side and Response Spectra (RS) for the same direction of excitation, the same points at height of the modelled board for the same damping on the other side. The compared spectra are similar, which means that the results derived from computer model are close to results from the tested specimen. A 3D computer model of the board to be analytically qualified is made using the calibration results of the model of already tested distribution board. The RS for given direction of excitation and given damping are generated for points of the analytically qualified board proportionally located to the points for which the TRS for the same direction of excitation and damping are generated. The RS should be enveloped by the TRS in order to be concluded, that the analytically tested distribution board can bear the seismic excitation specified by RRS and will stay functional after it. The RS for this specific analytically tested distribution board were not enveloped by the TRS for the tested board and an upgrade of the board was recommended. After the prescribed upgrade and modelling of the upgraded distribution board, was shown that the RS for the three directions of excitation are enveloped by the TRS. Conclusions about the functionality of the distribution board were made also. (authors)