Finite-element based vibration analysis of WWER-440 type reactors

A finite-element model describing the mechanical vibrations of the whole WW ER-440 primary circuit was established to support the early detection of me chanical component faults. A special fluid-structure module was developed t o consider the reaction forces of the fluid in the downcomer upon the movin g core barrel and the reactor pressure vessel. This fluid-structure interac tion (FSI) module is based on an approximated analytical 2D-solution of the coupled system of 3D fluid equations and the structural equations of motio ns. By means of the vibration model all eigenfrequencies up to 30 Hz and th e corresponding mode shapes were calculated. It is shown that the FSI stron gly influences those modes that lead to a relative displacement between rea ctor pressure vessel and core barrel. Moreover, by means of the model the s hift of eigenfrequencies due to the degradation or to the failure of intern al clamping and spring elements was investigated. Comparing the frequency s pectra of the normal and the faulty structure, it could be proved that a re cognition of such degradations and failures even inside the reactor pressur e vessel is possible by pure excore vibration measurements. (C) 1999 Elsevi er Science Ltd. All rights reserved.