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Finite Element-Based Vibration Analysis of WWER-440 Reactors

Eberhard Alstadt, Frank-Peter Weiss

Nuclear Technology / Volume 128 / Number 1 / Pages 46-57

October 1999

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A finite element model describing the mechanical vibrations of the whole WWER-440 primary circuit was established to support the early detection of mechanical component faults. A special fluid-structure module was developed to consider the reaction forces of the fluid in the downcomer upon the moving core barrel and the reactor pressure vessel (RPV). This fluid-structure interaction (FSI) module is based on an approximated analytical two-dimensional solution of the coupled system of three-dimensional fluid equations and the structural equations of motions. By means of the vibration model, all eigenfrequencies up to 30 Hz and the corresponding mode shapes were calculated. It is shown that the FSI strongly influences those modes that lead to a relative displacement between the RPV and the core barrel. Moreover, by means of the model, the shift of eigenfrequencies due to the degradation or to the failure of internal clamping and spring elements was investigated. Comparing the frequency spectra of the normal and the faulty structure, one could prove that recognizing such degradations and failures even inside the RPV is possible by pure ex-core vibration measurements.

 
 
 
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