Comprehensive analysis on core support barrel (CSB) movements in the ULJ1N Nuclear Plant is performed through noise and structural analysis techniques. Noise signals are taken from the lower channel outputs of ex-core instrumentation system during the full power reactor operation period. Then they are converted into auto-power spectral densities (APSDs) and coherence functions in the frequency range of 050Hz to obtain the vibratory information of CSB movements.From APSDs, the three different vibration peaks of CSB are detected around the frequencies of 8, 15 and 20Hz, distinctly. These results are also agreed well with those obtained from the structural analysis by ANSYS version 4.3 computer program, which is the finite element method (FEM). Three different vibration mechanisms of CSB at each resonant peaks are identified as two types of the beam mode vibrations (vig., pendulum motion and torsional motion) and the shell mode vibration, respectively.
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