3-DIMENSIONAL MODEL OF VIBRATION AND IMPACTING OF INSTRUMENT TUBES INA BOILING WATER-REACTOR AND TRANSFER FROM MECHANICAL TO NEUTRON NOISE

The vibration and impacting of an instrument tube against the surround ing fuel boxes in a boiling water reactor (BWR) was studied by means o f a three-dimensional, one-modal model. The transfer of the tube displ acements to neutron fluctuations of the fission chamber-instrument tub e assemblies was calculated by employing the adjoint function techniqu e and utilizing a two-dimensional, two-group diffusion theory. The res ults were used to interpret the particular measured noise spectra of a n instrument tube in the 1300-MW Gundremmingen C B WR. The root-mean-s quare of the displacements was estimated from the experimental neutron data.