Determination of the sensitivity volume of a BWR in-core detector

Reactor noise analysis is used to draw dynamic information while a nuclear reactor is operating at a steady power. By cross correlating the signal fluctuations (i.e. cross power spectral density (CPSD)) of two axially located detectors in a boiling water reactor (BWR), one can evaluate a velocity associated with the propagating noise. In the past several years, attention of several investigators has been devoted to the interpretation of this velocity. Determination of the detector sensitivity volume (i.e. field-of-view (FOV)) is needed because it is important to know if the measured velocity is an average or a localized quantity. By performing a series of 2-group, X-Y, S4 transport theory calculations, it is concluded that a cell homogeneous model is valid for the prediction of the adjoint function distribution around a line (i.e. infinite in Z) detector. The validity of the cell homogeneous model for the prediction of the adjoint function around a point detector (i.e. a finite detector) is confirmed by performing numerical (2-group, cell and bundle homogeneous, X-Y and X-Y-Z diffusion theory models) and analytical (1-D infinite homogeneous diffusion theory model) calculations. Comparison of the results of the combined method of transport and diffusion theories with the results obtained from diffusion theory, showed that an X-Y-Z cell homogeneous diffusion theory model is sufficient for the prediction of the detector FOV