Investigation of the relation between the RMS-neutron-noise and local void fraction in the bubbly flow region of a BWR

an attempt has been made to relate the RMS-neutron-noise in the frequency region above several Hz with the local volumetric void fraction in the lower part of a BWR-core. The model calculation assumes that the neutron fluctuations are induced by the propagating void fluctuations mainly via the thermalization process and sampled by the detector within a small sensitivity volume given by the lambda-component of the homogeneous two-group diffusion theory. The driving noise source is based on the formula derived by Kosaly for bubbly flow. Numerical results of the model calculation are compared with RMS-neutron-noise values measured in the core of an operating BWR. (author)