Departure from linearity of neutron cross-spectra phase in BWRs

The effects on neutron cross-spectra in BWRs, of boiling initiation not at the core inlet, but downstream from the inlet is investigated by numerical simulation using a two-dimensional, two-neutron group model. It is found that this may result in destruction of linearity and even zeroing of phase at higher frequencies and the estimation of transit time, hence of bubble velocity, from the linear part of the phase may be erroneous