Remarks on the possibility of identifying Subchannel behaviour in BWR neutron-noise measurements

In the past decade several authors have reported on neutron-noise experiments in BWRs. The high frequency investigations have been focused on the signals of incore detectors located in the same instrument guide tube. As a result of these investigations it has become common knowledge that the cross-correlation function (CCF) of the signals of detector peaks has a major peak, the location of which can be related to the propagation velocity of void fluctuations within the fuel bundles adjacent to the guide tube. It has also been reported that for detector pairs located in the upper part of the core, another peak appears in the CCF. Concerning the origin of the 'second transit-time effect' several interesting speculations have been put forward but no firm conclusion has been reached. The aim of this paper is to discuss the problem form the analyst's point of view. (author)