Nuclear reactor primary coolant loop flowmeter with phase shift tracking compensation

An improved nuclear reactor primary loop flowmeter has two spaced N-16 detectors (12 and 14) positioned along the primary loop piping for monitoring the N-16 activity within the coolant at the respective detector locations. The outputs of the two detectors are cross-correlated to determine the transit time of corresponding N-16 perturbations viewed at the two detector locations. The improvement comprises means for switching (34 and 36) the respective detector output electronic processing channels (18 and 20) between detectors (12 and 14) and measuring the maximum cross-correlation function (30 and 32) with the detector output channels in their original and switched positions to determine the true coolant transit time between detector locations and any phase shift induced by the detector output channels