Analytical techniques were developed to analyze pulsed neutron activation measuements in large pipes leading to a determination of the fluid velocity in the pipe. Neutron and gamma-ray Monte Carlo transport calculations were carried out at the neutron tagging and gamma-ray detector positions, for the piping sizes typical of the loss-of-fluid test (LOFT) experiment. Dispersion models were developed, to describe the transport and mixing of the irradiated fluid from the source to the detector location, and the L3-7 LOFT small break neutron activation test data were analyzed. The values of the fluid transport velocity obtained by a phenomenological model based on finite difference equations agree with those found from experiment.