Analytical study of operating reactor noise on a single channel and a single phase flow model, (1)

Basic formulas to describe the propagation of a periodically modulated driving source are derived on the distributed model of at-power reactors. Disturbances in the neutron field are regarded as being promptly spread over the whole core in the frequency domain of usual interest for noise and frequency response analyses. On the basis of this approximation, a coupled set of kinetic equations for neutrons, fuel and coolant temperature is derived and solved for the case where a driving source of unit strength is imparted. The relations between the solutions obtained and the formulas for analyzing experiments are established. Comparisons are made qualitatively between the results and those of the lumped model. The existence of a sink and a resonance frequency is examined. The power spectral density of neutron fluctuations in a water reactor under forced circulated cooling shows a sharply varying configuration when the inlet coolant temperature fluctuations are the major noise sources. When the reactor is under natural convective cooling or under liquid metal cooling, no such characteristic features appear.