An on-line, passive method for monitoring the moderator temperature coefficient (MTC) in a pressurized water reactor is described and compared to an analytical model. The method correlates fluctuations in the neutron flux with fluctuations in the coolant temperature. Results show that the frequency response function between the in-core neutron flux and thermocouple signals is proportional to the MTC and can be used to monitor changes in the MTC throughout the fuel cycle. An analytical model is also formulated and used to investigate how the neutron flux and coolant temperature fluctuations are related and change in the axial core direction. The analytical model results agree reasonably well with the experimental results. / Ph. D.