Measurement of stochastic flow-induced power fluctuations at LOFT

Investigation of power fluctuations at LOFT began after peak to peak power fluctuations of 1.5% of full power were observed prior to Loss of Coolant Experiment L2-3. The power fluctuations are caused by fluctuations in primary coolant flow. The fluctuations in coolant flow result in fluctuations in moderator temperature, which through the moderator coefficient of reactivity, cause the power fluctuations. This conclusion is supported experimentally by the high coherence between power and flow, and by the increase in power fluctuation magnitude with steady-state power and with increasing temperature coefficient. A theoretical model of the phenomenon is being developed to determine the power fluctuations' dependence on moderator and doppler coefficient, and predict fluctuation behavior during future operation