Method of experimental power reactor noise analysis without use of high power reactor

A method is proposed for conducting power reactor noise analysis without recourse to an actual high power reactor. The basic concept is to simulate the power reactor noise by integrating the different elements constituting the actual reactor noise, such as the random noise-generating force, the zero-power reactor transfer function, and feed-back loops between the reactor power and the noise-generating force. For the simulation study, a nucleate boiling noise generator and a single feed-back loop were divised to permit experiments with flux-related heater input using the fast neutron source reactor YAYOI of the University of Tokyo. This report discusses problems encountered in applying the proposed method to the simulation of power reactor noise, and presents some of the results obtained: Two kinds of change in amplitude were observed in the normalized auto power spectral density of the neutron flux, emanating form: (a) fluctuating displacements of the boiling zone bottom boundary, and (b) fluctuating number of passing vapor voids. Significant differences in the resulting data were observed between the runs performed with constant and with flux-related heater input in the case of step response experiment, but not in steady noise analyses. This apparent ineffectiveness of the feed-back system is due to the relatively small value of the product of the reactivity power coefficient and the reactor power (-- 5 x 10-2%Δk/k) in the present feed-back experiment. (auth.)