Measurement of power in research reactors using the neutron noise technique

Abstract A high-precision method based on the neutron noise technique in the frequency domain, with low dependence on both detectors and nuclear material types and locations, is proposed to measure the stationary power in a research reactor. An expression of the power spectral density (PSD) was obtained using a modal expansion of the detectors' field of view. The measured PSD data were fitted using the first term of the solution. Measurements were made in natural- and forced-convection regimes, in different critical arrangements, in the RA-6 research reactor located at the Centro Atomico Bariloche (CAB), Argentina. The principal theoretical hypotheses assumed in the method here proposed, experimentally verified as this work shows, were: the predominance of both the fission density fluctuation as the correlated source of noise and the fundamental adjoint kinetic eigenfunction in the detectors' field of view. For practical purposes it was found that the method can be applied between 10 W and 50 kW and it does not depend on detector and control rod locations. The method was used to calibrate other relative methods used to measure higher power. The measurements agree with the values obtained using heat balance techniques.