Investigation of the properties of neutron noise induced by localized perturbations in a sodium-cooled fast reactor has been\nperformed using amultigroup neutron noise simulator. Three representations of the noise source associated with the perturbations\nof absorption, fission, and scattering cross sections, respectively, were assumed to be located at the first fuel ring around the central\nassembly.The energy- and space-dependent noise, that is, the amplitude and the phase, was calculated in a wide range of frequencies,\nfor example, 0.1ââ?¬â??100Hz. The results show that in the important energy range (>1.0 keV) where the noise amplitude is significant the\nphase is almost constant with energy at the calculated frequencies despite the source types. At low frequencies, the variation of the\nphase is negligibly small at a large distance from the source. The perturbation in several fast groups has a significant contribution\nand dominates the amplitude and the phase of the induced noise.
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