Remarks on the inadequacy of one-group heterogeneous theories for the interpretation of incore neutron noise in BWRs

Abstract

By employing the frequency-dependent source-sink method of Feinberg and Galanin, it is shown that similarly to homogeneous diffusion theory, an explicit one-group heterogeneous theory with no slowing-down taken into account is not sufficient for the interpretation of incore neutron noise measurements in BWRs or in any other situation in which the distance between the perturbation and the detector is small. It is shown that, although in contrast to homogeneous one-group theory, in the heterogeneous approach there will always be a local component associated with attenuation effects in the pure moderator, if no slowing-down effects are taken into account, either the spatial relaxation length of the global component will be under-estimated, or the spatial relaxation length of the local component will be over-estimated.