On the dependence of the point-kinetic response of the neutron noise on the fraction of delayed neutrons

Paper in proceeding, 2026

The possibility of localizing point-like perturbations in nuclear cores from the neutron noise measured at a few selected locations depends greatly on the deviation of the reactor response from point-kinetics. As the spatial dependence of the neutron noise in case of point-kinetic behaviour is given by the static flux, a point-kinetic dominated reactor response does not exhibit any information about the location of the perturbation. In this paper, the dependence of the magnitude of the point-kinetic component on the fraction of delayed neutrons is studied, both analytically and through numerical simulations. At plateau frequencies, it is demonstrated that the deviation from point-kinetics decreases with decreasing values of the fraction of delayed
neutrons. For fuel typical of light water reactors, a decrease during fuel depletion due to Pu-239 build-up is noticed. The decrease is nevertheless not sufficient to jeopardize the possibility to infer from the measured neutron noise the position of the perturbation. For other systems, like
fast reactors loading with MOX fuel or reactors based on the thorium-uranium fuel cycle, the decrease could be important.