https://hal-cea.archives-ouvertes.fr/cea-02434557Rouchon, A.A.RouchonCEA-DES (ex-DEN) - CEA-Direction des Energies (ex-Direction de l'Energie Nucléaire) - CEA - Commissariat à l'énergie atomique et aux énergies alternativesSanchez, R.R.SanchezSNU - Seoul National University [Seoul]Zmijarevic, I.I.ZmijarevicCEA-DES (ex-DEN) - CEA-Direction des Energies (ex-Direction de l'Energie Nucléaire) - CEA - Commissariat à l'énergie atomique et aux énergies alternativesThe new 3-D multigroup diffusion neutron noise solver of APOLLO3 and a theoretical discussion of fission-modesnoiseHAL CCSD2017[PHYS.NEXP] Physics [physics]/Nuclear Experiment [nucl-ex][PHYS.NUCL] Physics [physics]/Nuclear Theory [nucl-th]amplexor, amplexor2020-01-10 10:47:242020-04-28 11:28:162020-01-29 11:25:24enConference papersapplication/pdf1Traditional neutron noise analysis addresses the description of time-dependent flux fluctuations induced by small global or local perturbations of the macroscopic cross-sections, which may occur in nuclear reactors due to stochastic density fluctuations of the coolant, to vibrations of fuel elements, control rods or any other structures in the core. Neutron noise equations are obtained by assuming small perturbations of macroscopic cross-sections around a steady-state neutron field and by subsequently taking the Fourier transform in the frequency domain. In this work, we present the new 3-D multigroup diffusion neutron noise solver implemented in APOLLO3, the new multi-purpose deterministic nuclear code under development in CEA. We illustrate the capacities of this new 3-D diffusion neutron noise solver by performing two neutron noise simulations in a large pressurized water reactor with heavy baffle in three dimensions a cross-sections oscillation and a traveling perturbation. Moreover, we give a separate analysis of the neutron noise anomaly recently observed in KWU PWRs while proving the existence of steady-state like global noise modes in the low frequency spectrum.