Neutron noise observations in German KWU built PWRs and analyses with the reactor dynamics code DYN3D

Obviously, more complex mechanisms than only temperature and/or mass flow fluctuations have to be considered. Simulated generic fluctuations of the local moderator density, that were introduced independently from thermal hydraulics, indicate that potentially deformations or vibrations of the fuel rod lattice or turbulent fluctuations of the coolant temperature and density inside the fuel rod bundles leading to variations of the local moderator content might be responsible for the observed neutronic noise. Therefore, advanced models coupling neutronics, thermal hydraulics, turbulence and mechanical modelling have to be developed.