Development and verification of a methodology for neutron noise response to fuel assembly vibrations

Nuclear reactors are stochastic systems, in which several parameters fluctuate even during steady-state conditions. In addition, structural components like fuel assemblies, vibrate due to strong hydraulic forces. This stochasticity is the cause of the neutron population fluctuating behavior; a phenomenon referred as neutron noise. This paper systematically analyzes the capabilities of the Studsvik's codes to model the fuel assembly vibration and to assess the neutron noise response. To this aim, the CASMO-5 code is utilized for generating cross sections by parametrizing the water-gap thickness of fuel segments. The fuel assembly vibration modelling is approximated by the dynamic modification of the water-gap widths between adjacent assemblies using the transient code SIMULATE-3K. The cross sections dependency on the water-gap width is analyzed and successfully compared against Serpent-2 reference results. Last, the utilized codes capability is verified qualitatively or/and quantitatively through a series of cases, at both lattice and nodal level. (C) 2020 The Author(s). Published by Elsevier Ltd.