A sensitivity study for reactor neutron noise calculations with a neutron absorber of variable strength

Paper in proceeding, 2018

The paper presents a sensitivity study for reactor neutron noise simulations. The objective is to investigate different modelling choices of the input uncertainties and to assess the influence of possible uncertainties in the nuclear macroscopic cross-sections and in the neutron noise source. A simplified light water reactor core with a localized thermal neutron absorber of variable strength is considered. For this analysis, the neutronic tool CORE SIM is combined with a statistical methodology for uncertainty and sensitivity analysis. Modelling the input uncertainties as uniformly or normally distributed is found to make no relevant difference in terms of the calculated neutron noise. The uncertainties of the thermal capture and removal cross-sections at the location of the neutron noise source affect the induced neutron noise at the location of the neutron noise source and at other locations. The effect of the uncertainty in the thermal fission cross-section at the position of the neutron noise source is mainly on the fast neutron noise and it tends to disappear far from the neutron noise source. The uncertainties of the cross-sections at a position away from the neutron noise source have a small impact on the induced neutron noise taken at the same location away from the neutron noise source (except for the removal cross-section) or at other locations. The uncertainty in the neutron noise source amplitude can significantly affect the neutron noise amplitude over the reactor, although the effect decreases with the distance from the source. Similar outcomes are obtained in the adjoint problems.