Influence of the neutron-kinetic feedback parameter variation on an anticipated transient without scram in a PWR

The complete failure of the reactor scram system upon request during an operational transient is called anticipated transient without scram (ATWS). The coupled code system DYN3D/ATHLET developed at FZD is applied to the analysis of an ATWS transient. The objective of the present work was to perform a best-estimate analysis with consequent use of a 3D neutron kinetics code (DYN3D) in combination with an advanced thermal hydraulic system code (ATHLET) together with a quantification of differences in the course and the results of transients, which arise from the uncertainties of neutron-physical conditions. Typically, the complete failure of the main feed water supply is assumed to be the bounding ATWS event with regard to the maximum primary coolant pressure, which can be reached during the transient. The limitation of the coolant pressure is a precondition for the integrity of the primary circuit. The maximum pressure determined in the calculations does not reach the allowed limit for the primary circuit even with a reasonable statistical variation of neutron-physical boundary conditions. (authors)