Application of Position-Dependent Delayed-Neutron Fractions to IQA Calculations for PT-SCWR

Abstract

Delayed-neutron fractions depend on fuel burnup and therefore they are position-dependent because fuel burnup is position dependent. This study investigates the use of position-dependent delayedneutron fractions for Improved Quasistatic kinetics calculations. A new module, MODPARA, is developed and implemented in the 3-D diffusion code DONJON for this purpose. The position dependence of delayed-neutron fractions is taken into account in the calculation of both the amplitude function and the flux shape function during the transient. The amplitude function is primarily influenced by the whole-core effective delayed neutron fractions which are now calculated by accounting for the spatial dependence of the local delayed-neutron fractions. Transient calculations for the Pressure-Tube Super-Critical-Water-cooled Reactor (PT-SCWR) show that accounting for the position dependence of the delayed-neutron fractions changes the time dependence of the amplitude function by as much as 11% compared to the case where position-independent delayed-neutron fractions are used and thus is a desirable enhancement to the IQS method.