Estimation of effective -fraction of the VVER-1000 reactor in terms of exposure using DRAGON5/DONJON5

The effective -fraction has a key role in the dynamic response of the reactor. This study aims to assess the suitability and accuracy of the detailed models of DRAGON5 and DONJON5 code for estimation of the effective fraction of delayed neutron for the VVER-1000 reactor core. DRAGON5 is adopted to homogenize and condense lattice physics constants of fuel assemblies during fuel burnup, followed by DONJON5, which is used to calculate forward and adjoint flux profiles on the reactor core geometry. A thermal-hydraulic subroutine is developed for VVER-1000 reactor hollow fuel pellets to embody the reactivity feedback raised by changing the reactor power profile. The effective -fraction is evaluated for each fissile and fertile isotopes in terms of fuel burnup. The results of the coupling scheme are evaluated using the KASKAD code package of Bushehr NPP-I (BNPP-I). The results indicate that the use of SHI and SYBILT modules of DRAGON5 are essential to achieve reasonably precise resolution.