Neutronic analysis of VVER-1000 fuel assembly with different types of burnable absorbers using Monte-Carlo code Serpent

A neutronic study on the fuel assembly of a Russian type nuclear reactor VVER-1000 fuelled with low enriched Uranium (LEU) plus 12 UO2+4%Gd2O3 rods was performed. This type of fuel requires validated computational methods and codes able to provide reliable predictions of the neutronics characteristics. Gadolinium self-shielding effect and isotopes accumulation in Rim region make it necessary to study the geometric modelling effect on the code calculations. The modelling of this fuel type was tested using Monte-Carlo and deterministic codes. In this study, Serpent results are verified using two nuclear data libraries ENDFb.6.8 and ENDFb.7. Also, this study investigates the effect UGd rods division into multiple radial layers on the reactivity, isotopic generation and burnup radial distribution. The same procedure is done on another type of neutron absorber Erbium (UEr) and the results are compared with UGd. The sensitivity of the results determines the validity of Monte-Carlo code in such a computational task comparing two types of neutron absorbers in addition to determining the geometric requirements.