Research of the influence of agglomerates with a high Pu content in MOX fuel on the neutron-physical characteristics of a nuclear reactor pin

The main topik of the reserch is to find out is it possible to load fully PWR's and BN-800's cores without consideretion of disperse structure of MOX-fuel. Two types of lattice were considered for PWR and BN-800: homogeneous and heterogeneous. At first, the calculation was for pins. Each fuel pin was divided axially or radially into zones. Different number of plutonium agglomerates were simulated in each zone, the volume fraction was 7%, 10% and 22% for each model. The typical diameter of Pu-rich agglomerate was selected: 30 μm as an average value and 50 μm as a probable maximum. The focus of the study was on the following characteristics: energy distribution in plutonium agglomerates and in uranium matrix; Doppler effect; reproduction coefficient. In conclusion, the more volume fraction of Pu-rich agglomerates - the more energy release in pins, but agglomerates' diameters have no influence and also there is no dependence of axial partition.