Effect of Neutron Leakage on Equilibrium U-Pu and Th-U Cycles for 16 Selected Reactors

Abstract Three papers related to the equilibrium fuel cycle in 16 selected reactors were submitted to ICONE 31 conference. In this last part, the effect of neutron leakage from a finite core is evaluated. This work deals with three main issues. The first goal is to verify when and how the modified one-group critical equation can be used to estimate the neutron leakage. Secondly, as the spectrum is changing together with the neutron leakage, it was another task to find how these changes would affect the equilibrium. And thirdly, because some of the reactors are supercritical in an infinite lattice, their minimal critical volume can be found and compared. It was found that the critical equation cannot be used for fast reactors, especially for the U-Pu cycle, because due to the neutron leakage, the spectrum is harder and migration area with infinite multiplication factor are changing. Much better results were obtained with thermal reactors and for the Th-U cycle. When using new values obtained from a finite volume, the results match the reality more closely. The same applies to the equilibrium calculation, where the largest differences were obtained for systems with large changes in the neutron spectrum. At the same time, it was found that the smaller the migration area, the smaller the volume is needed to show the change in the spectrum. All results were obtained using the EQL0D v4 procedure and with ENDF/B-VIII.0 nuclear data library.