The Impact of Isotopic Composition of Lead on the Neutron-Physical Characteristics of Fast Reactor with Liquid Metal Coolant

It is well known, that lead coolant, highly enriched by 208Pb, has some advantages over other coolants. It is predicted that the use of 208Pb in the reactor core will lead to an increase in the production of plutonium and transmutation of long-lived decay products. The main objective of this paper was to investigate the influence of the isotopic composition on the Fast reactor neutron-physical characteristics. For this purpose we used the RBETS-M benchmark - a Fast energy reactor that includes 12 zones with different sizes and temperatures of the materials. Calculations were performed for homogeneous and heterogeneous models. Our calculations show that the replacement of the coolant with the natural lead to 208Pb and 208Pb together with Bi can substantially improve the neutron-physical characteristics of the Fast reactor, in particular by reducing the initial reactivity margin. Studies of the heterogeneity effect in the reactor model showed an increase in the effective multiplication factor of about 1.5% at the end of the campaign