Patent Number: 
Section: claims

1. An active zone of a lead-cooled fast reactor, comprising a homogeneous uranium-plutonium nitride fuel which is contained in geometrically identical shells of cylindrical fuel elements, wherein the fuel elements are arranged in fuel assemblies so that a mass fraction of the fuel in the active zone is a minimum of 0.305, said fuel assemblies create a central part, an intermediate part and a peripheral part of the active zone, wherein a diameter (d1) of the central part of the active zone ranges from 0.4 to 0.5 of an effective diameter (D) of the active zone, while a height (h1) of the fuel column in the fuel elements of the fuel assemblies in the central part of the active zone is from 0.5 to 0.8 of a height (H) of the fuel column in the fuel elements arranged in the fuel assemblies in the peripheral part of the active zone, and a diameter (d2) of the stepped intermediate part of the active zone ranges from 0.5 to 0.85 of the effective diameter (D) of the active zone, while heights (h2) of the fuel columns in the fuel elements in the fuel assemblies forming the stepped intermediate part are from 0.55 to 0.9 of the height of the fuel column in the fuel elements arranged in the fuel assemblies in the peripheral part of the active zone.