FIELD: nuclear reactors and their fuel assemblies. SUBSTANCE: fuel assembly of seed-blanket modules has central seed region incorporating seed-region fuel elements of enriched uranium-235 and uranium-238, mentioned seed-region fuel elements being made so that when they are operating in mentioned seed region, moderator-to-fuel volume ratio in seed region ranges between 2.5 and 5.0; and circular blanket region around seed region that includes blanket fuel elements primarily of thorium and 10 volume percent or less of enriched uranium, mentioned blanket-region fuel elements being made so that when they are operating with moderator in mentioned blanket region, moderator-to-fuel volume ratio ranges between 1.5 and 2.0. As an alternative, fuel assembly may have central seed region incorporating plutonium fuel elements, each being composed of plutonium-zirconium alloy and mentioned seed- region fuel elements being made so that when they are operating with moderator in seed region, moderator-to-fuel volume ratio in seed region ranges between 2.5 and 3.5; and blanket region around seed region that incorporates blanket-region fuel elements primarily of thorium oxide with 1 volume percent or less of plutonium oxide and 5 volume percent or less of enriched uranium wastes, mentioned blanket-region fuel elements being made so that when they are operating with moderator in mentioned blanket region, moderator-to-fuel volume ratio ranges between 1.5 and 2.0. EFFECT: improved design; ability of consuming large amount of plutonium with thorium thereby reducing amount of wastes which are proliferative and highly radioactive materials. 12 cl, 8 dwg, 4 tbl
