Method for strengthening an existing fuel element for nuclear reactors, in particular boiling-water reactors, for transport and/or storage purposes, wherein the fuel element is formed from a plurality of fuel rods which extend in a longitudinal direction, wherein the fuel rods are arranged in rows and columns in a plane perpendicular to the longitudinal direction, wherein the columns are arranged in a first transverse direction, which extends perpendicularly to the longitudinal direction, and the rows are arranged in a second transverse direction, which extends perpendicularly to the longitudinal direction and perpendicularly to the first transverse direction, wherein the fuel element is provided with a first strengthening structure segment and a second strengthening structure segment for the storing of the fuel rods, wherein the first strengthening structure segment is formed from a first main body and multiple first support structures, which extend from the first main body at a right angle and parallel to one another, wherein the second strengthening structure segment is formed from a second main body and multiple second support structures, which extend from the second main body at a right angle and parallel to one another, comprising the following steps: a) defining a first position in the longitudinal direction for the storing of the fuel rods; b) introducing a first strengthening structure segment at the first position, wherein the first support structures are pushed between the fuel rods in the first transverse direction, and introducing a further first strengthening structure segment at the first position, wherein the first support structures are pushed between the fuel rods counter to the first transverse direction; c) introducing a second strengthening structure segment at the first position, wherein the second support structures are pushed between the fuel rods in the second transverse direction, and introducing a further second strengthening structure segment at the first position, wherein the second support structures are pushed between the fuel rods counter to the second transverse direction; wherein the fuel element is formed from a plurality of fuel rods which extend in a longitudinal direction, wherein the fuel rods are arranged in rows and columns in a plane perpendicular to the longitudinal direction, wherein the columns are arranged in a first transverse direction, which extends perpendicularly to the longitudinal direction, and the rows are arranged in a second transverse direction, which extends perpendicularly to the longitudinal direction and perpendicularly to the first transverse direction, wherein the fuel element is provided with a first strengthening structure segment and a second strengthening structure segment for the storing of the fuel rods, wherein the first strengthening structure segment is formed from a first main body and multiple first support structures, which extend from the first main body at a right angle and parallel to one another, wherein the second strengthening structure segment is formed from a second main body and multiple second support structures, which extend from the second main body at a right angle and parallel to one another, comprising the following steps: a) defining a first position in the longitudinal direction for the storing of the fuel rods; b) introducing a first strengthening structure segment at the first position, wherein the first support structures are pushed between the fuel rods in the first transverse direction, and introducing a further first strengthening structure segment at the first position, wherein the first support structures are pushed between the fuel rods counter to the first transverse direction; c) introducing a second strengthening structure segment at the first position, wherein the second support structures are pushed between the fuel rods in the second transverse direction, and introducing a further second strengthening structure segment at the first position, wherein the second support structures are pushed between the fuel rods counter to the second transverse direction; a) defining a first position in the longitudinal direction for the storing of the fuel rods; b) introducing a first strengthening structure segment at the first position, wherein the first support structures are pushed between the fuel rods in the first transverse direction, and introducing a further first strengthening structure segment at the first position, wherein the first support structures are pushed between the fuel rods counter to the first transverse direction; c) introducing a second strengthening structure segment at the first position, wherein the second support structures are pushed between the fuel rods in the second transverse direction, and introducing a further second strengthening structure segment at the first position, wherein the second support structures are pushed between the fuel rods counter to the second transverse direction;