An apparatus for reinforcing weakened portions of the top guide assembly in a boiling water reactor. The repair apparatus includes a cruciform lattice segment which reinforces the damaged or weakened region of the top guide beam lattice. This cruciform lattice segment is held in place atop the existing top guide with specially designed straps. The cruciform lattice segment and associated straps are arranged so that a beam segment of the cruciform lattice segment bridges the weakened region in the cracked top guide. Thus, the bridging beam segment transmits loads across the weakened region of the top guide. The straps are designed to avoid interference with removal and installation of the fuel assemblies and the control rod blade which is inserted between the fuel assemblies.