[en] An alignment system is provided for nucler fuel assemblies in a nuclear core. The core support structure of the nuclear reactor includes upwardly pointing alignment pins arranged in a square grid and engaged in peripheral depressions formed in the lateral periphery of the lower ends of each of the fuel assemblies of the core. The depressions are located at the corners of the fuel assemblies so that each depression includes on-quarter of a cylindrical void. Each fuel assembly is positioned and aligned by one-quarter of four separate alignment pins which engage the fuel assemblies at their lower exterior corners