The development of pressurized water reactors and boiling water reactors in the world necessitates complete critical experiments on this type of fuel for the validation of the methods used in criticality calculations and to resolve the various related problems. This paper presents the first results obtained at the Critical Mass Laboratory at Valduc during critical approaches achieved with lattices of 4.75-wt%-235U-enriched UO2 rods in water. Four square pitches (12.6, 16.0, 21.0, and 25.2 mm) and three triangular pitches (13.5, 17.2, and 22.6 mm) have been studied, and various configurations with fuel rods removed were investigated. Benchmark calculations are presented.