A series of critical experiments was performed with mixed plutonium-uranium nitrate solutions in two cylinders and in a variable thickness slab tank. The solution concentrations ranged from 12 to 174 g Pu/ℓ with Pu/Pu+U ratios of 0.5, 0.4, and 0.2. The criticality data were used to validate two versions of the SCALE computer code system (SCALE-4 and SCALE-2). Calculations were performed with the 27-energy-group cross-section library, derived from the Evaluated Nuclear Data File B-Version IV. The average calculated keff for all geometries (39 experiments) is 1.006 (σ = 0.006), calculated with SCALE-4, and 1.004 (σ = 0.007), calculated with SCALE-2. Overall, the range of calculated keff varied from 0.989 to 1.019. These experiments covered a wide range of parameters, with variations in physical, chemical, and neutronic parameters.