Experimental criticality data on borated raschig rings in plutonium nitrate solutions are presented for use in establishing criticality safety limits and in verifying calculational methods for these type systems. The data cover the concentration range between 63- and 412-g Pu/liter for borosilicate-glass raschig rings containing 0.5 and 4.0 wt% boron, and stainless-steel raschig rings containing 1 wt% boron.Criticality was possible in all three experimental vessels used (12-, 18-, and 24-in.-diam cylinders, 42-in. high) with no raschig rings. With rings randomly loaded in the vessels only the 24-in. cylinder could be made critical and then only when loaded with the 0.5 wt% borated rings. The minimum critical volume for this system, poisoned with 19.27 vol% borosilicate-glass rings containing 0.5 wt% boron, was determined to occur at about 300 g Pu/liter as compared to 175-to 200-g Pu/liter without the rings. The minimum critical mass occurred at ≈110-g Pu/liter with the system poisoned, as compared with 30-g Pu/liter if the system had not been poisoned. Exponential measurements on the subcritical assemblies, loaded with 4 wt% borated rings displacing 18.78 vol% solution, indicated that negative bucklings existed for all plutonium nitrate solutions having concentrations below 391-g Pu/liter. Similar measurements on the subcritical assemblies, loaded with 1 wt% borated stainless-steel rings displacing 27 vol% solution, indicated that negative bucklings existed for all concentrations below 412-g Pu/liter.Comparisons between the experimental data and the results of several calculational methods indicate that the validity of a particular calculational technique may be limited to a small concentration region. By treating the raschig rings as vertical parallel tubes displacing an equal volume of solution and using the Monte Carlo code KENO with GAMTEC-II cross sections averaged over the energy spectrum of the plutonium solution, keff values were calculated to within 2% of unity for the experimental critical assemblies presented in this paper. Other calculational methods and cross-section sets used resulted in values of keff departing from unity by as much as 12% low to 6% high, depending on the plutonium concentration. The various methods used are discussed in this paper.