Solubility of barium nitrate in highly active raffinates under evaporation conditions

Abstract

Usually highly active raft'mates evaporate, the residue is stored, the tramuranium elements are removed, and the remainder is vitrified [1, 2]. Economically and technically, it is advantageous to evaporate as much as possible. However then the hard-to-dissolve materials contained in the raffinates remain in the residue, so data on the solubility of these matedals is of practical interest.The highly active raft'mates are nitric acid solutions that contain various metal nitrates (from fission products, corrosion, etc.). Of these, one of the least soluble is barium nitrate.Below are our data on the solubility of barium nitrate in nitric acid solutions. To some degree these solutions imitate the composition of highly active raft'mates under evaporation conditions. These data either are not available in the scientific and engineering literature or extend what is available [3].The solubility was determined for isothermal (30 and 60"C) or isobaric (200, 465, and 1000 GPa) conditions. For the isothermal measurements, the barium nitrate was introduced into the solution as a salt; for the isobaric measurements, it was introduced as a water solution with a known concentration (8.4% by weight) and then evaporated until a precipitate started to form. Equilibrium between the saturated solution and the precipitate occurred after 2 h. Samples of the saturated solution were immediately diluted with water and analyzed for barium nitrate by chromate titration [4].The data in Tables 1-3 show that the solubility of barium nitrate increases with temperature and pressure, but decreases with increasing concentrations of nitric acid and the nitrates of sodium, calcium, and aluminum. Analogous results were also obtained for solutions containing a combination of nitrates of Fe 3+, Cr 3+, Ce 3+, lanthanum, cesium, strontium, and zirconium.

Influence of nitric acid and plutonium concentrations in dissolver solution of mixed oxide fuel on decontamination factors for uranyl nitrate hexahydrate crystal

“…Ba(NO 3 ) 2 has low solubility in uranyl nitrate solution e.g. 0.6 g/dm 3 in 200 g/dm 3 UO 2 (NO 3 ) 2 -5 mol/dm 3 HNO 3 solution at 10 • C and the solubility of Ba tends to decrease with increasing concentrations of HNO 3 [9]. In the crystallization process, uranyl ions crystallize as UNH, in the following equilibrium reaction:…”

Effect of crystal size on purity of uranyl nitrate hexahydrate crystalline particles grown in nitric acid medium

“…In the crystallization experiments with the dissolver solution of irradiated fast neutron reactor core fuel, a large UNH crystal size is advantageous for the DFs of liquid impurities such as Ru, Sb, Cs, Ce, Pu, Am and Cm for the UNH crystal before and after washing. Although part of the Pu(IV) precipitated with Cs as Cs 2 Pu(NO 3 ) 6 in the previous study, the precipitation of Cs 2 Pu(NO 3 ) 6 was suppressed in the course of U crystallization with low HNO 3 and Cs concentrations in the feed solution. Meanwhile, the DF of Ba did not change when the UNH crystal was washed with the HNO 3 solution because of the precipitation of Ba(NO 3 ) 2 .…”

“…The concentrations of HNO 3 and Cs in the feed solution were 3.8 mol/dm 3 and 0.8 g/dm 3 , respectively. Their concentrations were low enough to avoid the generation of Cs 2 Pu(NO 3 ) 6 . The DFs of the liquid impurities such as Ru, Sb, Ce, Cs, Pu, Am and Cm in RUN2-1 were higher than that of liquid impurities in RUN2-3 after crystal washing.…”

“…Ba(NO 3 ) 2 has low solubility in uranyl nitrate solution e.g. 0.4 g/dm 3 in 400 g/dm 3 UO 2 (NO 3 ) 2 −5 mol/dm 3 HNO 3 solution at 40 • C and its solubility tends to decrease with increasing concentrations of HNO 3 and Ba [6]. The precipitation of Ba(NO 3 ) 2 in the course of U crystallization caused its low DF for the UNH crystal even after washing.…”