Uranyl Nitrate Hexahydrate Crystals Research Articles

Mathematical Simulation of the Crystallization Process in a Continuous Linear Crystallizer

A mathematical model of the crystallization of uranium in a continuous linear crystallizer, designed for the crystallization separation of desired products in the processing of an irradiated nuclear fuel, is proposed. This model defines the dynamics of growth/dissolution of uranyl nitrate hexahydrate crystals in a nitric acid solution of uranyl nitrate. Results of a numerical simulation of the indicated process, pointing to the existence of stationary conditions in the working space of the crystallizer, are presented. On the basis of these results, the characteristic time of establishment of the stationary regime at different parameters of the process was estimated. The mathematical model proposed was validated on the basis of a comparison of the results of calculations carried out within its framework with experimental data.

Purification of uranium products in crystallization system for nuclear fuel reprocessing

Uranium crystallization system has been developed to establish an advanced aqueous reprocessing for fast breeder reactor (FBR) fuel cycle. In the crystallization system, most part of uranium in dissolved solution of spent FBR-MOX fuels is separated as uranyl nitrate hexahydrate (UNH) crystals by a cooling operation. The targets of U yield and decontamination factor (DF) on the crystallization system are decided from FBR cycle performance and plutonium enrichment management. The DF is lowered by involving liquid and solid impurities on and in the UNH crystals during crystallization. In order to achieve the DF performance (more than 100), we discuss the purification technology of UNH crystals using a Kureha Crystal Purifier (KCP). Results show that more than 90% of uranium in the feed crystals could be recovered as the purified crystals in all test conditions, and the DFs of solid and liquid impurities on the purified UNH crystals are more than 100 under longer residence time of crystals in the column of KCP device. The purification mechanism is mainly due to the repetition of sweating and recrystallization in the column under controlled temperature.

A small reactor design for 99Mo production with novel fuel

The central goal of this design is to meet U.S. demand for the medical isotope 99Mo with a water-cooled critical reactor featuring discrete, cladded fuel elements. 99Mo is produced within the solid fuel that is powering the fission reaction. The fuel is a low-enriched uranyl nitrate hexahydrate crystal, chosen to take advantage of a flexible uranium recovery process. The low melting temperature of the fuel material has required utilizing an annular fuel pin geometry. Preliminary heat transfer calculations and MCNP modeling have demonstrated the capability of such a design to produce the desired quantities of 99Mo.

Mathematic Simulation of Crystallization Refining Process of Spent Nuclear Fuel Reprocessing Desired Products in Linear Crystallizer

The object of research is crystallization refining process of uranyl nitrate (UN) from nitric acid solution. The process of crystallization refining is a working operation which can provide effective extraction and purification of desired products (fission materials) during spent nuclear fuel (SNF) reprocessing. The purpose of the work is mathematical description of the linear continuous crystallizer operating modes using the example of uranyl nitrate hexahydrate crystals sorting. The mathematical model presented in the work allows describing changes of crystallization process parameters in the active volume of crystallizer and choosing the most effective operating modes in terms of extraction of SNF reprocessing desired products.

Nitric Acid Concentration Dependence of Dicesium Plutonium(IV) Nitrate Formation during Solution Growth of Uranyl Nitrate Hexahydrate

A crystallization process has been under development for the recovery of U as uranyl nitrate hexahydrate (UNH) crystals. Two experiments, solubility of Cs2Pu(NO3)6 and U crystallization, were performed to evaluate the influence of HNO3 concentration in solution on the precipitation behavior of Cs2Pu(NO3)6. The solubility of Cs2Pu(NO3)6 in a uranyl nitrate solution has been found to decrease with increasing HNO3 concentration in the solution. These experimental results imply that Cs2Pu(NO3)6 is readily formed in high HNO3 concentration solutions. Based on the solubility of Cs2Pu(NO3)6 in uranyl nitrate solutions, U crystallization experiments were performed with a range of HNO3 concentrations in the feed solution. At an HNO3 concentration of 4.5 mol/dm3 in the feed solution, the HNO3 concentration of the mother liquor was 6.5 mol/dm3. The decontamination factor (DF) of Cs for the UNH crystals was 8.61 after crystal washing. In this case, Cs2Pu(NO3)6 precipitated upon cooling of the feed solution and was not separated from the UNH crystals after crystal washing. On the other hand, the DF of Cs was 174 after the UNH crystals were washed when the HNO3 concentration in the feed solution was 3.2 mol/dm3. With a lower HNO3 concentration in the feed solution, nearly all Cs remained in the mother liquor during the U crystallization process. Therefore, to suppress Cs2Pu(NO3)6 precipitation, a lower HNO3 concentration must be maintained in the feed solution.

Washing of Uranyl Nitrate Hexahydrate Crystals with Nitric Acid Aqueous Solution To Improve Crystal Quality

To develop a uranium crystallization process for advanced aqueous reprocessing, two method experiments were investigated to evaluate the effect of crystal washing on uranyl nitrate hexahydrate (UNH). In one experiment, crystal washing was carried out using a uranyl nitrate solution with varying concentrations of HNO3 in washing solutions, and in the other, it was conducted with a dissolver solution of the irradiated fast neutron reactor core fuel. In the crystal washing experiments with the uranyl nitrate solution, the UNH crystals were immersed into a uranyl nitrate solution containing Ce, which was washed out in the mother liquor on the surface of the UNH crystals using an HNO3 solution. The experimental results showed that the decontamination factor (DF) of Ce increased with decreasing HNO3 concentration of the washing solution. However, because the UNH crystals tended to dissolve in low HNO3 concentration solutions, the yield decreased as a result of the washing operation. In the crystallization exper...

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

Abstract Crystal washing experiments were carried out using a uranyl nitrate solution in order to confirm the effect of uranyl nitrate hexahydrate (UNH) crystalline particle size on the removal of liquid impurities. The UNH crystal was immersed in a Ce solution and was washed for removing the mother liquor on the surface of the UNH crystals. Larger UNH crystals were advantageous for increasing the decontamination factors (DFs) of liquid impurities. The large crystal size reduced the specific surface area of the crystals which in turn decreased the adhesion of liquid impurities on the surface of the crystals. Therefore, high DFs of liquid impurities were achieved before and after washing. In the crystallization experiments, the DFs of metals for the UNH crystal were evaluated using a dissolver solution derived from irradiated fast neutron reactor core fuel. The UNH crystal size did not affect the decontamination of solid impurities such as Ba and Np even after crystal washing in the U crystallization experiments.

Characteristics of Dicesium Plutonium(IV) Nitrate Formation in Separation System of Uranyl Nitrate Hexahydrate Crystal

There is a concerned that Cs and Pu double salt Cs2Pu(NO3)6 is formed under certain conditions in the course of U crystallization. The influence of the Cs concentration in a feed solution on Cs2Pu(NO3)6 formation was thus examined in the U crystallization process. Cesium and Pu were decontaminated after crystal washing with a decreasing Cs concentration in the feed solution. Although Cs remained in the mother liquor at a Cs concentration of 1.0g/dm3 in the feed solution, Cs2Pu(NO3)6 precipitated at a Cs concentration of 2.2g/dm3. There is, therefore, a lower limit for the Cs concentration in the feed solution at which Cs2Pu(NO3)6 precipitates, and this limit falls in the range from 1.0 to 2.2g/dm3 Cs.

Behavior of Actinide Elements and Fission Products in Recovery of Uranyl Nitrate Hexahydrate Crystal by Cooling Crystallization Method

To elucidate various kinds of actinide element and fission product behavior, U crystallization experiments were carried out with a uranyl nitrate solution and with a solution in which irradiated fast reactor core fuel was dissolved. Insoluble residue simulating that found in actual reactor operation was not incorporated into the uranyl nitrate hexahydrate (UNH) crystal in the course of the U crystallization. However, the decontamination factors (DFs) were below 10 even when the UNH crystal was washed because the mother liquor containing the simulated insoluble residue occupied the interspaces of the agglutinated UNH crystal. In the U crystallization process, the DF of Pu was >40 when the UNH crystal was washed. But, Np was not removed from the UNH crystal because Np was oxidized to Np(VI) in the feed solution and thus was co-crystallized with U(VI). Cesium exhibited different behavior depending on whether Pu was present. Although a high DF of Cs was obtained in the case of uranyl nitrate solution without Pu, Cs was hardly separated at all from the UNH crystal formed from the dissolver solution of irradiated fast reactor core fuel. It is likely that crystals of a mixed salt of Pu and Cs, Cs2Pu(NO3)6, precipitated from the dissolver solution. Since Ba precipitated as Ba(NO3)2 during the crystallization process, its DF was low after the UNH crystal was washed. On the other hand, Am, Cm, Rb, Sr, Zr, Nb, Ru, Sb, and rare earth elements remained in the mother liquor at the time of U crystallization. Therefore, portions of these elements in the mother liquor that was attached to the surface of the UNH crystal were washed away with HNO3 solution.

Enhancement of Decontamination Performance of Impurities for Uranyl Nitrate Hexahydrate Crystalline Particles by Crystal Purification Operation

A crystal purification process consisting of sweating and melt filtration was developed to improve decontamination factors (DFs) of fission product impurities from uranyl nitrate hexahydrate (UNH) crystal recovered from a dissolver solution of irradiated fast reactor core fuel. Batch experiments on the sweating and melt filtration processes were carried out at 56 to 80°C. Although the DFs of solid impurities such as Cs and Ba remain the same in the sweating process, those of liquid impurities such as Zr, Nb, Ru, Ce, and Eu were 2.32, 2.40, 2.50, 2.45, and 2.60 at 60°C. On the other hand, the DF of Pu for the UNH crystal slightly increased to 1.25 at 60°C. Because Pu incorporated the UNH crystal in both the solid impurities such as Cs2Pu(NO3)6 and in the liquid impurities, Pu in the liquid fraction was removed by the sweating operation. Decontamination of liquid impurities was effective with sweating time and with a rise in sweating temperature. In the melt filtration process, 0.45- to 5.0-μm–diam filters were used for the separation of the molten UNH crystal. The DF of Ba was approximately ten times as high as the crude crystal with 0.45- to 5.0–μm-diam filters. The particle size of Pu and Cs formed as Cs2Pu(NO3)6 was quite small. As a proof of this, although the decontamination of Pu and Cs was not effective with a 5.0-μm-diam filter, their DFs rose 2.7 times using a 0.45-μm-diam filter.

Removal of Liquid and Solid Impurities from Uranyl Nitrate Hexahydrate Crystalline Particles in Crystal Purification Process

The purification behavior of uranyl nitrate hexahydrate (UNH) was investigated to evaluate the decontamination performance of liquid and solid impurities using a dissolver solution of mixed oxide (MOX) fuel in batch experiments. The UNH crystal recovered from the MOX fuel dissolver solution containing simulated fission products (FPs) was purified by a sweating and melt filtration process. Although the decontamination factors (DFs) of Pu, Cs, and Ba did not change in the sweating process, that of Eu increased with increases in temperature and time. These results indicate that liquid impurities such as Eu were effectively removed by the sweating method, but solid impurities such as Pu, Cs, and Ba were minimally affected in the batch experiments. On the other hand, the DF of Ba increased with 0.45 and 5.0 μ filters in the melt filtration process. Since Pu and Cs formed as Cs2Pu(NO3)6 in the course of U crystallization and was accompanied with the UNH crystal, these behaviors were similar to each other. Although the DFs of Pu and Cs did not change with the 5.0 μ filter, it increased approximately twofold with the 0.45 μ filter. The particle size of Cs2Pu(NO3)6 is relatively small and might pass through the 5.0 μ filter in the melt filtration process. The liquid impurities as Eu remained in the molten UNH crystal with some filters.

Precipitation Behavior of Dicesium Tetravalent Plutonium Hexanitrate in Cooling Crystallization of Uranyl Nitrate Hexahydrate

There is concern that a binary salt of Pu(IV) and Cs forms deposits on the uranyl nitrate hexahydrate (UNH) crystal formed in the dissolver solution for U crystallization containing Cs. Precipitation behavior of dicesium tetravalent plutonium hexanitrate, Cs2Pu(NO3)6, in the U crystallization process is studied. In this work, the solubility of Cs2Pu(NO3)6 was measured in a HNO3 solution, and influence of Pu valence and Cs concentration in the dissolver solution on decontamination factors (DFs) of Pu and Cs in the crystal was examined in the U crystallization process. The solubility of Cs2Pu(NO3)6 increased with a decrease in the concentration of HNO3 in the mother liquor and a rise in temperature of the mother liquor. In the U crystallization process, although the DF of Cs was low where there was Pu(IV) since the two were difficult to separate in the feed solution, Cs was removed thoroughly where there was Pu(VI) in the feed solution. The Cs concentration in the feed solution affected the DFs of Pu and Cs after the UNH crystal was washed. The DFs of Pu and Cs had a tendency to decrease with increase of Cs concentration in the feed solution, because large amounts of Cs+ contributed to the formation of Cs2Pu(NO3)6.

Removal of Liquid and Solid Impurities from Uranyl Nitrate Hexahydrate Crystalline Particles in Crystal Purification Process

The purification behavior of uranyl nitrate hexahydrate (UNH) was investigated to evaluate the decontamination performance of liquid and solid impurities using a dissolver solution of mixed oxide (MOX) fuel in batch experiments. The UNH crystal recovered from the MOX fuel dissolver solution containing simulated fission products (FPs) was purified by a sweating and melt filtration process. Although the decontamination factors (DFs) of Pu, Cs, and Ba did not change in the sweating process, that of Eu increased with increases in temperature and time. These results indicate that liquid impurities such as Eu were effectively removed by the sweating method, but solid impurities such as Pu, Cs, and Ba were minimally affected in the batch experiments. On the other hand, the DF of Ba increased with 0.45 and 5.0 μ filters in the melt filtration process. Since Pu and Cs formed as Cs2Pu(NO3)6 in the course of U crystallization and was accompanied with the UNH crystal, these behaviors were similar to each other. Although the DFs of Pu and Cs did not change with the 5.0 μ filter, it increased approximately twofold with the 0.45 μ filter. The particle size of Cs2Pu(NO3)6 is relatively small and might pass through the 5.0 μ filter in the melt filtration process. The liquid impurities as Eu remained in the molten UNH crystal with some filters.

Purification Rate of Uranyl Nitrate Hexahydrate Crystal for Transuranium Elements on Isothermal Sweating Phenomenon

For the purpose of further increasing decontamination performance, the purification behavior of uranyl nitrate hexahydrate (UNH) crystals was studied in the static system. The approach to purification of UNH crystals recovered from the irradiated fast reactor core fuel using a dissolver solution was examined by an isothermal sweating process, which involves heating to the melting point of the crystal. Since transuranium (TRU) elements were present as liquid impurities in the UNH crystal, their decontamination factors (DFs) were improved using this process. The DFs of Cs and TRU elements for the UNH crystals had a tendency to increase with time and were kept virtually constant by 240 min. Not having been precipitated as Cs2Pu(NO3)6 during the crystallization, Pu remained in the mother liquor and was removed by the sweating process. The purification rate coefficients of UNH crystals for Cs and TRU elements were calculated using these experimental data. These values for Pu, 137Cs, 241Am, and 242Cm were evaluated to be 2.13 × 10−4, 2.73 × 10−4, 2.11 × 10−4, and 3.13 × 10−4 s−1 at 57 °C, respectively.

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

Abstract In order to examine the decontamination behavior of the Pu and fission products (FPs) that contained with the uranyl nitrate hexahydrate (UNH) crystals in the U crystallization process, experiments were carried out using mixed oxide (MOX) fuel dissolver solution. The experiments confirmed that Eu was adequately decontaminated by washing the UNH crystals with a HNO3 solution. However, Ba crystallized as Ba(NO3)2 and the washing was ineffective for the decontamination of Ba. High HNO3 and Pu concentrations in the mother liquor, the decontamination factor (DF) of Cs was low because Cs precipitated with Pu as Cs2Pu(NO3)6. The Pu clearly showed a reasonable DF because the amount of Pu in the dissolver solution was higher than that of Cs. Almost all the amount of Pu remains in the mother liquor except the one in the Cs2Pu(NO3)6 precipitate.

Unusual luminescence from uranyl nitrate

Temperature-induced luminescence was observed from uranyl nitrate hexahydrate crystals. Flashes of green light were detected when the crystal was cooled with liquid nitrogen and also when the cooled crystal was allowed to return to room temperature. They mostly occurred between 77 and 100K. More and stronger flashes were observed during cooling. The intensities of these flashes and the temperatures of the crystal were recorded and plotted. The intensity-temperature plots were different for the cooling and warming cycles of the same crystal and other crystals. The characteristics of the temperature-induced luminescence were compared to those of fluorescence and triboluminescence.

High pressure photoluminescence of uranyl nitrate hexahydrate crystals

High pressure photoluminescence of uranyl nitrate hexahydrate crystals

Production of Fission Product Xenon

Radioactive Xe isotopes were produced by in-pile melting of irradiated uranyl nitrate hexali yd rate crystals. An aluminum pipe closed at the end was placed adjacent to the reactor core of the TTR-1 (swimming pool type reactor), and uranyl nitrate hexahydrate crystals in a stainless steel capsule were irradiated therein at a neutron flux of 2×1011/cm2-sec. After in-pile cooling for 10–15hr, the capsule was heated to melt the crystals. The rare gas activity released from the crystals was led out of the reactor by helium sweep and collected in a charcoal trap cooled by liquid nitrogen. More than 99% of the rare gas activity was recovered. The composition of the activity at the time of separation, while depending on cooling time and target irradiation history, was in the present case 135Xe(–80%), 133Xe(–10%) and small amounts of Kr isotopes. The remaining uranyl nitrate, crystallizes again upon removal of heat, and can serve for succeeding irradiations. About 30 mCi of radioactive Xe isotopes were produced by 4 hr irradiation using 5 g of 13% enriched U. Radioactive Xe produced in this way is being used for medical purposes.

Production of Fission Product Xenon

Radioactive Xe isotopes were produced by in-pile melting of irradiated uranyl nitrate hexali yd rate crystals. An aluminum pipe closed at the end was placed adjacent to the reactor core of the TTR-1 (swimming pool type reactor), and uranyl nitrate hexahydrate crystals in a stainless steel capsule were irradiated therein at a neutron flux of 2×1011/cm2-sec. After in-pile cooling for 10–15hr, the capsule was heated to melt the crystals. The rare gas activity released from the crystals was led out of the reactor by helium sweep and collected in a charcoal trap cooled by liquid nitrogen. More than 99% of the rare gas activity was recovered. The composition of the activity at the time of separation, while depending on cooling time and target irradiation history, was in the present case 135Xe(–80%), 133Xe(–10%) and small amounts of Kr isotopes. The remaining uranyl nitrate, crystallizes again upon removal of heat, and can serve for succeeding irradiations. About 30 mCi of radioactive Xe isotopes were produced by 4 hr irradiation using 5 g of 13% enriched U. Radioactive Xe produced in this way is being used for medical purposes.