j safdari

In the first year of fuel loading of nuclear power reactors, uranium enriched at different levels is used (in the type of VVER-1000 reactor, the levels of enrichment are 4.0, 3.6, 3.3, 0.3, 2.4, 2.2, and 1.3%). In this work, for the production of enriched uranium in the first cycle, two parallel methods have been used, one using square cascades and the other using symmetrical tapered cascades. Computational codes have been developed for the design and optimization of the cascades. The meta-heuristic PSO method has been used for optimization. The results show that: 1. if square cascades are used, it is possible to directly produce all uranium enriched with different levels; 2. if tapered cascades are used, it is possible to produce all uranium indirectly, and uranium enrichment at different levels is only possible with a mixing unit in the enrichment facility; 3. The total number of centrifuges or cascades used to produce enriched uranium shows a reduction of about 22–39% compared to the square cascades. 4. If gas centrifuges with high separation capacities are used in square and tapered cascades, the total number of gas centrifuges required for the production of enriched uranium will be close.

In order to modeling the gas behavior inside the rotor of a gas centrifuge, a powerful tool is needed to overcome the computational constraints of gas inside the centrifuge along with the ability to apply all drives at the all flow regimes. Due to the suitability of the DSMC method for all flow regimes formed inside the centrifuge, in this paper, the DSMC method is used to analyze the separation performance of a centrifuge in axisymmetric coordinates. For this purpose, using a multi-scale CFD-MD method, first the momentum accommodation coefficients required to use the Cercignani-Lampis-Lord boundary condition are extracted and then, based on that, the behavior of the gas inside a centrifuge machine is investigated using the DSMC method and the amount of separation power is determined. Based on the comparison of the simulation results with the experimental test results, it was shown that using the proposed hybrid method to determine the amount of momentum accommodation coefficients used in the CLL boundary condition of the DSMC method, can increase the accuracy of determining the amount of separation power of the machine up to 8%.

One of the driving factors for creating axial flow inside the gas centrifuge rotor to increase the separation performance is the scoop. Due to the exposure of the scoop to the high Mach gas flow, the flow will be shocked, and strong gradients will occur in the flow.  In this research, the gas flow around the scoop in a two-dimensional state (r-θ) is simulated by the Direct Simulation Monte Carlo method (DSMC) using the dsmcFoam solver at different distances of the scoop from the rotor wall. The results show that increasing the distance of the scoop from the rotor wall and decreasing the contact angle of the gas flow with the scoop reduces the maximum temperature and drag force. For instance, increasing the distance of the scoop from the wall by 31% (from 8 to 10.5 mm) in 3800 Pa wall pressure and 85° contact angle, causing a maximum temperature decrease of 1.3% (from 596 to 588 K) and also the drag force is reduced by 49.4% (2412 to 1221 dyn). Furthermore, reducing the angle of the gas flow with the scoop by 11.8% (from 85 ° to 75 °) in 3800 Pa wall pressure and at the distance of the scoop from the wall equal to 10.5 mm causes a maximum temperature decrease of 6.8% (from 588 To 548 K) and the drag force is reduced by 50.3% (1552 to 771 dyn).

Among the noble gases, Xenon isotopes are the most widely used. So far, no specific strategy has been published for separating all Xenon stable isotopes with the highest number of stable isotopes. In this research, a computational code, SQCAS, is prepared to determine the target isotope separation strategy in light or heavy current. The prepared code investigates the separation of the natural isotopes in proportion to the feed concentration by changing the parameters of the square cascade and modeling it at each step. All stable isotopes of natural xenon are separated using a square cascade in 32 steps for the certain feed (200kg). The proposed square cascade has 20 stages. In each stage, 10 centrifuges were used. Also, the separation factor for the unit mass difference in this research equals 1.2. Using this strategy, the enrichment of nine isotopes increases from 0.9393, 0.0009, 0.01917, 0.2644, 0.408, 0.2118, 0.2689, 0.1044, and 0.087 to 98.72%, 91.3%, 92.79%, 92.63%, 83.77%, 90.12%, 91.64%, 95.68%, and 99.04%, respectively. The results show that the highest recovery is related to the end isotopes, and the lowest recovery is related to Xe-135 isotope.

One of the crucial parameters in designing the Q model cascade for the multi-component systems is the M* parameter. In this research, a code called MOTACAS has been developed to design a Q cascade, using the optimal value of the M* parameter. In this regard, the enrichment of the 8th isotope of tellurium at the heavy stream to 0.40, 0.7, 0.9, and 0.99, and the enrichment of the 4th isotope to 0.1, 0.3, 0.4, and 0.5 have been investigated. Also, in order to evaluate the effect of the separation factor on M*, optimal Q cascades for the enrichment of the 8th and the 4th isotopes with separation factors of 1.05 and 1.1 have been designed and compared with each other. The results show that the acceptable range of the M* decreases with increasing the desired isotope concentration. The optimal value of the M* does not change with reducing the separation factor. The relative inter-stage flow rate remains constant despite increasing the total inter-stage flow rate. Moreover, the required number of separation stages to reach the end component to a high concentration increased, but the enrichment of the middle component in the one cascade is limited despite increasing the stages.

To model a gas behavior within a centrifuge machine, a powerful tool is required similarly. With high-speed cover, all the computational limitations for applying the influential derives such as feed, scoop, baffle effects, etc., formed flow regimes. Therefore, achieving an applicable code or software to simulate the gas behavior within a centrifuge machine to investigate the effect of the derives on the separation in a centrifuge machine, including high-speed rotation, temperature, and mechanical derives, is required. Considering the fact of covering the method based on the molecular DSMC for the all formed flow regimes within the centrifuge machine, in the present work, the method of applying the all influential factors in a separation process of a centrifuge machine in the axial symmetric coordinates on the written code of DSMC and also the dsmcFOAM solver have been studies. The results have been compared with those obtained from the code, including pressure radial changes, axial mass flux, velocity components, and dsmcFOAM solver. A good agreement was found between the results corresponding to the written code and dsmcFOAM solver to simulate a centrifuge machine in the presence of all the parameters.

In the present research, mass transfer resistances of various steps of uranium biosorption using Pseudomonas putida @ Chitosan biosorbent in a fixed bed column were calculated. The description process dynamic parameters using dimensionless numbers showed that the Biot number was greater than 30 in all experiments which confirms the high mass transfer rate of the liquid film in comparison with intra-particle diffusion. Increment of the mass transfer driving force across the liquid film via enhancement in the inlet concentration along with a decrease in the liquid film thickness through a reduction in the sorbent particle size caused a decline in the mass transfer resistance of the liquid film. Furthermore, the Peclet number was found to be increased with increment of the bed height and decrement of the sorbent particle size which indicates a shortening in the mass transfer region thickness and reduction in the axial dispersion resistance. The biosorbent structure caused the pore diffusion flux to be negligible in comparison with the surface diffusion flux. The surface diffusion was the dominant intraparticle diffusion mechanism. The obtained results showed that intraparticle diffusion resistances were several times greater than liquid film resistances and axial dispersion resistances in all experiments, and also were the rate-controlling step. Since the change in operational conditions has a small effect on the intraparticle diffusion, the column efficiency was only proportional to the process residence time, varying between 0.00% to 53.00%.

One of the important parameters in the square cascade, which has a great influence on its performance in the separation of multicomponent isotopes, is the cascade cut. In this research work, at first, the effect of cascade cut on the separation of xenon middle isotopes in a square cascade with 20 stages was studied. These studies were carried out for two cases in which the separation factor was 1.2 and 1.1. Moreover, the minimum length for creating a long cascade by changing the Z/F value and cascade cut has been determined. Based on the calculations, if the separation factor is 1.2 and 1.1, the minimum number of cascade stages will be 55 and 110, that's not simply possible. The results showed that the appropriate cascade cut in the long cascade is different from the short cascade. Using the parametric studies of the short cascade, it is possible to determine the most appropriate cascade cut in which the desired isotope concentration reaches its maximum. In order to maximize the amount of Xe-129 in a 20 stages cascade, the suitable cut is 0.2 in the separation factor of 1.2 and 0.15 in the separation factor of 1.1.

In the present study, for the first time the R cascade under normal and optimal conditions with the constant and specified total number of cascade stages, the feed flow rate to the cascade, the factor of separation based on the unit mass difference, and the maximum and optimal of the feed flow into the centrifuge machine is assessed. The algorithm used for optimization is TLBO algorithm and the objective function is considered as a function of separation work for a single machine and match abundance ratio. The results show that in the cascade with the match abundance ratio for isotopes k1 and k2 the separation work in optimal cascade is more than conventional. If the abundance ratio is adapted for two pair of components, i.e., the “first and third” and the “second and third, the separation power in the optimal mode for the first and second cases is 1% and 9% more than those of conventional, respectively. Finally, a computational code named MISCC is written to determine and analyze the parameters of the match abundance ratio cascade in optimal and normal conditions.

In this study, recovery of uranium from leach liquor using solvent extraction technique in a horizontal pulsed sieve plate column was experimentally investigated. Extraction of uranium from an aqueous sulfate solution with 0.25M concentration acid, by using TOA solvent, diluted in kerosene and n-decanol modifier of 5%, 90% and 5% v/v respectively was studied and the influences of operation parameters including the phase flow rates along with pulsation intensity on the dispersed phase holdup, drop size and drop size distribution, as well as extraction efficiency, were evaluated. Increasing pulsation intensity along with the dispersed phase flow rate and decreasing the continuous phase flow rate caused to increase the extraction efficiency. Results showed that the horizontal pulsed sieve plate column has high efficiency for extraction of the uranium from leach liquor. Moreover, a comparative evaluation of available correlations proposed for the prediction of mean drop size and hold up in such columns have been conducted. New correlations for estimating mean drop size and hold up in a horizontal pulsed sieve-plate column were presented, which provided AARE of 7.7% and 8.2%, respectively.

In this study, the mass transfer performance of the Horizontal pulsed sieve plate column for the extraction of uranium from Bandar Abbas sulfate leach solution with Alamine 336 was investigated using a dispersion model. The organic phase contained 6% (v/v) Alamine 336 as extractant and 5% (v/v) isodecanol as a modifier in kerosene as diluent. The sulfate solution of Bandar Abbas containing 0.22 M sulfate and 250 ppm Uranium was used as the aqueous phase. The axial dispersion model was used to determine the mass transfer parameters and modeling of this system. Also, the effect of operating parameters such as pulsation intensity, the rate of phases flow on the volumetric overall mass transfer parameters was investigated; namely total volumetric coefficients of continuous phase mass transfer (Koca) and axial scattering coefficients of continuous and scattered phase (Ec and Ed). The obtained results showed that the mass transfer parameters are strongly dependent on the pulse intensity and turbulence degree of the system. In addition, the mass transfer performance of this column is high for the uranium extraction from sulfate leach liquors. Moreover, the practical and novel correlations have been determined for prognostication of mass transfer parameters which are closely matched with the experimental results in the horizontal pulsed column.

The Boltzmann equation which describes binary collisions between molecules is a very important equation in physics and fluid dynamics. Direct Monte Carlo simulation is one of the methods to solve the Boltzmann equation. The moisture can leak to the fluid pipelines in the various places of cascades so many times through the enrichment operations since the pressure of the most enrichment process units is less than the atmospheric pressure. It causes the solid uranium precipitation on the inner surfaces of rotor and HF production upon the reaction with UF6. In the present work, the effect of concentration and total pressure inside a hypothetical centrifuge for binary component conditions (ZUF6=0.97, ZHF=0.03), (ZUF6=0.93, ZHF=0.07), (ZUF6=0.9, ZHF=0.1), (ZUF6=0.85, ZHF=0.15), and three component conditions (ZUF6=0.9, ZHF=0.05, ZAir=0.05) and (ZUF6=0.8, ZHF=0.1, ZAir=0.1) have been investigated. The results have been compared with those of the Boltzmann distribution function. Moreover, increment in the amount of light gas along with UF6 results in the decrement of ρνz.

The management of waste produced in the reactor is an essential aspect of the nuclear fuel cycle. In this research, it has been tried to reduce the amount of reactor waste at the end of the cycle without substantial changes in the fuel dimension and the core structure of the research reactor. Minimized the heat generation. The MCNPX2.6 code is used to calculate the fuel consumption and neutronic parameters of the reactor core. The results show that without any significant change in the structure of the reference core, the amount of waste decreases only by increasing the fuel enrichment and reducing the reactor power. In this study, two core models are proposed and investigated. The waste activity at the end of the cycle in the converted reactor cores reaches 15% -19% of its original value in the reference core. Moreover, fuel burn- up has increased up to 32% -40% relative to the reference core.

In this paper, using a new combinatory meshing technique in the axisymmetric coordinate, a MCC-DSMC solver is introduced. Using this solver, the flow and the concentration variation inside a centrifuge machine in a rigid body rotation mode with the DSMC method for a variable hard sphere and a variable soft sphere models and for the mixing hydrogen, argon, and krypton gases are investigated. Our results are compared with the analytical solution. The results indicate that the two collision models are totally in agreement with each other, but the results have some differences with the analytical results obtained from the Boltzmann distribution function. The results show that the presence of the several gases with different molecular weights in a centrifuge shaped a multi-layered radial flow of gas inside the rotor, so that the heaviest gas in the area of the side wall of the rotor, the lightest gas in the region near the axis of the rotor and gases with the medium molecular mass were placed in a layer between them. Furthermore, the variation of the concentration for each component of the mixing gas in the axial direction is also investigated by the DSMC method, otherwise, that it is impossible to investigate it using the analytical solution of the Boltzmann distribution function.

The paper deals with the optimization of uranium back extraction from the Alamine-336 loaded by synthetic solution (synthetic LOS) and Bandarabbas leach liquor (real LOS) by means of stripping process method. In this regard, the impact of two essential parameters including the reagent concentration and phase ratio (O:A) for stripping of alkaline agent containing sodium hydroxide (NaOH) and sodium carbonate (Na2CO3) togather with the pH for sodium chloride (NaCl) were investigated. To study these effects, a central composite design (CCD) under the response surface methodology (RSM) was employed. Based on the design of the experiments, the second-order regression model has been constructed to evaluate the optimzation of the stripping efficiency of uranium from Alamine-336. The optimum conditions for these stripping agents have been determined as NaCl (0.6 molL-1) with the ratios of O:A (1.41) and pH (3.1) NaOH (1.33 mol  L-1) with the ratio of O:A (1.26) and Na2O3 (0.72 mol  L-1) with the ratio of O:A (1.16). Under these optimal conditions, the stripping efficiency values up to %31, %45 and %54 were obtained for NaCl, NaOH, and Na2CO3 cases, respectively.

Performance of Three commercially available nanofilter membranes (PES-2 , NF-1 and NF-2) in terms of rejection, permeate flux, and membrane selectivity under a variety of operational conditions was evaluated for selective separation of uranium (VI) ions from iron (III). The membranes permeate fluxes were  decreased with an increase in the pH range of 3-6, while the rejection of ions was increased. Uranium rejection with these membranes was lower than iron rejection and the PES-2 and NF-1 membranes had the maximum membrane selectivity of iron over uranium at pH 4. The maximum membrane selectivity of NF-2, however, was 2.97 at pH 3. The PES-2 membrane had the maximum iron rejection of 72.25% at the pressure 10 bar. For NF-1 the rejection of iron and uranium was found to be relatively constant (about 97% and 84%, respectively) against increasing the pressure. As the pressure increased from 5 to 20 bar, iron rejection by NF-2 was remained constant (about 97%) but uranium rejection by this membrane was decreased from 84.06% to 70.46%. It was found that the effect of increasing the iron concentration from 0.12 to 1mM on the behavior of these membranes is  different. The maximum membrane selectivity of uranium over iron by the NF-1 and NF-2 membranes was 43.71 and 13.59, respectively, which showed that NF-1 has a very desirable performance. It seams that the relatively new process of nanofiltration has a good potential for selective separation of uranium from iron.

Oxidation-reduction potential (ORP) in uranium bioleaching from a low grade ore by Acidithiobacillus ferrooxidans is measured experimentally under different conditions. The experimental results are fitted to the mixed potential model, obtained from Butler-Volmer equation. The results from this fitting showed that the model predictes the ORP in uranium bioleaching from 1th anomaly of Saghand ore with very high accuracy the relative error of the present applied model in the process of the used ore is less than 4%. The average values of the electrochemical rates constants km/kα, kc/kα and b related to the experiments with the pulp density of 5% and 10% (w/v) were obtained to be 260, 30606 and 0.01 respectively. The experimental results were also compared with the Nernst equation prediction for two cases of γi=1, γi≠1. The results showed that the relative error of this model is less than 45% with activity coefficients equal to one and less than 35% with real activity coefficients.