Spectral emission characteristics near 646 nm and plasma properties of laser-induced plasma of gaseous uranium hexafluoride

A responsive integrated dry route for uranium hexafluoride conversion using machine intelligence

Review of: "Redesign of a Nuclear Power Reactor Based on Enrichment With Uranium Hexafluoride Gas, or UF6"

Abstract The regulator is one of the most important equipment in the uranium enrichment centrifugal cascade, of which the main function is to automatically control the pressure and flowrate within the certain range. The regulator must operate under a low-pressure vacuum condition. Compression and expansion as well as the transonic and supersonic flow of gaseous Uranium hexafluoride (UF6) in the low-pressure vacuum are drastic and complicated, which makes it difficult and significant to analyze the flow field in the regulator. The computational fluid dynamics (CFD) technique has been introduced in the analysis of complex flow in recent years. The flow field characteristics in the regulator of six opening ratio under high and low inlet pressure conditions were studied based on the flow field numerical simulation. The transonic and supersonic flow field characteristics as well as the flow separation (boundary layer separation) were studied utilizing standard k-ε turbulence model. The results show that the velocity and Mach number oscillate when the opening ratio is Greater than or equal to 40 % for high inlet pressure condition, which indicates the opening ratio range of stable flow. The flow separation near the boundary layer emerges downstream of the nozzle at 20 % opening ratio for both high and low inlet pressure conditions. The regulator has piecewise linear characteristic. The research can provide guidance for design and application of the regulator in the uranium enrichment centrifugal cascade.

Uranium hexafluoride (UF6) undergoes a rapid hydrolysis reaction when exposed to atmospheric water. In addition to producing hazardous HF gas, the hydrolysis reaction produces uranyl fluoride (UO2F2), a radioactive solid phase particulate material. Because of the technological utility of UF6 in the nuclear fuel cycle, understanding the transport properties of UO2F2 aerosol produced via UF6 hydrolysis is important for accident scenarios. Moreover, the fundamental chemical and physical properties of the UF6 hydrolysis reaction are not completely understood. Recently, several experiments on the aerosol phase properties of UO2F2 produced in this way have shown that under most relevant conditions, the particle size distribution (PSD) of UO2F2 can be extremely small, approximately 3 to 5 nm, which is well below the threshold that can be routinely observed via scanning electron microscopy (SEM). Although readily observable in the aerosol phase, observation of nanometer-sized particles in the condensed phase (i.e. deposited on surfaces) remains a challenge. Here, we have used atomic force microscopy (AFM) to study the PSD and morphological characteristics of UO2F2 deposited at low and high concentrations under different humidity conditions, a primary variable in the hydrolysis reaction. We find strong agreement between PSD measured in the aerosol phase via scanning mobility particle sizing and PSD measured via AFM, with particle sizes peaked below 4 nm for low-humidity conditions. At higher humidity, the distribution is centered around 5 to 10 nm but extends up to 20 nm. These results are in stark contrast to previous measurements using SEM that show PSD on the order of 300- to 1000-nm particle sizes; moreover, these are the first direct measurements of individual particles of UO2F2 having been produced via UF6 hydrolysis deposited on surfaces. These measurements, therefore, open a new avenue for collecting and detecting UO2F2 in the condensed phase and further refine the PSD, which is critical for environmental transport determinations.

Numerical Study of the Influence of the Method of Feeding of Reactants to the Reactor on the Interaction of Uranium Hexafluoride with Methane and Oxygen in a Combustion Regime

Corrosion of iron in liquid uranium hexafluoride at 80 °C. Part II: Corrosion mechanism

Obtaining Hydrogen Fluoride During the Interaction of Depleted Uranium Hexafluoride with Methane and Oxygen in a Combustion Regime

Corrosion of iron in liquid uranium hexafluoride at 80 °C. Part I: Normal and abnormal experimental kinetics

Uranium hexafluoride (UF6) is a significant concern for material accountancy and verification in the international safeguards community. Verification of the contents of UF6 cylinders is generally attempted with gamma spectroscopy but the current methods assume a uniform, homogeneous UF6 mass distribution within the cylinder. In this work, it was found experimentally and confirmed via modeling, that under an external heat load (the sun), the UF6 and its daughter products undergo fractionation in the cylinder. This fractionation of the UF6 and daughter products can cause an errant measurement of the enrichment of the cylinder when using the current verification methods.

Two-cascade scheme of gas centrifuges for the purification of reprocessed uranium hexafluoride from 232, 234, 236U

Uranium hexafluoride ( UF 6 ) is used ubiquitously in the nuclear fuel cycle. Its spontaneous hydrolysis in the presence of atmospheric moisture is well known but the associated reaction mechanism is poorly understood. Here a computational study was undertaken with the aim of characterizing the rate-limiting step of the hydrolysis of UF 6 under dry conditions. Toward this end, we began by examining the convergence of various energy contributions to the atomization enthalpy ( Δ H at ) of UF 6 and its hydrolysis product, UO 2 F 2 . This enabled a refinement of our previous composite method, resulting in a composite method with improved accuracy that also scales well by leveraging existing massively-parallel codes. We find that extremely high levels of theory are required to obtain Δ H at within experimental error bars, in agreement with the literature. Having calibrated our composite scheme, we proceed to investigate approximations appropriate for computing accurate binding energies and barrier heights on the potential energy surface governing the hydrolysis of UF 6 . In combination with high-accuracy relative energies, a master equation approach is used to generate rate constants, and comparisons are made with recent measurements [Richards et al., RSC Adv., 2020, 10, 34729]. Based on kinetic and equilibrium arguments, we conclude that the hydrolysis of U F 6 , when proceeding under very dry conditions, is unlikely to be initiated via U F 6 + H 2 O → UF 5 OH + HF type reactions. Finally, computed equilibrium constants and rate coefficients are tabulated for the temperature range 300–1800 K.

Abstract A multiscale model describing the kinetics of the processes taking place during the radiolysis of uranium hexafluoride (UF6) has been developed using fundamental physical and chemical principles. The model incorporates both the radiolysis and thermal terms. The processes of the radiolysis products release from the gas phase to the solid and vice versa are taken into account. The predictions of the model are verified against the available experimental data.

This paper presents a numerical study on the condensation process of uranium hexafluoride (UF6) in the supply and extraction system of a uranium enrichment plant. The numerical study was conducted using a standard UF6 receiving container with a nominal diameter of 127 mm and a volume of 8L under constant temperature boundary conditions. A phase change heat and mass transfer model for the desublimation process of uranium hexafluoride gas was established, and this model was combined with the Euler two fluid model to predict the distribution of key parameters such as temperature, pressure, and volume fraction of each phase during the UF6 cooling process, as well as the gas flow characteristics inside the container. In addition, this study also investigated the influence of various factors on the cooling rate. The research results indicated that UF6 gas initially condensed on the container wall and gradually diffused inward, with the highest solid density observed on the wall. Furthermore, increasing the inlet gas temperature, inlet mass flow rate, and reducing the cooling temperature, initial pressure inside the container could all enhance the desublimation rate to various degrees. The optimization plan proposed based on the above influencing factors could increase the yield of UF6 solid by 64.20% in 2 h, compared to the basic operating conditions.

In this paper, numerical simulation methods are used to study issues related to the optimal operating modes of hyperspeed (rotor velocity 1000 m/s and above) model gas centrifuges (GCs) of various lengths and velocities of rotation. The possibility of gas extraction under optimal conditions is studied using three-dimensional modeling. It is shown that for hyperspeed GCs with the Pitot tube as gas extractor, simultaneous attainment of the optimal values for both friction power and waste flux, which are necessary for achieving the optimal operating mode, is unattainable, unlike GC models with a rotor velocity of 600 m/s. It is also shown that the working gas within the shockwave generated by the gas extractor can attain temperatures exceeding 1300 K, which raises the question of a possible accelerated decomposition of uranium hexafluoride.

Uranium measurements in the field using high-resolution cadmium zinc telluride detectors

A mass and energy balance for a specific refuelling of Angra 2 nuclear power plant from a life cycle perspective

Introduction: Uranium, which is the raw material basis of the nuclear industry, is capable of causing adverse medical and biological consequences for workers who come into contact with its compounds in the course of their professional activities. In order to study this effect and to study in detail the biomedical consequences of the effects of uranium compounds on the body of personnel of nuclear power facilities, it is necessary to form a cohort of persons engaged in work with uranium compounds. One of the key elements of the uranium conversion technology carried out within the framework of sublimation production is the production of raw uranium hexafluoride for subsequent isotopic enrichment. Purpose: To form and characterize a cohort of sublimate production of the personnel of the Siberian Chemical Plant involved in work with uranium compounds in the period 1953–2000. Material and methods: The source of information was the regional medical dosimetric register of Seversk Biophysical Research Center, containing information on all current and former employees of the Siberian Chemical Plant (about 65,000 people) from the moment of the company’s foundation to the present. Results: A cohort of Siberian Chemical Plant workers involved in work with uranium compounds in the period 1953–2000 has been formed and described. The cohort consists of 577 people (475 men and 102 women). Biomedical information and dosimetric information about the employees included in the cohort are included in the created database of the personnel of the Siberian Chemical Plant involved in working with uranium compounds in the period 1953–2000. Conclusion: The formed cohort and database will allow conducting epidemiological studies to assess the morbidity and mortality of personnel due to malignant neoplasms, as well as making scientifically sound conclusions about the role of uranium compounds in the occurrence and mortality due to malignant neoplasms.

HAXPES measurements were carried out using a Scienta Omicron HAXPES instrument to provide reference spectra for depleted uranium dioxide. High purity uranium dioxide, as confirmed by trace elemental analysis and x-ray diffraction, was synthesized via the integrated dry route from uranium hexafluoride. The material was fixed on double sided carbon tape for the analysis with charge control measures in place. The expanded energy range, using a Ga Kα x-ray source, presents core level photoelectrons not observed in traditional XPS. In addition, a region associated with the x-ray induced Auger transitions MNN is evident at binding energies only achievable with HAXPES. The reference spectra presented here act as the first in a line of proposed investigations into the comparison of XPS and HAXPES from surface to bulk as well as a fundamental understanding of the electronic structure of uranium materials.

A Cholesky decomposition (CD)-based implementation of relativistic two-component coupled-cluster (CC) and equation-of-motion CC (EOM-CC) methods using an exact two-component Hamiltonian augmented with atomic-mean-field spin-orbit integrals (the X2CAMF scheme) is reported. The present CD-based implementation of X2CAMF-CC and EOM-CC methods employs atomic-orbital-based algorithms to avoid the construction of two-electron integrals and intermediates involving three and four virtual indices. Our CD-based implementation extends the applicability of X2CAMF-CC and EOM-CC methods to medium-sized molecules with the possibility to correlate around 1000 spinors. Benchmark calculations for uranium-containing small molecules were performed to assess the dependence of the CC results on the Cholesky threshold. A Cholesky threshold of 10-4 is shown to be sufficient to maintain chemical accuracy. Example calculations to illustrate the capability of the CD-based relativistic CC methods are reported for the bond-dissociation energy of the uranium hexafluoride molecule, UF6, with up to quadruple-ζ basis sets, and the lowest excitation energy in the solvated uranyl ion [UO22+(H2O)12].