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At least 919 records · Page 51

Capture of Uranium Particles By Filtration: Effects of Filter Material and Air Humidity

Filtration of airborne particles is a standard technique for removal of radiological particles from the effluent of a nuclear reactor. The effects of humidity on filter performance and uranium particles are however less understood. We have conducted experimental runs in the Environmental Experimental Chamber (EEC) located at ORNL to study the capture of uranyl fluoride particles in supports of NNSA missions. Two filter types, one of Minimum Efficiency Reporting Value (MERV)-9 and the other of MERV-10 American Society of Heating, Refrigerating and Air-Conditioning Engineering) ASHRAE rating, were used in the investigations under two humidity conditions [15% and 65% Relative Humidity (Rh)]. Both MERV9 and MERV10 filters failed to capture uranyl fluoride particles that were smaller than 100 nm. The penetration efficiencies for both filter types were very high, greater than 80%, for particles from 10 to 100 nm. As particles became larger and wetter, the capturing efficiencies of both types of filter improved. Slightly greater than 50% of particles from 1 to 10 μm still escaped the capture by the MERV9 filters. However, MERV10 filters were able to capture higher than 50% of particles in the size range of 1 to 2 μm indicating it is likely to meet ASHRAE requirements. Overall, the capture efficiency of a filter is highly dependent on uranyl fluoride particle size, which humidity plays a major role. These two filter types simply are unable to capture particles smaller than 1 μm. A filter that has a higher ASHRAE rating like the HEPA filter has to be used to capture sub-micron particles. Questions on how uranyl fluoride behave in a condition higher than 65% Rh remain, because the particles could deliquescent at the higher humidity condition. That would complete change the size, shape, and surface properties of the uranyl fluoride particles which could lead to completely different filter performance and filtration dynamics. Furthermore, how high humidity affects filters of all MERV ratings remain unclear. Other filter characteristics such as surface charge could also be affected by high humidity condition and need to be investigated.

42 ENGINEERING↗

The Acute Inhalation Toxicity in Rats from the Pyrolysis Products of Four Fluoropolymers

Male Sprague-Dawley rats (225?250 g) were exposed to the thermal degradation products from four fluoropolymers. The three polymers containing vinylidene fluoride and hexafluoropropene (VF2/HFP) were pyrolyzed at 550? and 800?C, whereas polytetrafluoroethylene (PTFE) was pyrolyzed at 625 and 800?C. At the lower temperatures, the pyrolysate from the copolymer of vinylidene fluoride and hexafluoropropene (VF2/HFP) was less toxic than the pyrolysates from either the terpolymer of vinyidene fluoride, hexafluoropropene, and tetrafluoroethylene (VF2/HFP/TFE) or the copolymer of vinylidene fluoride and hexafluoropropene with ?additives? (VF2/HFP-A). However, the pyrolysates from the VF2/HFP-containing materials produced less toxic products than the pyrolysate from PTFE at 625?C. When the pyrolysis temperature was increased to 800?C, very little difference was noted between the pyrolysis toxicity for any of the VF2/HFP-containing polymers with the most toxic pyrolysate again produced by PTFE. Carbon monoxide levels were all sublethal. No correlation could be established between hydrolyzable fluoride levels and the lethality of the pyrolysates. Death following exposure occurred within 48 hr due to acute pulmonary edema and hemorrhage. Survival of this acute phase was followed by alveolar lymphocytic infiltration and peribronchial tissue proliferation.

Carter, V. L., Jr.↗

Assessment of effects on vegetation of degradation products from alternative fluorocarbons

Concern with the effects of fluorides on plants has been devoted to that resulting from dry deposition (mainly with reference to gaseous HF and secondarily with particulate forms). The occurrence of precipitation as rain or mist and the presence of dew or free water on the foliage has mainly been considered with respect to their effects on the accumulation of air-borne fluoride and not with fluoride in wet deposition. That is, precipitation has been viewed primarily with respect to its facilitation of the solution and subsequent absorption of deposits by the foliar tissues or its elution of deposited fluoride from foliage. Accordingly, our evaluation of inorganic fluoride from fluorocarbon degradation rests upon a comparison with what is known about the effects of industrial emissions and what could be considered the natural condition.

Mccune, D. C.↗

NASA Li/CF(x) cell problem analysis: Anion exchange chromatography analysis

An analysis was made of wiper samples used to wipe down lithium/chlorine fluorine battery components and production equipment. These components and equipment were potentially exposed to thionyl chloride vapors. In the presence of moisture, thionyl chloride decomposes to sulfur dioxide and hydrogen chloride. The wiper samples were analyzed for soluble chlorides and fluorides by anion exchange chromatography. During the examination of the test chromatographs, fluoride contamination was discovered in wiper samples from the test equipment. An analytical method to determine fluoride was developed. The first 3 extracts from the potentially exposed and clean wiper samples were tested, and the total fluoride from both groups determined. A comparison of the results from both groups was made to determine the extent of fluoride contamination.

Bytella, Joseph↗

Point defect formation in optical materials expos ed to the space environment

Point defect formation associated with early stages of optical damage was observed unexpectedly in two, and possibly three, different optical materials subjected to short-duration space exposure. Three calcium fluoride, two lithium fluoride, and three magnesium fluoride samples were flown on Space Shuttle flight STS-46 as part of the Evaluation of Oxygen Interactions with Materials - Third Phase experiment. One each of the calcium and magnesium fluoride samples was held at a fixed temperature of 60 C during the space exposure, while the temperatures of the other samples were allowed to vary with the ambient temperature of the shuttle cargo bay. Pre-flight and post-flight optical absorption measurements were performed on all of the samples. With the possible exception of the magnesium fluoride samples, every sample clearly showed the formation of F-centers in that section of the sample that was exposed to the low earth orbit environment. Solar vacuum ultraviolet radiation is the most probable primary cause of the defect formation; however, the resulting surface metallization may be synergistically altered by the atomic oxygen environment.

Allen, J. L.↗

Particle Morphology Effects on Flow Characteristics of PS304 Plasma Spray Coating Feedstock Powder Blend

The effects of BaF2-CaF 2 particle morphology on PS304 feedstock powder flow ability have been investigated. BaF2-CaF2 eutectic powders were fabricated by comminution (angular) and by gas atomization (spherical). The fluoride powders were added incrementally to the other powder constituents of the PS304 feedstock: nichrome, chromia, and silver powders. A linear relationship between flow time and concentration of BaF2-CaF2 powder was found. Flow of the powder blend with spherical BaF2-CaF2 was better than the angular BaF2-CaF2. Flow ability of the powder blend with angular fluorides decreased linearly with increasing fluoride concentration. Flow of the powder blend with spherical fluorides was independent of fluoride concentration. Results suggest that for this material blend, particle morphology plays a significant role in powder blend flow behavior, offering potential methods to improve powder flow ability and enhance the commercial potential. These findings may have applicability to other difficult-to-flow powders such as cohesive ceramics.

Stanford, Malcolm K.↗

Production of Gas-Phase Uranium Fluoroanions Via Solubilization of Uranium Oxides in the [1-Ethyl-3-Methylimidazolium]{sup +}[F(HF){sub 2.3}]{sup −} Ionic Liquid

A new methodology for gas-phase uranium ion formation is described in which UO{sub 2} is dissolved in neat N-ethyl,N′-methylimidazolium fluorohydrogenate ionic liquid [EMIm{sup +}][F(HF){sub 2.3}{sup −}], yielding a blue-green solution. The solution was diluted with acetonitrile and then analyzed by electrospray ionization mass spectrometry. UF{sub 6}{sup −} (a U(V) species) was observed at m/z = 352, and other than cluster ions derived from the ionic liquid, nothing else was observed. When the sample was analyzed using infusion desorption chemical ionization, UF{sub 6}{sup −} was the base peak, and it was accompanied by a less intense UF{sub 5}{sup −} that most likely was formed by elimination of a fluorine radical from UF{sub 6}{sup −}. Formation of UF{sub 6}{sup −} required dissolution of UO{sub 2} followed by or concurrent with oxidation of uranium from the + 4 to the + 5 state and finally formation of the fluorouranate. Dissolution of UO{sub 3} produced a bright yellow solution indicative of a U(VI) species; however, electrospray ionization did not produce abundant U-containing ions. The abundant UF{sub 6}{sup −} provides a vehicle for accurate measurement of uranium isotopic abundances free from interference from minor isotopes of other elements and a convenient ion synthesis route that is needed gas-phase structure and reactivity studies like infrared multiphoton dissociation and ion-molecule dissociation and condensation reactions. The reactive fluorohydrogenate ionic liquid may also enable conversion of uranium in oxidic matrices into uranium fluorides that slowly oxidize to uranyl fluoride under ambient conditions, liberating the metal for facile measurement of isotope ratios without extensive chemical separations. .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DRACS thermal performance evaluation for FHR

Direct Reactor Auxiliary Cooling System (DRACS) is a passive decay heat removal system proposed for the Fluoride-salt-cooled High-temperature Reactor (FHR) that combines coated particle fuel and a graphite moderator with a liquid fluoride salt as the coolant. The DRACS features three coupled natural circulation/convection loops, relying completely on buoyancy as the driving force. These loops are coupled through two heat exchangers, namely, the DRACS Heat Exchanger and the Natural Draft Heat Exchanger. In addition, a fluidic diode is employed to minimize the parasitic flow into the DRACS primary loop and correspondingly the heat loss to the DRACS during normal operation of the reactor, and to keep the DRACS ready for activation, if needed, during accidents. To help with the design and thermal performance evaluation of the DRACS, a computer code using MATLAB has been developed. This code is based on a one-dimensional formulation and its principle is to solve the energy balance and integral momentum equations. By discretizing the DRACS system in the axial direction, a bulk mean temperature is assumed for each mesh cell. The temperatures of all the cells, as well as the mass flow rates in the DRACS loops, are predicted by solving the governing equations that are obtained by integrating the energy conservation equation over each cell and integrating the momentum conservation equation over each of the DRACS loops. In addition, an intermediate heat transfer loop equipped with a pump has also been modeled in the code. This enables the study of flow reversal phenomenon in the DRACS primary loop, associated with the pump trip process. Experimental data from a High-Temperature DRACS Test Facility (HTDF) are not available yet to benchmark the code. A preliminary code validation is performed by using natural circulation experimental data available in the literature, which are as closely relevant as possible. The code is subsequently applied to the HTDF that is under construction at the Ohio State University.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗

Liquid phase preparation and fluorescence of flake-liked NdF{sub 3} nanomaterials

Graphical abstract: Room-temperature emission spectra of NdF{sub 3} nanoflakes exhibit a strong luminescence emission peak at 402 nm when irradiated by an excitation wavelength of 250 nm. Display Omitted Highlights: ► NdF{sub 3} nanoflakes have been successfully prepared by a facile and repeatable liquid phase preparation. ► The action of oxalic acid in the reaction process was studied, showing important in the morphology of neodymium fluorides. ► The study on the fluorescent properties of flake-like NdF{sub 3} nanomaterials shows a strong emission peak at 402 nm by the excitation wavelength of 250 nm. -- Abstract: Neodymium fluoride nanoflakes were successfully prepared by a facile liquid phase preparation with Nd(NO{sub 3}){sub 3} and NaF as raw materials. In the process, oxalic acid acting as template agent was found to play important roles in the morphology of neodymium fluorides. The as-synthesized NdF{sub 3} nanoflakes were characterized by various techniques of X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive X-ray spectrometer instrument (EDS). The fluorescent properties of neodymium fluoride nanoflakes were investigated, showing a strong luminescence emission peak at 402 nm by the excitation wavelength of 250 nm.

36 MATERIALS SCIENCE↗

Overview of the Salt at Wall Thermal Exchanges (SWATH) Experiment

Molten Salt Reactors have attracted increased attention in recent years because of the design and safety possibilities offered by the use of a liquid fuel. The European project SAMOFAR1 (2015-2019) is currently coordinating the research efforts on the Molten Fast Salt Reactor (MSFR) concept in Europe. The MSFR is a fast-spectrum breeder reactor with a large negative power coefficient that can be operated in a Thorium fuel cycle. The fast spectrum allows the reduction of the reprocessing requirements and a better reactor breeding ratio. Other advantages of the MSFR design are the possibility for actinide burning and extending fuel resources, on-line fuel loading and reprocessing and the use of novel passive safety systems such as the fuel salt draining system. The reference MSFR concept is a 3000 MW(th) reactor with three different circuits: the fuel circuit, the intermediate circuit and the power conversion system. The main components of the fuel circuit are the fuel salt which serves as fuel and coolant, the core cavity, the inlet and outlet pipes, the gas injection system (not shown in the figure), the salt-bubble separators, the fuel heat exchangers and the pumps. A lithium fluoride salt has been selected as the fuel matrix. The initial composition (non-irradiated) of the MSFR fuel salt is a mixture of a lithium fluoride, thorium fluoride salts and actinides fluoride (LiF-ThF{sub 4}-{sup 233}UF{sub 4} or LiF-ThF{sub 4}- {sup enr}UF{sub 4}-(Pu-MA)F{sub 3}), with the proportion of LiF fixed at about Development of accurate numerical models for the MSFR can only be accomplished by the use of a multiphysics approach which allows taking into account the coupling between relevant neutronics, thermal hydraulics and thermomechanics phenomena. As it is discussed in the next section, such a reactor model requires further progress on the knowledge of molten salt thermal hydraulics, in particular regarding the accuracy of the fuel salt Computational Fluid Dynamics (CFD) models. The Salt at Wall: Thermal Exchanges (SWATH) experiment is being designed to contribute to this particular point. SWATH is one of the experimental activities of the European H2020 SAMOFAR project and includes both experimental and numerical developments. The main objectives of SWATH are to: (i) Improve molten salt numerical models used for design and safety studies and (ii) Demonstrate the working principles of the cold plug device. The cold plug device is a key safety component of the salt draining system of the MSFR. The cold plug is intended to passively melt during accidental conditions thus allowing the flow of the nuclear fuel from the core cavity to the fuel salt draining tanks by gravity forces. The fuel salt draining tanks are designed to ensure that adequate margins are obtained regarding the fuel cooling capabilities and the reactivity control. The next sections provide an overview of the current challenges in molten salt thermal hydraulics modeling and the SWATH experiment design. (authors)

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

Polymorph (C{sub 2}N{sub 2}H{sub 10}){sub 0.5}RE{sub 3}F{sub 10}·xH{sub 2}O (RE = Ho-Lu, Y) and REF{sub 3} nanocrystals: Hydrothermal synthesis, characterization and luminescence

Graphical abstract: A hydrothermal system is developed to prepare one new polymorph of (C{sub 2}N{sub 2}H{sub 10}){sub 0.5}RE{sub 3}F{sub 10}·xH{sub 2}O and known rare earth fluorides involving REF{sub 3} nanocrystals under mild condition. Highlights: ► A new polymorph of (C{sub 2}N{sub 2}H{sub 10}){sub 0.5}RE{sub 3}F{sub 10}·xH{sub 2}O has been synthesized. ► The RE{sup 3+} radius decides the shape evolution and phase control for REF{sub 3} NCs. ► The RE{sup 3+} radius has influence on the microstructure and morphology of REF{sub 3} NCs. -- Abstract: In this paper, a solvents-thermal system is developed to prepare one new polymorph of (C{sub 2}N{sub 2}H{sub 10}){sub 0.5}Ho{sub 3}F{sub 10}·xH{sub 2}O and rare earth fluorides REF{sub 3} nanocrystals under mild condition. It is found that the ionic radius of RE{sup 3+} is the key factor responsible for the shape evolution and phase control for rare earth fluorides nanocrystals at selected temperatures, which has an influence on the microstructure and morphology of the products to some extent. With the increase of the atomic number, the shape of fluoride changes from hexagonal REF{sub 3} phase (RE = La, Sm) to orthorhombic REF{sub 3} phase (RE = Eu-Dy), and finally to diamond structure (C{sub 2}N{sub 2}H{sub 10}){sub 0.5}Ho{sub 3}F{sub 10}·xH{sub 2}O (RE = Ho, Er, Tm, Yb, Lu, Y). In addition, the characteristic energy level transition {sup 5}D{sub 0}–{sup 7}F{sub 1} of Eu{sup 3+} splits into 585 and 591 nm emission peaks, and the dominant peak is the orange emission at 591 nm.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Release path temperatures of shock-compressed tin from dynamic reflectance and radiance measurements

Dynamic reflectance and radiance measurements were conducted for tin samples shock compressed to 35 GPa and released to 15 GPa using high explosives. We determined the reflectance of the tin samples glued to lithium fluoride windows using an integrating sphere with an internal xenon flashlamp as an illumination source. The dynamic reflectance (R) was determined at near normal incidence in four spectral bands with coverage in visible and near-infrared spectra. Uncertainties in R/R{sub 0} are <2%, and uncertainties in absolute reflectance are <5%. In complementary experiments, thermal radiance from the tin/glue/lithium fluoride interface was recorded with similar shock stress and spectral coverage as the reflectance measurements. The two sets of experiments were combined to obtain the temperature history of the tin surface with an uncertainty of <2%. The stress at the interface was determined from photonic Doppler velocimetry and combined with the temperatures to obtain temperature-stress release paths for tin. We discuss the relationship between the experimental release paths and release isentropes that begin on the principal shock Hugoniot.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Complete Sensitivity/Uncertainty Analysis of LR-0 Reactor Experiments with MSRE FLiBe Salt and Perform Comparison with Molten Salt Cooled and Molten Salt Fueled Reactor Models

In September 2016, reactor physics measurements were conducted at Research Centre Rez (RC Rez) using the FLiBe (2 7 LiF + BeF 2 ) salt from the Molten Salt Reactor Experiment (MSRE) in the LR-0 low power nuclear reactor. These experiments were intended to inform on neutron spectral effects and nuclear data uncertainties for advanced reactor systems using FLiBe salt in a thermal neutron energy spectrum. Oak Ridge National Laboratory (ORNL), in collaboration with RC Rez, performed sensitivity/uncertainty (S/U) analyses of these experiments as part of the ongoing collaboration between the United States and the Czech Republic on civilian nuclear energy research and development. The objectives of these analyses were (1) to identify potential sources of bias in fluoride salt-cooled and salt-fueled reactor simulations resulting from cross section uncertainties, and (2) to produce the sensitivity of neutron multiplication to cross section data on an energy-dependent basis for specific nuclides. This report provides a final report on the S/U analyses of critical experiments at the LR-0 Reactor relevant to fluoride salt-cooled high temperature reactor (FHR) and liquid-fueled molten salt reactor (MSR) concepts. In the future, these S/U analyses could be used to inform the design of additional FLiBe-based experiments using the salt from MSRE. The key finding of this work is that, for both solid and liquid fueled fluoride salt reactors, radiative capture in 7 Li is the most significant contributor to potential bias in neutronics calculations within the FLiBe salt.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗

Thermal NF3 fluorination/oxidation of cobalt, yttrium, zirconium, and selected lanthanide oxides

This paper presents results of our continuing investigation on the use of nitrogen trifluoride as a fluorination or fluorination/oxidation agent for separating valuable constituents from used nuclear fuels by exploiting the different volatilities of the constituent fission product and actinide fluorides. This article focuses on fission products that do not have volatile fluorides or oxyfluorides at expected operations temperatures. Our thermodynamic calculations show that nitrogen trifluoride has the potential to completely fluorinate fission product oxides to their fluorides. Simultaneous thermogravimetric and differential thermal analyses show that the oxides of cobalt, zirconium, and the lanthanides are fluorinated but do not form volatile fluorides when treated with nitrogen trifluoride at temperatures up to 550°C. Our studies of gadolinium-doped commercial nuclear fuel indicate that nitrogen trifluoride can extract uranium from the non-volatile gadolinium.

Scheele, Randall D.↗

Characterizing the degradation of [(UO 2 F 2 )(H 2 O)] 7 4H 2 O under humid conditions

Under humid conditions, uranyl fluoride ([(UO 2 F 2 )(H 2 O)] 7 ·4H 2 O) undergoes a loss of fluorine to form a uranyl hydroxide species, which can be further hydrated to form a uranyl peroxide species. X-ray diffraction data of the uranyl peroxide product is presented for the first time. In addition, the temperature and humidity conditions under which these reactions occur have been clarified by a 220-day experiment using microRaman spectroscopy to track chemical changes in individual particles of uranyl fluoride. At 25 and 35 ° C, uranyl fluoride is found to be stable at 32% relative humidity but not stable at and above 59% relative humidity. We show that water vapor pressure is the driving factor in formation of both the hydroxide and peroxide products. The kinetics of the transformation from uranyl fluoride into uranyl hydroxide is consistent with a denucleation reaction following the absorption of water molecules.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗

Interaction of beryllium with 316H stainless steel in molten Li 2 BeF 4 (FLiBe)

The increased demand in renewable energy resources has led to a renewed interest in nuclear reactors including a new generation of molten salt reactors. One of the issues encountered in handling of molten chloride or fluoride salts is the inability of metals to form and retain a protective oxide surface layer, generally chromium oxide. The low chromium content, nickel-based alloy INOR-8, later marketed as Hastelloy N, was specifically developed to contain molten fluorides. This alloy had some deficiencies, but its composition resulted in it incurring far less chromium depletion by the molten fluoride salts than alloys like 316 stainless steel. For the next generation of molten salt reactors, an alloy with pressure vessel code approval and higher temperature capability than Hastelloy N is required. Consequently, several reactor designers have reportedly chosen to build the reactor containment vessel from 316H stainless steel. In order to minimize corrosion of the stainless steel by the molten fluoride salt (2LiF-BeF 2 ), it is proposed to add beryllium metal to the salt to react with impurities and provide a means to lower the oxidation potential thus making the salt less corrosive. Even so, there is a concern whether the beryllium would react with components of the stainless steel. To address this concern, static capsule tests were conducted in which selected amounts of beryllium were added to capsules containing 2LiF-BeF 2 (FLiBe) salt and 316H stainless steel and Hastelloy N samples. Following exposure, the samples were cleaned and examined using a variety of analysis techniques including, optical microscopy, SEM-EDS, XPS, LIBS, XRD and EPMA. Tensile samples were also exposed in capsules, and those were subjected to tensile testing. Notably, It was found that for the level of beryllium additions used in this study, intermetallic compounds were formed which could be detrimental to the long-term performance of the 316H stainless steel.

36 MATERIALS SCIENCE↗

Synthesis and Electronic Structure of a 3D Crystalline Stack of MXene-Like Sheets

Despite the interest in MXenes in the past decade, MXenes are often highly disordered, which can complicate their study and use. For example, nearly all MXenes have a random mixture of surface terminations (-O, -OH, -F). In addition, restacked 3D films have turbostratic disorder and often contain ions, solvent, and other species in between their layers. Here, we report Y 2 CF 2 , a layered crystal with a unit cell isostructural to a MXene, in which layers are capped only by fluoride anions. We directly synthesize the 3D crystal through a high-temperature solid-state reaction, which affords the 3D crystal in high yield and purity and ensures that only fluoride ions terminate the layers. We characterize the crystal structure and electronic properties using a combination of experimental and computational techniques. We find that relatively strong electrostatic interactions bind the layers together into a 3D crystal and further find that the lack of orbital overlap between layers gives rise to a description of Y 2 CF 2 as slabs of MXene-like sheets electrically insulated from one another. Therefore, we consider Y 2 CF 2 as a pure 3D crystalline stack of MXene-like sheets. In addition, Y 2 CF 2 is the first transition metal carbide fluoride experimentally synthesized. Finally, we hope this work inspires further exploration of transition metal carbide fluorides, which are potentially a large and useful class of compositions.

36 MATERIALS SCIENCE↗