Engineering topics

Voit, Stewart L.

Publications and source records attributed to Voit, Stewart L..

9 records

DOE OSTI2018

Vaporization behavior of an alkyl diphenyl ether and a commercial lubricant

The equilibrium vapor pressure as a function of temperature for an alkyl diphenyl ether with a vaporization coefficient significantly smaller than unity was characterized using the combined Langmuir free evaporation and mass loss Knudsen effusion technique. Results are compared using different cell designs and discrepancies, difficulties, and complications are discussed. In conclusion, the enthalpy and entropy of vaporization are estimated using the average temperature of the measurements.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2016

Quantification of process variables for carbothermic synthesis of UC 1-x N x fuel microspheres

This report details the continued investigation of process variables involved in converting sol-gel-derived, urania-carbon microspheres to ~820-μm-dia. UC 1-x N x fuel kernels in flow-through, vertical Mo and W crucibles at temperatures up to 2123 K. Experiments included calcining of air-dried UO 3 -H 2 O-C microspheres in Ar and H 2 -containing gases, conversion of the resulting UO 2 -C kernels to dense UO2:2UC in the same gases and vacuum, and its conversion in N 2 to UC 1-x N x (x = ~0.85). The thermodynamics of the relevant reactions were applied extensively to interpret and control the process variables. Producing the precursor UO 2 :2UC kernel of ~96% theoretical density was required, but its subsequent conversion to UC 1-x N x at 2123 K was not accompanied by sintering and resulted in ~83-86% of theoretical density. Increasing the UC 1-x N x kernel nitride component to ~0.98 in flowing N 2 -H 2 mixtures to evolve HCN was shown to be quantitatively consistent with present and past experiments and the only useful application of H 2 in the entire process.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2016

Characterization of Fresh Nuclear Fuel using Time-Of-Flight Neutrons

Neutrons offer excellent characterization capabilities for nuclear fuels and can provide non-destructive insight on micro structure, chemistry and crystallographic phase. Measurements are possible at reactors or pulsed sources, but the inherent energy resolution implicit at pulsed sources offers unique opportunities. Recent advances in 2D neutron detection enabled new capabilities of material characterization using neutron imaging and tomography for nuclear materials. Moreover, time-of-flight (TOF) neutron measurements can enable isotope specific tomography by deriving isotope densities from transmission spectra exhibiting neutron resonances, which are recorded for each pixel. Tomographic algorithms allow 3D reconstructions of the spatial distribution of isotopes, density and features in typical fuel pellet samples. The ability to select radiographs for different energies allows characterizing samples which are opaque for thermal neutrons, such as enriched fuels or fuels containing plutonium, by selecting epi-thermal neutron energies and by knowledge of the total neutron cross sections of the constituents, isotopic enrichment levels can be determined. Nuclear cross sections are typically not calculated directly and databases such as the Evaluated Nuclear Data File (ENDF) database provide this information with cross sections determined by standardized experimental measurements, such as neutron transmission measurements for individual isotopes. Utilizing the information in the ENDF database, the 'inverse' problem can be solved by assuming cross section parameters to be known parameters and areal densities can be determined. This work presents recent advances at the Los Alamos Neutron Science Center (LANSCE) facility at Los Alamos National Laboratory (LANL), which provides the infrastructure to handle radioactive samples, in the development of fuel characterization with TOF neutrons. Examples include recent work on prototype accident tolerant nuclear fuels (ATF). The potential application of these techniques for nondestructive examination of irradiated fuel is under consideration. Non-destructive access to materials features for specimens embedded in containers, particularly for hazardous samples, such as a radioactive nuclear fuel, is indispensable to characterize and ultimately license new fuel forms. Energy-resolve neutron imaging is a new tool for this research field. The results reported here present a new imaging technique, setting a milestone in the capabilities of measuring non-destructively absolute quantities of physical properties. The enabling physics behind this new technique are nuclear resonances. We have demonstrated how absolute areal densities can be extracted from radiographs utilizing pulsed neutron sources. This technique provides information that is otherwise difficult and costly to obtain. In the case of nuclear fuels, the results from energy-dispersive neutron imaging may guide destructive examination of irradiated fuel. This summery does not describe recent analysis, which is ongoing. Particularly, the implementation of calibration standards has improved the determination of enrichment levels without additional calibration. The analysis of the samples was performed with full tomographic reconstructions for isotope specific data and presents a first approach in absolute isotope specific 3D reconstruction. This work was predominantly funded by and received substantial support from the Fuel Cycle R and D program at Los Alamos National Laboratory. (authors)

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2016

A combined experimental and computational thermodynamic investigation of the U-Th-O system

Here, the thermodynamics of the U–Th–O system have been assessed using the Calphad method. The compound energy formalism (CEF) and a partially ionic two-sublattice liquid model (TSLM) were used for the fluorite U 1–y Th y O 2±x , γ-(U,Th) 4 O 9 , and the U–Th–O melt. The O 2 activity of fluorite U 1–y Th y O 2±x with temperature and composition was determined by thermogravimetric analysis. Thermodynamic studies for the Th–O binary and U–Th–O ternary available in the open literature were critically reviewed. A self-consistent data set was selected and compiled with the equilibrium oxygen pressures determined by thermogravimetry in order to optimize the adjustable parameters of models selected to represent the phases in the Th–O and U–Th–O systems.

36 MATERIALS SCIENCE↗

DOE OSTI2015

Cation and Vacancy Disorder in U 1-y Nd y O 2.00-X Alloys

In this study, the intermixing and clustering of U/Nd, O, and vacancies were studied by both laboratory and synchrotron-based x-ray diffraction in U 1-y Nd y O 2-X alloys. It was found that an increased holding time at the high experimental temperature during initial alloy preparation results in a lower disorder of the Nd distribution in the alloys. Adjustment of the oxygen concentration in the U 1-y Nd y O 2-X alloys with different Nd concentrations was accompanied by the formation of vacancies on the oxygen sublattice and a nanocrystalline component. The lattice parameters in the U 1-y Nd y O 2-X alloys were also found to deviate significantly from Vegard's law when the Nd concentration was high (53%) and decreased with increasing oxygen concentration. Such changes indicate the formation of large vacancy concentrations during oxygen adjustment at these high temperatures. Finally, the change in the vacancy concentration after the oxygen adjustment was estimated relative to Nd concentration and oxygen stoichiometry.

36 MATERIALS SCIENCE↗

DOE OSTI2015

Overview of the FUTURIX-FTA Irradiation Experiment in the Phénix Reactor

The Advanced Fuels Campaign utilizes the Advanced Test Reactor (ATR) for most of its irradiation testing. Cadmium-shrouded baskets are used in ATR to modify the neutron spectrum to simulate a fast reactor environment for the fuel. FUTURIX-FTA is an irradiation experiment conducted in the Phenix fast reactor in France. Results from FUTURIX-FTA and irradiation tests in ATR using identical fuel compositions will be compared to identify and evaluate any differences in fuel behavior due to differences in the irradiation source.

fast reactor↗

DOE OSTI2015

Chemical reactivity of CVC and CVD SiC with UO 2 at high temperatures

Two types of silicon carbide (SiC) synthesized using two different vapor deposition processes were embedded in UO 2 pellets and evaluated for their potential chemical reaction with UO 2 . While minor reactivity between chemical-vapor-composited (CVC) SiC and UO 2 was observed at comparatively low temperatures of 1100 and 1300 C, chemical-vapor-deposited (CVD) SiC did not show any such reactivity, according to microstructural investigations. But, both CVD and CVC SiCs showed some reaction with UO 2 at a higher temperature (1500 C). Elemental maps supported by phase maps obtained using electron backscatter diffraction indicated that CVC SiC was more reactive than CVD SiC at 1500 C. Moreover, this investigation indicated the formation of uranium carbides and uranium silicide chemical phases such as UC, USi 2 , and U 3 Si 2 as a result of SiC reaction with UO 2 .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2013

Decomposition Analysis of Neodymium Loaded Resin

In an effort to understand and quantify the carbon and sulfur contents of a curium oxide production process performed in the hot cells at Oak Ridge National Laboratory’s Radiochemical Engineering Development Center, a non-radioactive surrogate was used in a similar oxide formation process. Neodymium (Nd), which was chosen as a substitute for curium, was loaded onto a Dowex 50W-X8 resin by use of ion exchange column techniques and then treated under a variety of processing conditions. The surrogate product was analyzed for carbon and sulfur impurities, using inductively coupled plasma–mass spectrometry for sulfur assessment, a LECO combustion furnace/analyzer for carbon quantification, and X-ray diffraction for compound identification. The results indicate that the carbon and sulfur contents in the Nd oxide were similar to current estimations for curium oxide using the reference hot cell process. It was also seen that the major surrogate product of the hot cell process contained sulfur in a Nd oxysulfate (Nd2O2SO4) compound. Parametric analysis of the resin decomposition process revealed that increasing the temperature to 1400°C yielded considerably better removal of carbon and sulfur.

Curium Targets↗

DOE OSTI2010

Sol-gel Micro- Mini-Sphere Development

The Advanced Fuels Campaign ceramic fuels R&D effort, within The Department of Energy Fuel Cycle R&D Program, has undertaken an R&D approach that integrates fundamental R&D on ceramic fuel feedstock, fuel fabrication development, and separate effects irradiation testing. The goal is to achieve a fundamental understanding of the inter-relationships that exist between nuclear fuel materials properties, processing, and performance. In parallel with this type of basic research, it is important to advance the state of the art with respect to processing of nuclear fuel materials that must be handled in a controlled environment. Toward that end, it is important to consider ways to minimize processing losses associated with the synthesis and fabrication of nuclear fuel. One option may be to transition away from the standard powder-type fuel synthesis and pellet fabrication process and to use flowable, near-dustless spherical particles that can be pressed directly into pellets thus avoiding the use of dust generating milling and blending processes.

Feestock↗