Idaho Falls, ID, United States
Idaho Falls, ID, United States

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Bess J.D.,Idaho National Laboratory | Marshall M.A.,Center for Space Nuclear Research
Nuclear and Emerging Technologies for Space, NETS 2013 | Year: 2013

The baseline design for space nuclear power is a fission surface power (FSP) system: sodium-potassium (NaK) cooled, fast spectrum reactor with highly-enriched-uranium (HEU)-O2 fuel, stainless steel (SS) cladding, and beryllium reflectors with B4C control drums. Previous studies were performed to evaluate modeling capabilities and quantify uncertainties and biases associated with analysis methods and nuclear data. Comparison of Zero Power Plutonium Reactor (ZPPR)-20 benchmark experiments with the FSP design indicated that further reduction of the total design model uncertainty requires the reduction in uncertainties pertaining to beryllium and uranium cross-section data. Further comparison with three beryllium-reflected HEU-metal benchmark experiments performed at the Oak Ridge Critical Experiments Facility (ORCEF) concluded the requirement that experimental validation data have similar cross section sensitivities to those found in the FSP design. A series of critical experiments was performed at ORCEF in the 1960s to support the Medium Power Reactor Experiment (MPRE) space reactor design. The small, compact critical assembly (SCCA) experiments were graphite- or beryllium-reflected assemblies of SS-clad, HEU-O2 fuel on a vertical lift machine. All five configurations were evaluated as benchmarks. Two of the five configurations were beryllium reflected, and further evaluated using the sensitivity and uncertainty analysis capabilities of SCALE 6.1. Validation of the example FSP design model was successful in reducing the primary uncertainty constituent, the Be(n,n) reaction, from 0.27%δk/k to <0.0004%δk/k. Further assessment of additional reactor physics measurements performed on the SCCA experiments may serve to further validate FSP design and operation.

Zhang X.,Idaho National Laboratory | O'Brien J.E.,Idaho National Laboratory | O'Brien R.C.,Center for Space Nuclear Research | Housley G.K.,Idaho National Laboratory
Journal of Power Sources | Year: 2013

An experimental investigation on the performance and durability of single solid oxide cells (SOCs) is under way at the Idaho National Laboratory. Reversible operation of SOCs includes electricity generation in the fuel cell mode and hydrogen generation in the electrolysis mode. Degradation is a more significant issue when operating SOCs in the electrolysis mode. In order to understand and mitigate the degradation issues in high temperature electrolysis, single SOCs with different configurations from several manufacturers have been evaluated for initial performance and long-term durability. Cells were obtained from four industrial partners. Cells from Ceramatec Inc. and Materials and Systems Research Inc. (MSRI) showed improved durability in electrolysis mode compared to previous stack tests. Cells from Saint Gobain Advanced Materials Inc. (St. Gobain) and SOFCPower Inc. demonstrated stable performance in the fuel cell mode, but rapid degradation in the electrolysis mode, especially at high current density. Electrolyte-electrode delamination was found to have a significant impact on degradation in some cases. Enhanced bonding between electrolyte and electrode and modification of the electrode microstructure helped to mitigate degradation. Polarization scans and AC impedance measurements were performed during the tests to characterize cell performance and degradation. © 2013 Elsevier B.V. All rights reserved.

O'Brien R.C.,Center for Space Nuclear Research | Jerred N.D.,Center for Space Nuclear Research
Journal of Nuclear Materials | Year: 2013

About 50 vol.% 3 μm depleted uranium dioxide (UO2) powder was encapsulated within a tungsten super alloy matrix produced from sub-micron tungsten powders using the Spark Plasma Sintering (SPS) process. An additive of 25 atom-percent (at.%) rhenium was included within the tungsten matrix to improve the ductility and fracture toughness of the ceramic-metallic (cermet) matrix. Cermet fabrication to 97.9% of the theoretical cermet density was achieved by sintering at 1500 °C with 40 MPa of applied pressure for 20 min. The results presented are from the first known trials of W-UO2 and nuclear cermet production via SPS.

Zhang X.,Idaho National Laboratory | O'Brien J.E.,Idaho National Laboratory | O'Brien R.C.,Center for Space Nuclear Research | Hartvigsen J.J.,Ceramatec Inc | And 2 more authors.
International Journal of Hydrogen Energy | Year: 2013

An experimental study has been conducted at Idaho National Laboratory to demonstrate recent improvements in long-term durability of solid oxide electrolysis cells (SOEC) and stacks. Results of five stack tests are presented. Electrolyte-supported SOEC stacks were provided by Ceramatec Inc. and electrode-supported SOEC stacks were provided by Materials and Systems Research Inc. (MSRI), for these tests. Long-term durability tests were generally operated for durations of 1000 h or more. Stack tests based on technologies developed at Ceramatec and MSRI have shown significant improvement in durability in the electrolysis mode. Long-term degradation rates of 3.2%/khr and 4.6%/khr were observed for MSRI and Ceramatec stacks, respectively. One recent Ceramatec stack even showed negative degradation (performance improvement) over 1900 h of operation. Optimization of electrode and electrolyte materials, interconnect coatings, and electrolyte-electrode interface microstructures contribute to improve the durability of SOEC stacks. © 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Titarchuk L.,University of Ferrara | Titarchuk L.,Center for Space Nuclear Research | Seifina E.,Moscow State University
Astronomy and Astrophysics | Year: 2016

We report the results of Swift and Chandra observations of an ultraluminous X-ray source, ULX-1 in M101. We show strong observational evidence that M101 ULX-1 undergoes spectral transitions from the low/hard state to the high/soft state during these observations. The spectra of M101 ULX-1 are well fitted by the so-called bulk motion Comptonization (BMC) model for all spectral states. We have established the photon index (Γ) saturation level, Γsat = 2.8 ± 0.1, in the Γ versus mass accretion rate (M) correlation. This Γ-M correlation allows us to evaluate black hole (BH) mass in M101 ULX-1 to be MBH ∼ (3.2-4.3) × 104 M⊙, assuming the spread in distance to M101 (from 6.4 ± 0.5 Mpc to 7.4 ± 0.6 Mpc). For this BH mass estimate we apply the scaling method, using Galactic BHs XTE J1550-564, H 1743-322 and 4U 1630-472 as reference sources. The Γ vs. M correlation revealed in M101 ULX-1 is similar to that in a number of Galactic BHs and clearly exhibits the correlation along with the strong Γ saturation at ≈ 2.8. This is robust observational evidence for the presence of a BH in M101 ULX-1. We also find that the seed (disk) photon temperatures are low, on the order of 40-100 eV, which is consistent with high BH mass in M101 ULX-1. Thus, we suggest that the central object in M101 ULX-1 has intermediate BH mass on the order of 104 solar masses. © ESO, 2015.

Crawford D.S.,Center for Space Nuclear Research | Ring T.A.,University of Utah
Annals of Nuclear Energy | Year: 2012

Normalized neutron energy moments (moments) from the one-dimensional energy dependent neutron diffusion equation (EDNDE), Monte Carlo N Particle 5 version 1.40 (MCNP5) and Attila-7.1.0-beta version (Attila) are validated with the GODIVA experiment (GODIVA). Energy moments 0-5 for all three methods are compared to GODIVA moments. GODIVA moments are measured with two methods. The 1st method is a time of flight (T-O-F) measurement of the average energy (moment 1) of the leaking neutrons from the surface of GODIVA and the 2nd method is from back calculating moments from foil activation analysis of various metal foils at the center of GODIVA. The error range of the EDNDE normalized moments compared to GODIVA is from 0% to 24%. The MCNP5 error range compared to GODIVA is 0-12% and the Attila error range is 0-79%. The method of moments is shown to be a fast reliable method, compared to either Monte Carlo methods (MCNP5) or 30 multi-energy group methods (Attila) with regard to the GODIVA experiment. © 2012 Elsevier Ltd. All rights reserved.

Crawford D.S.,Center for Space Nuclear Research | Ring T.A.,University of Utah
Annals of Nuclear Energy | Year: 2012

The energy dependent neutron diffusion equation (EDNDE) is converted into a moment equation which is solved analytically for the 1-D problem of a bare sphere of pure 235U. The normalized moments 0-5 generated analytically are compared to normalized energy moments, from Monte Carlo N Particle 5 version 1.40 (MCNP5) and Attila-7.1.0-beta version (Attila). The analytic normalized neutron energy moments, fall between the results from MCNP5 (lower bound) and Attila (upper bound) and are accurate compared to MCNP5 neutron energy moments when error in this Monte Carlo simulation are considered. The error range is from 0% to 14%. The Attila moments are less accurate when compared to MCNP5 than the analytical moments derived in this work. The method of moments is shown to be a fast reliable method, compared to either Monte Carlo methods (MCNP5) or 30 multi-energy group methods (Attila). © 2012 Elsevier Ltd. All rights reserved.

Howe S.D.,Center for Space Nuclear Research
Nuclear and Emerging Technologies for Space 2011, NETS-2011 | Year: 2011

With an increasing demand for long-duration and energy intensive missions in space, alternatives to radioisotope power systems are being explored. Nuclear fission reactors can provide sufficient power while maintaining a low specific mass comparable to radioisotope power systems. One of the projects focused on designing a small scale nuclear reactor with a low specific mass for use on a fourteen year unmanned mission. The results show a craft can be made that requires no internal pumps or electrical input to run the power conversion system. The power conversion system selected consisted of free-piston Stirling engines. The core design is based upon a heat pipe thermal transport system using a U10Mo Core, while a liquid bath controls thermal conditions around the power conversion systems. The radiators are also designed with carbon composite materials. Results of this paper show a reduction in specific mass of the system.

Marshall M.A.,Idaho National Laboratory | Marshall M.A.,Center for Space Nuclear Research | Bess J.D.,Idaho National Laboratory
Nuclear Data Sheets | Year: 2014

In 1971 and 1972 experimenters at the Oak Ridge Critical Experiment Facility performed critical experiments using an unreflected metal sphere of highly enriched uranium (HEU). The sphere used for the criticality experiments, originally used for neutron leakage spectrum measurements by General Atomic Company, consisted of three main parts and were assembled with a vertical assembly machine. Two configurations were tested. The first was nearly spherical with a nominal radius of 3.467 inches and had a reactivity of 68.1 ± 2.0 cents. The sphere parts were then re-machined as a sphere with a nominal radius of 3.4425 inches. This assembly had a reactivity of -23 cents. The method, dimensions, and uncertainty of the critical experiment were extensively recorded and documented. The original purpose of the experiments was for comparison to GODIVA I experiments. The ORNL unreflected HEU Metal Spheres have been evaluated for inclusion in the International Handbook of Evaluated Criticality Safety Benchmark Experiments (scheduled for inclusion in the September 2013 edition). © 2014.

Liao C.,Abs Consulting | Best F.R.,Texas A&M University | Best F.R.,Center for Space Nuclear Research
Journal of Thermophysics and Heat Transfer | Year: 2010

Acomprehensive one-dimensional analytical model has been developed for gas ejector design and analysis. Unlike existing models, no assumptions have been made to simplify the momentum conservation equation for the ejector mixing chamber (that is, constant-pressure and constant-area models). Instead, the new model solves the momentum equation, which results in improved accuracy and versatility over existing models. Previous models can be derived from the new model as particular cases. These derivations provide new understanding of the relationships between the constant-pressure and constant-area one-dimensional ejector analytical models. The new model extends to the problems left unsolved by existing models and is efficient in analyzing off-design operating conditions, such as the shock that occurs in the primary stream. From the new model, the limitations on ejector design and operation are also recognized. Copyright © 2010 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

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