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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Recalculating Dissolver Curves for Critical Parameters for Nuclear Criticality Safety

The dissolver paradox is a phenomenon in criticality safety whereby a high density fissile material is being dissolved in a low fissile density solution and is subcritical before and after dissolution. However, as the metal is being dissolved, there may be an intermediate concentration that leads to a critical state. CCG-184 is a Y-12 report written in 1980 that provided critical parameter data for two separate dissolver paradox scenarios: solid metal spheres and hollow metal spheres with internal moderation effects. The sphere and shell are both surrounded by solution, however the shell contains solution of the same concentration within itself. In 1980, there are limitations to the computational methods to determine critical parameters. These are due to the lower number of energy groups utilized (16-group) at the time, smaller number of established cross-sectional data, as well as a larger uncertainty within the resonance region of neutron energies. With these constraints in mind, these critical parameters are recalculated with newer cross-sectional data, a newer Monte Carlo code: SCALE 6.1.3 using KENO V.a, and a larger number of energy bins.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2024

Constrained curve fitting for semi-parametric models with radial basis function networks

Common to many analysis pipelines in lattice gauge theory and the broader scientific discipline is the need to fit a semi-parametric model to data. We propose a fit method that utilizes a radial basis function network to approximate the non-parametric component of such models. The approximate parametric model is fit to data using the basin hopping global optimization algorithm. Parameter constraints are enforced through Gaussian priors. The viability of our method is tested by examining its use in a finite-size scaling analysis of the $q$-state Potts model and $p$-state clock model with $q=2,3$ and $p=4,\infty$.

Peterson, Curtis T.↗
DOE OSTI2024

Out-of-plane curved fluidic oscillator

Various implementations include, an out-of-plane feedback-type fluidic oscillator. including a first portion, a second portion, a middle portion coupled between the first portion and the middle portion, and an axis of rotation. The middle portion includes a first side, a second side opposite and spaced apart from the first side, and a middle plane, an interaction chamber, a fluid supply inlet, an outlet nozzle, a first feedback a channel, and a second feedback channel. The first side is coupled to the first portion, and the second side is coupled to the second portion. The first side, the second side, and the middle plane extend circumferentially around the axis of rotation. The middle plane is disposed equally distanced from the first side and the second side. The fluid stream oscillates as it flows through the interaction chamber such that the fluid stream oscillates as the fluid stream exits the outlet nozzle.

Hossain, Mohammad Arif↗
DOE OSTI2020

Non-contact Current-Voltage (I-V) Tracer for Photovoltaics

This report presents a non-contact approach to simultaneously obtain current-voltage (I-V) curves of photovoltaic (PV) substrings and modules in a string without the need of disconnecting the individual modules from the string. There are two types of I-V curve tracers currently available in the marketplace, capacitor-based and electronic load-based. The primary requirement of these conventional I-V tracers is the disconnection of individual modules in the string so the individual modules contacted through the connectors of the individual modules. These contact-tracers have three major limitations in the utility scale power plants: First limitation – Weather and Accuracy: The mass-produced commercial contact-tracers cannot obtain the I-V curves of both string and its modules (as high as 30 modules), almost simultaneously (within about 5 minutes) at, practically, a single irradiance level, a single module temperature, a single spectrum and a single AOI (angle of incidence). This inability of the contact-tracers forces the testing personnel to wait for an extended or multiple sunny (>800 W/m 2 ) duration(s) of a cloudy day. This is a serious limitation as waiting for the sunny conditions or days is a huge practical challenge in almost all locations, except desert locations. Also, since the I-V curves are obtained at different prevailing weather conditions, it becomes critical to translate all the measured I-V curves of 30 modules in the string to a single test condition, for example STC (standard test conditions), so the underperforming modules can be identified. The accuracy of translation equations is heavily influenced by the irradiance level and temperature, spectral and AOI ranges; Second limitation - Safety: The second limitation is related to the high voltage electrical safety of the test personnel during disconnecting and reconnecting of individual modules or cable connectors from the string under daylight conditions and damaging of the original module connectors (especially the field aged connectors) during the disconnecting and reconnecting process; Third limitation – Labor: The third limitation is related to the enormous amount of time and hardship for the test personnel under prevailing (often harsh) protracted field conditions. This project was executed by Arizona State University in collaboration with its industry partner, PV Measurements Inc. (PVM). To mitigate all the three challenges of the state-of-the-art equipment indicated above, we utilized a non-contact I-V (NCIV) tracer approach. In this approach, we utilized an electrostatic voltmeter (ESV) and voltage sensor/probe combination to obtain I-V curves. The ESV units are extensively used in the high voltage industry but not in the PV industry. To obtain the simultaneous I-V curves of the substrings and modules within a string, we utilized multiple commercial ESV-Probe sets. In this approach, we utilized a non-contact voltage sensor (called, Probe) placed on the glass surface of the module (above the last cell of the module). This probe senses the module voltage (with respect to ground) through measured capacitance which is dictated by the surface charges (which in turn is dictated by the module voltage) and transmits the sensed voltage to the voltmeter (called, ESV or NCV, non-contact voltmeter). The current is sensed by a non-contact hall sensor. In a 30-module string, the 30th probe obtains the entire string I-V along with the string I-V obtained by the electronic load. so that the I-V curves of the substrings and modules can be obtained by NCIV without the need of disconnecting the individual modules in the string. The string I-V curves obtained by the electronic load and NCIV can be compared for the accuracy determination. One can use 30 ESV units and 30 Probes to obtain 30 I-V curves of a 30-module string or use just 5 ESV units and 30 Probes in conjunction with 5 six-channel switchboxes (called, 6:1 switchboxes). To reduce the equipment cost, we utilized the 6:1 switchbox approach so the number of ESV units is reduced from 30 to 5. The approaches, achievements and challenges of this project are detailed in this report.

14 SOLAR ENERGY↗
DOE OSTI2020

Climate-Related Trends of Within-Storm Intensities Using Dimensionless Temporal-Storm Distributions

Huff curves are probabilistic time distributions of rainfall expressed as dimensionless cumulative percentages of storm depth and duration. Previous studies have documented development factors, spatial robustness, and the utility of Huff curves in practical applications. However, the effects of trending rainfall on Huff curve intensity patterns have not yet been studied. As such, the goal of this paper is to fill this gap by studying Huff curve patterns in a watershed with demonstrated increasing trends of temperature and precipitation, with the intention that it can be generalized to other areas in the US and the world. To achieve this goal, the high temporal resolution precipitation data collected from a high spatial density, 72-year precipitation-gauge network on the 4.25-km 2 North Appalachian Experimental Watershed in east-central Ohio were used. Seasonal storm pattern trends from 1939 to 2010 were investigated using dimensionless depth (with the frequency of 50%, $d_{50}$) and the curve variability $(V = d_{80} - d_{20})$ at three dimensionless within-storms time periods (three verticals). The Spearman rank correlation procedure (correlation coefficient, ρ and significance probability, p) was used to statistically determine trends over time using 8 periods of 4-season sets of Huff curves over the 72 years. Two averages of ρ and p were computed: (1) by averaging the individual ρ and p obtained from 10 gauges (AvgI); and (2) by grouped averaging of all individual gauge values of $d_{50}$ and V and then computing ρ and p (AvgG). The test results of individual gauges showed that 4 cases for $d_{50}$ and 23 cases for V were significant for all seasons and verticals (total of 120 cases for each variable). The test results of AvgI for $d_{50}$ and V and AvgG for $d_{50}$ showed no significant trends in all seasons and verticals. Only the AvgG for V led to a significant trend for V in spring and fall at different times within storm patterns. The data do not provide sufficient evidence at the p=0.05 significance level to reject the null hypothesis of unchanging position of the dimensionless depth of the 50% Huff curves for individual or averages for all seasons and verticals. Also, there is insufficient evidence to reject the null hypothesis of unchanging variability, V, using the average ρ of individual gauges (AvgI for V) for all seasons and verticals. AvgG results showed a significant trend in V; however, this analysis may be affected by the nonindependence of storm data. The results suggest that it is likely that there is little if any effect of trending climate over approximately 70 years on Huff curve patterns. The results of this study add to the robustness characteristics of Huff curves and to their potential use in hydrological practice as design storms, as the foundation of stochastic storm generation, and for storm disaggregation, and they deserve further investigation. These different forms of inputs to watershed models have the potential to improve runoff estimation. The results suggest that, if verified in other studies, they have applicability to provide useful stationary precipitation patterns across the US and other areas of the world in areas of nonstationary climate. Also, individual rain gauge data may not be representative of trends even over small areas, and seasonal differences were noticeable as found in other studies. Recommendations are provided.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

Reserve and energy scarcity pricing in United States power markets: A comparative review of principles and practices

Here, errors in forecasting load and renewable-based generation in restructured power systems mean that independent system operators (ISOs) must procure sufficient operating reserves to keep the real-time operation of the system reliable and secure. But when procured reserves turn out to be insufficient in real-time due to the lack of resource capacity or ramp capability, operators often set higher prices for reserves and energy to encourage more supply, and to motivate consumers to decrease usage or shift it to other times. This procedure, which is called scarcity or shortage pricing, is a core feature of U.S. electricity markets. It is receiving increased attention from market designers and stakeholders because scarcity will become more important for spot price formation in the future with the increased penetration of zero-marginal cost renewables, and the shrinking role of fuel costs in setting prices. Scarcity pricing is implemented in various ways by different ISOs. These differences have practical implications for the level of prices and incentives for investment, operations, and demand modification. In this paper, general approaches and specific calculation procedures for reserve and energy scarcity pricing practices and calculations across the seven ISO-based U.S. power markets are reviewed and compared. A consistent terminology is used to facilitate the comparison. Current scarcity pricing practices are grouped into three approaches: (1) imposing an adder after the spot market is run; (2) including stepwise demand curves within market clearing procedures for non-contingency reserve products (e.g., the novel flexiramp product), which tends to yield longer right tails for energy scarcity premium curves; and (3) having stepwise demand curves for traditional contingency reserve products only, which results in shorter right tails in energy scarcity curves. A generic numerical example is presented to highlight the large practical differences among the reserve scarcity pricing approaches and specific implementations. To further investigate factors that contribute the most to demand curves differences among ISOs, a sensitivity analysis is performed. This analysis shows that the largest source of differences among the curves is the scarcity prices assumed in the case of severe scarcity, while the number of steps used and whether flexiramp is considered also yields important differences in scarcity prices. As renewable penetration increases, it will become increasingly crucial to employ administrative demand curves so that spot prices more effectively motivate supply and demand adjustments exactly when and where they are needed. This study shows that the different assumptions yield very different scarcity premiums for reserves and energy, and are likely to provide divergent incentives for resources to respond to shortages. It is concluded that to promote market efficiency, a reserve shortage demand curve should have at least three features: inclusion of the marginal value of reserve products at each shortage level, consideration of the magnitude and probability of supply contingencies, and avoidance of abrupt price discontinuities that can cause excessively volatile market outcomes.

29 ENERGY PLANNING, POLICY, AND ECONOMY↗