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At least 883 records · Page 49
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Benchmark Simulation of Natural Circulation Cooling System with Salt Working Fluid Using SAM

Liquid salt-cooled reactors, such as the Fluoride Salt-Cooled High-Temperature Reactor (FHR), offer passive decay heat removal through natural circulation using Direct Reactor Auxiliary Cooling System (DRACS) loops. The behavior of such systems should be well-understood through performance analysis. The advanced system thermal-hydraulics tool System Analysis Module (SAM) from Argonne National Laboratory has been selected for this purpose. The work presented here is part of a larger study in which SAM modeling capabilities are being enhanced for the system analyses of FHR or Molten Salt Reactors (MSR). Liquid salt thermophysical properties have been implemented in SAM, as well as properties of Dowtherm A, which is used as a simulant fluid for scaled experiments, for future code validation studies. Additional physics modules to represent phenomena specific to salt-cooled reactors, such as freezing of coolant, are being implemented in SAM. This study presents a useful first benchmark for the applicability of SAM to liquid salt-cooled reactors: it provides steady-state and transient comparisons for a salt reactor system. A RELAP5-3D model of the Mark-1 Pebble-Bed FHR (Mk1 PB-FHR), and in particular its DRACS loop for emergency heat removal, provides steady state and transient results for flow rates and temperatures in the system that are used here for code-to-code comparison with SAM. The transient studied is a loss of forced circulation with SCRAM event. To the knowledge of the authors, this is the first application of SAM to FHR or any other molten salt reactors. While building these models in SAM, any gaps in the code’s capability to simulate such systems are identified and addressed immediately, or listed as future improvements to the code.

Ahmed, K. K.↗
DOE OSTI2022

SolarExPert: Large-Scale OPF, DSSE and HIL

This presentation, part of the ADMS Test Bed Webinar Series, discusses how to accelerate industry adoption of ADMS to improve normal operations with high levels of distributed energy resources (DERs) and improve resilience and reliability.

ADMS↗
DOE OSTI2022

Closed-loop brayton cycle system with turbine blade cooling

A closed-loop Brayton cycle system utilizes supercritical carbon dioxide as the working fluid for the system to achieve higher efficiencies than can be achieved with traditional open-loop gas turbine engines. A bleed channel is used to direct a flow of cooling fluid to cool the turbine blades during operation of the system, preventing damage to the turbine blades during operation of the system. The bleed channel includes a bleed inlet fluidly coupled between a first recuperator and a second recuperator and a bleed outlet fluidly coupled to the turbine blades. The bleed channel is configured to direct the flow of cooling fluid to the turbine blades at a desired temperature and pressure.

Taylor, Stephen H.↗
DOE OSTI2013

Characterization of Specimens Exposed in a Li Loop

A monometallic V-4Cr-4Ti thermal convection loop was run for 2,350 h with a peak temperature of 700 C and Li flow rate of 2-3 cm/s. Specimens of V-4Cr-4Ti exposed in the hot and cold leg were tensile tested in vacuum at 500 C showing an increase in the 0.2% yield and ultimate tensile strengths and a decrease in the serration amplitude with decreasing exposure temperature in the loop. However, only minor changes in ductility were measured. With the higher temperature exposures, there was a decrease in Vickers hardness measured but little change in the grain size. Characterization of the microstructure after exposure at 627 C in the loop showed an increase in the density of Ti- and N-rich grain boundary and matrix precipitates near the specimen surface after exposure corresponding to an increase in the hardness in the near-surface region. Two-layer V/Y2O3 coatings on V-4Cr-4Ti substrates also were exposed in the loop and initial room temperature characterization has been conducted.

Unocic, Kinga A↗
NASA NTRS1984

Modeling of energy buildup for a flare-productive region

A self-consistent MHD model of shearing magnetic loops is used to investigate magnetic energy buildup in active region AR 2372 (Boulder number), in the period of April 5-7, 1980. The magnetic field and sunspot motions in this region, derived using observational data obtained by the Marshall Space Flight Center Solar Observatory, suggest the initial boundary conditions for the model. It is found that the plasma parameters (i.e., density, temperature, and plasma flow velocity) do not change appreciably during the process of energy buildup as the magnetic loops are sheared. Thus, almost all of the added energy is stored in the magnetic field. Furthermore, it is shown that dynamical processes are not important during a slow buildup (i.e., for a shearing velocity less than 1 km/s). Finally, it is concluded that the amount of magnetic energy stored and the location of this stored magnetic energy depend on the initial magnetic field (whether potential or sheared) and the magnitude of the shearing motion.

Wu, S. T.↗
DOE OSTI2012

Model for a transformer-coupled toroidal plasma source

A two-dimensional fluid plasma model for a transformer-coupled toroidal plasma source is described. Ferrites are used in this device to improve the electromagnetic coupling between the primary coils carrying radio frequency (rf) current and a secondary plasma loop. Appropriate components of the Maxwell equations are solved to determine the electromagnetic fields and electron power deposition in the model. The effect of gas flow on species transport is also considered. The model is applied to 1 Torr Ar/NH{sub 3} plasma in this article. Rf electric field lines form a loop in the vacuum chamber and generate a plasma ring. Due to rapid dissociation of NH{sub 3}, NH{sub x}{sup +} ions are more prevalent near the gas inlet and Ar{sup +} ions are the dominant ions farther downstream. NH{sub 3} and its by-products rapidly dissociate into small fragments as the gas flows through the plasma. With increasing source power, NH{sub 3} dissociates more readily and NH{sub x}{sup +} ions are more tightly confined near the gas inlet. Gas flow rate significantly influences the plasma characteristics. With increasing gas flow rate, NH{sub 3} dissociation occurs farther from the gas inlet in regions with higher electron density. Consequently, more NH{sub 4}{sup +} ions are produced and dissociation by-products have higher concentrations near the outlet.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

End-of-life flows of multiple cycle consumer products

Explicit expressions for the end-of-life flows (EOL) of single and multiple cycle products (MCPs) are presented, including deterministic and stochastic EOL exit. The expressions are given in terms of the physical parameters (maximum lifetime, T, annual cycling frequency, f, number of cycles, N, and early discard or usage loss). EOL flows are also obtained for hi-tech products, which are rapidly renewed and thus may not attain steady state (e.g. electronic products, passenger cars). A ten-step recursive procedure for obtaining the dynamic EOL flow evolution is proposed. Applications of the EOL expressions and the ten-step procedure are given for electric household appliances, industrial machinery, tyres, vehicles and buildings, both for deterministic and stochastic EOL exit, (normal, Weibull and uniform exit distributions). The effect of the physical parameters and the stochastic characteristics on the EOL flow is investigated in the examples: it is shown that the EOL flow profile is determined primarily by the early discard dynamics; it also depends strongly on longevity and cycling frequency: higher lifetime or early discard/loss imply lower dynamic and steady state EOL flows. The stochastic exit shapes the overall EOL dynamic profile: Under symmetric EOL exit distribution, as the variance of the distribution increases (uniform to normal to deterministic) the initial EOL flow rise becomes steeper but the steady state or maximum EOL flow level is lower. The steepest EOL flow profile, featuring the highest steady state or maximum level, as well, corresponds to skew, earlier shifted EOL exit (e.g. Weibull). Since the EOL flow of returned products consists the sink of the reuse/remanufacturing cycle (sink to recycle) the results may be used in closed loop product lifecycle management operations for scheduling and sizing reverse manufacturing and for planning recycle logistics. Decoupling and quantification of both the full age EOL and of the early discard flows is useful, the latter being the target of enacted legislation aiming at increasing reuse.

29 ENERGY PLANNING, POLICY, AND ECONOMY↗
NASA NTRS1992

Prominence condensation and magnetic levitation in a coronal loop

The results of a model dynamic simulation of the formation and support of a narrow prominence at the apex of a coronal magnetic loop or arcade are described. The condensation process proceeds via an initial radiative cooling and pressure drop, and a secondary siphon flow from the dense chromospheric ends. The antibuoyancy effect as the prominence forms causes a bending of the confining magnetic field, which propagates toward the semirigid ends of the magnetic loop. Thus, a wide magnetic 'hammock' or well (of the normal-polarity Kippenhahn-Schlueter-type) is formed, which supports the prominence at or near the field apex. The simplicity of this 1.5-dimensional model, with its accompanying diagnostics, elucidates the various contributions to the nonlinear dynamics of prominence condensation and levitation.

Van Hoven, G.↗
NASA NTRS1992

Dynamic formation and magnetic support of loop or arcade prominences

The results of model dynamic simulations of the formation and support of a narrow prominence at the apex of a coronal magnetic loop or arcade are described. The condensation process proceeds via an initial radiative cooling and pressure drop, and a secondary siphon flow from the dense chromospheric ends. The antibuoyancy effect as the prominence forms causes a bending of a confining magnetic field, which propagates toward the semirigid ends of the magnetic loop. Thus, a wide magnetic 'hammock' or well (of a normal polarity Kippenhahn-Schlueter type) is formed, which supports the prominence at or near the field apex.

Vanhoven, Gerard↗
DOE OSTI2026

Heat Transfer Experiments of a 1st Stage Blade Cascade for Supercritical CO2 Oxy-Combustion Turbine Application

The results of internally cooled 1st stage blade (S1B) cascade testing in a supercritical CO2 environment is presented. The turbine blade design has been previously established for the end application of an oxy-combustion turbine operating in the Allam-Fetvedt cycle with turbine inlet conditions of 305 bar and 1150°C. The internally cooled blade features leading edge (LE) region impingement cooling, mid-section ribbed serpentine passages, and a pin-finned trailing edge (TE) region before cooling ejection holes. The geometry for the tested blade cascade has a cooled central blade with un-cooled blades on either side to match flowpath areas of the actual turbine. The flowpath reuses internal components previously employed for mid-section region ribbed serpentine passage experiments that established Nusselt number enhancement ratios over a range of Reynolds numbers from 100,000-400,000. New components include flow conditioning plates upstream and downstream of the blade cascade to adequately represent the flow field and blade external heat transfer coefficient profiles for the actual turbine. The cooled central blade utilizes uniform crystal temperature sensors (UCTS) with six sensors each on the blade pressure and suction surfaces distributed radially and from LE to TE. The post-processed UCTS quantified the maximum wall temperature seen at each installed sensor location. The test procedure consisted of establishing supercritical CO2 cooling flow temperature and flow rate and maintaining it throughout the test. The flow rate aims to match that for the actual in-service turbine blade design and is maintained through an orifice restriction to keep the pressure differential between internal cooling flow and external hot flow nearly constant. For the sCO2 flow path external to the blade, temperatures were ramped throughout the test via control of the test loop’s natural gas burner heater. The maximum temperature seen was 468°C and held constant for a duration of 10 minutes at which the blade metal temperature was predicted to be at its maximum before ramping down. For the turbine blade design for service inlet conditions, external flow path computational fluid dynamics (CFD) results and an internal cooling 1-D thermal and hydraulic flow network model using experimentally validated correlations served as thermal finite element (FE) boundary conditions to predict blade metal temperatures. These predicted temperatures were subsequently utilized in a structural FE model to predict blade life ratings dictated by Haynes 282 creep strength data, having a strong dependence on temperature. The boundary conditions experienced during testing are used in the same workflow and compared to the experimental results, with the goal of validating the analysis methodology and providing insight on the uncertainty in local metal temperature predictions.

20 FOSSIL-FUELED POWER PLANTS↗
DOE OSTI2020

Decentralized Control of Cascaded H-Bridge Inverters for Medium-Voltage Grid Integration: Preprint

This paper introduces a fully decentralized control strategy that allows for individualized active and reactive power control of H-bridge inverters connected in series. After formulating a model of the system power flows, we outline a communications-free approach where each inverter can act on independent commands. Inverter-level feedback is accomplished locally via a measurement of current flowing through the stack. A key feature is the lack of any centralized control routines or phase-locked loop. In this framework, the reactive power control loops achieve voltage synchronization among the converters and the grid, and the active power control loops modulate the terminal voltage amplitudes that influence power delivery. Furthermore, pole placement via state feedback is used to ensure stability of voltage synchronization while also enabling tracking of bidirectional power commands. Simulations are presented to validate the proposed approach.

communication-free modular converter control↗
DOE OSTI2025

The SAS4A/SASSYS-1 Version 5.8 Safety Analysis Code System

SAS4A/SASSYS-1 is a software simulation tool used to perform deterministic analysis of anticipated events as well as design basis and beyond design basis accidents for advanced nuclear reactors. Detailed, mechanistic models of steady-state and transient thermal, hydraulic, kinetic, and mechanical phenomena are employed to describe the response of the reactor core, the reactor primary and secondary coolant loops, the reactor control and protection systems, and the balance-of-plant to accidents caused by changes in coolant flow, loss of heat rejection, or reactivity insertion. The consequences of single and double-fault accidents can be modeled, including fuel and coolant heating, fuel and cladding mechanical behavior, core reactivity feedbacks, coolant loop performance including natural circulation, and decay heat removal. Analyses are typically terminated upon demonstration of reactor and plant shutdown to permanently coolable conditions, or upon violation of design basis margins. The objective of the analysis is to quantify accident consequences as measured by the transient behavior of system performance parameters, such as fuel and cladding temperatures, reactivity, and cladding strain. Originally developed for analysis of sodium cooled reactors with oxide fuel clad by stainless steel, the models were subsequently extended and specialized to metallic fuel clad with advanced alloys and to several other coolant options, including lead, LBE, and water.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
NASA NTRS1990

Cooling system and insulation concept for a Mach 5 turbo-ramjet aircraft

A cooling system and insulation concept for a Mach 5 cruise aircraft, using non-cryogenic fuel is presented. Catalytic endothermic reaction of petroleum fuel is used as the heat sink for engine cooling. A secondary closed-loop coolant circuit removes heat from the engine and transfers this heat to the catalytic reactor. Insulation on the engine flow path surfaces reduces the cooling requirements. A high temperature insulation system, which is capable of a surface temperature of 4,000 F, is used for the combustor and nozzle. A complete closed-loop cooling system design is shown in detail. Main features of this system include a fuel preheater, a catalytic fuel reactor, and engine wall cooling panels. A silicone-based liquid polymer, designed for extended use at 750 F, is used as the coolant. The preheater and reactor design are based on the results of recent experimental work. The cooling panels are designed using a thermal fluid analysis computer program, which was originally developed for the National Aero-Space Plane (NASP). Major components are analyzed structurally as well as thermally and weights are presented.

Jones, S. C.↗
DOE OSTI2017

SAS4A/SASSYS-1 VERSION 5.2 SAFETY ANALYSIS CODE SYSTEM

SAS4A/SASSYS-1 is a software simulation tool used to perform deterministic safety analysis of anticipated events as well as design basis and beyond design basis accidents for advanced nuclear reactors. This software can be used to assess the safety of a prescribed reactor design, but it cannot be used to configure a design to meet targeted performance objectives. Detailed, mechanistic models of steady-state and transient thermal, hydraulic, kinetic, and mechanical phenomena are employed to describe the response of the reactor core, the reactor primary and secondary coolant loops, the reactor control and protection systems and the balance-of-plant to accidents caused by changes in coolant flow, oss of heat rejection, or reactivity insertion. The consequences of single and double-fault accidents can be modeled, including fuel and coolant heating, fuel and cladding mechanical behavior, core reactivity feedbacks, coolant loop performance including natural circulation, and decay heat removal. Analyses are typically terminated upon demonstration of reactor and plant shutdown to permanently coolable conditions or upon violation of design basis margins. The objective of the analysis is to quantify accident consequences as measured by the transient behavior of system performance parameters, such as fuel and cladding temperatures, reactivity, and cladding strain. Originally developed for analysis of sodium cooled reactors with oxide fuel clad by stainless steel, the models In SAS4A/SASSYS-1 were subsequently extended and specialized to metallic fuel clad with advanced alloys and to several other coolant options including lead and LBE. METHOD OF SOLUTION: Each subassembly in the reactor core is represented with single or multiple-pin models. One channel represents one or more fuel pins and many channels are employed for a whole-core representation. Heat transfer in each pin is modeled with a two-dimensional (r/z) heat conduction equation. Single and two-phase coolant thermal-hydraulics are simulated with a unique, one-dimensional (axial) multiple-bubble liquid metal boiling model. The transient fuel and cladding mechanical behavior models are integrated with fission product production,release, and transport models. UNIQUE FEATURES: The physical models in SAS4AJSASSYS-1 are highly detailed 1umerical representations of reactor accident conditions based on extensive laboratory and test reactor results. The models are specialized to liquid metal (sodium) cooled fast reactors with oxide or metallic fuel clad with stainless steel.«

Fanning, Thomas↗
DOE OSTI2015

Further Development of Crack Growth Detection Techniques for US Test and Research Reactors

One of the key issues facing Light Water Reactors (LWRs) in extending lifetimes beyond 60 years is characterizing the combined effect of irradiation and water chemistry on material degradation and failure. Irradiation Assisted Stress Corrosion Cracking (IASCC), in which a crack propagates in a susceptible material under stress in an aggressive environment, is a mechanism of particular concern. Full understanding of IASCC depends on real time crack growth data acquired under relevant irradiation conditions. Techniques to measure crack growth in actively loaded samples under irradiation have been developed outside the US - at the Halden Boiling Water Reactor, for example. Several types of IASCC tests have also been deployed at the MITR, including passively loaded crack growth measurements and actively loaded slow strain rate tests. However, there is not currently a facility available in the US to measure crack growth on actively loaded, pre-cracked specimens in LWR irradiation environments. A joint program between the Idaho National Laboratory (INL) and the Massachusetts Institute of Technology (MIT) Nuclear Reactor Laboratory (NRL) is currently underway to develop and demonstrate such a capability for US test and research reactors. Based on the Halden design, the samples will be loaded using miniature high pressure bellows and a compact loading mechanism, with crack length measured in real time using the switched Direct Current Potential Drop (DCPD) method. The basic design and initial mechanical testing of the load system and implementation of the DCPD method have been previously reported. This paper presents the results of initial autoclave testing at INL and the adaptation of the design for use in the high pressure, high temperature water loop at the MITR 6 MW research reactor, where an initial demonstration is planned in mid-2015. Materials considerations for the high pressure bellows are addressed. Design modifications to the loading mechanism required by the size constraints of the MITR water loop are described. The safety case for operation of the high pressure gas-driven bellows mechanism is also presented. Key issues are the design and response of systems to limit gas flow in the event of a high pressure gas leak in the in-core autoclave. Integrity of the autoclave must be maintained and reactivity effects due to voiding of the loop coolant must be shown to be within the reactor technical specifications. The technical development of the crack growth monitor for application in the INL Advanced Test Reactor or the MITR can act as a template for adaptation of this technology in other reactors. (authors)

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2013

Advection of a passive vector field by the Gaussian velocity field with finite correlations in time

Using the field theoretic renormalization group technique the model of a passive vector field advected by an incompressible turbulent flow is investigated up to the second order of the perturbation theory (two-loop approximation). The turbulent environment is given by statistical fluctuations of the velocity field that has a Gaussian distribution with zero mean and defined noise with finite correlations in time. Two-loop analysis of all possible scaling regimes in general d-dimensional space is done in the plane of exponents ɛ − η, where ɛ characterizes the energy spectrum of the velocity field in the inertial range E ∝ k{sup 1−2ε}, and η is related to the correlation time at the wave number k which is scaled as k{sup −2+η}. It is shown that the scaling regimes of the present model of vector advection have essentially different properties than the scaling regimes of the corresponding model of passively advected scalar quantity. The results demonstrate the fact that within the present model of passively advected vector field the internal tensor structure of the advected field can have nontrivial impact on the diffusion processes deep inside in the inertial interval of given turbulent flow.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

MODELING OF REFLECTIVE PROPAGATING SLOW-MODE WAVE IN A FLARING LOOP

Quasi-periodic propagating intensity disturbances have been observed in large coronal loops in extreme ultraviolet images over a decade, and are widely accepted to be slow magnetosonic waves. However, spectroscopic observations from Hinode/EIS revealed their association with persistent coronal upflows, making this interpretation debatable. We perform a 2.5D magnetohydrodynamic simulation to imitate the chromospheric evaporation and the following reflected patterns in a flare loop. Our model encompasses the corona, transition region, and chromosphere. We demonstrate that the quasi periodic propagating intensity variations captured by the synthesized Solar Dynamics Observatory/Atmospheric Imaging Assembly 131, 94 Å emission images match the previous observations well. With particle tracers in the simulation, we confirm that these quasi periodic propagating intensity variations consist of reflected slow mode waves and mass flows with an average speed of 310 km s{sup −1} in an 80 Mm length loop with an average temperature of 9 MK. With the synthesized Doppler shift velocity and intensity maps of the Solar and Heliospheric Observatory/Solar Ultraviolet Measurement of Emitted Radiation Fe xix line emission, we confirm that these reflected slow mode waves are propagating waves.

79 ASTRONOMY AND ASTROPHYSICS↗