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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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The mechanisms for pinch formation in Dense Plasma Focus (DPF) devices, with the generation of high-energy ions beams and subsequent neutron production over a relatively short distance, are not fully understood. Here we report on high-fidelity 2D and 3D numerical magnetohydrodynamic (MHD) simulations using the LA-COMPASS code to study the pinch formation dynamics and its associated instabilities and neutron production.
Sandia's Dakota software (available at http://dakota.sandia.gov) supports science and engineering transformation through advanced exploration of simulations. Specifically, it manages and analyzes ensembles of simulations to provide broader and deeper perspective for analysts and decision makers. This enables them to enhance understanding of risk, improve products, and assess simulation credibility. This manual offers Consortium for Advanced Simulation of Light Water Reactors (LWRs) (CASL) partners a guide to conducting Dakota-based VUQ studies for CASL problems. It motivates various classes of Dakota methods and includes examples of their use on representative application problems. On reading, a CASL analyst should understand why and how to apply Dakota to a simulation problem.
An effective mathematical model is proposed to describe experiments on the indentation of samples with layered or functionally graded coatings. The model is based on the elastic contact problem corresponding to the penetration of a punch in a coated elastic half-space. A Berkovich indenter is considered. The results of the simulation and the experiments are compared for the indentation of two zirconium nitride (ZrN) coatings on substrates of monocrystalline (100) silicon and annealed copper. The agreement of the results is good.
The investigation of the diffusive transport of charged particles in a turbulent magnetic field remains a subject of considerable interest. Research has most frequently concentrated on determining the diffusion coefficient in the presence of a mean magnetic field. Here we consider the diffusion of charged particles in fully three-dimensional isotropic turbulent magnetic fields with no mean field, which may be pertinent to many astrophysical situations. We identify different ranges of particle energy depending upon the ratio of Larmor radius to the characteristic outer length scale of turbulence. Two different theoretical models are proposed to calculate the diffusion coefficient, each applicable to a distinct range of particle energies. The theoretical results are compared to those from computer simulations, showing good agreement.
We investigate the evolution of the cosmic web since z = 5 in grid-based cosmological hydrodynamical simulations, focusing on the mass and velocity fields of both baryonic and cold dark matter. The tidal tensor of density is used as the main method for web identification, with λ {sub th} = 0.2–1.2. The evolution trends in baryonic and dark matter are similar, although moderate differences are observed. Sheets appear early, and their large-scale pattern may have been set up by z = 3. In terms of mass, filaments supersede sheets as the primary collapsing structures from z ∼ 2–3. Tenuous filaments assembled with each other to form prominent ones at z < 2. In accordance with the construction of the frame of the sheets, the cosmic divergence velocity, v {sub div}, was already well-developed above 2–3 Mpc by z = 3. Afterwards, the curl velocity, v {sub curl}, grew dramatically along with the rising of filaments, becoming comparable to v {sub div}, for <2–3 Mpc at z = 0. The scaling of v {sub curl} can be described by the hierarchical turbulence model. The alignment between the vorticity and the eigenvectors of the shear tensor in the baryonic matter field resembles that in the dark matter field, and is even moderately stronger between ω and e{sub 1}, and ω and e{sub 3}. Compared with dark matter, there is slightly less baryonic matter found residing in filaments and clusters, and its vorticity developed more significantly below 2–3 Mpc. These differences may be underestimated because of the limited resolution and lack of star formation in our simulation. The impact of the change of dominant structures in overdense regions at z ∼ 2–3 on galaxy formation and evolution is shortly discussed.
The parallel Monte Carlo photon and electron transport code package penORNL was developed at Oak Ridge National Laboratory to enable advanced scanning electron microscope (SEM) simulations on high-performance computing systems. This paper discusses the implementations, capabilities and parallel performance of the new code package. penORNL uses PENELOPE for its physics calculations and provides all available PENELOPE features to the users, as well as some new features including source definitions specifically developed for SEM simulations, a pulse-height tally capability for detailed simulations of gamma and x-ray detectors, and a modified interaction forcing mechanism to enable accurate energy deposition calculations. The parallel performance of penORNL was extensively tested with several model problems, and very good linear parallel scaling was observed with up to 512 processors. penORNL, along with its new features, will be available for SEM simulations upon completion of the new pulse-height tally implementation.
Concepts for isolation of spent nuclear fuel have been studied by organizations in countries that employ nuclear power. These concepts typically involve a deep geological repository in bedrock, with processed radioactive waste encased in deposition canisters emplaced in underground excavations and surrounded by clay-based buffer. This multi-barrier approach is intended to provide long-term isolation of the waste package from the biosphere. According to many statistics, there is a tendency toward increasing numbers of earthquakes in the Korean peninsula each year. If an earthquake induced rock shear load occurs at a repository site, the engineered barrier system (EBS) can be sheared, resulting in a pressure increased in the buffer material. This is expected to result in damage to the canisters. Therefore, because the damage, which can be fatal to a disposal canister, can be given in case an earthquake occurs, the method protecting the canisters safely is needed. In this paper, 'an earthquake-resistance type buffer' was proposed using a method for protection from earthquake damage. To aid in achieving this objective, we have developed a technique for estimating the behavior of the EBS affected by earthquake induced rock shear using an analysis method, such as finite element method. As a first step, experimental tests are performed for understanding the behavior of the buffer material. Comparing the results of the numerical simulations to the experimental results can be used to verity the reliability of the analysis model. Then we developed the real scale analysis model of a nuclear waste repository. The main parameter having an effect on the earthquake-resistant performance was analyzed and an earthquake-resistance proof type buffer was designed. To improve the earthquake-resistance performance, we designed the buffer by putting the low- density buffer between the canister and buffer. The simulation results show that the earthquake-resistant performance was improved by about 65%. (authors)
The mechanical property and structural integrity of graphite structure have an important significance on the safe operation of high temperature gas cooled reactor. The graphite is porous media, the structural deficiencies such as microcracks and microvoids in it have great influence on its material mesoscopic structure and mechanical parameter. The shape and size distribution of microvoids and microcracks at different oxidation degree have a great influence on the overall performance. In order to simulate the geometric structure of the oxidized graphite, we used Python script to pre-process in Abaqus/CAE and this leads to different graphite models with different oxidation degrees. Then, these models were set with our pre-designed force boundary conditions and displacement boundary conditions. The models information was output to a FMBEM solver written by C++ code and the graphite s equivalent young s modulus and other mechanic parameters were calculated. In this paper, based on the 3- D microvoid and microcrack graphite models simulation, we studied the influence of the change of mesoscopic structure on graphite's mechanical property. (authors)
An important element of human factors engineering (HFE) pertains to measurement and evaluation (M and E). The role of HFE-M and E should be integrated throughout the entire control room modernization (CRM) process and be used for human-system performance evaluation and diagnostic purposes with resolving potential human engineering deficiencies (HEDs) and other human machine interface (HMI) design issues. NUREG-0711 describes how HFE in CRM should employ a hierarchical set of measures, particularly during integrated system validation (ISV), including plant performance, personnel task performance, situation awareness, cognitive workload, and anthropometric/ physiological factors. Historically, subjective measures have been primarily used since they are easier to collect and do not require specialized equipment. However, there are pitfalls with relying solely on subjective measures in M and E such that negatively impact reliability, sensitivity, and objectivity. As part of comprehensively capturing a diverse set of measures that strengthen findings and inferences made of the benefits from emerging technologies like advanced displays, this paper discusses the value of using eye tracking as an objective method that can be used in M and E. A brief description of eye tracking technology and relevant eye tracking measures is provided. Additionally, technical considerations and the unique challenges with using eye tracking in full-scaled simulations are addressed. Finally, this paper shares preliminary findings regarding the use of a wearable eye tracking system in a full-scale simulator study. These findings should help guide future full-scale simulator studies using eye tracking as a methodology to evaluate human-system performance. (authors)
The current severe accident prevention and mitigation strategies for OPR 1000 have emergency operating procedures (EOPs) and severe accident management guidelines (SAMGs), respectively. The main objective of SAMG is to prevent a release of radioactive materials from releasing into environment and mitigate severe accident phenomena during severe accident. The current SAMG entry condition is met when the core exit temperature (CET) reaches 650 deg. C in OPR 1000. Peak cladding temperature (PCT), which represents core integrity more precisely than CET does, cannot be used since it is not measurable in the main control room (MCR). Current SAMG entry condition for every kind of accident scenarios is not reasonable, since entry condition is determined without considering operator action time. Therefore, SAMG entry condition need to be verified with consider operator action time. Thus, an analysis methodology for SAMG entry condition was developed to verify the SAMG entry condition. A severe accident DB were also developed in order to analyze the SAMG entry condition. The analysis results of DB show that available operator action time from the SAMG entrance to RV fail is shorter than the required time in most cases. As a result, the proper SAMG entry condition was suggested through the results of DB analysis. When the SAMG entry condition is changed from CET to suggested condition, the available action time is increased about 350 to 4300 sec. Also, the suggested entry condition was verified through the simulation which considered operation action time and reflecting the suggested entry condition. (authors)
Fission chambers (FC) signal simulators are a useful means to test neutron flux instrumentation channels of the reactors control and protection systems (CPS). Well-known signal simulators do not provide a secondary equipment testing in all modes of measurement. A wide range simulator that simulates a full range of FC signal changes (pulse, fluctuation, current) was designed. The simulator takes into account the statistical nature of neutrons detection in the FC, including the shape of the pulse and the spectrum of the pulse amplitude distribution. The simulator uses the principle of mathematical simulation of the fission chambers signal with realtime calculations using the FPGA. The wide-range simulator reproduces a FC signal in the range of ten orders without switching ranges or playback modes while ensuring very good linearity. It allows to generate both static and dynamic test signals such as: stair-step, linearly and exponential varying signals, exponential varying signals with a linearly changing period or a signal change simulating the response of the nuclear reactor power to a given reactivity response. Continuity of reproduced signals and the ability to playback dynamic effects makes it possible the simulator using to check the algorithms of cross-linking of measuring paths, reactivity and period measuring tools and to monitor the operation of interlocking and alarm CPS functions. This article discusses the simulator's software and hardware, its features and specifications, user interface and example of the simulator using to check the neutron flux monitoring channels. (authors)
This paper summarizes the progress in the use of non-invasive methods for measuring liquid level in small modular nuclear reactors. High precision gravimeters are used to measure changes in liquid level in a test facility environment, and results are compared to simulations. Possible configurations for the meters use in the NuScale SMR are also discussed. (authors)
Probabilistic Risk Assessment (PRA) uses fault tree/event tree analysis to evaluate the environmental impacts of nuclear power plants due to internal or external initiating events. In a fault tree, basic failure events are assembled using primarily And/Or logic to determine the combinations of failures that lead to failure of the system as a whole. An event tree is forward-facing, and begins with a single initiating event. From there the analysis considers what event may occur next, and branches out among the possible configurations of occurrence and non-occurrence of that event. This branching continues until end states are reached. End states may include a safe and stable configuration of the plant, or any number of differing failure states. Both fault and event trees require basic event probabilities as inputs to provide insight on the likelihood of different outcomes. PRA has been applied to nuclear power plants as an analysis tool since the 1975 Reactor Safety Study. In a traditional PRA, the order of events is prescribed by the analyst and each event is typically a binary aleatory uncertainty: occurrence or non-occurrence. Discrete dynamic event tree (DDET) analysis eliminates this subjectivity in ordering of events by using the output of a dynamic system model (simulator) to inform the branching. Branching conditions are triggered by the existence of a relevant plant state in the code, and therefore only occur as physically appropriate. The DDET approach also allows consideration of both epistemic and aleatory uncertainties on a phenomenologically and stochastically consistent platform. One limitation of the DDET driver codes developed to date (namely ADAPT, ADS, and MCDET ) is that the tree is driven by a single simulator. The goal of this work is a general multi-simulator driver. This limits the parameter space that may be explored in a single DDET to that which may be covered by a single simulator. In this work, the Analysis of Dynamic Accident Progression Trees (ADAPT) code is extended to support multiple arbitrary simulators. This capability will increase the depth and breadth of phenomena that may be analyzed in a single DDET. For example, a large-scale system code may pass the analysis to a more detailed code if certain conditions are met, in order to capture relevant phenomena that would be lost if only the system code were to be used. In addition, the time required to cover a given uncertainty space may be reduced by dynamically identifying and running only the situations that are appropriate given the plant conditions in each simulator. The use of multiple simulators is expected to further reduce subjectivity in PRA by enabling high fidelity modeling of reality. (authors)
The quasi-differential neutron induced neutron emission reaction measurement (QD-NINE) method provides an additional benchmark which constrains cross-section evaluations and provides a measure of verification for existing evaluations. Experiments are preformed using an array of EJ-309 liquid scintillators at a variety of angles measuring the neutron scattering response from a sample.. An MCNP simulation is then compared to this experimental data and is run using various sets of evaluated nuclear data. Since the isotopes of interest for this measurement, {sup 235}U and {sup 239}Pu, are difficult to obtain, the WNR facility at LANL was chosen to perform the measurements utilizing the chi-nu detector array. A measurement of carbon has been performed and the high energy cutoff has been extended from 20 to 60 MeV compared with previous measurements using this method. An early stage simulation was compared to the experimental data and the results show good agreement. (authors)
In the safety analysis of loss-of-coolant-accident (LOCA) and steam generator tube rupture (SGTR) scenarios of light water reactors, a modeling of a break is very important to predict the accident's result. For example, the design of a break simulator to simulate a LOCA in light water reactors requires accurate knowledge of the leakage flow through the break, whose shape can be assumed as an orifice or a nozzle according to the characteristics of the break shape. In the case of a small-break LOCA (SBLOCA) scenario, the critical flow mostly occurs by sub-cooled and saturated liquid water including a two-phase water flow at relatively high-pressure conditions. Among previous critical flow maps, Moody's maps are well known for their critical flow rate and pressure of a single component and two-phase mixture with respect to the upstream enthalpy and pressure. In Moody's model, a slip ratio defined by maximizing the critical flow rate with respect to the slip ratio was introduced, and thus its predictions tended to be too conservative. Later, Moody suggested other maps based on a homogeneous equilibrium model (HEM), and they were useful to predict a choked condition for a given upstream condition. However, their predictions of the critical flow rate seemed to show quite an underestimation compared to various test data. The author suggested more practicable critical flow maps for a critical mass flux and pressure of a steam-water flow with respect to the upstream stagnation conditions using an extended Henry-Fauske model. From a comparison with the selected test data, suggested maps showed conservative predictions within reasonable ranges. In this report, a new correlation for the critical flow rate was developed to simulate the suggested critical flow maps within a reasonable range of error. (authors)
License applications for sodium fast reactors will include sodium fire analysis and subsequent mitigation strategies. Sodium leaks or ruptures from piping and support systems can lead to significant fires due to the reactive nature of sodium with air and water. Understanding the behavior of sodium fires is crucial for modeling and predicting accidents in sodium fast reactors. This paper describes the initial results of a control volume code, CONTAIN-LMR (CLMR), modeling effort for a sodium spray fire experiment conducted at Sandia National Laboratories (SNL) in Albuquerque, New Mexico in 2010. Additional sodium spray and pool fire tests were conducted at SNL in 2009 and 2010 and will be compared to CLMR results in future papers. The purpose of this analysis was extract information from the evolution of the SNL tests to better understand how to use CLMR in future sodium fire analysis. Thus the following CLMR simulations were not completely the result of blind benchmarking study. (authors)
A recent international inter-code comparison exercise for criticality excursion analysis demonstrated that the transient criticality codes participating the exercise are showed to reproduce well the initial peak power compared with measurements performed with TRACY and SILENE reactors. However the oscillatory behavior after peak power is less well reproduced. The integrated behavior in term of energy release is quite well reproduced. The recent experiments performed with TRACY JAEA's reactor and the analytic interpretation of void clustering during prompt critical have suggested a simplified vibration model of a damped oscillator. Finally a recent ICNC paper by present authors offered a perfect correlation between peak pressure and peak power. Owing to these three facts the present paper aims at proposing a new system of equations for the dynamic of a critical excursion taking into account gas bubble generation after exceeding the solubility threshold of dissolved radiolytic gas. The model explains why the simple vibration model of the JAEA school fairly represent pressure dynamic records at moderate peak pressure as measured with SILENE reactor. Also, an important parameter of the proposed model, namely the rate of transfer from dissolved gas to gas bubbles, is fixed by the correlation between peak pressure and peak power. Thus the model has one less tunable parameter and can predict a large range of critical low pressure excursions. After presentation of the model and discussion of some of its important features, some numerical simulations are made based upon SILENE and TRACY transient experiments ranging from tenths of kPa to several bars and comparisons are presented between calculated results and experimentally recorded one's. (authors)
A three-dimensional transient computational fluid dynamics (CFD) model was developed to investigate the material flow and heat transfer during friction stir processing (FSP) in an AZ31B magnesium alloy. The material was assumed to be a non-Newtonian viscoplastic fluid, and the Zener-Hollomon parameter was used to describe the dependence of material viscosity on temperature and strain rate. The material constants used in the constitutive equation were determined experimentally from compression tests of the AZ31B Mg alloy under a wide range of strain rates and temperatures. A dynamic mesh method, combining both Lagrangian and Eulerian formulations, was used to capture the material flow induced by the movement of the threaded tool pin. Massless inert particles were embedded in the simulation domain to track the detailed history of material flow. The actual FSP was also carried out on a wrought Mg plate where temperature profiles were recorded by embedding thermocouples. The predicted transient temperature history was found to be consistent with that measured during FSP. Finally, the influence of the thread on the simulated results of thermal history and material flow was studied by comparing two models: one with threaded pin and the other with smooth pin surface.