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At least 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Subchannel codes: CTF and VIPRE-01

In this chapter, two state-of-the-art and well-used subchannel codes are presented: CTF and VIPRE-01. As part of the Consortium for Advanced Simulation of Light Water Reactors, CTF is being used for single- and two-phase flow analysis under light-water reactor normal and anticipated transient operating conditions. Accurate determination of flow distribution, pressure drop, and void content is crucial for predicting margins to thermal crisis and ensuring more efficient nuclear power plant performance. In preparation for the intended applications, CTF is extensively validated against data from experimental facilities. Meanwhile, the licensed commercial code VIPRE-01 is used to generate a baseline set of simulations for the targeted tests and the solution parameters are compared to CTF results. The closure models in CTF that are in the greatest need of improvement are highlighted and discussed.

Zhao, Xingang↗
DOE OSTI2016

CASL COBRA-TF improvements for PWR DNB analysis

COBRA-TF (CTF) is a thermal hydraulic (T/H) subchannel code using either three-dimensional (3D) Cartesian or subchannel coordinate formulations for two-phase fluid flow and heat transfer solutions. CTF has been improved under the Consortium for Advanced Simulation of Light Water Reactors (CASL) program for Pressurized Water Reactor (PWR) applications, including software optimization, new closure models, pre- and post-processing and parallelization for modeling full reactor core T/H responses under normal operating and accident conditions. As a result of collaboration among CASL partners including the Westinghouse Electric Company, the Oak Ridge National Laboratory (ORNL), and the Sandia National Laboratories, additional modeling improvements were made to CTF specifically for PWR Departure from Nucleate Boiling (DNB) analysis, including a code option to evaluate fuel thermal margin in terms of DNB Ratio (DNBR) and an axial shape factor to account for effect of non-uniform axial power distribution on DNB. Multiple DNB correlations are now linked with CTF for different applications, including the Westinghouse proprietary WRB-1 correlation for fuel designs containing mixing vane grid spacers. The improved CTF code with the WRB-1 correlation (CTF/WRB-1) was validated using the DNB data from the PWR Subchannel Bundle Tests (PSBT). In addition to the comparison with the test data, the CTF/WRB-1 DNBR results and the associated local fluid conditions were compared to the results of the Westinghouse T/H design code, VIPRE-W, which is an enhanced version of the VIPRE-01 code originally developed by the Electric Power Research Institute (EPRI). The comparisons showed that CTF/WRB-1 DNBR predictions are in good agreement with the VIPRE-W results within the applicable range of the DNB correlation. A model sensitivity study was performed to confirm that the CTF void drift model had an insignificant effect on DNBR under the steam line break (SLB) low pressure condition. (authors)

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2014

488-4D ASH LANDFILL CLOSURE CAP HELP MODELING

At the request of Area Completion Projects (ACP) in support of the 488-4D Landfill closure, the Savannah River National Laboratory (SRNL) has performed Hydrologic Evaluation of Landfill Performance (HELP) modeling of the planned 488-4D Ash Landfill closure cap to ensure that the South Carolina Department of Health and Environmental Control (SCDHEC) limit of no more than 12 inches of head on top of the barrier layer (saturated hydraulic conductivity of no more than 1.0E-05 cm/s) in association with a 25-year, 24-hour storm event is not projected to be exceeded. Based upon Weber 1998 a 25-year, 24-hour storm event at the Savannah River Site (SRS) is 6.1 inches. The results of the HELP modeling indicate that the greatest peak daily head on top of the barrier layer (i.e. geosynthetic clay liner (GCL) or high density polyethylene (HDPE) geomembrane) for any of the runs made was 0.079 inches associated with a peak daily precipitation of 6.16 inches. This is well below the SCDHEC limit of 12 inches.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2022

A reinvestigation into Munson’s model for room closure in bedded rock salt

Accurate predictions of room closure are important for hazardous waste repositories in rock salt formations, such as the Waste Isolation Pilot Plant (WIPP). When Munson and co-workers simulated several room closure experiments conducted at the WIPP during the 1980’s and 1990’s, their simulated closure curves closely agreed with the closure measurements. A careful review of their work, however, raised concerns and prompted the reinvestigation in this paper. Here, to begin the reinvestigation, Munson’s legacy Room D closure simulation was reasonably recreated in a current-day finite element code. Next, special care was taken to obtain numerically converged results, re-introduce the anhydrite strata intermittently ignored by Munson, and calibrate the Munson–Dawson (M–D) constitutive model for salt as much as possible from laboratory test measurements. When this new model was used to simulate Room D’s closure, it under-predicted the horizontal and vertical closure rates by 2.34x and 3.10x, respectively, at 5.7 years after room excavation. As a result, the M–D model was extended to capture the newly established creep behavior at low equivalent stresses (<8 MPa) and replace the Tresca with the Hosford equivalent stress. Simulations using the new M–D model over-predicted the horizontal closure rate by 1.15x and under-predicted the vertical closure rate by 1.08x at 5.7 years, averaged over three room closure experiments. Although further improvements could be made, the new model has a stronger scientific foundation than Munson’s legacy model and appears ready for careful engineering use.

58 GEOSCIENCES↗
DOE OSTI2017

488-1D Ash Basin closure cap help modeling- Microdrain® liner option

At the request of Area Completion Engineering and in support of the 488-1D Ash Basin closure, the Savannah River National Laboratory (SRNL) performed hydrologic simulations of the revised 488-1D Ash Basin closure cap design using the Hydrologic Evaluation of Landfill Performance (HELP) model. The revised design substitutes a MicroDrain Liner®—60-mil low-density polyethylene geomembrane structurally integrated with 130-mil drainage layer—for the previously planned drainage/barrier system—300-mil geosynthetic drainage layer (GDL), 300-mil geosynthetic clay liner (GCL), and 6-inch common fill soil layer. For a 25-year, 24-hour storm event, HELP model v3.07 was employed to (1) predict the peak maximum daily hydraulic head for the geomembrane layer, and (2) ensure that South Carolina Department of Health and Environmental Control (SCDHEC) requirements for the barrier layer (i.e., ≤ 12 inches hydraulic head on top of a barrier having a saturated hydraulic conductivity ≤ 1.0E-05 cm/s) will not be exceeded. A 25-year, 24-hour storm event at the Savannah River Site (SRS) is 6.1 inches rainfall (Weber 1998). HELP model v3.07 results based upon the new planned cap design suggest that the peak maximum daily hydraulic head on the geomembrane barrier layer will be 0.15 inches for a minimum slope equal to 3%, which is two orders of magnitude below the SCDHEC upper limit of 12 inches.

58 GEOSCIENCES↗
NASA NTRS2018

Combining Progressive Nodal Release with the Virtual Crack Closure Technique to Model Fatigue Delamination Growth Without Re-Meshing

The present work summarizes an approach to model mixed-mode 3D fatigue crack growth using the Virtual Crack Closure Technique (VCCT) without requiring re-meshing. It is demonstrated that the proposed approach can be used to simulate crack shapes that do not conform to the underlying mesh. The proposed approach relies solely on Paris Law characterization data to model delamination growth. Growth is determined as a post-processing step at the end of each increment, and hence no convergence issues associated with the progressive nodal release are encountered. This approach can be readily applied using standard solid element formulations and is implemented via an interface user element in Abaqus/Standard.

Carvalho, N. V. De↗
DOE OSTI2020

Final Report for Tech-X Corporations’s contribution to Enhancing Understanding of High Energy Density Plasmas from Wire Array and Solid Liner Implosions Using Fluid Modeling with Kinetic Closures

Recent results from experiments and simulation of magnetically driven pulsed power liners have explored the role of the early-time electrothermal instability in the evolution of the magneto-Rayleigh-Taylor instability. Our focus will be on understanding the development of such instabilities and the potential stabilization mechanisms via electron thermal conduction, viscosity, and large magnetic fields which we expect could play a significant role in supporting the success of the MagLIF program. Experiments have shown that studies of high-energy density plasmas from wire-array implosions require physics modeling that goes well beyond simple models such as ideal magnetohydrodynamics. The goal of this work is to provide increased understanding of these experiments by employing simulations with a multi-fluid extended-MHD model which uses kinetic closures for thermal conduction, resistivity and viscosity. We will use codes easily available to the wider research community, including university students, with a secondary goal of providing the community with well-benchmarked tools capable of advanced modeling of high-energy-density plasmas.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS2013

Floating Node Method and Virtual Crack Closure Technique for Modeling Matrix Cracking-Delamination Interaction

A novel approach is proposed for high-fidelity modeling of progressive damage and failure in composite materials that combines the Floating Node Method (FNM) and the Virtual Crack Closure Technique (VCCT) to represent multiple interacting failure mechanisms in a mesh-independent fashion. In this study, the approach is applied to the modeling of delamination migration in cross-ply tape laminates. Delamination, matrix cracking, and migration are all modeled using fracture mechanics based failure and migration criteria. The methodology proposed shows very good qualitative and quantitative agreement with experiments.

DeCarvalho, N. V.↗
NASA NTRS2013

Floating Node Method and Virtual Crack Closure Technique for Modeling Matrix Cracking-Delamination Migration

A novel approach is proposed for high-fidelity modeling of progressive damage and failure in composite materials that combines the Floating Node Method (FNM) and the Virtual Crack Closure Technique (VCCT) to represent multiple interacting failure mechanisms in a mesh-independent fashion. In this study, the approach is applied to the modeling of delamination migration in cross-ply tape laminates. Delamination, matrix cracking, and migration are all modeled using fracture mechanics based failure and migration criteria. The methodology proposed shows very good qualitative and quantitative agreement with experiments.

DeCarvalho, Nelson V.↗
DOE OSTI2019

Execution of an Alternative Modeling Strategy for Closure of the Rainier Mesa Corrective Action Unit at the Nevada National Security Site - 19099

The Underground Test Area (UGTA) Project of the U.S Department of Energy (DOE) is investigating radionuclide contaminant movements in groundwater derived from a decades-long period of underground nuclear testing at the Nevada National Security Site (NNSS) to support regulatory corrective action and closure requirements. The project is built around an integrated campaign of drilling and sampling, data interpretation, computer modeling, and broader monitoring activities conducted under a joint Federal Facilities Agreement and Consent Order (1996 as amended) (FFACO) between the State of Nevada, the DOE, and the U.S. Department of Defense. The FFACO strategy is applied to individual Corrective Action Units (CAUs) that roughly envelop disparate geographic testing areas at the NNSS. The Rainier Mesa/Shoshone Mountain (RMSM) CAU is a geologically and hydrologically complex system lying in a remote up-gradient section of the NNSS. It was the site of 67 underground tests conducted between 1957 and 1992, 61 at Rainier Mesa proper, and 6 at Shoshone Mountain, isolated to its south. The original strategy to close the RMSM CAU required a simulation-based investigation to define the evolution of contaminated volumes of groundwater (in 3D) under uncertainty as a means to define a surface-projected contaminant boundary and to serve as a basis for longer term monitoring activities. Early models developed under this strategy proved to be quite complex and difficult to calibrate. Additional costs required to better characterize the system were judged to be out of balance with the low risks associated with this particular CAU. As a result, an Alternative Modeling Strategy (AMS) was adopted. The AMS removes the requirement for developing ensembles of 3D simulations and replaces it with a simpler one requiring the generation of multiple 1D streamline models. These are meant to encompass a range of alternative, yet plausible release and transport scenarios as a means to bound the overall lateral extent of contaminant transport. This paper will review the modeling approach developed under the AMS and its application to the Rainier Mesa portion of the CAU. Preliminary model results made under different parametric assumptions and boundary condition scenarios will be presented. Additional refinements of the model and its further application will be discussed. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
NASA NTRS1991

On recontamination and directional-bias problems in Monte Carlo simulation of PDF turbulence models

Turbulent combustion can not be simulated adequately by conventional moment closure turbulence models. The difficulty lies in the fact that the reaction rate is in general an exponential function of the temperature, and the higher order correlations in the conventional moment closure models of the chemical source term can not be neglected, making the applications of such models impractical. The probability density function (pdf) method offers an attractive alternative: in a pdf model, the chemical source terms are closed and do not require additional models. A grid dependent Monte Carlo scheme was studied, since it is a logical alternative, wherein the number of computer operations increases only linearly with the increase of number of independent variables, as compared to the exponential increase in a conventional finite difference scheme. A new algorithm was devised that satisfies a restriction in the case of pure diffusion or uniform flow problems. Although for nonuniform flows absolute conservation seems impossible, the present scheme has reduced the error considerably.

Hsu, Andrew T.↗
DOE OSTI2015

Evaluating convective parameterization closures using cloud‐resolving model simulation of tropical deep convection

Abstract Closure is an important component of a mass flux‐based convective parameterization scheme, and it determines the amount of convection with the aid of a large‐scale variable (closure variable) that is sensitive to convection. In this study, we have evaluated and quantified the relationship between commonly used closure variables and convection for a range of global climate model (GCM) horizontal resolutions, taking convective precipitation and mass flux at 600 hPa as measures for deep convection. We have used cloud‐resolving model simulation data to create domain averages representing GCM horizontal resolutions of 128 km, 64 km, 32 km, 16 km, 8 km, and 4 km. Lead‐lag correlation analysis shows that except moisture convergence and turbulent kinetic energy, none of the other closure variables evaluated in this study show any relationship with convection for the six subdomain sizes. It is found that the correlation between moisture convergence and convective precipitation is largest when moisture convergence leads convection. This correlation weakens as the subdomain size decreases to 8 km or smaller. Although convective precipitation and mass flux increase with moisture convergence at a given subdomain size, as the subdomain size increases, the rate at which they increase becomes smaller. This suggests that moisture convergence‐based closure should scale down the predicted mass flux for a given moisture convergence as GCM resolution increases.

Suhas, E.↗
DOE OSTI2020

Opportunities to Update the Model of Tank Closure Grout Aging (SRNL-STI-2012-00404) Based on Experimental Results by the Savannah River Ecology Laboratory

The purpose of this report was to review the results of experiments on evolution of tank grout pore fluids performed by the Savannah River Ecology Laboratory (SREL) and reported in Seaman et al. (2020) and highlight opportunities for updating the model of tank grout degradation presented in Denham and Millings (2012). The SREL experimental results validate some assumptions used in the 2012 grout degradation model and provide information useful for updating the model. All experiments on tank grout degradation have limitations because of reaction rates and the enormous disparity between duration of the experiments and the duration of the degradation of the real tank grout system. Given these limitations, the experimental results form the basis for several recommendations for updating the grout degradation model described in this report.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2017

Implementing an Alternative Modeling Strategy for Closure of the Rainier Mesa Corrective Action Unit at the Nevada National Security Site - 17481

The strategy to close the Rainier Mesa/Shoshone Mountain (RMSM) Corrective Action Unit (CAU) of the Underground Test Area (UGTA) Project at the Nevada National Security Site (NNSS) is defined under a joint agreement between the State of Nevada, the U.S. Department of Energy (DOE) and the Department of Defense (DoD). That strategy required a corrective action investigation (CAI) to define the evolution of contaminated volumes of groundwater under uncertainty as a means to define a surface-projected contaminant boundary and serve as a basis for longer term monitoring. As the initial phase of the CAI was nearing completion in 2012, concerns were raised as to whether the original Federal Facility Agreement and Consent Order (FFACO) strategy was achievable. This was evident when the complexity of the system and the additional costs required to sufficiently characterize it were judged to be out of balance with the overall perceived risks (low) associated with this particular CAU. As a result, an Alternative Modeling Strategy (AMS) and New FFACO Strategy Decision Process for UGTA RM/SM CAU were approved in November 2013. The AMS removes the requirement for developing ensembles of 3D contaminant transport simulations and replaces it with a simpler one requiring the generation of multiple 1D streamline models. These are meant to encompass a range of alternative, yet plausible release and transport scenarios as a means to bound the overall lateral extent of contaminant transport. The new Decision Process is streamlined and progresses from the revised CAI stage, to an external peer review, and then, upon favorable evaluation, directly to a closure stage. Although the project has suffered some delays from implementation of the new strategy, the new process of achieving closure is expected to save several years in time and several million dollars over the original process while still protecting human health and the environment over the 1,000-year compliance period stipulated in the FFACO. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2024

Model emulation and closure tests for (3+1)D relativistic heavy-ion collisions

In nuclear and particle physics, reconciling sophisticated simulations with experimental data is vital for understanding complex systems like the Quark Gluon Plasma (QGP) generated in heavy ion collisions. However, computational demands pose challenges, motivating using Gaussian Process emulators for efficient parameter extraction via Bayesian calibration. We conduct a comparative analysis of Gaussian Process emulators in heavy-ion physics to identify the most adept emulator for parameter extraction with minimal uncertainty. Furthermore, our study contributes to advancing computational techniques in heavy-ion physics, enhancing our ability to interpret experimental data and understand QGP properties.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2013

A Dual Regime Reactive Transport Model for Simulation of High Level Waste Tank Closure Scenarios - 13375

A numerical simulation framework is presented in this paper for estimating evolution of pH and release of major species from grout within high-level waste tanks after closure. This model was developed as part of the Cementitious Barriers Partnership. The reactive transport model consists of two parts - (1) transport of species, and (2) chemical reactions. The closure grout can be assumed to have varying extents of cracking and composition for performance assessment purposes. The partially or completely degraded grouted tank is idealized as a dual regime system comprising of a mobile region having solid materials with cracks and macro-pores, and an immobile/stagnant region having solid matrix with micropores. The transport profiles of the species are calculated by incorporating advection of species through the mobile region, diffusion of species through the immobile/stagnant region, and exchange of species between the mobile and immobile regions. A geochemical speciation code in conjunction with the pH dependent test data for a grout material is used to obtain a mineral set that best describes the trends in the test data of the major species. The dual regime reactive transport model predictions are compared with the release data from an up-flow column percolation test. The coupled model is then used to assess effects of crack state of the structure, rate and composition of the infiltrating water on the pH evolution at the grout-waste interface. The coupled reactive transport model developed in this work can be used as part of the performance assessment process for evaluating potential risks from leaching of a cracked tank containing elements of human health and environmental concern. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2018

Triadic Closure in Configuration Models with Unbounded Degree Fluctuations

The configuration model generates random graphs with any given degree distribution, and thus serves as a null model for scale-free networks with power-law degrees and unbounded degree fluctuations. For this setting, we study the local clustering c(k), i.e., the probability that two neighbors of a degree-k node are neighbors themselves. We show that c(k) progressively falls off with k and the graph size n and eventually for k=Ω(√n) settles on a power law c(k)∼n{sup 5−2τ}k{sup −2(3−τ)} with τ∈(2,3) the power-law exponent of the degree distribution. This fall-off has been observed in the majority of real-world networks and signals the presence of modular or hierarchical structure. Our results agree with recent results for the hidden-variable model and also give the expected number of triangles in the configuration model when counting triangles only once despite the presence of multi-edges. We show that only triangles consisting of triplets with uniquely specified degrees contribute to the triangle counting.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗