28 research outputs found
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EOS for critical slurry and solution systems
In a fire involving fissile material, the mixture of the fissile material ash with fire fighting water may lead to a criticality excursion if there are nearby sumps that permit a critical geometry. The severity of the resulting energy release and pressure pulse is dependent on the rate at which the mixing occurs. To calculate these excursions, a non-equilibrium equation of state for the water ash mixture or slurry is needed that accounts for the thermal non-equilibrium that occurs due to finite heat transfer rates. We are developing the slurry EOS as well as a lumped neutronic and hydrodynamic model to serve as a testing ground for the non-equilibrium EOS before its incorporation into more sophisticated neutronic-hydrodynamics codes. Though the model lacks spatial dependence, it provides estimates of energy release and pressure pulses for various mixture assembly rates. We are also developing a non-equilibrium EOS for critical solution systems in which the fissile material is dissolved in water, which accounts for chemical non-equilibrium due to finite mass transfer rates. In contrast to previously published solution EOS, our solution EOS specifically accounts for mass diffusion of dissolved radiolytic gas to bubble nucleation sites. This EOS was developed to check our overall modeling against published solution excursion experiments and to compare solution excursions with slurry excursions initiated under the same conditions. Preliminary results indicate a good match between solution EOS calculations and experiments involving premixed 60-80 g U/l solutions for both low rate and high rate reactivity insertions. Comparison between slurry and solution calculations for the same composition show comparable energy release and pressure peaks for both low and high rate reactivity insertions with the slurry releasing less energy but generating more pressure than the solution for the amount of energy released. Calculations more appropriate to actual fire fighting scenarios will also be presented
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Extension to 3-D of the low-frequency electromagnetic plasma simulation models, LDRD Final Report 95-ERD-036
Low-frequency electromagnetic simulation models have a wide range of industrial applications. We have built several models, differentiated by slightly different physics approximations or computational solution methods, that have proven quite useful in a variety of applications. Our models been used to investigate beam plasma interactions in ICF targets, antenna plasma coupling in plasma processing, and magnetic implosion drive in Z-pinch pulsed power generators. The common feature of these models is that they retain inductive effects but implicitly ignore computationally intensive, fully electromagnetic effects. However, the preponderance of our work has been limited to only two dimensions. We have made significant progress modeling low-frequency electromagnetic physics with a new model in 2-D that is now capable of modeling antenna structures in 3-D. Although LLNL`s interest in plasma processing has diminished, we have certainly added to LLNL`s capabilities. Interestingly, we have already found another application, the magnetic behavior of read/write heads in the magnetic storage industry, that can make use of many of the computational methods described here, rewarding us again for maintaining a strong core competency in low-frequency EM plasmas
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High-power laser source evaluation
This document reports progress in these areas: EXPERIMENTAL RESULTS FROM NOVA: TAMPED XENON UNDERDENSE X-RAY EMITTERS; MODELING MULTI-KEV RADIATION PRODUCTION OF XENON-FILLED BERYLLIUM CANS; MAPPING A CALCULATION FROM LASNEX TO CALE; HOT X RAYS FROM SEEDED NIF CAPSULES; HOHLRAUM DEBRIS MEASUREMENTS AT NOVA; FOAM AND STRUCTURAL RESPONSE CALCULATIONS FOR NIF NEUTRON EXPOSURE SAMPLE CASE ASSEMBLY DESIGN; NON-IGNITION X-RAY SOURCE FLUENCE-AREA PRODUCTS FOR NUCLEAR EFFECTS TESTING ON NIF. Also appended are reprints of two papers. The first is on the subject of ``X-Ray Production in Laser-Heated Xe Gas Targets.`` The second is on ``Efficient Production and Applications of 2- to 10-keV X Rays by Laser-Heated Underdense Radiators.`
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Cold X-Ray Impulse Estimates
The purpose of this short note is to document comparisons between a simple analytic model and the BUCKL[1]x-ray deposition and impulse code and to briefly demonstrate the effect of deposition time on impulse
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Analytic and experimental validation of thermo elastic plastic material response calculation
We compare the thermo-elastic-plastic response of fissionable metals calculated by the solid mechanics code DYNA to an analytic model for the case of a uniformly heated thin spherical shell and to experimental data for the case of a thin rod heated in a pulsed reactor. In both cases, the materials are volumetrically heated by neutron exposure. We find good agreement between the code and the analytic model and experimental data for the first and second case, respectively. For very fast heating times, macroscopic displacement may be replaced by microscopic plastic flow. To verify this behavior, an experiment to be done at SNLA SPR III is described. Validation of the code in these simple geometries is a necessary step if calculations involving more complicated geometries are to be understood and trusted
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Form and structural response calculations for NIF neutron exposure sample case assembly design
We describe the calculations used to design an aluminum foam protection layer for a stainless steel neutron exposure sample case. The layer protects the case from impulsive loads generated by a 20 MJ NIF capsule 10 cm from the sample case assembly. Impulse only from ablating x-rays and hohlraum plasma debris is considered. One dimensional CALE foam response calculations and analytic estimates are used to show that 1 cm of aluminum 6101-T6 foam 10 % of solid density is sufficient to attenuate the incoming peak pressure without complete melting on crush-up. Two dimensional DYNA calculations show that a 304 stainless steel spherical shell sample case with an inner radius of 1 cm and a wall thickness of 2 mm encased in 1 cm of foam does not yield to the pressure that is transmitted through the foam by a 220 Pa-sec (2.2 ktap), 2 GPa (20 kbar) load due to recoil of x- ray ablation. An unprotected spherical shell case subjected to a gentler load with peak pressure reduced to 0.2 GPa (2 kbar) not only yields but its effective plastic strain exceeds the failure point of 0.4 in 304 stainless steel after 160 microseconds. Doubling the impulse for the protected case to approximately account for debris loading results in very localized yield and an effective plastic strain that does not exceed 0.014. (U
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Two dimensional self-consistent fluid simulation of rf inductive sources
The two-dimensional (R - Z) electromagnetic code FMRZ has been written to model inductive sources self-consistently in time. The code models an argon plasma with momentum-transfer, excitation and ionization as electron-neutral reactions and scattering and charge-exchange for the ion-neutral reactions. The electrons and ions are treated as Maxwellian fluid species and a reduced set of Maxwell`s equations is used to advance the electromagnetic fields. The set of equations used in FMRZ is not subject to typical numerical constraints present in many time dynamic codes allowing one to choose appropriate the and space scales to resolve only the frequencies and scale lengths of interest. The model retains nonlinear driving terms which give rise to a pondermotive force that distorts the density profile. Density and power profiles will be used to illustrate the physical effects of various terms in the equations. Trends in average density and temperature compare well with an analytic model
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Experiments and modeling with a large-area inductively coupled plasma (ICP) source
We describe initial experiments with a large (30 in.) plasma source chamber to explore the problems associated with large-area Inductively coupled plasma (ICP) sources to produce high density plasmas useful for processing 400 mm semiconductor wafers. Our experiments typically use a 25 in. diameter planar ICP coil driven at 13.56 MHz. Plasma and system data are taken in Ar and N{sub 2} over the pressure range 3--50 mtorr. R.F. Inductive power was run up to 2000W, but typically data were taken over the range 100--1000W. Diagnostics Include optical emission spectroscopy, Langmuir probes, and B-dot probes as well as electrical circuit measurements. The B-dot and E-M measurements are compared with models based on commercial E-M codes. Initial indications are that uniform plasmas suitable for 400 mm processing are attainable. We present a comparison between computer modeling and experimental results for this source. Computer simulations using the fluid code INDUCT94 are used to explain variations In the plasma density profile measurements as a function of Inductive power, gas pressure and gas composition. Both Argon and Nitrogen discharges are modeled. INDUCT94 solves the 2D time-dependent fluid equations for electrons, ions and neutrals Including effects of both Inductive and capacitive coupling. Detailed volume and surface chemistry reactions are treated. We discuss the effects of pressure and power on plasma uniformity
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Use of Lasers to Study the Impact of Fractionation and Condensation on the Toxicity of Nuclear Weapon Fallout
An experimental concept has been developed to collect data to aid in the refinement of simulation programs designed to predict the fallout effects arising from surface and shallowly buried nuclear weapon detonations. These experiments, called the Condensation Debris Experiments (CDE), are intended to study the condensation/fractionation of material that is liberated following an initial deposition of laser energy onto a small, characterized target. The CDE effort also encompasses target development and material studies as well as supporting computational efforts studying radiation hydrodynamics, computational fluid dynamics, and relevant neutron activation processes (not discussed here)