Gary Edward Mueller

Prediction of radial porosity distributions in randomly packed fixed beds of uniformly sized spheres in cylindrical containers

The purpose of the investigation is to correlate the experimental data of Roblee et al. (1958) Brosilow (1959), Benenati and Brosilow (1962) and Ridgway and Tarbuck (1966) to produce an empirical model which consists of one principal equation for the radial porosity distribution and includes the damped oscillations. The radial porosity model is correlated in terms of the diameter aspect ratio and a non dimensional distance from the container wall. The model can be used in analytical transport models for simulating packed beds of uniform spheres in cylindrical containers

Numerical simulation of packed beds with monosized spheres in cylindrical containers

Abstract Several sequential packing models are applied to numerically construct packed beds of identical spheres in right circular cylindrical containers. The fixed packed beds are assembled on a base layer so that a newly added sphere is always placed at a vertical location that is stable under gravity. The newly added sphere may be positioned so that it is in contact with two spheres and the container wall (wall spheres) or three other spheres in the interior of the packing (inner spheres). The particular procedure by which wall spheres and inner spheres are added to the packing is determined by a given model. The sequential models calculate the center coordinates of each newly added sphere. The center coordinates are used to determine the overall void fraction and the radial void fraction in cylindrical containers with D / d ≥3 and are compared with experimental data.

A heat transfer model for volumetrically heated nuclear debris beds

Abstract The thermal response of a fixed porous volumetrically heated debris bed is analyzed. The Modified Dispersion-Concentric Model (D-C model) is used in the analysis of forced flow cooling through a volumetrically heated fixed porous debris bed. The fundamental equations are based on the assumptions of dispersed plug flow and concentric intra-particle temperature profiles. The model is theoretically sound provided that a large axial effective fluid thermal dispersion coefficient is assumed. The fundamental equations are rather simple and can be easily solved in terms of temperature profiles for the solid and fluid phases. The theoretical model for the temperature profile for the fluid phase in the subcooled liquid region and in the superheated vapor region compares well with existing experimental measurements.

Transient Analytical Temperature Distributions in Cylindrical Packed Beds Volumetrically Heated by Radiogenic Decay Energy

Abstract Analytical solutions are presented for the problem of the transient distribution of fluid and solid phase temperatures in a packed, porous, cylindrical particle bed with constant thermophysical properties. The packed particle bed is volumetrically heated by radiogenic decay energy from fission products. Flowing through the particle bed by forced convection is a single-phase fluid, either subcooled liquid or superheated vapor. The dynamic response of the packed bed is for low Reynolds numbers. In this case the transient will develop through the packed bed slowly enough for interphase heat transfer to keep the fluid and solid phase temperatures from having large differences. The two-dimensional, time-dependent Modified Dispersion-Concentric Model (D-C model) is used in the analysis of this problem. The D-C model energy equations are solved using Greens function. The mathematical solution characteristics for the transient fluid and solid phase temperature distributions are presented for three different volumetric heat generation terms: two-dimensional, time-dependent; simplified two-dimensional, time-dependent; and two-dimensional, time-independent. Using the two time-dependent volumetric heat generation terms, a comparison is presented for the transient fluid and solid phase temperatures and the radioactive decay heat power coming from the fission products in the particles.

Analytical Solution for the Transient Thermal Response of Volumetrically Heated Fixed Porous Nuclear Debris Beds

Abstract An analytical solution is presented for the problem of the transient distribution of fluid and solid temperatures in a volumetrically heated fixed porous nuclear debris bed through which a single-phase fluid, either subcooled liquid or superheated vapor, is flowing. The one-dimensional, time-dependent Modified Dispersion-Concentric Model (D-C Model) is used in the analysis of this problem. The method of solution is based on transformations that reduce the equations and then the application of Greens function in a straightforward manner. The mathematical solution characteristics for the transient fluid and solid temperature distributions are analyzed for subcooled liquid flow and for superheated vapor flow. Also, the transient fluid and solid phase temperature distributions for infinite time are compared with steady-state experimental data.

Dynamic Finite Element Analysis of Third Size Charpy Specimens of V-4Cr-4Ti

Abstract A 2-D finite element analysis (FEA) of precracked, one-third-scale CVN specimens of V–4Cr–4Ti was performed to investigate the sensitivity of model results to key material parameters such as yield strength, failure strain and work hardening characteristics. Calculations were carried out at temperatures of −196°C and 50°C. Dynamic FEAs were performed using ABAQUS/Explicit v5.4. Finite element results are compared to experimental Charpy results from the production-scale heat of V–4Cr–4Ti (Heat #832665) as a benchmark. Agreement between the finite element model and the experimental data was very good at −196°C, whereas at 50°C the model predicted an absorbed energy slightly below the experimental value.

Discrete Element Method–Based Investigations of Granular Flow in a Pebble Bed Reactor

Abstract In a pebble bed reactor (PBR) core, nuclear fuel in the form of pebbles moves slowly under the influence of gravity. Due to the dynamic nature of the core, a thorough understanding about slow and dense granular flow of pebbles is required from both a reactor safety point of view and a performance evaluation point of view. In the current study, validation of discrete element method (DEM)–based simulation for the pebble flow in a PBR was carried out. Validation of DEM-based simulations necessitates validation of the employed numerical method of simulating packed structure. Hence, a parametric sensitivity study of packing interaction properties was initially conducted and also validation of the numerical method simulating packed structure at first. The parametric sensitivity analysis suggests that static friction characteristics play an important role from a packed/pebble bed structural characterization point of view. In addition, the simulated packed structure approach has shown a good agreement with the available benchmark data. Afterward, the effect of two different half-cone angles of 30 deg and 60 deg on pebble flow field in a PBR was studied by EDEMTM-based simulations. Results of streamlines, velocity radial profiles, and direct observation of discharge indicated a plug-type flow in the upper cylindrical region, whereas results indicated converging-type flow near the bottom conical region. EDEMTM results of granular flow were validated against experimental benchmark data and show a fair agreement in terms of Lagrangian trajectories and velocity profile. Therefore, this validated EDEMTM-based simulation can be used to obtain reliable results of pebble dynamics in a PBR and to enhance understanding of this phenomenon in a PBR. However, additional experimental investigations are recommended to be carried out for different sizes of test reactors, different bottom cone angles, and different sizes of pebbles to further assess DEM simulation results before using them for full-scale reactor simulations.

A thermocouple-based beam profile monitor for an 800 MeV proton accelerator

Abstract A thermocouple-based proton beam profile monitor is designed for use in front of the Los Alamos Neutron Scattering Center target. The purpose of the device is to determine the location and standard deviation of the incident proton beam using thermocouple temperatures. The beam profile monitor consists of two perpendicular planes of thermocouple wires mounted in 1 cm increments on Macor ceramic rings. Temperatures are measured from heat generated volumetrically in the thermocouple wires by the incident proton beam. Operating requirements for the device include the ability to work in pressure ranges of 0.1 to 10 Torr and at beam currents of 5 μA to 100 μA. Temperature data from a beam test are compared with predictions from an analytical model, a finite elements analysis using the code TOPAZ2D, and an automated curve fitting routine. Average relative errors of less than 10% are calculated from the analytical solution and the finite elements analysis. The curve fitting routine provides quick estimates of the proton beam parameters which are useful during beam tuning.

Design of a Target and Moderator at the Los Alamos Spallation Radiation Effects Facility (LASREF) as a Neutron Source for Fusion Reactor Materials Development

x Thm LASREF facllicy in locatad in the beam ●top arsa at LAf4PF. Tha neutron spectrum xs f~ssion-like with tha ●ddition of ● 3% to St component with E > 20 FleV. rho proaont study waAuatac thlimits on geometry ●nd mator:al selectlon that will maximxza the nmtron flux. HCNP and LAHET were used tc predict the neutron flux ●nd ●nergy 8pectrum for a variety of geomocri99. The problem considers 760 HOV protons incidenu on tungmten. The resulting neutrons ●re multiplied Ln uranium through (n,xn) re&ctions. CXlculatlonm mhow that a neutran flux greater than 10’3n/m2/9 is achievable. The helium to dpa ratio ●nd thO tranmmutatlon product generation are calculated. These results ●ra compared to Expectations for tne proponed DEMO fusion reactor and to QP’T?.