Arthur E. Ruggles

Calculation of attainable superheats and predicted embryonic flux rates in commercial water isotope targets

Phase change in a fluid subject to a large spectrum of radiations is examined. The statistical variation in the fluid energy is considered in concert with the radiation field attributes to establish conditions for spinodal decomposition and bulk nucleation. This approach is developed in general and carried forward for the specific case of (18)O-enriched water used in commercial targets for the production of (18)F. Sensitivities of the outcome to specific attributes of the fluid state model are examined. The possibility for very high bulk nucleation site densities is exposed and may explain the observed thermal-fluid behavior in commercial water targets. These targets operate at elevated pressure and temperatures at and in excess of the saturation temperature. They are also subjected to a large spectrum of radiations, with differing levels of energy deposition. The conditions for spinodal decomposition and bulk nucleation (with and without radiation) in these targets are evaluated. It is likely that some bulk nucleation is occurring, and causing the density reduction locally in the target. Suitable experiments to evaluate this potential are more fully possible.

Vapor volume fraction, flow regime, and vapor velocity inference using fluid conductivity measurements

An array of conductivity sensors is presented that infers the vapor volume fraction, flow regime, and vapor velocity in a two-phase flow. The frequency response of the sensors is up to 40 Hz, which allows for dynamic signal processing to ascertain flow characteristics additional to the time average vapor volume fraction, such as the vapor velocity and flow regime. The sensor array, associated driving circuitry, and signal processing techniques are presented, and the performance of the array is evaluated for an air–water flow at one atmosphere and a steam water flow at 0.095 MPa.

Thermal performance of CTI, Inc. enriched water targets

Oxygen 18 enriched water targets are bombarded with 10.5 MeV protons to produce Fluorine 18 in cyclotron targets manufactured by CTI, inc. A thermal model of the target and target holder is developed that allows the relationship between the beam power applied to the target and the vapor volume produced in the target to be predicted. The model is compared with data on vapor volume production during bombardment for a range of beam power. The data agree well with predictions from the thermal model.

Numerical Simulation of Acoustic Streaming in Gas-Liquid Two-Phase Flow

Acoustic streaming phenomena pertaining to liquid-gas two-phase flow in a one-dimensional rigid duct is investigated numerically. The oscillatory bubbly flow is generated due to the sinusoidal vibration of the vertical left wall of the enclosure. Time-averaged streaming flow patterns exist in the duct as a consequence of interaction between gas bubbles and liquid which are similar to the Rayleigh-type acoustic streaming phenomena extensively investigated in single-phase flow. The liquid is treated as incompressible with a homogeneous distribution of non-condensable gas bubbles. The system is modeled with coupled nonlinear and flux-conservative partial differential equations combined with the Rayleigh-Plesset equation governing the bubble radius. The viscous interaction between bubbles and the surrounding incompressible liquid phase is the main mechanism for attenuation of the wave energy considered in this analysis. The numerical solutions are obtained by a control-volume based finite-volume Lagrangian method.Copyright

Three-dimensional spatiotemporal tracking of fluorine-18 radiolabeled yeast cells via positron emission particle tracking

A method for Positron Emission Particle Tracking (PEPT) based on optical feature point identification techniques is demonstrated for use in low activity tracking experiments. A population of yeast cells of approximately 125,000 members is activated to roughly 55 Bq/cell by 18F uptake. An in vitro particle tracking experiment is performed with nearly 20 of these cells after decay to 32 Bq/cell. These cells are successfully identified and tracked simultaneously in this experiment. This work extends the applicability of PEPT as a cell tracking method by allowing a number of cells to be tracked together, and demonstrating tracking for very low activity tracers.

Mercury Scaling of a Swirling Jet Micro-Bubble Generator

Swirling jets with co-axial gas filament flow have been used for production of small bubbles in environmental and chemical processing industries for some time. The modeling of the physics for the gas filament break-up is not well established, and this impedes scaling of the device to use with fluids other than water and organics where data is available. High speed photographic studies of the gas filament break-up are used to examine the physical phenomena, and support model development for the bubble production that may be used to scale the device to alternate applications, such as bubble production in liquid metals. Bubble break-up models based on energy dissipation generate a power-law, with exponent of α = 8/5, relating Weber number to Reynolds number at the nozzle exit. Those models are compared to empirical models found in the literature providing a link between mechanistic models, scaling arguments, and legacy empirical models.Copyright

Analysis of the Bubbly-Churn Regime Transition in a Scaled Model Boiling Water Reactor

A scaled model boiling water reactor (SMBWR) uses water at 0.095 MPa in a transparent heated channel 0.5 m in length with four electrical heated fuel simulator rods. The axial void profile in the channel is measured using conductivity probes. The boiling channel exhibits bubbly and churn flow regimes. In the present study, the bubbly-churn regime transition is investigated using the variance, kurtosis, and skewness of the probability density function (pdf) derived from the conductivity measurements. The positioning of five conductivity sensors along the boiling water channel allows examination of the gradual changes in the flow regime characteristics. The results indicate it is possible to detect the bubbly-to-churn flow regime transition using the pdf distribution attributes of the conductivity probes.

Experiments and Simulations With Large Gas Bubbles in Mercury Towards Establishing a Gas Layer to Mitigate Cavitation Damage

One of several options that shows promise for protecting solid surfaces from cavitation damage in liquid metal spallation targets, involves introducing an interstitial gas layer between the liquid metal and the containment vessel wall. Several approaches toward establishing such a protective gas layer are being investigated at the Oak Ridge National Laboratory including large bubble injection, and methods that involve stabilization of the layer by surface modifications to enhance gas hold-up on the wall or by inserting a porous media. It has previously been reported that using a gas layer configuration in a test target showed an order-of-magnitude decrease in damage for an in-beam experiment. Video images that were taken of the successful gas/mercury flow configuration have been analyzed and correlated. The results show that the success was obtained under conditions where only 60% of the solid wall was covered with gas. Such a result implies that this mitigation scheme may have much more potential. Additional experiments with gas injection into water are underway. Multi-component flow simulations are also being used to provide direction for these new experiments. These simulations have been used to size the gas layer and position multiple inlet nozzles.

RELAP5-3D Validation Study Using MB-2 Prototypical Steam Generator Steady-State Data

Abstract A validation study of RELAP5-3D is performed using data from the Model Boiler Number 2 (MB-2) Prototypical Steam Generator Testing Program. The MB-2 is a 6.67-MW(thermal) power-scaled representation of the Westinghouse Model F steam generator. Comparisons with previous simulations using RELAP5/MOD3.2 are also offered. Limit cycles predicted by the RELAP5/MOD3.2 simulation are reduced in the RELAP5-3D simulation using identical nodalization. Steady-state data from the MB-2 tests used in the validation do not exhibit a limit cycle. The sources of the predicted limit cycles are investigated and feedback mechanisms contributing to the limit cycles are explained.

Measurement of safety injection fluid transport in a scaled reactor test

An existing geometric and fluid-fluid scaled facility is applied to investigate the transport of borated safety injection (SI) fluid in the Westinghouse AP600 reactor vessel during a main steam-line rupture (MSLR) event. The AP600 reactor has coaxial injection into the vessel downcomer rather than the cold-leg cross-flow injection typical of operating power reactors. This gas-flow test facility has unique detail in the representation of the SI nozzle-to-core inlet path most important to SI transport. Analysis of the transport phenomena expected in the reactor and the scaled facility, given MSLR conditions, indicates that both buoyancy and turbulent diffusion can have comparable influences on SI transport. It is shown that different reactor-to-experiment velocity ratios are required to scale each phenomenon. Tests are performed to evaluate transient SI fluid concentration at the core inlet using the appropriate velocity ratios to scale buoyancy and diffusion. Two asymmetric loop-flow boundary conditions representative of the MSLR event as well as a symmetric flow condition are applied. While no one test result is fully similar to the expected reactor transport, this ensemble of tests provides data that are valuable for AP600 numerical model benchmarking.