Philippe M. Bardet

Options for Scaled Experiments for High Temperature Liquid Salt and Helium Fluid Mechanics and Convective Heat Transfer

Abstract Liquid fluoride salts and helium have desirable properties for use as working fluids for high-temperature (500 to 1000°C) heat transport in fission and fusion applications. This paper presents recent progress in the design and analysis of scaled thermal-hydraulic experiments for fluid mechanics and convective heat transfer in liquid salt and helium systems. It presents a category of heat transfer fluids and a category of light mineral oils that can be used for scaled experiments simulating convective heat transfer in liquid salts. By optimally selecting the length, velocity, average temperature, and temperature difference scales of the experiment, it is possible to simultaneously match the Reynolds, Froude, Prandtl, and Grashof numbers in geometrically scaled experiments operating at low-temperature, reduced length, and velocity scales. Mechanical pumping power and heat input are reduced to ~1 to 2% of the prototype power inputs. Helium fluid mechanics and heat transfer likewise can be simulated by nitrogen following the same procedure. The resulting length, velocity, temperature, and power scales for simulating helium are quite similar to those for the liquid salts, and the pressure scale is reduced greatly compared to the prototypical pressure scale. Steady state and transient heat transfer to a steel and graphite structure can be reproduced with moderate distortion using Pyrex and high-thermal-conductivity epoxies, respectively. Thermal radiation heat transfer cannot be reproduced, so the use of these simulant fluids is limited to those cases where radiation heat transport is small compared to convective heat transport, or where corrections for thermal radiation heat transfer can be introduced in models using convective heat transfer data from the simulant fluids. Likewise for helium flows, compressibility effects are not reproduced.

Control of the heavy-ion beam line gas pressure and density in the HYLIFE thick-liquid chamber

Abstract Controlling the density and pressure of the background gas in the beam lines of thick-liquid heavy-ion fusion chambers is of paramount importance for the beams to focus and propagate properly. Additionally, transport and deposition of debris material onto metal beam-tube surfaces may reduce the breakdown voltage and permit arcing with the beam. The strategy to control the gas pressure and the rate of debris deposition is twofold. First, the cool thick-liquid jet structures will mitigate the venting to the beam tubes. The ablation and venting of debris through thick-liquid structures must be modelled to predict the quantities of debris reaching the beam ports. TSUNAMI calculations have been performed to estimate the mass and energy flux histories at the entrance of the beam ports in a 9×9 HYLIFE pocket geometry. Secondly, additional renewable shielding will be interposed in the beam tubes themselves. Thick-liquid vortexes are planned to coat the inside of the beam tubes and provide a quasi-continuous protection of the beam-tube walls up to the final focus magnets. A three-component molten salt, flinabe, with a low melting temperature and vapor pressure, has been identified as a candidate liquid for the vortexes. The use of flinabe may actually eliminate the necessity of mechanical shutters to rapidly close the beam tubes after target ignition.

Dynamics of Liquid-Protected Fusion Chambers

Abstract This paper presents an update of the work done at University of California, Berkeley (UCB) on thick-liquid protection of inertial fusion energy (IFE) chambers. UCB is focusing on microsecond, millisecond, and quasi-steady phenomena. Over microsecond time scales, numerical simulations, performed with the code TSUNAMI permit modeling of IFE chambers gas dynamics. For the millisecond range, the liquid jets response to the fusion reaction impulse loading is being studied for both Z-Pinch and HYLIFE-II-type chambers. A new mineral oil has been identified that allows scaled molten salt experiments with low distortion. Vortex tube flow, a key liquid structure of the 2002 Robust Point Design has been investigated in scaled experiments using the mineral oil, while a new design for thick liquid wall protection is under development. In quasi-steady phenomena, recent work has measured the Flibe vapor pressure and composition at near melting point temperature using mass spectrometry.

Liquid Vortex Shielding for Fusion Energy Applications

Abstract Swirling liquid vortices can be used in fusion chambers to protect their first walls and critical elements from the harmful conditions resulting from fusion reactions. The beam tube structures in heavy ion fusion (HIF) must be shielded from high energy particles, such as neutrons, x-rays and vaporized coolant, that will cause damage. Here an annular wall jet, or vortex tube, is proposed for shielding and is generated by injecting liquid tangent to the inner surface of the tube both azimuthally and axially. Its effectiveness is closely related to the vortex tube flow properties. 3-D particle image velocimetry (PIV) is being conducted to precisely characterize its turbulent structure. The concept of annular vortex flow can be extended to a larger scale to serve as a liquid blanket for other inertial fusion and even magnetic fusion systems. For this purpose a periodic arrangement of injection and suction holes around the chamber circumference are used, generating the layer. Because it is important to match the index of refraction of the fluid with the tube material for optical measurement like PIV, a low viscosity mineral oil was identified and used that can also be employed to do scaled experiments of molten salts at high temperature.

Experimental study of shear layer instability below a free surface

Relaxation of a laminar boundary layer at a free surface is an inviscidly unstable process and can lead to millimeter-scale surface waves, influencing interfacial processes. Due to the small time- and length-scales involved, previous experimental studies have been limited to visual observations and point-wise measurements of the surface profile to determine instability onset and frequency. However, effects of viscosity, surface tension, and non-linearity of the wave profile have not been systematically studied. In fact, no data have been reported on the velocity fields associated with this instability. In the present study, planar laser induced fluorescence and particle image velocimetry provide surface profiles coupled with liquid phase velocity fields for this instability in a time resolved manner. Wave steepness (ak, with a the amplitude and k the wave number) and Reynolds and Weber numbers based on momentum thickness range from 0 to 1.2, 143 to 177, and 4.79 to 6.61, respectively. Large datasets are a...

Particle Image Velocimetry Applications Using Fluorescent Dye-Doped Particles

Polystyrene latex sphere particles are widely used to seed flows for velocimetry techniques such as Particle Image Velocimetry (PIV) and Laser Doppler Velocimetry (LDV). These particles may be doped with fluorescent dyes such that signals spectrally shifted from the incident laser wavelength may be detected via Laser Induced Fluorescence (LIF). An attractive application of the LIF signal is achieving velocimetry in the presence of strong interference from laser scatter, opening up new research possibilities very near solid surfaces or at liquid/gas interfaces. Additionally, LIF signals can be used to tag different fluid streams to study mixing. While fluorescence-based PIV has been performed by many researchers for particles dispersed in water flows, the current work is among the first in applying the technique to micron-scale particles dispersed in a gas. A key requirement for such an application is addressing potential health hazards from fluorescent dyes; successful doping of Kiton Red 620 (KR620) has enabled the use of this relatively safe dye for fluorescence PIV for the first time. In this paper, basic applications proving the concept of PIV using the LIF signal from KR620-doped particles are exhibited for a free jet and a two-phase flow apparatus. Results indicate that while the fluorescence PIV techniques produce a signal roughly 3 orders of magnitude weaker than Mie scattering, they provide a viable method for obtaining data in flow regions previously inaccessible via standard PIV. These techniques have the potential to also complement Mie scattering signals, for example in multi-stream and/or multi-phase experiments.

Fuel Assembly Oscillation-Induced Flow in Initially Stagnant Fluid

Abstract The effect of water on the dynamics response of fuel bundles in pressurized water reactors during external forcing is studied experimentally inside a large facility that houses a full-height bundle and is operated on an earthquake shake table. This configuration is directly relevant to earthquakes and loss-of-coolant accidents. Most data to date have been focused on structural response and some pointwise measurements of liquid velocity. Here, structure displacement coupled with velocity field are investigated with nonintrusive optical diagnostics in initially stagnant water. Data indicate that a flow develops as the structure oscillates: both a cross flow through the bundle and an axial pulsatile flow that was not anticipated. A physical mechanism is proposed as a source of this structure-induced flow that is driven by pressure gradients around the fuel bundle.

Experimental Investigation of Z-Pinch IFE Chamber Liquid Structure Response

Abstract Z-Pinch IFE chamber fluid mechanics can be studied using simulant fluids such as water in reduced scale facilities. The use of porous liquid and solid blanket materials provides the key to mitigating blast effects from fusion reaction. The UCB Vacuum Hydraulics Experiment (VHEX) was recently upgraded with a large, annular inlet nozzle system to produce an annular porous liquid curtains to study Z-Pinch IFE chamber response. Explosives experiments in VHEX studied the response of the liquid structure to the detonation of high explosive C-4. The experiments demonstrated that the crushing of porous liquid structures is effective in transferring momentum uniformly into the blanket mass. No significant high-speed jetting or spall was observed exiting the shocked liquid structure. Independent measurement of the transient pressure history, coupled with high-speed video of the blanket response and final velocity, will provide the basis to validate gas dynamics and blanket response models.

Z-inertial fusion energy: power plant final report FY 2006.

This report summarizes the work conducted for the Z-inertial fusion energy (Z-IFE) late start Laboratory Directed Research Project. A major area of focus was on creating a roadmap to a z-pinch driven fusion power plant. The roadmap ties ZIFE into the Global Nuclear Energy Partnership (GNEP) initiative through the use of high energy fusion neutrons to burn the actinides of spent fuel waste. Transmutation presents a near term use for Z-IFE technology and will aid in paving the path to fusion energy. The work this year continued to develop the science and engineering needed to support the Z-IFE roadmap. This included plant system and driver cost estimates, recyclable transmission line studies, flibe characterization, reaction chamber design, and shock mitigation techniques.