Helium Gas Injection Research Articles

Gas puff imaging on the TCV tokamak.

We present the design and operation of a suite of Gas Puff Imaging (GPI) diagnostic systems installed on the Tokamak à Configuration Variable (TCV) for the study of turbulence in the plasma edge and Scrape-Off-Layer (SOL). These systems provide the unique ability to simultaneously collect poloidal 2D images of plasma dynamics at the outboard midplane, around the X-point, in both the High-Field Side (HFS) and Low-Field Side (LFS) SOL, and in the divertor region. We describe and characterize an innovative control system for deuterium and helium gas injection, which is becoming the default standard for the other gas injections at TCV. Extensive pre-design studies and the different detection systems are presented, including an array of avalanche photodiodes and a high-speed CMOS camera. First results with spatial and time resolutions of up to ≈2 mm and 0.5µs, respectively, are described, and future upgrades of the GPI diagnostics for TCV are discussed.

Quantifying the reduction in cavitation-induced erosion damage in the Spallation Neutron Source mercury target by means of small-bubble gas injection

A model developed to represent the progress of erosion damage in liquid-metal spallation target vessels was modified to incorporate the effect of gas injection on the erosion rate. The liquid mercury target system for the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory now operates with helium gas injection to reduce target vessel fatigue stress and cavitation-induced erosion damage. Erosion damage is a primary degradation phenomenon affecting the service life of SNS target vessels, and cavitation mitigation techniques, such as small-bubble gas injection, have been implemented to reduce damage and extend target lifetimes. Erosion depths in samples removed from SNS targets after operation were measured using laser line scanning. These measurements confirmed that gas injection reduced erosion damage. However, quantifying the damage reduction due to gas injection was complicated by variations in lifetime, power, and gas injection rates between different targets. In this study, the operating power and gas injection rate of targets were incorporated into an erosion damage prediction model to quantify their effects on erosion damage reduction. Values of a power scaling factor, β, were calculated by comparing modeled with measured erosion damage. These values indicate that the use of gas injection at the SNS reduced damage to a level equivalent to operating targets without gas injection at 35–47% of the actual beam power. To account for the gas injection effect on the cavitation damage, a simple exponential form based on analysis of the scaling factor β was developed to incorporate the gas rate history with a scaling factor γ in the erosion damage modeling.

Control method of natural circulation flow by helium gas injection

There is a possibility that the mixture gas of air and helium diffuse into the reactor core at the depressurization accident of a HTGR. In order to investigate a method to control natural circulation flow of air and helium, we have conducted an experiment using an apparatus that simulates the flow path configuration of the HTGR. The experimental apparatus consists of two vertical channels with rectangular cross-sections, a connecting channel at the top of the channels, and a storage vessel at the bottom of the channels. The temperature of the heated and cooled walls and the temperature of the mixture gas in the vertical slots were measured. The concentration of air was also measured by ultrasonic concentration meter. From the results obtained in this experiment, it was confirmed that the natural circulation flow stopped for a while after helium gas injection. We will also describe the results obtained in the three-dimensional numerical analysis.

Experimental investigation on subcooling of liquid hydrogen by helium gas injection through evacuation

AbstractSubcooling is the process of bringing down the temperature of liquids lower than that of the boiling point of the corresponding vapor pressure. The performance of subcooling of cryogenic liquids mainly depends on the heat‐inleak of the system, the helium injection mass flow rate, helium injection temperature, and helium injection nozzle pattern. This paper presents an alternative method, by making use of the least heat in the leakage of the liquid hydrogen storage container, which is quite possible because containers with excellent thermal insulation are commercially available nowadays. The process involved is rapid evacuation through gas ejectors, thus reducing the effect of temperature. The advantage and the process of evacuation leading to subcooling in a unique manner are the objective of this article. The experimental results are discussed in comparison with the thermophysical process involved in the subcooling operation. A comparative study is also carried out with the theoretical heat exchange process in which helium is used as a medium for the economy of the stated process. It is stated that the current process of subcooling through evacuation is superior to the conventional heat exchange process.

Effects of helium massive gas injection level on disruption mitigation on EAST

In this study, NIMROD simulations are performed to investigate the effects of massive helium gas injection level on the induced disruption on EAST tokamak. It is demonstrated in simulations that two different scenarios of plasma cooling (complete cooling and partial cooling) take place for different amounts of injected impurities. For the impurity injection above a critical level, a single MHD activity is able to induce a complete core temperature collapse. For impurity injection below the critical level, a series of multiple minor disruptions occur before the complete thermal quench.

Fatigue analysis of the Spallation Neutron Source 2 MW target design

Upgrades to the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory are under way with two major projects. The first project is the Proton Power Upgrade (PPU), which will double the power capacity of the SNS accelerator system to enable the operation of a future second neutron source target station—the second project. PPU also will increase power to the SNS first target station – which currently operates at 1.4 MW with 1.0 GeV protons – to 2 MW with 1.3 GeV protons. Final design of the PPU 2 MW target module is finished, including all necessary design and analysis calculations. The fatigue evaluation described herein is an assessment of the fitness of the PPU 2 MW target mercury vessel to resist failure from cyclic loading from the pulsed 60 Hz proton beam and thermal changes from disrupted operation. In addition to the reliability predictions, the method, detail, and depth of this fatigue evaluation are superior to those of past target design assessments. The thermal fatigue life is predicted to exceed 3125 thermal cycles per 1250 h of operation for all load cases. The design also meets the (relative) fatigue design goal for combined thermal and pulse loading of greater than 0.5 times the minimum fatigue life calculated for a jet-flow target design operating at 1.4 MW—the most robust design to date in terms of resistance to fatigue failure. From the onset of the PPU, it has been known that pulse loading requires effective application of helium gas injection into the target mercury to reduce beam pressure loading. For the PPU 2 MW target, none of the pulse load cases requires a maximum strain reduction from gas injection of more than 50% (for base material) to meet the fatigue design goal. This level of reduction is achievable from gas injection, according to historical strain measurements from 1.4 MW target operation. Overall, the PPU 2 MW target design is predicted to have superior resistance to fatigue failure compared with past target designs.

Review of Filtered Rayleigh Scattering technique for mixing studies in supersonic air flow

Filtered Rayleigh Scattering or FRS is a non-intrusive laser diagnostic technique that is utilized to observe and quantify various flow properties in high-speed gas flows. In this technique, a laser beam is used to irradiate a portion of the gas under investigation. The receiving gas molecules scatter the incident laser beam in all the directions. The scattered radiation from a single molecule stems from the induced oscillations of the electron cloud that acts as a classical dipole radiator. The intensity of the net scattered radiation from all the molecules that are in random motion depend on the spatio-temporal fluctuations of the dielectric permittivity of the gas. The thermodynamic properties of the gas govern the nature of these variations and the resulting spectra of the scattered radiation is referred to as Rayleigh Brillouin spectrum. In high-speed gas flows applications, the bulk velocity of the gas molecules causes the entire scattered spectrum to be Doppler shifted from the lasing frequency. The extent of this shift is very significant in supersonic flows and this enables the isolation of the scattered spectrum from the laser reflections using a molecular notch filter. Measurement of flow properties can be made based on the intensity of the RBS signal that is collected by a charged coupled device. The FRS technique is also utilized to perform mixing measurements in binary mixture of gases in high-speed flows. In non-reacting mixing studies, helium is often used as a passive scalar and simulant gas for hydrogen fuel. Helium concentration measurements in supersonic flows based on the FRS technique require two independent experiments. The first experiment involves injection of helium gas and the second separate experiment requires air injection. The helium mole-fraction is retrieved from the FRS imaging data under the key assumptions that the total number density profiles and the extent of the Doppler shift that is associated with each one of the two independent experiments at the measuring plane are identically the same. In this review, the theory governing Rayleigh scattering and the FRS technique to retrieve helium mole-fraction in supersonic flow will be discussed in detail. Measurement results from recent FRS studies on complex vortex interactions in supersonic flow will be also presented and discussed as well as the impact on the results of a departure from the key assumptions in FRS mixing studies will be analyzed for a canonical parallel injection using strut injector in supersonic flow.

Cooling behaviors of liquid hydrogen by helium gas injection

The cooling method of helium bubbling is of great importance in the acquisition system of densified liquid hydrogen because of its safety, reliability and easy operation. To obtain better cooling effect in the cooling system, in this paper, a mathematical model of instantaneous heat and mass transfer is developed by using two-film theory to describe the cooling behavior of a single helium bubble. The solubility and diffusion processes for the single helium bubble injected into liquid hydrogen are quantitatively analyzed. The dominant factors affecting the cooling capacity are obtained on the basis of discussion on several influencing factors. Taking these as important basis of the assumption, a thermodynamic model considering effects of static pressure and thermo-physical properties is established to accurately predict the temperature dropping process of liquid hydrogen by helium bubbling. Compared with the associated experimental data, it is found that the calculating results using the thermodynamic model proposed in the present paper are well consistent with the experimental data. The cooling effect becomes better with the decreases of ullage pressure, injected helium temperature and environmental heat flux. The helium gas consumption gradually reduces with the increase of helium injection rate and the decrease of environment heat flux. Meanwhile, the same method is also used for the cooling of liquid oxygen, liquid nitrogen and liquid methane. It shows that the cooling effect using the method of helium gas bubbling varies for different cryogenic liquids. The triple-point temperatures of LN2 and LCH4 can easily be reached by the helium injection, but it is hardly cooled down to their freezing points for the LH2 and LO2. Among the four cryogenic liquids, the LH2 cooling needs the largest consumption of GHe to meet the requirement of a certain subcooling degree.

Strain measurement in the recent SNS mercury target with gas injection

High-radiation-tolerant fiber-optic strain sensors were recently developed to measure the transient proton-beam-induced strain profiles on the mercury target vessel at the Spallation Neutron Source (SNS). Here we report the strain measurement results and radiation-resistance performance on the latest SNS mercury target vessel equipped with helium gas injection. The results have demonstrated the efficacy of gas injection to reduce the cyclic stress on the target module.

Disruption mitigation with high-pressure helium gas injection on EAST tokamak

High pressure noble gas injection is a promising technique to mitigate the effect of disruptions in tokamaks. In this paper, results of mitigation experiments with low-Z massive gas injection (helium) on the EAST tokamak are reported. A fast valve has been developed and successfully implemented on EAST, with valve response time ⩽150 μs, capable of injecting up to particles, corresponding to 300 times the plasma inventory.Different amounts of helium gas were injected into stable plasmas in the preliminary experiments. It is seen that a small amount of helium gas () can not terminate a discharge, but can trigger MHD activity. Injection of 40 times the plasma inventory impurity () can effectively radiate away part of the thermal energy and make the electron density increase rapidly. The mitigation result is that the current quench time and vertical displacement can both be reduced significantly, without resulting in significantly higher loop voltage. This also reduces the risk of runaway electron generation. As the amount of injected impurity gas increases, the gas penetration time decreases slowly and asymptotes to (∼7 ms). In addition, the impurity gas jet has also been injected into VDEs, which are more challenging to mitigate that stable plasmas.

Fractal characterization of pores in shales using NMR: A case study from the Lower Cambrian Niutitang Formation in the Middle Yangtze Platform, Southwest China

The fractal dimensions of the Lower Cambrian Niutitang Formation shales in the Middle Yangtze Platform, Southwest China were investigated for pore structure and fractal characteristics using low-field nuclear magnetic resonance (NMR) and N2 adsorption. The field emission scanning electron microscopy (FE-SEM), N2 and CO2 adsorption, NMR, porosity and permeability analysis were performed on six shale samples collected from outcrops. The NMR T2 distributions are consistent with the combination of pore size distributions from N2 and CO2 adsorption. The discrepancy of fractal dimensions between NMR and N2 adsorption resulting from the pore size distribution indicates that NMR fractal dimensions provide more accurate insight into the fractal characteristics of pore structure in shales than N2 adsorption fractal dimensions. The results show that the min(DNMR), with respect to the shorter relaxation times, reflects the roughness of the micropore surface area and the max(DNMR), with respect to the longer relaxation times, reflects pore volume for larger pores. The surface fractal dimension min(DNMR) has a positive correlation with TOC contents and thermal maturity, attributable to the conversion of kerogen and occurrence of organic matter pores. Min(DNMR) increases with increasing quartz content, while max(DNMR) increases with increasing clay content. The porosity from helium gas injection ranges from 2.8% to 6.7%, and permeability is between 3.55 and 6.62 × 10−2 mD. The min(DNMR) has a positive correlation with permeability, and the max(DNMR) exhibits a positive correlation with porosity, indicating that the volume fractal dimension max(DNMR) and surface fractal dimension min(DNMR) provide new indicators to measure porosity and permeability, respectively.

Experiments and numerical analysis of a control method for natural circulation through helium gas injection

This study investigated a control method for natural circulation of air by helium gas injection. A depressurization accident is a design-basis accident of a very high temperature reactor. When a primary pipe rupture accident occurs, air is expected to enter the reactor pressure vessel from the breach. Thus, in-core graphite structures are oxidized. In order to predict and analyze the phenomena of air ingress during a depressurization accident, numerical analysis was carried out using a one-dimensional (1D) analysis code and three-dimensional computational fluid dynamics (3D CFD). An experiment was carried out regarding natural circulation using a circular pipe consisting of a reverse U-shaped channel. The channel consisted of two vertical heated and cooled pipes. The temperature difference between the vertical pipes was maintained at 40–80K, and a small amount of helium gas was injected into the channel. The injected volume of helium was about 3.1–12.5% of the total channel volume. After injecting helium gas, each component gas moved through molecular diffusion and very weak natural circulation. After approximately 1180s, ordinary natural circulation of air was suddenly produced. The numerical results of the 3D CFD code were in good agreement with the experimental results. The numerical results also showed that the natural circulation of air can be controlled by helium gas injection.

鉛直流体層内の2成分気体混合過程に関する研究

The purpose of this study is to investigate the effect of natural convection and molecular diffusion on the mixing process under the stable density stratified fluid layer of two component gas. An experiment has been carried out to investigate a control method of natural circulation of air by injection of helium gas. The experimental apparatus consists of a reverse U-sharped vertical slot and a storage tank. The left side vertical slot consists of the heated wall and cooled wall. The right side vertical slot does not insert anything. Experimental results regarding mixing process of two component gases in vertical fluid layer were as follows. The heavy gas was transported to the slot by the molecular diffusion and natural convection. As time elapses, natural circulation of heavy gas suddenly occurs through the reverse U-shaped slot. As a result of experiments, the onset time of natural circulation is affected by not only molecular diffusion coefficient but also the strength of natural convection. When the helium gas is injected into the channel, it is possible to control the natural circulation of air. The onset time of the reproduction of the natural circulation can be varied by changing the injection rate of the helium gas.

Pyrochemical reprocessing of molten salt fast reactor fuel: focus on the reductive extraction step

Abstract The nuclear fuel reprocessing is a prerequisite for nuclear energy to be a clean and sustainable energy. In the case of the molten salt reactor containing a liquid fuel, pyrometallurgical way is an obvious way. The method for treatment of the liquid fuel is divided into two parts. In-situ injection of helium gas into the fuel leads to extract the gaseous fission products and a part of the noble metals. The second part of the reprocessing is performed by ‘batch’. It aims to recover the fissile material and to separate the minor actinides from fission products. The reprocessing involves several chemical steps based on redox and acido-basic properties of the various elements contained in the fuel salt. One challenge is to perform a selective extraction of actinides and lanthanides in spent liquid fuel. Extraction of actinides and lanthanides are successively performed by a reductive extraction in liquid bismuth pool containing metallic lithium as a reductive reagent. The objective of this paper is to give a description of the several steps of the reprocessing retained for the molten salt fast reactor (MSFR) concept and to present the initial results obtained for the reductive extraction experiments realized in static conditions by contacting LiF-ThF4-UF4-NdF3 with a lab-made Bi-Li pool and for which extraction efficiencies of 0.7% for neodymium and 14.0% for uranium were measured. It was concluded that in static conditions, the extraction is governed by a kinetic limitation and not by the thermodynamic equilibrium.

Influence of helium puff on divertor asymmetry in Experimental Advanced Superconducting Tokamak

Divertor asymmetries with helium puffing are investigated in various divertor configurations on Experimental Advanced Superconducting Tokamak (EAST). The outer divertor electron temperature decreases significantly during the gas injection at the outer midplane. As soon as the gas is injected into the edge plasma, the power deposition drops sharply at the lower outer target while increases gradually at the lower inner target in LSN configuration; the power deposition increases quickly at the upper outer target while remains unchanged at the upper inner target in upper single null configuration; the power deposition increases slightly at the outer targets while shows no obvious variation at the inner targets in double null configuration. The radiated power measured by the extreme ultraviolet arrays increases significantly due to helium gas injection, especially in the outer divertor. The edge parameters are measured by reciprocating probes at the outer midplane, showing that the electron temperature and density increase but the parallel Mach number decreases significantly due to the gas injection. Effects of poloidal E × B drifts and parallel SOL flows on the divertor asymmetry observed in EAST are also discussed.

A233 加圧水型原子炉の加圧器スプレー配管における温度変動現象の解明(OS2 保全設備診断技術(5))

Gas liquid interface is formed in a pressurizer spray pipe of a pressurized water reactor when flow rate is small at normal reactor operation. Temperature fluctuation may occur if the interface moves periodically. Measurement of inner wall and fluid temperature in the test section simulating the real pressurizer spray pipe was conducted to study mechanism of the temperature fluctuation phenomena. The effect of non-condensable gas was investigated by injecting helium gas into test section. When helium gas was injected, the condensation of the vapor was suppressed and the temperature fluctuation was reduced. Richardson number increases with the helium gas injection, which is higher than 0.25 in all conditions of the present experiment. Brunt Vaisala frequency nearly equal to the peak of temperature power spectral density. It seemed that the internal gravity waves caused temperature fluctuations in water layer below the interface.

Study on control method of natural circulation by injection of helium gas

This study is to investigate a control method of natural circulation of air by injection of helium gas. A depressurization accident is one of the design-basis accidents of a very high temperature reactor (VHTR). When the primary pipe rupture accident occurs in the VHTR, air is expected to enter into the reactor pressure vessel from the breach and oxidize in-core graphite structures. Finally, it seems to be probable that the natural circulation flow of air in the reactor pressure vessel produce continuously. In order to predict or analyze the air ingress phenomena during the depressurization accident of the VHTR, therefore, it is important to develop the method for prevention of air ingress during the accident. The experiment has been carried out regarding natural circulation using a circular tube consisting of a reverse U-shaped type. The vertical channel consists of the one side heated tube and the other side cooled tube. The experimental procedure is as follows. Firstly, the apparatus is filled with air and one vertical tube is heated. Then, natural circulation of air will be produced in the channel. After the steady state is established, a very small amount of helium gas injects from the top of the channel. The velocity, temperature of gas, and temperature of the tube wall are measured during the experiment. The analysis also has been carried out regarding natural circulation. The results were obtained as follows. The temperature difference between the vertical pipes was 50–130K, and a small amount of helium gas injected to the channel. The volume of injected helium gas is about 3.5–10% of the total volume of the channel. When the temperature difference between the vertical tubes was kept at 52K, the velocity of natural circulation flow became about 0.12m/s. During a steady state, a small amount of helium gas injected into the channel. Then, the flow velocity of natural circulation suddenly decreased. The volume of injected helium gas is about 3% of the total volume of the channel. The velocity became around zero. After 1500s elapsed, the natural circulation suddenly produced again. The experimental and analytical results show that the natural circulation flow of air can be controlled by injecting of helium gas.

パルス高速噴射によるセラミック膜形成

Coating techniques utilizing the collision and adhesion of microparticles on a substrate have recently been attracting attention. However, the bonding between particles deposited on the substrate at room temperature and atmospheric pressure is weak because the kinetic energy of particles during their collision with a substrate is small. The aim of this study is to form ceramic films under these conditions, which is considered difficult. Concretely, the pressurized gas at the surface of the workpiece to be processed is released by the pulsed injection of helium gas using alumina microparticles to form coatings, while preventing the collision speed of the alumina microparticles from decreasing. By pulsed gas injection for 5 min, we succeeded in forming 10-µm-thick alumina ceramic films with a hardness of approximately 40% of that of a sintered alumina body. The results of a friction wear experiment indicated that the coefficient of friction of the films was stable and low (0.15). In addition, the quenched steel balls used in the experiment were worn out, demonstrating that the formed films have good abrasion resistance and adhesion.

804 ヘリウムガスによる自然循環流の制御法に関する研究(G01-1 熱伝達I,G01 熱流体部門)

804 ヘリウムガスによる自然循環流の制御法に関する研究(G01-1 熱伝達I,G01 熱流体部門)

헬륨가스 주입식 유리섬유 냉각장치의 냉각성능 해석

A modern optical fiber manufacturing process requires the sufficient cooling of glass fibers freshly drawn from the heated and softened silica preform in the furnace, since the inadequately cooled glass fibers are known to cause improper polymer resin coating on the fiber surface and to adversely affect the product quality of optical fibers. In order to greatly enhance the fiber cooling effectiveness at increasingly high fiber drawing speed, it is necessary to use a dedicated glass fiber cooling unit with helium gas injection between glass fiber drawing and coating processes. The present numerical study features a series of three-dimensional flow and heat transfer computations on the cooling gas and the fast moving glass fiber to analyze the cooling performance of glass fiber cooling unit, in which the helium is supplied through the discretely located rectangular injection holes. The air entrainment into the cooling unit at the fiber inlet is also included in the computational model and it is found to be critical in determining the helium purity in the cooling gas and the cooling effectiveness on glass fiber. The effects of fiber drawing speed and helium injection rate on the helium purity decrease by air entrainment and the glass fiber cooling are also investigated and discussed.