An electrochemical hydrogen meter for measuring hydrogen in sodium using a ternary electrolyte mixture

An electrochemical sensor for measuring hydrogen concentration in liquid sodium that is based on a ternary mixture of LiCl, CaCl₂ and CaHCl as the electrolyte has been developed. DSC experiments showed the eutectic temperature of this ternary system to be ∼725 K. Impedance spectroscopic analysis of the electrolyte indicated ionic conduction through a molten phase at ∼725 K. Two electrochemical hydrogen sensors were constructed using the ternary electrolyte of composition 70 mol% LiCl:16 mol% CaHCl:14 mol% CaCl₂ and tested at 723 K in a mini sodium loop and at hydrogen levels of 60-250 ppb in sodium. The sensors show linear response in this concentration range and are capable of detecting a change of 10 ppb hydrogen in sodium over a background level of 60 ppb. Identification of this electrolyte system and its use in a sensor for measuring hydrogen in sodium are described in this paper.     

Experiments on Reactivity Balance as Malfunction Detector for Research Reactor

An amalgamation method is described for the determination of both hydroxide and non-hydroxide hydrogen in sodium. Using a mercury ejector pump and a Toepler pump, hydrogen (non-hydroxide hydrogen) liberated from sodium amalgam at 200°C under vacuum is collected and determined by gas chromatography. Then, the vessel containing the remaining sodium amalgam is filled with argon to a pressure of 600 mmHg and heated at 400°C under argon stream. The hydrogen (hydroxide hydrogen) collected is in the gas phase of a cold trap maintained at liquid nitrogen temperature, which condenses the argon but not hydrogen. The hydrogen thus collected is determined by gas chromatography. The detection limits for non-hydroxide and hydroxide hydrogen possible with this proposed method are 0.05 and 0.1 ppm in sodium, respectively.     

Analysis of Control Rod Effect on Neutronics in FBR by Three-Dimensional Calculation

Experiments were carried out to study the mass transfer of iodine from a xenon-iodine mixed gas bubble to a liquid sodium pool. The bubble was generated in the pool by cracking a quartz glass ball which contains the xenon-iodine mixed gas. The mixed gas released into the argon cover gas was collected to determine the transferred iodine mass into the sodium pool. A rising velocity of the bubble was measured by Chen-type sensors arranged vertically in the pool. From the measured rising velocity and another observation of bubble behavior in simulated water experiments, it is found that the generated bubble breaks up into several smaller bubbles of spherical cap type during the rising period. Transferred iodine mass per the unit initial bubble volume from the bubbles to the sodium pool shows increases with increasing time and the initial iodine concentration. A mass transfer rate obtained by differentiating the transferred iodine mass with respect to the time indicates a rapid decrease just after the bubble generation and a slow decrease for the successive period. Measured decontamination factors are described as a function of the time and the iodine concentration.     

Sodium Mist Behavior in Cover Gas Space of LMFBR Out-Pile Experiment

Sodium mist behavior in argon cover gas space over sodium pool was investigated experimentally using of a test vessel having cover gas volume of ～100l. Mass concentration and gravitational settling flux of the mist (i.e. sodium aerosol) were determined between pool temperature range of 290～520°C. Apparatuses used for the concentration determination were a He-Ne laser mist concentration meter (LCM) and mist traps, which were developed specifically for the present experiment. The mist gravitational settling flux φ was determined by using of collection plates, which were exposed to the mist entrained cover gas over sodium pool.

The experimental results revealed that the concentration C was very high from 0.15 to 20g/m³. It increased with pool temperature. The mist particle radii, which were determined from the gravitational settling flux φ and decay curve of the concentration, were from 1.5 to 13 μm in the range of the present experiment. The vapor evaporation rate φe from the pool surface, which were also determined from the experimental φ data, were found to increase with saturated vapor pressure P_s at pool surface. This rate did not depend so strongly on experimental geometries and cover gas flow convection pattern over sodium pool. Evaluations of transient C changing and steady state C fluctuation indicated that the mist formation was occurred near the pool surface.     

Influence of Microwave Power on the Properties of Hydrogenated Diamond-Like Carbon Films Prepared by ECR Plasma Enhanced DC Magnetron Sputtering

Electron cyclotron resonance (ECR) plasma was applied to enhance the direct current magnetron sputtering to prepare hydrogenated diamond-like carbon (H-DLC) films. For different microwave powers, both argon and hydrogen gas are introduced separately as the ECR working gas to investigate the influence of microwave power on the microstructure and electrical property of the H-DLC films deposited on P-type silicon substrates. A series of characterization methods including the Raman spectrum and atomic force microscopy are used. Results show that, within a certain range, the increase in microwave power affects the properties of the thin films, namely the sp3 ratio, the hardness, the nanoparticle size and the resistivity all increase while the roughness decreases with the increase in microwave power. The maximum of resistivity amounts to 1.1×109 Ωcm. At the same time it is found that the influence of microwave power on the properties of H-DLC films is more pronounced when argon gas is applied as the ECR working gas, compared to hydrogen gas.     

放射性氩气中一氧化碳和甲烷的分析

以1∶1模拟了正在建造的中国实验快堆的气体回路,建立了一个放射性氩气取样系统以及氩气中杂质CO和CH₄的间断性在线分析方法。通过热导检测器使出口气体可以排放入通风系统,避免了使用氢火焰离子化检测器以后,放射性氩气扩散排放到气体分析实验室产生工作环境的放射性污染问题。分析下限（φ）为5×10^-6,精密度好于3%,与标准值相差±5%。方法能满足中国实验快堆规定的氩气中杂质CO和CH₄的分析要求。     

Enhanced removal of X-ray-induced carbon contamination using radio-frequency Ar/H_2 plasma

Removal of X-ray-induced carbon contamination on beamline optics was studied using radio-frequency plasma with an argon/hydrogen(Ar/H_2) mixture. Experiments demonstrated that the carbon removal rate with Ar/H_2 plasma was higher than that with pure hydrogen or argon. The possible mechanism for this enhanced removal was discussed. The key working parameters for Ar/H_2 plasma removal were determined, including the optimal vacuum pressure, gas mixing ratio, and source power. The optimal process was performed on a carbon-coated multilayer, and the reflectivity was recovered.     

氧化锡气体传感器的电子束辐照效应

There are many traditional ways to improve sensitivity and selectivity of semiconductor gas sensors, such as metal ions adulteration and surface modification. In this paper 1.75 MeV electron beam was used to modify surface structure of tin dioxide gas sensors, and the gas sensing characteristics were studied. Results showed that the sensitivity and selectivity of SnO2 sensors were improved after the electron beam irradiation.     

Development of a hydrogen permeation sensor for future tritium applications

Tritium monitoring in lithium–lead eutectic is of great importance for the performance of liquid blankets in fusion reactors. In addition, tritium measurements will be required in order to proof tritium self-sufficiency in liquid metal breeding systems. On-line hydrogen (isotopes) sensors must be design and tested in order to accomplish these goals.In this work, an experimental set up was designed in order to test the permeation hydrogen sensors at 500 °C. This experimental set-up allowed working with controlled environments (different hydrogen partial pressures) and the temperature was measured using a thermocouple connected to a temperature controller that regulated an electrical heater.In a first set of experiments, a hydrogen sensor was constructed using an α-iron capsule as an active hydrogen area. The sensor was mounted and tested in the experimental set up. In a second set of experiments the α-iron capsule was replaced by a welded thin palladium disk in order to minimize the death volume. The experiments performed using both membranes (α-iron and palladium) showed that the operation of the sensors in the equilibrium mode required at least several hours to reach the hydrogen equilibrium pressure.     

金属钠蒸发行为研究#br#

钠的蒸发问题在钠冷快堆技术发展中不容忽视,钠蒸气将会引起众多钠冷快堆的运行问题。通过设计钠蒸发釜,搭建钠蒸发装置,对系列温度和压力下的钠蒸发速率进行了研究。经过大量实验,获得了温度200～550 ℃,氩气压力为5 Pa~51 MPa（a）下钠的蒸发速率。同时研究了蒸发面积、冷却面与钠液面距离对钠蒸发速率的影响。经过对实验数据拟合的结果表明,在同一压力下,钠的蒸发速率随温度的升高而呈指数升高,其变化规律符合Langmuir公式;在相同温度下,钠的蒸发速率随着氩气压力的升高呈对数下降,且与氩气压力自然对数的四项式相关;对于温度和压力的综合影响,得到了两个拟合关系式,该蒸发速率关系式能应用于5 Pa～51 MPa(a)、200～550 ℃范围内钠蒸发速率的预估。     

Effect of dilution gas composition on the evolution of graphite electrode characteristics in the spark gap switch

As the widely implemented electrode material, graphite has the characteristic of sublimation by the thermal shock of the switching arc, and the produced carbon vapor is easy to condense into carbon powders and deposit in the switch. The impact of the type of dilution gas in a mixture of20% oxygen and 80% dilution gas on the sublimation and oxidation characteristics of the graphite electrode is investigated. It is found that when nitrogen dilution gas was replaced by argon, the heat flux to the electrodes decreased, which led to a 63% reduction of graphite sublimation. At the same time, the cooling rate of the arc was slower in argon, which promotes oxidation of the carbon vapor. The residual solid carbon can be reduced by 70%–85% by using argon as the dilution gas. Consequently, it is demonstrated that the stability and working life of the switch could be increased by appropriate selection of the dilution gas.     

Liquid metal cooled fast breeder reactor development and its mechanical-structural requirements and problems

After a brief survey about the history and the present status of liquid metal cooled fast reactors the paper explains the specific properties of liquid sodium and the principal layout of sodium-cooled fast reactor plants. The most important mechanical-structural requirements and problems are broken down into fields of sodium containment, core structure, and special mechanisms to be operated in sodium and the cover gas atmosphere.     

Hydrogen Extraction Characteristics of Proton-conducting Ceramics under a Wet Air Atmosphere for a Tritium Stack Monitor

For the purpose of designing a tritium monitoring system combined with proton-conducting ceramics as a membrane separator, the hydrogen pump characteristics of CaZr_0.9In_0.1O_3–α proton-conducting ceramics were evaluated. In the experiments, argon gas containing 20.7% oxygen and 1.2% water vapor was fed to the anode at a rate of 47–137 ml/min at 600–800°C and an applied voltage until 3.5 V. The resulting hydrogen evolution rate reached maximally 0.67ml/min and the hydrogen recovery rate was 60%. However, the proton transport number decreased to 0.52 because the electron-hole current increased along with protonic current according to the defect equilibrium reaction occurring under a wet atmosphere containing oxygen. During operation, the hydrogen evolution rate fluctuates over time by at least 0.1 ml/min, which is approximately 20% of the hydrogen evolution rate. Additionally, the hydrogen evolution rate increased with an increase in the partial pressure of water vapor at the anode. It is important to design the tritium monitoring system taking into consideration the fluctuation in hydrogen evolution rate.     

Gas absorption and discharge behaviors of lead-lithium

The absorption of rare gas in the lead-lithium has been quite low and the gas is used as a cover-gas to control the environment of experiment. In our previous thermo-fluid experiment by using lithium-lead, it was found the cover gas pressure enclosed in the very leak tight container of lithium-lead was decreased with time, that is, the gas-absorption of the solid lithium-lead occurred at room temperature under atmospheric pressure. The variation of pressure exceeded the retention of argon in lead-lithium which is expected by the published data. Therefore, we aim to confirm those phenomena under well-controlled experimental condition by using argon, nitrogen and helium. According to the results of gas exposure tests, the absorption of argon in the lead-lithium is comparable with that of helium even at the solid state. For the molten state of lead-lithium, the absorption of argon could be larger than that of helium. It is also observed from the TPD-MS analysis that the argon tends to desorb when the phase change of lead-lithium occurs. If the retention of argon in the lead-lithium cannot be ignored, the problem of Ar-41 activity should be taken into consideration as well as the problem of argon bubble in the lead-lithium.     

An equilibrium and kinetic study of the liquid sodium-hydrogen reaction and its relevance to sodium-water leak detection in LMFBR systems

A detailed study of the thermodynamic and kinetic properties of the liquid sodium-hydrogen system has been made. The technique employed was to measure the rate of absorption to equilibrium of successive hydrogen additions by a vigorously stirred excess of liquid sodium (< 10 ppm dissolved oxygen) in an isothermal, constant volume, stainless steel (316) reaction vessel in the temperature range 610–677 K. The results have been used to estimate the variation of hydrogen pressure with time for a given, steady, water leak rate into the argon gas blanket above the liquid sodium level in a secondary heat exchanger of an LMFBR, and also to calculate solution rates of hydrogen bubbles (formed from a sodiumwater reaction under the liquid sodium surface) as a function of initial bubble radius.     

Comparative Observation of Ar, Ar-H2 and Ar-N2 DC Arc Plasma Jets and Their Arc Root Behaviour at Reduced Pressure

Results observed experimentally are presented, about the DC arc plasma jets and their arc-root behaviour generated at reduced gas pressure without or with an applied magnetic field. Pure argon, argon-hydrogen or argon-nitrogen mixture was used as the plasma-forming gas. A specially designed copper mirror was used for a better observation of the arc-root behaviour on the anode surface of the DC non-transferred arc plasma torch. It was found that in the cases without an applied magnetic field, the laminar plasma jets were stable and approximately axisymmetrical. The arc-root attachment on the anode surface was completely diffusive when argon was used as the plasma-forming gas, while the arc-root attachment often became constrictive when hydrogen or nitrogen was added into the argon. As an external magnetic field was applied, the arc root tended to rotate along the anode surface of the non-transferred arc plasma torch.     

Exothermic hydrogen production system in supercritical water from biomass and usual domestic wastes with an exploitation of RuO2 catalyst

This paper deals with a method of producing hydrogen from biomass and sewage disposals in supercritical water by use of ruthenium dioxides as a catalyst. Experiments were carried out under argon atmosphere with a batch reactor made of INCONEL625. Reaction temperatures and pressures were changed in the ranges of 400–500 °C and 30–50 MPa, respectively. The gas produced was quantitatively analyzed by on-line gas chromatography. In conclusion, considerably high ratios of hydrogen up to 38.5% were produced from the sewage disposals. This value was even higher than the hydrogen production ratios from other biomass: 15.0% from cellulose, 14.1% from pulp, 16.0% from waste paper, and 27.0% from paper sludge. The heat balance was calculated in the present reaction system using ruthenium oxide as the catalyst in supercritical water for the reaction of naphthalene and cellulose. The result showed that the total reaction was exothermic. This is rather surprising, because most of the hydrogen forming reactions are endothermic. The present result should be due to the excess heat derived by the partial formation of carbon dioxide.     

DN300钠阀冷冻密封腔室的分析与设计

钠阀的冷冻密封腔室是一个重要的部件,直接关系到钠阀是否会发生泄漏。本文以大口径钠阀的国产化项目为依托,对冷冻密封腔室进行分析与设计。冷冻密封腔室是一个狭小的空间,内部有氩气、液态钠、凝固钠。本文利用FLUENT的冷凝模型结合氩气的基本气体方程,计算冷冻密封腔室内部钠的冷凝情况,确定凝固钠的位置;在此基础上,利用FLUENT计算得到的温度和文献中钠剪切力与温度的关系式,分析钠固封塞的受力情况。最终确定冷冻密封腔室加工尺寸为1.5 mm,钠固封塞高度为197 mm。     

Effect of Barriers on Sodium Mist Deposition on LMFBR Components

Tests were made to evaluate the effect of two barriers (a convection barrier and a drip receiver) against sodium mist deposition on LMFBR conponents in the cover gas space. Two models of LMFBR rotating shield plugs (1,800 mm in height, 680 and 850 mm in diameter) and a sodium test tank were manufactured for this purpose, and the mist deposition rate on the walls of these models was measured both in the cases with and without a barrier. The sodium pool temperature during the test was 580°C. In parallel with these tests, the relation between the form of deposit and the wall temperature was examined to determine the critical wall temperature above which deposits do not accumulate. This was conducted by exposing a vertical stainless steel cylinder to cover gas entrained with mist over 500°C sodium for 30 to 1,000 h.

The test results revealed that the barriers functioned effectively, and they reduced the local deposition rate near top of the annulus by three orders of magnitude relative to the cases without a barrier. The critical wall temperature to avoid deposit accumulation was found to be 100 to 150°C.     

Electrochemical techniques for monitoring dissolved carbon, hydrogen and oxygen in liquid sodium

Potential chemical problems associated with the use of liquid sodium as a coolant for fast reactors have led to the need for special analytical techniques, in particular, for dissolved carbon, hydrogen and oxygen. Consideration of the chemical monitoring requirements involved shows methods based on electrochemical cells to be particularly suitable. After a summary of the relevant background phenomena, the development and operational experience of specific electrochemical carbon, hydrogen and oxygen meters are described.