Corrosion Behaviors of Structural Materials in Liquid Gallium and Gallium Alloy Environments for Nuclear Application

Interdisciplinary School of Green EnergyLiquid Metal Fast Breeder Reactor (LMFBR) is one of promising candidates among Gen IV nuclear energy systems. Among liquid metal, sodium is a spotlighted coolant material for designing fast breeder reactor. However, high activity of sodium with water and air is the major disadvantage that forces to search for alternatives. On the other aspects, the liquid metal including gallium generally interacts with structural materials, and it may cause Liquid-Metal-Embrittlement (LME) to materials in certain condition. The purpose of this work is to examine the interaction between steels and liquid gallium or gallium alloys to evaluate the potential application of gallium for fast reactor coolants. In fact, gallium could be a good candidate for use as a liquid metal in the field of GEN IV nuclear system since it has low melting point (29??C), high boiling point (2204??C) and high safety against explosion. However, gallium has a high affinity for many metals and alloys, especially steels. For the prevention of liquid gallium corrosion with stainless steels, an active control of oxygen partial pressure which has been extensively studied for lead-bismuth corrosion could be adopted in this gallium environment. The liquidus of gallium alloy (Ga-14Sn-6Zn and Ga-8Sn-6Zn) is 26??C and 19.5??C, respectively. Simultaneously, neutron absorption cross-section is reduced by these alloy process. In this study, SS 316L and pre-oxidized specimens were exposed to static gallium and gallium alloys (Ga-14Sn-6zn and Ga-8Sn-6Zn) at 500??C for time up to 700 hr both in air and vacuum conditions (5x10-6 torr). The results have shown that the corrosion resistance of pre-oxidized specimens was improved compared to bare specimens in metal loss data. The weight change and metal loss were generally reduced in vacuum condition and also in gallium alloy environments. General behavior of developing reaction layer within the effect of pre-oxidation was that pre-oxidized specimens, in any conditions, had developed as thick as reaction layers on bare specimens.ope

A Study on Corrosion Behaviors of Ferritic/Martensitic Steels in Liquid Sodium Condition for Sodium-cooled Fast Reactor Application

Department of Nuclear EngineeringResearch purpose is the study on corrosion of Gr. 92 steel (ferritic/martensitic steel) with liquid sodium for advanced nuclear reactors application. Moreover, development of new measurement methods of oxygen and carbon dissolved in sodium has been carried in this study. In this study, ASTM A182 Grade 92 steel was exposed to liquid sodium at 650??C in order to investigate surface oxidation and corrosion behavior as well as microstructure changes, especially production of precipitates. Comparisons were made to the same material exposed to argon gas at 650??C. In sodium-exposed specimens, intergranular oxidation and chromium depletion were observed at the near surface by an electron probe micro analyzer (EPMA) used for elemental analysis. The chromium, oxygen, and sodium X-ray images overlapped, indicating NaCrO2 oxidation. Since, the carbon image overlapped on NaCrO2 oxide, the carbon was trapped in the oxide. The chromium image shows the chromium-depleted zone. With the argon-exposed specimen, however, this behavior at the surface was not observed. Different types of precipitates in the Gr.92 steel matrix were observed. At the interface between the Cr-depleted zone and the bulk steel matrix in specimens exposed to 650??C liquid sodium showed mainly M23C6 carbide, while specimens in the bulk steel matrixes which exposed to 650??C sodium as well as argon showed mainly a M2(W,Mo) phase. These differences may be mainly a result of oxidation (NaCrO2) and chromium depletion, and presumably decarburization observed in the sodium-exposed specimens, which are different from the precipitate behavior in the case of the bulk steel matrix in sodium as well as argon-exposed specimens. Non-metallic elements, such as carbon, oxygen, and nitrogen in sodium have a large effect on the mechanical behavior and corrosion rates of materials in the primary and secondary coolant heat transport system in sodium-cooled fast reactors (SFRs). Austenitic Fe-18%Cr-8%Ni foil and ferritic Fe foil were equilibrated at 550??C sodium. After the equilibration, the concentration of carbon in the foils was analyzed by carbon analyzer (Leco). The carbon activity in liquid sodium was calculated. Also the thermodynamic activity of carbon in ferrite iron (Fe-C alloy) were calculated in the temperature range of 682 - 848??C. An equilibrium method using ferrite iron steel has been developed to measure the activity of carbon in liquid sodium. The results obtained are discussed and a new expression is proposed relating carbon activity with the composition of steel. The thermodynamics of carbide equilibrium in the steel are discussed by characterizing the carbide phase. These data have been analyzed using regular solution model for the carbide phase, Fe3C and based on this observed composition of Fe3C as well as the variation of the carbon potential of steel with temperature have been explained.ope

Are Histrionic Personality Traits Associated with Irritability during Conscious Sedation Endoscopy?

Aim. We aimed to evaluate whether histrionic personality traits are associated with irritability during conscious sedation endoscopy (CSE). Materials and Methods. A prospective cross-sectional study was planned. Irritability during CSE was classified into five grades: 0, no response; I, minimal movement; II, moderate movement; III, severe movement; IV, fighting against procedure. Patients in grades III and IV were defined as the irritable group. Participants were required to complete questionnaire sheet assessing the extent of histrionic personality traits, extraversion-introversion, and current psychological status. The present authors also collected basic sociodemographic data including alcohol use history. Results. A total of 32 irritable patients and 32 stable patients were analyzed. The histrionic personality trait score of the irritable group was higher than that of the stable group (9.5 ± 3.1 versus 6.9 ± 2.9; P = 0.001), as was the anxiety score (52.8 ± 8.6 versus 46.1 ± 9.6; P = 0.004). Heavy alcohol use was more frequently observed in the irritable group (65.6% versus 28.1%; P = 0.003). In multivariate analysis, all these three factors were independently correlated with irritability during CSE. Conclusion. This study revealed that histrionic personality traits, anxiety, and heavy alcohol use can affect irritability during CSE

Anomaly detection of aircraft engine in FDR (flight data recorder) data

This paper deals with detection of anomalous behaviour of aircraft engines in FDR (flight data recorder) data to improve airline maintenance operations. To this end, each FDR data that records different flight patterns is first sampled at a fixed time interval starting at the take-off phase, in order to map each FDR data into comparable data space. Next, the parameters related to the aircraft engine are only selected from the sampled FDR data. In this analysis, the feature points are chosen as the mean value of each parameter within the sampling interval. For each FDR data, the feature vector is then formed by arranging all feature points. The proposed method compares the feature vectors of all FDR data and detects an FDR data in which the abnormal behaviour of the aircraft engine is recorded. The clustering algorithm called DBSCAN (density-based spatial clustering of applications with noise) is applied for this purpose. In this paper, the proposed method is tested using realistic FDR data provided by NASA's open database. The results indicate that the proposed method can be used to automatically identify an FDR data in which the abnormal behaviour of the aircraft engine is recorded from a large amount of FDR data. Accordingly, it can be utilized for a high-level diagnosis of engine failure in airline maintenance operations

Energy-optimal waypoint-following guidance considering autopilot dynamics

This paper addresses the problem of energy-optimal waypoint-following guidance for an Unmanned Aerial Vehicle with the consideration of a general autopilot dynamics model. The proposed guidance law is derived as a solution of a linear quadratic optimal control problem in conjunction with a linearized kinematics model. The algorithm developed integrates path planning and following into a single step and is able to be applied to a general waypoint-following mission. Theoretical analysis reveals that previously suggested optimal point-to-point guidance laws are special cases of the proposed approach. Nonlinear numerical simulations clearly demonstrate the effectiveness of the proposed formulations

A new multiple flights routing and scheduling algorithm in terminal manoeuvring area

We address multiple flights planning problems from its initial waypoint to its destination while satisfying the minimum separation requirement between each aircraft at all times in a Terminal Manoeuvring Area (TMA) to maintain or increase runway throughput. Due to operational constraints for safety, most of the current aircraft fly over or by waypoints, and along nominal routes in the airspace. Where the waypoints and routes in the airspace can be modelled as a weighted digraph, called airspace graph. We propose a problem that consists of determining a flight path (routing problem) and its speed profile (scheduling problem) in a given airspace graph in which a time-based weighting scheme of the airspace graph is proposed to reflect a speed-limitation-compliant schedule that satisfy the minimum separation requirement. For multiple flights cases, the flight paths and schedules are obtained by iteratively solving the problem for each flight by applying the First Come First Served (FCFS) algorithm to determine an arrival sequence. The main contributions of this paper are increasing a solution search space by solving two problems simultaneously, efficient computational time, and providing the separation-compliant flight path and speed profile within the speed limitation for each flight. We demonstrate the advantages of the proposed approach through a case study in which multiple flights arrive at a single airport, and we compare the results with Regulated Tactical Flight Model (RTFM) obtained from EUROCONTROL Demand Data Repository 2 (DDR2). Although, we consider only a single airport and make an assumption to simplify flight routes from holding stacks to a Final Approach Fix (FAF), the results show the potential usage of the proposed algorithm as a Decision Support Tool (DST) for Air Traffic Controllers (ATCOs) if the following considerations are taken into account: detailed routes-based flights after the holding stacks, multiple airports, departing aircraft, all possibe aircraft types, and uncertainties produced by external sources

Nonlinear acceleration controller for exo-atmospheric and endo-atmospheric interceptors with TVC

In this paper, we propose a nonlinear acceleration controller that can be used for both the endo- and exo-atmospheric interceptors with thrust vector control (TVC) without changing the control configuration. The acceleration perpendicular to the velocity vector is selected as the output to be controlled. Then apply the feedback linearization and the specific form of the desired error dynamics to create the resulting controller which is given by the well-known three loop control structure with parameter-varying control gains. According to changes in altitude operating conditions, the proposed controller can adaptively allocate the aerodynamic force and the thrust to produce the required normal acceleration. Also, we can have confidence in the reliability of the proposed controller because it is given by a similar form of the well-known three loop controller. Numerical simulations are performed to show the validity of the proposed method

A new command shaping guidance law using Lagrange multiplier

This article presents a new command shaping guidance law by change of Lagrange multiplier (LM), called CSGL-LM. The Schwarz inequality approach is used to solve the optimal guidance problems considering both terminal constraints on interception and impact angle control. LM is introduced to combine two terminal constraints into a single equation. The main idea of this paper is to use LM as a design parameter for shaping the guidance command as well as controlling the terminal constraints. The guidance command of CSGL-LM is given a unified functional form of the time-to-go, the state variables, and LM. Therefore, through an appropriate choice of LM, we can achieve various shapes of the guidance commands for the interception case, as well as the impact angle control case. As illustrative examples, this paper also shows that a class of previous guidance laws is just one of particular solutions of CSGL-LM. Numerical simulations are performed to validate the properties of CSGL-LM, compared with the conventional guidance law

FLUIDIZATION TECHNOLOGY FOR STABLE STARTUP OF COMMERCIAL FCC UNIT

Conditions for maintaining good fluidization in the start-up of FCC have been determined. Catalyst defluidization and consequent catalyst losses from reactor cyclone are mainly affected by catalyst properties and stripper operating condition based on previous commercial startup experiences. Effect of fine catalyst contents on bed fluidity was determined. Bed fluidity in stripper was analyzed with slip velocity. Finally new startup guide was proposed and it was successfully applied to commercial FCC process of SK energy, Korea