Removal Path Research Articles

Analysis of SBO ATWS for Maanshan PWR

AbstractStation blackout anticipated transient without scram (SBO ATWS) is considered as loss of off-site and on-site power but no credit for automatic reactor trip. SBO ATWS causes reactor coolant pump (RCP) trip, loss of all main feedwater pumps and turbine trip, then the reactor coolant system (RCS) pressure rises rapidly due to loss of heat removal paths. The ASME Code Level C service limit criteria of 22.06 MPa (3200 psig) is assumed to be an unacceptable plant condition in SECY-83-293. The simulation is performed by TRACE which is a thermal-hydraulic code developed by U.S. NRC. Three different AFW flows are modeled to ensure the pressures will not be beyond the criteria. RCP seal-leakage is concerned as a SBLOCA due to loss of RCP seal-cooling. Four possible leakage flows are modeled to examine the reactor core water level and temperature variation.

A quality controlled laser-chemical process for micro metal machining

A laser-chemical process combines advantages of both laser ablation and electro-chemical machining and is used to produce free form micro forming tools. The desired geometry results from a sequence of overlapping removal paths with different cross section. Due to the high requirements of geometry accuracy and surface roughness, a three-level quality control system is developed for this process. Based on causal analysis between removal profile and process parameters a post-process controller designs the position and cross section for the removal paths. With an in situ quality control loop the deviation from the desired removal profile along the feed direction could be compensated by using a state observer and an interferometer. At an in-process level the required process parameters are real time observed and controlled.

Clinical application of surface projection in the localization of metal foreign bodies using computed tomography scan.

To analyse the clinical efficacy of surface projection in the localization and removal of metal foreign bodies using CT scan. Total 795 cases with 1008 metal foreign bodies were treated at our hospital in 2012. Pre-operative surface projection was performed to localize foreign bodies in patients under the guidance of CT scan. The removal path from the skin surface to foreign body and puncture site were then determined. Finally, the foreign bodies were extracted using proper foreign body forceps which were chosen according to the size, depth and position of the foreign bodies in different parts of the human body. The incision length, operative time and intraoperative blood loss were recorded. Additionally, outpatient follow-up was scheduled post-operatively for 1 week. The accurate localization rate under the guidance of CT scan was 100%, and 1008 pieces of metal foreign bodies were all successfully removed with a removal rate of 100%. The mean incision length was 0.4 ± 0.1 cm, the mean operative time was 4.1 ± 2.0 min and the intraoperative blood loss was 1.1 ± 0.5 ml. These results showed minimal invasiveness, shorter operative time and minimal blood loss, respectively. Additionally, the results of outpatient follow-up showed that the wound healed spontaneously. Moreover, there were no significant bleeding, incision infections or complications. Surface projection may be an accurate and effective method for the pre-operative localization and extraction of metal foreign bodies. (1) Surface projection was applied for localization of metal foreign bodies in our study. (2) The accurate localization rate of surface projection under the guidance of CT scan was 100%. (3) All foreign bodies were successfully removed with a removal rate of 100%. (4) Surface projection technique has advantages in the removal of foreign bodies.

Recording the Tilt of a Cast on a Surveyor.

Some patients are not satisfied with removable partial dentures (RPDs), when it is not stable during mastication.A dental surveyor can be used to prevent problems related to production of RPDs. Determining the best path of insertion and removal is an initial and fundamental step in RDPs planning. The path of insertion record enables the technician to reproducing the cast in the same position on a surveyor that the dentist selected. This article describes new method for this purpose that could be useful for recording and reproducing the tilt of casts.

Atmospheric reactions of methylcyclohexanes with Cl atoms and OH radicals: determination of rate coefficients and degradation products.

As the result of biogenic and anthropogenic activities, large quantities of chemical compounds are emitted into the troposphere. Alkanes, in general, and cycloalkanes are an important chemical class of hydrocarbons found in diesel, jet and gasoline, vehicle exhaust emissions, and ambient air in urban areas. In general, the primary atmospheric fate of organic compounds in the gas phase is the reaction with hydroxyl radicals (OH). The oxidation by Cl atoms has gained importance in the study of atmospheric reactions because they may exert some influence in the boundary layer, particularly in marine and coastal environments, and in the Arctic troposphere. The aim of this paper is to study of the atmospheric reactivity of methylcylohexanes with Cl atoms and OH radicals under atmospheric conditions (in air at room temperature and pressure). Relative kinetic techniques have been used to determine the rate coefficients for the reaction of Cl atoms and OH radicals with methylcyclohexane, cis-1,4-dimethylcyclohexane, trans-1,4-dimethylcyclohexane, and 1,3,5-trimethylcyclohexane at 298 ± 2K and 720 ± 5Torr of air by Fourier transform infrared) spectroscopy and gas chromatography-mass spectrometry (GC-MS) in two atmospheric simulation chambers. The products formed in the reaction under atmospheric conditions were investigated using a 200-L Teflon bag and employing the technique of solid-phase microextraction coupled to a GC-MS. The rate coefficients obtained for the reaction of Cl atoms with the studied compounds are the following ones (in units of 10(-10)cm(3)molecule(-1)s(-1)): (3.11 ± 0.16), (2.89 ± 0.16), (2.89 ± 0.26), and (2.61 ± 0.42), respectively. For the reactions with OH radicals the determined rate coefficients are (in units of 10(-11)cm(3)molecule(-1)s(-1)): (1.18 ± 0.12), (1.49 ± 0.16), (1.41 ± 0.15), and (1.77 ± 0.23), respectively. The reported error is twice the standard deviation. A detailed mechanism for ring-retaining product channels is proposed to justify the observed reaction products. The global tropospheric lifetimes estimated from the reported OH- and Cl-rate coefficients show that the main removal path for the investigated methylcyclohexanes is the reaction with OH radicals. But in marine environments, after sunrise, Cl reactions become more important in the tropospheric degradation. Thus, the estimated lifetimes range from 16 to 24h for the reactions of the OH radical (calculated with [OH] = 10(6)atomscm(-3)) and around 7-8h in the reactions with Cl atoms in marine environments (calculated with [Cl] = 1.3 × 10(5)atomscm(-3)). The reaction of Cl atoms and OH radicals and methylcylohexanes can proceed by H abstraction from the different positions.

N2O5 uptake coefficients and nocturnal NO2 removal rates determined from ambient wintertime measurements

Heterogeneous N2O5 uptake onto aerosol is the primary nocturnal path for removal of NOx (= NO + NO2) from the atmosphere and can also result in halogen activation through production of ClNO2. The N2O5 uptake coefficient has been the subject of numerous laboratory studies; however, only a few studies have determined the uptake coefficient from ambient measurements, and none has been focused on winter conditions, when the portion of NOx removed by N2O5 uptake is the largest. In this work, N2O5 uptake coefficients are determined from ambient wintertime measurements of N2O5 and related species at the Boulder Atmospheric Observatory in Weld County, CO, a location that is highly impacted by urban pollution from Denver, as well as emissions from agricultural activities and oil and gas extraction. A box model is used to analyze the nocturnal nitrate radical chemistry and predict the N2O5 concentration. The uptake coefficient in the model is iterated until the predicted N2O5 concentration matches the measured concentration. The results suggest that during winter, the most important influence that might suppress N2O5 uptake is aerosol nitrate but that this effect does not suppress uptake coefficients enough to limit the rate of NOx loss through N2O5 hydrolysis. N2O5 hydrolysis was found to dominate the nocturnal chemistry during this study consuming ~80% of nocturnal gas phase nitrate radical production. Typically, less than 15% of the total nitrate radical production remained in the form of nocturnal species at sunrise when they are photolyzed and reform NO2.

Control of decay heat removal through alternate system in PFBR

In the Prototype Fast Breeder Reactor (PFBR) decay heat is removed directly from the reactor core through Safety Grade Decay Heat Removal (SGDHR) circuit. Operation Grade Decay Heat Removal (OGDHR) system offers an alternate decay heat removal path using the heat removal capacity of the main heat transport system. It is preferred path during planned shutdown and also during plant upset conditions when at least one secondary sodium system, steam water system and offsite power are available. Besides removing the decay heat, this system decreases the reactor coolant temperature at a controlled rate and it is able to maintain the plant at cold shutdown condition for fuel handling or maintenance for up to 30 days. This alternate decay heat removal system of PFBR is described in the paper along with system dynamics, analysed based on in-house developed thermal hydraulics code, sequence of the system deployment, system operation and control.

해파리 퇴치용 자율 수상 로봇의 설계 및 구현

Recently, the number of jellyfish has been rapidly grown because of the global warming, the increase of marine structures, pollution, and etc. The increased jellyfish is a threat to the marine ecosystem and induces a huge damage to fishery industries, seaside power plants, and beach industries. To overcome this problem, a manual jellyfish dissecting device and pump system for jellyfish removal have been developed by researchers. However, the systems need too many human operators and their benefit to cost is not so good. Thus, in this paper, the design, implementation, and experiments of autonomous jellyfish removal robot system, named JEROS, have been presented. The JEROS consists of an unmanned surface vehicle (USV), a device for jellyfish removal, an electrical control system, an autonomous navigation system, and a vision-based jellyfish detection system. The USV was designed as a twin hull-type ship, and a jellyfish removal device consists of a net for gathering jellyfish and a blades-equipped propeller for dissecting jellyfish. The autonomous navigation system starts by generating an efficient path for jellyfish removal when the location of jellyfish is received from a remote server or recognized by a vision system. The location of JEROS is estimated by IMU (Inertial Measurement Unit) and GPS, and jellyfish is eliminated while tracking the path. The performance of the vision-based jellyfish recognition, navigation, and jellyfish removal was demonstrated through field tests in the Masan and Jindong harbors in the southern coast of Korea.

PHOTOCHEMISTRY IN TERRESTRIAL EXOPLANET ATMOSPHERES. I. PHOTOCHEMISTRY MODEL AND BENCHMARK CASES

We present a comprehensive photochemistry model for exploration of the chemical composition of terrestrial exoplanet atmospheres. The photochemistry model is designed from the ground up to have the capacity to treat all types of terrestrial planet atmospheres, ranging from oxidizing through reducing, which makes the code suitable for applications for the wide range of anticipated terrestrial exoplanet compositions. The one-dimensional chemical transport model treats up to 800 chemical reactions, photochemical processes, dry and wet deposition, surface emission and thermal escape of O, H, C, N and S bearing species, as well as formation and deposition of elemental sulfur and sulfuric acid aerosols. We validate the model by computing the atmospheric composition of current Earth and Mars and find agreement with observations of major trace gases in Earth's and Mars' atmospheres. We simulate several plausible atmospheric scenarios of terrestrial exoplanets, and choose three benchmark cases for atmospheres from reducing to oxidizing. The most interesting finding is that atomic hydrogen is always a more abundant reactive radical than the hydroxyl radical in anoxic atmospheres. Whether atomic hydrogen is the most important removal path for a molecule of interest also depends on the relevant reaction rates. We also find that volcanic carbon compounds (i.e., CH4 and CO2) are chemically long-lived and tend to be well mixed in both reducing and oxidizing atmospheres, and their dry deposition velocities to the surface control the atmospheric oxidation states. Furthermore, we revisit whether photochemically produced oxygen can cause false positives for detecting oxygenic photosynthesis, and find that in 1-bar CO2-rich atmospheres oxygen and ozone may build up to levels that have been previously considered unique signatures of life, if there is no surface emission of reducing gases...

The effect of aeration position on the spatial distribution and reduction of pollutants in the landfill stabilization process – a pilot scale study

Three pilot-scale simulators with different aeration systems were constructed to explore the effects of aeration position on the reduction of pollutants. The simulator with a bottom aeration system successfully distributed oxygen and efficiently inhibited methane production. A close relationship was found between the oxygen distribution and the removal of pollutants, especially that of nitrogen. The transition between nitrification and denitrification in the longitude direction of the simulator with a bottom aeration system contributed to nitrogen removal in aerobic conditions. This process can be defined as a new path for nitrogen removal in addition to simultaneous nitrification and denitrification. The concentration of NH4+ -N total nitrogen and total organic carbon dropped to 3, 78 and 204 mg L(-1), respectively, after 312 days of bottom aeration and to 514, 659 and 828 mg L(-1), respectively, after 312 days of top aeration. These results indicate that the bottom aeration system was more efficient for reducing pollutants than the top aeration system.

Decay heat removal in pool type fast reactor using passive systems

Post shutdown decay heat removal in a fast reactor is one of the most important safety functions which must be accomplished with a very high reliability. To achieve high reliability, the fast breeder reactor design has emphasized on passive or near passive decay heat removal systems utilizing the natural convection in the heat removal path. A typical passive decay heat removal system used in recent designs of fast breeder reactors consists of a sodium to sodium heat exchanger and sodium to air heat exchanger which together remove heat directly from the hot pool to the final heat sink, which is air. Since these are safety systems, it is necessary to confirm the design with detailed numerical analysis. The numerical studies include pool hydraulics, natural convection phenomena in closed loops, flow through narrow gaps between SA, multi-scale modeling, etc. Toward understanding the evolution of thermal hydraulic parameters during natural convection decay heat removal, a three-dimensional CFD model for the primary system coupled with an appropriate one-dimensional model for the secondary system is proposed. The model has been validated against the results of natural convection test conducted in PHENIX reactor. Adopting the model for the Indian PFBR, six different decay heat removal cases have been studied which bring out the effect of safety grade decay heat removal system (SGDHRS) capacity, secondary sodium inventory and inter-wrapper flow heat transfer on the subassembly outlet temperatures that are important for safety evaluation of the reactor. From the results, it is concluded that the delay in initiation of SGDHRS, replacement of intermediate sodium in SGDHRS with NaK and a decrease in the AHX air inlet temperature do not change the temperatures of the primary circuit significantly. The secondary sodium inventory plays an important role in reducing the temperatures in the primary coolant. The beneficial effect of inter-wrapper flow heat transfer on primary temperatures is limited to about 20K in the fissile zone and 50K in the blanket zone. These results are very important and give direction for future designs of fast breeder reactors.

Calcium Influx Rescues Adenylate Cyclase-Hemolysin from Rapid Cell Membrane Removal and Enables Phagocyte Permeabilization by Toxin Pores

Bordetella adenylate cyclase toxin-hemolysin (CyaA) penetrates the cytoplasmic membrane of phagocytes and employs two distinct conformers to exert its multiple activities. One conformer forms cation-selective pores that permeabilize phagocyte membrane for efflux of cytosolic potassium. The other conformer conducts extracellular calcium ions across cytoplasmic membrane of cells, relocates into lipid rafts, translocates the adenylate cyclase enzyme (AC) domain into cells and converts cytosolic ATP to cAMP. We show that the calcium-conducting activity of CyaA controls the path and kinetics of endocytic removal of toxin pores from phagocyte membrane. The enzymatically inactive but calcium-conducting CyaA-AC− toxoid was endocytosed via a clathrin-dependent pathway. In contrast, a doubly mutated (E570K+E581P) toxoid, unable to conduct Ca2+ into cells, was rapidly internalized by membrane macropinocytosis, unless rescued by Ca2+ influx promoted in trans by ionomycin or intact toxoid. Moreover, a fully pore-forming CyaA-ΔAC hemolysin failed to permeabilize phagocytes, unless endocytic removal of its pores from cell membrane was decelerated through Ca2+ influx promoted by molecules locked in a Ca2+-conducting conformation by the 3D1 antibody. Inhibition of endocytosis also enabled the native B. pertussis-produced CyaA to induce lysis of J774A.1 macrophages at concentrations starting from 100 ng/ml. Hence, by mediating calcium influx into cells, the translocating conformer of CyaA controls the removal of bystander toxin pores from phagocyte membrane. This triggers a positive feedback loop of exacerbated cell permeabilization, where the efflux of cellular potassium yields further decreased toxin pore removal from cell membrane and this further enhances cell permeabilization and potassium efflux.

Surface ozone scenario at Pune and Delhi during the decade of 1990s

Data on surface ozone concentration compiled for a 10-year period from 1990 to 1999 for Pune and Delhi are analyzed in terms of its frequency distribution, annual trend, diurnal variation and its relation with various meteorological and chemical parameters. It is found that the surface ozone concentration range showing highest frequency of occurrence at Pune is 0–5 ppb during winter and post-monsoon seasons and 15–20 ppb and 5–10 ppb during summer and monsoon seasons, respectively. It is 0–5 ppb at Delhi during all the seasons. The surface ozone concentration has shown a decreasing trend at Pune during the observational period with an average rate of decrease of 1.54 ppb/year. On the other hand, there is no trend whatsoever in the variation of surface ozone concentration at Delhi. Minimum value of surface ozone occurs before sunrise and maximum in the afternoon hours. Regression analyses of surface ozone with maximum temperature (r = 0.46 for Pune and 0.51 for Delhi, significant at more than 0.1%) and NO2 at respective locations indicate that surface ozone at these locations is mainly produced by photochemistry. Transport mechanism is also understood to have contributed significantly to the total concentration of ozone. Inverse relationship obtained between surface ozone concentration and relative humidity indicates that major photochemical paths for removal of ozone become effective when humidity increases at these locations.

Field-structured magnetic platelets as a route to improved thermal interface materials

The development of high-performance thermal interface materials (TIMs) is crucial to enabling future generations of microelectronics because the TIM is usually the limiting thermal resistance in the heat removal path. Typical TIMs achieve modest thermal conductivities by including large volume fractions of randomly-dispersed, highly-conductive, spherical particles in a polymer resin. This paper explores field-structured magnetic platelet composites as a new approach to more effective TIMs. The motivation for this approach is rooted in shape functional theory, which shows that when the particle material has a significantly higher thermal conductivity than that of the polymer, the particle shape and orientation are the factors that limit conductivity enhancement. Oriented platelets are highly effective for heat transfer and if these are magnetic, then magnetic fields can be used to both orient and agglomerate these into structures that efficiently direct heat flow. In this paper we show that such field-structured composites have a thermal conductivity anisotropy of ∼3, and at the highest particle loading of 16 vol.% we have achieved a 23-fold conductivity enhancement, which is 3-times larger than that achieved in unstructured platelet composites and 8-times greater than unstructured spherical particle composites.

Removal and transformation of hexavalent chromium in sequencing batch reactor

The objectives of this study are to evaluate the efficiency of removal of hexavalent chromium (Cr(VI)) in a sequencing batch reactor (SBR) and to ascertain the fate of Cr(VI) in the treatment process. An SBR was operated with the FILL, REACT, SETTLE, DRAW and IDLE periods in the time ratio of 2:12:2:1.5:6.5 for a cycle time of 24 h. The study was divided into 5 phases with the addition of 0.5, 2.0, 3.0 and 5.0 mg/l of Cr(VI) in Phases II, III, IV and V for a duration of 46, 75, 43 and 16 operational cycles, respectively. The Cr(VI) removal efficiencies for SBR were found to be 79.8, 88.4 and 99.8% in Phases III, IV and V, respectively. The results revealed that Cr(VI) removal efficiency improved with acclimated activated sludge. Determination of Cr in the suspended sludge showed that around 95% of the Cr species were Cr(III). Determination of Cr concentration profiles during the FILL and REACT periods showed that the predominant species was Cr(III) as Cr(VI) was bio-reduced. The proposed Cr(VI) removal mechanism involves bioreduction to Cr(III) which was subsequently precipitated and adsorbed by activated sludge. Precipitation rather than sorption is envisaged to be the main path of removal of Cr(III) from the solution. Keywords: Sequencing batch reactor, hexavalent chromium, removal, transformation, mechanism

Design and evaluation of Operation Grade Decay Heat Removal System of PFBR

The decay heat removal (DHR) system removes the decay heat generated (by radioactive decay of fission products) in the core after the reactor is shut down, thereby ensuring proper cooling of the core sub assemblies and limiting main vessel, internals and sodium temperature within safe limits. There are two diverse paths for removal of decay heat from the reactor, namely, Safety Grade Decay Heat Removal System (SGDHRS) and Operation Grade Decay Heat Removal System (OGDHRS). OGDHR circuit is used when at least one secondary sodium loop, DHR related steam water circuit and off site power supply is available and SGDHR circuit is used when OGDHR system is not available or when both the secondary loops are not available for DHR. This paper provides brief details of the design and evaluation of OGDHRS.

Species Invasion as Catastrophe: The Case of the Brown Tree Snake

This paper develops a two-stage model for the optimal management of a potential invasive species. The arrival of an invasive species is modeled as an irreversible event with an uncertain arrival time. The model is solved in two stages, beginning with the post-invasion stage. Once the arrival occurs, the optimal path of species removal is that which minimizes the present value of damage and removal costs plus the expected present value of prevention costs. An expenditure-dependent, conditional hazard rate describing species arrival is developed based on discussions with natural resource managers. We solve for the optimal sequence of prevention expenditures, given the minimum invasion penalty as just described. For the case of the Brown Tree Snake potentially invading Hawaii, we find that pre-invasion expenditures on prevention are inverse U-shaped in the hazard rate. Efficient prevention should be approximately $2.9 million today and held constant until invasion. Once invasion occurs, optimal prevention requires $3.1 million annually and $1.6 million per year on species removal to keep the population at its steady state level, due to high search costs at very small population levels.

Photochemical Oxidation Removal of NO and SO2 from Simulated Flue Gas of Coal-Fired Power Plants by Wet Scrubbing Using UV/H2O2 Advanced Oxidation Process

Photochemical oxidation removal of NO and SO2 from simulated flue gas of coal-fired power plants by wet scrubbing using UV/H2O2 advanced oxidation process was studied in a semicontinuous and small-scale ultraviolet (UV)-bubble column reactor with different conditions, including UV, H2O2 concentration, solution initial pH value, solution temperature, and liquid layer height. The results show that under all conditions studied, the SO2 is removed completely. The UV has an obvious impact on NO removal efficiency. With the increase of H2O2 concentration or liquid layer height, the NO removal efficiency greatly increases at first, and then the growth rate of NO removal efficiency gradually become smaller. The NO removal process is enhanced by the solution initial pH value, but it is inhibited by the solution temperature. The gaseous and liquid reaction products are determined using ion chromatography and gas analyzer, respectively. The removal path of NO and SO2 are also preliminarily discussed.

Performance Evaluation of Preemption Algorithms in MPLS Networks

Preemption is a traffic engineering technique in Multiprotocol Switching Networks that enables creation of high priority paths when there is not enough free bandwidth left on the route. Challenging part of any preemption method is to select the best set of paths for removal. Several heuristic methods are available but no wider comparison had been published before. In this paper, we discuss the dilemmas in implementing preemption methods and present the simulation study of well known existing algorithms. Based on the results, we provide recommendations for deployment of preemption for the two most common evaluation criteria: number of preemptions and preempted bandwidth.

Simultaneous Removal of SO2 and NOx by Calcium Hydroxide at Low Temperature: Effect of SO2 Absorption on NO2 Removal

A fixed reactor was employed to investigate the influence of SO2 absorption process on NO2 removal by Ca(OH)2 under low-temperature and humid circumstance. The step experiments and pretreatment experiments were carried out to investigate the effect of the desulfurization product CaSO3 on NO2 removal. The roles of gas components (O2, H2O) and reaction temperature in SO2 enhancing NO2 removal were discussed by comparing their influences on NO2 removal in and without the presence of SO2. It is interesting to observe that NOx removal first increases and then decreases with the increase of SO2 concentration. The presence of SO2 in the flue gas was found to restrain NO release and enhance NO2 removal. SO2 removal product CaSO3 did provide an additional reaction path for NO2 removal, but the reaction rate of NO2 and CaSO3 was lower than that of Ca(OH)2 due to the lower solubility of CaSO3. The enhancement effect of SO2 on NO2 removal can be explained by the presence of SO32− and HSO3− ions derived from the hydro...