bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Salicylic Acid on Salinity‐induced Changes in Brassica juncea
Authors: Yusuf Mohammad , Hasan Syed Aiman , Ali Barket , Hayat Shamsul , Fariduddin Qazi , Ahmad Aqil
Published: September 2008

Seeds of Indian mustard (Brassica juncea (L.) Czern. et Coss.) were exposed to 0, 50, 100 and 150 mmol/L NaCl for 8 h and seeds were sown in an earthen pot. These stressed seedlings were subsequently sprayed with 10 μmol/L salicylic acid (SA) at 30 d and were sampled at 60 d to assess the changes in growth, photosynthesis and antioxidant enzymes. The seedlings raised from the seeds treated with NaCl had significantly reduced growth and the activities of carbonic anhydrase, nitrate reductase and photosynthesis, and the decrease was proportional to the increase in NaCl concentration. However, the antioxidant enzymes (catalase, peroxidase and superoxide dismutase) and proline content was enhanced in response to NaCl and/or SA treatment, where their interaction had an additive effect. Moreover, the toxic effects generated by the lower concentration of NaCl (50 mmol/L) were completely overcome by the application of SA. It was, therefore, concluded that SA ameliorated the stress generated by NaCl through the alleviated antioxidant system.
Arabidopsis Indole Synthase, a Homolog of Tryptophan Synthase Alpha, is an Enzyme Involved in the Trp‐independent Indole‐containing Metabolite Biosynthesis
Authors: Zhang Rui , Wang Bing , Ouyang Jian , Li Jiayang , Wang Yonghong
Published: September 2008

The plant tryptophan (Trp) biosynthetic pathway produces many secondary metabolites with diverse functions. Indole‐3‐acetic acid (IAA), proposed as a derivative from Trp or its precursors, plays an essential role in plant growth and development. Although the Trp‐dependant and Trp‐independent IAA biosynthetic pathways have been proposed, the enzymes, reactions and regulatory mechanisms are largely unknown. In Arabidopsis, indole‐3‐glycerol phosphate (IGP) is suggested to serve as a branchpoint component in the Trp‐independent IAA biosynthesis. To address whether other enzymes in addition to Trp synthase α (TSA1) catalyze IGP cleavage, we identified and characterized an indole synthase (INS) gene, a homolog of TSA1 in Arabidopsis. INS exhibits different subcellular localization from TSA1 owing to the lack of chloroplast transit peptide (cTP). In silico data show that the expression levels of INS and TSA1 in all examined organs are quite different. Histochemical staining of INS promoter‐GUS transgenic lines indicates that INS is expressed in vascular tissue of cotyledons, hypocotyls, roots and rosette leaves as well as in flowers and siliques. INS is capable of complementing the Trp auxotrophy of Escherichia coliΔtrpA strain, which is defective in Trp synthesis due to the deletion of TSA. This implies that INS catalyzes the conversion of IGP to indole and may be involved in the biosynthesis of Trp‐independent IAA or other secondary metabolites in Arabidopsis.
Invisible Americans: Migration, Transnationalism, and the Politics of Difference in HIV/AIDS Research
Authors: Sangaramoorthy Thurka
Published: September 2008

Using the scholarship on transnationalism and citizenship, this paper examines the politics of difference in HIV/AIDS prevention programmes in the United States and their impact on Haitian migrants and immigrants. It finds that there is a tremendous amount of complex movement of knowledge production and expertise among various constituents who work in the field of HIV/AIDS, and these individuals circulate ideas and technologies of HIV/AIDS across different fields in multiple ways. Through these circulations, information about HIV/AIDS becomes entangled in the debates about relevant knowledge bases, and as a result, questions over culture and modernity. This paper traces how such discourses become framed under the rubric of risk and difference and operate at the level of situated experience. Through ethnographic fieldwork observations and interviews, this paper argues that notions of individual responsibility in HIV/AIDS risk management often become inseparable from notions of racial, ethnic and immigrant identity.
Contesting Ethnicity: Emerging Regional Identity in Vojvodina
Authors: Dragojević Mila
Published: September 2008

This case study of the northern Serbian Province of Vojvodina explores the basis of regional shared group understandings in the absence of ethnic difference between the majority in the region and the center. It addresses the question of whether there is an emerging regional identity in Vojvodina within the political elite discourse at the time of the passage of the Omnibus Law in 2002, which devolved part of autonomy that the Province had lost following the 1991 Constitution. The method of content analysis was employed to uncover the collective sense of social purpose (i.e. desire for greater autonomy) and the shared views toward groups perceived as ‘others’. The findings show that the principal supporters of autonomy are the center‐based civic‐oriented parties, as well as the regional parties. On the other hand, the opposition to autonomy comes from the center‐based nationalist parties.
Low expression of Kv7/M channels facilitates intrinsic and network bursting in the developing rat hippocampus
Authors: Safiulina Victoria F. , Zacchi Paola , Taglialatela Maurizio , Yaari Yoel , Cherubini Enrico
Published: September 2008

Early in development, network activity in the hippocampus is characterized by recurrent synchronous bursts, whose cellular correlates are giant depolarizing potentials (GDPs). The propensity for generating GDPs is attributed to GABAergic synaptic transmission being depolarizing and excitatory in neonatal neurons. However, developmental regulation of intrinsic conductances may also influence GDPs generation. A likely candidate is the non‐inactivating, low‐threshold, muscarinic‐sensitive K+current (M current;Im), which down‐regulates intrinsic bursting activity in adult hippocampal pyramidal neurons. Western blot analysis of homogenates of the CA3 hippocampal region showed that expression of the Kv7.2 subunit, one of the constituents of neuronal M channels, is weak in neonatal neurons, and markedly increases after the first postnatal week. Likewise, the density ofImwas very low in neonatal CA3 pyramidal cells and increased later on. Spontaneously occurring intrinsic bursts in neonatal neurons were longer and more robust, and recurred more regularly, than in juvenile neurons. TheImblocker linopirdine only mildly affected intrinsic bursting in neonatal neurons, but strongly facilitated and regularized it in juvenile neurons. We conclude that the low expression of Kv7/M channels and the depolarizing action of GABA early after birth enhance intrinsic bursting and neuronal synchronization leading to generation of GDPs within the hippocampal network.
Gating of human ClC‐2 chloride channels and regulation by carboxy‐terminal domains
Authors: Garcia‐Olivares Jennie , Alekov Alexi , Boroumand Mohammad Reza , Begemann Birgit , Hidalgo Patricia , Fahlke Christoph
Published: September 2008

Eukaryotic ClC channels are dimeric proteins with each subunit forming an individual protopore. Single protopores are gated by a fast gate, whereas the slow gate is assumed to control both protopores through a cooperative movement of the two carboxy‐terminal domains. We here study the role of the carboxy‐terminal domain in modulating fast and slow gating of human ClC‐2 channels, a ubiquitously expressed ClC‐type chloride channel involved in transepithelial solute transport and in neuronal chloride homeostasis. Partial truncation of the carboxy‐terminus abolishes function of ClC‐2 by locking the channel in a closed position. However, unlike other isoforms, its complete removal preserves function of ClC‐2. ClC‐2 channels without the carboxy‐terminus exhibit fast and slow gates that activate and deactivate significantly faster than in WT channels. In contrast to the prevalent view, a single carboxy‐terminus suffices for normal slow gating, whereas both domains regulate fast gating of individual protopores. Our findings demonstrate that the carboxy‐terminus is not strictly required for slow gating and that the cooperative gating resides in other regions of the channel protein. ClC‐2 is expressed in neurons and believed to open at negative potentials and increased internal chloride concentrations after intense synaptic activity. We propose that the function of the ClC‐2 carboxy‐terminus is to slow down the time course of channel activation in order to stabilize neuronal excitability
A New Three-Dimensional Exponential Material Model of the Coronary Arterial Wall to Include Shear Stress Due to Torsion
Authors: Van Epps J. Scott , Vorp David A.
Published: September 2008

The biomechanical milieu of the coronary arteries is unique in that they experience mechanical deformations of twisting, bending, and stretching due to their tethering to the epicardial surface. Spatial variations in stresses caused by these deformations could account for the heterogeneity of atherosclerotic plaques within the coronary tree. The goal of this work was to utilize previously reported shear moduli to calculate a shear strain parameter for a Fung-type exponential model of the arterial wall and determine if this single constant can account for the observed behavior of arterial segments under torsion. A Fung-type exponential strain-energy function was adapted to include a torsional shear strain term. The material parameter for this term was determined from previously published data describing the relationship between shear modulus and circumferential stress and longitudinal stretch ratio. Values for the shear strain parameter were determined for three geometries representing the mean porcine left anterior descending coronary artery dimensions plus or minus one standard deviation. Finite element simulation of triaxial biomechanical testing was then used to validate the model. The mean value calculated for the shear strain parameter was 0.0759±0.0009 (N=3 geometries). In silico triaxial experiments demonstrated that the shear modulus is directly proportional to the applied pressure at a constant longitudinal stretch ratio and to the stretch ratio at a constant pressure. Shear moduli determined from these simulations showed excellent agreement to shear moduli reported in literature. Previously published models describing the torsional shear behavior of porcine coronary arteries require a total of six independent constants. We have reduced that description into a single parameter in a Fung-type exponential strain-energy model. This model will aid in the estimation of wall stress distributions of vascular segments undergoing torsion, as such information could provide insight into the role of mechanical stimuli in the localization of atherosclerotic plaque formation.
A Phantom Tissue System for the Calibration of Perfusion Measurements
Authors: Mudaliar Ashvinikumar V. , Ellis Brent E. , Ricketts Patricia L. , Lanz Otto I. , Scott Elaine P. , Diller Thomas E.
Published: September 2008

A convenient method for testing and calibrating surface perfusion sensors has been developed. A phantom tissue model is used to simulate the nondirectional blood flow of tissue perfusion. A computational fluid dynamics (CFD) model was constructed in Fluent® to design the phantom tissue and validate the experimental results. The phantom perfusion system was used with a perfusion sensor based on clearance of thermal energy. A heat flux gage measures the heat flux response of tissue when a thermal event (convective cooling) is applied. The blood perfusion and contact resistance are estimated by a parameter estimation code. From the experimental and analytical results, it was concluded that the probe displayed good measurement repeatability and sensitivity. The experimental perfusion measurements in the tissue were in good agreement with those of the CFD models and demonstrated the value of the phantom tissue system.
Effect of Laser Welding on Formability of DP980 steel
Authors: Sreenivasan N. , Xia M. , Lawson S. , Zhou Y.
Published: September 2008

Limiting dome height (LDH) tests were used to evaluate the formability of laser butt welded blanks of the dual phase 980 steel in comparison with the base metal. Two different lasers were used: diode and Nd:YAG, giving a wide range of welding thermal cycles. A sharp decrease in LDH was observed in the welded specimens due to the formation of a softened zone in the outer heat affected zone. Softened zone characteristics were correlated with the LDH. Larger softened zones led to a larger reduction in the LDH. The welding orientation relative to the rolling direction or to the punch surface did not influence the formability, as the softened zone dominated the formability behavior. It was observed that in both uniaxial and biaxial strain tests, the fracture occurred in the softened zone of the welded samples consistently slightly farther out from the weld centerline than in the location of the minimum hardness.
Development of a Multiaxial Fatigue Damage Model for High Strength Alloys Using a Critical Plane Methodology
Authors: Erickson Matthew , Kallmeyer Alan R. , Van Stone Robert H. , Kurath Peter
Published: September 2008

The prediction of fatigue life for metallic components subjected to complex multiaxial stress states is a challenging aspect in design. Equivalent-stress approaches often work reasonably well for uniaxial and proportional load paths; however, the analysis of nonproportional load paths brings forth complexities, such as the identification of cycles, definition of mean stresses, and phase shifts, that the equivalent-stress approaches have difficulties in modeling. Shear-stress based critical-plane approaches, which consider the orientation of the plane on which the crack is assumed to nucleate, have shown better success in correlating experimental results for a broader variety of load paths than equivalent-stress models. However, while the interpretation of the ancillary stress terms in a critical-plane parameter is generally straightforward within proportional loadings, there is often ambiguity in the definition when the loading is nonproportional. In this study, a thorough examination of the variables responsible for crack nucleation is presented in the context of the critical-plane methodology. Uniaxial and multiaxial fatigue data from Ti–6Al–4V and three other alloys, namely, Rene’104, Rene’88DT, and Direct Age 718, are used as the basis for the evaluation. The experimental fatigue data include axial, torsional, proportional, and a variety of nonproportional tension/torsion load paths. Specific attention is given to the effects of torsional mean stresses, the definition of the critical plane, and the interpretation of normal stress terms on the critical plane within nonproportional load paths. A new modification to a critical-plane parameter is presented, which provides a good correlation of experimental fatigue data.
Numerical Simulations and Experimental Results of Tensile Test Behavior of Laser Butt Welded DP980 Steels
Authors: Panda S. K. , Sreenivasan N. , Kuntz M. L. , Zhou Y.
Published: September 2008

Laser welding of advanced high strength steels for fabrication of tailor welded blanks is of increasing interest for continued improvements in vehicle performance and safety without an increase in weight. Experimental results have shown that formability of welded dual-phase (DP) steels is significantly reduced by the formation of a softened region in the heat-affected zone (HAZ). In this study, a finite element simulation of welded DP980 samples undergoing transverse uniaxial tensile testing was used to evaluate the effects of soft zone width and strength on formability characteristics. Both the strength and the ductility of laser welded blanks decreased compared with those of unwelded blanks due to the formation of a softened outer-HAZ, where strain localization and final fracture occurred during tensile testing. The magnitude of softening and the width of the HAZ depend on the laser specific energy. It was observed from tensile test experiments and numerical simulations that both a decrease in strength and an increase in width of the softened HAZ were responsible for a decrease in the overall strength and ductility of the welded blanks.
Low-Dimensional Sagittal Plane Model of Normal Human Walking
Authors: Srinivasan S. , Raptis I. A. , Westervelt E. R.
Published: September 2008

This paper applies a robotics-inspired approach to derive a low-dimensional forward-dynamic hybrid model of human walking in the sagittal plane. The low-dimensional model is derived as a subdynamic of a higher-dimensional anthropomorphic hybrid model. The hybrid model is composed of models for single support (SS) and double support (DS), with the transition from SS to DS modeled by a rigid impact to account for the impact at heel-contact. The transition from DS to SS occurs in a continuous manner. Existing gait data are used to specify, via parametrization, the low-dimensional model that is developed. The primary result is a one-degree-of-freedom model that is an exact subdynamic of the higher-dimensional anthropomorphic model and describes the dynamics of walking. The stability properties of the model are evaluated using the method of Poincaré. The low-dimensional model is validated using the measured human gait data. The validation demonstrates the observed stability of the measured gait.
A Dynamic Analytical Model for Impact Evaluation of Percutaneous Implants
Authors: Swain R. , Faulkner G. , Raboud D. , Wolfaardt J.
Published: September 2008

The ongoing need for a clinically effective noninvasive technique for monitoring implant stability has led to a number of testing methods based on the concept of resonant frequency. Resonant frequency measurements are an indirect measure of the bone-implant interface integrity and do not provide any specific measures of the physical properties of the interface itself. In this study, an analytical model has been developed to interpret the measurement results of an impact testing method based on the Periotest® handpiece. Model results are compared to a variety of in vitro tests to verify model predictions and to gain an understanding of the parameters influencing the measurements. Model simulations are then used to predict how changes in the supporting stiffness properties, material loss around the neck of the implant, and the presence of an implant flange will affect the measurements. The developed analytical model, in conjunction with the impact measurements, allows direct estimation of the bone properties that support implants. Model simulations show the impact testing technique to be sensitive to bone loss and stiffness changes that would correspond to poorly integrated implants (ones which may be in danger of failing). Similarly, for implants with very stiff support, little useful quantitative data can be obtained about the bone supporting the implant, as the stiffness of the other components of the system dominate the response. However, such implants are generally considered healthy.
Investigations on Hydrogen Distribution and Mitigation Measures in the Containment Under Severe Accident
Authors: Xiao Jian-Jun , Zhou Zhi-Wei , Jing Xing-Qing
Published: September 2008

During severe accident oxidation of the metallic components of the reactor core and the core-concrete interaction will produce hydrogen which may threaten the integrity of the containment. It is important to predict hydrogen transport and mixing in the containment, in order to determine whether the mixture can locally reach flammability limits, and install the hydrogen mitigation devices at a reasonable and suitable position. Several turbulence models in FLUENT and GASFLOW were adopted in this paper to investigate hydrogen transport and mixing in the containment, and the results were compared. The study indicates that RNG k–ε model can obtain better simulation in parameter fluctuation, velocity field, and hydrogen concentration field than the other models’. The results calculated by algebraic model in GASFLOW are largely different from the other results in the simulation of mass diffusion, momentum diffusion, and parameter fluctuation. The results of k–ε model in GASFLOW have the similar trend as the results of FLUENT in velocity field and concentration field. Three hydrogen mitigation measures were also studied in a simple closed room using the code GASFLOW. The results indicate that the combination of recombiners and igniters is a safe and effective way to reduce the risk of hydrogen combustion.
Corrosion Behaviour Inconel 617 in VHTR Environment
Authors: Kaczorowski Damien , Chapovaloff J.
Published: September 2008

As it was observed in the past Gas Cooled Reactors, it is expected that the VHTR’s cooling gas will be polluted by air ingresses, in-leakages or the degassing of adsorbed species out of the large amount of graphite. These impureties are reactive and may interact with the core graphite and with the metallic materials and may cause some loss or damage of their properties.
Nuclear Safety Risk Management in Refueling Outage of Qinshan Nuclear Power Plant
Authors: Wu Meijing , Shen Guozhang
Published: September 2008

The NPP is used to planning maintenance, in-service inspection, surveillance test, fuel handling and design modification in the refueling outage; the operator response capability will be reduced plus some of the plant systems out of service or loss of power at this time. Based on 8 times refueling outage experiences of the Qinshan NPP, this article provide some good practice and lesson learned for the nuclear safety risk management focus at four safety function areas of Residual Heat Removal Capability, Inventory Control, Power availability and Reactivity control.
Stress Intensity Factors for a Crack Emanating Non-Radially From a Circular Hole Under Arbitrary Loading
Authors: Sheng Simon C. F.
Published: September 2008

Stress intensity factors are found for a crack emanating from a circular hole in an elastic solid which is in a state of plane deformation resulting from loads applied at infinity or pressure applied internally at the faces of the crack and the hole. The results, including Mode-I (opening) and Mode-II (shearing) stress intensity factors, are obtained numerically by means of a dislocation model which conveniently allows for general loading and, consequently, can easily handle the case where a crack emanates non-radially from a hole. Good agreement is found with published values for the special case when the crack is radial and the loading consists of remote tension and uniform pressure at the surface of the hole. Also included in the present paper are results for the case when both the hole and the crack are pressurized. Although the subject elastic solid is an infinite medium, the results of this paper serve as good estimates when the hole is relatively small in a finite component and is distant from the component edge. Since in most circumstances a real crack does not orient itself radially from a hole, this paper provides analysts information to decide whether Mode-II fracture needs to be considered in assessing the structural integrity of a component with a hole. Similarly, when the problem is 3-dimensional, the results of this paper imply that Mode-III (tearing) fracture may also need to be considered.
Bolted Flanged Connection for Critical Plant/Piping Systems
Authors: Efremov Anatoly
Published: September 2008

A novel type of Bolted Flanged Connection with bolts and gasket manufactured on a basis of advanced Shape Memory Alloys is examined. Presented approach combined with inverse flexion flange design of plant/piping joint reveals a significant increase of internal pressure under conditions of a variety of operating temperatures relating to critical plant/piping systems.
Deep Atomic Binding (DAB) Hypothesis: A New Approach of Fission Product Chemistry
Authors: Ajlouni Abdul-Wali M. S.
Published: September 2008

Former studies assumed that, after fission process occurs, the highly ionized new born atoms (20–22 positive charge), ionize the media in which they pass through before becoming stable atoms in a manner similar to 4-MeV-particles. Via ordinary chemical reactions with the surroundings, each stable atom has a probability to form chemical compound. Since there are about 35 different elemental atoms created through fission processes, a large number of chemical species were suggested to be formed. But, these suggested chemical species were not found in the environment after actual releases of FP during accidents like TMI (USA, 1979), and Chernobyl (former USSR, 1986), also the models based on these suggested reactions and species could not interpret the behavior of these actual species. It is assumed here that the ionization states of the new born atoms and the long term high temperature were not dealt with in an appropriate way and they were the reasons of former models failure. Our new approach of DEEP ATOMIC BINDING (DAB) based on the following: 1. The new born atoms which are highly ionized, 10–12 electrons associated with each nucleus, having a large probability to create bonds between them to form molecules. These bonds are at the L, or M shells, and we call it DAB. 2. The molecules stay in the reactor at high temperatures for long periods, so they undergo many stages of composition and decomposition to form giant molecules. By applying DAB approach, field data from Chernobyl, TMI and nuclear detonations could be interpreted with a wide coincidence resulted.
Deep Atomic Binding (DAB) Approach in Interpretation of Fission Pruducts Behavior in Human Body, and Health Consequences
Authors: Ajlouni Abdul-Wali M. S.
Published: September 2008

According to models used to predict health effects of fission products enter the human body, a large number of fatalities, malignancies, thyroid cancer, born (genetic) defects, ...etc.. But the actual data after Chernobyl and TMI accidents, and nuclear detonations in USA and Marshal Islands, were not consistent with these models. According to DAB, these data could be interpreted, and conflicts between former models predictions and actual field data explained.
ACR-1000 Passive Features
Authors: Lekakh B. , Hau K. , Ford S.
Published: September 2008

The Advanced CANDU Reactor™ (ACR™) is a Generation III+ pressure tube type reactor using light water coolant and heavy water moderator. The ACR-1000 reactor design is an evolutionary extension of the proven CANDU reactor design. The ACR-1000 incorporates multiple and diverse passive systems for accident mitigation. Where necessary, one or more features that are passive in nature have been included for mitigation of any postulated accident event. This paper describes how the use of passive design elements complements active features enhances reliability and improves safety margins.
RELAP5-SCDAP RIA Type Tests Model
Authors: Negut Gheorghe , Prisecaru Ilie , Danila Nicolae
Published: September 2008

Extended tests on fuel behavior in Reactivity Initiated Accidents type were carried out in the Annular Core Pulse Reactor (ACPR). The tests were performed in a specially designed capsule filled with 7 liters of water at atmospheric pressure and at temperature of 25 C. The fuel specimen is of CANDU design with 10 fuel pellets and 10% U235 enrichment. The tests aimed to establish the clad failure threshold. Over 40 tests were carried out. The fuel behavior during the transient was modeled with the RELAP5-SCDAP computer code. Clad temperatures recorded during the tests were compared with clad temperatures predicted by the RELAP-SCDAP code. Some tests in ACPR in RIA conditions are presented. The paper includes recorded temperatures compared with the RELAP-SCDAP calculations, as well as the RELAP SCDAP models. Put abstract text here.
Treatment of Uncertainties: Output Updating in Complex Thermal-Hydraulics (TH) Computational Codes
Authors: Pourgol-Mohamad Mohammad , Mosleh Ali , Modarres Mohammad
Published: September 2008

Uncertainty analysis methodology in complex system models requires a comprehensive treatment of many different types and sources of uncertainty sources. Proposed methodology as part of a broader research by the authors for an integrated methodology for uncertainty analysis of TH computational codes, allows updating of uncertainties upon availability of new information about inputs, models or output. This methodology is a statistical approach for output-based updating, with non-paired data. The proposed method employs a Gibbs MCMC sampler to estimate output distribution. Winbugs code was developed to implement the Bayesian solution proposed in this paper. The methodology is applied to the data from 200% cold leg LBLOCA test of LOFT facility [4].
Influence of Low Boron Core Design on PWR Transient Behavior
Authors: Papukchiev Angel Aleksandrov , Liu Yubo , Schaefer Anselm
Published: September 2008

In conventional pressurized water reactor (PWR) designs, the concentration of boron in primary coolant is limited by the requirement of having a negative moderator density coefficient. As high boron concentrations have significant impact on reactivity feedback properties, design changes to reduce boron concentration in the reactor coolant are of general interest in view of improving PWR inherent safety. In the framework of an investigation into the feasibility of low boron design, a PWR core configuration based on fuel with higher gadolinium (Gd) content has been developed which permits to reduce the natural boron concentration at begin of cycle (BOC) by approx. 50% compared to current German PWR technology. For the assessment of the potential safety advantages, a Loss-of-Feedwater Anticipated Transient Without Scram (ATWS LOFW) has been simulated with the system code ATHLET for two PWR core designs: a low boron design and a standard core design. The most significant difference in the transient performance of both designs is the total primary fluid mass released through the pressurizer (PRZ) valves. It is reduced by a factor of four for the low boron reactor, indicating its improved density reactivity feedback.
Investigation of Swirling Flow in Rod Bundle Subchannels Using Computational Fluid Dynamics
Authors: Holloway Mary V. , Beasley Donald E. , Conner Michael E.
Published: September 2008

The fluid dynamics for turbulent flow through rod bundles representative of those used in pressurized water reactors is examined using computational fluid dynamics (CFD). The rod bundles of the pressurized water reactor examined in this study consist of a square array of parallel rods that are held on a constant pitch by support grids spaced axially along the rod bundle. Split-vane pair support grids are often used to create swirling flow in the rod bundle in an effort to improve the heat transfer characteristics for the rod bundle during both normal operating conditions and in accident condition scenarios. Computational fluid dynamics simulations for a two subchannel portion of the rod bundle were used to model the flow downstream of a split-vane pair support grid. A high quality computational mesh was used to investigate the choice of turbulence model appropriate for the complex swirling flow in the rod bundle subchannels. Results document a central swirling flow structure in each of the subchannels downstream of the split-vane pairs. Strong lateral flows along the surface of the rods, as well as impingement regions of lateral flow on the rods are documented. In addition, regions of lateral flow separation and low axial velocity are documented next to the rods. Results of the CFD are compared to experimental particle image velocimetry (PIV) measurements documenting the lateral flow structures downstream of the split-vane pairs. Good agreement is found between the computational simulation and experimental measurements for locations close to the support grid.
Oxygen Transport in Liquid Lead Bismuth Eutectic Filled Cavity by Natural Convection
Authors: Tan Xianfang , Chen Yitung , Tan Taide , Chen Huajun
Published: September 2008

This paper numerically analyzes the oxygen transport in an active oxygen controlled lead-bismuth eutectic (LBE) system. Corrosion in near wall areas and oxide-layer formations on container surfaces are included. Simulations are carried out on a simplified rectangle container. Different temperature boundary conditions are added to the container to induce pure natural-convection LBE flows. The strength of the flows is measured by the Rayleigh number (Ra). Three laminar cases: (a) heated from the bottom and cooled from the top of the container; (b) heated from the sidewalls and cooled from the top of the container; (c) one sidewall heated and the opposite wall cooled, and one fully turbulent case with one sidewall heated and the opposite sidewall cooled are selected and analyzed in detail. In each case, the characteristic velocity and oxygen diffusion time are estimated, the change of oxygen distribution with time are obtained, and the bulk concentration of oxygen and the efficiency of oxide layer formation on different liquid-solid interfaces are calculated. Based on the analysis, several conclusions are finally obtained.
Hydrogen: The Fuel That Drill Bits Cannot Reach
Authors: Miller Alistair I. , Duffey Romney B.
Published: September 2008

As realization grows of the damaging cumulative effects of CO2 on our biosphere, the prospect of substituting hydrogen for oil-based fuels attracts growing attention. Japan provides a leading example of remedial action with the expectation of five million fuel-cell-powered vehicles in operation by 2020. But where will the fuel for these and the rest of a “Hydrogen Age” come from? The hydrogen market used to be straightforward: small-scale or high-purity markets were supplied relatively expensively by electrolysis; the other 95% was supplied much more cheaply by reforming hydrocarbons — mostly using steam-methane reforming (SMR) and low-cost natural gas. The recent rise in the price of hydrocarbons — natural gas as well as oil — plus the need to sequester CO2 has disrupted this scenario. It seems likely that this is a permanent shift driven by growing demand for limited low-cost sources of fluid hydrocarbons. So the traditional SMR route to hydrogen will be in competition with reforming of heavier hydrocarbons (particularly coal and residual oils) as well as with electrolysis based on electricity produced from low-CO2-emitting sources. By 2025, new high-temperature thermochemical or thermoelectrolytic sources based on high-temperature nuclear reactors could be in contention. This paper assesses the economics of all these potential sources of hydrogen and their price sensitivities. It also considers their environmental footprints. Is hydrogen from “clean coal” or other lower value hydrocarbons cost-effective if it is also CO2-free? Is intermittent low-temperature electrolysis based on nuclear- and wind-produced electricity (NuWind©) the best way or does the hydrogen future belong to thermochemistry or thermoelectrolytic sources? How can one produce hydrogen to upgrade Canada’s vast oilsands resources without the detraction of a large CO2 processing penalty? Fortunately for our planet, switching to hydrogen is no more than a technical challenge with a range of possible solutions but we need to make that point clearly to the political decision-takers and be able to provide assurance that the preferred solution will not be a source of new problems.
Investigation on Heat Transfer Characteristics of Water Through Narrow Annulus
Authors: Lu Guangyao , Wang Jing
Published: September 2008

A study is carried out to investigate the forced convective heat transfer characteristics of water through narrow annulus. For most works undertaken before were mainly concerned with the heat transfer characteristics of heat removal systems, the experiments herein are conducted to detect the heat transfer characteristics of heated fluid, as well as cooled fluid, flowing through narrow annulus. In the experiments, directions of flow include horizontal, upstream and downstream. The Reynolds number range, based on the annular hydraulic diameter, of 10 to 30,000 is covered in the experiments. During the experiments, the transitions from laminar to turbulent convective heat transfer are carefully observed. It is found that fully turbulent convective heat transfer is achieved at a lower Reynolds number in narrow annulus than that in larger tubes. When the Reynolds number is lower than 150, the heat transfer is degraded attributed to the slow flow rate and axial heat conduction. The experimental results indicate that the heat transfer characteristics of narrow annular flow are different from that of lager, more conventionally sized pipe flow. A convective heat transfer correlation is developed and the comparisons are made with the correlations of other works.
Gamma Ray Attenuation Coefficient Measurement in Energies 1172 keV and 1332 keV for Neutron Absorbent Saturated Solutions
Authors: Jalali Majid
Published: September 2008

The compounds, Na2B4O7, H3BO3, CdCl2 and NaCl and their solutions, attenuate gamma rays in addition to neutron absorption. These compounds are widely used in shielding of neutron sources, reactor control and neutron converters. Mass attenuation coefficients of gamma related to saturated solutions of the above four compounds, in energies 1172 keV and 1332 keV have been measured by NaI detector and agree very well with the results obtained by Xcom code. Experiment and computation show that, H3BO3 has the highest gamma ray attenuation coefficient among the aforementioned compounds.
Small Break LOCA Analysis of ACR-700 NPP
Authors: Zheng Limin , Shen Sen , Wright David
Published: September 2008

A small break loss of coolant accident (SB-LOCA) analysis to assess a preliminary conceptual design of the ACR-700 PHWR nuclear power plant (NPP) developed by AECL has been performed with CATHENA MOD 3.5d, a PHWR system thermal-hydraulic analysis code. The limiting break size has been found by performing a sensitivity study for three different break locations [i.e. reactor inlet header (RIH), HTS pump suction (PS) pipe and reactor outlet head (ROH)] under the limiting case (i.e. SB-LOCA with subsequent loss of class IV power with all safety systems available). The analysis results indicate that the SB-LOCA acceptance criteria are satisfied.
Advanced Process Model for Polymer Pyrolysis and Uranium Ceramic Material Processing
Authors: Wang Xiaolin , Zunjarrao Suraj C. , Zhang Hui , Singh Raman P.
Published: September 2008

Silicon carbide (SiC) based uranium ceramic material can be fabricated as hosts for ultra high temperature applications, such as gas-cooled fast reactor fuels and in-core materials. A pyrolysis-based material processing technique allows for the fabrication of SiC based uranium ceramic materials at a lower temperature compared to sintering route. Modeling of the process is considered important for optimizing the fabrication and producing material with high uniformity. This study presents a process model describing polymer pyrolysis and uranium ceramic material processing, including heat transfer, polymer pyrolysis, SiC crystallization, chemical reactions, and species transport of a porous uranium oxide mixed polymer. Three key reactions for polymer pyrolysis and one key reaction for uranium oxide polymer interaction are established for the processing. Included in the model formulation are the effects of transport processes such as heat-up, polymer decomposition, and volatiles escape. The model is capable of accurately predicting the polymer pyrolysis and chemical reactions of the source material. Processing of a sample with certain geometry is simulated. The effects of heating rate, particle size and volume ratio of uranium oxide and polymer on porosity evolution, species uniformity, reaction rate are investigated.
Steady State and Dynamic Analyses of Supercritical CO2 Natural Circulation Loop
Authors: Jain Prashant , Uddin Rizwan
Published: September 2008

Numerical studies have been carried out to investigate supercritical flow instabilities in a CO2 natural circulation loop. For the steady state and dynamic analyses of the loop under supercritical conditions, a single-channel, one-dimensional model is developed. In this model, equations for the conservation of mass, momentum and energy are discretized using an implicit finite difference scheme. A computer code called FIASCO (Flow Instability Analysis under SuperCritical Operating conditions) is developed in FORTRAN90 to simulate the dynamics of natural circulation loops with supercritical fluid. Results obtained for the stability boundary substantially deviate from the results reported by previous investigators, and thus contradict some of the reported findings. The disagreement in results is most likely due to the undesirable dissipative and dispersive effects produced from the large time steps used in previous studies, thereby leading to a larger stable region than those found using smaller time step. Results presented here suggest that the stability boundary of a natural circulation loop with supercritical fluid, is not confined to the near-peak region of the (steady state) flow-power curve. Additional and more extensive experimental data are needed to resolve the differences between results obtained here and those reported earlier. However, results obtained for the range of parameter values used in this investigation always predict the stability threshold to be in the positive slope region of the (steady state) flow-power curve. Parametric studies for different operating conditions reveal the similarity of stability characteristics under supercritical conditions with those in two-phase flows.
An Investigation of Flow, Heat Transfer Characteristic of Annular Flow and Critical Heat Flux in Vertical Upward Round Tube
Authors: Pu Fan , Qiu Suizheng , Su Guanghui , Jia Dounan
Published: September 2008

The term annular flow is used to describe the configuration of vapor-liquid flow in which part of the liquid travels as a film on the wall and the rest is entrained as drops by the vapor core in the center of the channel. The objective of this paper is to develop a hydrodynamic model for vertical upward annular flow. A separated flow model is developed and the conservations of Mass, Momentum, Energy, entrainment rate correlation in wide range of conditions and interfacial frictional correlation are used to research the flow and heat transfer characteristic of annular flow. The liquid film thickness, liquid film mass flow rate, two-phase heat transfer coefficient pressure along axial position, local velocity profiles along radial position are predicted theoretically. The influence of the mass flux, heat flux on liquid film thickness, heat transfer coefficient etc. are investigated in detail. The critical heat flux are also predicted in vertical upward round tube according to the theory that the dryout in vertical annular flow emerges at the point where the film is depleted due to the integrating result of entrainment, deposition and evaporation. The influence of mass flux, inlet mass quality and tube diameter on critical heat flux is also predicted in this paper. Finally the predicted result of critical heat flux is compared with experimental data, and the theoretical CHF values are higher than that of experimental data, with error within 30%.
Calculation of Inter-Subchannel Turbulent Mixing Rate and Heat Transfer in a Triangular-Arrayed Rod Bundle Using Direct Numerical Simulation
Authors: Yudov Yury V.
Published: September 2008

The direct numerical simulation, extended to boundary-fitted coordinate, has been carried out for a fully-developed turbulent flow thermal hydraulics in a triangular rod bundle. The rod bundle is premised to be an infinite array. The spacer grid effects are ignored. The purpose of this work is to verify DNS methodology to be applied for deriving coefficients for inter-subchannel turbulent mixing and heat transfer on a rod. These coefficients are incorporated in subchannel analysis codes. To demonstrate the validity of this methodology, numerical calculation was performed for the bundle with the pitch to diameter ratio 1.2, at friction Reynolds number of 600 and Prandtl number of 1. The results for the hydraulic parameters are compared with published DNS data, and the results for the heat exchange coefficients — with those obtained using semi-empirical correlations.
Nuclear Energy—Hydrogen Production—Fuel Cell: A Road Towards Future China’s Sustainable Energy Strategy
Authors: Zhou Zhiwei
Published: September 2008

Sustainable development of Chinese economy in 21st century will mainly rely on self-supply of clean energy with indigenous natural resources. The burden of current coal-dominant energy mix and the environmental stress due to energy consumptions has led nuclear power to be an indispensable choice for further expanding electricity generation capacity in China and for reducing greenhouse effect gases emission. The application of nuclear energy in producing substitutive fuels for road transportation vehicles will also be of importance in future China’s sustainable energy strategy. This paper illustrates the current status of China’s energy supply and the energy demand required for establishing a harmonic and prosperous society in China. In fact China’s energy market faces following three major challenges, namely (1) gaps between energy supply and demand; (2) low efficiency in energy utilization, and (3) severe environmental pollution. This study emphasizes that China should implement sustainable energy development policy and pay great attention to the construction of energy saving recycle economy. Based on current forecast, the nuclear energy development in China will encounter a high-speed track. The demand for crude oil will reach 400–450 million tons in 2020 in which Chinese indigenous production will remain 180 million tons. The increase of the expected crude oil will be about 150 million tons on the basis of 117 million tons of imported oil in 2004 with the time span of 15 years. This demand increase of crude oil certainly will influence China’s energy supply security and to find the substitution will be a big challenge to Chinese energy industry. This study illustrates an analysis of the market demands to future hydrogen economy of China. Based on current status of technology development of HTGR in China, this study describes a road of hydrogen production with nuclear energy. The possible technology choices in relation to a number of types of nuclear reactors are compared and assessed. The analysis shows that only high temperature gas cooled reactor (HTGR) and sodium fast breed reactor might be available in China in 2020 for hydrogen production. Further development of very high temperature gas cooled reactor (VHTR) and gas-cooled fast reactor (GCFR) is necessary to ensure China’s future capability of hydrogen production with nuclear energy as the primary energy. It is obvious that hydrogen production with high efficient nuclear energy will be a suitable strategic technology road, through which future clean vehicles burning hydrogen fuel cells will become dominant in future Chinese transportation industry and will play sound role in ensuring future energy security of China and the sustainable prosperity of Chinese people.