scholarly journals Rate controls on silicate dissolution in cementitious environments

2017 ◽  
Vol 2 ◽  
pp. 67-73 ◽  
Author(s):  
Tandre Oey ◽  
Yi-Hsuan Hsiao ◽  
Erika Callagon ◽  
Bu Wang ◽  
Isabella Pignatelli ◽  
...  
Keyword(s):  
Dissolution Rate ◽  
Nuclear Power ◽  
Power Plants ◽  
Chemical Reactivity ◽  
Aqueous Media ◽  
Dissolution Rates ◽  
Alkaline Environments ◽  
Silicate Dissolution ◽  
Quantitative Basis ◽  
Dynamics Simulations

The dissolution rate of silicate minerals and glasses in alkaline environments is of importance in cementitious systems due to its influences on: (a) early-age reactivity that affects the rate of strength gain and microstructure formation, and/or, (b) chemical durability of aggregates; compromises in which can result deleterious processes such as alkali-silica reaction (ASR). In spite of decades of study, quantitative linkages between the atomic structure of silicates and their dissolution rate in aqueous media (i.e., chemical reactivity) has remained elusive. Recently, via pioneering applications of molecular dynamics simulations and nanoscale-resolved measurements of dissolution rates using vertical scanning interferometry, a quantitative basis has been established to link silicate dissolution rates to the topology (rigidity) of their atomic networks. Specifically, an Arrhenius-like expression is noted to capture the dependence between silicate dissolution rates and the average number of constraints placed on a central atom in a network (nc, i.e., an indicator of the network’s rigidity). This finding is demonstrated by: (i) ordering fly ashes spanning Ca-rich/poor variants in terms of their reactivity, and, (ii) assessing alterations in the reactivity of albite, and quartz following irradiation due to their potential to induce ASR in concrete exposed to radiation, e.g., in nuclear power plants.       

A Study of Nanoparticle-Enhanced Heat Transfer

2010 ◽  
Author(s):  
Lawrence M. Jones ◽  
Timothy Sirk ◽  
Eugene Brown
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Molecular Dynamics ◽  
Heat Flux ◽  
Nuclear Power ◽  
Power Plants ◽  
Md Simulations ◽  
Theoretical Description ◽  
Different Temperatures ◽  
Dynamics Simulations

The study of the heat transfer characteristics of nanofluids, i.e. fluids that are suspensions of nanometer size particles, has gained significant attention in the search for new coolants that can effectively service a variety of needs ranging from the increasing heat transfer demands of ever smaller microelectronic devices to mitigating the effects of loss of coolant accidents in nuclear power plants. Experimental data has shown large increases in thermal conductivity and associated increases in the level of critical heat flux in nuclear reactors; however, in some cases the range of the applicability of the experimental results is uncertain and there is a lack of a theory by which this can be resolved. Complicating the theoretical description of heat transfer in nanofluids is the fact that fluids in the vicinity of the nanoparticles are a complex combination of phase transition, interfacial, and transport phenomena. This paper describes a study in which molecular dynamics simulations were used to enhance the understanding of the effect of nanoparticles on heat transfer. The molecular dynamics (MD) simulations presented here model a Lennard-Jones fluid in a channel where the walls are maintained at different temperatures. The heat flux is calculated for a variety of nanoparticle sizes and concentrations. The results are compared to experimental data in order to provide information that will more confidently bound the data and provide information that will guide the development of more comprehensive theories. We also anticipate that this work could contribute to the design of biosensors where suspended molecules are transported through micro- and nano-channels in the presence of heat transfer.

scholarly journals Investigation of the capacity of train stations in case of a large-scale emergency evacuation

10.29007/j32s ◽  
2019 ◽  
Author(s):  
Anna Braun ◽  
Mohcine Chraibi ◽  
Lukas Arnold
Keyword(s):  
Urban Areas ◽  
Nuclear Power ◽  
Power Plants ◽  
Large Scale ◽  
Emergency Evacuation ◽  
Railway Transportation ◽  
Pedestrian Dynamics ◽  
Train Station ◽  
Dynamics Simulations ◽  
Hurricanes Katrina And Rita

Nature and human-made hazards, like hurricanes, inundations, terroristic attacks or in- cidents in nuclear power plants, make it necessary to evacuate large urban areas in a short time. So far, the consideration of railway transportation is rarely part of the evacuation strategies. One of the reasons is the unknown capacity of this infrastructure.In the case of hurricanes Katrina and Rita (USA) the evacuation was accomplished with pri- vate vehicles and buses. In Germany, especially in the conurbation of Nordrhein-Westfalen, where many roads are overloaded during the daily rush hours, it will not be possible to use only road dependent vehicles like private cars or busses to evacuate a large number of people into save areas.After the nuclear power plant disaster of Fukushima, the working group ‘AG Fukushima’ was founded, which recommends the use of trains for large-scale emergency evacuations. However, it is not clear if the capacity of train stations is enough to handle these large evacuations in time. Hence, this work deals with the question of how the capacity of train stations can be quantified and optimised for this application. In order to estimate the capacity of train stations we use and further develop the Ju ̈lich Pedestrian Simula- tor (JuPedSim), a software for pedestrian dynamics simulations. Therefore, a model of a train station is built in JuPedSim and several parameters like the inflow and outflow of the pedestrians are examined, to find the best routing strategy and organisational ac- tions inside the station. The focus of this contribution lies in the identification of critical bottlenecks. An estimation of which parameters are influencing congestion at these bottle- necks is presented. Additionally, organisational strategies are outlined, which can prevent congestion and increase the capacity of a train station.

The Influence of Incorporated and Adsorbed Fluoride on the Dissolution of Powdered and Pelletized Hydroxyapatite in Fluoridated and Non-fluoridated Acid Buffers

1987 ◽  
Vol 66 (12) ◽  
pp. 1735-1741 ◽  
Author(s):  
L. Wong ◽  
T.W. Cutress ◽  
J.F. Duncan
Keyword(s):  
Dissolution Rate ◽  
Diffusion Rate ◽  
Chemical Reactivity ◽  
Surface Chemical ◽  
Dissolution Rates ◽  
Surface Chemical Reactivity ◽  
Determining Factor ◽  
Apatite Surface

The effects of fluoride (F) incorporated into hydroxyapatite (HA), adsorbed onto the HA surface, and fluoride in solution were studied during HA dissolution. Dissolution rates at pH 5. and 25°C were determined in fluoridated (0.1, 5.0 μg/mL) and non-fluoridated buffers for the following powdered and pelletized synthesized HAs: non-fluoridated HA, partially-fluoridated (100, 1000, 37,000 μglg) HA, and surface-adsorbed fluoridated (100, 1000 μg/g) HA. The dissolution rate curves were used to derive two components we have called 'diffusion' and 'surface chemical reactivity'. With powders, the rate-determining factor was surface chemical reactivity during the first 60 min. Diffusion was reduced by increasing the F levels in the apatite or buffer. In non-fluoridated buffers, diffusion was reduced 29% for apatite with 100 μg/g incorporated F and 99% with 37,000 μg/g-Diffusion was reduced by 37% and 81 % by 0.1 and 5.0 μg/mL F, respectively, in the buffer. With pelletized HA, the rate-determining factor during the first 10 min was surface chemical reactivity. Diffusion then became relatively more important, but the diffusion rate was independent of F content. During the dissolution of powdered apatites, F was taken up by the remaining apatite solid, as evidenced by the lower F concentration in solution than that calculated to be released during dissolution. There was also a decrease in the F concentration of the 0.1 μg/mL buffer as reaction progressed. Pelletized apatites did not release enough F to influence dissolution significantly. Surface-adsorbed F was more effective than incorporated F in reducing HA dissolution. However, solution F present at the apatite surface in small concentrations (<5.0 μg/mL) was more effective than much higher concentrations (1000 μg/g) of adsorbed or incorporated F in reducing dissolution.

scholarly journals Corrosion Behaviours of Aged Haynes 282 and Inconel 718 in Acidic and Alkaline Environments

2018 ◽  
Vol 3 (2) ◽  
Author(s):  
Muideen A Bodude ◽  
Wasiu A Ayoola ◽  
Harrinson O Onovo
Keyword(s):  
Corrosion Resistance ◽  
Inconel 718 ◽  
Nuclear Power ◽  
Power Plants ◽  
Oil And Gas ◽  
Corrosion Behaviour ◽  
Corrosion Current ◽  
Turbine Engines ◽  
Gas Turbine Engines ◽  
Alkaline Environments

Haynes 282 and Inconel 718 are superalloy materials originally designed and used in aero- and land-based gas turbine engines. However, they are being considered and used in challenging environments such as nuclear power plants, chemical, and petrochemical plants due largely to their high creep strength and corrosion resistance at low and high temperatures. Recently, there is quest for their uses in the oil and gas refineries. This work examines the corrosion behaviour of these two materials in acidic and alkaline environments; similar to that in the petroleum refinery. The samples were cut, aged, and electrochemically characterized using VersaSTAT 3 model potentiostat with graphite counter electrode and Ag-AgCl SCE. The Linear polarization corrosion test conducted revealed that the corrosion rate, break down potential(Ecorr) and the corrosion current(Icorr)  of the aged Haynes 218 are 0.05mmpy, 0.198V, 5.032µA in dilute HNO3 ; 0.145mmpy,16.23V,13.48 µA in dilute NaOH while those of aged Inconel 718 are 0.068mmpy,96.5V,63.56 µA in the dilute HNO3  and 0.026mmpy,0.41V,2.478 µA in the dilute NaOH respectively. These results showed that aged Haynes 282 has a higher corrosion resistance than aged Inconel 718  in the acidic medium ,but, the reverse in the alkaline medium .However better corrosion  passivation was obtained in HNO3 for the two materials than in NaOH.Keywords- Superalloys, Haynes 282, Inconel 718, Tafel  Extrapolation Method.

The Effects of Ion Implantation on the Surface Features of Inconel 600

1985 ◽  
Vol 43 ◽  
pp. 288-289
Author(s):  
John D. Rubio
Keyword(s):  
Grain Boundary ◽  
Ion Implantation ◽  
Nuclear Power ◽  
Power Plants ◽  
Surface Region ◽  
Selective Dissolution ◽  
Boundary Region ◽  
Near Surface ◽  
Inconel 600 ◽  
Steam Generator Tubing

The degradation of steam generator tubing at nuclear power plants has become an important problem for the electric utilities generating nuclear power. The material used for the tubing, Inconel 600, has been found to be succeptible to intergranular attack (IGA). IGA is the selective dissolution of material along its grain boundaries. The author believes that the sensitivity of Inconel 600 to IGA can be minimized by homogenizing the near-surface region using ion implantation. The collisions between the implanted ions and the atoms in the grain boundary region would displace the atoms and thus effectively smear the grain boundary.To determine the validity of this hypothesis, an Inconel 600 sample was implanted with 100kV N2+ ions to a dose of 1x1016 ions/cm2 and electrolytically etched in a 5% Nital solution at 5V for 20 seconds. The etched sample was then examined using a JEOL JSM25S scanning electron microscope.

Work structure in nuclear power plants

1983 ◽  
Author(s):  
Marjorie B. Bauman ◽  
Richard F. Pain ◽  
Harold P. Van Cott ◽  
Margery K. Davidson
Keyword(s):  
Nuclear Power ◽  
Power Plants ◽  
Nuclear Power Plants ◽  
Work Structure

Life Extension of Nuclear Power Plants: World Situation and the USA Case

2010 ◽  
pp. 50-56 ◽  
Author(s):  
Pablo T. León ◽  
Loreto Cuesta ◽  
Eduardo Serra ◽  
Luis Yagüe
Keyword(s):  
Nuclear Power ◽  
Power Plants ◽  
Nuclear Power Plants ◽  
Life Extension ◽  
The Usa

Fuzzy multi-objective decision making approach for nuclear power plant installation

2020 ◽  
Vol 39 (5) ◽  
pp. 6339-6350
Author(s):  
Esra Çakır ◽  
Ziya Ulukan
Keyword(s):  
Linear Programming ◽  
Power Plant ◽  
Nuclear Power Plant ◽  
Energy Supply ◽  
Energy Demand ◽  
Nuclear Power ◽  
Power Plants ◽  
Total Duration ◽  
Objective Functions ◽  
Multi Objective

Due to the increase in energy demand, many countries suffer from energy poverty because of insufficient and expensive energy supply. Plans to use alternative power like nuclear power for electricity generation are being revived among developing countries. Decisions for installation of power plants need to be based on careful assessment of future energy supply and demand, economic and financial implications and requirements for technology transfer. Since the problem involves many vague parameters, a fuzzy model should be an appropriate approach for dealing with this problem. This study develops a Fuzzy Multi-Objective Linear Programming (FMOLP) model for solving the nuclear power plant installation problem in fuzzy environment. FMOLP approach is recommended for cases where the objective functions are imprecise and can only be stated within a certain threshold level. The proposed model attempts to minimize total duration time, total cost and maximize the total crash time of the installation project. By using FMOLP, the weighted additive technique can also be applied in order to transform the model into Fuzzy Multiple Weighted-Objective Linear Programming (FMWOLP) to control the objective values such that all decision makers target on each criterion can be met. The optimum solution with the achievement level for both of the models (FMOLP and FMWOLP) are compared with each other. FMWOLP results in better performance as the overall degree of satisfaction depends on the weight given to the objective functions. A numerical example demonstrates the feasibility of applying the proposed models to nuclear power plant installation problem.

Sign in / Sign up

Export Citation Format

Share Document