Reaction Heating Rate Research Articles

New Approach for the Root Cause of Fukushima Meltdown Accident

The purpose of this Commentary is to clarify as much as possible the whole history of reactor and containment pressure changes in the Fukushima meltdown accident. It is based on a new approach for film boiling, which is kept after the Zr-H₂O reactions. Most important point of this approach is that the author applied film boiling based on boiling curve, which is basic theory in boiling phenomena, for the Fukushima accident phenomena. As the reaction rate is proportional to the reactor or containment pressure under film boiling, it increases rapidly and stops suddenly, keeping the film boiling. The containment pressure change consists of three phases, namely pressurizing, keeping the high pressure and de-pressurizing. The containment is pressurized by H₂ gas and steam produced by the Zr-H₂O reactions and de-pressurized by a heatsink such as the containment wall and inner shield concrete after reaction stops. The high pressure between these pressure changes is kept by balancing the H₂ gas produced by reaction with the leaked gas from the gap between the top lid and the containment. Core decay heat is large, but its change is negligibly small. So, the pressurization is calculated from H₂ gas and steam produced by the Zr- H₂O reactions. The heatsink balances with the reaction during the high pressure condition. The de-pressurization occurs after the reaction is over, so the reaction heat rate can be calculated by the heat rate of the heatsink, which is equal to the condensation rate during de-pressurization. The leak rate of the leak gas can be calculated using the reaction rate. It is very important that the rection rate is slowed by the insufficient steam supply, as the melted reactor cores in the Fukushima accident were covered with H₂ gas and steam (film boiling) at 0.8MPa or lower pressure. This is different from the rate (at approx. 7MPa) in the Three Mile Island accident, as the steam specific volume at 0.8 MPa is ten times larger than that at 7 MPa. The calculation results based on this assumption show that almost all the Zr in each core of Units 1, 2 and 3 reacted with water.

Effect of reaction time, heating and stirring rate on the morphology of HAp obtained by hydrothermal synthesis

Hydroxyapatite (HAp) whiskers were prepared in reaction of calcium lactate pentahydrate and orthophosphoric acid. Synthesis were carried out in different conditions with using hydrothermal reactor. The benefit of the hydrothermal technique is the simple and precise control of the HAp crystals morphology, which is achieved by employing varying initial concentrations of starting reagents as well as different conditions of synthesis. The effect of time of synthesis, stirring and heating rate of the reaction on HAp morphology and composition was investigated. During the synthesis the following experimental parameters were varied independently: time of synthesis (3, 5, 7 h), stirring rate (0, 62.5, 125, 250, 500, 750 rpm), the reaction heating rate (0.2, 0.5, 0.7, 1.0, 1.5, 2.5 °C min−1). All syntheses were carried out with the constant molar Ca/P ratio of 1.67 in starting solutions, which is equivalent to that of stoichiometric HAp. The Ca2+ ion concentrations in starting solutions for synthesis were 0.05 and 0.1 mol dm−3. Syntheses were carried out under 20 bar. The obtained products were characterized using different method like XRD, SEM, and FTIR. It was shown that the significant majority of samples prepared were identified as pure HAp.

New approach for describing reactor and containment pressure change after loss of core cooling at Fukushima meltdown accident

The purpose of this comment is to clarify the whole history of reactor and containment pressure change during the Fukushima meltdown accident. It is based on a new approach for film boiling, which is sustained after the Zr–H2O reaction. As the reaction rate is proportional to the reactor or containment vessel pressure under film boiling, it increases rapidly and stops abruptly while sustaining film boiling. The containment vessel pressure change consists of three phases, namely, pressurization, holding a high pressure and depressurization. The containment vessel is pressurized with H2 gas and steam produced by the Zr–H2O reaction and depressurized by heat removal by heatsinks such as the containment vessel wall and inner concrete after the reaction stops. The high pressure between these pressure changes is sustained by balancing the amount of H2 gas produced by the reaction and that of gas leaking from the gap of the top hat of the containment vessel. The amount of core decay heat is large, but the change of this is negligible. Thus, pressurization is calculated from the amounts of H2 gas and steam produced by the Zr–H2O reaction. The amount removed by the heatsink balances with that produced by the reaction during the high-pressure phase. Depressurization occurs after the reaction is over, so the reaction heat rate can be calculated from the heat removal rate of the heatsink, which is equal to the condensation rate during depressurization. The rate of gas leakage can be calculated from the reaction rate. It is very important that the reaction rate was slow owing to the insufficient steam supply, as the melted core in the Fukushima accident was covered with H2 gas and steam at a pressure of 0.8 MPa or lower. This is different from the rate (at approximately 7 MPa) in the Three Mile Island accident, as the specific volume of steam at 0.8 MPa is ten times larger than that at 7 MPa. The calculation results based on this assumption show that almost all the Zr in each core of Units 1, 2 and 3 reacted with water. The location of a small penetration hole produced by the contact of the high-temperature H2 gas with the suppression chamber wall, is estimated in Unit 2.

Optimizing the Binding Energy of the Surfactant to Iron Oxide Yields Truly Monodisperse Nanoparticles.

Despite the great progress in the synthesis of iron oxide nanoparticles (NPs) using a thermal decomposition method, the production of NPs with low polydispersity index is still challenging. In a thermal decomposition synthesis, oleic acid (OAC) and oleylamine (OAM) are used as surfactants. The surfactants bind to the growth species, thereby controlling the reaction kinetics and hence playing a critical role in the final size and size distribution of the NPs. Finding an optimum molar ratio between the surfactants oleic OAC/OAM is therefore crucial. A systematic experimental and theoretical study, however, on the role of the surfactant ratio is still missing. Here, we present a detailed experimental study on the role of the surfactant ratio in size distribution. We found an optimum OAC/OAM ratio of 3 at which the synthesis yielded truly monodisperse (polydispersity less than 7%) iron oxide NPs without employing any post synthesis size-selective procedures. We performed molecular dynamics simulations and showed that the binding energy of oleate to the NP is maximized at an OAC/OAM ratio of 3. The optimum OAC/OAM ratio of 3 is allowed for the control of the NP size with nanometer precision by simply changing the reaction heating rate. The optimum OAC/OAM ratio has no influence on the crystallinity and the superparamagnetic behavior of the Fe3O4 NPs and therefore can be adopted for the scaled-up production of size-controlled monodisperse Fe3O4 NPs.

Surfactant-Mediated Resistance to Surface Oxidation in MnO Nanostructures.

The intrinsic physical properties of nanostructures of metals and their oxides are altered when they are prone to surface oxidation in ambient atmosphere. To overcome this limitation, novel synthesis methodologies are required. In this study, solid octahedral shapes of MnO limit the inward oxygen diffusion compared to that of the MnO-nanoparticle-assembled octahedra. In addition to morphology control, which restricts the thickness of the Mn3O4 surface layer, the binding chemistry of the surfactants plays an essential role. For example, the Mn3O4 surface layer is 0.4 nm thinner with trioctylphosphine oxide than with trioctylamine as the surfactant. The nanostructures were prepared by varying the surfactants, surfactant-to-precursor molar ratio, accelerating agent, and reaction heating rate. The surface oxidation of MnO nano-octahedra was probed by Rietveld analysis of X-ray diffraction patterns and X-ray photoelectron spectroscopy and characterized by magnetic measurements, as the presence of ferrimagnetic Mn3O4 shell on the antiferromagnetic MnO core provides an exchange coupling at the core–shell interface. Thicker the Mn3O4 shell, higher is the exchange-biased hysteresis loop shift.

Dominance of chemical heating over dynamics in causing a few large mesospheric inversion layer events during January–February 2011

AbstractUsing mesospheric temperature information obtained by Rayleigh lidar observations over Gadanki (13.5°N, 79.2°E) and temperature, chemical constituents, and their exothermic chemical reaction heating rates obtained by Sounding of Atmosphere by Broadband Emission Radiometry instrument onboard Thermosphere Ionosphere Mesosphere Energetics and Dynamics satellite over and near to Gadanki location, the dominant role of chemical heating for the occurrence of a few large mesospheric inversion layer (MIL) events during January–February 2011 is demonstrated. The heating rates due to exothermic chemical reactions among atomic oxygen (O), atomic hydrogen (H), molecular oxygen (O2), ozone (O3), and hydroxyl (OH) species are the key factors involved in the MIL formation. As relatively larger (lower) ozone mixing ratios are observed at the top (bottom) of the inversion layers, large heating rate (~ 15 K/day) is found to occur between 80 and 85 km due to the exothermic reaction between atomic hydrogen and ozone H + O3 → OH + O2, which dominates all other important exothermic chemical reactions during these MIL events, and the large volume emission rates of energy of O2 and OH are found to be mostly due to the reaction between H and O3. It is also demonstrated that dynamics plays a negligible role in the formation of these MILs as conditions for the convective and dynamic instability are found to be not satisfied during these MIL events.

The Effect of Mechanical Activation of Elemental Powders on Combustion Synthesis of NbAl<sub>3</sub>

The effect of mechanical activation procedures on the combustion synthesis of NbAl3 was investigated. The activation was carried out by a two-step high energy ball milling procedure. In the first milling, aluminum and niobium were milled separately (pre-activation). The mixture of pre-activated powders was then activated in the second milling. Reaction synthesis, by simultaneous combustion mode, was conducted on compacted pellets made of powder mixtures with and without pre-activation. The thermal behavior of the compacted pellets upon heating was recorded and the main thermal combustion reaction characteristics were evaluated. The two-step procedure produced aggregates with a globular dispersion of niobium due to increased particle hardness and decreasing mean particle size during pre-activation milling. Analysis of pellet thermal behavior showed the two-step milling procedure could enhance reaction performance by increasing maximum reaction heating rate and temperature gain during reaction.

Synthesis of pyramidal, cubical and truncated octahedral magnetite nanocrystals by controlling reaction heating rate

Pyramidal, cubical and truncated octahedral magnetite nanocrystals have been synthesized by thermal de-composition of iron (III) acetylacetone (Fe(acac)3) in the presence of oleic acid under various reaction rate controlled by heating rate. The magnetite nanocrystals were characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). High-resolution transmission electron microscopy (HRTEM) was applied to reveal the structural information of single magnetite (Fe3O4) nanocrystals. Magnetization curves of the three types of magnetite nanocrystals show that the pyramidal crystals exhibit a slight hysteresis compared to the other two despite of the similar size range. The results suggest that in addition to the surfactant selective capping and varying reaction temperature, the reaction rate variation is also an effective means for controlling the morphology and functions of the magnetite nanocrystals.

The important role of pressure in supercritical fluid process development revealed by reaction calorimetry

AbstractThe technique of reaction calorimetry adapted for use with reactions in supercritical fluids was used to study some safety aspects of the free‐radical dispersion polymerization of methyl methacrylate in scCO2. The reaction heat rate profile was found to change very little once the dispersion was well formed. Furthermore, it provided valuable information for the calculation of the maximum temperature attainable by the synthesis reaction (MTSR) in the case of a hypothetical cooling system failure. Finally, a series of failure scenarios demonstrated the importance of the pressure as far as the safety of the process is concerned, due to the particularity of the supercritical state of the solvent. It was found that the acceleration phase of the reaction is the most critical period, since a cooling system failure during this phase leaves very little time before the pressure overcomes the operational limit of the equipment and results in an accident. Hence, the utility and the importance of defining the reaction heat rate profile become obvious and several safety features have to be taken into consideration when designing a SCF process. © 2009 American Institute of Chemical Engineers Process Saf Prog 2009

Industrial SBR Process: Computer Simulation Study for Online Estimation of Steady‐State Variables Using Neural Networks

AbstractThis work investigates the industrial production of styrene‐butadiene rubber in a continuous reactor train, and proposes a soft sensor for online monitoring of several processes and polymer quality variables in each reactor. The soft sensor includes two independent artificial neural networks (ANN). The first ANN estimates monomer conversion, solid content, polymer production, average particle diameter, and average copolymer composition; the second ANN estimates average molecular weights and average branching degrees. The required ANN inputs are: (i) the reagent feed rates into the first reactor and (ii) the reaction heat rate in each reactor. The proposed ANN‐based soft sensor proved robust to several measurement errors, and is suitable for online estimation and closed‐loop control strategies.magnified image

Kinetic Effects on Hydroxyapatite Whiskers Synthesized by the Chelate Decomposition Method

Hydroxyapatite (HA) whiskers have been synthesized using a number of chemical solution methods, including the chelate decomposition method. Numerous previous studies have investigated the effects of the reagents, reagent concentrations, solution pH, and reaction temperature on HA whisker morphology and composition. However, purely kinetic effects, such as the reaction heating and stirring rates, have not been rigorously investigated and are rarely reported in the literature. Therefore, the objective of this study was to investigate kinetic effects on the morphology of HA whiskers synthesized using the chelate decomposition method. In order to study the kinetic effects on the morphology of HA whiskers, three experimental parameters were varied independently: the reaction heating rate (0.36°–3.0°C/min), stirring rate (0–250 rpm), and temperature (80°–200°C). At all heating and stirring rates, precipitated whiskers were confirmed by XRD and FT‐IR to comprise phase‐pure, calcium‐deficient HA (Ca/P=1.57–1.62). The length and aspect ratio of HA whiskers increased with decreased heating rate, decreased stirring rate, and increased reaction temperature. The mean length and aspect ratio of HA whiskers increased approximately twofold with decreased heating rate over the range studied, following a power‐law relationship. Therefore, the reaction heating rate is a key variable that can be used to tailor the morphology of HA whiskers and ought to be reported in the literature. The reaction heating rate and temperature had relatively little effect on the width of HA whiskers. However, the precipitate morphology was altered significantly from micro‐scale whiskers to nano‐scale plates with increased stirring rate. These results offered new insights and provided clarification regarding the reaction mechanism, which is discussed in detail.

Effect of reaction kinetics of polymer electrolyte on the ion‐conductive behavior for poly(oligo oxyethylene methacrylate)–LiTFSI mixtures

AbstractThe effect of the reaction kinetics on the ionic conductivity for a comblike‐type polyether (MEO) electrolyte with lithium bis(trifluoromethane sulfonyl)imide (LiTFSI) was characterized by DSC, complex impedance measurements, and 1H pulse NMR spectroscopy. The ionic conductivity of these electrolytes was affected by the reaction condition of the methacrylate monomer and revealed by the glass transition temperature (Tg), spin–spin relaxation time (T2), steric effects of the terminal groups, and the number of charge carriers indicated by the VTF kinetic parameter. In this system, the electrolytes prepared by the reaction heating rate of 10°C/min of MEO–H and 15°C/min of MEO–CH3 showed maximum ionic conductivity, σi, two to three times higher in magnitude than that of the σi of the others at room temperature. As experimental results, the reaction kinetic rate affected the degree of conversion, the ionic conductivity, and the relaxation behaviors of polyether electrolytes. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2149–2156, 2003

Parameter Estimator Design with Application to a Chemical Reactor

A new method of on-line parameter estimation for a class of nonlinear systems is presented in this paper. The parameter estimator includes a left inverse of process model and at each time instant calculates least-squared-error estimates of parameters by using readily available on-line measurements. The estimator is computationally efficient and easy to implement. The application and performance of the parameter estimation method are illustrated and compared with those of parameter estimation via state estimation, by using a jacketed chemical reactor example for which the reaction-heat rate and overall heat-transfer coefficient are estimated. The simulation results show that the inversion-based estimator outperforms the state-estimation-based parameter estimator in the presence of measurement noise and plant−model mismatch.

Photon heating of the atmosphere at F-region heights

The transfer of energy from an ionizing photon to the atoms and molecules of the neutral gas in the F-region of the atmosphere is investigated. It is found that photoionization heating should be divided into two parts: (1) photoelectron heating associated with the slowing down of the fast photoelectrons formed by photoionization; and (2) reaction heating associated with the chemical reactions undergone by the ions formed in the photoionization process. The photoelectron heating will take place near the time and place of photoionization while the reaction heating will occur at the time and place of the ionic reactions. Photoelectron and reaction heating rates per unit column are computed for the daytime, and reaction heating rates per unit column are computed for the nighttime. It is concluded that: (1) chemical reactions at night lead to a small but significant amount of F-region heating; and (2) reaction heating during the day is nearly proportional to the cosine of the solar zenith angle except near sunrise and sunset.