Steam Content Research Articles

Laser Method of Measuring the Steam Content of Coolant in Water Nuclear Power Reactors

Laser Method of Measuring the Steam Content of Coolant in Water Nuclear Power Reactors

Investigation on jet scrubbing in nuclear reactor accidents: From experimental data to an empirical correlation

The Fukushima accident stressed the significance of suppression pools as passive systems for fission product trapping. Even though pool scrubbing was extensively investigated in the past, there are gaps in the existing data base and modeling that need to be addressed, particularly those relative to high gas injection velocities in the pool. In this paper, the main results of an experimental campaign (PSP tests) on particles scrubbing at the pool inlet region when the carrier gas forms a submerged jet (“jet scrubbing”), are presented and discussed. The tests have been conducted in the PECA-PS facility of the Laboratory for Analysis of Safety Systems (LASS) and the experimental conditions have been based on two non-dimensional variables: the Weber non-dimensional number, which has been set to values over the threshold from globule to jet regime; and the gas saturation ratio, which has ranged from under saturation to over-saturation. Jet scrubbing efficiency at the pool inlet has been measured to be over 90% whenever the gas enters the pool within the jet regime (Wetest ≥ Wec), regardless thermal boundary conditions. Analysis of gas steam content, though, has not shown any clear trend. Based on the PSP experiments and some others gathered from the open literature, a tentative correlation dependent on non-dimensional Stokes number (Stk), which accounts for inertial impaction, and saturation ratio (S), which captures diffusiophoretic deposition, has been proposed as a first step to empirically model jet scrubbing. Finally, some lessons learned for forthcoming experiments have been withdrawn, particularly concerning the high impact of hydrodynamics.This work has been done within the framework of the 7th FWP of EURATOM through the EU-PASSAM project (Grant agreement No. 323217 – Euratom 7FP).

Tailoring Chemical Expansion in Zirconate-Cerate Proton Conductors

Stoichiometric chemical expansion is the lattice expansion accompanying non-integer changes in stoichiometry, such as oxygen loss in mixed ionic and electronic conducting oxides, Li intercalation in battery electrodes, H uptake in hydrogen storage materials, or hydration in proton conductors. The coefficient of chemical expansion (CCE) normalizes this chemical strain (εC) to the compositional change, so for the case of hydration in proton conductors it can be defined as CCE = εC/Δ[(OH)• O]. The chemical stresses that develop from such compositional changes can be large enough to cause mechanical failure, such as cracking or delamination, with implications for component processing, in situ characterization, and device lifetime. One way to lower the magnitude of chemical stress is to engineer materials with lower CCEs, but relatively few design principles exist to guide such engineering. In the present work we investigated the hypothesis that lower crystal symmetry could lead to lower macroscopic CCEs in polycrystalline ceramics. There are indications that such a correlation may exist among mixed ionic and electronic conducting perovskites that expand upon losing oxygen due to enlargement of multivalent cations upon gaining electrons for charge compensation. To examine whether a similar effect may be present also for the case of hydration-induced expansion, which has a different mechanism involving filling of oxygen vacancies and introduction of interstitial hydrogen, we fabricated a series of perovskite-structured proton conductors, BaY0.1Ce0.9-xZrxO3 (x=0, 0.3, 0.6, 0.9), having tailored tolerance factors – an indicator of symmetry. Bar-shaped samples were prepared by a sol-gel route and sintering to 1500 °C, and their crystal structures and lattice parameters were analyzed by X-ray diffraction with Rietveld analysis. For each composition, the isothermal expansion upon increasing H2O content in the gas atmosphere by a fixed amount was measured by dilatometry at various temperatures up to 680 °C. The corresponding changes in (OH)• O content were determined by thermogravimetric analysis under the same conditions. By normalizing the chemical strains to the changes in proton content, the CCEs at each temperature were determined for each composition and compared. X-ray diffraction confirmed that the crystal structure became more cubic and the symmetry increased with increasing x, as expected on the basis of the calculated tolerance factors. At the same time the unit cell volume increased, which could also in principle contribute to modifying the chemical expansion behavior. Proton uptake (for a given steam content) was smaller for higher x values, but the lower proton uptake did not correspond with the smallest chemical strains. In fact, the normalized CCEs monotonically increased with increasing x for all but the highest temperatures, consistent with the hypothesis of higher CCEs for higher symmetry, for these randomly oriented, polycrystalline samples. These results suggest that lowering symmetry may be a promising approach for minimizing chemical expansion behavior across multiple classes of materials, with the potential to improve material and device durability. At the same time, future studies should aim to separate the effects of unit cell size vs. crystal symmetry.

Corrosion of SiC layers on coated zirconia particles in wet atmosphere

Properties of SiC coating layer in the postulated accident condition of air and water ingress is crucial to the in-pile safety of tristructural-isotropic (TRISO) coated fuel particles of high temperature gas-cooled reactors (HTR). Particles of ZrO2 kernels coated with low-density pyrolytic carbon buffer layer, high-density pyrolytic carbon layer and SiC layer fabricated by fluidized-bed chemical vapour deposition (FBCVD) were used to simulate real fuel particles in this research. The coated particles were tested at 1673 K in a certain flowing air with different water content between 0 and 100 g/m3 for 10 h. Analysis results show that the corrosion reaction took place mainly on the outer surface of SiC layer with changing infiltration depth according to the flowing gas compositions. Steam content was controlled according to the relationship between saturated water vapour pressure and environment temperature. SiO2 layer was the main product formed on the surface with thickness increase from 1.5 µm to 3 µm along with the content of water vapour in air. Formation of two types of micro-cracks after oxidation are observed: micro-cracks on spherulitic SiO2 and penetrating micro-cracks on flat SiO2. Micro-stress generation mechanism is illustrated. Three are also some bubbles are observed either in SiO2 layer or between SiO2 and SiC layers. Results showed that no fracture occurred in the SiC layer after wet oxidation.

CFD simulation of hydrogen mitigation by a passive autocatalytic recombiner

In the case of a nuclear severe accident, hydrogen produced by the metal-water reaction and core-concrete interaction is released in the containment in which large amounts of oxygen are present. The flammable mixture can deflagrate or even lead to detonation, increasing the pressure and potentially endangering the integrity of the containment. To mitigate the hydrogen risk, Passive Autocatalytic Recombiners (PARs) are used in many power plants to passively remove the hydrogen by recombination with the oxygen in air. The PAR presence in the containment volume induces secondary flows that are three dimensional in nature and hence Computational Fluid Dynamics (CFD) tools are most appropriate to tackle PAR issues in containments. This paper aims to validate a CFD model for hydrogen consumption by a PAR using experimental data in reduced-scale geometries.The CFD PAR model is implemented in the ANSYS Fluent code and makes use of a correlation given by the PAR manufacturer to compute the reaction rate of hydrogen. The PAR unit is considered as a channel where the reaction takes place without any chemistry details. The CFD model is validated against two experimental tests (HR2 and HR5), which were performed in the THAI facility in the frame of the OECD/NEA THAI project. The tests, conducted with no initial steam content, were designed to investigate PAR response to different starting pressures (1 and 3 bar).The simulations show that the predictions of the main variables (hydrogen recombination rates, hydrogen concentration, temperature, pressure) agree well with the experimental data. This demonstrates the suitability of CFD treatments of PAR behavior in a single compartment. Future validations should address the presence of steam in the initial mixture as well as multi-compartment geometries in order to increase confidence in CFD methods before upscaling to full containment scales.

Effects of steam dilution on laminar flame speeds of H2/air/H2O mixtures at atmospheric and elevated pressures

The laminar flame speeds of H2/air with steam dilution (up to 33 vol%) were measured over a wide range of equivalence ratio (0.9–3.0) at atmospheric and elevated pressures (up to 5 atm) by an improved Bunsen burner method. Burke, Sun, HP (High Pressure H2/O2 mechanism), and Davis mechanisms were employed to calculate the laminar flame speeds and analyze different effects of steam addition. Four studied mechanisms all underestimated the laminar flame speeds of H2/air/H2O mixtures at medium equivalence ratios while the Burke mechanism provided the best estimates. When the steam concentration was lower than 12%, increasing pressure first increased and then decreased the laminar flame speed, the inflection point appeared at 2.5 atm. When the steam concentration was greater than 12%, increasing the pressure monotonously decrease the laminar flame speed. The chemical effect was amplified by elevated pressure and it played an important role for the inhibiting effect of the pressure on laminar flame speed. The fluctuations of the chemical effect at 1 atm were mainly caused by three-body reactions, while the turn at 5 atm was mainly caused by the direct reaction effect. Elevated pressure and steam addition amplified the influences of uncertainties in the rate constants for elementary reactions, which might leaded to the disagreement between experimental and simulation results.

Role of fixed carbon and metal oxides in char during the catalytic conversion of tar from RDF gasification

The catalytic activity of char (fixed carbon + metal oxides) recovered from a commercial waste gasification plant and char-derived ash (metal oxides only) from the oxidation of the char (i.e. the controlled oxidation of the amorphous carbon in the char) was investigated for the cracking and steam reforming of tar. The latter was obtained following the soxhet extraction of sludge collected during a cleaning process (water scrubbing) on primary syngas. The tar was evaporated along with water in an evaporator maintained at 650 °C and entrained by a nitrogen flow. Tar in the gas phase was sent to a reformer where cracking + reforming tests were carried-out at 900 °C and 1 bar using char and char-derived ash pellets as catalysts. These catalysts were characterized using TGA, AE, XRD, SEM, EDX, XRF, ICP-MS, BET and Matersizer. Char-derived ash and char both hold similar metals and mineral structures. Following a 2 h conditioning at 900 °C, the fixed carbon in the char exhibited a larger surface area and pore volume while the char-derived ash revealed larger particle from the merging of vicinal minerals. No metal evaporation was observed after 24 h at 900 °C. During cracking and reforming, the initial 2–6 rings tar mixture extracted from the gasification residues sludge, loaded in the stream of nitrogen + steam at 65 g/Nm3, was reduced to 173.3 and 90.2 mg/Nm3, when using char-derived ash and char respectively. Pure syngas (CO + H2) was produced as the only permanent gases while carbon deposition was noticed in the solid beds. Even though the extent and type of tar were essentially similar when char and char-derived ash were used, the kinetics to reach steady state were slower for the char-derived ash. Steam content did not seem to impact on the tar conversion. However WG and WGS reactions most probably occurred, which might contribute to modulate the H2/CO molar ratio in the produced gas according to its targeted downstream utilization.

Fast pyrolysis and steam gasification of pellets prepared from olive oil mill residues

This paper examines the fast pyrolysis coupled with the steam gasification of agropellets prepared from the olive oil industries by-products via Macro-thermogravimetry. Three pellets samples were prepared from exhausted olive mill solid waste, impregnated olive mill wastewater/exhausted olive mill solid waste and impregnated olive mill wastewater/pine sawdust. The behavior of the three pellets during the fast pyrolysis and the char gasification stages were generally comparable despite some small differences in the conversion rates or char yields. The gasification of impregnated olive mill wastewater/exhausted olive mill solid waste pellets was selected as a promising route for their valorization and the reduction of the pollution impacts of olive mill wastewater. The impregnated olive mill wastewater/exhausted olive mill solid waste pellets pyrolysis rate was affected significantly by the temperature in the range of 750°C–950 °C. The mean char gasification rate was linearly dependent on temperature and steam molar fractions in the respective ranges of 750°C–950 °C and 10%–30% of steam concentration. The provided data on the fast pyrolysis and char gasification of the formulated impregnated olive mill wastewater/exhausted olive mill solid waste pellets constitute new set of experimental data that can serve for the design of gasifiers working with such kind of wastes.

Overview of hydrogen combustion experiments performed in a large scale vented vessel at Canadian Nuclear Laboratories

Hydrogen combustion inside a post-accident containment environment may pose a threat to the integrity of the containment structure and equipment. In CANDU reactors, combustion-generated overpressures in an accident will be relieved by venting to adjacent from one compartment volumes through relief panels or existing openings. To have a better understanding of the fundamental mechanisms that control the overpressures resulting from a vented hydrogen deflagration, a 120 m3 large scale vented combustion test facility was constructed at Canadian Nuclear Laboratories. A number of experiments have been completed in this facility to investigate hydrogen combustion behavior simulated in a post-accident reactor containment environment. A selected number of experimental results are presented in this paper to demonstrate several parameter effects on vented combustion dynamics by varying the number of chambers (single, two or three interconnected), volume and vent size, initial turbulence (quiescent vs. turbulent), initial temperature and steam concentration, mixture uniformity (well mixed vs. highly stratified), vent locations, and number of igniters. These results have provided useful insights for hydrogen management for the Canadian nuclear industry and CANDU utilities participating in the CANDU Owners Group research program. Most experimental data have been used for validation of combustion models and development of user guidelines.

Fluidized Bed Incineration of Sewage Sludge in O2/N2 and O2/CO2 Atmospheres

Sewage sludge incineration in a fluidized bed is considered to be one of the most suitable ways of sewage sludge disposal. This process reduces the volume of the waste and causes the destruction of organic contaminants such as POPs, pharmaceuticals and other compounds with endocrine-disrupting potential. Oxygen-enriched air combustion and oxy-fuel combustion can increase the combustion efficiency, reduce the amount of flue gas and make possible CO2 capture more effective. However, the influence of incineration medium composition has not yet been thoroughly investigated in case of sewage sludge incineration. In this paper, the incineration of sewage sludge in a bubbling fluidized bed reactor was studied at oxygen-enriched air conditions, oxy-fuel conditions and oxy-fuel conditions with zero and non-zero concentrations of steam, CO, NO, N2O and SO2 in the inlet combustion medium. Consequently, the effects of various operating parameters on pollutants formation were comprehensively described with emphasis on...

New, Efficient, and Reliable Air Electrode Material for Proton-Conducting Reversible Solid Oxide Cells.

Driven by the demand to minimize fluctuation in common renewable energies, reversible solid oxide cells (RSOCs) have drawn increasing attention for they can operate either as fuel cells to produce electricity or as electrolysis cells to store electricity. Unfortunately, development of proton-conducting RSOCs (P-RSOCs) faces a major challenge of poor reliability because of the high content of steam involved in air electrode reactions, which could seriously decay the lifetime of air electrode materials. In this work, a very stable and efficient air electrode, SrEu2Fe1.8Co0.2O7-δ (SEFC) with layer structure, is designed and deployed in P-RSOCs. X-ray diffraction analysis and High-angle annular dark-filed scanning transmission electron microscopy images of SEFC reveal that Sr atoms occupy the center of perovskite slabs, whereas Eu atoms arrange orderly in the rock-salt layer. Such a special structure of SEFC largely depresses its Lewis basicity and therefore its reactivity with steam. Applying the SEFC air electrode, our button switches smoothly between both fuel cell and electrolysis cell (EC) modes with no obvious degradation over a 135 h long-term test under wet H2 (∼3% H2O) and 10% H2O-air atmospheres. A record of over 230 h is achieved in the long-term stability test in the EC mode, doubling the longest test that had been previously reported. Besides good stability, SEFC demonstrates great catalytic activity toward air electrode reactions when compared with traditional La0.6Sr0.4Co0.2Fe0.8O3-δ air electrodes. This research highlights the potential of stable and efficient P-RSOCs as an important part in a sustainable new energy power system.

CO2 sequestration by direct gas–solid carbonation of fly ash with steam addition

Abstract Mineral carbonation using alkaline industrial solid wastes is a promising CO2 sequestration technology. In this work, the effects of temperature, CO2 content, steam content, and reaction time on CO2 sequestration at atmospheric pressure were studied by the direct gas–solid carbonation of circulating fluid bed fly ash in a thermogravimetric analyzer and a fixed bed reactor system. Results indicate that increasing the temperature and the content of CO2 and H2O(g) can improve the CO2 sequestration efficiency of the circulating fluid bed fly ash. However, the effect of CO2 content is not as significant as that of temperature and H2O(g). The maximum CO2 sequestration capacity of 60 g CO2/kg fly ash with a maximum sequestration efficiency of 28.74% was achieved at 600 °C with 20% H2O(g) addition. The Brunauer–Emmett–Teller surface area and the pore volume decreased with the increase in average pore size after carbonation, due to the formation of a dense carbonate protective layer and pore blockage. With steam addition, the surface area and the pore volume increase, which contributes to the conversion of CaO to CaCO3. The production of Ca(OH)2 or transient Ca(OH)2 and the enhancement of CO2 molecular mobility account for the promotion of steam in the carbonation process. The promotion mechanism of steam in different stages of reaction and temperature were explored in detail. Given the rich reserves of fly ash in China, it shows a good application prospect to use the Chinese fly ash as a mineral carbonation feedstock, which may not only reduces CO2 emission, but also stabilizes the wastes.

Effect of NTP Pretreatment on Thermal Resistance and Fouling Components of Oilfield Wastewater

In order to prevent scaling in the process of oilfield wastewater evaporation, low temperature plasma is used for pretreatment of heavy oil wastewater. It reacts with the ions and radicals produced by the low-temperature plasma and then is send into the evaporator. The changes of various indexes of the distilled water and the distribution of fouling in the evaporation process of heavy oil wastewater after plasma pretreatment were studied. The results showed that the content and hardness of silica in wastewater were decreased after plasma pretreatment, which was more suitable for evaporation treatment. At the same time, the content of salt and oil in distilled water is reduced, and the quality is improved. In addition, when the steam concentration was 30∼40 times, the suspended solids in the concentrated solution of the wastewater increased significantly after the plasma treatment. Correspondingly, the fouling at the bottom of evaporator is greatly reduced. Comparing the various indexes of distilled water and the feed water index of gas injection boiler, it can be seen that the excessive oil content in distilled water is the biggest obstacle to the recovery of distilled water to boiler feed water. Low temperature plasma pretreatment can provide a quick and new way to solve the scaling problems and water quality problems in the recovery of distilled water from a large number of heavy oil wastewater.

The BLEVE Research of Reaction Runaway Based on the Aspen Plus-Fluent

Abstract A new scene analysis method of reactor thermal explosion accident based on process simulation and CFD method is proposed. The thermal runaway of batch reactor with methanol and acetic anhydride is simulated by Aspen Plus. The molecular weight and component concentration of steam after explosion overpressure are studied. The vapor cloud explosion is simulated by Fluent. The propagation law of vapor cloud explosion pressure wave and flame front is analyzed based on the simulation results.

Analysis of the effect of water steam concentration on water drop cooling process efficiency in conditions of water cooling towers of thermal power plants

Numerical investigation of transient distribution of temperature in water drops cooled in cool blast in conditions typical for high capacity evaporative water cooling towers has been done. Water drops cooling through thermal conductivity and water evaporation has been taken into consideration. It has been proved that the analysis of temperature distribution along the radius of water drop increases reliability of evaluation results of average temperature of water drops when they are cooled. Effect of water steam concentration in steam-gas mixture layer surrounding a water drop on water cooling towers efficiency has been evaluated.

Catalytic steam gasification of Mengdong coal in the presence of iron ore for hydrogen-rich gas production

Hydrogen-rich gas production from catalytic steam gasification of coal was investigated in the presence of iron ore in a vertical fixed bed reactor. The addition of iron ore significantly promoted the H2 yields. The effects of operation parameters (upper zone temperature, lower zone temperature, steam concentration, and iron to coal ratio) on the yield of selected gaseous products (H2 and CO) during catalytic steam gasification, were studied using Taguchi method. The results of signal-to-noise ratio indicated that steam concentration and iron to coal ratio were the most important parameters in determining the yield of H2 and CO, respectively. Semi-quantification X-ray diffraction analysis of iron ores indicated that increase in steam concentration intensified the oxidization of low valence iron compounds to Fe3O4. In addition, formation of Fe3O4 was also favored with increasing reaction temperatures (600 °C–900 °C). However, the formation of Fe3O4 was inhibited at higher reaction temperature (1000 °C) due to the destruction of porous structures of the iron ore.

Variation of Char Reactivity during Catalytic Gasification with Steam: Comparison among Catalytic Gasification by Ion-Exchangeable Na, Ca, and Na/Ca Mixture

The reactivity profile of char during catalytic gasification is crucial for designing and optimizing the gasification process, and it is greatly affected by the types and changes in activity of the catalyst during gasification. The catalytic gasification of Na-Char, Ca-Char, and Na/Ca-Char mixtures with different concentrations of steam was conducted within the temperature range of 700–900 °C using a microfluidized bed reaction analyzer. The results indicate that the reactivity of Na-Char is always higher than that of Ca-Char during the initial gasification stage (0–Xi) and then lower than that of Ca-Char in the later stage. The observations are mainly attributed to the different deactivation paths for the Na and Ca catalysts. The drastic loss of Na during gasification corresponds well to the sharp decrease of Na-Char reactivity within the initial carbon conversion, and the gradual change of the Ca dispersion contributes to the deactivation of the Ca catalyst. It is also demonstrated that the catalysis of...

Benzene Conversion in a Packed Bed Loaded with Biomass Char Particles

This study investigates the conversion of benzene in a packed bed containing fine char particles. Benzene and steam were simultaneously supplied to a tubular ceramic reactor that was heated electrically. Fragmented char particles were suspended and continuously supplied via a separate supply line. A packed bed of crushed alumina balls was positioned in the reactor to retain the char particles. The benzene conversion in the hot char bed was investigated by varying the bed temperature (900–1100 °C), steam concentration (0–27 vol %), and char concentration (5–50 g Nm–3). The highest conversions achieved in the experiments were approximately 75%. At comparable char concentrations, similar benzene conversions occurred at 900 and 1000 °C. Increasing the temperature to 1100 °C or increasing the steam concentration reduced the benzene conversion. The results indicate that the reduced conversion was due to enhanced char gasification reactions at elevated temperatures and steam concentrations and thus to reduced ch...

Numerical investigation of natural convection inside the containment with recovering passive containment cooling system using GASFLOW-MPI

The condensation on containment shell drives the nearby gas downwards creating a natural convection in containments which plays a key role for long-term passive containment cooling. In late phase of accident where hydrogen and steam accumulate in containment, recovery of containment cooling can cause the loss of steam-inert status for the containment atmosphere leading to hydrogen risk in containment. This process is analyzed in this paper focusing on the natural convection driven by wall condensation, and its influence on hydrogen distribution. Firstly, both convective heat transfer model and condensation model are validated with two separate effect experiments. The analogy argument among monument, heat and mass transfer is adopted in GASFLOW-MPI to analysis monument, mass and energy transfer between structure surface and fluid. The simulation result shows good agreement with experiment data. Then a simplified containment model including two steam generator compartments and pressurizer compartment is built and analyzed with GASFLOW-MPI with a postulated accident condition. To avoid long time calculation, the initial condition is calculated with a methodology that is designed to estimate containment status during severe accident provided by EPRI. Two cases are simulated, one without steam injection, where the natural convection drives only by condensation. Other one considers the decay heat that is postulated as a constant steam injection to simulate the natural circulation in containments. Result shows that, during the containment cooling, a transient stratification will occur, leading to high concentration of steam in the dome while low concentration at bottom. This is because the condensed gas is driven downwards near containment shell, pushing steam-rich gas at bottom upwards. The stratification of steam results in a reverse stratification of hydrogen, with high concentration at bottom while low concentration in the dome. Combustibility cloud shows that there is still a stratification of combustibility in containment, though the hydrogen distribution is quite uniform at the end of computation. Therefore, the hydrogen risk should be concerned when implementing containment cooling, especially the local hydrogen concentrate happening at the bottom of containment.

Effect of torrefaction on the high temperature steam gasification of cellulose based upon the Gibbs free energy minimization

The steam gasification can convert biomass into syngas, which can be conveniently used as fuels or chemical raw materials. Cellulose, as an important component of biomass, has a significant effect on the gasification behavior. Steam gasification behaviors of raw and torrefied cellulose at high temperature were investigated using a non-stoichiometric equilibrium model. The effect of torrefaction severity on the high temperature steam gasification of cellulose was evaluated. With increasing of steam/cellulose molar ratio, the molar numbers of hydrogen and carbon dioxide increased, whereas the molar number of carbon monoxide decreased. Less than 1.0 molar ratio of steam/cellulose was recommended for raw and torrefied celluloses. The methane steam reaction for severely torrefied cellulose at low steam/cellulose molar ratio was found. The molar number of the hydrogen increased from 1.992 to 2.016 mol with the increasing of torrefaction temperature from 250 to 300 °C. The influence of steam content on the water-gas reaction was more obvious than that of reaction temperature. This study will promote the development of steam gasification of biomass for the purpose of high efficiency utilization.