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An accurate prediction of the hydrogen behaviors in the accident and management process is a crucial topic for both the hydrogen safety assessment and safety analysis in the confined enclosure like the containment of the nuclear power plant (NPP). Hence, the hydrogen behaviors including the transient light gas release, stratification and dissolution in the TH22 test facility for the NPP containment are analyzed and compared using the 3-D CFD code GASFLOW-MPI in this study. In this paper, the light gas helium is adopted as a substitute for the hydrogen in the calculations in accordance with the experiment. Firstly, the detached eddy simulation (DES) turbulence model, 3-D numerical model and experiment setup are introduced. Then, the hydrogen behaviors with the GASFLOW-MPI including the light gas release, stratification and dissolution are analyzed and validated with the experiment data. In addition, the velocity profiles, light gas concentrations, dimensionless numbers and temperature distributions are evaluated for the characteristics of the hydrogen behaviors. The results indicate that the calculation results agree well with the experiment data. Foremostly, the relative errors between the calculation results and experiment data during the phase of the dissolution of the light gas cloud are within 11.9%. Meanwhile, the relative errors of the time for the complete dissolution during the phase of the dissolution of the light gas cloud are within 5.0%. For the light gas release and stratification phase, the jet flow dominates as the Froude (Fr) number exceeds 10 during the time t = 600 s–800 s. Additionally, the time averaged centerline velocity and light gas concentration after the potential core region decay with a slop of 1/z which coincide with the theoretical jet limit. Lastly, the light gas concentrations and temperature distributions in all three phases are captured clearly with the GAFLOW-MPI. It demonstrates that the GASFLOW-MPI can accurately described the details of the related hydrogen behaviors in the accident and management process in the confined enclosure like the NPP. This paper can provide guidance for the numerical computation of the hydrogen safety issues in the confined space.

Hydrogen energy is expanding world-widely in recent years, while hydrogen safety issues have drawn considerable attention. It is widely accepted that accidental hydrogen release in an open-air environment will disperse quickly, hence not causing significant hydrogen hazards. A hydrogen hazard is more likely to occur when hydrogen is accidentally released in a confined place, i.e. parking garages and tunnels. Prediction the main accident process, including the hydrogen release, dispersion, and combustion, is important for hydrogen safety assessment, and ensuring the safety installations during accidents. Hence, a postulated accident scenario induced by the operation of Thermal Pressure Relief Device in a tunnel is analysed for hydrogen fuel cell vehicles with GASFLOW-MPI in this study. GASFLOW-MPI is a well validated parallel CFD code focusing on the transport, combustion, and detonation of hydrogen. It solves compressible Navier-Stokes equations with a powerful all-speed Arbitrary-Lagrangian-Eulerian (ALE) method; hence can cover both the non-compressible flow during the hydrogen release and dispersion phases, and the compressible flow during deflagration and detonation. In this study, a 3D model of real-scaled tunnel is modelled, firstly. Then the hydrogen dispersion in the tunnel is calculated to evaluate the risk of Flame acceleration and the Deflagration-Detonation Transient (DDT). The case with jet fire is analysed with assuming that the hydrogen is ignited right after being injected forming a jet fire in the tunnel, the consequence of this case is limited considering the small hydrogen inventory. The detonation in the tunnel is calculated by assuming a strong ignition at the top of the tunnel at an unfavourable time and location. The pressure loads are calculated to evaluate the consequence of the hazard. The analysis shows that the GASFLOW-MPI is applicable at a widely range for tunnel accidents, meanwhile, the safety issues related to tunnel accidents is worthy further study considering the complexity of tunnels.

The liquid product from biomass direct pyrolysis is usually complex and difficult to effectively utilize. By combining hydrothermal conversion and low-temperature pyrolysis, the hemicellulose and cellulose of biomass can be transformed into value-added furfural and levoglucosan (LG), respectively. The effects of temperature during hydrothermal treatment (160–240 °C) and subsequent pyrolysis (340–400 °C) on the production of furfural and LG were investigated by using three typical agricultural wastes, namely corn stalk, peanut shells, and rice stalk. The maximum furfural yield of 4.2% was achieved upon hydrolysis of peanut shells at 200 °C. The hydrochar produced from peanut shells presented the highest LG yield of 7.3% (based on original biomass weight) for a pyrolysis temperature of 360 °C. Under this optimal condition, the total revenue from various products of the hybrid thermochemical process was estimated at $0.362 per kilogram of peanut shells, whereas furfural and LG account for 90% of the revenue.

A series of experiments were conducted to study the pressure and combustion characteristics of the high-pressure hydrogen during the occurrence of spontaneous ignition and the conversion from spontaneous ignition to a jet fire and explosion. Different initial conditions including release pressure (4–10 MPa), tube diameter (10/15 mm), and tube length (0.3/0.7/1.2/1.7/2.2/3 m) were tested. The variation of the pressure and flame signal inside and outside of the tube and the development of the jet flame were recorded. The experimental results revealed that the minimum ignition pressure required for self-ignition of hydrogen at different tube diameters decreased first and then increased with the extension of tubes. The minimum ignition pressure for tubes diameters of 10 mm and 15 mm is no more than 4 MPa and the length of the tubes is L = 1.7 m. The minimum release pressure required for spontaneous ignition of a tube D = 15 mm is always lower than that of a tube D = 10 mm at the same tube length. When the spontaneous ignition occurred, it did not absolutely trigger the jet fire. The transition from spontaneous ignition to a jet fire must go through the specific stages.

Catalytic hydrotreatment under supercritical ethanol conditions is an effective method for improving the performance of wood tar. In this study, the physicochemical properties of industrial wood ta...

To understanding the biomass pyrolysis process in depth, the pyrolysis mechanism of cellulose was investigated based on the combination of gas and liquid product releasing behavior with the structu...

Experiment and simulation were conducted to study the development process of jet fire and explosion induced by the high-pressure hydrogen spontaneous ignition. The pressurized hydrogen was released under different tube length and release pressure in the experiment. The overpressure generated by the leading shock and the light signal of the flame with different conditions were recorded. The propagation of the external jet flame was captured by a high-speed camera. Different parameters including velocity, temperature, and concentration distribution were analyzed based on the simulated results. It is revealed that the jet fire and explosion, which are induced by hydrogen self-ignition, must go through a series of specific stages of development, and this process has no significant correlation with pipe length and release pressure. This process consists of several stages, including the formation of the combustion zone downstream of the Mach disk; the flame chases the top of the jet along the shear layer; the flow velocity at the top of the jet decreases causing the ring vortex to disappear and the combustible gas to accumulate; the shear layer flame propagates to the top of the jet causing the explosion. Besides, the explosion will inevitably occur along with the jet fire, which is caused by the spontaneous ignition induced by the sudden release of high-pressure hydrogen and is developed in the open space.

Background Metastasis and recurrence, wherein circulating tumour cells (CTCs) play an important role, are the leading causes of death in colorectal cancer (CRC). Metastasis-initiating CTCs manage to maintain intravascular survival under anoikis, immune attack, and importantly shear stress; however, the underlying mechanisms remain poorly understood. Methods In view of the scarcity of CTCs in the bloodstream, suspended colorectal cancer cells were flowed into the cyclic laminar shear stress (LSS) according to previous studies. Then, we detected these suspended cells with a CK8+/CD45−/DAPI+ phenotype and named them mimic circulating tumour cells (m-CTCs) for subsequent CTCs related researches. Quantitative polymerase chain reaction, western blotting, and immunofluorescence were utilised to analyse gene expression change of m-CTCs sensitive to LSS stimulation. Additionally, we examined atonal bHLH transcription factor 8 (ATOH8) expressions in CTCs among 156 CRC patients and mice by fluorescence in situ hybridisation and flow cytometry. The pro-metabolic and pro-survival functions of ATOH8 were determined by glycolysis assay, live/dead cell vitality assay, anoikis assay, and immunohistochemistry. Further, the concrete up-and-down mechanisms of m-CTC survival promotion by ATOH8 were explored. Results The m-CTCs actively responded to LSS by triggering the expression of ATOH8, a fluid mechanosensor, with executive roles in intravascular survival and metabolism plasticity. Specifically, ATOH8 was upregulated via activation of VEGFR2/AKT signalling pathway mediated by LSS induced VEGF release. ATOH8 then transcriptionally activated HK2-mediated glycolysis, thus promoting the intravascular survival of colorectal cancer cells in the circulation. Conclusions This study elucidates a novel mechanism that an LSS triggered VEGF-VEGFR2-AKT-ATOH8 signal axis mediates m-CTCs survival, thus providing a potential target for the prevention and treatment of hematogenous metastasis in CRC.

During a severe accident involving a Nuclear Power Plant (NPP), a hydrogen-enriched stratification may occur in the dome of the containment. This is due to the gaseous density difference of a steam/hydrogen turbulent jet released from the break. This accident scenario is one of the high-ranking phenomena identified in the Phenomena Identification and Ranking Table (PIRT) for containment safety thermal hydraulics. In this work, the temporal evolution of the stratification erosion is analysed using the parallel CFD code GASFLOW-MPI with comparison to the experimental data from the THAI TH-20 benchmark, where helium is used as a hydrogen simulate. Identifying a suitable turbulence model is an important issue for a successful stratification erosion simulation due to turbulent mixing between the stratification and turbulent jet featured with the sharp velocity and density gradients. Three well-known turbulence models: 1. The classic k-e model, 2. Large Eddy Simulation (LES) model and 3. Detached Eddy Simulation (DES) model are employed to evaluate their performances. Due to the negative buoyancy effect resulting from the light gas layer, the jet gradually loses its initial momentum and cannot penetrate the stratified layer in depth. The interaction Froude (Fr) number which is used to categorize the mixing mechanism is close to 1 in this work, indicating that the erosion process of the stratified layer is dominated by both the molecular diffusion and the momentum transport. The experimental data measured at different heights in THAI TH-20 benchmark, from the pure air region at the lower containment region up into the large helium concentration gradient region, and further up to high helium concentration region at the top of the containment. The calculated results show that the LES and DES turbulence models can capture time histories of helium concentration at all of the sensor points accurately, while the k-e turbulence model predictions are always delayed due to its overestimating the turbulence mixing in the stratified layer. Moreover, compared with the k-e model, more detailed turbulent eddy structure is resolved by the LES model and DES model, whose frequency satisfies the negative −5/3 energy decay rate for a wide region of frequency. Therefore, the LES and DES models are recommended for the stratification erosion simulation. This can provide guidance for nuclear engineers analysing hydrogen distribution phenomena during severe accidents.

The effect of potassium in biomass on the catalytic activity of ZSM-5 zeolite in the fast pyrolysis of biomass was investigated using 2-methylfuran (2-MF) as the typical model compound. The mechanism of action of potassium was explored in detail, along with the physicochemical properties of ZSM-5, including crystallinity, pore structure, and surface acidity. The physicochemical properties of ZSM-5 deteriorated to varying degrees after being tainted with different potassium sources (KOH, K2CO3, KAc, and KCl). Compared with neutral KCl and strong alkali KOH, K2CO3, and KAc, with weaker alkalinity but larger crystal structure, exerted a larger influence on ZSM-5. Changes in ZSM-5 tainted with K2CO3 were the greatest, and crystallinity, surface area, acidity, and the corresponding yields of valuable aromatic hydrocarbons and gas products, all declined significantly, compared with raw ZSM-5. When the amount of K(CO32−) on ZSM-5 was less than 0.5 wt%, only minor (

Power-to-Gas technologies could play an important role in future energy systems, since they make it possible to store surplus electric energy from fluctuating renewable energy sources such as solar and wind. In Power-to-Gas concepts, the first step towards storage is the production of H2 by electrolysis, a possible further step is methanation. The Engler-Bunte-Institute, Fuel Technology at Karlsruhe Institute of Technology is conducting research on catalytic methanation in slurry bubble column reactors, which represent a highly load flexible reactor technology. To obtain experimental data at a semi-industrial scale a methanation pilot plant was built and commissioned. The plant is equipped with various safety valves, which may release the hazardous gases H2, CO and CH4 in the chemical reactor into the environment in the unintended case of overpressure, which may lead to a flammable and/or toxic cloud, threatening the safety of the workers and other humans near the plant. In this work, the safety evaluation of the accidental release in the methanation plant is performed using the numerical tool GASFLOW-MPI. Both toxicity and flammability of the hazardous gas cloud are analyzed and discussed. A local-global two-step simulation strategy, including a local computational model and a global computational model, is employed to calculate the hazardous gas dispersion efficiently and accurately. In the first step, a local detailed computational model with fine mesh is used to calculate the release mass flow through the exhaust tube and the complicated shock waves directly without any further assumption model such as the notional nozzle model. In the second step, a large-scale model with the relatively coarse mesh is chosen to efficiently predict the hazardous gas dispersion around the entire methanation plant. Moreover, the performances of two different types of exhaust pipes are compared and discussed, and the recommended exhaust pipe design is provided. The simulation results show that version B of the exhaust tubes is more recommendable from the viewpoint of safety.

With the rapid development of photonic integrated circuit, waveguide-based electro-optic modulators are widely used in the fields of optical communication, optical signal processing and optical sensors. The Mach-Zehnder modulator is one of the most widely used device structures as a particular kind of optical switching element, which has the advantages of great accuracy and high sensitivity. We investigate two types of Mach-Zehnder modulators (using balanced and unbalanced interferometers) based on lithium niobate (LiNbO3) through theoretical and numerical analysis. The transmission characteristics of the balanced Mach-Zehnder modulator are numerically analyzed while the electric field is applied across the waveguide in one of the arms (or the two arms) of the interferometer, and the transmission characteristics of the unbalanced Mach-Zehnder modulator with different length differences between the two waveguide arms are studied. Numerical calculation results show that the transmission of the waveguide in the Mach-Zehnder structure changes sinusoidally, with alternately switching between port 2 and port 4. The theoretical results in the present work can provide some guidance for developing the practical optical modulator devices.

Hydrogen fires may pose serious safety issues in vented compartments of nuclear reactor containment and fuel cell systems under hypothetical accidents. Experimental studies on vented hydrogen fires have been performed with the HYKA test facility at Karlsruhe Institute of Technology (KIT) within Work Package 4 (WP4) - hydrogen jet fire in a confined space of the European HyIndoor project. It has been observed that heat losses of the combustion products can significantly affect the combustion regimes of hydrogen fire as well as the pressure and thermal loads on the confinement structures. Dynamics of turbulent hydrogen jet fire in a vented enclosure was investigated using the CFD code GASFLOW-MPI. Effects of heat losses, including convective heat transfer, steam condensation and thermal radiation, have been studied. The unsteady characteristics of hydrogen jet fires can be successfully captured when the heat transfer mechanisms are considered. Both initial pressure peak and pressure decay were very well predicted compared to the experimental data. A pulsating process of flame extinction due to the consumption of oxygen and then self-ignition due to the inflow of fresh air was captured as well. However, in the adiabatic case without considering the heat loss effects, the pressure and temperature were considerably over-predicted and the major physical phenomena occurring in the combustion enclosure were not able to be reproduced while showing large discrepancies from the experimental observations. The effect of sustained hydrogen release on the jet fire dynamics was also investigated. It indicates that heat losses can have important implications and should be considered in hydrogen combustion simulations.

In this study, we provided a solvent-free method to modify allyl methacrylate (AMA) with 1,1,1,3,5,5,5-heptamethyltrisiloxane (MDHM) through hydrosilylation reaction catalyzed by Speier’s catalyst. The results from Fourier transform infrared spectroscopy (FT-IR) and ultraviolet spectrometer (UV) clearly indicated that AMA was modified by MDHM through the hydrosilylation on the C C of isopropenyl segment with the C C of propenyl group remaining to obtain unsaturated acrylate containing organosiloxane chain segment. We also studied the application of MDHM modified AMA in waterborne self-matting styrene-acrylic emulsions through in-situ copolymerization. The surface gloss, wettability, chemical composition and morphology of the prepared emulsion coating films were investigated. The results showed that organosiloxane chain segments were successfully introduced, which made film get a fine rough surface, which increase the film surface water contact angle and help to obtain a kind of waterborne semi-gloss styrene-acrylic resin film.

Developing cost-effective and high-performance catalysts in biomass chemistry is motivated by creating sustainable technologies dependent on inexpensive and abundant resources. The existing methods for the direct preparation of 5-methylfurfural (5-MF) from biomass-derived fructose mediated by hydrogen iodide (HI) mainly require precious metal catalysts. This research showed that low-cost tungsten carbide (WC) was capable to produce HI from iodine (I2) via liquid-phase hydrogenation, but a pivotal limitation was the poor stability under the combination effects of water and I2. To solve this problem, the bulk WC and the high dispersion supported WC were modified by hydrophobic organosilicones through simple liquid phase deposition. Both of the two superhydrophobic WC materials had better stability and their catalytic activity were comparable to the expensive palladium-carbon (Pd/C) catalyst in the preparation of 5-MF, especially the superhydrophobic high dispersion supported WC. This work highlights the potential of the low-cost WC with simple superhydrophobic modification in assisting the direct preparation of 5-MF from fructose mediated by HI, which has high significance to the sustainable development of the low-cost biomass chemical engineering.

The balise transmission system (BTS) is an automatic identification system for vehicle–ground communication based on radio frequency identification (RFID) technology. The electromagnetic coupling characteristics of BTS have a very important effect on the transmission quality of the uplink telegram signals. However, signal transmission problems of BTS often occur due to unreasonable installation mode or parameter setting. In order to solve these problems, it is necessary to fully discuss the electromagnetic coupling characteristics of the BTS. In this paper, the transmission process of energy and data between the onboard antenna unit and the balise was analyzed using digital twin technology. A high-precision dynamic electromagnetic coupling model of the BTS was established from four aspects of three-dimensional structure, physical properties, behavior patterns, and rule restrictions. Then the accuracy of the model was verified by experiments. Finally, the influence of typical parameters on the uplink signal is calculated and analyzed quantitatively. The results showed that compared with other factors discussed in this paper, the vertical distance and the installation mode had greater effects on the uplink signal. These results can be used to guide the engineering installation and related optimization of the BTS.

The core-melt in Fukushima-Daiichi Unit 1 represents a new class of severe accidents in which combustible gas from core degradation leaked from the containment into the surrounding air-filled reactor building, formed there a highly reactive gas mixture, and exploded 25 h after begin of the station black-out. Since TMI-2 hydrogen safety research and management has focussed on processes and counter-measures inside the containment but the reactor building remained unprotected against hydrogen threats. The code GASFLOW-MPI is currently under development to simulate hydrogen behaviors, including distribution and combustion, for scenarios with containment leakage. This paper describes a first analysis of the hydrogen explosion in Unit 1. It investigates gas dispersion in the reactor building, assuming a leak at the drywell head flange, shows the evolution of a stratified, inhomogeneous H 2 –O 2 –N 2 –steam mixture in the refueling bay, simulates the combustion of the reactive gas mixture, and predicts pressure loads to walls and internal structures of the reactor building. The blast wave propagated essentially sideways, which explains why all side walls were blown out and the ceiling just collapsed onto the floor of the refueling bay. The blast wave propagation into the free environment was also simulated. The over-pressure amplitudes are sufficiently high to cause damage to adjacent buildings and to injure people. The hitherto existing presumption that the blow-out panel of Unit 2 was removed by the Unit 1 explosion can be confirmed which likely prevented a hydrogen explosion in the Unit 2. GASFLOW-MPI provides validated models for the integral simulations of leakage related core-melt scenarios. Furthermore, the code contains extensively tested submodels for catalytic recombiners, igniters and burst foils, which allow design of new hydrogen risk mitigation systems for currently unprotected spaces in reactor buildings.

To investigate the influence of bifurcation structure in tubes on the spontaneous ignition of high-pressure hydrogen, a series of experiments were conducted. The tubes including T-shaped and straight tubes with the length of 0.7/1.2/1.7 m were tested. The burst pressure ranged from 4–10 MPa. The pressure and light signals in the tube and the external flame images were recorded. The results show that the T-shaped structure has a significant influence on the occurrence of spontaneous ignition. The critical release pressure required for self-ignition in short T-shaped tube was lower than that in straight tube, because the strong reflect shock wave near the bifurcation point heated the combustible mixtures near the contact surface. However, with the extension of the tube length, the critical pressure increased, because the distance between the leading shock and contact surface increased when the leading shock reached the bifurcation point. Consequently, the reflect shock cannot heat the combustible mixture near the contact surface, but the air instead. Besides, comparing with the straight tube, the formation of jet fire was inhibited in the T-shaped long tube (1.2/1.7 m) and the shock wave attenuated rapidly after pass through the bifurcation point.

To gain an improved understanding of the hemicellulose pyrolysis mechanism, two-dimensional correlation infrared spectroscopy (2D-PCIS) was employed to analyze the functional group evolution in xylan chars between 200 and 600 °C, and through combination with the obtained volatiles releasing properties. Simultaneously, the pathway of xylan decomposition was deduced to illustrate the pyrolysis mechanism. The depolymerization and ring-opening reactions of xylan started at 200℃. After that, it was mainly xylan matrix degradation reaction to form char structure which mainly consisted of phenyl rings and oxygen-containing cyclic compounds with aliphatic chains. With temperature increasing (300–450 ℃), the decarbonylation reaction, removal of C C and fatty chains reactions were intensified and the molecular structures of xylan char reconstructed to form fused-ring compounds on the order of 1 × 2 and 2 × 2 through condensation. Dehydrogenation and polycondensation reaction of xylan increased at higher temperature (450–600 °C). The char structure was composed of high-order fused-ring compounds, and the production of H2 and CH4 increased greatly.

In hydrogen safety analysis, structure response due to the pressure and thermal loads from the combustion is of great concern. It is of high significance to understand not only the combustion process itself, but also the heat losses from the combustion products to the solid structures which may have strong impacts on the pressure and temperature decays. In many previous numerical simulations, heat losses from turbulent hydrogen flames to the confinement structures were usually considered to be negligible or less important. However, it has been revealed by many experimental studies that modeling of heat losses from the combustion products is important for accurate predictions. Our objectives are to study the importance of various heat transfer mechanisms and their relative contributions to the total energy losses. Numerical investigations on the mechanisms of heat losses caused by propagating turbulent flames were performed using a semi-implicit pressure-based all-speed CFD code GASFLOW-MPI. Heat losses from turbulent sonic flames to the structures of the ENACCEF facility at IRSN were studied. It appears that the effect of heat losses on the flame propagation properties is not significant. However, the impacts of heat losses on the pressure peak and pressure decay after hydrogen combustions should not be neglected. It indicates from our simulation results that the convective heat transfer and thermal radiative heat transfer are the main contributors of the total energy losses to the structures of ENACCEF. In our cases, the effect of steam condensation heat transfer is relatively small but not negligible. The relative contributions of various heat transfer mechanisms could be different in other experimental facilities with various geometrical configurations, various internal structures, and various optical and thermal characteristics of the burnable gas mixtures. In general, it is suggested to include the heat transfer mechanisms in order to improve the reliability and accuracy of numerical analyses of hydrogen safety issues.

In the present work release and ignition experiments with horizontal cryogenic hydrogen jets at temperatures of 35–65 K and pressures from 0.7 to 3.5 MPa were performed in the ICESAFE facility at KIT. This facility is specially designed for experiments under steady-state sonic release conditions with constant temperature and pressure in the hydrogen reservoir. In distribution experiments the temperature, velocity, turbulence and concentration distribution of hydrogen with different circular nozzle diameters and reservoir conditions was investigated for releases into stagnant ambient air. Subsequent combustion experiments of hydrogen jets included investigations on the stability of the flame and its propagation behaviour as function of the ignition position. Furthermore combustion pressures and heat radiation from the sonic jet flame during the combustion process were measured. Safety distances were evaluated and an extrapolation model to other jet conditions was proposed. The results of this work provide novel data on cryogenic sonic hydrogen jets and give information on the hazard potential arising from leaks in liquid hydrogen reservoirs.

The dynamic blow-down process of a high pressure gaseous hydrogen (GH 2 ) reservoir in case of a small leak is a complex process involving a chain of distinct flow regimes and gas states. This paper presents models to predict the hydrogen concentration and velocity field in the vicinity of a postulated small leak. An isentropic expansion model with a real gas equation of state for normal hydrogen is used to calculate the time dependent gas state in the reservoir and at the leak. The subsequent gas expansion to 0.1 MPa is predicted with a zero-dimensional model. The gas conditions after expansion serve as input to a newly developed integral model for a round free turbulent H 2 -jet into ambient air. Predictions are made for the blow-down of hydrogen reservoirs with 10, 30 and 100 MPa initial pressure. A normalized hydrogen concentration field in the free jet is presented which allows for a given leak scenario the prediction of the axial and radial range of flammable H 2 –air mixtures.

In the ITER wet bypass scenario, water leakage, air ingress and hot dust (Be, W, and C) in the vacuum vessel could generate combustible hydrogen–air–steam mixture. Hydrogen combustion may threaten the integrity of the ITER VV and lead to radioactivity release. To prevent hydrogen energetic combustion, nitrogen injection system in VV and hydrogen recombination system in the pressure suppression tank (ST) were proposed. The main objectives of this analysis are to study the distribution of hydrogen–air–steam mixtures in the ITER sub-volumes, to investigate the feasibility of the nitrogen injection system to fully inert the atmosphere in the VV and to evaluate the capability and efficiency of the hydrogen recombination system to remove hydrogen in the ST. 3D computational fluid dynamics (CFD) code GASFLOW was used to calculate the evolution of the mixtures and to evaluate the hydrogen combustion risks in the ITER sub-volumes. The results indicate that the proposed hydrogen risk mitigation systems will generally prevent the risks of hydrogen detonation and fast deflagration. However, the atmosphere in ITER sub-volumes cannot be completely inerted at the early stage of the scenario. Slow deflagrations could still generate quasi-static pressures above 1 bar in the VV. The structural impact of the thermal and pressure loads generated by hydrogen combustions will be investigated in future studies.

Hydrogen combustion in a nuclear power plant containment building may threaten the integrity of the containment. Hydrogen recombiners and igniters are two methods to reduce hydrogen levels in containment buildings during severe accidents. The purpose of this paper is to evaluate the safety implementation of hydrogen igniters and recombiners. This paper analyzes the risk of deliberate hydrogen ignition and investigates three mitigation measures using igniters only, hydrogen recombiners only or a combination of recombiners and igniters. The results indicate that steam can effectively control the hydrogen flame acceleration and the deflagration-to-detonation transition.

Nitrogen injection system in the vacuum vessel (VV) was proposed to prevent hydrogen explosions during International Thermonuclear Experimental Reactor (ITER) accident scenario. In previous studies, the nitrogen injection system for the mitigation of the hydrogen explosion risk under wet bypass scenario was investigated using CFD codes, GASFLOW and CAST3M. In order to further verify the capability of the codes, experiments in large scale facility MISTRA were carried out at CEA. In this paper, two cases with and without nitrogen inerting were analyzed using two classical turbulence models in GASFLOW code. Subsequently the numerical results have been compared against the experimental results from MISTRA, showing the effect of the turbulence modelling in the prediction of gas mixing.Copyright © 2012 by ASME

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 -- {epsilon} 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 -- {epsilon} 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 themore » risk of hydrogen combustion. (authors)« less