Fires, Explosions, and Venting in Nuclear Reactors (original) (raw)
Related papers
A Hydrogen Ignition Mechanism for Explosions in Nuclear Facility Pipe Systems
ASME 2010 Pressure Vessels and Piping Conference: Volume 3, 2010
Hydrogen and oxygen generation due to the radiolysis of water is a recognized hazard in pipe systems used in the nuclear industry, where the accumulation of hydrogen and oxygen at high points in the pipe system is expected, and explosive conditions exist. Pipe ruptures at nuclear facilities were attributed to hydrogen explosions inside pipelines, in nuclear facilities, i.e., Hamaoka, Nuclear Power Station in Japan, and Brunsbuettel in Germany. Prior to these accidents an ignition source for hydrogen was questionable, but these accidents, demonstrated that a mechanism was, in fact, available to initiate combustion and explosion. Hydrogen explosions may occur simultaneously with water hammer accidents in nuclear facilities, and a theoretical mechanism to relate water hammer to hydrogen deflagrations and explosions is presented herein.
In case of a core melt accident in a European light water nuclear reactor the pressure vessel may fail, in spite of depressurization of the primary circuit, still at an elevated pressure of 1 to 2 MPa. Then, the molten core debris will be ejected forcefully into the reactor cavity and beyond, depending on the specific reactor design. This may pressurize the reactor containment building beyond its failure pressure. The pressurization of the containment is due to the debris-to-gas heat transfer but also to a large part to hydrogen combustion. Hydrogen combustion contributes to peak containment pressure if the energy release rate is greater than the heat transfer rate to structures and occurs concurrent with the debris-to-gas heat transfer. This paper presents experimental and analytical results of the combustion of hydrogen jets blown into a scaled reactor containment with a prototypic atmosphere of air, steam and preexisting hydrogen. Experimental data are the pressure and temperatur...
Hydrogen combustion in a flat semi-confined layer with respect to the Fukushima Daiichi accident
Nuclear Engineering and Design, 2015
Hydrogen accumulation at the top of containment or reactor building may occur due to an interaction of molten corium and water followed by a severe accident of a nuclear reactor (TMI, Chernobyl, Fukushima Daiichi). The hydrogen, released from the reactor, accumulates usually as a stratified semi-confined layer of hydrogen-air mixture. A series of large scale experiments on hydrogen combustion and explosion in a semi-confined layer of uniform and non-uniform hydrogen-air mixtures in presence of obstructions or without them was performed at the Karlsruhe Institute of Technology (KIT). Different flame propagation regimes from slow subsonic to relative fast sonic flames and then to the detonations were experimentally investigated in different geometries and then simulated with COM3D code with respect to evaluate an amount of burnt hydrogen taken place during the Fukushima Daiichi Accident (FDA). The experiments were performed in a horizontal semi-confined layer with dimensions of 9x3x0.6 m with/without obstacles opened from below. Hydrogen concentration in the mixtures with air was varied in the range of 0-34 vol.% without or with a gradient of 0-60 vol. %H2/m. Effects of the hydrogen concentration gradient, thickness of the layer, geometry of the obstructions, average and maximum hydrogen concentration on flame propagation regimes were investigated with respect to evaluate the maximum pressure loads of internal structures. Blast wave strength and dynamics of propagation after explosion of the layer of hydrogen-air mixture was numerically simulated to reproduce the hydrogen explosion process during the Fukushima Daiichi Accident.
Experimental and Analytical Study of Hydrogen Jet Fire in a Vented Enclosure
2016
An experimental and numerical study of hydrogen jet fire in a confined space was performed for hydrogen safety purposes within the European HyIndoor project (www.hyindoor.eu). An existence of two combustion regimes was numerically found and then experimentally confirmed. Depending on hydrogen mass flow rate, volume of the enclosure and vent area a well-ventilated or under-ventilated jet fire may occur. A chamber of 1x1x1 m 3 with upper and lower vent positions, vent areas from 1 to 90 cm 2 and different hydrogen mass flow rates from 0.027 to 1.087 g/s were used for numerical simulations and experimental validation. A lower axial position of a jet fire produced by immediate ignition of a hydrogen leak was established in the tests. A Background Oriented Schlieren (BOS) technique combined with high speed camera, pressure and temperature measurements were utilized in the tests to evaluate dynamics of the combustion process. In case of small hydrogen release rate and large vent area, a relatively stable well-ventilated regime leading to over-pressure not more than 0.8 mbar and a maximum internal temperature of 540 C was established. In case of very high hydrogen mass flow rate and relatively small vent sizes three different scenario of under-ventilated jet fire behaviour with self-extinction, re-ignition and external flame modes leading to very high overpressure of 10-100 mbar and maximum temperatures of 1000-1200 C were experimentally measured. Strong influence of steam condensation on under-ventilated jet fire behaviour results in reduced sub-atmospheric pressures inside the chamber and intensive air ingress into the chamber. It may result in re-ignition of the quenched flame and then again to the extinction.
Experimental and numerical investigations of hydrogen jet fire in a vented compartment
International Journal of Hydrogen Energy, 2018
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.
Hydrogen detonation and detonation transition data from the High-Temperature Combustion Facility
1995
The BNL High-Temperature Combustion Facility (HTCF) is an experimental research tool capable of investigating the effects of initial thermodynamic state on the high-speed combustion characteristic of reactive gas mixtures. The overall experimental program has been designed t o provide data t o help characterize the influence of elevated gas-mixture temperature (and pressure) on the inherent sensitivity of hydrogen-air-steam mixtures t o undergo detonation, on the potential for flames accelerating in these mixtures t o transition into detonations, on the effects of gas venting on the flameaccelerating process, on the phenomena of initiation of detonations in these mixtures by jets of hot reactant products, and on the capability of detonations within a confined space t o transmit into another, larger confined space. This paper presents results obtained from the completion of t w o of the overall test series that was designed t o characterize high-speed combustion phenomena in initially high-temperature gas mixtures. These t w o test series are the intrinsic detonability test series and the deflagration-todetonation (DOT) test series. A brief description of the facility is provided below. 'This work was performed under the auspices of the U. S. Nuclear Regulatory Commission and the Japanese Nuclear Power Engineering Corporation.
Upward Flame Propagation Experiments on Hydrogen Combustion in a 220 cub. m Vessel
Volume 3: Next Generation Reactors and Advanced Reactors; Nuclear Safety and Security, 2014
During a hypothetical severe accident in a pressurized water reactor (PWR) of nuclear power plant, hydrogen would be generated during the degradation of the reactor core. The ignition and ensuing combustion of hydrogen could cause a sharp pressure increase, which could threaten the integrity of the containment.
Vented combustion of hydrogen-oxygen-diluent mixtures in a large volume
The Canadian Journal of Chemical Engineering, 1986
Combustion of hydrogen-oxygen-diluent mixtures was carried out in a 2.3-m-diameter sphere with venting to a cylinder of 10.3-m3 volume. It was found that stoichiometric hydrogen-oxygen mixtures with helium as the primary diluent led to detonation for all hydrogen concentrations above 20% by volume. Addition of small amounts (5 to 10%) of a secondary diluent such as carbon dioxide or steam suppressed detonation. Carbon dioxide, because of its higher molecular weight, was found to be a better detonation suppressant than steam. Transition to detonation was more difficult to achieve at I O O T than at room temperature.
Ignition of hydrogen jet fires from high pressure storage
International Journal of Hydrogen Energy, 2014
Highly transient jets from hydrogen high pressure tanks were investigated up to 30 MPa. These hydrogen jets might self-initiate when released from small orifices of high pressure storage facilities. The related effects were observed by high speed video technics including time resolved spectroscopy. Ignition, flame head jet velocity, flame contours, pressure wave propagation, reacting species and temperatures were evaluated. The evaluation used video cross correlation method BOS, brightness subtraction and 1 dimensional image contraction to obtain traces of all movements. On burst of the rupture disc, the combustion of the jet starts close to the nozzle on the outer shell of it at the boundary layer to the surrounding air. It propagates with a deceleration approximated by a drag force of constant value which is obtained by analysing the head velocity. The burning at the outer shell develops to an explosion converting a nearly spherical volume at the jet head, the movement of the centroid is nearly unchanged and follows the jet front in parallel. The progress of the nearly spherical explosion could be evaluated on an averaged flame ball radius. An apparent flame velocity could be derived to be about 20 m/s. It seems to increase slightly on the pressure in the tank or the related initial jet momentum. Self-initiation is nearly always achieved especially induced the interaction of shock waves and their reflections from the orifice. The results are compared to thermodynamic calculations and radiation measurements. The combustion process is composed of a shell combustion of the jet cone at the bases with a superimposed explosion of the decelerating jet head volume.
Comparison of the performance of several recent hydrogen combustion mechanisms
Combustion and Flame, 2014
A large set of experimental data was accumulatedfor hydrogen combustion: ignition measurements in shock tubes (770 data points in 53 datasets) and rapid compression machines (229/20), concentration-time profiles in flow reactors (355/16), outlet concentrations in jetstirred reactors (152/9) and flame velocity measurements (631/73) covering wide ranges of temperature, pressure and equivalence ratio. The performance of 19 recently published hydrogen combustion mechanisms was tested against these experimental data, and the dependence of accuracy on the types of experiment and the experimental conditions was investigated. The best mechanism for the reproduction of ignition delay times and flame velocities is Kéromnès-2013, while jet-stirred reactor (JSR) experiments and flow reactor profiles are reproduced best by GRI3.0-1999 and Ahmed-2007, respectively. According to the reproduction of all experimental data, the Kéromnès-2013 mechanism is currently the best, but the mechanisms NUIG-NGM-2010, ÓConaire-2004, Konnov-2008 and Li-2007 have similarly good overall performances. Several clear trends were found when the performance of the best mechanisms was investigated in various categories of experimental data. Low-temperature ignition delay times measured in shock tubes (below 1000 K) and in RCMs (below 960 K) could not be well-predicted. The accuracy of the reproduction of an ignition delay time did not change significantly with pressure and equivalence ratio. Measured H 2 and O 2 concentrations in JSRs could be better reproduced than the corresponding H 2 O profiles. Large differences were found between the mechanisms in their capability to predict flow reactor data. The reproduction of the measured laminar flame velocities improved with increasing pressure and total diluent concentration, and with decreasing equivalence ratio. Reproduction of the flame velocities measured using the flame cone method, the outwardly propagating spherical flame method, the counterflow twin-flame technique, and the heat flux burner method improved in this order. Flame cone method data were especially poorly reproduced. The investigation of the correlation of the simulation results revealed similarities of mechanisms that were published by the same research groups. Also, simulation