•Higher melt mass results in higher vapour explosion probability.•Higher melt mass did not affect the vapour explosion intensity.•Increasing melt temperature caused a higher explosion depth and ...intensity.•The temperature had varying effects in combination with gas column aspect ratio ARgas.•At low/high temperature, probability and intensity de-/increased with reducing ARgas.
Vapour explosions are a known hazard in pyrometallurgy that can cause equipment damage, injuries or even casualties. Therefore, molten metal droplet impingement experiments (2.5–20 g) with low-melting metals (Hg, Sn) were performed to study the vapour explosion phenomenon more thoroughly. A hydrophone and a high-speed camera continuously monitored these experiments. The influence of temperature and mass on the resulting interaction was investigated. Specific attention was given to the reproducibility of the experiments, most certainly in case the droplet fragmented into multiple droplets before entering the water bath.
Mercury at room temperature was used to study the fragmentation step upon alloy-water impact without vapour formation. Air was seen to be dragged into the water as a column, where the observed aspect ratio of the gas columns decreased, i.e. the columns became longer, when the vertical length of the droplets was elongated.
Molten tin (350–800 °C) was used to study the influence of vapour formation on fragmentation, and the effect of the hot phase mass and temperature on the explosion. The gas column occurrence frequency increased as compared to mercury experiments, and such gas column could potentially inhibit vapour explosions. Furthermore, an increased temperature resulted in an increased explosion probability, explosion energy, and depth of the spontaneous interaction. Lastly, increasing the melt mass resulted in an increased explosion probability and intensity.
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For the investigation of vapour explosions, droplet impingement experiments were performed with the binary system Pb–Sn and the pseudo-binary system PbS–Cu2S. The experiments were performed with a ...melt at 600 °C (Pb–Sn) or 700 °C (PbS–Cu2S) and a water bath at ambient temperature and pressure. A hydrophone and a high-speed camera were used to study the interaction and from this data, the explosion probability and intensity were determined.
The explosion probability had a single minimum around 70 wt% Sn, close to the eutectic composition. Moreover, the explosion probability increased approximately linearly with changing composition towards the pure melts, and was similar for pure tin and pure lead. On the other hand, the explosion intensity was comparable for tin and the eutectic alloy while clearly lower for lead. Almost all intermediate alloys had a reduced explosion intensity.
Based on the variation in composition, the effects of the liquidus or solidus temperature and the liquidus-solidus gap on the explosion behaviour were also investigated. The explosion probability in both systems increased with increasing liquidus temperature. Also, the maximum explosion intensity in the Pb–Sn system increased with increasing liquidus temperature. Both could be related to easier triggering due to (partial) solidification. On the other hand, the explosion intensity was found to decrease with increasing gap between liquidus and solidus temperature, as was also found in literature. No significant trends for the explosion intensity were found for experiments with PbS–Cu2S.
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•With Pb–Sn, lowering the liquidus-solidus gap increased the explosion probability.•With PbS–Cu2S, raising the liquidus-solidus gap increased the explosion probability.•No statistically significant trend for the hydrophone peak signal.•With PbS–Cu2S, the explosion intensity showed no statistically significant trend.•With Pb–Sn, the explosion diameter increased with decreasing liquidus-solidus gap.
Caravan explosions due to gas cylinder explosions or gas leaks are responsible for a small but significantly injured group of burns patients. This is a single‐centre case series of patients with ...caravan‐related burns identified using the burns data registry at the Royal Brisbane and Women's Hospital. The objective was to seek evidence of primary blast wave injury by comparing the injury pattern between groups.
Background
Caravan explosions due to gas cylinder explosions or gas leaks are responsible for a small but significantly injured group of burns patients. Those involved in explosions are sometimes assumed to be at risk of primary blast wave injury; however, the likelihood of such injuries is unclear. The aim of this research was to seek evidence of primary blast injury in groups defined by clinicians as having sustained burns in explosive and non‐explosive events.
Methods
This is a single‐centre case series of patients with caravan‐related burns from 2009 to 2019, identified using the burns data registry at the Royal Brisbane and Women's Hospital. Patients were divided into two groups based on the mechanism of injury, with injuries sustained from either a gas bottle explosion (group 1) or from gas ignition (group 2).
Results
Twenty‐one patients were identified over the 10‐year period. The explosion group suffered more extensive burns, with a median % total body surface area of 31% (23.5–43.5) and 9.5% (5–20) in group 1 and group 2, respectively (P = 0.01). There was a numerically longer median hospital and intensive care unit length of stay in group 1. In multivariable analysis, there were no statistically significant predictors of intensive care unit or hospital length of stay. None of the patients appeared to have suffered any of the expected effects of primary blast wave injury.
Conclusion
Gas bottle explosions in caravans uncommonly, if ever, result in a blast wave of sufficient energy to cause primary blast injury.
•Premixed layer formation in stratified fuel–coolant configuration is presented.•Mechanisms for the premixed layer formation are identified and a model for the melt-coolant premixed layer formation ...in stratified configuration is presented.•Simulations of premixed layer formation and explosion in the PULiMS E6 and SES S1 experiments are performed with MC3D code.
A hypothetical severe accident in a nuclear power plant can lead to significant core damage, including melting of the core. The interaction between the molten core and the coolant water is known as a fuel–coolant interaction. One of the consequences can be a rapid transfer of a significant part of the molten corium thermal energy to the coolant in a time scale smaller than the characteristic time of the pressure relief of the created and expanding vapour. Such a phenomenon is known as a vapour explosion. Given possibly a large amount of thermal energy, initially stored in the liquid corium melt at about 3000 K, and pressure peaks of the order of 100 MPa, vapour explosion can be a credible threat to the structures, systems and components inside the reactor containment. It can also threaten the integrity of the reactor containment itself, which would lead to the release of radioactive material into the environment and threaten the general public safety. In analyses of severe accidents in nuclear power plants, a fuel–coolant interaction was mostly addressed in a geometry of a melt jet poured into a coolant pool. Based on some experimental and analytical work from the past a geometry with a continuous layer of melt under a layer of water, called stratified configuration, was believed to be incapable of producing energetic fuel–coolant interaction of sufficient magnitude to likely fail the containment. However, the results from recent experiments performed at the PULiMS and SES facilities (KTH, Sweden) with corium simulants materials contradict this hypothesis. In some of the tests, a premixing layer of ejected melt drops in water was clearly visible and was followed by strong spontaneous vapour explosions.
The purpose of our research is to improve the knowledge, understanding and modelling of the fuel–coolant interaction and vapour explosion in stratified configuration. Based on the past experimental and analytical research, mechanisms for the premixed layer formation are identified and a model for the melt-coolant premixed layer formation in stratified configuration is presented. The analyses on the PULiMS and SES experimental results demonstrate the model’s capability to describe the premixed layer formation.
•Sensitivity analysis on main parameters of model for premixed layer formation in stratified configuration is performed.•Model’s parameters are varied for simulation of premixing and explosion phase ...with the fuel–coolant interaction code MC3D.•Effects of melt fragmentation rate, melt drops size and ejection velocity for FCI in stratified configuration are discussed.
Experiments of fuel–coolant interaction in stratified geometry at the PULiMS and SES (KTH, Sweden) test facilities resulted in spontaneous steam explosions. Prior to the explosion, a premixed layer of ejected melt drops in the water layer was observed in the experiments. Based on the experimental and analytical knowledge, we have recently developed a model for premixed layer formation in the Fuel-Coolant Interaction code MC3D and applied it to estimate steam explosion energetics.
In the paper, a sensitivity study of this model is performed on the three main uncertain parameters of the premixed layer formation model, which define the melt fragmentation rate, the size of the ejected melt drops and the ejected melt drop velocity. The analysis is performed against the SES S1 and the PULiMS E6 experimental results. The chosen tests were selected as in both of them the same material was used, the geometry was similar, and both of them resulted in a spontaneous steam explosion. The effects can be observed in all the performed analyses and they are consistent in simulations of both experiments, affecting the premixed layer height as well as the explosion strength and duration. Some uncertainty of the experimental results is assessed, with the main limitation related to the visual observations. The combination of both analyses provides us with the assessment of future work necessity and prioritization.
The presented sensitivity analysis of the premixed layer formation model enables a more reliable assessment of the stratified vapour explosion risk and its uncertainty in nuclear power plants and other industries.
•Dynamic response of tunnels subjected to internal BLEVE is investigated.•Damage modes of tunnels under internal BLEVEs are revealed.•Tunnel responses to BLEVE and its equivalent TNT explosion load ...are compared.•Key parameters influencing on BLEVE-resistant performance of tunnels are identified.
During service life, road tunnels may face threats of accidental explosions, e.g., Boiling Liquid Expansion Vapour Explosions (BLEVEs) due to accidents of vehicles transporting hazardous goods inside the tunnels. However, very limited study has investigated the influence of BLEVEs inside a tunnel on its dynamic response. The present study numerically investigates the dynamic response of an arched tunnel subjected to an internal BLEVE by using the software LS-DYNA. The BLEVE load is directly simulated by using commercial code FLACS or approximated by the commonly used TNT equivalency method to investigate the influences of loading predictions on the tunnel responses. The results show that the corner and upper arc of arched lining are more prone to be damaged under the directly predicted BLEVE loads. Compared to the directly predicted BLEVE loads, explosion loads estimated by the TNT equivalency method induce more significant damage to the lining due to its higher peak pressure, but smaller peak displacements since the corresponding impulse is lower than that of the BLEVE load. In addition, parametric studies are conducted to investigate the effects of concrete grade, concrete thickness, steel reinforcement ratio, and stiffness of surrounding rock mass on dynamic response of the arched tunnel subjected to the internal BLEVE. It is found that increasing concrete grade and thickness and enhancing the stiffness of surrounding rock mass are more effective than increasing steel reinforcement ratio in improving the performance of the arched tunnel against internal BLEVE loadings.
•Algorithms to compute a three-phase flow model with immiscible phases.•Verification test cases of a three-phase flow model.•Simulation of Chauvin’s shock tube experiment.•Preliminary simulations of ...vapour explosion.
This paper is devoted to the simulation of the three-phase flow model 20, in order to account for immiscible components. The whole model is first recalled, and the main properties of the closed set are given, with particular focus on the Riemann problem associated with the convective subset that contains non-conservative terms, and also on the relaxation process. The model is hyperbolic, far from resonance occurrence, and a physically relevant entropy inequality holds for smooth solutions of the whole system. Owing to the uniqueness of jump conditions, specific solutions of the one-dimensional Riemann problem can be built, and these are useful (and mandatory) for the verification procedure. The fractional step method proposed herein complies with the continuous entropy inequality, and implicit schemes that are considered to account for relaxation terms take their roots on the true relaxation process. Once verification tests have been achieved, focus is given on the simulation of the experimental setup 8, 9, in order to simulate a cloud of droplets that is hit by an incoming gas shock-wave. Finally, the study of a three-phase flow setup involving thermal effects is presented, it is based on the KROTOS experiment 25 which focuses on vapour explosion simulation.
•Understanding and modelling of key vapour explosion processes in sodium is discussed.•Capability of MC3D code to simulate vapour explosions in sodium is supported.•Pressurization in sodium seems to ...be intrinsically limited to moderate pressures.•Vapour explosions in sodium might be simulated as an intensive premixing phase.
The aim of the paper is to highlight the research priorities for the sodium vapour explosion modelling with the fuel-coolant interaction codes. Several simulations were performed with the MC3D code (IRSN, France) to support the qualitative and quantitative assessment of the modelling challenges. The main findings are: (1) the MC3D code is capable to cover vapour explosions in sodium, (2) the need for super-critical sodium tables is indicated, (3) the vapour explosion in sodium might be considered as an intensive premixing phase, (4) the experimentally observed limitation of the pressure to some MPa is also observed with simulations, (5) in future the thermal fine fragmentation modelling might be needed and (6) an experimental study of the heat transfer around the fine fragments shall be performed.
The influence of an ambient fluid flow on the fragmentation of hot molten tin droplets (initially at 800°C) and cold low melting point alloy droplets (initially at 70°C) in water is investigated with ...high-speed photography and flash radiography. The water is accelerated using a converging nozzle to a constant speed of up to 30 m/s using a double piston arrangement designed to eliminate the formation of a shock wave that is present in most earlier studies. At low flow velocities, the fragmentation of hot droplets is governed by thermal effects and vapour formation, growth, and collapse. At high flow velocities, vapour formation is suppressed and the droplet fragmentation is determined by hydrodynamic effects in which hydrodynamic instabilities (Rayleigh-Taylor and Kelvin-Helmholtz) and wavecrest stripping all play a role in the droplet breakup. At intermediate flow velocities, both thermal and hydrodynamic effects play a role. Quantitative image analysis of the radiographs is used to determine the spatial distribution of the droplet mass during the fragmentation process. Comparison with earlier work in which the ambient flow is preceded by a strong shock wave indicates that the transition from thermal to hydrodynamic breakup is strongly dependent on the pressure field.
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