Coolant Interaction Research Articles

Development of a simple model for estimating the design limit of core void reactivity to prevent re-criticality of MOX-fueled cores in liquid metal-cooled fast reactors

The mixed oxide (MOX)-fueled core for liquid metal-cooled fast reactors has such high core performance and favorable neutron economy as to achieve an average fuel burnup of over 90 GWD/t with high power density. However, traditional MOX-fueled cores which are the ones without specific design measures to reduce the positive void reactivity worth has the potential to exceed prompt criticality during hypothetical core disruptive accidents (CDAs). Should the prompt criticality be exceeded, the core materials would heat up until their temperatures would exceed their boiling points. As a result, a release of significant mechanical energy cannot be ruled out, imposing serious damage on the reactor vessel. The released mechanical energy, termed “energetics,” is dominated by a rapid insertion of positive reactivity due to a fuel–coolant interaction (FCI) during the initiating phase of an unprotected loss-of-flow (ULOF) event. Considering the mechanism of energetics generation, a simple model was developed to estimate the design limit of positive component of core void reactivity against a ULOF event for traditional MOX-fueled cores. This simple model is constructed to evaluate the design limit based on the relation between the allowable positive reactivity insertion rate defined by the core characteristics and that assumed by the effect of FCI phenomena. The validity of the model is discussed by comparison with SAS4A which is the CDA analysis code devoted to calculate the initiating phase.

ГИДРОДИНАМИКА ТЕПЛОНОСИТЕЛЯ В АКТИВНОЙ ЗОНЕ РЕАКТОРА ВВЭР С ТВСА РАЗЛИЧНЫХ КОНСТРУКЦИЙ

The results of experimental studies of the interassembly interaction of coolant in VVER reactor core which consists of TVSA-T and upgraded TVSA are presented. The modeling of coolant flow in the fuel assembly (FA) was carried out on an aerodynamic stand. The studies were carried out on a fragment model of VVER reactor core and consisted in measuring the velocity vector modulus in the characteristic zones of both TVSA and interassembly space of VVER reactor core. The measurements were carried out by a five-channel pneumometric probe. An analysis of the spatial distribution of projections of the absolute flow velocity allowed to detail the pattern of flow-round by the coolant flow of spacer, mixing and combined spacer grids TVSA. The results of study of interassembly interaction of coolant between neighboring TVSA-T and upgraded TVSA were adopted for practical use by JSC “Afrikantov OKBM” in assessing heat engineering reliability of VVER reactor cores and are included in the data-base for verification of computational fluid dynamics programs (CFD codes) and detailed cellular calculation of VVER reactor core.

Research of mechanisms of interaction of melt and coolant by means of small-sized experiments with solid and liquid metal samples

Several basic fragmentation hypotheses described in the literature for the case of fine-scale spontaneous vapor explosion, when single hot drops are falling in the coolant, are analyzed. It is shown that all of them, depending on the experimental conditions, describe the real physical phenomena. It is highlighted, that the process of fragmentation during the spontaneous vapor explosion is directly connected to the regime of the film boiling collapse of the underheated liquid, which is still underexplored. The experiments on the liquid drops fragmentation are complemented by those with surface boiling at the solid metal samples of semi-spherical form. The connection between the vapor explosion of water and the increase of the surface wettability is confirmed. The video material, indicating the possibility of formation of liquid jets that strike the hot surface during the collapse of the vapor shell, is obtained. The time interval (duration of the contact) between the first contact of the coolant with the hot surface and the explosion boiling of the liquid is experimentally determined. The dependence of the contact duration on the temperature of the overheated wall is determined and its comparison with the theoretical estimations is provided.

Hydrodynamics of coolant in VVER reactor core with fuel assemblies of various designs

The article presents the results from experimental investigations into local coolant flow fluid dynamics that were carried out on the fragmental model of a VVER-type pressurized water reactor’s mixed core consisting of two types of fuel assemblies (FAs): TVSA-T (one segment) and TVSA-T.mod.2 (two segments). The coolant flow processes in the fuel rod bundle were simulated on an aerodynamic test bench. The pressure field in the flow was measured using a five-channel pneumometric probe. The obtained pressure field in the flow was recalculated for the coolant velocity vector according to the dependences derived during calibration. For drawing up a detailed flow motion pattern, a characteristic model cross section area was separated, which included the space between the assemblies and four fuel rod rows in each TVSA-type fuel assembly. The spatial distribution of coolant flow velocity projections was analyzed, as a result of which it became possible to reveal the regularities associated with the streamlining of spacer, mixing-, and combined-spacer grids in TVSA assemblies by coolant; to determine coolant cross flows resulting from streamlining of hydraulically nonidentical grids and to determine their localization in the experimental model longitudinal and cross sections; and to reveal the effect of accumulating flow hydrodynamic disturbances in the model longitudinal and cross sections resulting from the staggered arrangement of hydraulically nonidentical grids. The results obtained from investigations of interassembly interaction of coolant between the neighboring TVSA-T and TVSA-T.mod.2 assemblies have been adopted for practical use at JSC “Afrikantov OKBM” in estimating the thermal reliability of VVER-type reactor cores and have been included in the database for verification of computation fluid dynamics computer programs (CFD codes) and detailed cell-wise numerical analysis of VVER reactors’ core.

Using the characteristics of rootless cone deposits to estimate the energetics of explosive lava–water interactions

During volcanic eruptions, the interaction of magma and groundwater can produce thermohydraulic explosions capable of significantly increasing the eruption energy. The most well-known mechanism by which explosive magma–water interactions occur, molten fuel–coolant interaction (MFCI), is a complex series of macro- and microscale processes which have been simulated using laboratory-scale experiments. As a natural analog for MFCI experiments, we utilize rootless cone beds formed by lava–water explosions to estimate explosion energy. The specific mechanical energy of the lava–water explosions studied here occurs over a broader range (4 to 178 kJ/kg) than MFCI experiments and includes estimates for the highest-energy lava–water explosions studied to date. Explosion energy is partitioned similarly over the two systems, with kinetic transport and fragmentation energy making up 25–40% and 42–80% of the mechanical energy, respectively, which overlap the ranges estimated for MFCI experiments. Our study of lava–water explosions therefore provides a field-scale analog of MFCI laboratory experiments for understanding the energetics, and therefore hazards, of MFCI in natural systems.

The Mesoproterozoic Stac Fada Member, NW Scotland: an impact origin confirmed but refined

The origin of the Stac Fada Member has been debated for decades with several early hypotheses being proposed, but all invoking some connection to volcanic activity. In 2008, the discovery of shocked quartz led to the hypothesis that the Stac Fada Member represents part the continuous ejecta blanket of a meteorite impact crater, the location of which was, and remains, unknown. In this paper, we confirm the presence of shock-metamorphosed and -melted material in the Stac Fada Member; however, we also show that its properties are unlike any other confirmed and well documented proximal impact ejecta deposits on Earth. Instead, the properties of the Stac Fada Member are most similar to the Onaping Formation of the Sudbury impact structure (Canada) and impact melt-bearing breccias from the Chicxulub impact structure (Mexico). We thus propose that, like the Sudbury and Chicxulub deposits, Melt Fuel Coolant Interactions – akin to what occur during phreatomagmatic volcanic eruptions – played a fundamental role in the origin of the Stac Fada Member. We conclude that these rocks are not primary impact ejecta but instead were deposited beyond the extent of the continuous ejecta blanket as high-energy ground-hugging sediment gravity flows.

Jet Fragmentation Characteristics During Molten Fuel and Coolant Interactions

Jet fragmentation greatly influences the possibility of steam explosion and the formation of a debris bed when a molten corium jet falls into subcooled coolant during a severe accident of a nuclear reactor—which is called fuel and coolant interaction (FCI). The characteristics of different jet fragmentation mechanisms and the conditions under which they play a major role are still in doubt. Experiments were carried out to investigate the fragmentation characteristics of melt jet interaction with water at medium temperature (~680°C) and high temperature (1800°C to 2150°C). Molten metal [tin or Type 304 stainless steel (304SS)], oxide (alumina), and their mixture (304SS-alumina) were used as melt materials to obtain different fragmentation mechanisms. In addition, the effects of melt temperature, water subcooling, and water depth on jet fragmentation were also studied. Through comprehensive analysis of high-speed photography, dynamic pressure, water temperature variation, and jet breakup length during interactions as well as the morphology and size of debris after interactions, it was found that the characteristics of jet fragmentation varied greatly at different melt temperatures and water subcooling due to competition between hydrodynamic fragmentation and thermodynamic fragmentation caused by boiling. In addition, under high-temperature conditions, fragmentation of alumina was much greater than 304SS due to the fracture of solidifying melt caused by thermal stress. Finally, five kinds of mechanisms of melt jet fragmentation under different conditions are summarized.

Numerical study on melt drop collision and hydraulic fragmentation during FCI of a nuclear reactor severe accident

Melt drop collision is an important phenomenon in the circumstance of pressure wave propagation during fuel–coolant interaction (FCI). The deformation and fragmentation of melt drops can increase the contact area with coolant, and as a result will affect the heat transfer and melt oxidation. In this study, a numerical model was established by considering surface tension and validated with the experimental results that were obtained from water droplet collision in gaseous environment. Then, the head-on collision of two UO2 melt drops in water pool was investigated at different Weber numbers, and the melt morphology, contact area, and the number and size distribution of children droplets were analyzed. The results show that interfacial waves and wrinkles could be clearly observed on the melt film, and the finger structures presented at the rim of melt film and finally separated into children melt droplets. The increase of fuel–coolant contact area could be divided into the inducements by deformation and fragmentation. The melt deformation only had influence to the area increase at intermediate process but no effect to that at steady state. By contrast, the final fuel–coolant contact area was determined by the intensity of melt fragmentation. The size distribution of melt children droplets was like an off-centered normal distribution, where the maximum number of children droplets existed in the size range of 0.03 < D/D0 < 0.045, but the droplets in this size range contributed little to the fuel–coolant contact area. With the above analysis, an empirical model to calculate the contact area was developed. The model had a discrepancy of ±10% in the range of Wec = 290–1815 that the model was established in, but the discrepancies were about 13.3% and 19.3% for the cases of Wec at 2196 and 2612, respectively.

Analysis of the experiment KROTOS-44 of melt-water explosive interaction using the code VAPEX

The basic aim of KROTOS test facility is to provide experimental data on fuel coolant interaction phenomena during severe accidents in nuclear power plants. The presented article is devoted to validate the VAPEX code developed at the Department of NPP in Moscow Power Engineering Institute. The experiment K-44 was simulated using the VAPEX code, this experiment has a significant importance because it allows to clearly observe the growth and propagation of pressure waves. The calculated data for the explosion stage obtained by the VAPEX code are in a good agreement with the experimental data, which confirms the adequacy of the VAPEX code for the analysis of fuel coolant interaction in case of severe accidents in nuclear power plants.

Analysis of the Effect of Vessel Failure and Melt Release on Risk of Containment Failure Due to Ex-Vessel Steam Explosion in Nordic Boiling Water Reactor Using ROAAM+ Framework

Abstract Nordic boiling water reactor (BWR) design employs ex-vessel debris coolability in a deep pool of water as a severe accident management (SAM) strategy. Depending on melt release conditions from the vessel and core–melt coolant interactions, containment integrity can be threatened by: (i) formation of noncoolable debris bed or (ii) energetic steam explosion. Melt is released from the vessel affect ex-vessel phenomena and is recognized as the major source of uncertainty. The risk-oriented accident analysis methodology (ROAAM+) is used for quantification of the risk of containment failure in Nordic BWR where melt ejection mode surrogate model (MEM SM) provides initial conditions for the analysis of debris agglomeration and ex-vessel steam explosion which determine the respective loads on the containment. Melt ejection SM is based on the system analysis code methods for estimation of leakages and consequences of releases (computer code) (MELCOR). Modeling of vessel failure and melt release from the vessel in MELCOR is based on parametric models, allowing a user to select different assumptions that effectively control lower head (LH) behavior and melt release. The work addresses the effect of epistemic uncertain parameters and modeling assumptions in MEM SM on the containment loads due to ex-vessel steam explosion in Nordic BWR. Sensitivity and uncertainty analysis performed to identify the most influential parameters and uncertainty in the risk of containment failure due to ex-vessel steam explosion. The results of the analysis provide valuable insights regarding the effect of MELCOR models, modeling parameters, and sensitivity coefficients on melt release conditions and predictions of ex-vessel steam explosion loads on the containment structures.

환형 섹터 터빈 노즐 캐스케이드에서 팬 형상 막냉각 홀의 복합분사각도 적용에 따른 막냉각 효율 특성

The present study investigated the effect of compound angle injection of fan-shaped film cooling holes on film cooling performance on the nozzle vane surface in an annular sector cascade. Two different configurations were examined to investigate effect of compound angle injection. The baseline has streamwise injection holes on the pressure and suction side surfaces and normal injection holes in leading edge region. The other configuration has compound angle injection holes on the leading edge and the pressure side surface. An annular sector turbine cascade test facility was used and the measurements using an infrared thermography method were conducted at the exit Reynolds number of 2.2x10<SUP>6</SUP> and exit Mach number of 0.8. Total coolant mass flow rate ranges between 5 and 10% of mainstream. The results showed that the baseline configuration shows skewed trajectory of coolant downstream of holes on the pressure side surface, which is not observed in ‘flat-plate’ study and strongly related to mainstream flow direction near the nozzle surface. On the other hands, the coolant follows the mainstream direction and spread more uniformly on the pressure side surface with compound angle injection configuration. However as coolant mass flow rate increases, compound angle injection induces stronger interaction of mainstream and coolant and film cooling effectiveness drops quickly in the downstream region. Also, film cooling effectiveness in the suction side surface shows lower values for compound angle injection configuration since compound angle injection on the showerhead region causes non-uniform distributions of film cooling effectiveness due to stronger secondary flow.

Experimental study on local fuel–coolant interaction in molten pool with different melts

In a Core Disruptive Accident (CDA) of Sodium-cooled Fast Reactor (SFR), by supposing rather pessimistic condition, a large molten fuel pool would be possibly formed that contains enough fuel with the potential to exceed prompt criticality due to fuel compactive motion. Local fuel-coolant interaction (FCI) in the molten pool is identified as one of the typical inducing factors that may result in such compactive motion. To understand the characteristics of this interaction, owing to the PMCI (Pressurization characteristics in Melt-Coolant Interaction) facility recently established at the Sun Yat-sen University, in our earlier publications two series of simulated experiments, i.e. Coolant-Injection (CI) experiments and Melt-Injection (MI) experiments, have been conducted, in which water and low-melting-point Bi-Sn-In alloy (60% Bi, 20% In and 20% Sn) were used respectively as the simulant materials for sodium and molten fuel. In this study, aimed at checking the generality of the experimental findings as well as achieving further enhanced understanding on this interaction, a large number of experiments are newly performed through delivering water into a simulated molten fuel pool comprised of Lead-Bismuth Eutectic (LBE) alloy (another low-melting-point alloy). Through detailed comparisons (with the CI-mode experiments using Bi-Sn-In alloy), it is found that a similar trend in the transient pressure and temperate history as well as the overall effect of experimental parameters (such as water quantity, melt and water temperature, water-lump shape and melt depth) on the pressurization characteristics can be reproduced for the new LBE experiments. Despite a much lower thermal diffusivity, for the LBE experiments it is confirmed that the most likely reason resulting in the limited pressurization as water volume increases should be also primarily owing to the isolation effect of vapor bubbles generated at the melt-water interface. Possibly due to the enhanced melt density which facilitates the penetration of melt through vapor bubbles, under the same parametric condition the pressurization in LBE experiments is generally much higher than that in Bi-Sn-In experiments. Compared to melt static pressure, the pressurization under different melt depths is supposed to be more influenced by the varied easiness of melt penetration. Current work provides a large amount of favorable experimental database and insight for promoted understanding on actual CDAs and improved verifications of SFR severe accident codes in China.

Effect of Internal Heat Generation on Solidification of Molten Fuel Droplet during its Interaction with Coolant in a Nuclear Reactor

One of the important issues in safety analysis of severe accidents in fast reactors is Molten Fuel Coolant Interaction (MFCI). MFCI is the phenomenon in which fragmentation of the molten fuel takes place when it comes in direct contact with liquid sodium coolant. For complete understanding of MFCI, we need to study the solidification of the molten fuel happening along with fragmentation. Solidification / melting of any material initially held at its melting temperature is the classic Stefan’s problem. In the case of a severe reactor accident the molten fuel might have a significant amount of decay heat, even though nuclear fission reactions have been stopped by reactor shut down systems. The presence of decay heat in this case, makes the transient Stefan problem more difficult to solve analytically. Here, an investigation of this special case of Stefan’s problem with internal heat generation in nuclear materials has been carried out considering a typical droplet size of 4 mm diameter. The numerical heat transfer analysis has been carried out using the commercial software Fluent. The validation of the problem is done with the steady state analytical solution available for the position of phase change front. Parametric studies have been carried out by varying internal heat generation rates and convective heat transfer coefficient at the surface of the droplet. Temperature profiles and liquid fraction are obtained at different instants. Solidification time and final equilibrium temperature are estimated from the results. It is observed that there is significant increase in drop solidification time for heat generation rates (HG) greater than 100 MW/m3 for the drop size of 4 mm. The maximum HG which is tolerated by the droplet without reaching its boiling point is about 6 GW/m3 when the heat transfer coefficient from its surface is fixed at h=56000W/m2K.

Implementation of framework for assessment of severe accident management effectiveness in Nordic BWR

Nordic Boiling Water Reactor (BWR) design employs ex-vessel debris coolability in a deep pool of water as a severe accident management (SAM) strategy. Depending on melt release conditions from the vessel and core-melt coolant interactions, containment integrity can be threatened by (i) formation of non-coolable debris bed, or (ii) energetic steam explosion.In order to assess the effectiveness of SAM the Risk Oriented Accident Analysis Methodology framework (ROAAM+) has been developed. The framework is further extension of the approach originally developed and applied by Prof. Theofanous and co-workers.This paper presents the implementation of ROAAM+ probabilistic framework for uncertainty quantification and risk analysis.We further apply ROAAM+ to the analysis of steam explosion risk in Nordic BWR assuming different state-of-knowledge situations and different containment fragilities. We employ an iterative processes of knowledge refinement using risk analysis as a guiding tool in identification of the major sources of uncertainty. We estimate failure domains and discuss ROAAM+ results in terms of possibility vs necessity of containment failure.

Combined Numerical and Experimental Investigations into the Local Fluid Dynamics of Coolant Flow in the Mixed Core of a VVER Reactor

The article presents the results from experimental investigations into local coolant flow fluid dynamics that were carried out on the fragmental model of a VVER-type pressurized water reactor’s mixed core consisting of two types of fuel assemblies (FAs): TVSA-T (one segment) and TVSA-T.mod.2 (two segments). The coolant flow processes in the fuel rod bundle were simulated on an aerodynamic test bench. The pressure field in the flow was measured using a five-channel pneumometric probe. The obtained pressure field in the flow was recalculated for the coolant velocity vector according to the dependences derived during calibration. For drawing up a detailed flow motion pattern, a characteristic model cross section area was separated, which included the space between the assemblies and four fuel rod rows in each TVSA-type fuel assembly. The spatial distribution of coolant flow velocity projections was analyzed, as a result of which it became possible to reveal the regularities associated with the streamlining of spacer-, mixing-, and combined-spacer grids in TVSA assemblies by coolant; to determine coolant cross flows resulting from streamlining of hydraulically nonidentical grids and determine their localization in the experimental model longitudinal and cross sections; and to reveal the effect of accumulating flow hydrodynamic disturbances in the model longitudinal and cross sections resulting from the staggered arrangement of hydraulically nonidentical grids. The results obtained from investigations of inter-assembly interaction of coolant between the neighboring TVSA-T and TVSA-T.mod.2 assemblies have been adopted for practical use at AO Afrikantov OKBM in estimating the thermal reliability of VVER-type reactor cores and have been included in the database for verification of computation fluid dynamics computer programs (CFD codes) and detailed cell-wise numerical analysis of the core of VVER reactors.

Experimental study on the effects of boiling during molten jet and coolant interactions

In nuclear power plants, core melt accidents are often accompanied with fuel–coolant interactions (FCI), which may escalate to steam explosion destroying the integrity of structural components and even the containment under certain conditions. The vapor film and two-phase region formed by boiling around the molten jet at high temperature have a great influence on the fragmentation of the jet and the possibility of steam explosion. In this study, by changing the initial temperature of coolant, a series of experiments on the interactions of molten tin at high temperature with water have been done and several distinct interactions under different boiling conditions including stable film boiling, unstable film boiling and nucleate or transition boiling were observed. These interactions were distinguished by the high-speed photography, liquid level swell, dynamic pressure, water temperature variation and jet breakup length during interactions as well as the morphology and size of debris after interactions synthetically. It was found that energetic jet-water interactions were only possible under unstable film boiling, and nucleate or transition boiling conditions. While under the stable film boiling, the jet was surrounded by a very stable vapor film, so only mild interactions occur. With the decrease of coolant temperature, the boiling mode transferred from stable film boiling to nucleate or transition boiling. Significant differences in jet breakup length as well as size and morphology of the debris were observed. Because less steam was generated, the melt was more likely to action with water than steam, and water was more conducive to the fragmentation caused by interfacial instability due to higher density. In addition, the thermodynamic fragmentation caused by violent boiling gradually played a more important role. Furthermore, the results were compared with existing theories which ensured the effects of boiling during FCI.

2D MPS analysis of hydrodynamic fine fragmentation of melt drop with initial steam film during fuel–coolant interaction

The hydrodynamic fine fragmentation of melt drops, which increases the melt–coolant contact area and affects heat transfer and melt oxidation, is an important phenomenon during fuel–coolant interaction. The presence of a steam film surrounding the melt drops complicates the breakup simulation, including interface instabilities and high-density ratio. In this study, we modeled the breakup behavior of a melt drop with an initial steam film by using the meshless moving particle semi-implicit (MPS) method in the Lagrangian frame. Numerical models were validated step by step by simulating Kelvin–Helmholtz instability, Rayleigh–Taylor instability, and liquid drop breakup. The breakup behavior of a UO2 melt drop with and without initial steam film was simulated in 2D, and the fragment number, size distribution, and melt–coolant contact perimeter were comparatively analyzed. Results indicate that the initial steam film rapidly moved away from the melt drop and separated into two main bubbles, which had insignificant influence on either the melt drop deformation or the fragment number and the perimeter. The total number of fragments increased at the initial moments of the breakup process due to the flow inertia force and then decreased under the effect of surface tension. The number of small fragments (d/d0 = 0.01–0.03) increased and decreased in variations, but other relatively large fragments continuously increased in the entire duration. The perimeter contribution of small fragments was larger than those of other fragment groups in the initial duration of the melt drop breakup at We = 655, but it reversed subsequently. By contrast, the perimeter contribution by fragments with d/d0 = 0.01–0.02 and 0.02–0.03 was constantly larger than those of other groups at We = 2618. Moreover, the summations of perimeter contributions by all fragments in the present statistics were approximately 50% and 60%–80% for cases of We = 655 and 2618, respectively.

Enhancement of Heat transfer of Cylinder liner and Coolant jacket for High powered Diesel engine

The cooling system of an Armoured Fighting Vehicles (AFV) is critical and complex when compared to other automobiles mainly because of the severe temperature and dust conditions in which they operate. For proper working of the engine, it is very important that the engine be maintained at optimum temperature during its operation to have desired performance levels. Usually high powered engines employ water cooled cooling systems with compact radiators. Also the cooling system in AFV Engine is very critical as the air space available is very less. This is due to the fact that the engine is enclosed in a compartment where the ram air due to vehicle movement cannot be used to cool the radiators. Hence any small improvement in the heat transfer improves the performance of the engine. The main aim of the study is to enhance the heat transfer between the engine liner and the coolant for AFV engines. The heat transfer rate is enhanced by modifications on the surface of the liner coolant interaction with an aim to induce turbulence in the coolant flow through the jacket. For each modification, the heat transfer coefficient is found out through CFD analysis in Ansys Fluent. The combustion temperatures and heat transfer coefficients obtained using simulation software AVL BOOST® were used to calculate the wall temperature of liner. Simulations on modified geometry of liner walls yielded up to a maximum of 18% improvement in heat transfer which is very significant.

Experimental Investigation on Fuel Coolant Interaction Using Simulant Ceramic Melts in Water: Insights and Conclusions

Steam explosion is one of the crucial and poorly understood phenomena which may occur during severe accident scenario and may lead to containment failure. In spite of several experimental and analytical studies, the root cause of steam explosion has not been understood. Recent claims in the literature suggest that the presence of fine fragmentation during steam explosion causes its occurrence. In order to investigate this and understand the root cause of steam explosion, series of experiments were performed with 50 g to 2500 g of CaO-B2O3, a corium simulant in 4.5 litre of water. It was observed that steam explosion may occur even in the absence of fine fragments, which is contrary to the claims in the literature. To investigate further, conversion efficiency analysis was performed. This suggested that the amount of thermal energy converted to mechanical energy is more important deciding factor in explaining the occurrence of steam explosion. The present study discusses the importance of conversion efficiency in deciding steam explosion and also gives a new perspective to look at steam explosion phenomenology.

Explosive interaction of impact melt and seawater following the Chicxulub impact event

Abstract The impact of asteroids and comets with planetary surfaces is one of the most catastrophic, yet ubiquitous, geological processes in the solar system. The Chicxulub impact event, which has been linked to the Cretaceous-Paleogene (K-Pg) mass extinction marking the beginning of the Cenozoic Era, is arguably the most significant singular geological event in the past 100 million years of Earth’s history. The Chicxulub impact occurred in a marine setting. How quickly the seawater re-entered the newly formed basin after the impact, and its effects of it on the cratering process, remain debated. Here, we show that the explosive interaction of seawater with impact melt led to molten fuel–coolant interaction (MFCI), analogous to what occurs during phreatomagmatic volcanic eruptions. This process fractured and dispersed the melt, which was subsequently deposited subaqueously to form a series of well-sorted deposits. These deposits bear little resemblance to the products of impacts in a continental setting and are not accounted for in current classification schemes for impactites. The similarities between these Chicxulub deposits and the Onaping Formation at the Sudbury impact structure, Canada, are striking, and suggest that MFCI and the production of volcaniclastic-like deposits is to be expected for large impacts in shallow marine settings.