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STEX-II, International Steam Explosion Experimental Data Base

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STEX Database, phase II.

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Program name Package id Status Status date
STEX-II CSNI2007/02 Arrived 04-MAY-2010

Machines used:

Package ID Orig. computer Test computer
CSNI2007/02 Many Computers
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STEX Database is a compilation of the experimental work conducted to investigate the phenomenon of "STeam Explosion", an extensively studied problem in the area of nuclear safety. Steam explosion (also known as vapor explosion) is a physical phenomenon in which the internal energy of a hot liquid is rapidly transferred to a colder and more volatile liquid, which as a result vaporizes at high pressure and expands against the inertial constraint of the surrounding structure as well as the mixture. In the context of nuclear safety, the hot liquid is the molten 'fuel' and the colder more volatile liquid is the 'coolant'. A steam explosion is therefore a class of fuel-coolant interactions in which the timescale for heat transfer between the liquids is smaller than the timescale for pressure wave propagation and expansion in a local region of the fuel-coolant mixture.


Steam explosion experiments are numerous and can be categorized in different ways depending on the scale or the conditions of the experiment:

  • In-pile vs. out-of-pile experiments.
    An in-pile experiment is one that is conducted inside a nuclear reactor core, where the fresh and irradiated fuels are used, whereas an out-of-pile experiment is one that is conducted in an experimental chamber outside the reactor. In an in-pile experiment, fuel-coolant interactions in addition to a number of other phenomena may be investigated, while out-of-pile experiments focus only on fuel-coolant interactions and hence allow for better measurement of initial conditions as well as better interpretation of the test results.

  • Small, intermediate or large scale experiments.
    An experiment is classified as small scale when the amount of fuel (or coolant) is (either relatively or absolutely) very small when compared to the mass of the other liquid. While small scale experiments allow for a better understanding of the mixing, and fragmentation phenomena involved in fuel-coolant interactions, they fail to address the phenomenon of steam explosion as a safety issue, hence the need for large scale experiments.

  • Pouring, injection, or stratified contact mode.
    Because direct contact between the fuel and coolant is essential for a steam explosion, experiments have employed various modes to introduce the molten fuel to the coolant. In the pouring mode, the fuel is poured into the coolant and as it falls, it fragments and mixes with the latter. In the injection mode, one of the liquids (usually the coolant) is injected into the other via a needle. In the stratified mode, a layer of one of the liquid lies on top of the other, i.e. both liquids are separated from one another due to density difference.


Currently, the STEX database is exclusively focused on out-of-pile, intermediate to large scale experiments in which the pouring mode has been employed to cause direct contact between the molten fuel and the coolant. Due to the large number of experiments that fit into this category, STEX focuses on experiments performed at six facilities: the FARO facility, the KROTOS facility, the TROI facility, the WFCI facility, the ZREX facility, and the FITS facility.


Phase II of the STEX database includes experiments from EXO-FITS, SNL Efficiency Scaling Steam Explosion Tests, ANL R-22 Vapor Explosion Tests, UKAEA Vapor Explosion Tests from Molten Fuel Test Facility (MFTF) & MIXA facility, QUEOS and ALPHA facilities.


FARO Programme: Experimental Investigations of Large Scale Melt Quenching in Water

The FARO facility is a large multipurpose test facility designed to provide experimental data on a number of phenomena (FCI, melt quenching and spreading) associated with severe accidents in water cooled reactors. What distinguishes the experiments performed at FARO, is that they aim at characterization of the interaction process of a large mass of corium with water under realistic melt composition and prototypical accident conditions.


The FARO facility is composed of a furnace, an isolation valve unit, a release vessel, a venting system and an interaction vessel (TERMOS designed for 10 Mpa at 300°C or FAT designed for 8 Mpa at 373°C). The interaction vessel, is connected to the FARO furnace via the release tube, and isolated from it during interaction via an isolation valve unit and the release vessel. The furnace is capable of handling up to 200 kg of fuel at temperatures up to 3,270 K. The orifice/valve system provide a controlled release mode of the melt into the interaction vessel (i.e., gravity or forced).

A major drawback in the FARO experiments is the small number of tests performed relative to the large number of governing parameters. In addition, the uncertainties in the conditions of the melt as it penetrates into the water need to be reduced between tests.

The FARO quenching experiments aim at studying the characteristics of melt jet breakup, energy release, debris structure, and bottom plate thermal load. In addition, the importance of zirconium oxidation is also investigated by varying the initial melt composition.


DESCRIPTION OF TESTS: The corium is melted at low pressure (0.1-0.2 Mpa) while the pressure in the interaction vessel is maintained at the required test pressure (2-5 Mpa). These low and high pressure regions are separated by the release vessel closing flap. At the end of the corium melting the main isolation valve is opened and the melt is released from the furnace to the catcher and then the main isolation valve is closed again. The release vessel serves as a pressure equalizer. Upon pressure equalization, the release vessel hinged flap is automatically opened and the melt is delivered by gravity to the water.

TESTS PERFORMED: Several large scale quenching tests (L-06, L-08, L-11, L-14, L-19, L-20, L-24, L-29, L-31) have been conducted in either the FAT FCI vessel or the TERMOS vessel at the FARO facility using prototypic reactor material, UO2-ZrO2-Zr.

PHYSICAL QUANTITIES MEASURED: The main physical parameters measured in the FARO experiments are the transient pressures, temperatures, hydrogen production, level swell as well as debris characteristics.


The FARO tests have been designed to provide data on mixing and quenching of large masses of real corium melt in water under severe accident prototypical conditions. Since the melt quantities used in the FARO experiments is about an order of magnitude higher than what has been used previously in quenching experiments, the FARO data represent a major contribution to the study of the water potential to quench the core material before it reaches the bottom of the reactor.


KROTOS FCI Experiments: Alumina versus Corium Melts

The KROTOS facility is an experimental installation devoted to investigate the effects of initial and mixing conditions on the energetics of an FCI phenomenon in a controlled geometry. Several different types of simulant materials for fuel have been tested, e.g. tin, aluminum oxide and corium.


The KROTOS test arrangement consists of a radiation furnace, release tube and the test section underneath. The furnace is comprised of a cylindrical tungsten heater element which encloses the crucible containing the melt material. Depending on the crucible design and melt composition, 1-10 kg melt masses of temperatures up to 3300 K, can be used. The lower part of the KROTOS facility consists of a stainless steel pressure vessel and test section. The cylindrical pressure vessel, which is 400 mm inner diameter and 2.21 m in height (0.290 m3 in volume), is designed for 2.5 Mpa at 493 K. The stainless steel test section has an inner diameter 200 mm and outer diameter 240 mm. In the KROTOS test facility, the water level is variable up to about 1.3 m and the bottom of the test section can be closed by either a flat plate or with a gas trigger device which consists of a gas chamber (15 cm3 in volume) which can be charged by argon to a pressure of up to 20 Mpa.

  1. The effect of melt physical and chemical characteristics (alumina vs. corium) on the energetics of the melt/water interaction has been explored.

  2. Parameters that may cause suppression of a spontaneous steam explosion (eg. Degree of subcooling, environment pressurization) have also been studied.


DESCRIPTION OF TEST: The test starts by loading the furnace with the melt of desired composition. After the melt reaches the desired temperature, the crucible containing the melt is released from the furnace and falls by gravity through the release tube. During its fall, the crucible strikes a retainer ring and a conical shaped spike pierces the bottom of the crucible, allowing the melt to be released into the water. High speed videos of the melt as it through the water are captured, in addition to the measurement of the dynamic pressures during the melt/water interaction.
The KROTOS experiments were conducted using either an alumina/water system, or a corium/water system. In both sets of experiments, the effect of the water condition (either highly subcooled or near saturation) was investigated. In addition, the effect of melt superheat and initial pressure on the energetics of the interaction was also explored.

  1. visualization of the melt injection process as well as the jet breakup during the interaction,

  2. investigation of the differences in explosivity between corium and alumina melts,

  3. exploration of the various parameters that may cause the suppression of a spontaneous steam explosion (coolant subcooling, melt temperature and initial pressure).

TESTS PERFORMED: Several tests have been conducted in the KROTOS facility with different simulant fuels. Initially, tin melt was used, while later tests employed alumina or corium melts.

The risk of a steam explosion with the tests, set the limit on the viewing and illumination area which limited visualization capacity.

PHYSICAL QUANTITIES MEASURED: The following are measured/assessed:

  • dynamic pressure at various locations using piezoelectric transducers

  • integral void fraction during mixing is measured by monitoring water level

  • vessel pressurization due to steaming or production of non-condensable gases

  • water level swell

  • melt penetration

  • estimation of propagation speed

  • estimation of the starting location of the explosion

  • estimation of explosion efficiency

  • debris analysis


TROI (Test for Real cOrium Interaction with water) Steam Explosion Experiments in a Multidimensional Geometry

The test facility consists of a furnace vessel, a lower pressure vessel, a sliding valve and a test section located in the lower pressure vessel. The furnace vessel contains a crucible and a melt-release assembly. K-type thermocouples are installed in the pressure vessel, in addition to dynamic and static pressure sensors. Moreover, gas sampling bottles and a high speed camera are installed in the pressure vessel. In the interaction vessel, a number of temperature sensors, dynamic pressure sensors and a force sensor are installed. While an optical bi-chromatic pyrometer is installed on top of the furnace to measure the melt temperature through a viewing port.

A limitation of the TROI experiments is the limited amounts of corium melt (~10 kg) were used. In addition, no data is provided on level swell or void fraction.


The main objective of the TROI experiments is to determine whether the corium would lead to energetic steam explosion as a result of interaction with cold water at low pressure in a multi-dimensional test section. Based on these experiments, it is concluded that corium with a composition of 80% UO2 : 20% ZrO2 is less likely to trigger a spontaneous explosion compared to corium with the eutectic composition (70% UO2 : 30% ZrO2).


DESCRIPTION OF TEST: In the TROI experiments the fuel/coolant interaction is initiated between the melt and water by releasing the crucible from the furnace -by gravity- into a pool of water in the test section.

  • use of real reactor material

  • possibility of using either 1-D or 3-D geometry

  • visualization capabilities

  • hydrogen production data

TESTS PERFORMED: Several tests have been conducted in the TROI facility to answer the fundamental question about the explosivity of reactor materials. Some of these tests employed ZrO2 as melt whereas others employed a mixture of UO2-ZrO2 or UO2-ZrO2-Zr.

PHYSICAL QUANTITIES MEASURED: The dynamic pressure, dynamic load and morphology of the debris and hydrogen generation were among the major quantities measured. In addition, high speed videos of the melt jet delivery were captured.


WFCI (Wisconsin Fuel-Coolant Interaction Facility) Vapor Explosions in Large Scale 1-D Geometry

The WFCI facility consists of a furnace, transfer vessel, upper funnel, test section, slide gate, expansion section, quench tank and trigger.


The furnace is cylindrical with a heating volume of about 8.3 liters and a temperature rating of about 1200°C. It is mounted in a vertical position but can be tilted by a motor to an almost horizontal position. The transfer vessel is made of alumina and lined with alumina paper to prevent crack development as the hot metal is poured into the cold vessel. It also has a spring loaded stainless steel plug at its bottom to prevent the melt from falling. The funnel is an expanded section of the test chamber and separated from it by means of the slide gate. The test section is vertical stainless steel two part tube lined with plexiglass with a total volume of 0.087 m3. The expansion section is a horizontal stainless steel three-part tube attached to the upper part of the test section and delivers the explosion expansion products to the downstream quench tank.


In the WFCI experiments the effect of the external trigger, axial constraint and temperature effects of both fuel and coolant on the energetics of the interaction have been investigated. In addition, the effect of coolant viscosity on the suppression of the steam explosion was studied by adding polymer additives to the coolant.

What distinguishes the WFCI tests is that they form a well-characterized set of experiments which investigates the effect of particular initial and boundary conditions (trigger strength, fuel mass and temperature, coolant mass, viscosity, and temperature, as well as system constraint) on the energetics of a simulant melt/water interaction.


DESCRIPTION OF TEST: The test starts by allowing the melt to reach the desired temperature in the furnace which is then tilted to an almost horizontal position to pour the melt into the transfer vessel. The transfer vessel is then moved by a motor on a transport rail system to a position over the funnel above the test chamber. The transfer vessel has a spring loaded stainless steel plug at its bottom to keep the melt from falling. At the appropriate moment, the pin that holds the loaded spring at the bottom of the transfer vessel is removed by a pneumatic cylinder thus allowing the melt to pour into the test section.

TESTS PERFORMED: A total of 37 tests in eight different series (A through H), have been conducted with tin as a simulant fuel and water as coolant. Molten tin with initial temperature ranging from 491°C to 983°C was poured in water (pure or with additives) at a temperature ranging from 25°C to 93°C. In these tests the degree of coolant subcooling ranged from 7°C to 75°C, while the coolant to fuel mass ratio varied from ~ 2 to ~ 12.

PHYSICAL QUANTITIES MEASURED: Tin as a simulant fuel. One-D geometry.

The main physical parameters measured in the WFCI experiments are the transient pressures, temperatures and level swell histories. In addition, the explosion propagation velocity, piston-slug displacement and fragmented fuel debris distribution were also measured. The complete sequence of the experiment has been recorded via a video camera.


ZREX: ZiRconium Explosion

The test facility used for the ZREX/ZRSS tests is one-dimensional in nature. It consists of a melt furnace/drop assembly and a rigid cylindrical interaction vessel. The radial constraint imposed by the rigidity of the interaction vessel, rendered the explosion propagation and expansion one-dimensional and hence maximized the axial output of the mechanical energy release.


All components of the experimental apparatus were placed in an inerted containment chamber with the possibility of collection of gas samples before and after the interaction. The collected gas samples allowed the estimation of the hydrogen gas generated as a result of the interaction. The containment chamber also provides blast protection in the case of explosive events.


The phenomena tested was the effect of the melt zirconium content on the energetics of the explosion.

What distinguishes the ZREX/ZRSS experiments is that it explores the augmentation of the energetics of a vapor explosion as a result of the chemical potential of the molten fuel.


DESCRIPTION OF TEST: In both ZREX and ZR/SS tests, the melt was prepared by induction heating in a graphite crucible. When the melt was ready, the tests started by dropping either 1-kg batches of zirconium/zirconium dioxide (Zr/ZrO2) or 1.2-kg batches of zirconium/stainless steel (Zr/SS) mixtures in a column of water.

The primary objective of the tests was to determine the effect of the content of Zr in the melt, hence the melt composition was varied from 60 to 100 % for the Zr/ZrO2 mixtures and from 0 to 100 % in the Zr/SS mixtures. A total of 14 tests (9 of which were externally triggered) were performed using Zr/ZrO2 mixtures, while a total of 8 tests (5 of which were externally triggered) were performed using Zr/SS mixtures.

TESTS PERFORMED: Several tests have been conducted with Zr/ZrO2 mixtures whereas others have been conducted using Zr/SS mixtures. In addition, a number of scoping experiments were performed to develop the experimental techniques.

PHYSICAL QUANTITIES MEASURED: One-dimensional geometry. Temperature, pressure, and debris characterization.


FITS: Fully Instrumented Test Series

The FITS facility consists of a closed containment chamber, a water chamber, a furnace, along with auxiliary equipment for performing in-chamber tests in one site and the instrumentation and control are located at a different site. The chamber is cylindrical in shape with a diameter of ~1.5 m and a height of ~5.0 m. It is designed to withstand a maximum pressure of 350 psi at a temperature of 650°F. The chamber is mounted vertically on a base with an access port at the bottom to allow for collection and post-test analysis of the debris.


The furnace is isolated from the pressure vessel by means of a knife valve that closes within 75~100 ms of closure signal. The melt (either iron-alumina or corium A+R) is prepared by induction heating in a graphite crucible mounted to the housing of the furnace. The crucible is mechanically transported to the furnace by means of an air cylinder which also supports the crucible within the furnace.


The water chamber is made of optically clear plexiglass to allow for visualisation of the melt entry, mixing, propagation and reaction processes. Although the plexiglass is strong enough to withstand the perturbations associated with melt entry into the water and subsequent mixing, it offers very little resistance to the explosion energetics that follow. The dimensions of the water chamber were chosen to provide the required water to melt mass ratio (ranging from 1.5 : 1 to 50 : 1) as well as to insure full entry of the delivered melt into the water before contact with the bottom.


The main purpose of the FITS tests was to estimate the explosion conversion ratio as a function of ambient pressure, fuel composition, coolant-to-fuel mass ratio, coolant subcooling, and other initial conditions in an enclosed, fully instrumented chamber.


It was observed that only 1 ~ 3 % of the initial internal energy of the melt was converted to mechanical energy. In addition, it was found that spontaneous explosions could be suppressed by raising the pressure of the surrounding environment. However, if a powerful enough external trigger signal was provided, a steam explosion occurred even at elevated pressures.


It was also observed that use of saturated water did not spontaneously cause a propagating explosion to occur (at least at the studied melt mass scale). On the other hand, double explosions occurred in some of the FITS tests when subcooled water was used.


DESCRIPTION OF TEST: A major characteristic feature of the FITS experiments is the possibility of visually capturing the details of the various phases of the fuel-coolant interaction up to the point of the explosion.

The test started by delivering the melt to the water. This was accomplished by allowing the melt to fall under gravity into the water by removing the bottom of the crucible (a separate graphite disk). A fall height of approximately 1.2 m was used to achieve terminal velocities of about 4.5 ~ 6.0 m/s, which was deemed necessary for proper dispersion of the melt in the water.

High speed cameras were used to observe the melt as it fell into the water as well as the subsequent mixing and propagation leading to a possibly explosive event up to the detonation point. The velocity of melt dispersion and subsequent reaction speeds were then inferred from the captured images using some reference length in the test section.

TESTS PERFORMED: Four test series have been conducted (A through D) with two different fuel types: iron-alumina thermite (Fe-Al2O3) and corium A+R (53 w/o UO2, 16 w/o ZrO2, 2 w/o NiO, 27 w/o SS and 2 w/o Mo).

  • No attempt was made to measure the melt temperature, hence, the melt thermal energy was unknown precisely but was estimated to calculate the conversion ratio of the explosion.

  • The weak confinement of the test chamber allowed the expansion to be multidimensional. This led, in some cases, to coarse fragmentation which in turn limited the energetics of the explosion.

PHYSICAL QUANTITIES MEASURED: The instrumentation used in the FITS facility provided the following data:

  • short-term as well as long-term pressure data in both the liquid and gas phases

  • characterization of the fuel debris

  • visualization of the melt entry, mixing, propagation and explosion processes

  • measurement of impulse at chamber head and base



The EXO-FITS test facility at Sandia National Lab is composed of an open lucite chamber for holding water and a graphite crucible to hold and release the melt after the thermite reaction. The experimental setup is surrounded by a support structure but the interaction vessel is left open for all test series. The EXO-FITS experiments were scooping experiments with limited instrumentation. Three cameras were employed one at a speed of ~200-1000 fps and the other two at ~8000 fps.

The facility is an open test area where developmental melting and delivery experiments were performed that allows for rapid turn-around. Although less instrumented, these experiments provided a qualitative insight for designing the fully instrumented facility, FITS.


The MD series (included a total of 19 runs) is a melt-crucible delivery developmental set of experiments. The first 6 runs involved no water whereas the remaining 13 experiments were performed by dropping Al2O3 into water at an ambient pressure.

The MDC series (included 13 runs) was designed to gain familiarity with the preparation and delivery of corium A+R and all included an external trigger.

The MDF series, which included 5 scooping experiments, was developed to determine the effect of hydrogen generation during the mixing phase of a melt/coolant interaction on suppressing or enhancing the triggering of a steam explosion using Fe3O4.

The RC test series involved 2 runs that were conducted after replacing the lucite interaction water chamber with a 25 mm thick steel pipe 0.6 m in diameter to assess the effect rigid radial constraint on the FCI.

For the CM (coarse mixing) series, a total of 12 experiments were performed to investigate the mixing characteristics of an FCI to assist in development of the mixing phase models.

The OM (oxide melt) series involved 4 runs designed to contrast the behavior of metallic to oxidic melts and investigate the effect of melt composition on the probability of occurrence of spontaneous interactions and on the melt dispersal behavior and hence the extent of the reaction.

The key research question for the ACM series was whether this alternate contact mode (of pouring water onto the melt) would support an energetic steam explosion.


DESCRIPTION OF TEST: The EXO-FITS tests were conducted by dropping ~ 5-20 kg melt into the water lucite chamber. For these experimental series, the water temperature ranged from ambient to the saturation temperature at the ambient pressure of ~ 0.082 Mpa.

TESTS PERFORMED: Several large scale tests have been conducted in the EXO-FITS test facility: MD, MDF, MDC, RC, CM, OM, ACM and NPR/FCI test series.

Experiments conducted in the EXO-FITS series were meant to be scooping test to aid in investigating certain aspect of the FCI and aid in designing the later fully instrumented test facility, FITS. Hence the collected data is limited to visual observations gathered by the three cameras installed in the facility as well as qualitative analysis of the collected debris.

PHYSICAL QUANTITIES MEASURED: As mentioned earlier, no measurements were taken for these early test series (MD, MDC, MDF, RC, CM, OM, ACM), except for testing the melt preparation and delivery system in addition to the visual recordings of the cameras employed. These photographs were used to calculate the melt-coolant mixture diameter, length and propagation velocity.


SNL Efficiency Scaling Steam Explosion Tests

The interaction vessel used in the majority of the tests was a 10 mm thick steel tank, 0.9 m in diameter and 1.1 m high, with a semi-elliptic bottom. A steel cylinder placed underneath and tack welded to the bottom of the vessel provided support. The support cylinder was in turn tack welded to a base plate (25 mm thick in the first 10 experiments and 50 mm thick in the remaining runs). The melt generator, which was basically a capped internally insulated pipe in which the thermite powder was placed and the chemical reaction initiated, was suspended 0.5 m above the interaction vessel by a bracket.


The bottom of the melt generator was an insulated steel plate with a pour hole bored in the middle. Later the design was modified to include a trapdoor to provide high pour rates. In several tests a coaxial cylinder was placed inside the interaction vessel to restrict the volume of water available to interact with the dropped melt. Two different restricting cylinders were used: one had a diameter of 0.46 m and a height of 0.46 m, while the other had a diameter of 0.31 m and a height of 0.38 m. 0.1-0.125 m thick crucible aluminum honeycomb blocks were inserted between the interaction vessel and the base plate to measure the reaction energy of the interaction vessel in response to downward forces upon explosion. Normal and high speed cinematography was employed to monitor the motion of the interaction vessel and water/fuel ejecta. Melt dispersal devices (coarse mesh or a splatter) were used.


The OG series (known as the efficiency scaling test series) was conducted to determine the conversion ratio of the fuel thermal energy into mechanical work at large scale. The SNL efficiency scaling test represent one of the first test series that used prototypic fuel melts to investigate the effect of various initial conditions on explosion efficiencies. A characteristic feature of this experimental program, though used in one run only, is the use of air injection to simulate the vigorous boiling condition in an FCI.


DESCRIPTION OF TEST: The open geometry test series were intended to be scoping in nature. These tests were designated "open geometry" experiments because they performed in an open vessel with minimum instrumentation. Most experiments used thermatically generated fuel simulant, Fe-Al2O3 since it is non-hazardous, easy to produce and inexpensive. A few of the experiments used Corium A+R (Stainless Steel 59%, UO2 23%, ZrO2 15%, NiO 3%).

The fuel melt was generated in an insulated cylinder which was held above the water tank, and the melt was then poured into the water. Melt quantities ranged between 1-20 kg at a temperature of ~ 3000 K. Regular tap water was used in quantities of approximately 175-840 kg at a temperature of about 300 K. In a few experiments, the water was heated using immersion-type electric heaters. In one experiment, the water was subjected to air injection to simulate a highly vigorous boiling situation. The interaction vessel was coated by lard to eliminate/reduce the probability of spontaneously initiated explosions.

The mechanical work generated by the explosion was determined by measuring the impulse delivered downward to crushable honeycomb blocks and by estimating the potential energy of the upward ejected water and/or fuel.

TESTS PERFORMED: Almost 60 large scale tests have been conducted in the OG test series at Sandia National Laboratory. 49 tests used Fe-Al2O3as melt while the remaining 11 tests were performed using Corium A+R.

Because the experiments were performed in an open vessel, very little of the debris could be recovered for post explosion analysis. Hence there is no guarantee that even the recovered debris is representative of the entire debris.

PHYSICAL QUANTITIES MEASURED: Pressure transducers placed directly in the water in addition to wall mounted quartz gages were used to measure the magnitude of the pressure produced in the explosion. The deformation in the aluminum honeycomb blocks was used to estimate the reaction energy of the interaction vessel in response to downward forces upon explosion. Moreover, pretest and posttest measurement of the interaction vessel diameter at various locations was used to estimate the amount of plastic work performed in deforming the vessel. Normal (64 fps) and high speed (3000-5000 fps) cinematography was employed to monitor the motion of the interaction vessel and water/fuel ejecta to provide estimates of the kinetic energy generated by the explosion. In addition visual inspection of the debris collected after the explosion also provided some insight into the FCI.


ANL R-22 Vapor Explosion Tests

The experimental setup consisted of a 100-liter water container, an R-22 tank with a mechanism for releasing R-22 at a designated time into the water, and instrumentation.

The first experiments used a glass aquarium for the water, and to assess the effect of the containment strength, the fourth test employed a 70-liter garbage can. For the remaining runs, a new water container was built with rigid walls to eliminate the effect of containment strength. The container included viewing ports at different angles to allow for optical access for various subsurface high-speed recording of the FCI event.

Two high speed cameras were employed; one at a rate 5000 fps, the other at 10000 fps. Three pressure transducers were used to measure the pressure signature.


The test series conducted under this experimental program aimed at investigating the tank and stream geometry, and the water temperature as the dominant system parameters. Constrained and unconstrained release modes were used.


DESCRIPTION OF TEST: Tests were performed by dropping a constrained and an unconstrained mass of R-22 into water. For the unconstrained runs, R-22 was allowed to fall freely into water whose temperature was varied from 55-100°C. The constrained runs were conducted to test the hypothesis that high explosion pressures are generated as a result of the inertial constraint of the water. The idea was to suddenly release R-22 into water when it is totally submerged. Several mechanisms were attempted to suddenly release the R-22 charge under the water. Ultimately a cylindrically rubber and mesh container was used to hold the R-22 as it penetrates into the water. The event is initiated by rupturing the R-22 container using a scalpel blade positioned near the bottom of the water tank. 26 runs were conducted with this mechanism using water temperatures ranging from 0-100°C.

TESTS PERFORMED: About 50 large scale tests have been conducted at Argonne National Laboratory using R-22/water pair.

Use of R-22 instead of prototypic reactor materials.

PHYSICAL QUANTITIES MEASURED: In addition to the high speed movies recorded at different subsurface locations, pressure distributions in the water chamber were also measure.


MFTF (Molten Fuel Test Facility) & MIXA UKAEA Vapor Explosion Tests

The MFTF facility was a large pressure vessel with a volume of 1.7 m3, equipped with a thermite charge container. To release the melt from this container, two different methods were applied: the free and restricted release modes. In the free release mode, the melt was released freely into the surrounding water. In the restricted release mode, the melt was constrained by an open catchpot and ejected with the end cap of the charge container.


The MIXA facility consisted of a vessel made from steel and glass, the inner dimensions are 0.37 m by 0.37 m by 1.60 m height. The vessel was open to the atmosphere via a 100 mm vent line, which contained a flow meter. The water in the vessel was heated and mixed by a recirculation system prior to each experiment. The interaction vessel is surrounded by a concrete cell which provided protection against blast and missile release of materials in case of an explosive interaction. Molten fuel simulant (uranium dioxide-molybdenum alloy) at a temperature ~ 3600 K, is released over an array of carbon bars. These bars split the melt streams into droplets and this configuration is thus called a droplet former. A cylindrical steel skirt is located below the droplet former to constrain the jet spread.


MFTF tests, study the effect of release mode, which in essence limits the amount of coolant available for interaction, on the interaction.


Whereas the MIXA tests focus on the effect of dispersal characteristics on the interaction. This test series involved 7 runs. The MIXA tests used variable length skirts around the droplet former and therefore resulted in a range of pour shapes from one-dimensional (pour over most of the vessel width) to center pour (pour over a small region in the center of the vessel).


DESCRIPTION OF TEST: The two series of experiments performed at MFTF facility, SUW and WUMT, used thermite generated uranium dioxide/molybdenum melt (81% UO2, 19% Mo) at an initial temperature of 3600 K in quantities up to 24 kg released into water.

Overall, twelve experiments were performed in the SUW series. Nine of which were conducted by dropping 24 kg of melt simulant into the coolant in free release mode, while the remaining three were in the restricted mode. Some of these tests investigated the effect of increased system pressure and reduced cover gas volume on the melt dispersion. While the rest investigated the effect of water subcooling on the interaction. For the last two experimental runs in the SUW series, the melt mass was reduced to 8 kg and were carried out in the restricted mode at pressures of 0.1 and 1.0 Mpa and 60°C subcooling. After each experiment, the solidified melt debris was dried and the particle size distribution measured by sieving.

In the WUMT series of experiments 24 kg of melt was poured into a square-section mixing vessel containing water. These experiments were carried out to examine mixing; thus various combinations of melt/water mass ratio, vessel size, water depth and melt pour diameter were used in the experiments.

TESTS PERFORMED: Intermediate to large scale tests have been conducted at Winfrith, UKAEA. Test series SUW and WUMT were performed in the MFTF facility, while MIXA test series were performed at the MIXA facility.

The limited number of tests.

PHYSICAL QUANTITIES MEASURED: In the MFTF facility, transient pressures developed within the MFTF pressure vessel were measured by 12 piezoelectric pressure transducers. Three of these were located in the roof to measure the cover gas pressure, 6 in the side wall and 3 in the bottom to measure the pressure in the water. Two similar pressure transducers monitored the pressure in the charge container. In addition, two high speed cine-cameras with frame rates of 1500 fps recorded the release of the ment and its interaction with the water. Hydrogen generated as a result of the interaction is assessed by measuring the partial pressure for each experiment.

In the MIXA facility, the mixing process was recorded using high speed cine photography using two cameras. The pressure in the vessel was measured using four pressure transducers, the water temperature was measured using a thermocouple and eight thermocouples measure the glass walls and the vapor. The flow rate of steam was measured using a flowmeter installed on the vent line.


Among the special features of these experiments is the use of restricted and free release modes. In addition to investigation of the scaling effect since SUW series is a replica of small scale experiments previously conducted at the MFTF facility.

The MIXA test series represent the first experiments in which stream of droplets of prototypic material are poured into water.


ALPHA (Assessment of Loads and Performance of Containment in a Hypothetical Accident) Program Vapor Explosion Tests

The ALPHA facility simulates the containment with a diameter of 3.9 m, a height of 5.7 m. The melt, which is a mixture of Fe and Al2O3, was generated by a thermatic reaction in the melt generator located at the top of the vessel. Upon completion of the thermetic reaction, the melt was dropped into the water pool located inside the containment vessel. Two kinds of water pool were employed, one was cylindrical and the other was cubical. Several viewing windows are provided in the vessel for visual observations during the experiments. The containment vessel was pressurized by nitrogen in a number of experiments.


The specific objectives of these experiments are to phenomenologically understand steam explosions in a relatively large-scale geometry and to quantify the conditions to suppress spontaneous steam explosions and finally to obtain additional information to develop and/or validate analytical models. To this end, the experiments conducted under the ALPHA program were designed to investigate the effect of various parameters (melt mass, ambient pressure, water temperature, melt dispersion) on melt-water interaction.


DESCRIPTION OF TEST: The first test series, designated by STX-series, was performed to study the effects of ambient pressure, fuel mass, and melt dispersion on the energetics of the FCI. A total of 21 experiments were conducted in the STX-series. Another test series, designated by MJB (melt jet breakup), studied the jet breakup and fragmentation of a molten lead-bismuth eutectic alloy into a deep pool of water.

TESTS PERFORMED: Several large scale tests have been conducted in the ALPHA facility at JAERI to investigate the fuel-coolant interaction phenomenon which would threaten the nuclear containment integrity under severe accident conditions.

The use of simulant material for the melt is one limitation. Another limitation is the use of only two high speed cameras at 90 deg. From one another to quantify the void fractions of the melt, water and steam.

PHYSICAL QUANTITIES MEASURED: In the STX-series, volume fractions of the melt, water and steam in the mixing region prior to the occurrence of spontaneous steam explosions were quantified. In addition, other characteristics of melt-coolant interactions were evaluated: settling velocity of the melt in water, propagation and expansion velocities, energy conversion ratio and debris size distribution. A number of piezoelectric pressure transducers were suspended into the water pool to measure the pressure history. Four thermocouples were used to measure the rapid temperature response in the containment atmosphere. Liquid level detectors were used to measure the water level swell after the melt dropped into the water pool. Optical void probes were used to measure the local void fractions in the mixing region. In addition high speed recordings were also used to qualitatively and quantitatively investigate the steam explosion.


What characterizes the experiments performed in the ALPHA facility is the use of a three-dimensional test chamber with large quantities of simulant material. Another characteristic feature is the use of intensive instrumentation, to give a clear picture of the mixing and propagation characteristics of the explosion. The use of two high speed cameras at 90 deg. From one another to quantify the void fractions of the melt, water and steam, along with level swell measurement, debris analysis, in addition to the pressure temperature measurement.



The QUEOS facility consists of a test vessel, the furnace and the valve system separating the two. The spheres are heated in an electric radiation furnace in an argon atmosphere. The hot spheres are released and allowed to fall freely into the water vessel. The water vessel is made of stainless steel frames and glass with inner cross section of 72x72 cm and a height of 138 cm.


The QUEOS test series focuses on the transient multiphase interaction of hot particles with the objective of establishing a database for testing the models of heat, mass and momentum transfer in multifluid codes and the codes' capability to correctly describe multiphase flows as they occur in the premixing phase of steam explosion.


DESCRIPTION OF TEST: In QUEOS, hot solid particles are used instead of molten material. To simulate the melt jet as closely as possible, the hot spheres are released as one or three cylindrical jets into a three dimensional test vessel. Three types of spheres with two different densities (zirconia and molybdenum spheres were used) and three different diameters are used. With masses ranging from 7-14 kg for spheres made of zirconia, and 10-20 kg for spheres made from molybdenum, this leads to numbers between 2300 and 49000 spheres per run. To capture the radiation effects in a prototypical situation, the temperature of the spheres were up to 2200 K (for zirconia spheres) and 2500 K (for molybdenum spheres).

TESTS PERFORMED: Approximately 60 large scale tests have been conducted in the QUEOS facility. A few of the tests used steel as melt, whereas the majority of the tests used wither molybdenum or zirconium dioxide as melt.

Use of solid spheres, hence the experiments focus on investigating the premixing phase only.

PHYSICAL QUANTITIES MEASURED: The temperature of the spheres in the furnace is monitored by high-temperature thermocouples and pyrometers. Six pressure transducers measure the vessel pressure while the steaming rate is measured by a flowmeter. The water level is measured by two impedance level meters and local void is measured by conductivity probes placed below the water level. Two high speed film cameras and two video cameras are used to collect pictures of the interaction from two sides of the vessel.


The use of solid spheres in place of molten material offers the advantage that the shape, size and surface area of the hot material are known and can be varied in a systematic way. Moreover, the geometry is three dimensional geometry and large volume fractions used. In addition, the interaction vessel is closed and connected to the ambient through a venting pipe which allows a slight increase in pressure leading to a varying subcooling of the water. This is similar to prototypic situations and also provides important data for code validation.


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Package ID Status date Status
CSNI2007/02 04-MAY-2010 Masterfiled restricted
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  1. [D. Magallon and I. Huhtiniemi, Corium melt quenching tests at low pressure and subcooled water in FARO, Nuclear Engineering and Design 204 (2001) 369-376.

  2. D. Magallon and H. Hohmann, Experimental investigation of 150 kg scale of corium melt jet quenching in water, Nuclear Engineering and Design 177 (1997) 321-337.

  3. D. Magallon and H. Hohmann, High pressure corium melt quenching tests In FARO, Nuclear Engineering and Design 155 (1995) 253-270.

  4. D. Magallon, I. Huhtiniemi and H. Hohmann, Lessons learnt from FARO-TERMOS corium melt, Nuclear Engineering and Design 189 (1999) 223-238.


  1. H. Hohmann, D. Magallon, H.Schins, and A.Yerkess, FCI Experiments in the Aluminum Oxide/Water System, Nuclear Engineering and Design, 155 (1995), 391-403.

  2. I. Huhtiniemi and D. Magallon, Insight into Steam Explosions with Corium Melts in KROTOS, Nuclear Engineering and Design 204 (2001) 391-400.

  3. I. Huhtiniemi, D. Magallon, H. Hohmann, Results of Recent KROTOS FCI Tests: Alumina versus Corium Melts, Nuclear Engineering and Design, 189 (1999), 379-389.

  4. I. Huhtiniemi, H. Hohmann, D. Magallon, FCI Experiments in the Corium/Water System, Nuclear Engineering and Design, 177 (1997), 339-349.


  1. J. H. Kim, I. K. Park, B. T. Min, S. W. Hong, Y. S. Shin, J. H. Song and H. D. Kim,The Influence of Variations in the Water Depth and Melt Composition on a Spontaneous Steam Explosion in the TROI Experiments, Proceedings of ICAPP'04, Pittsburgh, PA USA, June 13-17, 2004, pp. 1210-1219.

  2. J. H. Kim, I. K. Park, B. T. Min, S. W. Hong, J. H. Song and H. D. Kim, Results of the Triggered TROI Steam Explosion Experiments with a Narrow Interaction Vessel, Proceedings of ICAPP'06, Reno, NV USA, June 4-8, 2006, pp. 1322-1331.

  3. J. H. Song, I. K. Park, Y. S. Shin, J. H. Kim, S. W. Hong, B. T. Min and H. D. Kim, Fuel Coolant Interaction Experiments in TROI using a UO2/ZrO2Mixture, Nuc. Eng. & Des., 222 (2003), pp. 1-15.

  4. J. H. Kim, I. K. Park, B. T. Min, S. W. Hong, Y. S. Shin, J. H. Song and H. D. Kim, An Experimental Study on Intermediate Scale Steam Explosions With Molten Zirconia and Corium in the TROI Facilities, 10th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-10), Seoul, Korea, October 5-9, 2003.

  5. J. H. Kim, I. K. Park, B. T. Min, S. W. Hong, S. H. Hong, J. H. Song and H. D. Kim, Results of the Triggered Steam Explosions From the TROI Experiment, Nucl. Tech., 58 (2007), pp. 378-395.

  6. J. H. Song, I. K. Park, Y. J. Chang, Y. S. Shin, J. H. Kim, B. T. Min, S. W. Hong and H. D. Kim, Experiments on the Interactions of Molten ZrO2 with Water Using TROI Facility, Nucl. Eng. & Des., 213 (2002), pp. 970-110.

  7. Jin Ho SONG, Seong Wan HONG, Jong Hwan KIM, Young Jo CHANG, Yong Seung SHIN, Beong Tae MIN and Hee Dong KIM, Insights from the Recent Steam Explosions Experiments in TROI, J. of Nucl. Sci. & Tech., 40 (2003), pp. 783-795.


  1. Hyun-Sun Park, Vapor Explosions in One-Dimensional Large Scale Geometry, PhD. Thesis, University of Wisconsin-Madison (1995).

  2. Park, H.S.; Yoon, C.; Corradini, M.L.; Bang, K.H., Experiments on the trigger effect for 1-D large scale vapor explosions, Proceedings of the International Conference on New Trends in Nuclear System Thermohydraulics, 1994, pt. 2, p 271-80 vol.2


  • D. H. Cho, D. R Armstrong, and W. H. Gunther, Experiments on Interactions between Zirconium-Containing Melt and Water, NUREG-CR-5372.


  1. D. E. Mitchell, M. L. Corradini, and W. W. Tarbell, Intermediate Scale Steam Explosion Phenomena: Experiments and Analysis, NUREG/CR-2145, SAND81-0124.

  2. D. E. Mitchell, and N. A. Evans, Steam Explosion Experiments on Intermediate Scale: FITSB Series, NUREG/CR-3983, SAND83-1057.

  3. B. W. Marshall, Jr., Recent Fuel-Coolant Interaction Experiments Conducted In The FITS Vessel, SAND87-2467C.


  1. Billy W. Marshall, Jr., Marshall Berman, Melvin S. Krein, Recent Intermediate-Scale Experiments On Fuel-Coolant Interactions In An Open Geometry (Exo-Fits), SAND85-1615C

  2. MJ. Rightley, D.F. Beck, NPR/FCI EXO-FITS Experiment Series Report, SAND91-1544

SNL Efficiency Scaling Tests

  1. Lawrence D. Buxton, William B. Benedick, "Steam Explosion Efficiency Studies", SAND-79-1399

  2. L. D. Buxton, W. B. Benedick, M. L. Corradini, "Steam Explosion Efficiency Studies: Part II Corium Experiments", SAND-80-1324

ANL R-22

  1. [1] R. Armstrong and R. P. Anderson, "Large- scale Experimental Study of Vapor Explosions in an R-22/Water System", Reactor Development Program Progress Report," ANL-RDP-49, pg. 7-10, March 1976

  2. [2] R. Armstrong and R. P. Anderson, "R-22 Vapor Explosions", Nucl. React. Saf. Heat Transfer, Presented at Winter Annu. Meet of ASME, November 27, 1977 - December 2, 1977., ASME, p 31-45, 1977


  1. M.J. Bird, "Thermal Interactions Between Molten Uranium Dioxide And Water: An Experimental Study Using Thermite Generated Uranium Dioxide", American Society of Mechanical Engineers, Heat Transfer Division, HTD, p 41-47, 1981

  2. M. J. Bird, P. Naylor and R. B. Tattersall, "Experimental Studies Of Thermal Interactions Between Thermite Generated Molten Fuel And Sodium", Proceedings of the L.M.F.B.R. Safety Topical Meeting, p 439-48 vol.3, 1982

  3. M. J. Bird, "An Experimental Study Of Scaling In Core Melt/Water Interactions", PWR/SAWG/P (84) 71. Presented at Natl. Heat Transfer Conf., 22nd, Niagara Falls


  1. N. Yamano, Y. Maruyama, T. Kudo, A. Hidaka, J. Sugimoto, Phenomenological studies on melt-coolant interactions in the ALPHA program, Nuclear Engineering and Design 155 (1995) 369-389

  2. Norihiro Yamano, Kiyofumi Moriyama, Yu Maruyama, Hyunsun Park, Yanhua Yang, Jun Sugimoto, Study on premixing phase of steam explosion at JAERI, Nuclear Engineering and Design 189 (1999) 205-221


  1. L. Meyer, "QUEOS, An Experimental Investigation of the Premixing Phase with Hot Spheres", Nuclear Engineering and Design, 189 (1999), 191-204

  2. Leonhard Meyer, Gustav Schumacher, Helmut Jacobs, Kalman Thurnay, "Investigation of the premixing phase of a steam explosion with hot spheres", Nuclear Technology, 123 (1998), 142-155

  3. L. Meyer, D. Kuhn, The Interaction Of Very Hot Particles Falling Into Water, The 2nd International Symposium on Two-Phase Flow Modelling and Experimentation, Pisa 23-26 May, 1999

  4. L. Meyer, The Interaction of a Falling Mass of Spheres with Water, Citation

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No specified programming language
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The STEX database has been compiled by the University of Wisconsin-Madison on behalf of the Nuclear Energy Agency.


Michael L. Corradini and Aya Diab

1500 Engr. Dr.

University of Wisconsin

Madison WI 53706, USA


D. Magallon
European Commission-Joint Research Centre
Institute for Systems, Informatics and Safety
Ispra 21020 (VA)


Jin Ho Song
Korea Atomic Energy Research Institute
150 Dukjin-Dong, Yusong-Gu, Daejon, 305-353
Rep. of Korea


D. H. Cho
Argonne National Laboratory
9700 South Cass Avenue
Argonne, IL 60439, USA


Michael L. Corradini
University of Wisconsin-Madison
1500 Engineering Dr.
Madison, WI 53706, USA


D. E. Mitchell
Sandia National Laboratories
Albuquerque, NM 87185, USA


Billy W. Marshall, & Marshall Berman
Sandia National Laboratories
Albuquerque, New Mexico, USA


SNL Efficiency Scaling Tests:
Lawrence D. Buxton
Sandia Laboratories
Albuquerque, NM 87185, USA


ANL R-22:
R. Armstrong and R. P. Anderson
Reactor Analysis & Safety Division
Argonne National Laboratory,
Argonne, IL 60439, USA


UKAEA Tests:
M. J. Bird
United Kingdom Atomic Energy Authority
Atomic Energy Establishment, Winfrith,
Dorchester, Dorset, UK


Norihiro Yamano
Severe Accident Research Laboratory
2-4 Shirakata-shirane, Tokai-mura, Ibaraki-ken 319-1195, Japan


L. Meyer
Forschungszentrum Karlsruhe
Institut fur Neutronenphysik und Reaktortechnik
P.O.Box 3640
D-76021 Karlsruhe, Germany

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Figures and equations in jpg format
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  • Y. Integral Experiments Data, Databases, Benchmarks

Keywords: database, fuel coolant interaction, severe accident, steam explosion.