Editing Steam explosion (section)

==Examples==
[[File:NYC steam explosion 2.jpg|thumb|right|A jet of steam rising higher than the [[Chrysler Building]] during the [[2007 New York City steam explosion]]]]
High steam generation rates can occur under other circumstances, such as boiler-drum failure, or at a quench front (for example when water re-enters a hot dry boiler). Though potentially damaging, they are usually less energetic than events in which the hot ("fuel") phase is molten and so can be finely fragmented within the volatile ("coolant") phase. Some examples follow:
===Natural===
Steam explosions are naturally produced by certain [[volcano]]es, especially [[stratovolcano]]es, and are a major cause of human fatalities in volcanic eruptions. They are often encountered where hot [[lava]] meets sea water or ice. Such an occurrence is also called a '''''littoral explosion'''''. A dangerous steam explosion can also be created when liquid water or ice encounters hot, molten metal. As the water explodes into steam, it splashes the burning hot liquid metal along with it, causing an extreme risk of severe burns to anyone located nearby and creating a fire hazard.

===Boiler explosions===
{{Main|Boiler explosion}}
[[File:Boiler explosion of a narrow gauge steam locomotive.jpg|thumb|right|Boiler explosions are a type of steam explosion.]]
When a pressurized container such as the waterside of a steam [[boiler]] ruptures, it is always followed by some degree of steam explosion. A common [[operating temperature]] and pressure for a marine boiler is around {{cvt|950|psi|||}} and {{convert|850|F|||}} at the outlet of the superheater. A steam boiler has an interface of steam and water in the steam drum, which is where the water is finally evaporating due to the heat input, usually oil-fired burners. When a water tube fails due to any of a variety of reasons, it causes the water in the boiler to expand out of the opening into the furnace area that is only a few psi above atmospheric pressure. This will likely extinguish all fires and expands over the large surface area on the sides of the boiler. To decrease the likelihood of a devastating explosion, boilers have gone from the "[[Fire-tube boiler|fire-tube]]" designs, where the heat was added by passing hot gases through tubes in a body of water, to "[[Water-tube boiler|water-tube]]" boilers that have the water inside of the tubes and the furnace area is around the tubes. Old "fire-tube" boilers often failed due to poor build quality or lack of maintenance (such as corrosion of the fire tubes, or [[Metal fatigue|fatigue]] of the boiler shell due to constant expansion and contraction). A failure of fire tubes forces large volumes of high pressure, high temperature steam back down the fire tubes in a fraction of a second and often blows the burners off the front of the boiler, whereas a failure of the pressure vessel surrounding the water would lead to a [[BLEVE|full and entire evacuation of the boiler's contents]] in a large steam explosion. On a marine boiler, this would certainly destroy the ship's propulsion plant and possibly the corresponding end of the ship.

Tanks containing [[Petroleum|crude oil]] and certain commercial oil cuts, such as some [[Diesel fuel|diesel oils]] and [[kerosene]], may be subject to [[boilover]], an extremely hazardous situation in which a water layer under an open-top tank pool fire starts boiling, which results in a significant increase in fire intensity accompanied by violent expulsion of burning fluid to the surrounding areas. In many cases, the underlying water layer is [[Superheated water|superheated]], in which case part of it goes through explosive boiling. When this happens, the abruptness of the expansion further enhances the expulsion of blazing fuel.{{sfnp|Ferrero|2006|p=6}}<ref>{{Cite magazine |last=Garrison |first=William W. |year=1984 |title=C.A. La Electricidad de Caracas, December 19, 1982, Fire (Near) Caracas, Venezuela |url=https://www.icheme.org/media/5781/lpb_issue057p026.pdf |archive-url=https://web.archive.org/web/20230722153934/https://www.icheme.org/media/5781/lpb_issue057p026.pdf |archive-date=22 July 2023 |access-date=22 July 2023 |journal=[[Loss Prevention Bulletin]] |publisher=[[Institution of Chemical Engineers|Institution of Chemical Engineers (IChemE)]] |pages=26–30 |issue=57 |issn=0260-9576}}</ref><ref>{{Cite journal |last1=Broeckmann |first1=Bernd |last2=Schecker |first2=Hans-Georg |date=1995 |title=Heat Transfer Mechanisms and Boilover in Burning Oil–Water Systems |journal=[[Journal of Loss Prevention in the Process Industries]] |volume=8 |issue=3 |pages=137–147 |doi=10.1016/0950-4230(95)00016-T |bibcode=1995JLPPI...8..137B |issn=0950-4230 |eissn=1873-3352}}</ref>

===Nuclear reactor meltdown===
 {{overly detailed|section|date=June 2024}}
Events of this general type are also possible if the fuel and fuel elements of a water-cooled nuclear reactor gradually melt. The mixture of molten core structures and fuel is often referred to as "Corium". If such corium comes into contact with water, vapour explosions may occur from the violent interaction between molten fuel (corium) and water as coolant. Such explosions are seen to be '''fuel–coolant interactions''' (FCI).{{Citation needed|reason=Water is used to cool any water-moderated nuclear reactor (PWR, BWR, etc.), and thus fuel-coolant interactions are required.|date=August 2010}}
<ref>{{cite journal |last1=Theofanous |first1=T.G. |last2=Najafi |first2=B. |last3=Rumble |first3=E. |title=An Assessment of Steam-Explosion-Induced Containment Failure. Part I: Probabilistic Aspects |journal=Nuclear Science and Engineering |date=1987 |volume=97 |issue=4 |pages=259–281 |doi=10.13182/NSE87-A23512|bibcode=1987NSE....97..259T }}</ref>
<ref>{{cite journal |last1=Magallon |first1=D. |title=Status and Prospects of Resolution of the Vapour Explosion Issue in Light Water Reactors |journal=Nuclear Engineering and Technology |date=2009 |volume=41 |issue=5 |pages=603–616|doi=10.5516/NET.2009.41.5.603 |doi-access=free }}</ref>
The severity of a steam explosion based on fuel-coolant interaction (FCI) depends strongly on the so-called premixing process, which describes the mixing of the melt with the surrounding water-steam mixture. In general, water-rich premixtures are considered more favorable than steam-rich environments in terms of steam explosion initiation and strength.
The theoretical maximum for the strength of a steam explosion from a given mass of molten corium, which can never be achieved in practice, is due to its optimal distribution in the form of molten corium droplets of a certain size. These droplets are surrounded by a suitable volume of water, which in principle results from the max. possible mass of vaporized water at instantaneous heat exchange between the molten droplet fragmenting in a shock wave and the surrounding water. On the basis of this very conservative assumption, calculations for alpha containment failure were carried out by Theofanous.<ref>{{cite journal |last1=Theofanous |first1=T.G. |last2=Yuen |first2=W.W. |title=The probability of alpha-mode containment failure |journal=Nuclear Engineering and Design |date=2 April 1995 |volume=155 |issue=1–2 |pages=459–473 |doi=10.1016/0029-5493(94)00889-7|bibcode=1995NuEnD.155..459T }}</ref>
However, these optimal conditions used for conservative estimates do not occur in the real world. For one thing, the entire molten reactor core will never be in premixture, but only in the form of a part of it, e.g., as a jet of molten corium impinging a water pool in the lower plenum of the reactor, fragmenting there by ablation and allowing by this the formation of a premixture in the vicinity of the melt jet falling through the water pool. Alternatively, the melt may arrive as a thick jet at the bottom of the lower plenum, where it forms a pool of melt overlaid by a pool of water. In this case, a premixing zone can form at the interface between the melt pool and the water pool. In both cases, it is clear that by far not the entire molten reactor inventory is involved in premixing, but rather only a small percentage. Further limitations arise from the saturated nature of the water in the reactor, i.e., water with appreciable supercooling is not present there. In the case of penetration of a fragmenting melt jet there, this leads to increasing evaporation and an increasing steam content in the premixture, which, from a content > 70% in the water/steam mixture, prevents the explosion altogether or at least limits its strength. Another counter-effect is the solidification of the molten particles, which depends, among other things, on the diameter of the molten particles. That is, small particles solidify faster than larger ones. Furthermore, the models for instability growth at interfaces between flowing media (e.g. Kelvin-Helmholtz, Rayleigh-Taylor, Conte-Miles, ...) show a correlation between particle size after fragmentation and the ratio of the density of the fragmenting medium (water-vapor mixture) to the density of the fragmented medium, which can also be demonstrated experimentally. In the case of corium (density of ~ 8000 kg/m³), much smaller droplets (~ 3 - 4 mm) result than when alumina (Al2O3) is used as a corium simulant with a density of just under half that of corium with droplet sizes in the range of 1 - 2 cm. Jet fragmentation experiments conducted at JRC ISPRA under typical reactor conditions with masses of molten corium up to 200 kg and melt jet diameters of 5 - 10 cm in diameter in pools of saturated water up to 2 m deep resulted in success with respect to steam explosions only when Al2O3 was used as the corium simulant. Despite various efforts on the part of the experimenters, it was never possible to trigger a steam explosion in the corium experiments in FARO.(Will be continued ...)

If a steam explosion occurs in a confined tank of water due to rapid heating of the water, the pressure wave and rapidly expanding steam can cause severe [[water hammer]]. This was the mechanism that, in Idaho, USA, in 1961, caused the [[SL-1]] nuclear reactor vessel to jump over {{convert|9|ft}} in the air when it was destroyed by a [[criticality accident]]. In the case of SL-1, the fuel and fuel elements vaporized from instantaneous overheating.

In January 1961, operator error caused the [[SL-1]] reactor to instantly destroy itself in a steam explosion. The 1986 [[Chernobyl nuclear disaster]] in the Soviet Union was feared to cause major steam explosion (and resulting [[Europe]]-wide [[nuclear fallout]]) upon melting the [[lava]]-like [[nuclear fuel]] through the [[nuclear reactor|reactor]]'s basement towards contact with residue fire-fighting water and [[groundwater]]. The threat was averted by frantic [[tunnel]]ing underneath the reactor in order to pump out water and reinforce underlying soil with [[concrete]].

In a [[nuclear meltdown]], the most severe outcome of a steam explosion is early [[containment building]] failure. Two possibilities are the ejection at high pressure of molten fuel into the containment, causing rapid heating; or an in-vessel steam explosion causing ejection of a missile (such as the [[upper head]]) into, and through, the containment. Less dramatic but still significant is that the molten mass of fuel and reactor core melts through the floor of the reactor building and reaches [[ground water]]; a steam explosion might occur, but the debris would probably be contained, and would in fact, being dispersed, probably be more easily cooled. See [[WASH-1400]] for details.

===Further examples===
Molten aluminium produces a strong exothermic reaction with water, which is observed in some building fires.<ref>{{cite journal |title=Thermodynamics of Tower-Block Infernos: Effects of Water on Aluminum Fires |journal=Entropy |date=2019-12-20 |last1=Maguire |first1=John F. |last2=Woodcock |first2=Leslie V. |volume=22 |issue=1 |page=14 |doi=10.3390/e22010014 |doi-access=free |pmid=33285789 |pmc=7516436 |bibcode=2019Entrp..22...14M }}</ref><ref>{{cite journal |title=Why the World Trade Center collapsed |journal=Aluminium International Today |date=2011 |last=Simensen |first= Christian J.|url=https://www.proquest.com/docview/1009034663 |accessdate=2024-06-20 |id={{ProQuest|1009034663}} }}{{subscription required}}</ref>

In a more domestic setting, steam explosions can be a result of trying to extinguish burning oil with water, in a process called [[Boilover#Related phenomena|slopover]]. When oil in a pan is on fire, the natural impulse may be to extinguish it with water; however, doing so will cause the hot oil to superheat the water. The resulting steam will disperse upwards and outwards rapidly and violently in a spray also containing the ignited oil. The correct method to extinguish such fires is to use either a damp cloth or a tight lid on the pan; both methods deprive the fire of [[oxygen]], and the cloth also cools it down. Alternatively, a non-volatile purpose designed [[fire retardant]] agent or simply a [[fire blanket]] can be used.