Steam explosion
But many large-scale events, including foundry accidents, show evidence of an energy-release front propagating through the material (see description of FCI below), where the forces create fragments and mix the hot phase into the cold volatile one; and the rapid heat transfer at the front sustains the propagation.
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).
Some examples follow: Steam explosions are naturally produced by certain volcanoes, especially stratovolcanoes, and are a major cause of human fatalities in volcanic eruptions.
A dangerous steam explosion can also be created when liquid water or ice encounters hot, molten metal.
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 full and entire evacuation of the boiler's contents in a large steam explosion.
[citation needed] [4] [5] 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.
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.
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.
This was the mechanism that, in Idaho, USA, in 1961, caused the SL-1 nuclear reactor vessel to jump over 9 feet (2.7 m) in the air when it was destroyed by a criticality accident.
The threat was averted by frantic tunneling underneath the reactor in order to pump out water and reinforce underlying soil with concrete.
[7][8] In a more domestic setting, steam explosions can be a result of trying to extinguish burning oil with water, in a process called slopover.
[9][10] A water vapor explosion creates a high volume of gas without producing environmentally harmful leftovers.
Newer steam engines use heated oil to force drops of water to explode and create high pressure in a controlled chamber.
A vessel (such as a pot or frying-pan cover) is then used to quickly seal the steam-flash reaction, dispersing much of the steamed water on the cheese and patty.
This results in a large release of heat, transferred via vaporized water condensing back into a liquid (a principle also used in refrigerator and freezer production).
