Editing Nuclear meltdown (section)

===Speculative failure modes===

One scenario consists of the reactor pressure vessel failing all at once, with the entire mass of corium dropping into a pool of water (for example, coolant or moderator) and causing extremely rapid generation of steam. The pressure rise within the containment could threaten integrity if rupture disks could not relieve the stress. Exposed flammable substances could burn, but there are few, if any, flammable substances within the containment.

Another theory, called an "alpha mode" failure by the 1975 Rasmussen ([[WASH-1400]]) study, asserted steam could produce enough pressure to blow the head off the reactor pressure vessel (RPV). The containment could be threatened if the RPV head collided with it. (The WASH-1400 report was replaced by better-based{{original research inline |date=March 2011}} newer studies, and now the [[Nuclear Regulatory Commission]] has disavowed them all and is preparing the overarching [[State-of-the-Art Reactor Consequence Analyses]] <nowiki>[SOARCA]</nowiki> study - see the Disclaimer in [[NUREG-1150]].)

By 1970, there were doubts about the ability of the emergency cooling systems of a nuclear reactor to prevent a loss-of-coolant accident and the consequent meltdown of the fuel core; the subject proved popular in the technical and the popular presses.<ref name="eleven">Walker, J. Samuel (2004). ''Three Mile Island: A Nuclear Crisis in Historical Perspective'' (Berkeley: University of California Press), p. 11.</ref> In 1971, in the article ''Thoughts on Nuclear Plumbing'', former [[Manhattan Project]] [[Nuclear physics|nuclear physicist]] [[Ralph Lapp]] used the term "China syndrome" to describe a possible burn through of the containment structures, and the subsequent escape of radioactive material(s) into the atmosphere and environment. The hypothesis derived from a 1967 report by a group of nuclear physicists, headed by [[W. K. Ergen]].<ref name="Lapp, Ralph E 1971">{{cite news |last=Lapp |first=Ralph E |title=Thoughts on nuclear plumbing |newspaper=The New York Times |date=12 December 1971 |page=E11 |url=https://www.nytimes.com/1971/12/12/archives/thoughts-on-nuclear-plumbing.html |access-date=2024-05-26 |postscript=,}} referencing {{cite tech report |editor-last=Ergen |editor-first=W.K. |title=Emergency Core Cooling, Report of Task Force Established by the US Atomic Energy Commission to Study Fuel Cooling Systems of Nuclear Power Plants |publisher=USAEC |year=1967 |postscript=none}} (undocumented, see summary in {{cite tech report |title=Emergency core-cooling systems for light-water-cooled power reactors |last=Lawson |first=C.G. |year=1968 |institution=Oak Ridge National Lab |number=ORNL-NSIC-24; OSTI 4825588 |doi=10.2172/4825588}}) <!-- this summary suggestion is given in ORNL/TM-2021/2176 doi:10.2172/1824962 citation #1 --></ref> Some fear that a molten reactor core could penetrate the reactor pressure vessel and containment structure and burn downwards to the level of the [[groundwater]].<ref name="Pitta2015">{{cite book|url=https://books.google.com/books?id=8raOCgAAQBAJ&pg=PT25|title=Catastrophe: A Guide to World's Worst Industrial Disasters|author=Terra Pitta|date=5 August 2015|publisher=Vij Books India Pvt Ltd|isbn=978-93-85505-17-1|pages=25–}}</ref>

It has not been determined to what extent a molten mass can melt through a structure (although that was tested in the loss-of-fluid-test reactor described in [[Test Area North]]'s fact sheet<ref>{{cite web|url=http://www.id.doe.gov/insideNEID/PDF/tan-fsheet.pdf|title=Test Area North|access-date=7 September 2008|archive-date=13 June 2011|archive-url=https://web.archive.org/web/20110613043146/http://www.id.doe.gov/insideNEID/PDF/tan-fsheet.pdf|url-status=dead}}</ref>). The Three Mile Island accident provided real-life experience with a molten core: the corium failed to melt through the reactor pressure vessel after over six hours of exposure due to dilution of the melt by the control rods and other reactor internals, validating the emphasis on defense in depth against core damage incidents.