Nuclear meltdown  

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Kunstformen der Natur (1904) by Ernst Haeckel
Kunstformen der Natur (1904) by Ernst Haeckel

A nuclear meltdown is an informal term for a severe nuclear reactor accident that results in core damage from overheating. The term has been defined to mean the accidental melting of the core of a nuclear reactor, and is in common usage a reference to the core's either complete or partial collapse. "Core melt accident" and "partial core melt" are the analogous technical terms for a meltdown.

China Syndrome

The China syndrome (loss-of-coolant accident) is a hypothetical nuclear reactor operations accident characterized by the severe meltdown of the core components of the reactor, which then burn through the containment vessel, the housing building, then notionally through the crust and body of the Earth until reaching the other side, which in the United States is jokingly referred to as being China.

In reality, under a complete loss of coolant scenario, the fast erosion phase of the concrete basement lasts for about an hour and progresses into about one meter depth, then slows to several centimeters per hour, and stops completely when the corium melt cools below the decomposition temperature of concrete (about 1100 °C). Complete melt-through can occur in several days, even through several meters of concrete; the corium then penetrates several meters into the underlying soil, spreads around, cools, and solidifies.

The real scare, however, came from a quote in the 1979 film "The China Syndrome," which stated, "It melts right down through the bottom of the plant-theoretically to China, but of course, as soon as it hits ground water, it blasts into the atmosphere and sends out clouds of radioactivity. The number of people killed would depend on which way the wind was blowing, rendering an area the size of Pennsylvania permanently uninhabitable." The actual threat of this was tested just 12 days after the release of the film when a meltdown at Pennsylvania's Three Mile Island Plant 2 (TMI-2) created a molten core that moved 15 millimeters toward "China" before the core froze at the bottom of the reactor pressure vessel. Thus, the TMI-2 reactor fuel and fission products broached the fuel plates, the melted core itself did not break the containment of the reactor vessel. Hours after the meltdown, concern about hydrogen build-up led operators to release some radioactive gasses into the atmosphere, including gaseous fission products. Release of the fission products led to a temporary evacuation of the surrounding area, but no injuries.

An instance eerily similar to the actual China syndrome quote from the movie occurred during the early stages of the Chernobyl disaster: after the reactor was destroyed and began to burn, the liquid corium mass from the melted core began to breach the concrete floor of the reactor vessel, underneath which lay the bubbler pool (a large water reservoir for the emergency pumps also designed to safely contain steam pipe ruptures). The RBMK had no allowance or planning for core meltdowns, and the imminent interaction of the core mass with the bubbler pool would have produced a massive steam explosion that would have likely destroyed the entire plant and vastly increased the spread and magnitude of the radioactive plume. However, the initial explosion had broken the control circuitry which allowed the pool to be emptied. Three volunteer divers gave their lives to manually operate the valves necessary to drain this pool, and later images of the corium mass in the pipes of the bubbler pool's basement reinforced the heroic necessity of their actions.


The system design of the nuclear power plants built in the late 1960s raised questions of operational safety, and raised the concern that a severe reactor accident could release large quantities of radioactive materials into the atmosphere and environment. By 1970, there were doubts about the ability of the emergency core cooling system 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. In 1971, in the article Thoughts on Nuclear Plumbing, former Manhattan Project (1942–1946) nuclear physicist Ralph Lapp used the term "China syndrome" to describe a possible burn-through, after a loss of coolant accident, of the nuclear fuel rods and core components melting 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. In the event, Lapp’s hypothetical nuclear accident was cinematically adapted as The China Syndrome (1979).

See also

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